compiler/rustc_resolve/src/late.rs

   1 // ignore-tidy-filelength
   2 //! "Late resolution" is the pass that resolves most of names in a crate beside imports and macros.
   3 //! It runs when the crate is fully expanded and its module structure is fully built.
   4 //! So it just walks through the crate and resolves all the expressions, types, etc.
   5 //!
   6 //! If you wonder why there's no `early.rs`, that's because it's split into three files -
   7 //! `build_reduced_graph.rs`, `macros.rs` and `imports.rs`.
   8
   9 use RibKind::*;
  10
  11 use crate::{path_names_to_string, BindingError, Finalize, LexicalScopeBinding};
  12 use crate::{Module, ModuleOrUniformRoot, NameBinding, ParentScope, PathResult};
  13 use crate::{ResolutionError, Resolver, Segment, UseError};
  14
  15 use rustc_ast::ptr::P;
  16 use rustc_ast::visit::{self, AssocCtxt, BoundKind, FnCtxt, FnKind, Visitor};
  17 use rustc_ast::*;
  18 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
  19 use rustc_errors::{DiagnosticArgValue, DiagnosticId, IntoDiagnosticArg};
  20 use rustc_hir::def::Namespace::{self, *};
  21 use rustc_hir::def::{self, CtorKind, DefKind, LifetimeRes, PartialRes, PerNS};
  22 use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID, LOCAL_CRATE};
  23 use rustc_hir::{BindingAnnotation, PrimTy, TraitCandidate};
  24 use rustc_middle::middle::resolve_lifetime::Set1;
  25 use rustc_middle::ty::DefIdTree;
  26 use rustc_middle::{bug, span_bug};
  27 use rustc_session::lint;
  28 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  29 use rustc_span::{BytePos, Span};
  30 use smallvec::{smallvec, SmallVec};
  31
  32 use rustc_span::source_map::{respan, Spanned};
  33 use std::assert_matches::debug_assert_matches;
  34 use std::borrow::Cow;
  35 use std::collections::{hash_map::Entry, BTreeSet};
  36 use std::mem::{replace, swap, take};
  37
  38 mod diagnostics;
  39
  40 type Res = def::Res<NodeId>;
  41
  42 type IdentMap<T> = FxHashMap<Ident, T>;
  43
  44 /// Map from the name in a pattern to its binding mode.
  45 type BindingMap = IdentMap<BindingInfo>;
  46
  47 use diagnostics::{
  48     ElisionFnParameter, LifetimeElisionCandidate, MissingLifetime, MissingLifetimeKind,
  49 };
  50
  51 #[derive(Copy, Clone, Debug)]
  52 struct BindingInfo {
  53     span: Span,
  54     annotation: BindingAnnotation,
  55 }
  56
  57 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
  58 pub enum PatternSource {
  59     Match,
  60     Let,
  61     For,
  62     FnParam,
  63 }
  64
  65 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
  66 enum IsRepeatExpr {
  67     No,
  68     Yes,
  69 }
  70
  71 impl PatternSource {
  72     pub fn descr(self) -> &'static str {
  73         match self {
  74             PatternSource::Match => "match binding",
  75             PatternSource::Let => "let binding",
  76             PatternSource::For => "for binding",
  77             PatternSource::FnParam => "function parameter",
  78         }
  79     }
  80 }
  81
  82 impl IntoDiagnosticArg for PatternSource {
  83     fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
  84         DiagnosticArgValue::Str(Cow::Borrowed(self.descr()))
  85     }
  86 }
  87
  88 /// Denotes whether the context for the set of already bound bindings is a `Product`
  89 /// or `Or` context. This is used in e.g., `fresh_binding` and `resolve_pattern_inner`.
  90 /// See those functions for more information.
  91 #[derive(PartialEq)]
  92 enum PatBoundCtx {
  93     /// A product pattern context, e.g., `Variant(a, b)`.
  94     Product,
  95     /// An or-pattern context, e.g., `p_0 | ... | p_n`.
  96     Or,
  97 }
  98
  99 /// Does this the item (from the item rib scope) allow generic parameters?
 100 #[derive(Copy, Clone, Debug)]
 101 pub(crate) enum HasGenericParams {
 102     Yes(Span),
 103     No,
 104 }
 105
 106 /// May this constant have generics?
 107 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 108 pub(crate) enum ConstantHasGenerics {
 109     Yes,
 110     No,
 111 }
 112
 113 impl ConstantHasGenerics {
 114     fn force_yes_if(self, b: bool) -> Self {
 115         if b { Self::Yes } else { self }
 116     }
 117 }
 118
 119 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 120 pub(crate) enum ConstantItemKind {
 121     Const,
 122     Static,
 123 }
 124
 125 /// The rib kind restricts certain accesses,
 126 /// e.g. to a `Res::Local` of an outer item.
 127 #[derive(Copy, Clone, Debug)]
 128 pub(crate) enum RibKind<'a> {
 129     /// No restriction needs to be applied.
 130     NormalRibKind,
 131
 132     /// We passed through an impl or trait and are now in one of its
 133     /// methods or associated types. Allow references to ty params that impl or trait
 134     /// binds. Disallow any other upvars (including other ty params that are
 135     /// upvars).
 136     AssocItemRibKind,
 137
 138     /// We passed through a closure. Disallow labels.
 139     ClosureOrAsyncRibKind,
 140
 141     /// We passed through an item scope. Disallow upvars.
 142     ItemRibKind(HasGenericParams),
 143
 144     /// We're in a constant item. Can't refer to dynamic stuff.
 145     ///
 146     /// The item may reference generic parameters in trivial constant expressions.
 147     /// All other constants aren't allowed to use generic params at all.
 148     ConstantItemRibKind(ConstantHasGenerics, Option<(Ident, ConstantItemKind)>),
 149
 150     /// We passed through a module.
 151     ModuleRibKind(Module<'a>),
 152
 153     /// We passed through a `macro_rules!` statement
 154     MacroDefinition(DefId),
 155
 156     /// All bindings in this rib are generic parameters that can't be used
 157     /// from the default of a generic parameter because they're not declared
 158     /// before said generic parameter. Also see the `visit_generics` override.
 159     ForwardGenericParamBanRibKind,
 160
 161     /// We are inside of the type of a const parameter. Can't refer to any
 162     /// parameters.
 163     ConstParamTyRibKind,
 164
 165     /// We are inside a `sym` inline assembly operand. Can only refer to
 166     /// globals.
 167     InlineAsmSymRibKind,
 168 }
 169
 170 impl RibKind<'_> {
 171     /// Whether this rib kind contains generic parameters, as opposed to local
 172     /// variables.
 173     pub(crate) fn contains_params(&self) -> bool {
 174         match self {
 175             NormalRibKind
 176             | ClosureOrAsyncRibKind
 177             | ConstantItemRibKind(..)
 178             | ModuleRibKind(_)
 179             | MacroDefinition(_)
 180             | ConstParamTyRibKind
 181             | InlineAsmSymRibKind => false,
 182             AssocItemRibKind | ItemRibKind(_) | ForwardGenericParamBanRibKind => true,
 183         }
 184     }
 185
 186     /// This rib forbids referring to labels defined in upwards ribs.
 187     fn is_label_barrier(self) -> bool {
 188         match self {
 189             NormalRibKind | MacroDefinition(..) => false,
 190
 191             AssocItemRibKind
 192             | ClosureOrAsyncRibKind
 193             | ItemRibKind(..)
 194             | ConstantItemRibKind(..)
 195             | ModuleRibKind(..)
 196             | ForwardGenericParamBanRibKind
 197             | ConstParamTyRibKind
 198             | InlineAsmSymRibKind => true,
 199         }
 200     }
 201 }
 202
 203 /// A single local scope.
 204 ///
 205 /// A rib represents a scope names can live in. Note that these appear in many places, not just
 206 /// around braces. At any place where the list of accessible names (of the given namespace)
 207 /// changes or a new restrictions on the name accessibility are introduced, a new rib is put onto a
 208 /// stack. This may be, for example, a `let` statement (because it introduces variables), a macro,
 209 /// etc.
 210 ///
 211 /// Different [rib kinds](enum@RibKind) are transparent for different names.
 212 ///
 213 /// The resolution keeps a separate stack of ribs as it traverses the AST for each namespace. When
 214 /// resolving, the name is looked up from inside out.
 215 #[derive(Debug)]
 216 pub(crate) struct Rib<'a, R = Res> {
 217     pub bindings: IdentMap<R>,
 218     pub kind: RibKind<'a>,
 219 }
 220
 221 impl<'a, R> Rib<'a, R> {
 222     fn new(kind: RibKind<'a>) -> Rib<'a, R> {
 223         Rib { bindings: Default::default(), kind }
 224     }
 225 }
 226
 227 #[derive(Clone, Copy, Debug)]
 228 enum LifetimeUseSet {
 229     One { use_span: Span, use_ctxt: visit::LifetimeCtxt },
 230     Many,
 231 }
 232
 233 #[derive(Copy, Clone, Debug)]
 234 enum LifetimeRibKind {
 235     // -- Ribs introducing named lifetimes
 236     //
 237     /// This rib declares generic parameters.
 238     /// Only for this kind the `LifetimeRib::bindings` field can be non-empty.
 239     Generics { binder: NodeId, span: Span, kind: LifetimeBinderKind },
 240
 241     // -- Ribs introducing unnamed lifetimes
 242     //
 243     /// Create a new anonymous lifetime parameter and reference it.
 244     ///
 245     /// If `report_in_path`, report an error when encountering lifetime elision in a path:
 246     /// ```compile_fail
 247     /// struct Foo<'a> { x: &'a () }
 248     /// async fn foo(x: Foo) {}
 249     /// ```
 250     ///
 251     /// Note: the error should not trigger when the elided lifetime is in a pattern or
 252     /// expression-position path:
 253     /// ```
 254     /// struct Foo<'a> { x: &'a () }
 255     /// async fn foo(Foo { x: _ }: Foo<'_>) {}
 256     /// ```
 257     AnonymousCreateParameter { binder: NodeId, report_in_path: bool },
 258
 259     /// Replace all anonymous lifetimes by provided lifetime.
 260     Elided(LifetimeRes),
 261
 262     // -- Barrier ribs that stop lifetime lookup, or continue it but produce an error later.
 263     //
 264     /// Give a hard error when either `&` or `'_` is written. Used to
 265     /// rule out things like `where T: Foo<'_>`. Does not imply an
 266     /// error on default object bounds (e.g., `Box<dyn Foo>`).
 267     AnonymousReportError,
 268
 269     /// Signal we cannot find which should be the anonymous lifetime.
 270     ElisionFailure,
 271
 272     /// FIXME(const_generics): This patches over an ICE caused by non-'static lifetimes in const
 273     /// generics. We are disallowing this until we can decide on how we want to handle non-'static
 274     /// lifetimes in const generics. See issue #74052 for discussion.
 275     ConstGeneric,
 276
 277     /// Non-static lifetimes are prohibited in anonymous constants under `min_const_generics`.
 278     /// This function will emit an error if `generic_const_exprs` is not enabled, the body
 279     /// identified by `body_id` is an anonymous constant and `lifetime_ref` is non-static.
 280     AnonConst,
 281
 282     /// This rib acts as a barrier to forbid reference to lifetimes of a parent item.
 283     Item,
 284 }
 285
 286 #[derive(Copy, Clone, Debug)]
 287 enum LifetimeBinderKind {
 288     BareFnType,
 289     PolyTrait,
 290     WhereBound,
 291     Item,
 292     Function,
 293     Closure,
 294     ImplBlock,
 295 }
 296
 297 impl LifetimeBinderKind {
 298     fn descr(self) -> &'static str {
 299         use LifetimeBinderKind::*;
 300         match self {
 301             BareFnType => "type",
 302             PolyTrait => "bound",
 303             WhereBound => "bound",
 304             Item => "item",
 305             ImplBlock => "impl block",
 306             Function => "function",
 307             Closure => "closure",
 308         }
 309     }
 310 }
 311
 312 #[derive(Debug)]
 313 struct LifetimeRib {
 314     kind: LifetimeRibKind,
 315     // We need to preserve insertion order for async fns.
 316     bindings: FxIndexMap<Ident, (NodeId, LifetimeRes)>,
 317 }
 318
 319 impl LifetimeRib {
 320     fn new(kind: LifetimeRibKind) -> LifetimeRib {
 321         LifetimeRib { bindings: Default::default(), kind }
 322     }
 323 }
 324
 325 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 326 pub(crate) enum AliasPossibility {
 327     No,
 328     Maybe,
 329 }
 330
 331 #[derive(Copy, Clone, Debug)]
 332 pub(crate) enum PathSource<'a> {
 333     // Type paths `Path`.
 334     Type,
 335     // Trait paths in bounds or impls.
 336     Trait(AliasPossibility),
 337     // Expression paths `path`, with optional parent context.
 338     Expr(Option<&'a Expr>),
 339     // Paths in path patterns `Path`.
 340     Pat,
 341     // Paths in struct expressions and patterns `Path { .. }`.
 342     Struct,
 343     // Paths in tuple struct patterns `Path(..)`.
 344     TupleStruct(Span, &'a [Span]),
 345     // `m::A::B` in `<T as m::A>::B::C`.
 346     TraitItem(Namespace),
 347 }
 348
 349 impl<'a> PathSource<'a> {
 350     fn namespace(self) -> Namespace {
 351         match self {
 352             PathSource::Type | PathSource::Trait(_) | PathSource::Struct => TypeNS,
 353             PathSource::Expr(..) | PathSource::Pat | PathSource::TupleStruct(..) => ValueNS,
 354             PathSource::TraitItem(ns) => ns,
 355         }
 356     }
 357
 358     fn defer_to_typeck(self) -> bool {
 359         match self {
 360             PathSource::Type
 361             | PathSource::Expr(..)
 362             | PathSource::Pat
 363             | PathSource::Struct
 364             | PathSource::TupleStruct(..) => true,
 365             PathSource::Trait(_) | PathSource::TraitItem(..) => false,
 366         }
 367     }
 368
 369     fn descr_expected(self) -> &'static str {
 370         match &self {
 371             PathSource::Type => "type",
 372             PathSource::Trait(_) => "trait",
 373             PathSource::Pat => "unit struct, unit variant or constant",
 374             PathSource::Struct => "struct, variant or union type",
 375             PathSource::TupleStruct(..) => "tuple struct or tuple variant",
 376             PathSource::TraitItem(ns) => match ns {
 377                 TypeNS => "associated type",
 378                 ValueNS => "method or associated constant",
 379                 MacroNS => bug!("associated macro"),
 380             },
 381             PathSource::Expr(parent) => match parent.as_ref().map(|p| &p.kind) {
 382                 // "function" here means "anything callable" rather than `DefKind::Fn`,
 383                 // this is not precise but usually more helpful than just "value".
 384                 Some(ExprKind::Call(call_expr, _)) => match &call_expr.kind {
 385                     // the case of `::some_crate()`
 386                     ExprKind::Path(_, path)
 387                         if path.segments.len() == 2
 388                             && path.segments[0].ident.name == kw::PathRoot =>
 389                     {
 390                         "external crate"
 391                     }
 392                     ExprKind::Path(_, path) => {
 393                         let mut msg = "function";
 394                         if let Some(segment) = path.segments.iter().last() {
 395                             if let Some(c) = segment.ident.to_string().chars().next() {
 396                                 if c.is_uppercase() {
 397                                     msg = "function, tuple struct or tuple variant";
 398                                 }
 399                             }
 400                         }
 401                         msg
 402                     }
 403                     _ => "function",
 404                 },
 405                 _ => "value",
 406             },
 407         }
 408     }
 409
 410     fn is_call(self) -> bool {
 411         matches!(self, PathSource::Expr(Some(&Expr { kind: ExprKind::Call(..), .. })))
 412     }
 413
 414     pub(crate) fn is_expected(self, res: Res) -> bool {
 415         match self {
 416             PathSource::Type => matches!(
 417                 res,
 418                 Res::Def(
 419                     DefKind::Struct
 420                         | DefKind::Union
 421                         | DefKind::Enum
 422                         | DefKind::Trait
 423                         | DefKind::TraitAlias
 424                         | DefKind::TyAlias
 425                         | DefKind::AssocTy
 426                         | DefKind::TyParam
 427                         | DefKind::OpaqueTy
 428                         | DefKind::ForeignTy,
 429                     _,
 430                 ) | Res::PrimTy(..)
 431                     | Res::SelfTyParam { .. }
 432                     | Res::SelfTyAlias { .. }
 433             ),
 434             PathSource::Trait(AliasPossibility::No) => matches!(res, Res::Def(DefKind::Trait, _)),
 435             PathSource::Trait(AliasPossibility::Maybe) => {
 436                 matches!(res, Res::Def(DefKind::Trait | DefKind::TraitAlias, _))
 437             }
 438             PathSource::Expr(..) => matches!(
 439                 res,
 440                 Res::Def(
 441                     DefKind::Ctor(_, CtorKind::Const | CtorKind::Fn)
 442                         | DefKind::Const
 443                         | DefKind::Static(_)
 444                         | DefKind::Fn
 445                         | DefKind::AssocFn
 446                         | DefKind::AssocConst
 447                         | DefKind::ConstParam,
 448                     _,
 449                 ) | Res::Local(..)
 450                     | Res::SelfCtor(..)
 451             ),
 452             PathSource::Pat => {
 453                 res.expected_in_unit_struct_pat()
 454                     || matches!(res, Res::Def(DefKind::Const | DefKind::AssocConst, _))
 455             }
 456             PathSource::TupleStruct(..) => res.expected_in_tuple_struct_pat(),
 457             PathSource::Struct => matches!(
 458                 res,
 459                 Res::Def(
 460                     DefKind::Struct
 461                         | DefKind::Union
 462                         | DefKind::Variant
 463                         | DefKind::TyAlias
 464                         | DefKind::AssocTy,
 465                     _,
 466                 ) | Res::SelfTyParam { .. }
 467                     | Res::SelfTyAlias { .. }
 468             ),
 469             PathSource::TraitItem(ns) => match res {
 470                 Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) if ns == ValueNS => true,
 471                 Res::Def(DefKind::AssocTy, _) if ns == TypeNS => true,
 472                 _ => false,
 473             },
 474         }
 475     }
 476
 477     fn error_code(self, has_unexpected_resolution: bool) -> DiagnosticId {
 478         use rustc_errors::error_code;
 479         match (self, has_unexpected_resolution) {
 480             (PathSource::Trait(_), true) => error_code!(E0404),
 481             (PathSource::Trait(_), false) => error_code!(E0405),
 482             (PathSource::Type, true) => error_code!(E0573),
 483             (PathSource::Type, false) => error_code!(E0412),
 484             (PathSource::Struct, true) => error_code!(E0574),
 485             (PathSource::Struct, false) => error_code!(E0422),
 486             (PathSource::Expr(..), true) => error_code!(E0423),
 487             (PathSource::Expr(..), false) => error_code!(E0425),
 488             (PathSource::Pat | PathSource::TupleStruct(..), true) => error_code!(E0532),
 489             (PathSource::Pat | PathSource::TupleStruct(..), false) => error_code!(E0531),
 490             (PathSource::TraitItem(..), true) => error_code!(E0575),
 491             (PathSource::TraitItem(..), false) => error_code!(E0576),
 492         }
 493     }
 494 }
 495
 496 #[derive(Default)]
 497 struct DiagnosticMetadata<'ast> {
 498     /// The current trait's associated items' ident, used for diagnostic suggestions.
 499     current_trait_assoc_items: Option<&'ast [P<AssocItem>]>,
 500
 501     /// The current self type if inside an impl (used for better errors).
 502     current_self_type: Option<Ty>,
 503
 504     /// The current self item if inside an ADT (used for better errors).
 505     current_self_item: Option<NodeId>,
 506
 507     /// The current trait (used to suggest).
 508     current_item: Option<&'ast Item>,
 509
 510     /// When processing generics and encountering a type not found, suggest introducing a type
 511     /// param.
 512     currently_processing_generics: bool,
 513
 514     /// The current enclosing (non-closure) function (used for better errors).
 515     current_function: Option<(FnKind<'ast>, Span)>,
 516
 517     /// A list of labels as of yet unused. Labels will be removed from this map when
 518     /// they are used (in a `break` or `continue` statement)
 519     unused_labels: FxHashMap<NodeId, Span>,
 520
 521     /// Only used for better errors on `fn(): fn()`.
 522     current_type_ascription: Vec<Span>,
 523
 524     /// Only used for better errors on `let x = { foo: bar };`.
 525     /// In the case of a parse error with `let x = { foo: bar, };`, this isn't needed, it's only
 526     /// needed for cases where this parses as a correct type ascription.
 527     current_block_could_be_bare_struct_literal: Option<Span>,
 528
 529     /// Only used for better errors on `let <pat>: <expr, not type>;`.
 530     current_let_binding: Option<(Span, Option<Span>, Option<Span>)>,
 531
 532     /// Used to detect possible `if let` written without `let` and to provide structured suggestion.
 533     in_if_condition: Option<&'ast Expr>,
 534
 535     /// Used to detect possible new binding written without `let` and to provide structured suggestion.
 536     in_assignment: Option<&'ast Expr>,
 537     is_assign_rhs: bool,
 538
 539     /// If we are currently in a trait object definition. Used to point at the bounds when
 540     /// encountering a struct or enum.
 541     current_trait_object: Option<&'ast [ast::GenericBound]>,
 542
 543     /// Given `where <T as Bar>::Baz: String`, suggest `where T: Bar<Baz = String>`.
 544     current_where_predicate: Option<&'ast WherePredicate>,
 545
 546     current_type_path: Option<&'ast Ty>,
 547
 548     /// The current impl items (used to suggest).
 549     current_impl_items: Option<&'ast [P<AssocItem>]>,
 550
 551     /// When processing impl trait
 552     currently_processing_impl_trait: Option<(TraitRef, Ty)>,
 553
 554     /// Accumulate the errors due to missed lifetime elision,
 555     /// and report them all at once for each function.
 556     current_elision_failures: Vec<MissingLifetime>,
 557 }
 558
 559 struct LateResolutionVisitor<'a, 'b, 'ast> {
 560     r: &'b mut Resolver<'a>,
 561
 562     /// The module that represents the current item scope.
 563     parent_scope: ParentScope<'a>,
 564
 565     /// The current set of local scopes for types and values.
 566     /// FIXME #4948: Reuse ribs to avoid allocation.
 567     ribs: PerNS<Vec<Rib<'a>>>,
 568
 569     /// The current set of local scopes, for labels.
 570     label_ribs: Vec<Rib<'a, NodeId>>,
 571
 572     /// The current set of local scopes for lifetimes.
 573     lifetime_ribs: Vec<LifetimeRib>,
 574
 575     /// We are looking for lifetimes in an elision context.
 576     /// The set contains all the resolutions that we encountered so far.
 577     /// They will be used to determine the correct lifetime for the fn return type.
 578     /// The `LifetimeElisionCandidate` is used for diagnostics, to suggest introducing named
 579     /// lifetimes.
 580     lifetime_elision_candidates: Option<Vec<(LifetimeRes, LifetimeElisionCandidate)>>,
 581
 582     /// The trait that the current context can refer to.
 583     current_trait_ref: Option<(Module<'a>, TraitRef)>,
 584
 585     /// Fields used to add information to diagnostic errors.
 586     diagnostic_metadata: Box<DiagnosticMetadata<'ast>>,
 587
 588     /// State used to know whether to ignore resolution errors for function bodies.
 589     ///
 590     /// In particular, rustdoc uses this to avoid giving errors for `cfg()` items.
 591     /// In most cases this will be `None`, in which case errors will always be reported.
 592     /// If it is `true`, then it will be updated when entering a nested function or trait body.
 593     in_func_body: bool,
 594
 595     /// Count the number of places a lifetime is used.
 596     lifetime_uses: FxHashMap<LocalDefId, LifetimeUseSet>,
 597 }
 598
 599 /// Walks the whole crate in DFS order, visiting each item, resolving names as it goes.
 600 impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
 601     fn visit_attribute(&mut self, _: &'ast Attribute) {
 602         // We do not want to resolve expressions that appear in attributes,
 603         // as they do not correspond to actual code.
 604     }
 605     fn visit_item(&mut self, item: &'ast Item) {
 606         let prev = replace(&mut self.diagnostic_metadata.current_item, Some(item));
 607         // Always report errors in items we just entered.
 608         let old_ignore = replace(&mut self.in_func_body, false);
 609         self.with_lifetime_rib(LifetimeRibKind::Item, |this| this.resolve_item(item));
 610         self.in_func_body = old_ignore;
 611         self.diagnostic_metadata.current_item = prev;
 612     }
 613     fn visit_arm(&mut self, arm: &'ast Arm) {
 614         self.resolve_arm(arm);
 615     }
 616     fn visit_block(&mut self, block: &'ast Block) {
 617         self.resolve_block(block);
 618     }
 619     fn visit_anon_const(&mut self, constant: &'ast AnonConst) {
 620         // We deal with repeat expressions explicitly in `resolve_expr`.
 621         self.with_lifetime_rib(LifetimeRibKind::AnonConst, |this| {
 622             this.with_lifetime_rib(LifetimeRibKind::Elided(LifetimeRes::Static), |this| {
 623                 this.resolve_anon_const(constant, IsRepeatExpr::No);
 624             })
 625         })
 626     }
 627     fn visit_expr(&mut self, expr: &'ast Expr) {
 628         self.resolve_expr(expr, None);
 629     }
 630     fn visit_local(&mut self, local: &'ast Local) {
 631         let local_spans = match local.pat.kind {
 632             // We check for this to avoid tuple struct fields.
 633             PatKind::Wild => None,
 634             _ => Some((
 635                 local.pat.span,
 636                 local.ty.as_ref().map(|ty| ty.span),
 637                 local.kind.init().map(|init| init.span),
 638             )),
 639         };
 640         let original = replace(&mut self.diagnostic_metadata.current_let_binding, local_spans);
 641         self.resolve_local(local);
 642         self.diagnostic_metadata.current_let_binding = original;
 643     }
 644     fn visit_ty(&mut self, ty: &'ast Ty) {
 645         let prev = self.diagnostic_metadata.current_trait_object;
 646         let prev_ty = self.diagnostic_metadata.current_type_path;
 647         match ty.kind {
 648             TyKind::Rptr(None, _) => {
 649                 // Elided lifetime in reference: we resolve as if there was some lifetime `'_` with
 650                 // NodeId `ty.id`.
 651                 // This span will be used in case of elision failure.
 652                 let span = self.r.session.source_map().start_point(ty.span);
 653                 self.resolve_elided_lifetime(ty.id, span);
 654                 visit::walk_ty(self, ty);
 655             }
 656             TyKind::Path(ref qself, ref path) => {
 657                 self.diagnostic_metadata.current_type_path = Some(ty);
 658                 self.smart_resolve_path(ty.id, &qself, path, PathSource::Type);
 659
 660                 // Check whether we should interpret this as a bare trait object.
 661                 if qself.is_none()
 662                     && let Some(partial_res) = self.r.partial_res_map.get(&ty.id)
 663                     && let Some(Res::Def(DefKind::Trait | DefKind::TraitAlias, _)) = partial_res.full_res()
 664                 {
 665                     // This path is actually a bare trait object.  In case of a bare `Fn`-trait
 666                     // object with anonymous lifetimes, we need this rib to correctly place the
 667                     // synthetic lifetimes.
 668                     let span = ty.span.shrink_to_lo().to(path.span.shrink_to_lo());
 669                     self.with_generic_param_rib(
 670                         &[],
 671                         NormalRibKind,
 672                         LifetimeRibKind::Generics {
 673                             binder: ty.id,
 674                             kind: LifetimeBinderKind::PolyTrait,
 675                             span,
 676                         },
 677                         |this| this.visit_path(&path, ty.id),
 678                     );
 679                 } else {
 680                     visit::walk_ty(self, ty)
 681                 }
 682             }
 683             TyKind::ImplicitSelf => {
 684                 let self_ty = Ident::with_dummy_span(kw::SelfUpper);
 685                 let res = self
 686                     .resolve_ident_in_lexical_scope(
 687                         self_ty,
 688                         TypeNS,
 689                         Some(Finalize::new(ty.id, ty.span)),
 690                         None,
 691                     )
 692                     .map_or(Res::Err, |d| d.res());
 693                 self.r.record_partial_res(ty.id, PartialRes::new(res));
 694                 visit::walk_ty(self, ty)
 695             }
 696             TyKind::ImplTrait(..) => {
 697                 let candidates = self.lifetime_elision_candidates.take();
 698                 visit::walk_ty(self, ty);
 699                 self.lifetime_elision_candidates = candidates;
 700             }
 701             TyKind::TraitObject(ref bounds, ..) => {
 702                 self.diagnostic_metadata.current_trait_object = Some(&bounds[..]);
 703                 visit::walk_ty(self, ty)
 704             }
 705             TyKind::BareFn(ref bare_fn) => {
 706                 let span = ty.span.shrink_to_lo().to(bare_fn.decl_span.shrink_to_lo());
 707                 self.with_generic_param_rib(
 708                     &bare_fn.generic_params,
 709                     NormalRibKind,
 710                     LifetimeRibKind::Generics {
 711                         binder: ty.id,
 712                         kind: LifetimeBinderKind::BareFnType,
 713                         span,
 714                     },
 715                     |this| {
 716                         this.visit_generic_params(&bare_fn.generic_params, false);
 717                         this.with_lifetime_rib(
 718                             LifetimeRibKind::AnonymousCreateParameter {
 719                                 binder: ty.id,
 720                                 report_in_path: false,
 721                             },
 722                             |this| {
 723                                 this.resolve_fn_signature(
 724                                     ty.id,
 725                                     false,
 726                                     // We don't need to deal with patterns in parameters, because
 727                                     // they are not possible for foreign or bodiless functions.
 728                                     bare_fn
 729                                         .decl
 730                                         .inputs
 731                                         .iter()
 732                                         .map(|Param { ty, .. }| (None, &**ty)),
 733                                     &bare_fn.decl.output,
 734                                 )
 735                             },
 736                         );
 737                     },
 738                 )
 739             }
 740             _ => visit::walk_ty(self, ty),
 741         }
 742         self.diagnostic_metadata.current_trait_object = prev;
 743         self.diagnostic_metadata.current_type_path = prev_ty;
 744     }
 745     fn visit_poly_trait_ref(&mut self, tref: &'ast PolyTraitRef) {
 746         let span = tref.span.shrink_to_lo().to(tref.trait_ref.path.span.shrink_to_lo());
 747         self.with_generic_param_rib(
 748             &tref.bound_generic_params,
 749             NormalRibKind,
 750             LifetimeRibKind::Generics {
 751                 binder: tref.trait_ref.ref_id,
 752                 kind: LifetimeBinderKind::PolyTrait,
 753                 span,
 754             },
 755             |this| {
 756                 this.visit_generic_params(&tref.bound_generic_params, false);
 757                 this.smart_resolve_path(
 758                     tref.trait_ref.ref_id,
 759                     &None,
 760                     &tref.trait_ref.path,
 761                     PathSource::Trait(AliasPossibility::Maybe),
 762                 );
 763                 this.visit_trait_ref(&tref.trait_ref);
 764             },
 765         );
 766     }
 767     fn visit_foreign_item(&mut self, foreign_item: &'ast ForeignItem) {
 768         match foreign_item.kind {
 769             ForeignItemKind::TyAlias(box TyAlias { ref generics, .. }) => {
 770                 self.with_generic_param_rib(
 771                     &generics.params,
 772                     ItemRibKind(HasGenericParams::Yes(generics.span)),
 773                     LifetimeRibKind::Generics {
 774                         binder: foreign_item.id,
 775                         kind: LifetimeBinderKind::Item,
 776                         span: generics.span,
 777                     },
 778                     |this| visit::walk_foreign_item(this, foreign_item),
 779                 );
 780             }
 781             ForeignItemKind::Fn(box Fn { ref generics, .. }) => {
 782                 self.with_generic_param_rib(
 783                     &generics.params,
 784                     ItemRibKind(HasGenericParams::Yes(generics.span)),
 785                     LifetimeRibKind::Generics {
 786                         binder: foreign_item.id,
 787                         kind: LifetimeBinderKind::Function,
 788                         span: generics.span,
 789                     },
 790                     |this| visit::walk_foreign_item(this, foreign_item),
 791                 );
 792             }
 793             ForeignItemKind::Static(..) => {
 794                 self.with_static_rib(|this| {
 795                     visit::walk_foreign_item(this, foreign_item);
 796                 });
 797             }
 798             ForeignItemKind::MacCall(..) => {
 799                 panic!("unexpanded macro in resolve!")
 800             }
 801         }
 802     }
 803     fn visit_fn(&mut self, fn_kind: FnKind<'ast>, sp: Span, fn_id: NodeId) {
 804         let previous_value = self.diagnostic_metadata.current_function;
 805         match fn_kind {
 806             // Bail if the function is foreign, and thus cannot validly have
 807             // a body, or if there's no body for some other reason.
 808             FnKind::Fn(FnCtxt::Foreign, _, sig, _, generics, _)
 809             | FnKind::Fn(_, _, sig, _, generics, None) => {
 810                 self.visit_fn_header(&sig.header);
 811                 self.visit_generics(generics);
 812                 self.with_lifetime_rib(
 813                     LifetimeRibKind::AnonymousCreateParameter {
 814                         binder: fn_id,
 815                         report_in_path: false,
 816                     },
 817                     |this| {
 818                         this.resolve_fn_signature(
 819                             fn_id,
 820                             sig.decl.has_self(),
 821                             sig.decl.inputs.iter().map(|Param { ty, .. }| (None, &**ty)),
 822                             &sig.decl.output,
 823                         );
 824
 825                         this.record_lifetime_params_for_async(
 826                             fn_id,
 827                             sig.header.asyncness.opt_return_id(),
 828                         );
 829                     },
 830                 );
 831                 return;
 832             }
 833             FnKind::Fn(..) => {
 834                 self.diagnostic_metadata.current_function = Some((fn_kind, sp));
 835             }
 836             // Do not update `current_function` for closures: it suggests `self` parameters.
 837             FnKind::Closure(..) => {}
 838         };
 839         debug!("(resolving function) entering function");
 840
 841         // Create a value rib for the function.
 842         self.with_rib(ValueNS, ClosureOrAsyncRibKind, |this| {
 843             // Create a label rib for the function.
 844             this.with_label_rib(ClosureOrAsyncRibKind, |this| {
 845                 match fn_kind {
 846                     FnKind::Fn(_, _, sig, _, generics, body) => {
 847                         this.visit_generics(generics);
 848
 849                         let declaration = &sig.decl;
 850                         let async_node_id = sig.header.asyncness.opt_return_id();
 851
 852                         this.with_lifetime_rib(
 853                             LifetimeRibKind::AnonymousCreateParameter {
 854                                 binder: fn_id,
 855                                 report_in_path: async_node_id.is_some(),
 856                             },
 857                             |this| {
 858                                 this.resolve_fn_signature(
 859                                     fn_id,
 860                                     declaration.has_self(),
 861                                     declaration
 862                                         .inputs
 863                                         .iter()
 864                                         .map(|Param { pat, ty, .. }| (Some(&**pat), &**ty)),
 865                                     &declaration.output,
 866                                 )
 867                             },
 868                         );
 869
 870                         this.record_lifetime_params_for_async(fn_id, async_node_id);
 871
 872                         if let Some(body) = body {
 873                             // Ignore errors in function bodies if this is rustdoc
 874                             // Be sure not to set this until the function signature has been resolved.
 875                             let previous_state = replace(&mut this.in_func_body, true);
 876                             // Resolve the function body, potentially inside the body of an async closure
 877                             this.with_lifetime_rib(
 878                                 LifetimeRibKind::Elided(LifetimeRes::Infer),
 879                                 |this| this.visit_block(body),
 880                             );
 881
 882                             debug!("(resolving function) leaving function");
 883                             this.in_func_body = previous_state;
 884                         }
 885                     }
 886                     FnKind::Closure(binder, declaration, body) => {
 887                         this.visit_closure_binder(binder);
 888
 889                         this.with_lifetime_rib(
 890                             match binder {
 891                                 // We do not have any explicit generic lifetime parameter.
 892                                 ClosureBinder::NotPresent => {
 893                                     LifetimeRibKind::AnonymousCreateParameter {
 894                                         binder: fn_id,
 895                                         report_in_path: false,
 896                                     }
 897                                 }
 898                                 ClosureBinder::For { .. } => LifetimeRibKind::AnonymousReportError,
 899                             },
 900                             // Add each argument to the rib.
 901                             |this| this.resolve_params(&declaration.inputs),
 902                         );
 903                         this.with_lifetime_rib(
 904                             match binder {
 905                                 ClosureBinder::NotPresent => {
 906                                     LifetimeRibKind::Elided(LifetimeRes::Infer)
 907                                 }
 908                                 ClosureBinder::For { .. } => LifetimeRibKind::AnonymousReportError,
 909                             },
 910                             |this| visit::walk_fn_ret_ty(this, &declaration.output),
 911                         );
 912
 913                         // Ignore errors in function bodies if this is rustdoc
 914                         // Be sure not to set this until the function signature has been resolved.
 915                         let previous_state = replace(&mut this.in_func_body, true);
 916                         // Resolve the function body, potentially inside the body of an async closure
 917                         this.with_lifetime_rib(
 918                             LifetimeRibKind::Elided(LifetimeRes::Infer),
 919                             |this| this.visit_expr(body),
 920                         );
 921
 922                         debug!("(resolving function) leaving function");
 923                         this.in_func_body = previous_state;
 924                     }
 925                 }
 926             })
 927         });
 928         self.diagnostic_metadata.current_function = previous_value;
 929     }
 930     fn visit_lifetime(&mut self, lifetime: &'ast Lifetime, use_ctxt: visit::LifetimeCtxt) {
 931         self.resolve_lifetime(lifetime, use_ctxt)
 932     }
 933
 934     fn visit_generics(&mut self, generics: &'ast Generics) {
 935         self.visit_generic_params(
 936             &generics.params,
 937             self.diagnostic_metadata.current_self_item.is_some(),
 938         );
 939         for p in &generics.where_clause.predicates {
 940             self.visit_where_predicate(p);
 941         }
 942     }
 943
 944     fn visit_closure_binder(&mut self, b: &'ast ClosureBinder) {
 945         match b {
 946             ClosureBinder::NotPresent => {}
 947             ClosureBinder::For { generic_params, .. } => {
 948                 self.visit_generic_params(
 949                     &generic_params,
 950                     self.diagnostic_metadata.current_self_item.is_some(),
 951                 );
 952             }
 953         }
 954     }
 955
 956     fn visit_generic_arg(&mut self, arg: &'ast GenericArg) {
 957         debug!("visit_generic_arg({:?})", arg);
 958         let prev = replace(&mut self.diagnostic_metadata.currently_processing_generics, true);
 959         match arg {
 960             GenericArg::Type(ref ty) => {
 961                 // We parse const arguments as path types as we cannot distinguish them during
 962                 // parsing. We try to resolve that ambiguity by attempting resolution the type
 963                 // namespace first, and if that fails we try again in the value namespace. If
 964                 // resolution in the value namespace succeeds, we have an generic const argument on
 965                 // our hands.
 966                 if let TyKind::Path(ref qself, ref path) = ty.kind {
 967                     // We cannot disambiguate multi-segment paths right now as that requires type
 968                     // checking.
 969                     if path.segments.len() == 1 && path.segments[0].args.is_none() {
 970                         let mut check_ns = |ns| {
 971                             self.maybe_resolve_ident_in_lexical_scope(path.segments[0].ident, ns)
 972                                 .is_some()
 973                         };
 974                         if !check_ns(TypeNS) && check_ns(ValueNS) {
 975                             // This must be equivalent to `visit_anon_const`, but we cannot call it
 976                             // directly due to visitor lifetimes so we have to copy-paste some code.
 977                             //
 978                             // Note that we might not be inside of an repeat expression here,
 979                             // but considering that `IsRepeatExpr` is only relevant for
 980                             // non-trivial constants this is doesn't matter.
 981                             self.with_constant_rib(
 982                                 IsRepeatExpr::No,
 983                                 ConstantHasGenerics::Yes,
 984                                 None,
 985                                 |this| {
 986                                     this.smart_resolve_path(
 987                                         ty.id,
 988                                         qself,
 989                                         path,
 990                                         PathSource::Expr(None),
 991                                     );
 992
 993                                     if let Some(ref qself) = *qself {
 994                                         this.visit_ty(&qself.ty);
 995                                     }
 996                                     this.visit_path(path, ty.id);
 997                                 },
 998                             );
 999
1000                             self.diagnostic_metadata.currently_processing_generics = prev;
1001                             return;
1002                         }
1003                     }
1004                 }
1005
1006                 self.visit_ty(ty);
1007             }
1008             GenericArg::Lifetime(lt) => self.visit_lifetime(lt, visit::LifetimeCtxt::GenericArg),
1009             GenericArg::Const(ct) => self.visit_anon_const(ct),
1010         }
1011         self.diagnostic_metadata.currently_processing_generics = prev;
1012     }
1013
1014     fn visit_assoc_constraint(&mut self, constraint: &'ast AssocConstraint) {
1015         self.visit_ident(constraint.ident);
1016         if let Some(ref gen_args) = constraint.gen_args {
1017             // Forbid anonymous lifetimes in GAT parameters until proper semantics are decided.
1018             self.with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
1019                 this.visit_generic_args(gen_args)
1020             });
1021         }
1022         match constraint.kind {
1023             AssocConstraintKind::Equality { ref term } => match term {
1024                 Term::Ty(ty) => self.visit_ty(ty),
1025                 Term::Const(c) => self.visit_anon_const(c),
1026             },
1027             AssocConstraintKind::Bound { ref bounds } => {
1028                 walk_list!(self, visit_param_bound, bounds, BoundKind::Bound);
1029             }
1030         }
1031     }
1032
1033     fn visit_path_segment(&mut self, path_segment: &'ast PathSegment) {
1034         if let Some(ref args) = path_segment.args {
1035             match &**args {
1036                 GenericArgs::AngleBracketed(..) => visit::walk_generic_args(self, args),
1037                 GenericArgs::Parenthesized(p_args) => {
1038                     // Probe the lifetime ribs to know how to behave.
1039                     for rib in self.lifetime_ribs.iter().rev() {
1040                         match rib.kind {
1041                             // We are inside a `PolyTraitRef`.  The lifetimes are
1042                             // to be intoduced in that (maybe implicit) `for<>` binder.
1043                             LifetimeRibKind::Generics {
1044                                 binder,
1045                                 kind: LifetimeBinderKind::PolyTrait,
1046                                 ..
1047                             } => {
1048                                 self.with_lifetime_rib(
1049                                     LifetimeRibKind::AnonymousCreateParameter {
1050                                         binder,
1051                                         report_in_path: false,
1052                                     },
1053                                     |this| {
1054                                         this.resolve_fn_signature(
1055                                             binder,
1056                                             false,
1057                                             p_args.inputs.iter().map(|ty| (None, &**ty)),
1058                                             &p_args.output,
1059                                         )
1060                                     },
1061                                 );
1062                                 break;
1063                             }
1064                             // We have nowhere to introduce generics.  Code is malformed,
1065                             // so use regular lifetime resolution to avoid spurious errors.
1066                             LifetimeRibKind::Item | LifetimeRibKind::Generics { .. } => {
1067                                 visit::walk_generic_args(self, args);
1068                                 break;
1069                             }
1070                             LifetimeRibKind::AnonymousCreateParameter { .. }
1071                             | LifetimeRibKind::AnonymousReportError
1072                             | LifetimeRibKind::Elided(_)
1073                             | LifetimeRibKind::ElisionFailure
1074                             | LifetimeRibKind::AnonConst
1075                             | LifetimeRibKind::ConstGeneric => {}
1076                         }
1077                     }
1078                 }
1079             }
1080         }
1081     }
1082
1083     fn visit_where_predicate(&mut self, p: &'ast WherePredicate) {
1084         debug!("visit_where_predicate {:?}", p);
1085         let previous_value =
1086             replace(&mut self.diagnostic_metadata.current_where_predicate, Some(p));
1087         self.with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
1088             if let WherePredicate::BoundPredicate(WhereBoundPredicate {
1089                 ref bounded_ty,
1090                 ref bounds,
1091                 ref bound_generic_params,
1092                 span: predicate_span,
1093                 ..
1094             }) = p
1095             {
1096                 let span = predicate_span.shrink_to_lo().to(bounded_ty.span.shrink_to_lo());
1097                 this.with_generic_param_rib(
1098                     &bound_generic_params,
1099                     NormalRibKind,
1100                     LifetimeRibKind::Generics {
1101                         binder: bounded_ty.id,
1102                         kind: LifetimeBinderKind::WhereBound,
1103                         span,
1104                     },
1105                     |this| {
1106                         this.visit_generic_params(&bound_generic_params, false);
1107                         this.visit_ty(bounded_ty);
1108                         for bound in bounds {
1109                             this.visit_param_bound(bound, BoundKind::Bound)
1110                         }
1111                     },
1112                 );
1113             } else {
1114                 visit::walk_where_predicate(this, p);
1115             }
1116         });
1117         self.diagnostic_metadata.current_where_predicate = previous_value;
1118     }
1119
1120     fn visit_inline_asm(&mut self, asm: &'ast InlineAsm) {
1121         for (op, _) in &asm.operands {
1122             match op {
1123                 InlineAsmOperand::In { expr, .. }
1124                 | InlineAsmOperand::Out { expr: Some(expr), .. }
1125                 | InlineAsmOperand::InOut { expr, .. } => self.visit_expr(expr),
1126                 InlineAsmOperand::Out { expr: None, .. } => {}
1127                 InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
1128                     self.visit_expr(in_expr);
1129                     if let Some(out_expr) = out_expr {
1130                         self.visit_expr(out_expr);
1131                     }
1132                 }
1133                 InlineAsmOperand::Const { anon_const, .. } => {
1134                     // Although this is `DefKind::AnonConst`, it is allowed to reference outer
1135                     // generic parameters like an inline const.
1136                     self.resolve_inline_const(anon_const);
1137                 }
1138                 InlineAsmOperand::Sym { sym } => self.visit_inline_asm_sym(sym),
1139             }
1140         }
1141     }
1142
1143     fn visit_inline_asm_sym(&mut self, sym: &'ast InlineAsmSym) {
1144         // This is similar to the code for AnonConst.
1145         self.with_rib(ValueNS, InlineAsmSymRibKind, |this| {
1146             this.with_rib(TypeNS, InlineAsmSymRibKind, |this| {
1147                 this.with_label_rib(InlineAsmSymRibKind, |this| {
1148                     this.smart_resolve_path(sym.id, &sym.qself, &sym.path, PathSource::Expr(None));
1149                     visit::walk_inline_asm_sym(this, sym);
1150                 });
1151             })
1152         });
1153     }
1154 }
1155
1156 impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
1157     fn new(resolver: &'b mut Resolver<'a>) -> LateResolutionVisitor<'a, 'b, 'ast> {
1158         // During late resolution we only track the module component of the parent scope,
1159         // although it may be useful to track other components as well for diagnostics.
1160         let graph_root = resolver.graph_root;
1161         let parent_scope = ParentScope::module(graph_root, resolver);
1162         let start_rib_kind = ModuleRibKind(graph_root);
1163         LateResolutionVisitor {
1164             r: resolver,
1165             parent_scope,
1166             ribs: PerNS {
1167                 value_ns: vec![Rib::new(start_rib_kind)],
1168                 type_ns: vec![Rib::new(start_rib_kind)],
1169                 macro_ns: vec![Rib::new(start_rib_kind)],
1170             },
1171             label_ribs: Vec::new(),
1172             lifetime_ribs: Vec::new(),
1173             lifetime_elision_candidates: None,
1174             current_trait_ref: None,
1175             diagnostic_metadata: Box::new(DiagnosticMetadata::default()),
1176             // errors at module scope should always be reported
1177             in_func_body: false,
1178             lifetime_uses: Default::default(),
1179         }
1180     }
1181
1182     fn maybe_resolve_ident_in_lexical_scope(
1183         &mut self,
1184         ident: Ident,
1185         ns: Namespace,
1186     ) -> Option<LexicalScopeBinding<'a>> {
1187         self.r.resolve_ident_in_lexical_scope(
1188             ident,
1189             ns,
1190             &self.parent_scope,
1191             None,
1192             &self.ribs[ns],
1193             None,
1194         )
1195     }
1196
1197     fn resolve_ident_in_lexical_scope(
1198         &mut self,
1199         ident: Ident,
1200         ns: Namespace,
1201         finalize: Option<Finalize>,
1202         ignore_binding: Option<&'a NameBinding<'a>>,
1203     ) -> Option<LexicalScopeBinding<'a>> {
1204         self.r.resolve_ident_in_lexical_scope(
1205             ident,
1206             ns,
1207             &self.parent_scope,
1208             finalize,
1209             &self.ribs[ns],
1210             ignore_binding,
1211         )
1212     }
1213
1214     fn resolve_path(
1215         &mut self,
1216         path: &[Segment],
1217         opt_ns: Option<Namespace>, // `None` indicates a module path in import
1218         finalize: Option<Finalize>,
1219     ) -> PathResult<'a> {
1220         self.r.resolve_path_with_ribs(
1221             path,
1222             opt_ns,
1223             &self.parent_scope,
1224             finalize,
1225             Some(&self.ribs),
1226             None,
1227         )
1228     }
1229
1230     // AST resolution
1231     //
1232     // We maintain a list of value ribs and type ribs.
1233     //
1234     // Simultaneously, we keep track of the current position in the module
1235     // graph in the `parent_scope.module` pointer. When we go to resolve a name in
1236     // the value or type namespaces, we first look through all the ribs and
1237     // then query the module graph. When we resolve a name in the module
1238     // namespace, we can skip all the ribs (since nested modules are not
1239     // allowed within blocks in Rust) and jump straight to the current module
1240     // graph node.
1241     //
1242     // Named implementations are handled separately. When we find a method
1243     // call, we consult the module node to find all of the implementations in
1244     // scope. This information is lazily cached in the module node. We then
1245     // generate a fake "implementation scope" containing all the
1246     // implementations thus found, for compatibility with old resolve pass.
1247
1248     /// Do some `work` within a new innermost rib of the given `kind` in the given namespace (`ns`).
1249     fn with_rib<T>(
1250         &mut self,
1251         ns: Namespace,
1252         kind: RibKind<'a>,
1253         work: impl FnOnce(&mut Self) -> T,
1254     ) -> T {
1255         self.ribs[ns].push(Rib::new(kind));
1256         let ret = work(self);
1257         self.ribs[ns].pop();
1258         ret
1259     }
1260
1261     fn with_scope<T>(&mut self, id: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
1262         if let Some(module) = self.r.get_module(self.r.local_def_id(id).to_def_id()) {
1263             // Move down in the graph.
1264             let orig_module = replace(&mut self.parent_scope.module, module);
1265             self.with_rib(ValueNS, ModuleRibKind(module), |this| {
1266                 this.with_rib(TypeNS, ModuleRibKind(module), |this| {
1267                     let ret = f(this);
1268                     this.parent_scope.module = orig_module;
1269                     ret
1270                 })
1271             })
1272         } else {
1273             f(self)
1274         }
1275     }
1276
1277     fn visit_generic_params(&mut self, params: &'ast [GenericParam], add_self_upper: bool) {
1278         // For type parameter defaults, we have to ban access
1279         // to following type parameters, as the InternalSubsts can only
1280         // provide previous type parameters as they're built. We
1281         // put all the parameters on the ban list and then remove
1282         // them one by one as they are processed and become available.
1283         let mut forward_ty_ban_rib = Rib::new(ForwardGenericParamBanRibKind);
1284         let mut forward_const_ban_rib = Rib::new(ForwardGenericParamBanRibKind);
1285         for param in params.iter() {
1286             match param.kind {
1287                 GenericParamKind::Type { .. } => {
1288                     forward_ty_ban_rib
1289                         .bindings
1290                         .insert(Ident::with_dummy_span(param.ident.name), Res::Err);
1291                 }
1292                 GenericParamKind::Const { .. } => {
1293                     forward_const_ban_rib
1294                         .bindings
1295                         .insert(Ident::with_dummy_span(param.ident.name), Res::Err);
1296                 }
1297                 GenericParamKind::Lifetime => {}
1298             }
1299         }
1300
1301         // rust-lang/rust#61631: The type `Self` is essentially
1302         // another type parameter. For ADTs, we consider it
1303         // well-defined only after all of the ADT type parameters have
1304         // been provided. Therefore, we do not allow use of `Self`
1305         // anywhere in ADT type parameter defaults.
1306         //
1307         // (We however cannot ban `Self` for defaults on *all* generic
1308         // lists; e.g. trait generics can usefully refer to `Self`,
1309         // such as in the case of `trait Add<Rhs = Self>`.)
1310         if add_self_upper {
1311             // (`Some` if + only if we are in ADT's generics.)
1312             forward_ty_ban_rib.bindings.insert(Ident::with_dummy_span(kw::SelfUpper), Res::Err);
1313         }
1314
1315         self.with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
1316             for param in params {
1317                 match param.kind {
1318                     GenericParamKind::Lifetime => {
1319                         for bound in &param.bounds {
1320                             this.visit_param_bound(bound, BoundKind::Bound);
1321                         }
1322                     }
1323                     GenericParamKind::Type { ref default } => {
1324                         for bound in &param.bounds {
1325                             this.visit_param_bound(bound, BoundKind::Bound);
1326                         }
1327
1328                         if let Some(ref ty) = default {
1329                             this.ribs[TypeNS].push(forward_ty_ban_rib);
1330                             this.ribs[ValueNS].push(forward_const_ban_rib);
1331                             this.visit_ty(ty);
1332                             forward_const_ban_rib = this.ribs[ValueNS].pop().unwrap();
1333                             forward_ty_ban_rib = this.ribs[TypeNS].pop().unwrap();
1334                         }
1335
1336                         // Allow all following defaults to refer to this type parameter.
1337                         forward_ty_ban_rib
1338                             .bindings
1339                             .remove(&Ident::with_dummy_span(param.ident.name));
1340                     }
1341                     GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
1342                         // Const parameters can't have param bounds.
1343                         assert!(param.bounds.is_empty());
1344
1345                         this.ribs[TypeNS].push(Rib::new(ConstParamTyRibKind));
1346                         this.ribs[ValueNS].push(Rib::new(ConstParamTyRibKind));
1347                         this.with_lifetime_rib(LifetimeRibKind::ConstGeneric, |this| {
1348                             this.visit_ty(ty)
1349                         });
1350                         this.ribs[TypeNS].pop().unwrap();
1351                         this.ribs[ValueNS].pop().unwrap();
1352
1353                         if let Some(ref expr) = default {
1354                             this.ribs[TypeNS].push(forward_ty_ban_rib);
1355                             this.ribs[ValueNS].push(forward_const_ban_rib);
1356                             this.with_lifetime_rib(LifetimeRibKind::ConstGeneric, |this| {
1357                                 this.resolve_anon_const(expr, IsRepeatExpr::No)
1358                             });
1359                             forward_const_ban_rib = this.ribs[ValueNS].pop().unwrap();
1360                             forward_ty_ban_rib = this.ribs[TypeNS].pop().unwrap();
1361                         }
1362
1363                         // Allow all following defaults to refer to this const parameter.
1364                         forward_const_ban_rib
1365                             .bindings
1366                             .remove(&Ident::with_dummy_span(param.ident.name));
1367                     }
1368                 }
1369             }
1370         })
1371     }
1372
1373     #[instrument(level = "debug", skip(self, work))]
1374     fn with_lifetime_rib<T>(
1375         &mut self,
1376         kind: LifetimeRibKind,
1377         work: impl FnOnce(&mut Self) -> T,
1378     ) -> T {
1379         self.lifetime_ribs.push(LifetimeRib::new(kind));
1380         let outer_elision_candidates = self.lifetime_elision_candidates.take();
1381         let ret = work(self);
1382         self.lifetime_elision_candidates = outer_elision_candidates;
1383         self.lifetime_ribs.pop();
1384         ret
1385     }
1386
1387     #[instrument(level = "debug", skip(self))]
1388     fn resolve_lifetime(&mut self, lifetime: &'ast Lifetime, use_ctxt: visit::LifetimeCtxt) {
1389         let ident = lifetime.ident;
1390
1391         if ident.name == kw::StaticLifetime {
1392             self.record_lifetime_res(
1393                 lifetime.id,
1394                 LifetimeRes::Static,
1395                 LifetimeElisionCandidate::Named,
1396             );
1397             return;
1398         }
1399
1400         if ident.name == kw::UnderscoreLifetime {
1401             return self.resolve_anonymous_lifetime(lifetime, false);
1402         }
1403
1404         let mut lifetime_rib_iter = self.lifetime_ribs.iter().rev();
1405         while let Some(rib) = lifetime_rib_iter.next() {
1406             let normalized_ident = ident.normalize_to_macros_2_0();
1407             if let Some(&(_, res)) = rib.bindings.get(&normalized_ident) {
1408                 self.record_lifetime_res(lifetime.id, res, LifetimeElisionCandidate::Named);
1409
1410                 if let LifetimeRes::Param { param, .. } = res {
1411                     match self.lifetime_uses.entry(param) {
1412                         Entry::Vacant(v) => {
1413                             debug!("First use of {:?} at {:?}", res, ident.span);
1414                             let use_set = self
1415                                 .lifetime_ribs
1416                                 .iter()
1417                                 .rev()
1418                                 .find_map(|rib| match rib.kind {
1419                                     // Do not suggest eliding a lifetime where an anonymous
1420                                     // lifetime would be illegal.
1421                                     LifetimeRibKind::Item
1422                                     | LifetimeRibKind::AnonymousReportError
1423                                     | LifetimeRibKind::ElisionFailure => Some(LifetimeUseSet::Many),
1424                                     // An anonymous lifetime is legal here, go ahead.
1425                                     LifetimeRibKind::AnonymousCreateParameter { .. } => {
1426                                         Some(LifetimeUseSet::One { use_span: ident.span, use_ctxt })
1427                                     }
1428                                     // Only report if eliding the lifetime would have the same
1429                                     // semantics.
1430                                     LifetimeRibKind::Elided(r) => Some(if res == r {
1431                                         LifetimeUseSet::One { use_span: ident.span, use_ctxt }
1432                                     } else {
1433                                         LifetimeUseSet::Many
1434                                     }),
1435                                     LifetimeRibKind::Generics { .. } => None,
1436                                     LifetimeRibKind::ConstGeneric | LifetimeRibKind::AnonConst => {
1437                                         span_bug!(ident.span, "unexpected rib kind: {:?}", rib.kind)
1438                                     }
1439                                 })
1440                                 .unwrap_or(LifetimeUseSet::Many);
1441                             debug!(?use_ctxt, ?use_set);
1442                             v.insert(use_set);
1443                         }
1444                         Entry::Occupied(mut o) => {
1445                             debug!("Many uses of {:?} at {:?}", res, ident.span);
1446                             *o.get_mut() = LifetimeUseSet::Many;
1447                         }
1448                     }
1449                 }
1450                 return;
1451             }
1452
1453             match rib.kind {
1454                 LifetimeRibKind::Item => break,
1455                 LifetimeRibKind::ConstGeneric => {
1456                     self.emit_non_static_lt_in_const_generic_error(lifetime);
1457                     self.record_lifetime_res(
1458                         lifetime.id,
1459                         LifetimeRes::Error,
1460                         LifetimeElisionCandidate::Ignore,
1461                     );
1462                     return;
1463                 }
1464                 LifetimeRibKind::AnonConst => {
1465                     self.maybe_emit_forbidden_non_static_lifetime_error(lifetime);
1466                     self.record_lifetime_res(
1467                         lifetime.id,
1468                         LifetimeRes::Error,
1469                         LifetimeElisionCandidate::Ignore,
1470                     );
1471                     return;
1472                 }
1473                 LifetimeRibKind::AnonymousCreateParameter { .. }
1474                 | LifetimeRibKind::Elided(_)
1475                 | LifetimeRibKind::Generics { .. }
1476                 | LifetimeRibKind::ElisionFailure
1477                 | LifetimeRibKind::AnonymousReportError => {}
1478             }
1479         }
1480
1481         let mut outer_res = None;
1482         for rib in lifetime_rib_iter {
1483             let normalized_ident = ident.normalize_to_macros_2_0();
1484             if let Some((&outer, _)) = rib.bindings.get_key_value(&normalized_ident) {
1485                 outer_res = Some(outer);
1486                 break;
1487             }
1488         }
1489
1490         self.emit_undeclared_lifetime_error(lifetime, outer_res);
1491         self.record_lifetime_res(lifetime.id, LifetimeRes::Error, LifetimeElisionCandidate::Named);
1492     }
1493
1494     #[instrument(level = "debug", skip(self))]
1495     fn resolve_anonymous_lifetime(&mut self, lifetime: &Lifetime, elided: bool) {
1496         debug_assert_eq!(lifetime.ident.name, kw::UnderscoreLifetime);
1497
1498         let missing_lifetime = MissingLifetime {
1499             id: lifetime.id,
1500             span: lifetime.ident.span,
1501             kind: if elided {
1502                 MissingLifetimeKind::Ampersand
1503             } else {
1504                 MissingLifetimeKind::Underscore
1505             },
1506             count: 1,
1507         };
1508         let elision_candidate = LifetimeElisionCandidate::Missing(missing_lifetime);
1509         for rib in self.lifetime_ribs.iter().rev() {
1510             debug!(?rib.kind);
1511             match rib.kind {
1512                 LifetimeRibKind::AnonymousCreateParameter { binder, .. } => {
1513                     let res = self.create_fresh_lifetime(lifetime.id, lifetime.ident, binder);
1514                     self.record_lifetime_res(lifetime.id, res, elision_candidate);
1515                     return;
1516                 }
1517                 LifetimeRibKind::AnonymousReportError => {
1518                     let (msg, note) = if elided {
1519                         (
1520                             "`&` without an explicit lifetime name cannot be used here",
1521                             "explicit lifetime name needed here",
1522                         )
1523                     } else {
1524                         ("`'_` cannot be used here", "`'_` is a reserved lifetime name")
1525                     };
1526                     rustc_errors::struct_span_err!(
1527                         self.r.session,
1528                         lifetime.ident.span,
1529                         E0637,
1530                         "{}",
1531                         msg,
1532                     )
1533                     .span_label(lifetime.ident.span, note)
1534                     .emit();
1535
1536                     self.record_lifetime_res(lifetime.id, LifetimeRes::Error, elision_candidate);
1537                     return;
1538                 }
1539                 LifetimeRibKind::Elided(res) => {
1540                     self.record_lifetime_res(lifetime.id, res, elision_candidate);
1541                     return;
1542                 }
1543                 LifetimeRibKind::ElisionFailure => {
1544                     self.diagnostic_metadata.current_elision_failures.push(missing_lifetime);
1545                     self.record_lifetime_res(lifetime.id, LifetimeRes::Error, elision_candidate);
1546                     return;
1547                 }
1548                 LifetimeRibKind::Item => break,
1549                 LifetimeRibKind::Generics { .. } | LifetimeRibKind::ConstGeneric => {}
1550                 LifetimeRibKind::AnonConst => {
1551                     // There is always an `Elided(LifetimeRes::Static)` inside an `AnonConst`.
1552                     span_bug!(lifetime.ident.span, "unexpected rib kind: {:?}", rib.kind)
1553                 }
1554             }
1555         }
1556         self.record_lifetime_res(lifetime.id, LifetimeRes::Error, elision_candidate);
1557         self.report_missing_lifetime_specifiers(vec![missing_lifetime], None);
1558     }
1559
1560     #[instrument(level = "debug", skip(self))]
1561     fn resolve_elided_lifetime(&mut self, anchor_id: NodeId, span: Span) {
1562         let id = self.r.next_node_id();
1563         let lt = Lifetime { id, ident: Ident::new(kw::UnderscoreLifetime, span) };
1564
1565         self.record_lifetime_res(
1566             anchor_id,
1567             LifetimeRes::ElidedAnchor { start: id, end: NodeId::from_u32(id.as_u32() + 1) },
1568             LifetimeElisionCandidate::Ignore,
1569         );
1570         self.resolve_anonymous_lifetime(&lt, true);
1571     }
1572
1573     #[instrument(level = "debug", skip(self))]
1574     fn create_fresh_lifetime(&mut self, id: NodeId, ident: Ident, binder: NodeId) -> LifetimeRes {
1575         debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
1576         debug!(?ident.span);
1577
1578         // Leave the responsibility to create the `LocalDefId` to lowering.
1579         let param = self.r.next_node_id();
1580         let res = LifetimeRes::Fresh { param, binder };
1581
1582         // Record the created lifetime parameter so lowering can pick it up and add it to HIR.
1583         self.r
1584             .extra_lifetime_params_map
1585             .entry(binder)
1586             .or_insert_with(Vec::new)
1587             .push((ident, param, res));
1588         res
1589     }
1590
1591     #[instrument(level = "debug", skip(self))]
1592     fn resolve_elided_lifetimes_in_path(
1593         &mut self,
1594         path_id: NodeId,
1595         partial_res: PartialRes,
1596         path: &[Segment],
1597         source: PathSource<'_>,
1598         path_span: Span,
1599     ) {
1600         let proj_start = path.len() - partial_res.unresolved_segments();
1601         for (i, segment) in path.iter().enumerate() {
1602             if segment.has_lifetime_args {
1603                 continue;
1604             }
1605             let Some(segment_id) = segment.id else {
1606                 continue;
1607             };
1608
1609             // Figure out if this is a type/trait segment,
1610             // which may need lifetime elision performed.
1611             let type_def_id = match partial_res.base_res() {
1612                 Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => self.r.parent(def_id),
1613                 Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => self.r.parent(def_id),
1614                 Res::Def(DefKind::Struct, def_id)
1615                 | Res::Def(DefKind::Union, def_id)
1616                 | Res::Def(DefKind::Enum, def_id)
1617                 | Res::Def(DefKind::TyAlias, def_id)
1618                 | Res::Def(DefKind::Trait, def_id)
1619                     if i + 1 == proj_start =>
1620                 {
1621                     def_id
1622                 }
1623                 _ => continue,
1624             };
1625
1626             let expected_lifetimes = self.r.item_generics_num_lifetimes(type_def_id);
1627             if expected_lifetimes == 0 {
1628                 continue;
1629             }
1630
1631             let node_ids = self.r.next_node_ids(expected_lifetimes);
1632             self.record_lifetime_res(
1633                 segment_id,
1634                 LifetimeRes::ElidedAnchor { start: node_ids.start, end: node_ids.end },
1635                 LifetimeElisionCandidate::Ignore,
1636             );
1637
1638             let inferred = match source {
1639                 PathSource::Trait(..) | PathSource::TraitItem(..) | PathSource::Type => false,
1640                 PathSource::Expr(..)
1641                 | PathSource::Pat
1642                 | PathSource::Struct
1643                 | PathSource::TupleStruct(..) => true,
1644             };
1645             if inferred {
1646                 // Do not create a parameter for patterns and expressions: type checking can infer
1647                 // the appropriate lifetime for us.
1648                 for id in node_ids {
1649                     self.record_lifetime_res(
1650                         id,
1651                         LifetimeRes::Infer,
1652                         LifetimeElisionCandidate::Named,
1653                     );
1654                 }
1655                 continue;
1656             }
1657
1658             let elided_lifetime_span = if segment.has_generic_args {
1659                 // If there are brackets, but not generic arguments, then use the opening bracket
1660                 segment.args_span.with_hi(segment.args_span.lo() + BytePos(1))
1661             } else {
1662                 // If there are no brackets, use the identifier span.
1663                 // HACK: we use find_ancestor_inside to properly suggest elided spans in paths
1664                 // originating from macros, since the segment's span might be from a macro arg.
1665                 segment.ident.span.find_ancestor_inside(path_span).unwrap_or(path_span)
1666             };
1667             let ident = Ident::new(kw::UnderscoreLifetime, elided_lifetime_span);
1668
1669             let missing_lifetime = MissingLifetime {
1670                 id: node_ids.start,
1671                 span: elided_lifetime_span,
1672                 kind: if segment.has_generic_args {
1673                     MissingLifetimeKind::Comma
1674                 } else {
1675                     MissingLifetimeKind::Brackets
1676                 },
1677                 count: expected_lifetimes,
1678             };
1679             let mut should_lint = true;
1680             for rib in self.lifetime_ribs.iter().rev() {
1681                 match rib.kind {
1682                     // In create-parameter mode we error here because we don't want to support
1683                     // deprecated impl elision in new features like impl elision and `async fn`,
1684                     // both of which work using the `CreateParameter` mode:
1685                     //
1686                     //     impl Foo for std::cell::Ref<u32> // note lack of '_
1687                     //     async fn foo(_: std::cell::Ref<u32>) { ... }
1688                     LifetimeRibKind::AnonymousCreateParameter { report_in_path: true, .. } => {
1689                         let sess = self.r.session;
1690                         let mut err = rustc_errors::struct_span_err!(
1691                             sess,
1692                             path_span,
1693                             E0726,
1694                             "implicit elided lifetime not allowed here"
1695                         );
1696                         rustc_errors::add_elided_lifetime_in_path_suggestion(
1697                             sess.source_map(),
1698                             &mut err,
1699                             expected_lifetimes,
1700                             path_span,
1701                             !segment.has_generic_args,
1702                             elided_lifetime_span,
1703                         );
1704                         err.note("assuming a `'static` lifetime...");
1705                         err.emit();
1706                         should_lint = false;
1707
1708                         for id in node_ids {
1709                             self.record_lifetime_res(
1710                                 id,
1711                                 LifetimeRes::Error,
1712                                 LifetimeElisionCandidate::Named,
1713                             );
1714                         }
1715                         break;
1716                     }
1717                     // Do not create a parameter for patterns and expressions.
1718                     LifetimeRibKind::AnonymousCreateParameter { binder, .. } => {
1719                         // Group all suggestions into the first record.
1720                         let mut candidate = LifetimeElisionCandidate::Missing(missing_lifetime);
1721                         for id in node_ids {
1722                             let res = self.create_fresh_lifetime(id, ident, binder);
1723                             self.record_lifetime_res(
1724                                 id,
1725                                 res,
1726                                 replace(&mut candidate, LifetimeElisionCandidate::Named),
1727                             );
1728                         }
1729                         break;
1730                     }
1731                     LifetimeRibKind::Elided(res) => {
1732                         let mut candidate = LifetimeElisionCandidate::Missing(missing_lifetime);
1733                         for id in node_ids {
1734                             self.record_lifetime_res(
1735                                 id,
1736                                 res,
1737                                 replace(&mut candidate, LifetimeElisionCandidate::Ignore),
1738                             );
1739                         }
1740                         break;
1741                     }
1742                     LifetimeRibKind::ElisionFailure => {
1743                         self.diagnostic_metadata.current_elision_failures.push(missing_lifetime);
1744                         for id in node_ids {
1745                             self.record_lifetime_res(
1746                                 id,
1747                                 LifetimeRes::Error,
1748                                 LifetimeElisionCandidate::Ignore,
1749                             );
1750                         }
1751                         break;
1752                     }
1753                     // `LifetimeRes::Error`, which would usually be used in the case of
1754                     // `ReportError`, is unsuitable here, as we don't emit an error yet.  Instead,
1755                     // we simply resolve to an implicit lifetime, which will be checked later, at
1756                     // which point a suitable error will be emitted.
1757                     LifetimeRibKind::AnonymousReportError | LifetimeRibKind::Item => {
1758                         for id in node_ids {
1759                             self.record_lifetime_res(
1760                                 id,
1761                                 LifetimeRes::Error,
1762                                 LifetimeElisionCandidate::Ignore,
1763                             );
1764                         }
1765                         self.report_missing_lifetime_specifiers(vec![missing_lifetime], None);
1766                         break;
1767                     }
1768                     LifetimeRibKind::Generics { .. } | LifetimeRibKind::ConstGeneric => {}
1769                     LifetimeRibKind::AnonConst => {
1770                         // There is always an `Elided(LifetimeRes::Static)` inside an `AnonConst`.
1771                         span_bug!(elided_lifetime_span, "unexpected rib kind: {:?}", rib.kind)
1772                     }
1773                 }
1774             }
1775
1776             if should_lint {
1777                 self.r.lint_buffer.buffer_lint_with_diagnostic(
1778                     lint::builtin::ELIDED_LIFETIMES_IN_PATHS,
1779                     segment_id,
1780                     elided_lifetime_span,
1781                     "hidden lifetime parameters in types are deprecated",
1782                     lint::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
1783                         expected_lifetimes,
1784                         path_span,
1785                         !segment.has_generic_args,
1786                         elided_lifetime_span,
1787                     ),
1788                 );
1789             }
1790         }
1791     }
1792
1793     #[instrument(level = "debug", skip(self))]
1794     fn record_lifetime_res(
1795         &mut self,
1796         id: NodeId,
1797         res: LifetimeRes,
1798         candidate: LifetimeElisionCandidate,
1799     ) {
1800         if let Some(prev_res) = self.r.lifetimes_res_map.insert(id, res) {
1801             panic!(
1802                 "lifetime {:?} resolved multiple times ({:?} before, {:?} now)",
1803                 id, prev_res, res
1804             )
1805         }
1806         match res {
1807             LifetimeRes::Param { .. } | LifetimeRes::Fresh { .. } | LifetimeRes::Static => {
1808                 if let Some(ref mut candidates) = self.lifetime_elision_candidates {
1809                     candidates.push((res, candidate));
1810                 }
1811             }
1812             LifetimeRes::Infer | LifetimeRes::Error | LifetimeRes::ElidedAnchor { .. } => {}
1813         }
1814     }
1815
1816     #[instrument(level = "debug", skip(self))]
1817     fn record_lifetime_param(&mut self, id: NodeId, res: LifetimeRes) {
1818         if let Some(prev_res) = self.r.lifetimes_res_map.insert(id, res) {
1819             panic!(
1820                 "lifetime parameter {:?} resolved multiple times ({:?} before, {:?} now)",
1821                 id, prev_res, res
1822             )
1823         }
1824     }
1825
1826     /// Perform resolution of a function signature, accounting for lifetime elision.
1827     #[instrument(level = "debug", skip(self, inputs))]
1828     fn resolve_fn_signature(
1829         &mut self,
1830         fn_id: NodeId,
1831         has_self: bool,
1832         inputs: impl Iterator<Item = (Option<&'ast Pat>, &'ast Ty)> + Clone,
1833         output_ty: &'ast FnRetTy,
1834     ) {
1835         // Add each argument to the rib.
1836         let elision_lifetime = self.resolve_fn_params(has_self, inputs);
1837         debug!(?elision_lifetime);
1838
1839         let outer_failures = take(&mut self.diagnostic_metadata.current_elision_failures);
1840         let output_rib = if let Ok(res) = elision_lifetime.as_ref() {
1841             LifetimeRibKind::Elided(*res)
1842         } else {
1843             LifetimeRibKind::ElisionFailure
1844         };
1845         self.with_lifetime_rib(output_rib, |this| visit::walk_fn_ret_ty(this, &output_ty));
1846         let elision_failures =
1847             replace(&mut self.diagnostic_metadata.current_elision_failures, outer_failures);
1848         if !elision_failures.is_empty() {
1849             let Err(failure_info) = elision_lifetime else { bug!() };
1850             self.report_missing_lifetime_specifiers(elision_failures, Some(failure_info));
1851         }
1852     }
1853
1854     /// Resolve inside function parameters and parameter types.
1855     /// Returns the lifetime for elision in fn return type,
1856     /// or diagnostic information in case of elision failure.
1857     fn resolve_fn_params(
1858         &mut self,
1859         has_self: bool,
1860         inputs: impl Iterator<Item = (Option<&'ast Pat>, &'ast Ty)>,
1861     ) -> Result<LifetimeRes, (Vec<MissingLifetime>, Vec<ElisionFnParameter>)> {
1862         enum Elision {
1863             /// We have not found any candidate.
1864             None,
1865             /// We have a candidate bound to `self`.
1866             Self_(LifetimeRes),
1867             /// We have a candidate bound to a parameter.
1868             Param(LifetimeRes),
1869             /// We failed elision.
1870             Err,
1871         }
1872
1873         // Save elision state to reinstate it later.
1874         let outer_candidates = self.lifetime_elision_candidates.take();
1875
1876         // Result of elision.
1877         let mut elision_lifetime = Elision::None;
1878         // Information for diagnostics.
1879         let mut parameter_info = Vec::new();
1880         let mut all_candidates = Vec::new();
1881
1882         let mut bindings = smallvec![(PatBoundCtx::Product, Default::default())];
1883         for (index, (pat, ty)) in inputs.enumerate() {
1884             debug!(?pat, ?ty);
1885             self.with_lifetime_rib(LifetimeRibKind::Elided(LifetimeRes::Infer), |this| {
1886                 if let Some(pat) = pat {
1887                     this.resolve_pattern(pat, PatternSource::FnParam, &mut bindings);
1888                 }
1889             });
1890
1891             // Record elision candidates only for this parameter.
1892             debug_assert_matches!(self.lifetime_elision_candidates, None);
1893             self.lifetime_elision_candidates = Some(Default::default());
1894             self.visit_ty(ty);
1895             let local_candidates = self.lifetime_elision_candidates.take();
1896
1897             if let Some(candidates) = local_candidates {
1898                 let distinct: FxHashSet<_> = candidates.iter().map(|(res, _)| *res).collect();
1899                 let lifetime_count = distinct.len();
1900                 if lifetime_count != 0 {
1901                     parameter_info.push(ElisionFnParameter {
1902                         index,
1903                         ident: if let Some(pat) = pat && let PatKind::Ident(_, ident, _) = pat.kind {
1904                             Some(ident)
1905                         } else {
1906                             None
1907                         },
1908                         lifetime_count,
1909                         span: ty.span,
1910                     });
1911                     all_candidates.extend(candidates.into_iter().filter_map(|(_, candidate)| {
1912                         match candidate {
1913                             LifetimeElisionCandidate::Ignore | LifetimeElisionCandidate::Named => {
1914                                 None
1915                             }
1916                             LifetimeElisionCandidate::Missing(missing) => Some(missing),
1917                         }
1918                     }));
1919                 }
1920                 let mut distinct_iter = distinct.into_iter();
1921                 if let Some(res) = distinct_iter.next() {
1922                     match elision_lifetime {
1923                         // We are the first parameter to bind lifetimes.
1924                         Elision::None => {
1925                             if distinct_iter.next().is_none() {
1926                                 // We have a single lifetime => success.
1927                                 elision_lifetime = Elision::Param(res)
1928                             } else {
1929                                 // We have have multiple lifetimes => error.
1930                                 elision_lifetime = Elision::Err;
1931                             }
1932                         }
1933                         // We have 2 parameters that bind lifetimes => error.
1934                         Elision::Param(_) => elision_lifetime = Elision::Err,
1935                         // `self` elision takes precedence over everything else.
1936                         Elision::Self_(_) | Elision::Err => {}
1937                     }
1938                 }
1939             }
1940
1941             // Handle `self` specially.
1942             if index == 0 && has_self {
1943                 let self_lifetime = self.find_lifetime_for_self(ty);
1944                 if let Set1::One(lifetime) = self_lifetime {
1945                     // We found `self` elision.
1946                     elision_lifetime = Elision::Self_(lifetime);
1947                 } else {
1948                     // We do not have `self` elision: disregard the `Elision::Param` that we may
1949                     // have found.
1950                     elision_lifetime = Elision::None;
1951                 }
1952             }
1953             debug!("(resolving function / closure) recorded parameter");
1954         }
1955
1956         // Reinstate elision state.
1957         debug_assert_matches!(self.lifetime_elision_candidates, None);
1958         self.lifetime_elision_candidates = outer_candidates;
1959
1960         if let Elision::Param(res) | Elision::Self_(res) = elision_lifetime {
1961             return Ok(res);
1962         }
1963
1964         // We do not have a candidate.
1965         Err((all_candidates, parameter_info))
1966     }
1967
1968     /// List all the lifetimes that appear in the provided type.
1969     fn find_lifetime_for_self(&self, ty: &'ast Ty) -> Set1<LifetimeRes> {
1970         struct SelfVisitor<'r, 'a> {
1971             r: &'r Resolver<'a>,
1972             impl_self: Option<Res>,
1973             lifetime: Set1<LifetimeRes>,
1974         }
1975
1976         impl SelfVisitor<'_, '_> {
1977             // Look for `self: &'a Self` - also desugared from `&'a self`,
1978             // and if that matches, use it for elision and return early.
1979             fn is_self_ty(&self, ty: &Ty) -> bool {
1980                 match ty.kind {
1981                     TyKind::ImplicitSelf => true,
1982                     TyKind::Path(None, _) => {
1983                         let path_res = self.r.partial_res_map[&ty.id].full_res();
1984                         if let Some(Res::SelfTyParam { .. } | Res::SelfTyAlias { .. }) = path_res {
1985                             return true;
1986                         }
1987                         self.impl_self.is_some() && path_res == self.impl_self
1988                     }
1989                     _ => false,
1990                 }
1991             }
1992         }
1993
1994         impl<'a> Visitor<'a> for SelfVisitor<'_, '_> {
1995             fn visit_ty(&mut self, ty: &'a Ty) {
1996                 trace!("SelfVisitor considering ty={:?}", ty);
1997                 if let TyKind::Rptr(lt, ref mt) = ty.kind && self.is_self_ty(&mt.ty) {
1998                     let lt_id = if let Some(lt) = lt {
1999                         lt.id
2000                     } else {
2001                         let res = self.r.lifetimes_res_map[&ty.id];
2002                         let LifetimeRes::ElidedAnchor { start, .. } = res else { bug!() };
2003                         start
2004                     };
2005                     let lt_res = self.r.lifetimes_res_map[&lt_id];
2006                     trace!("SelfVisitor inserting res={:?}", lt_res);
2007                     self.lifetime.insert(lt_res);
2008                 }
2009                 visit::walk_ty(self, ty)
2010             }
2011         }
2012
2013         let impl_self = self
2014             .diagnostic_metadata
2015             .current_self_type
2016             .as_ref()
2017             .and_then(|ty| {
2018                 if let TyKind::Path(None, _) = ty.kind {
2019                     self.r.partial_res_map.get(&ty.id)
2020                 } else {
2021                     None
2022                 }
2023             })
2024             .and_then(|res| res.full_res())
2025             .filter(|res| {
2026                 // Permit the types that unambiguously always
2027                 // result in the same type constructor being used
2028                 // (it can't differ between `Self` and `self`).
2029                 matches!(
2030                     res,
2031                     Res::Def(DefKind::Struct | DefKind::Union | DefKind::Enum, _,) | Res::PrimTy(_)
2032                 )
2033             });
2034         let mut visitor = SelfVisitor { r: self.r, impl_self, lifetime: Set1::Empty };
2035         visitor.visit_ty(ty);
2036         trace!("SelfVisitor found={:?}", visitor.lifetime);
2037         visitor.lifetime
2038     }
2039
2040     /// Searches the current set of local scopes for labels. Returns the `NodeId` of the resolved
2041     /// label and reports an error if the label is not found or is unreachable.
2042     fn resolve_label(&mut self, mut label: Ident) -> Result<(NodeId, Span), ResolutionError<'a>> {
2043         let mut suggestion = None;
2044
2045         for i in (0..self.label_ribs.len()).rev() {
2046             let rib = &self.label_ribs[i];
2047
2048             if let MacroDefinition(def) = rib.kind {
2049                 // If an invocation of this macro created `ident`, give up on `ident`
2050                 // and switch to `ident`'s source from the macro definition.
2051                 if def == self.r.macro_def(label.span.ctxt()) {
2052                     label.span.remove_mark();
2053                 }
2054             }
2055
2056             let ident = label.normalize_to_macro_rules();
2057             if let Some((ident, id)) = rib.bindings.get_key_value(&ident) {
2058                 let definition_span = ident.span;
2059                 return if self.is_label_valid_from_rib(i) {
2060                     Ok((*id, definition_span))
2061                 } else {
2062                     Err(ResolutionError::UnreachableLabel {
2063                         name: label.name,
2064                         definition_span,
2065                         suggestion,
2066                     })
2067                 };
2068             }
2069
2070             // Diagnostics: Check if this rib contains a label with a similar name, keep track of
2071             // the first such label that is encountered.
2072             suggestion = suggestion.or_else(|| self.suggestion_for_label_in_rib(i, label));
2073         }
2074
2075         Err(ResolutionError::UndeclaredLabel { name: label.name, suggestion })
2076     }
2077
2078     /// Determine whether or not a label from the `rib_index`th label rib is reachable.
2079     fn is_label_valid_from_rib(&self, rib_index: usize) -> bool {
2080         let ribs = &self.label_ribs[rib_index + 1..];
2081
2082         for rib in ribs {
2083             if rib.kind.is_label_barrier() {
2084                 return false;
2085             }
2086         }
2087
2088         true
2089     }
2090
2091     fn resolve_adt(&mut self, item: &'ast Item, generics: &'ast Generics) {
2092         debug!("resolve_adt");
2093         self.with_current_self_item(item, |this| {
2094             this.with_generic_param_rib(
2095                 &generics.params,
2096                 ItemRibKind(HasGenericParams::Yes(generics.span)),
2097                 LifetimeRibKind::Generics {
2098                     binder: item.id,
2099                     kind: LifetimeBinderKind::Item,
2100                     span: generics.span,
2101                 },
2102                 |this| {
2103                     let item_def_id = this.r.local_def_id(item.id).to_def_id();
2104                     this.with_self_rib(
2105                         Res::SelfTyAlias {
2106                             alias_to: item_def_id,
2107                             forbid_generic: false,
2108                             is_trait_impl: false,
2109                         },
2110                         |this| {
2111                             visit::walk_item(this, item);
2112                         },
2113                     );
2114                 },
2115             );
2116         });
2117     }
2118
2119     fn future_proof_import(&mut self, use_tree: &UseTree) {
2120         let segments = &use_tree.prefix.segments;
2121         if !segments.is_empty() {
2122             let ident = segments[0].ident;
2123             if ident.is_path_segment_keyword() || ident.span.rust_2015() {
2124                 return;
2125             }
2126
2127             let nss = match use_tree.kind {
2128                 UseTreeKind::Simple(..) if segments.len() == 1 => &[TypeNS, ValueNS][..],
2129                 _ => &[TypeNS],
2130             };
2131             let report_error = |this: &Self, ns| {
2132                 let what = if ns == TypeNS { "type parameters" } else { "local variables" };
2133                 if this.should_report_errs() {
2134                     this.r
2135                         .session
2136                         .span_err(ident.span, &format!("imports cannot refer to {}", what));
2137                 }
2138             };
2139
2140             for &ns in nss {
2141                 match self.maybe_resolve_ident_in_lexical_scope(ident, ns) {
2142                     Some(LexicalScopeBinding::Res(..)) => {
2143                         report_error(self, ns);
2144                     }
2145                     Some(LexicalScopeBinding::Item(binding)) => {
2146                         if let Some(LexicalScopeBinding::Res(..)) =
2147                             self.resolve_ident_in_lexical_scope(ident, ns, None, Some(binding))
2148                         {
2149                             report_error(self, ns);
2150                         }
2151                     }
2152                     None => {}
2153                 }
2154             }
2155         } else if let UseTreeKind::Nested(use_trees) = &use_tree.kind {
2156             for (use_tree, _) in use_trees {
2157                 self.future_proof_import(use_tree);
2158             }
2159         }
2160     }
2161
2162     fn resolve_item(&mut self, item: &'ast Item) {
2163         let name = item.ident.name;
2164         debug!("(resolving item) resolving {} ({:?})", name, item.kind);
2165
2166         match item.kind {
2167             ItemKind::TyAlias(box TyAlias { ref generics, .. }) => {
2168                 self.with_generic_param_rib(
2169                     &generics.params,
2170                     ItemRibKind(HasGenericParams::Yes(generics.span)),
2171                     LifetimeRibKind::Generics {
2172                         binder: item.id,
2173                         kind: LifetimeBinderKind::Item,
2174                         span: generics.span,
2175                     },
2176                     |this| visit::walk_item(this, item),
2177                 );
2178             }
2179
2180             ItemKind::Fn(box Fn { ref generics, .. }) => {
2181                 self.with_generic_param_rib(
2182                     &generics.params,
2183                     ItemRibKind(HasGenericParams::Yes(generics.span)),
2184                     LifetimeRibKind::Generics {
2185                         binder: item.id,
2186                         kind: LifetimeBinderKind::Function,
2187                         span: generics.span,
2188                     },
2189                     |this| visit::walk_item(this, item),
2190                 );
2191             }
2192
2193             ItemKind::Enum(_, ref generics)
2194             | ItemKind::Struct(_, ref generics)
2195             | ItemKind::Union(_, ref generics) => {
2196                 self.resolve_adt(item, generics);
2197             }
2198
2199             ItemKind::Impl(box Impl {
2200                 ref generics,
2201                 ref of_trait,
2202                 ref self_ty,
2203                 items: ref impl_items,
2204                 ..
2205             }) => {
2206                 self.diagnostic_metadata.current_impl_items = Some(impl_items);
2207                 self.resolve_implementation(generics, of_trait, &self_ty, item.id, impl_items);
2208                 self.diagnostic_metadata.current_impl_items = None;
2209             }
2210
2211             ItemKind::Trait(box Trait { ref generics, ref bounds, ref items, .. }) => {
2212                 // Create a new rib for the trait-wide type parameters.
2213                 self.with_generic_param_rib(
2214                     &generics.params,
2215                     ItemRibKind(HasGenericParams::Yes(generics.span)),
2216                     LifetimeRibKind::Generics {
2217                         binder: item.id,
2218                         kind: LifetimeBinderKind::Item,
2219                         span: generics.span,
2220                     },
2221                     |this| {
2222                         let local_def_id = this.r.local_def_id(item.id).to_def_id();
2223                         this.with_self_rib(Res::SelfTyParam { trait_: local_def_id }, |this| {
2224                             this.visit_generics(generics);
2225                             walk_list!(this, visit_param_bound, bounds, BoundKind::SuperTraits);
2226                             this.resolve_trait_items(items);
2227                         });
2228                     },
2229                 );
2230             }
2231
2232             ItemKind::TraitAlias(ref generics, ref bounds) => {
2233                 // Create a new rib for the trait-wide type parameters.
2234                 self.with_generic_param_rib(
2235                     &generics.params,
2236                     ItemRibKind(HasGenericParams::Yes(generics.span)),
2237                     LifetimeRibKind::Generics {
2238                         binder: item.id,
2239                         kind: LifetimeBinderKind::Item,
2240                         span: generics.span,
2241                     },
2242                     |this| {
2243                         let local_def_id = this.r.local_def_id(item.id).to_def_id();
2244                         this.with_self_rib(Res::SelfTyParam { trait_: local_def_id }, |this| {
2245                             this.visit_generics(generics);
2246                             walk_list!(this, visit_param_bound, bounds, BoundKind::Bound);
2247                         });
2248                     },
2249                 );
2250             }
2251
2252             ItemKind::Mod(..) | ItemKind::ForeignMod(_) => {
2253                 self.with_scope(item.id, |this| {
2254                     visit::walk_item(this, item);
2255                 });
2256             }
2257
2258             ItemKind::Static(ref ty, _, ref expr) | ItemKind::Const(_, ref ty, ref expr) => {
2259                 self.with_static_rib(|this| {
2260                     this.with_lifetime_rib(LifetimeRibKind::Elided(LifetimeRes::Static), |this| {
2261                         this.visit_ty(ty);
2262                     });
2263                     this.with_lifetime_rib(LifetimeRibKind::Elided(LifetimeRes::Infer), |this| {
2264                         if let Some(expr) = expr {
2265                             let constant_item_kind = match item.kind {
2266                                 ItemKind::Const(..) => ConstantItemKind::Const,
2267                                 ItemKind::Static(..) => ConstantItemKind::Static,
2268                                 _ => unreachable!(),
2269                             };
2270                             // We already forbid generic params because of the above item rib,
2271                             // so it doesn't matter whether this is a trivial constant.
2272                             this.with_constant_rib(
2273                                 IsRepeatExpr::No,
2274                                 ConstantHasGenerics::Yes,
2275                                 Some((item.ident, constant_item_kind)),
2276                                 |this| this.visit_expr(expr),
2277                             );
2278                         }
2279                     });
2280                 });
2281             }
2282
2283             ItemKind::Use(ref use_tree) => {
2284                 self.future_proof_import(use_tree);
2285             }
2286
2287             ItemKind::ExternCrate(..) | ItemKind::MacroDef(..) => {
2288                 // do nothing, these are just around to be encoded
2289             }
2290
2291             ItemKind::GlobalAsm(_) => {
2292                 visit::walk_item(self, item);
2293             }
2294
2295             ItemKind::MacCall(_) => panic!("unexpanded macro in resolve!"),
2296         }
2297     }
2298
2299     fn with_generic_param_rib<'c, F>(
2300         &'c mut self,
2301         params: &'c [GenericParam],
2302         kind: RibKind<'a>,
2303         lifetime_kind: LifetimeRibKind,
2304         f: F,
2305     ) where
2306         F: FnOnce(&mut Self),
2307     {
2308         debug!("with_generic_param_rib");
2309         let LifetimeRibKind::Generics { binder, span: generics_span, kind: generics_kind, .. }
2310             = lifetime_kind else { panic!() };
2311
2312         let mut function_type_rib = Rib::new(kind);
2313         let mut function_value_rib = Rib::new(kind);
2314         let mut function_lifetime_rib = LifetimeRib::new(lifetime_kind);
2315         let mut seen_bindings = FxHashMap::default();
2316         // Store all seen lifetimes names from outer scopes.
2317         let mut seen_lifetimes = FxHashSet::default();
2318
2319         // We also can't shadow bindings from the parent item
2320         if let AssocItemRibKind = kind {
2321             let mut add_bindings_for_ns = |ns| {
2322                 let parent_rib = self.ribs[ns]
2323                     .iter()
2324                     .rfind(|r| matches!(r.kind, ItemRibKind(_)))
2325                     .expect("associated item outside of an item");
2326                 seen_bindings
2327                     .extend(parent_rib.bindings.iter().map(|(ident, _)| (*ident, ident.span)));
2328             };
2329             add_bindings_for_ns(ValueNS);
2330             add_bindings_for_ns(TypeNS);
2331         }
2332
2333         // Forbid shadowing lifetime bindings
2334         for rib in self.lifetime_ribs.iter().rev() {
2335             seen_lifetimes.extend(rib.bindings.iter().map(|(ident, _)| *ident));
2336             if let LifetimeRibKind::Item = rib.kind {
2337                 break;
2338             }
2339         }
2340
2341         for param in params {
2342             let ident = param.ident.normalize_to_macros_2_0();
2343             debug!("with_generic_param_rib: {}", param.id);
2344
2345             if let GenericParamKind::Lifetime = param.kind
2346                 && let Some(&original) = seen_lifetimes.get(&ident)
2347             {
2348                 diagnostics::signal_lifetime_shadowing(self.r.session, original, param.ident);
2349                 // Record lifetime res, so lowering knows there is something fishy.
2350                 self.record_lifetime_param(param.id, LifetimeRes::Error);
2351                 continue;
2352             }
2353
2354             match seen_bindings.entry(ident) {
2355                 Entry::Occupied(entry) => {
2356                     let span = *entry.get();
2357                     let err = ResolutionError::NameAlreadyUsedInParameterList(ident.name, span);
2358                     self.report_error(param.ident.span, err);
2359                     if let GenericParamKind::Lifetime = param.kind {
2360                         // Record lifetime res, so lowering knows there is something fishy.
2361                         self.record_lifetime_param(param.id, LifetimeRes::Error);
2362                         continue;
2363                     }
2364                 }
2365                 Entry::Vacant(entry) => {
2366                     entry.insert(param.ident.span);
2367                 }
2368             }
2369
2370             if param.ident.name == kw::UnderscoreLifetime {
2371                 rustc_errors::struct_span_err!(
2372                     self.r.session,
2373                     param.ident.span,
2374                     E0637,
2375                     "`'_` cannot be used here"
2376                 )
2377                 .span_label(param.ident.span, "`'_` is a reserved lifetime name")
2378                 .emit();
2379                 // Record lifetime res, so lowering knows there is something fishy.
2380                 self.record_lifetime_param(param.id, LifetimeRes::Error);
2381                 continue;
2382             }
2383
2384             if param.ident.name == kw::StaticLifetime {
2385                 rustc_errors::struct_span_err!(
2386                     self.r.session,
2387                     param.ident.span,
2388                     E0262,
2389                     "invalid lifetime parameter name: `{}`",
2390                     param.ident,
2391                 )
2392                 .span_label(param.ident.span, "'static is a reserved lifetime name")
2393                 .emit();
2394                 // Record lifetime res, so lowering knows there is something fishy.
2395                 self.record_lifetime_param(param.id, LifetimeRes::Error);
2396                 continue;
2397             }
2398
2399             let def_id = self.r.local_def_id(param.id);
2400
2401             // Plain insert (no renaming).
2402             let (rib, def_kind) = match param.kind {
2403                 GenericParamKind::Type { .. } => (&mut function_type_rib, DefKind::TyParam),
2404                 GenericParamKind::Const { .. } => (&mut function_value_rib, DefKind::ConstParam),
2405                 GenericParamKind::Lifetime => {
2406                     let res = LifetimeRes::Param { param: def_id, binder };
2407                     self.record_lifetime_param(param.id, res);
2408                     function_lifetime_rib.bindings.insert(ident, (param.id, res));
2409                     continue;
2410                 }
2411             };
2412
2413             let res = match kind {
2414                 ItemRibKind(..) | AssocItemRibKind => Res::Def(def_kind, def_id.to_def_id()),
2415                 NormalRibKind => Res::Err,
2416                 _ => span_bug!(param.ident.span, "Unexpected rib kind {:?}", kind),
2417             };
2418             self.r.record_partial_res(param.id, PartialRes::new(res));
2419             rib.bindings.insert(ident, res);
2420         }
2421
2422         self.lifetime_ribs.push(function_lifetime_rib);
2423         self.ribs[ValueNS].push(function_value_rib);
2424         self.ribs[TypeNS].push(function_type_rib);
2425
2426         f(self);
2427
2428         self.ribs[TypeNS].pop();
2429         self.ribs[ValueNS].pop();
2430         let function_lifetime_rib = self.lifetime_ribs.pop().unwrap();
2431
2432         // Do not account for the parameters we just bound for function lifetime elision.
2433         if let Some(ref mut candidates) = self.lifetime_elision_candidates {
2434             for (_, res) in function_lifetime_rib.bindings.values() {
2435                 candidates.retain(|(r, _)| r != res);
2436             }
2437         }
2438
2439         if let LifetimeBinderKind::BareFnType
2440         | LifetimeBinderKind::WhereBound
2441         | LifetimeBinderKind::Function
2442         | LifetimeBinderKind::ImplBlock = generics_kind
2443         {
2444             self.maybe_report_lifetime_uses(generics_span, params)
2445         }
2446     }
2447
2448     fn with_label_rib(&mut self, kind: RibKind<'a>, f: impl FnOnce(&mut Self)) {
2449         self.label_ribs.push(Rib::new(kind));
2450         f(self);
2451         self.label_ribs.pop();
2452     }
2453
2454     fn with_static_rib(&mut self, f: impl FnOnce(&mut Self)) {
2455         let kind = ItemRibKind(HasGenericParams::No);
2456         self.with_rib(ValueNS, kind, |this| this.with_rib(TypeNS, kind, f))
2457     }
2458
2459     // HACK(min_const_generics,const_evaluatable_unchecked): We
2460     // want to keep allowing `[0; std::mem::size_of::<*mut T>()]`
2461     // with a future compat lint for now. We do this by adding an
2462     // additional special case for repeat expressions.
2463     //
2464     // Note that we intentionally still forbid `[0; N + 1]` during
2465     // name resolution so that we don't extend the future
2466     // compat lint to new cases.
2467     #[instrument(level = "debug", skip(self, f))]
2468     fn with_constant_rib(
2469         &mut self,
2470         is_repeat: IsRepeatExpr,
2471         may_use_generics: ConstantHasGenerics,
2472         item: Option<(Ident, ConstantItemKind)>,
2473         f: impl FnOnce(&mut Self),
2474     ) {
2475         self.with_rib(ValueNS, ConstantItemRibKind(may_use_generics, item), |this| {
2476             this.with_rib(
2477                 TypeNS,
2478                 ConstantItemRibKind(
2479                     may_use_generics.force_yes_if(is_repeat == IsRepeatExpr::Yes),
2480                     item,
2481                 ),
2482                 |this| {
2483                     this.with_label_rib(ConstantItemRibKind(may_use_generics, item), f);
2484                 },
2485             )
2486         });
2487     }
2488
2489     fn with_current_self_type<T>(&mut self, self_type: &Ty, f: impl FnOnce(&mut Self) -> T) -> T {
2490         // Handle nested impls (inside fn bodies)
2491         let previous_value =
2492             replace(&mut self.diagnostic_metadata.current_self_type, Some(self_type.clone()));
2493         let result = f(self);
2494         self.diagnostic_metadata.current_self_type = previous_value;
2495         result
2496     }
2497
2498     fn with_current_self_item<T>(&mut self, self_item: &Item, f: impl FnOnce(&mut Self) -> T) -> T {
2499         let previous_value =
2500             replace(&mut self.diagnostic_metadata.current_self_item, Some(self_item.id));
2501         let result = f(self);
2502         self.diagnostic_metadata.current_self_item = previous_value;
2503         result
2504     }
2505
2506     /// When evaluating a `trait` use its associated types' idents for suggestions in E0412.
2507     fn resolve_trait_items(&mut self, trait_items: &'ast [P<AssocItem>]) {
2508         let trait_assoc_items =
2509             replace(&mut self.diagnostic_metadata.current_trait_assoc_items, Some(&trait_items));
2510
2511         let walk_assoc_item =
2512             |this: &mut Self, generics: &Generics, kind, item: &'ast AssocItem| {
2513                 this.with_generic_param_rib(
2514                     &generics.params,
2515                     AssocItemRibKind,
2516                     LifetimeRibKind::Generics { binder: item.id, span: generics.span, kind },
2517                     |this| visit::walk_assoc_item(this, item, AssocCtxt::Trait),
2518                 );
2519             };
2520
2521         for item in trait_items {
2522             match &item.kind {
2523                 AssocItemKind::Const(_, ty, default) => {
2524                     self.visit_ty(ty);
2525                     // Only impose the restrictions of `ConstRibKind` for an
2526                     // actual constant expression in a provided default.
2527                     if let Some(expr) = default {
2528                         // We allow arbitrary const expressions inside of associated consts,
2529                         // even if they are potentially not const evaluatable.
2530                         //
2531                         // Type parameters can already be used and as associated consts are
2532                         // not used as part of the type system, this is far less surprising.
2533                         self.with_lifetime_rib(
2534                             LifetimeRibKind::Elided(LifetimeRes::Infer),
2535                             |this| {
2536                                 this.with_constant_rib(
2537                                     IsRepeatExpr::No,
2538                                     ConstantHasGenerics::Yes,
2539                                     None,
2540                                     |this| this.visit_expr(expr),
2541                                 )
2542                             },
2543                         );
2544                     }
2545                 }
2546                 AssocItemKind::Fn(box Fn { generics, .. }) => {
2547                     walk_assoc_item(self, generics, LifetimeBinderKind::Function, item);
2548                 }
2549                 AssocItemKind::Type(box TyAlias { generics, .. }) => self
2550                     .with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
2551                         walk_assoc_item(this, generics, LifetimeBinderKind::Item, item)
2552                     }),
2553                 AssocItemKind::MacCall(_) => {
2554                     panic!("unexpanded macro in resolve!")
2555                 }
2556             };
2557         }
2558
2559         self.diagnostic_metadata.current_trait_assoc_items = trait_assoc_items;
2560     }
2561
2562     /// This is called to resolve a trait reference from an `impl` (i.e., `impl Trait for Foo`).
2563     fn with_optional_trait_ref<T>(
2564         &mut self,
2565         opt_trait_ref: Option<&TraitRef>,
2566         self_type: &'ast Ty,
2567         f: impl FnOnce(&mut Self, Option<DefId>) -> T,
2568     ) -> T {
2569         let mut new_val = None;
2570         let mut new_id = None;
2571         if let Some(trait_ref) = opt_trait_ref {
2572             let path: Vec<_> = Segment::from_path(&trait_ref.path);
2573             self.diagnostic_metadata.currently_processing_impl_trait =
2574                 Some((trait_ref.clone(), self_type.clone()));
2575             let res = self.smart_resolve_path_fragment(
2576                 &None,
2577                 &path,
2578                 PathSource::Trait(AliasPossibility::No),
2579                 Finalize::new(trait_ref.ref_id, trait_ref.path.span),
2580             );
2581             self.diagnostic_metadata.currently_processing_impl_trait = None;
2582             if let Some(def_id) = res.expect_full_res().opt_def_id() {
2583                 new_id = Some(def_id);
2584                 new_val = Some((self.r.expect_module(def_id), trait_ref.clone()));
2585             }
2586         }
2587         let original_trait_ref = replace(&mut self.current_trait_ref, new_val);
2588         let result = f(self, new_id);
2589         self.current_trait_ref = original_trait_ref;
2590         result
2591     }
2592
2593     fn with_self_rib_ns(&mut self, ns: Namespace, self_res: Res, f: impl FnOnce(&mut Self)) {
2594         let mut self_type_rib = Rib::new(NormalRibKind);
2595
2596         // Plain insert (no renaming, since types are not currently hygienic)
2597         self_type_rib.bindings.insert(Ident::with_dummy_span(kw::SelfUpper), self_res);
2598         self.ribs[ns].push(self_type_rib);
2599         f(self);
2600         self.ribs[ns].pop();
2601     }
2602
2603     fn with_self_rib(&mut self, self_res: Res, f: impl FnOnce(&mut Self)) {
2604         self.with_self_rib_ns(TypeNS, self_res, f)
2605     }
2606
2607     fn resolve_implementation(
2608         &mut self,
2609         generics: &'ast Generics,
2610         opt_trait_reference: &'ast Option<TraitRef>,
2611         self_type: &'ast Ty,
2612         item_id: NodeId,
2613         impl_items: &'ast [P<AssocItem>],
2614     ) {
2615         debug!("resolve_implementation");
2616         // If applicable, create a rib for the type parameters.
2617         self.with_generic_param_rib(
2618             &generics.params,
2619             ItemRibKind(HasGenericParams::Yes(generics.span)),
2620             LifetimeRibKind::Generics {
2621                 span: generics.span,
2622                 binder: item_id,
2623                 kind: LifetimeBinderKind::ImplBlock,
2624             },
2625             |this| {
2626                 // Dummy self type for better errors if `Self` is used in the trait path.
2627                 this.with_self_rib(Res::SelfTyParam { trait_: LOCAL_CRATE.as_def_id() }, |this| {
2628                     this.with_lifetime_rib(
2629                         LifetimeRibKind::AnonymousCreateParameter {
2630                             binder: item_id,
2631                             report_in_path: true
2632                         },
2633                         |this| {
2634                             // Resolve the trait reference, if necessary.
2635                             this.with_optional_trait_ref(
2636                                 opt_trait_reference.as_ref(),
2637                                 self_type,
2638                                 |this, trait_id| {
2639                                     let item_def_id = this.r.local_def_id(item_id);
2640
2641                                     // Register the trait definitions from here.
2642                                     if let Some(trait_id) = trait_id {
2643                                         this.r
2644                                             .trait_impls
2645                                             .entry(trait_id)
2646                                             .or_default()
2647                                             .push(item_def_id);
2648                                     }
2649
2650                                     let item_def_id = item_def_id.to_def_id();
2651                                     let res = Res::SelfTyAlias {
2652                                         alias_to: item_def_id,
2653                                         forbid_generic: false,
2654                                         is_trait_impl: trait_id.is_some()
2655                                     };
2656                                     this.with_self_rib(res, |this| {
2657                                         if let Some(trait_ref) = opt_trait_reference.as_ref() {
2658                                             // Resolve type arguments in the trait path.
2659                                             visit::walk_trait_ref(this, trait_ref);
2660                                         }
2661                                         // Resolve the self type.
2662                                         this.visit_ty(self_type);
2663                                         // Resolve the generic parameters.
2664                                         this.visit_generics(generics);
2665
2666                                         // Resolve the items within the impl.
2667                                         this.with_current_self_type(self_type, |this| {
2668                                             this.with_self_rib_ns(ValueNS, Res::SelfCtor(item_def_id), |this| {
2669                                                 debug!("resolve_implementation with_self_rib_ns(ValueNS, ...)");
2670                                                 let mut seen_trait_items = Default::default();
2671                                                 for item in impl_items {
2672                                                     this.resolve_impl_item(&**item, &mut seen_trait_items);
2673                                                 }
2674                                             });
2675                                         });
2676                                     });
2677                                 },
2678                             )
2679                         },
2680                     );
2681                 });
2682             },
2683         );
2684     }
2685
2686     fn resolve_impl_item(
2687         &mut self,
2688         item: &'ast AssocItem,
2689         seen_trait_items: &mut FxHashMap<DefId, Span>,
2690     ) {
2691         use crate::ResolutionError::*;
2692         match &item.kind {
2693             AssocItemKind::Const(_, ty, default) => {
2694                 debug!("resolve_implementation AssocItemKind::Const");
2695                 // If this is a trait impl, ensure the const
2696                 // exists in trait
2697                 self.check_trait_item(
2698                     item.id,
2699                     item.ident,
2700                     &item.kind,
2701                     ValueNS,
2702                     item.span,
2703                     seen_trait_items,
2704                     |i, s, c| ConstNotMemberOfTrait(i, s, c),
2705                 );
2706
2707                 self.visit_ty(ty);
2708                 if let Some(expr) = default {
2709                     // We allow arbitrary const expressions inside of associated consts,
2710                     // even if they are potentially not const evaluatable.
2711                     //
2712                     // Type parameters can already be used and as associated consts are
2713                     // not used as part of the type system, this is far less surprising.
2714                     self.with_lifetime_rib(LifetimeRibKind::Elided(LifetimeRes::Infer), |this| {
2715                         this.with_constant_rib(
2716                             IsRepeatExpr::No,
2717                             ConstantHasGenerics::Yes,
2718                             None,
2719                             |this| this.visit_expr(expr),
2720                         )
2721                     });
2722                 }
2723             }
2724             AssocItemKind::Fn(box Fn { generics, .. }) => {
2725                 debug!("resolve_implementation AssocItemKind::Fn");
2726                 // We also need a new scope for the impl item type parameters.
2727                 self.with_generic_param_rib(
2728                     &generics.params,
2729                     AssocItemRibKind,
2730                     LifetimeRibKind::Generics {
2731                         binder: item.id,
2732                         span: generics.span,
2733                         kind: LifetimeBinderKind::Function,
2734                     },
2735                     |this| {
2736                         // If this is a trait impl, ensure the method
2737                         // exists in trait
2738                         this.check_trait_item(
2739                             item.id,
2740                             item.ident,
2741                             &item.kind,
2742                             ValueNS,
2743                             item.span,
2744                             seen_trait_items,
2745                             |i, s, c| MethodNotMemberOfTrait(i, s, c),
2746                         );
2747
2748                         visit::walk_assoc_item(this, item, AssocCtxt::Impl)
2749                     },
2750                 );
2751             }
2752             AssocItemKind::Type(box TyAlias { generics, .. }) => {
2753                 debug!("resolve_implementation AssocItemKind::Type");
2754                 // We also need a new scope for the impl item type parameters.
2755                 self.with_generic_param_rib(
2756                     &generics.params,
2757                     AssocItemRibKind,
2758                     LifetimeRibKind::Generics {
2759                         binder: item.id,
2760                         span: generics.span,
2761                         kind: LifetimeBinderKind::Item,
2762                     },
2763                     |this| {
2764                         this.with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
2765                             // If this is a trait impl, ensure the type
2766                             // exists in trait
2767                             this.check_trait_item(
2768                                 item.id,
2769                                 item.ident,
2770                                 &item.kind,
2771                                 TypeNS,
2772                                 item.span,
2773                                 seen_trait_items,
2774                                 |i, s, c| TypeNotMemberOfTrait(i, s, c),
2775                             );
2776
2777                             visit::walk_assoc_item(this, item, AssocCtxt::Impl)
2778                         });
2779                     },
2780                 );
2781             }
2782             AssocItemKind::MacCall(_) => {
2783                 panic!("unexpanded macro in resolve!")
2784             }
2785         }
2786     }
2787
2788     fn check_trait_item<F>(
2789         &mut self,
2790         id: NodeId,
2791         mut ident: Ident,
2792         kind: &AssocItemKind,
2793         ns: Namespace,
2794         span: Span,
2795         seen_trait_items: &mut FxHashMap<DefId, Span>,
2796         err: F,
2797     ) where
2798         F: FnOnce(Ident, String, Option<Symbol>) -> ResolutionError<'a>,
2799     {
2800         // If there is a TraitRef in scope for an impl, then the method must be in the trait.
2801         let Some((module, _)) = &self.current_trait_ref else { return; };
2802         ident.span.normalize_to_macros_2_0_and_adjust(module.expansion);
2803         let key = self.r.new_key(ident, ns);
2804         let mut binding = self.r.resolution(module, key).try_borrow().ok().and_then(|r| r.binding);
2805         debug!(?binding);
2806         if binding.is_none() {
2807             // We could not find the trait item in the correct namespace.
2808             // Check the other namespace to report an error.
2809             let ns = match ns {
2810                 ValueNS => TypeNS,
2811                 TypeNS => ValueNS,
2812                 _ => ns,
2813             };
2814             let key = self.r.new_key(ident, ns);
2815             binding = self.r.resolution(module, key).try_borrow().ok().and_then(|r| r.binding);
2816             debug!(?binding);
2817         }
2818         let Some(binding) = binding else {
2819             // We could not find the method: report an error.
2820             let candidate = self.find_similarly_named_assoc_item(ident.name, kind);
2821             let path = &self.current_trait_ref.as_ref().unwrap().1.path;
2822             let path_names = path_names_to_string(path);
2823             self.report_error(span, err(ident, path_names, candidate));
2824             return;
2825         };
2826
2827         let res = binding.res();
2828         let Res::Def(def_kind, id_in_trait) = res else { bug!() };
2829
2830         match seen_trait_items.entry(id_in_trait) {
2831             Entry::Occupied(entry) => {
2832                 self.report_error(
2833                     span,
2834                     ResolutionError::TraitImplDuplicate {
2835                         name: ident.name,
2836                         old_span: *entry.get(),
2837                         trait_item_span: binding.span,
2838                     },
2839                 );
2840                 return;
2841             }
2842             Entry::Vacant(entry) => {
2843                 entry.insert(span);
2844             }
2845         };
2846
2847         match (def_kind, kind) {
2848             (DefKind::AssocTy, AssocItemKind::Type(..))
2849             | (DefKind::AssocFn, AssocItemKind::Fn(..))
2850             | (DefKind::AssocConst, AssocItemKind::Const(..)) => {
2851                 self.r.record_partial_res(id, PartialRes::new(res));
2852                 return;
2853             }
2854             _ => {}
2855         }
2856
2857         // The method kind does not correspond to what appeared in the trait, report.
2858         let path = &self.current_trait_ref.as_ref().unwrap().1.path;
2859         let (code, kind) = match kind {
2860             AssocItemKind::Const(..) => (rustc_errors::error_code!(E0323), "const"),
2861             AssocItemKind::Fn(..) => (rustc_errors::error_code!(E0324), "method"),
2862             AssocItemKind::Type(..) => (rustc_errors::error_code!(E0325), "type"),
2863             AssocItemKind::MacCall(..) => span_bug!(span, "unexpanded macro"),
2864         };
2865         let trait_path = path_names_to_string(path);
2866         self.report_error(
2867             span,
2868             ResolutionError::TraitImplMismatch {
2869                 name: ident.name,
2870                 kind,
2871                 code,
2872                 trait_path,
2873                 trait_item_span: binding.span,
2874             },
2875         );
2876     }
2877
2878     fn resolve_params(&mut self, params: &'ast [Param]) {
2879         let mut bindings = smallvec![(PatBoundCtx::Product, Default::default())];
2880         self.with_lifetime_rib(LifetimeRibKind::Elided(LifetimeRes::Infer), |this| {
2881             for Param { pat, .. } in params {
2882                 this.resolve_pattern(pat, PatternSource::FnParam, &mut bindings);
2883             }
2884         });
2885         for Param { ty, .. } in params {
2886             self.visit_ty(ty);
2887         }
2888     }
2889
2890     fn resolve_local(&mut self, local: &'ast Local) {
2891         debug!("resolving local ({:?})", local);
2892         // Resolve the type.
2893         walk_list!(self, visit_ty, &local.ty);
2894
2895         // Resolve the initializer.
2896         if let Some((init, els)) = local.kind.init_else_opt() {
2897             self.visit_expr(init);
2898
2899             // Resolve the `else` block
2900             if let Some(els) = els {
2901                 self.visit_block(els);
2902             }
2903         }
2904
2905         // Resolve the pattern.
2906         self.resolve_pattern_top(&local.pat, PatternSource::Let);
2907     }
2908
2909     /// build a map from pattern identifiers to binding-info's.
2910     /// this is done hygienically. This could arise for a macro
2911     /// that expands into an or-pattern where one 'x' was from the
2912     /// user and one 'x' came from the macro.
2913     fn binding_mode_map(&mut self, pat: &Pat) -> BindingMap {
2914         let mut binding_map = FxHashMap::default();
2915
2916         pat.walk(&mut |pat| {
2917             match pat.kind {
2918                 PatKind::Ident(annotation, ident, ref sub_pat)
2919                     if sub_pat.is_some() || self.is_base_res_local(pat.id) =>
2920                 {
2921                     binding_map.insert(ident, BindingInfo { span: ident.span, annotation });
2922                 }
2923                 PatKind::Or(ref ps) => {
2924                     // Check the consistency of this or-pattern and
2925                     // then add all bindings to the larger map.
2926                     for bm in self.check_consistent_bindings(ps) {
2927                         binding_map.extend(bm);
2928                     }
2929                     return false;
2930                 }
2931                 _ => {}
2932             }
2933
2934             true
2935         });
2936
2937         binding_map
2938     }
2939
2940     fn is_base_res_local(&self, nid: NodeId) -> bool {
2941         matches!(
2942             self.r.partial_res_map.get(&nid).map(|res| res.expect_full_res()),
2943             Some(Res::Local(..))
2944         )
2945     }
2946
2947     /// Checks that all of the arms in an or-pattern have exactly the
2948     /// same set of bindings, with the same binding modes for each.
2949     fn check_consistent_bindings(&mut self, pats: &[P<Pat>]) -> Vec<BindingMap> {
2950         let mut missing_vars = FxHashMap::default();
2951         let mut inconsistent_vars = FxHashMap::default();
2952
2953         // 1) Compute the binding maps of all arms.
2954         let maps = pats.iter().map(|pat| self.binding_mode_map(pat)).collect::<Vec<_>>();
2955
2956         // 2) Record any missing bindings or binding mode inconsistencies.
2957         for (map_outer, pat_outer) in pats.iter().enumerate().map(|(idx, pat)| (&maps[idx], pat)) {
2958             // Check against all arms except for the same pattern which is always self-consistent.
2959             let inners = pats
2960                 .iter()
2961                 .enumerate()
2962                 .filter(|(_, pat)| pat.id != pat_outer.id)
2963                 .flat_map(|(idx, _)| maps[idx].iter())
2964                 .map(|(key, binding)| (key.name, map_outer.get(&key), binding));
2965
2966             for (name, info, &binding_inner) in inners {
2967                 match info {
2968                     None => {
2969                         // The inner binding is missing in the outer.
2970                         let binding_error =
2971                             missing_vars.entry(name).or_insert_with(|| BindingError {
2972                                 name,
2973                                 origin: BTreeSet::new(),
2974                                 target: BTreeSet::new(),
2975                                 could_be_path: name.as_str().starts_with(char::is_uppercase),
2976                             });
2977                         binding_error.origin.insert(binding_inner.span);
2978                         binding_error.target.insert(pat_outer.span);
2979                     }
2980                     Some(binding_outer) => {
2981                         if binding_outer.annotation != binding_inner.annotation {
2982                             // The binding modes in the outer and inner bindings differ.
2983                             inconsistent_vars
2984                                 .entry(name)
2985                                 .or_insert((binding_inner.span, binding_outer.span));
2986                         }
2987                     }
2988                 }
2989             }
2990         }
2991
2992         // 3) Report all missing variables we found.
2993         let mut missing_vars = missing_vars.into_iter().collect::<Vec<_>>();
2994         missing_vars.sort_by_key(|&(sym, ref _err)| sym);
2995
2996         for (name, mut v) in missing_vars.into_iter() {
2997             if inconsistent_vars.contains_key(&name) {
2998                 v.could_be_path = false;
2999             }
3000             self.report_error(
3001                 *v.origin.iter().next().unwrap(),
3002                 ResolutionError::VariableNotBoundInPattern(v, self.parent_scope),
3003             );
3004         }
3005
3006         // 4) Report all inconsistencies in binding modes we found.
3007         let mut inconsistent_vars = inconsistent_vars.iter().collect::<Vec<_>>();
3008         inconsistent_vars.sort();
3009         for (name, v) in inconsistent_vars {
3010             self.report_error(v.0, ResolutionError::VariableBoundWithDifferentMode(*name, v.1));
3011         }
3012
3013         // 5) Finally bubble up all the binding maps.
3014         maps
3015     }
3016
3017     /// Check the consistency of the outermost or-patterns.
3018     fn check_consistent_bindings_top(&mut self, pat: &'ast Pat) {
3019         pat.walk(&mut |pat| match pat.kind {
3020             PatKind::Or(ref ps) => {
3021                 self.check_consistent_bindings(ps);
3022                 false
3023             }
3024             _ => true,
3025         })
3026     }
3027
3028     fn resolve_arm(&mut self, arm: &'ast Arm) {
3029         self.with_rib(ValueNS, NormalRibKind, |this| {
3030             this.resolve_pattern_top(&arm.pat, PatternSource::Match);
3031             walk_list!(this, visit_expr, &arm.guard);
3032             this.visit_expr(&arm.body);
3033         });
3034     }
3035
3036     /// Arising from `source`, resolve a top level pattern.
3037     fn resolve_pattern_top(&mut self, pat: &'ast Pat, pat_src: PatternSource) {
3038         let mut bindings = smallvec![(PatBoundCtx::Product, Default::default())];
3039         self.resolve_pattern(pat, pat_src, &mut bindings);
3040     }
3041
3042     fn resolve_pattern(
3043         &mut self,
3044         pat: &'ast Pat,
3045         pat_src: PatternSource,
3046         bindings: &mut SmallVec<[(PatBoundCtx, FxHashSet<Ident>); 1]>,
3047     ) {
3048         // We walk the pattern before declaring the pattern's inner bindings,
3049         // so that we avoid resolving a literal expression to a binding defined
3050         // by the pattern.
3051         visit::walk_pat(self, pat);
3052         self.resolve_pattern_inner(pat, pat_src, bindings);
3053         // This has to happen *after* we determine which pat_idents are variants:
3054         self.check_consistent_bindings_top(pat);
3055     }
3056
3057     /// Resolve bindings in a pattern. This is a helper to `resolve_pattern`.
3058     ///
3059     /// ### `bindings`
3060     ///
3061     /// A stack of sets of bindings accumulated.
3062     ///
3063     /// In each set, `PatBoundCtx::Product` denotes that a found binding in it should
3064     /// be interpreted as re-binding an already bound binding. This results in an error.
3065     /// Meanwhile, `PatBound::Or` denotes that a found binding in the set should result
3066     /// in reusing this binding rather than creating a fresh one.
3067     ///
3068     /// When called at the top level, the stack must have a single element
3069     /// with `PatBound::Product`. Otherwise, pushing to the stack happens as
3070     /// or-patterns (`p_0 | ... | p_n`) are encountered and the context needs
3071     /// to be switched to `PatBoundCtx::Or` and then `PatBoundCtx::Product` for each `p_i`.
3072     /// When each `p_i` has been dealt with, the top set is merged with its parent.
3073     /// When a whole or-pattern has been dealt with, the thing happens.
3074     ///
3075     /// See the implementation and `fresh_binding` for more details.
3076     fn resolve_pattern_inner(
3077         &mut self,
3078         pat: &Pat,
3079         pat_src: PatternSource,
3080         bindings: &mut SmallVec<[(PatBoundCtx, FxHashSet<Ident>); 1]>,
3081     ) {
3082         // Visit all direct subpatterns of this pattern.
3083         pat.walk(&mut |pat| {
3084             debug!("resolve_pattern pat={:?} node={:?}", pat, pat.kind);
3085             match pat.kind {
3086                 PatKind::Ident(bmode, ident, ref sub) => {
3087                     // First try to resolve the identifier as some existing entity,
3088                     // then fall back to a fresh binding.
3089                     let has_sub = sub.is_some();
3090                     let res = self
3091                         .try_resolve_as_non_binding(pat_src, bmode, ident, has_sub)
3092                         .unwrap_or_else(|| self.fresh_binding(ident, pat.id, pat_src, bindings));
3093                     self.r.record_partial_res(pat.id, PartialRes::new(res));
3094                     self.r.record_pat_span(pat.id, pat.span);
3095                 }
3096                 PatKind::TupleStruct(ref qself, ref path, ref sub_patterns) => {
3097                     self.smart_resolve_path(
3098                         pat.id,
3099                         qself,
3100                         path,
3101                         PathSource::TupleStruct(
3102                             pat.span,
3103                             self.r.arenas.alloc_pattern_spans(sub_patterns.iter().map(|p| p.span)),
3104                         ),
3105                     );
3106                 }
3107                 PatKind::Path(ref qself, ref path) => {
3108                     self.smart_resolve_path(pat.id, qself, path, PathSource::Pat);
3109                 }
3110                 PatKind::Struct(ref qself, ref path, ..) => {
3111                     self.smart_resolve_path(pat.id, qself, path, PathSource::Struct);
3112                 }
3113                 PatKind::Or(ref ps) => {
3114                     // Add a new set of bindings to the stack. `Or` here records that when a
3115                     // binding already exists in this set, it should not result in an error because
3116                     // `V1(a) | V2(a)` must be allowed and are checked for consistency later.
3117                     bindings.push((PatBoundCtx::Or, Default::default()));
3118                     for p in ps {
3119                         // Now we need to switch back to a product context so that each
3120                         // part of the or-pattern internally rejects already bound names.
3121                         // For example, `V1(a) | V2(a, a)` and `V1(a, a) | V2(a)` are bad.
3122                         bindings.push((PatBoundCtx::Product, Default::default()));
3123                         self.resolve_pattern_inner(p, pat_src, bindings);
3124                         // Move up the non-overlapping bindings to the or-pattern.
3125                         // Existing bindings just get "merged".
3126                         let collected = bindings.pop().unwrap().1;
3127                         bindings.last_mut().unwrap().1.extend(collected);
3128                     }
3129                     // This or-pattern itself can itself be part of a product,
3130                     // e.g. `(V1(a) | V2(a), a)` or `(a, V1(a) | V2(a))`.
3131                     // Both cases bind `a` again in a product pattern and must be rejected.
3132                     let collected = bindings.pop().unwrap().1;
3133                     bindings.last_mut().unwrap().1.extend(collected);
3134
3135                     // Prevent visiting `ps` as we've already done so above.
3136                     return false;
3137                 }
3138                 _ => {}
3139             }
3140             true
3141         });
3142     }
3143
3144     fn fresh_binding(
3145         &mut self,
3146         ident: Ident,
3147         pat_id: NodeId,
3148         pat_src: PatternSource,
3149         bindings: &mut SmallVec<[(PatBoundCtx, FxHashSet<Ident>); 1]>,
3150     ) -> Res {
3151         // Add the binding to the local ribs, if it doesn't already exist in the bindings map.
3152         // (We must not add it if it's in the bindings map because that breaks the assumptions
3153         // later passes make about or-patterns.)
3154         let ident = ident.normalize_to_macro_rules();
3155
3156         let mut bound_iter = bindings.iter().filter(|(_, set)| set.contains(&ident));
3157         // Already bound in a product pattern? e.g. `(a, a)` which is not allowed.
3158         let already_bound_and = bound_iter.clone().any(|(ctx, _)| *ctx == PatBoundCtx::Product);
3159         // Already bound in an or-pattern? e.g. `V1(a) | V2(a)`.
3160         // This is *required* for consistency which is checked later.
3161         let already_bound_or = bound_iter.any(|(ctx, _)| *ctx == PatBoundCtx::Or);
3162
3163         if already_bound_and {
3164             // Overlap in a product pattern somewhere; report an error.
3165             use ResolutionError::*;
3166             let error = match pat_src {
3167                 // `fn f(a: u8, a: u8)`:
3168                 PatternSource::FnParam => IdentifierBoundMoreThanOnceInParameterList,
3169                 // `Variant(a, a)`:
3170                 _ => IdentifierBoundMoreThanOnceInSamePattern,
3171             };
3172             self.report_error(ident.span, error(ident.name));
3173         }
3174
3175         // Record as bound if it's valid:
3176         let ident_valid = ident.name != kw::Empty;
3177         if ident_valid {
3178             bindings.last_mut().unwrap().1.insert(ident);
3179         }
3180
3181         if already_bound_or {
3182             // `Variant1(a) | Variant2(a)`, ok
3183             // Reuse definition from the first `a`.
3184             self.innermost_rib_bindings(ValueNS)[&ident]
3185         } else {
3186             let res = Res::Local(pat_id);
3187             if ident_valid {
3188                 // A completely fresh binding add to the set if it's valid.
3189                 self.innermost_rib_bindings(ValueNS).insert(ident, res);
3190             }
3191             res
3192         }
3193     }
3194
3195     fn innermost_rib_bindings(&mut self, ns: Namespace) -> &mut IdentMap<Res> {
3196         &mut self.ribs[ns].last_mut().unwrap().bindings
3197     }
3198
3199     fn try_resolve_as_non_binding(
3200         &mut self,
3201         pat_src: PatternSource,
3202         ann: BindingAnnotation,
3203         ident: Ident,
3204         has_sub: bool,
3205     ) -> Option<Res> {
3206         // An immutable (no `mut`) by-value (no `ref`) binding pattern without
3207         // a sub pattern (no `@ $pat`) is syntactically ambiguous as it could
3208         // also be interpreted as a path to e.g. a constant, variant, etc.
3209         let is_syntactic_ambiguity = !has_sub && ann == BindingAnnotation::NONE;
3210
3211         let ls_binding = self.maybe_resolve_ident_in_lexical_scope(ident, ValueNS)?;
3212         let (res, binding) = match ls_binding {
3213             LexicalScopeBinding::Item(binding)
3214                 if is_syntactic_ambiguity && binding.is_ambiguity() =>
3215             {
3216                 // For ambiguous bindings we don't know all their definitions and cannot check
3217                 // whether they can be shadowed by fresh bindings or not, so force an error.
3218                 // issues/33118#issuecomment-233962221 (see below) still applies here,
3219                 // but we have to ignore it for backward compatibility.
3220                 self.r.record_use(ident, binding, false);
3221                 return None;
3222             }
3223             LexicalScopeBinding::Item(binding) => (binding.res(), Some(binding)),
3224             LexicalScopeBinding::Res(res) => (res, None),
3225         };
3226
3227         match res {
3228             Res::SelfCtor(_) // See #70549.
3229             | Res::Def(
3230                 DefKind::Ctor(_, CtorKind::Const) | DefKind::Const | DefKind::ConstParam,
3231                 _,
3232             ) if is_syntactic_ambiguity => {
3233                 // Disambiguate in favor of a unit struct/variant or constant pattern.
3234                 if let Some(binding) = binding {
3235                     self.r.record_use(ident, binding, false);
3236                 }
3237                 Some(res)
3238             }
3239             Res::Def(DefKind::Ctor(..) | DefKind::Const | DefKind::Static(_), _) => {
3240                 // This is unambiguously a fresh binding, either syntactically
3241                 // (e.g., `IDENT @ PAT` or `ref IDENT`) or because `IDENT` resolves
3242                 // to something unusable as a pattern (e.g., constructor function),
3243                 // but we still conservatively report an error, see
3244                 // issues/33118#issuecomment-233962221 for one reason why.
3245                 let binding = binding.expect("no binding for a ctor or static");
3246                 self.report_error(
3247                     ident.span,
3248                     ResolutionError::BindingShadowsSomethingUnacceptable {
3249                         shadowing_binding: pat_src,
3250                         name: ident.name,
3251                         participle: if binding.is_import() { "imported" } else { "defined" },
3252                         article: binding.res().article(),
3253                         shadowed_binding: binding.res(),
3254                         shadowed_binding_span: binding.span,
3255                     },
3256                 );
3257                 None
3258             }
3259             Res::Def(DefKind::ConstParam, def_id) => {
3260                 // Same as for DefKind::Const above, but here, `binding` is `None`, so we
3261                 // have to construct the error differently
3262                 self.report_error(
3263                     ident.span,
3264                     ResolutionError::BindingShadowsSomethingUnacceptable {
3265                         shadowing_binding: pat_src,
3266                         name: ident.name,
3267                         participle: "defined",
3268                         article: res.article(),
3269                         shadowed_binding: res,
3270                         shadowed_binding_span: self.r.opt_span(def_id).expect("const parameter defined outside of local crate"),
3271                     }
3272                 );
3273                 None
3274             }
3275             Res::Def(DefKind::Fn, _) | Res::Local(..) | Res::Err => {
3276                 // These entities are explicitly allowed to be shadowed by fresh bindings.
3277                 None
3278             }
3279             Res::SelfCtor(_) => {
3280                 // We resolve `Self` in pattern position as an ident sometimes during recovery,
3281                 // so delay a bug instead of ICEing.
3282                 self.r.session.delay_span_bug(
3283                     ident.span,
3284                     "unexpected `SelfCtor` in pattern, expected identifier"
3285                 );
3286                 None
3287             }
3288             _ => span_bug!(
3289                 ident.span,
3290                 "unexpected resolution for an identifier in pattern: {:?}",
3291                 res,
3292             ),
3293         }
3294     }
3295
3296     // High-level and context dependent path resolution routine.
3297     // Resolves the path and records the resolution into definition map.
3298     // If resolution fails tries several techniques to find likely
3299     // resolution candidates, suggest imports or other help, and report
3300     // errors in user friendly way.
3301     fn smart_resolve_path(
3302         &mut self,
3303         id: NodeId,
3304         qself: &Option<P<QSelf>>,
3305         path: &Path,
3306         source: PathSource<'ast>,
3307     ) {
3308         self.smart_resolve_path_fragment(
3309             qself,
3310             &Segment::from_path(path),
3311             source,
3312             Finalize::new(id, path.span),
3313         );
3314     }
3315
3316     fn smart_resolve_path_fragment(
3317         &mut self,
3318         qself: &Option<P<QSelf>>,
3319         path: &[Segment],
3320         source: PathSource<'ast>,
3321         finalize: Finalize,
3322     ) -> PartialRes {
3323         debug!(
3324             "smart_resolve_path_fragment(qself={:?}, path={:?}, finalize={:?})",
3325             qself, path, finalize,
3326         );
3327         let ns = source.namespace();
3328
3329         let Finalize { node_id, path_span, .. } = finalize;
3330         let report_errors = |this: &mut Self, res: Option<Res>| {
3331             if this.should_report_errs() {
3332                 let (err, candidates) =
3333                     this.smart_resolve_report_errors(path, path_span, source, res);
3334
3335                 let def_id = this.parent_scope.module.nearest_parent_mod();
3336                 let instead = res.is_some();
3337                 let suggestion =
3338                     if res.is_none() { this.report_missing_type_error(path) } else { None };
3339
3340                 this.r.use_injections.push(UseError {
3341                     err,
3342                     candidates,
3343                     def_id,
3344                     instead,
3345                     suggestion,
3346                     path: path.into(),
3347                     is_call: source.is_call(),
3348                 });
3349             }
3350
3351             PartialRes::new(Res::Err)
3352         };
3353
3354         // For paths originating from calls (like in `HashMap::new()`), tries
3355         // to enrich the plain `failed to resolve: ...` message with hints
3356         // about possible missing imports.
3357         //
3358         // Similar thing, for types, happens in `report_errors` above.
3359         let report_errors_for_call = |this: &mut Self, parent_err: Spanned<ResolutionError<'a>>| {
3360             if !source.is_call() {
3361                 return Some(parent_err);
3362             }
3363
3364             // Before we start looking for candidates, we have to get our hands
3365             // on the type user is trying to perform invocation on; basically:
3366             // we're transforming `HashMap::new` into just `HashMap`.
3367             let path = match path.split_last() {
3368                 Some((_, path)) if !path.is_empty() => path,
3369                 _ => return Some(parent_err),
3370             };
3371
3372             let (mut err, candidates) =
3373                 this.smart_resolve_report_errors(path, path_span, PathSource::Type, None);
3374
3375             // There are two different error messages user might receive at
3376             // this point:
3377             // - E0412 cannot find type `{}` in this scope
3378             // - E0433 failed to resolve: use of undeclared type or module `{}`
3379             //
3380             // The first one is emitted for paths in type-position, and the
3381             // latter one - for paths in expression-position.
3382             //
3383             // Thus (since we're in expression-position at this point), not to
3384             // confuse the user, we want to keep the *message* from E0433 (so
3385             // `parent_err`), but we want *hints* from E0412 (so `err`).
3386             //
3387             // And that's what happens below - we're just mixing both messages
3388             // into a single one.
3389             let mut parent_err = this.r.into_struct_error(parent_err.span, parent_err.node);
3390
3391             // overwrite all properties with the parent's error message
3392             err.message = take(&mut parent_err.message);
3393             err.code = take(&mut parent_err.code);
3394             swap(&mut err.span, &mut parent_err.span);
3395             err.children = take(&mut parent_err.children);
3396             err.sort_span = parent_err.sort_span;
3397             err.is_lint = parent_err.is_lint;
3398
3399             // merge the parent's suggestions with the typo suggestions
3400             fn append_result<T, E>(res1: &mut Result<Vec<T>, E>, res2: Result<Vec<T>, E>) {
3401                 match res1 {
3402                     Ok(vec1) => match res2 {
3403                         Ok(mut vec2) => vec1.append(&mut vec2),
3404                         Err(e) => *res1 = Err(e),
3405                     },
3406                     Err(_) => (),
3407                 };
3408             }
3409             append_result(&mut err.suggestions, parent_err.suggestions.clone());
3410
3411             parent_err.cancel();
3412
3413             let def_id = this.parent_scope.module.nearest_parent_mod();
3414
3415             if this.should_report_errs() {
3416                 if candidates.is_empty() {
3417                     // When there is no suggested imports, we can just emit the error
3418                     // and suggestions immediately. Note that we bypass the usually error
3419                     // reporting routine (ie via `self.r.report_error`) because we need
3420                     // to post-process the `ResolutionError` above.
3421                     err.emit();
3422                 } else {
3423                     // If there are suggested imports, the error reporting is delayed
3424                     this.r.use_injections.push(UseError {
3425                         err,
3426                         candidates,
3427                         def_id,
3428                         instead: false,
3429                         suggestion: None,
3430                         path: path.into(),
3431                         is_call: source.is_call(),
3432                     });
3433                 }
3434             } else {
3435                 err.cancel();
3436             }
3437
3438             // We don't return `Some(parent_err)` here, because the error will
3439             // be already printed either immediately or as part of the `use` injections
3440             None
3441         };
3442
3443         let partial_res = match self.resolve_qpath_anywhere(
3444             qself,
3445             path,
3446             ns,
3447             path_span,
3448             source.defer_to_typeck(),
3449             finalize,
3450         ) {
3451             Ok(Some(partial_res)) if let Some(res) = partial_res.full_res() => {
3452                 if source.is_expected(res) || res == Res::Err {
3453                     partial_res
3454                 } else {
3455                     report_errors(self, Some(res))
3456                 }
3457             }
3458
3459             Ok(Some(partial_res)) if source.defer_to_typeck() => {
3460                 // Not fully resolved associated item `T::A::B` or `<T as Tr>::A::B`
3461                 // or `<T>::A::B`. If `B` should be resolved in value namespace then
3462                 // it needs to be added to the trait map.
3463                 if ns == ValueNS {
3464                     let item_name = path.last().unwrap().ident;
3465                     let traits = self.traits_in_scope(item_name, ns);
3466                     self.r.trait_map.insert(node_id, traits);
3467                 }
3468
3469                 if PrimTy::from_name(path[0].ident.name).is_some() {
3470                     let mut std_path = Vec::with_capacity(1 + path.len());
3471
3472                     std_path.push(Segment::from_ident(Ident::with_dummy_span(sym::std)));
3473                     std_path.extend(path);
3474                     if let PathResult::Module(_) | PathResult::NonModule(_) =
3475                         self.resolve_path(&std_path, Some(ns), None)
3476                     {
3477                         // Check if we wrote `str::from_utf8` instead of `std::str::from_utf8`
3478                         let item_span =
3479                             path.iter().last().map_or(path_span, |segment| segment.ident.span);
3480
3481                         self.r.confused_type_with_std_module.insert(item_span, path_span);
3482                         self.r.confused_type_with_std_module.insert(path_span, path_span);
3483                     }
3484                 }
3485
3486                 partial_res
3487             }
3488
3489             Err(err) => {
3490                 if let Some(err) = report_errors_for_call(self, err) {
3491                     self.report_error(err.span, err.node);
3492                 }
3493
3494                 PartialRes::new(Res::Err)
3495             }
3496
3497             _ => report_errors(self, None),
3498         };
3499
3500         if !matches!(source, PathSource::TraitItem(..)) {
3501             // Avoid recording definition of `A::B` in `<T as A>::B::C`.
3502             self.r.record_partial_res(node_id, partial_res);
3503             self.resolve_elided_lifetimes_in_path(node_id, partial_res, path, source, path_span);
3504         }
3505
3506         partial_res
3507     }
3508
3509     fn self_type_is_available(&mut self) -> bool {
3510         let binding = self
3511             .maybe_resolve_ident_in_lexical_scope(Ident::with_dummy_span(kw::SelfUpper), TypeNS);
3512         if let Some(LexicalScopeBinding::Res(res)) = binding { res != Res::Err } else { false }
3513     }
3514
3515     fn self_value_is_available(&mut self, self_span: Span) -> bool {
3516         let ident = Ident::new(kw::SelfLower, self_span);
3517         let binding = self.maybe_resolve_ident_in_lexical_scope(ident, ValueNS);
3518         if let Some(LexicalScopeBinding::Res(res)) = binding { res != Res::Err } else { false }
3519     }
3520
3521     /// A wrapper around [`Resolver::report_error`].
3522     ///
3523     /// This doesn't emit errors for function bodies if this is rustdoc.
3524     fn report_error(&mut self, span: Span, resolution_error: ResolutionError<'a>) {
3525         if self.should_report_errs() {
3526             self.r.report_error(span, resolution_error);
3527         }
3528     }
3529
3530     #[inline]
3531     /// If we're actually rustdoc then avoid giving a name resolution error for `cfg()` items.
3532     fn should_report_errs(&self) -> bool {
3533         !(self.r.session.opts.actually_rustdoc && self.in_func_body)
3534     }
3535
3536     // Resolve in alternative namespaces if resolution in the primary namespace fails.
3537     fn resolve_qpath_anywhere(
3538         &mut self,
3539         qself: &Option<P<QSelf>>,
3540         path: &[Segment],
3541         primary_ns: Namespace,
3542         span: Span,
3543         defer_to_typeck: bool,
3544         finalize: Finalize,
3545     ) -> Result<Option<PartialRes>, Spanned<ResolutionError<'a>>> {
3546         let mut fin_res = None;
3547
3548         for (i, &ns) in [primary_ns, TypeNS, ValueNS].iter().enumerate() {
3549             if i == 0 || ns != primary_ns {
3550                 match self.resolve_qpath(qself, path, ns, finalize)? {
3551                     Some(partial_res)
3552                         if partial_res.unresolved_segments() == 0 || defer_to_typeck =>
3553                     {
3554                         return Ok(Some(partial_res));
3555                     }
3556                     partial_res => {
3557                         if fin_res.is_none() {
3558                             fin_res = partial_res;
3559                         }
3560                     }
3561                 }
3562             }
3563         }
3564
3565         assert!(primary_ns != MacroNS);
3566
3567         if qself.is_none() {
3568             let path_seg = |seg: &Segment| PathSegment::from_ident(seg.ident);
3569             let path = Path { segments: path.iter().map(path_seg).collect(), span, tokens: None };
3570             if let Ok((_, res)) =
3571                 self.r.resolve_macro_path(&path, None, &self.parent_scope, false, false)
3572             {
3573                 return Ok(Some(PartialRes::new(res)));
3574             }
3575         }
3576
3577         Ok(fin_res)
3578     }
3579
3580     /// Handles paths that may refer to associated items.
3581     fn resolve_qpath(
3582         &mut self,
3583         qself: &Option<P<QSelf>>,
3584         path: &[Segment],
3585         ns: Namespace,
3586         finalize: Finalize,
3587     ) -> Result<Option<PartialRes>, Spanned<ResolutionError<'a>>> {
3588         debug!(
3589             "resolve_qpath(qself={:?}, path={:?}, ns={:?}, finalize={:?})",
3590             qself, path, ns, finalize,
3591         );
3592
3593         if let Some(qself) = qself {
3594             if qself.position == 0 {
3595                 // This is a case like `<T>::B`, where there is no
3596                 // trait to resolve.  In that case, we leave the `B`
3597                 // segment to be resolved by type-check.
3598                 return Ok(Some(PartialRes::with_unresolved_segments(
3599                     Res::Def(DefKind::Mod, CRATE_DEF_ID.to_def_id()),
3600                     path.len(),
3601                 )));
3602             }
3603
3604             // Make sure `A::B` in `<T as A::B>::C` is a trait item.
3605             //
3606             // Currently, `path` names the full item (`A::B::C`, in
3607             // our example).  so we extract the prefix of that that is
3608             // the trait (the slice upto and including
3609             // `qself.position`). And then we recursively resolve that,
3610             // but with `qself` set to `None`.
3611             let ns = if qself.position + 1 == path.len() { ns } else { TypeNS };
3612             let partial_res = self.smart_resolve_path_fragment(
3613                 &None,
3614                 &path[..=qself.position],
3615                 PathSource::TraitItem(ns),
3616                 Finalize::with_root_span(finalize.node_id, finalize.path_span, qself.path_span),
3617             );
3618
3619             // The remaining segments (the `C` in our example) will
3620             // have to be resolved by type-check, since that requires doing
3621             // trait resolution.
3622             return Ok(Some(PartialRes::with_unresolved_segments(
3623                 partial_res.base_res(),
3624                 partial_res.unresolved_segments() + path.len() - qself.position - 1,
3625             )));
3626         }
3627
3628         let result = match self.resolve_path(&path, Some(ns), Some(finalize)) {
3629             PathResult::NonModule(path_res) => path_res,
3630             PathResult::Module(ModuleOrUniformRoot::Module(module)) if !module.is_normal() => {
3631                 PartialRes::new(module.res().unwrap())
3632             }
3633             // In `a(::assoc_item)*` `a` cannot be a module. If `a` does resolve to a module we
3634             // don't report an error right away, but try to fallback to a primitive type.
3635             // So, we are still able to successfully resolve something like
3636             //
3637             // use std::u8; // bring module u8 in scope
3638             // fn f() -> u8 { // OK, resolves to primitive u8, not to std::u8
3639             //     u8::max_value() // OK, resolves to associated function <u8>::max_value,
3640             //                     // not to non-existent std::u8::max_value
3641             // }
3642             //
3643             // Such behavior is required for backward compatibility.
3644             // The same fallback is used when `a` resolves to nothing.
3645             PathResult::Module(ModuleOrUniformRoot::Module(_)) | PathResult::Failed { .. }
3646                 if (ns == TypeNS || path.len() > 1)
3647                     && PrimTy::from_name(path[0].ident.name).is_some() =>
3648             {
3649                 let prim = PrimTy::from_name(path[0].ident.name).unwrap();
3650                 PartialRes::with_unresolved_segments(Res::PrimTy(prim), path.len() - 1)
3651             }
3652             PathResult::Module(ModuleOrUniformRoot::Module(module)) => {
3653                 PartialRes::new(module.res().unwrap())
3654             }
3655             PathResult::Failed { is_error_from_last_segment: false, span, label, suggestion } => {
3656                 return Err(respan(span, ResolutionError::FailedToResolve { label, suggestion }));
3657             }
3658             PathResult::Module(..) | PathResult::Failed { .. } => return Ok(None),
3659             PathResult::Indeterminate => bug!("indeterminate path result in resolve_qpath"),
3660         };
3661
3662         if path.len() > 1
3663             && let Some(res) = result.full_res()
3664             && res != Res::Err
3665             && path[0].ident.name != kw::PathRoot
3666             && path[0].ident.name != kw::DollarCrate
3667         {
3668             let unqualified_result = {
3669                 match self.resolve_path(&[*path.last().unwrap()], Some(ns), None) {
3670                     PathResult::NonModule(path_res) => path_res.expect_full_res(),
3671                     PathResult::Module(ModuleOrUniformRoot::Module(module)) => {
3672                         module.res().unwrap()
3673                     }
3674                     _ => return Ok(Some(result)),
3675                 }
3676             };
3677             if res == unqualified_result {
3678                 let lint = lint::builtin::UNUSED_QUALIFICATIONS;
3679                 self.r.lint_buffer.buffer_lint(
3680                     lint,
3681                     finalize.node_id,
3682                     finalize.path_span,
3683                     "unnecessary qualification",
3684                 )
3685             }
3686         }
3687
3688         Ok(Some(result))
3689     }
3690
3691     fn with_resolved_label(&mut self, label: Option<Label>, id: NodeId, f: impl FnOnce(&mut Self)) {
3692         if let Some(label) = label {
3693             if label.ident.as_str().as_bytes()[1] != b'_' {
3694                 self.diagnostic_metadata.unused_labels.insert(id, label.ident.span);
3695             }
3696
3697             if let Ok((_, orig_span)) = self.resolve_label(label.ident) {
3698                 diagnostics::signal_label_shadowing(self.r.session, orig_span, label.ident)
3699             }
3700
3701             self.with_label_rib(NormalRibKind, |this| {
3702                 let ident = label.ident.normalize_to_macro_rules();
3703                 this.label_ribs.last_mut().unwrap().bindings.insert(ident, id);
3704                 f(this);
3705             });
3706         } else {
3707             f(self);
3708         }
3709     }
3710
3711     fn resolve_labeled_block(&mut self, label: Option<Label>, id: NodeId, block: &'ast Block) {
3712         self.with_resolved_label(label, id, |this| this.visit_block(block));
3713     }
3714
3715     fn resolve_block(&mut self, block: &'ast Block) {
3716         debug!("(resolving block) entering block");
3717         // Move down in the graph, if there's an anonymous module rooted here.
3718         let orig_module = self.parent_scope.module;
3719         let anonymous_module = self.r.block_map.get(&block.id).cloned(); // clones a reference
3720
3721         let mut num_macro_definition_ribs = 0;
3722         if let Some(anonymous_module) = anonymous_module {
3723             debug!("(resolving block) found anonymous module, moving down");
3724             self.ribs[ValueNS].push(Rib::new(ModuleRibKind(anonymous_module)));
3725             self.ribs[TypeNS].push(Rib::new(ModuleRibKind(anonymous_module)));
3726             self.parent_scope.module = anonymous_module;
3727         } else {
3728             self.ribs[ValueNS].push(Rib::new(NormalRibKind));
3729         }
3730
3731         let prev = self.diagnostic_metadata.current_block_could_be_bare_struct_literal.take();
3732         if let (true, [Stmt { kind: StmtKind::Expr(expr), .. }]) =
3733             (block.could_be_bare_literal, &block.stmts[..])
3734             && let ExprKind::Type(..) = expr.kind
3735         {
3736             self.diagnostic_metadata.current_block_could_be_bare_struct_literal =
3737             Some(block.span);
3738         }
3739         // Descend into the block.
3740         for stmt in &block.stmts {
3741             if let StmtKind::Item(ref item) = stmt.kind
3742                 && let ItemKind::MacroDef(..) = item.kind {
3743                 num_macro_definition_ribs += 1;
3744                 let res = self.r.local_def_id(item.id).to_def_id();
3745                 self.ribs[ValueNS].push(Rib::new(MacroDefinition(res)));
3746                 self.label_ribs.push(Rib::new(MacroDefinition(res)));
3747             }
3748
3749             self.visit_stmt(stmt);
3750         }
3751         self.diagnostic_metadata.current_block_could_be_bare_struct_literal = prev;
3752
3753         // Move back up.
3754         self.parent_scope.module = orig_module;
3755         for _ in 0..num_macro_definition_ribs {
3756             self.ribs[ValueNS].pop();
3757             self.label_ribs.pop();
3758         }
3759         self.ribs[ValueNS].pop();
3760         if anonymous_module.is_some() {
3761             self.ribs[TypeNS].pop();
3762         }
3763         debug!("(resolving block) leaving block");
3764     }
3765
3766     fn resolve_anon_const(&mut self, constant: &'ast AnonConst, is_repeat: IsRepeatExpr) {
3767         debug!("resolve_anon_const {:?} is_repeat: {:?}", constant, is_repeat);
3768         self.with_constant_rib(
3769             is_repeat,
3770             if constant.value.is_potential_trivial_const_param() {
3771                 ConstantHasGenerics::Yes
3772             } else {
3773                 ConstantHasGenerics::No
3774             },
3775             None,
3776             |this| visit::walk_anon_const(this, constant),
3777         );
3778     }
3779
3780     fn resolve_inline_const(&mut self, constant: &'ast AnonConst) {
3781         debug!("resolve_anon_const {constant:?}");
3782         self.with_constant_rib(IsRepeatExpr::No, ConstantHasGenerics::Yes, None, |this| {
3783             visit::walk_anon_const(this, constant)
3784         });
3785     }
3786
3787     fn resolve_expr(&mut self, expr: &'ast Expr, parent: Option<&'ast Expr>) {
3788         // First, record candidate traits for this expression if it could
3789         // result in the invocation of a method call.
3790
3791         self.record_candidate_traits_for_expr_if_necessary(expr);
3792
3793         // Next, resolve the node.
3794         match expr.kind {
3795             ExprKind::Path(ref qself, ref path) => {
3796                 self.smart_resolve_path(expr.id, qself, path, PathSource::Expr(parent));
3797                 visit::walk_expr(self, expr);
3798             }
3799
3800             ExprKind::Struct(ref se) => {
3801                 self.smart_resolve_path(expr.id, &se.qself, &se.path, PathSource::Struct);
3802                 visit::walk_expr(self, expr);
3803             }
3804
3805             ExprKind::Break(Some(label), _) | ExprKind::Continue(Some(label)) => {
3806                 match self.resolve_label(label.ident) {
3807                     Ok((node_id, _)) => {
3808                         // Since this res is a label, it is never read.
3809                         self.r.label_res_map.insert(expr.id, node_id);
3810                         self.diagnostic_metadata.unused_labels.remove(&node_id);
3811                     }
3812                     Err(error) => {
3813                         self.report_error(label.ident.span, error);
3814                     }
3815                 }
3816
3817                 // visit `break` argument if any
3818                 visit::walk_expr(self, expr);
3819             }
3820
3821             ExprKind::Break(None, Some(ref e)) => {
3822                 // We use this instead of `visit::walk_expr` to keep the parent expr around for
3823                 // better diagnostics.
3824                 self.resolve_expr(e, Some(&expr));
3825             }
3826
3827             ExprKind::Let(ref pat, ref scrutinee, _) => {
3828                 self.visit_expr(scrutinee);
3829                 self.resolve_pattern_top(pat, PatternSource::Let);
3830             }
3831
3832             ExprKind::If(ref cond, ref then, ref opt_else) => {
3833                 self.with_rib(ValueNS, NormalRibKind, |this| {
3834                     let old = this.diagnostic_metadata.in_if_condition.replace(cond);
3835                     this.visit_expr(cond);
3836                     this.diagnostic_metadata.in_if_condition = old;
3837                     this.visit_block(then);
3838                 });
3839                 if let Some(expr) = opt_else {
3840                     self.visit_expr(expr);
3841                 }
3842             }
3843
3844             ExprKind::Loop(ref block, label, _) => {
3845                 self.resolve_labeled_block(label, expr.id, &block)
3846             }
3847
3848             ExprKind::While(ref cond, ref block, label) => {
3849                 self.with_resolved_label(label, expr.id, |this| {
3850                     this.with_rib(ValueNS, NormalRibKind, |this| {
3851                         let old = this.diagnostic_metadata.in_if_condition.replace(cond);
3852                         this.visit_expr(cond);
3853                         this.diagnostic_metadata.in_if_condition = old;
3854                         this.visit_block(block);
3855                     })
3856                 });
3857             }
3858
3859             ExprKind::ForLoop(ref pat, ref iter_expr, ref block, label) => {
3860                 self.visit_expr(iter_expr);
3861                 self.with_rib(ValueNS, NormalRibKind, |this| {
3862                     this.resolve_pattern_top(pat, PatternSource::For);
3863                     this.resolve_labeled_block(label, expr.id, block);
3864                 });
3865             }
3866
3867             ExprKind::Block(ref block, label) => self.resolve_labeled_block(label, block.id, block),
3868
3869             // Equivalent to `visit::walk_expr` + passing some context to children.
3870             ExprKind::Field(ref subexpression, _) => {
3871                 self.resolve_expr(subexpression, Some(expr));
3872             }
3873             ExprKind::MethodCall(box MethodCall { ref seg, ref receiver, ref args, .. }) => {
3874                 self.resolve_expr(receiver, Some(expr));
3875                 for arg in args {
3876                     self.resolve_expr(arg, None);
3877                 }
3878                 self.visit_path_segment(seg);
3879             }
3880
3881             ExprKind::Call(ref callee, ref arguments) => {
3882                 self.resolve_expr(callee, Some(expr));
3883                 let const_args = self.r.legacy_const_generic_args(callee).unwrap_or_default();
3884                 for (idx, argument) in arguments.iter().enumerate() {
3885                     // Constant arguments need to be treated as AnonConst since
3886                     // that is how they will be later lowered to HIR.
3887                     if const_args.contains(&idx) {
3888                         self.with_constant_rib(
3889                             IsRepeatExpr::No,
3890                             if argument.is_potential_trivial_const_param() {
3891                                 ConstantHasGenerics::Yes
3892                             } else {
3893                                 ConstantHasGenerics::No
3894                             },
3895                             None,
3896                             |this| {
3897                                 this.resolve_expr(argument, None);
3898                             },
3899                         );
3900                     } else {
3901                         self.resolve_expr(argument, None);
3902                     }
3903                 }
3904             }
3905             ExprKind::Type(ref type_expr, ref ty) => {
3906                 // `ParseSess::type_ascription_path_suggestions` keeps spans of colon tokens in
3907                 // type ascription. Here we are trying to retrieve the span of the colon token as
3908                 // well, but only if it's written without spaces `expr:Ty` and therefore confusable
3909                 // with `expr::Ty`, only in this case it will match the span from
3910                 // `type_ascription_path_suggestions`.
3911                 self.diagnostic_metadata
3912                     .current_type_ascription
3913                     .push(type_expr.span.between(ty.span));
3914                 visit::walk_expr(self, expr);
3915                 self.diagnostic_metadata.current_type_ascription.pop();
3916             }
3917             // `async |x| ...` gets desugared to `|x| async {...}`, so we need to
3918             // resolve the arguments within the proper scopes so that usages of them inside the
3919             // closure are detected as upvars rather than normal closure arg usages.
3920             ExprKind::Closure(box ast::Closure {
3921                 asyncness: Async::Yes { .. },
3922                 ref fn_decl,
3923                 ref body,
3924                 ..
3925             }) => {
3926                 self.with_rib(ValueNS, NormalRibKind, |this| {
3927                     this.with_label_rib(ClosureOrAsyncRibKind, |this| {
3928                         // Resolve arguments:
3929                         this.resolve_params(&fn_decl.inputs);
3930                         // No need to resolve return type --
3931                         // the outer closure return type is `FnRetTy::Default`.
3932
3933                         // Now resolve the inner closure
3934                         {
3935                             // No need to resolve arguments: the inner closure has none.
3936                             // Resolve the return type:
3937                             visit::walk_fn_ret_ty(this, &fn_decl.output);
3938                             // Resolve the body
3939                             this.visit_expr(body);
3940                         }
3941                     })
3942                 });
3943             }
3944             // For closures, ClosureOrAsyncRibKind is added in visit_fn
3945             ExprKind::Closure(box ast::Closure {
3946                 binder: ClosureBinder::For { ref generic_params, span },
3947                 ..
3948             }) => {
3949                 self.with_generic_param_rib(
3950                     &generic_params,
3951                     NormalRibKind,
3952                     LifetimeRibKind::Generics {
3953                         binder: expr.id,
3954                         kind: LifetimeBinderKind::Closure,
3955                         span,
3956                     },
3957                     |this| visit::walk_expr(this, expr),
3958                 );
3959             }
3960             ExprKind::Closure(..) => visit::walk_expr(self, expr),
3961             ExprKind::Async(..) => {
3962                 self.with_label_rib(ClosureOrAsyncRibKind, |this| visit::walk_expr(this, expr));
3963             }
3964             ExprKind::Repeat(ref elem, ref ct) => {
3965                 self.visit_expr(elem);
3966                 self.with_lifetime_rib(LifetimeRibKind::AnonConst, |this| {
3967                     this.with_lifetime_rib(LifetimeRibKind::Elided(LifetimeRes::Static), |this| {
3968                         this.resolve_anon_const(ct, IsRepeatExpr::Yes)
3969                     })
3970                 });
3971             }
3972             ExprKind::ConstBlock(ref ct) => {
3973                 self.resolve_inline_const(ct);
3974             }
3975             ExprKind::Index(ref elem, ref idx) => {
3976                 self.resolve_expr(elem, Some(expr));
3977                 self.visit_expr(idx);
3978             }
3979             ExprKind::Assign(ref lhs, ref rhs, _) => {
3980                 if !self.diagnostic_metadata.is_assign_rhs {
3981                     self.diagnostic_metadata.in_assignment = Some(expr);
3982                 }
3983                 self.visit_expr(lhs);
3984                 self.diagnostic_metadata.is_assign_rhs = true;
3985                 self.diagnostic_metadata.in_assignment = None;
3986                 self.visit_expr(rhs);
3987                 self.diagnostic_metadata.is_assign_rhs = false;
3988             }
3989             _ => {
3990                 visit::walk_expr(self, expr);
3991             }
3992         }
3993     }
3994
3995     fn record_candidate_traits_for_expr_if_necessary(&mut self, expr: &'ast Expr) {
3996         match expr.kind {
3997             ExprKind::Field(_, ident) => {
3998                 // FIXME(#6890): Even though you can't treat a method like a
3999                 // field, we need to add any trait methods we find that match
4000                 // the field name so that we can do some nice error reporting
4001                 // later on in typeck.
4002                 let traits = self.traits_in_scope(ident, ValueNS);
4003                 self.r.trait_map.insert(expr.id, traits);
4004             }
4005             ExprKind::MethodCall(ref call) => {
4006                 debug!("(recording candidate traits for expr) recording traits for {}", expr.id);
4007                 let traits = self.traits_in_scope(call.seg.ident, ValueNS);
4008                 self.r.trait_map.insert(expr.id, traits);
4009             }
4010             _ => {
4011                 // Nothing to do.
4012             }
4013         }
4014     }
4015
4016     fn traits_in_scope(&mut self, ident: Ident, ns: Namespace) -> Vec<TraitCandidate> {
4017         self.r.traits_in_scope(
4018             self.current_trait_ref.as_ref().map(|(module, _)| *module),
4019             &self.parent_scope,
4020             ident.span.ctxt(),
4021             Some((ident.name, ns)),
4022         )
4023     }
4024
4025     /// Construct the list of in-scope lifetime parameters for async lowering.
4026     /// We include all lifetime parameters, either named or "Fresh".
4027     /// The order of those parameters does not matter, as long as it is
4028     /// deterministic.
4029     fn record_lifetime_params_for_async(
4030         &mut self,
4031         fn_id: NodeId,
4032         async_node_id: Option<(NodeId, Span)>,
4033     ) {
4034         if let Some((async_node_id, span)) = async_node_id {
4035             let mut extra_lifetime_params =
4036                 self.r.extra_lifetime_params_map.get(&fn_id).cloned().unwrap_or_default();
4037             for rib in self.lifetime_ribs.iter().rev() {
4038                 extra_lifetime_params.extend(
4039                     rib.bindings.iter().map(|(&ident, &(node_id, res))| (ident, node_id, res)),
4040                 );
4041                 match rib.kind {
4042                     LifetimeRibKind::Item => break,
4043                     LifetimeRibKind::AnonymousCreateParameter { binder, .. } => {
4044                         if let Some(earlier_fresh) = self.r.extra_lifetime_params_map.get(&binder) {
4045                             extra_lifetime_params.extend(earlier_fresh);
4046                         }
4047                     }
4048                     LifetimeRibKind::Generics { .. } => {}
4049                     _ => {
4050                         // We are in a function definition. We should only find `Generics`
4051                         // and `AnonymousCreateParameter` inside the innermost `Item`.
4052                         span_bug!(span, "unexpected rib kind: {:?}", rib.kind)
4053                     }
4054                 }
4055             }
4056             self.r.extra_lifetime_params_map.insert(async_node_id, extra_lifetime_params);
4057         }
4058     }
4059 }
4060
4061 struct LifetimeCountVisitor<'a, 'b> {
4062     r: &'b mut Resolver<'a>,
4063 }
4064
4065 /// Walks the whole crate in DFS order, visiting each item, counting the declared number of
4066 /// lifetime generic parameters.
4067 impl<'ast> Visitor<'ast> for LifetimeCountVisitor<'_, '_> {
4068     fn visit_item(&mut self, item: &'ast Item) {
4069         match &item.kind {
4070             ItemKind::TyAlias(box TyAlias { ref generics, .. })
4071             | ItemKind::Fn(box Fn { ref generics, .. })
4072             | ItemKind::Enum(_, ref generics)
4073             | ItemKind::Struct(_, ref generics)
4074             | ItemKind::Union(_, ref generics)
4075             | ItemKind::Impl(box Impl { ref generics, .. })
4076             | ItemKind::Trait(box Trait { ref generics, .. })
4077             | ItemKind::TraitAlias(ref generics, _) => {
4078                 let def_id = self.r.local_def_id(item.id);
4079                 let count = generics
4080                     .params
4081                     .iter()
4082                     .filter(|param| matches!(param.kind, ast::GenericParamKind::Lifetime { .. }))
4083                     .count();
4084                 self.r.item_generics_num_lifetimes.insert(def_id, count);
4085             }
4086
4087             ItemKind::Mod(..)
4088             | ItemKind::ForeignMod(..)
4089             | ItemKind::Static(..)
4090             | ItemKind::Const(..)
4091             | ItemKind::Use(..)
4092             | ItemKind::ExternCrate(..)
4093             | ItemKind::MacroDef(..)
4094             | ItemKind::GlobalAsm(..)
4095             | ItemKind::MacCall(..) => {}
4096         }
4097         visit::walk_item(self, item)
4098     }
4099 }
4100
4101 impl<'a> Resolver<'a> {
4102     pub(crate) fn late_resolve_crate(&mut self, krate: &Crate) {
4103         visit::walk_crate(&mut LifetimeCountVisitor { r: self }, krate);
4104         let mut late_resolution_visitor = LateResolutionVisitor::new(self);
4105         visit::walk_crate(&mut late_resolution_visitor, krate);
4106         for (id, span) in late_resolution_visitor.diagnostic_metadata.unused_labels.iter() {
4107             self.lint_buffer.buffer_lint(lint::builtin::UNUSED_LABELS, *id, *span, "unused label");
4108         }
4109     }
4110 }