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