compiler/rustc_resolve/src/late.rs

   1 //! "Late resolution" is the pass that resolves most of names in a crate beside imports and macros.
   2 //! It runs when the crate is fully expanded and its module structure is fully built.
   3 //! So it just walks through the crate and resolves all the expressions, types, etc.
   4 //!
   5 //! If you wonder why there's no `early.rs`, that's because it's split into three files -
   6 //! `build_reduced_graph.rs`, `macros.rs` and `imports.rs`.
   7
   8 use RibKind::*;
   9
  10 use crate::{path_names_to_string, BindingError, CrateLint, LexicalScopeBinding};
  11 use crate::{Module, ModuleOrUniformRoot, ParentScope, PathResult};
  12 use crate::{ResolutionError, Resolver, Segment, UseError};
  13
  14 use rustc_ast::ptr::P;
  15 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
  16 use rustc_ast::*;
  17 use rustc_ast_lowering::ResolverAstLowering;
  18 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  19 use rustc_errors::DiagnosticId;
  20 use rustc_hir::def::Namespace::{self, *};
  21 use rustc_hir::def::{self, CtorKind, DefKind, PartialRes, PerNS};
  22 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX};
  23 use rustc_hir::{PrimTy, TraitCandidate};
  24 use rustc_middle::{bug, span_bug};
  25 use rustc_session::lint;
  26 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  27 use rustc_span::Span;
  28 use smallvec::{smallvec, SmallVec};
  29
  30 use rustc_span::source_map::{respan, Spanned};
  31 use std::collections::{hash_map::Entry, BTreeSet};
  32 use std::mem::{replace, take};
  33 use tracing::debug;
  34
  35 mod diagnostics;
  36 crate mod lifetimes;
  37
  38 type Res = def::Res<NodeId>;
  39
  40 type IdentMap<T> = FxHashMap<Ident, T>;
  41
  42 /// Map from the name in a pattern to its binding mode.
  43 type BindingMap = IdentMap<BindingInfo>;
  44
  45 #[derive(Copy, Clone, Debug)]
  46 struct BindingInfo {
  47     span: Span,
  48     binding_mode: BindingMode,
  49 }
  50
  51 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
  52 enum PatternSource {
  53     Match,
  54     Let,
  55     For,
  56     FnParam,
  57 }
  58
  59 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
  60 enum IsRepeatExpr {
  61     No,
  62     Yes,
  63 }
  64
  65 impl PatternSource {
  66     fn descr(self) -> &'static str {
  67         match self {
  68             PatternSource::Match => "match binding",
  69             PatternSource::Let => "let binding",
  70             PatternSource::For => "for binding",
  71             PatternSource::FnParam => "function parameter",
  72         }
  73     }
  74 }
  75
  76 /// Denotes whether the context for the set of already bound bindings is a `Product`
  77 /// or `Or` context. This is used in e.g., `fresh_binding` and `resolve_pattern_inner`.
  78 /// See those functions for more information.
  79 #[derive(PartialEq)]
  80 enum PatBoundCtx {
  81     /// A product pattern context, e.g., `Variant(a, b)`.
  82     Product,
  83     /// An or-pattern context, e.g., `p_0 | ... | p_n`.
  84     Or,
  85 }
  86
  87 /// Does this the item (from the item rib scope) allow generic parameters?
  88 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  89 crate enum HasGenericParams {
  90     Yes,
  91     No,
  92 }
  93
  94 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  95 crate enum ConstantItemKind {
  96     Const,
  97     Static,
  98 }
  99
 100 /// The rib kind restricts certain accesses,
 101 /// e.g. to a `Res::Local` of an outer item.
 102 #[derive(Copy, Clone, Debug)]
 103 crate enum RibKind<'a> {
 104     /// No restriction needs to be applied.
 105     NormalRibKind,
 106
 107     /// We passed through an impl or trait and are now in one of its
 108     /// methods or associated types. Allow references to ty params that impl or trait
 109     /// binds. Disallow any other upvars (including other ty params that are
 110     /// upvars).
 111     AssocItemRibKind,
 112
 113     /// We passed through a closure. Disallow labels.
 114     ClosureOrAsyncRibKind,
 115
 116     /// We passed through a function definition. Disallow upvars.
 117     /// Permit only those const parameters that are specified in the function's generics.
 118     FnItemRibKind,
 119
 120     /// We passed through an item scope. Disallow upvars.
 121     ItemRibKind(HasGenericParams),
 122
 123     /// We're in a constant item. Can't refer to dynamic stuff.
 124     ///
 125     /// The `bool` indicates if this constant may reference generic parameters
 126     /// and is used to only allow generic parameters to be used in trivial constant expressions.
 127     ConstantItemRibKind(bool, Option<(Ident, ConstantItemKind)>),
 128
 129     /// We passed through a module.
 130     ModuleRibKind(Module<'a>),
 131
 132     /// We passed through a `macro_rules!` statement
 133     MacroDefinition(DefId),
 134
 135     /// All bindings in this rib are generic parameters that can't be used
 136     /// from the default of a generic parameter because they're not declared
 137     /// before said generic parameter. Also see the `visit_generics` override.
 138     ForwardGenericParamBanRibKind,
 139
 140     /// We are inside of the type of a const parameter. Can't refer to any
 141     /// parameters.
 142     ConstParamTyRibKind,
 143 }
 144
 145 impl RibKind<'_> {
 146     /// Whether this rib kind contains generic parameters, as opposed to local
 147     /// variables.
 148     crate fn contains_params(&self) -> bool {
 149         match self {
 150             NormalRibKind
 151             | ClosureOrAsyncRibKind
 152             | FnItemRibKind
 153             | ConstantItemRibKind(..)
 154             | ModuleRibKind(_)
 155             | MacroDefinition(_)
 156             | ConstParamTyRibKind => false,
 157             AssocItemRibKind | ItemRibKind(_) | ForwardGenericParamBanRibKind => true,
 158         }
 159     }
 160 }
 161
 162 /// A single local scope.
 163 ///
 164 /// A rib represents a scope names can live in. Note that these appear in many places, not just
 165 /// around braces. At any place where the list of accessible names (of the given namespace)
 166 /// changes or a new restrictions on the name accessibility are introduced, a new rib is put onto a
 167 /// stack. This may be, for example, a `let` statement (because it introduces variables), a macro,
 168 /// etc.
 169 ///
 170 /// Different [rib kinds](enum.RibKind) are transparent for different names.
 171 ///
 172 /// The resolution keeps a separate stack of ribs as it traverses the AST for each namespace. When
 173 /// resolving, the name is looked up from inside out.
 174 #[derive(Debug)]
 175 crate struct Rib<'a, R = Res> {
 176     pub bindings: IdentMap<R>,
 177     pub kind: RibKind<'a>,
 178 }
 179
 180 impl<'a, R> Rib<'a, R> {
 181     fn new(kind: RibKind<'a>) -> Rib<'a, R> {
 182         Rib { bindings: Default::default(), kind }
 183     }
 184 }
 185
 186 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 187 crate enum AliasPossibility {
 188     No,
 189     Maybe,
 190 }
 191
 192 #[derive(Copy, Clone, Debug)]
 193 crate enum PathSource<'a> {
 194     // Type paths `Path`.
 195     Type,
 196     // Trait paths in bounds or impls.
 197     Trait(AliasPossibility),
 198     // Expression paths `path`, with optional parent context.
 199     Expr(Option<&'a Expr>),
 200     // Paths in path patterns `Path`.
 201     Pat,
 202     // Paths in struct expressions and patterns `Path { .. }`.
 203     Struct,
 204     // Paths in tuple struct patterns `Path(..)`.
 205     TupleStruct(Span, &'a [Span]),
 206     // `m::A::B` in `<T as m::A>::B::C`.
 207     TraitItem(Namespace),
 208 }
 209
 210 impl<'a> PathSource<'a> {
 211     fn namespace(self) -> Namespace {
 212         match self {
 213             PathSource::Type | PathSource::Trait(_) | PathSource::Struct => TypeNS,
 214             PathSource::Expr(..) | PathSource::Pat | PathSource::TupleStruct(..) => ValueNS,
 215             PathSource::TraitItem(ns) => ns,
 216         }
 217     }
 218
 219     fn defer_to_typeck(self) -> bool {
 220         match self {
 221             PathSource::Type
 222             | PathSource::Expr(..)
 223             | PathSource::Pat
 224             | PathSource::Struct
 225             | PathSource::TupleStruct(..) => true,
 226             PathSource::Trait(_) | PathSource::TraitItem(..) => false,
 227         }
 228     }
 229
 230     fn descr_expected(self) -> &'static str {
 231         match &self {
 232             PathSource::Type => "type",
 233             PathSource::Trait(_) => "trait",
 234             PathSource::Pat => "unit struct, unit variant or constant",
 235             PathSource::Struct => "struct, variant or union type",
 236             PathSource::TupleStruct(..) => "tuple struct or tuple variant",
 237             PathSource::TraitItem(ns) => match ns {
 238                 TypeNS => "associated type",
 239                 ValueNS => "method or associated constant",
 240                 MacroNS => bug!("associated macro"),
 241             },
 242             PathSource::Expr(parent) => match parent.as_ref().map(|p| &p.kind) {
 243                 // "function" here means "anything callable" rather than `DefKind::Fn`,
 244                 // this is not precise but usually more helpful than just "value".
 245                 Some(ExprKind::Call(call_expr, _)) => match &call_expr.kind {
 246                     // the case of `::some_crate()`
 247                     ExprKind::Path(_, path)
 248                         if path.segments.len() == 2
 249                             && path.segments[0].ident.name == kw::PathRoot =>
 250                     {
 251                         "external crate"
 252                     }
 253                     ExprKind::Path(_, path) => {
 254                         let mut msg = "function";
 255                         if let Some(segment) = path.segments.iter().last() {
 256                             if let Some(c) = segment.ident.to_string().chars().next() {
 257                                 if c.is_uppercase() {
 258                                     msg = "function, tuple struct or tuple variant";
 259                                 }
 260                             }
 261                         }
 262                         msg
 263                     }
 264                     _ => "function",
 265                 },
 266                 _ => "value",
 267             },
 268         }
 269     }
 270
 271     fn is_call(self) -> bool {
 272         matches!(self, PathSource::Expr(Some(&Expr { kind: ExprKind::Call(..), .. })))
 273     }
 274
 275     crate fn is_expected(self, res: Res) -> bool {
 276         match self {
 277             PathSource::Type => matches!(
 278                 res,
 279                 Res::Def(
 280                     DefKind::Struct
 281                         | DefKind::Union
 282                         | DefKind::Enum
 283                         | DefKind::Trait
 284                         | DefKind::TraitAlias
 285                         | DefKind::TyAlias
 286                         | DefKind::AssocTy
 287                         | DefKind::TyParam
 288                         | DefKind::OpaqueTy
 289                         | DefKind::ForeignTy,
 290                     _,
 291                 ) | Res::PrimTy(..)
 292                     | Res::SelfTy(..)
 293             ),
 294             PathSource::Trait(AliasPossibility::No) => matches!(res, Res::Def(DefKind::Trait, _)),
 295             PathSource::Trait(AliasPossibility::Maybe) => {
 296                 matches!(res, Res::Def(DefKind::Trait | DefKind::TraitAlias, _))
 297             }
 298             PathSource::Expr(..) => matches!(
 299                 res,
 300                 Res::Def(
 301                     DefKind::Ctor(_, CtorKind::Const | CtorKind::Fn)
 302                         | DefKind::Const
 303                         | DefKind::Static
 304                         | DefKind::Fn
 305                         | DefKind::AssocFn
 306                         | DefKind::AssocConst
 307                         | DefKind::ConstParam,
 308                     _,
 309                 ) | Res::Local(..)
 310                     | Res::SelfCtor(..)
 311             ),
 312             PathSource::Pat => matches!(
 313                 res,
 314                 Res::Def(
 315                     DefKind::Ctor(_, CtorKind::Const) | DefKind::Const | DefKind::AssocConst,
 316                     _,
 317                 ) | Res::SelfCtor(..)
 318             ),
 319             PathSource::TupleStruct(..) => res.expected_in_tuple_struct_pat(),
 320             PathSource::Struct => matches!(
 321                 res,
 322                 Res::Def(
 323                     DefKind::Struct
 324                         | DefKind::Union
 325                         | DefKind::Variant
 326                         | DefKind::TyAlias
 327                         | DefKind::AssocTy,
 328                     _,
 329                 ) | Res::SelfTy(..)
 330             ),
 331             PathSource::TraitItem(ns) => match res {
 332                 Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) if ns == ValueNS => true,
 333                 Res::Def(DefKind::AssocTy, _) if ns == TypeNS => true,
 334                 _ => false,
 335             },
 336         }
 337     }
 338
 339     fn error_code(self, has_unexpected_resolution: bool) -> DiagnosticId {
 340         use rustc_errors::error_code;
 341         match (self, has_unexpected_resolution) {
 342             (PathSource::Trait(_), true) => error_code!(E0404),
 343             (PathSource::Trait(_), false) => error_code!(E0405),
 344             (PathSource::Type, true) => error_code!(E0573),
 345             (PathSource::Type, false) => error_code!(E0412),
 346             (PathSource::Struct, true) => error_code!(E0574),
 347             (PathSource::Struct, false) => error_code!(E0422),
 348             (PathSource::Expr(..), true) => error_code!(E0423),
 349             (PathSource::Expr(..), false) => error_code!(E0425),
 350             (PathSource::Pat | PathSource::TupleStruct(..), true) => error_code!(E0532),
 351             (PathSource::Pat | PathSource::TupleStruct(..), false) => error_code!(E0531),
 352             (PathSource::TraitItem(..), true) => error_code!(E0575),
 353             (PathSource::TraitItem(..), false) => error_code!(E0576),
 354         }
 355     }
 356 }
 357
 358 #[derive(Default)]
 359 struct DiagnosticMetadata<'ast> {
 360     /// The current trait's associated items' ident, used for diagnostic suggestions.
 361     current_trait_assoc_items: Option<&'ast [P<AssocItem>]>,
 362
 363     /// The current self type if inside an impl (used for better errors).
 364     current_self_type: Option<Ty>,
 365
 366     /// The current self item if inside an ADT (used for better errors).
 367     current_self_item: Option<NodeId>,
 368
 369     /// The current trait (used to suggest).
 370     current_item: Option<&'ast Item>,
 371
 372     /// When processing generics and encountering a type not found, suggest introducing a type
 373     /// param.
 374     currently_processing_generics: bool,
 375
 376     /// The current enclosing (non-closure) function (used for better errors).
 377     current_function: Option<(FnKind<'ast>, Span)>,
 378
 379     /// A list of labels as of yet unused. Labels will be removed from this map when
 380     /// they are used (in a `break` or `continue` statement)
 381     unused_labels: FxHashMap<NodeId, Span>,
 382
 383     /// Only used for better errors on `fn(): fn()`.
 384     current_type_ascription: Vec<Span>,
 385
 386     /// Only used for better errors on `let x = { foo: bar };`.
 387     /// In the case of a parse error with `let x = { foo: bar, };`, this isn't needed, it's only
 388     /// needed for cases where this parses as a correct type ascription.
 389     current_block_could_be_bare_struct_literal: Option<Span>,
 390
 391     /// Only used for better errors on `let <pat>: <expr, not type>;`.
 392     current_let_binding: Option<(Span, Option<Span>, Option<Span>)>,
 393
 394     /// Used to detect possible `if let` written without `let` and to provide structured suggestion.
 395     in_if_condition: Option<&'ast Expr>,
 396
 397     /// If we are currently in a trait object definition. Used to point at the bounds when
 398     /// encountering a struct or enum.
 399     current_trait_object: Option<&'ast [ast::GenericBound]>,
 400
 401     /// Given `where <T as Bar>::Baz: String`, suggest `where T: Bar<Baz = String>`.
 402     current_where_predicate: Option<&'ast WherePredicate>,
 403 }
 404
 405 struct LateResolutionVisitor<'a, 'b, 'ast> {
 406     r: &'b mut Resolver<'a>,
 407
 408     /// The module that represents the current item scope.
 409     parent_scope: ParentScope<'a>,
 410
 411     /// The current set of local scopes for types and values.
 412     /// FIXME #4948: Reuse ribs to avoid allocation.
 413     ribs: PerNS<Vec<Rib<'a>>>,
 414
 415     /// The current set of local scopes, for labels.
 416     label_ribs: Vec<Rib<'a, NodeId>>,
 417
 418     /// The trait that the current context can refer to.
 419     current_trait_ref: Option<(Module<'a>, TraitRef)>,
 420
 421     /// Fields used to add information to diagnostic errors.
 422     diagnostic_metadata: DiagnosticMetadata<'ast>,
 423
 424     /// State used to know whether to ignore resolution errors for function bodies.
 425     ///
 426     /// In particular, rustdoc uses this to avoid giving errors for `cfg()` items.
 427     /// In most cases this will be `None`, in which case errors will always be reported.
 428     /// If it is `true`, then it will be updated when entering a nested function or trait body.
 429     in_func_body: bool,
 430 }
 431
 432 /// Walks the whole crate in DFS order, visiting each item, resolving names as it goes.
 433 impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
 434     fn visit_item(&mut self, item: &'ast Item) {
 435         let prev = replace(&mut self.diagnostic_metadata.current_item, Some(item));
 436         // Always report errors in items we just entered.
 437         let old_ignore = replace(&mut self.in_func_body, false);
 438         self.resolve_item(item);
 439         self.in_func_body = old_ignore;
 440         self.diagnostic_metadata.current_item = prev;
 441     }
 442     fn visit_arm(&mut self, arm: &'ast Arm) {
 443         self.resolve_arm(arm);
 444     }
 445     fn visit_block(&mut self, block: &'ast Block) {
 446         self.resolve_block(block);
 447     }
 448     fn visit_anon_const(&mut self, constant: &'ast AnonConst) {
 449         // We deal with repeat expressions explicitly in `resolve_expr`.
 450         self.resolve_anon_const(constant, IsRepeatExpr::No);
 451     }
 452     fn visit_expr(&mut self, expr: &'ast Expr) {
 453         self.resolve_expr(expr, None);
 454     }
 455     fn visit_local(&mut self, local: &'ast Local) {
 456         let local_spans = match local.pat.kind {
 457             // We check for this to avoid tuple struct fields.
 458             PatKind::Wild => None,
 459             _ => Some((
 460                 local.pat.span,
 461                 local.ty.as_ref().map(|ty| ty.span),
 462                 local.kind.init().map(|init| init.span),
 463             )),
 464         };
 465         let original = replace(&mut self.diagnostic_metadata.current_let_binding, local_spans);
 466         self.resolve_local(local);
 467         self.diagnostic_metadata.current_let_binding = original;
 468     }
 469     fn visit_ty(&mut self, ty: &'ast Ty) {
 470         let prev = self.diagnostic_metadata.current_trait_object;
 471         match ty.kind {
 472             TyKind::Path(ref qself, ref path) => {
 473                 self.smart_resolve_path(ty.id, qself.as_ref(), path, PathSource::Type);
 474             }
 475             TyKind::ImplicitSelf => {
 476                 let self_ty = Ident::with_dummy_span(kw::SelfUpper);
 477                 let res = self
 478                     .resolve_ident_in_lexical_scope(self_ty, TypeNS, Some(ty.id), ty.span)
 479                     .map_or(Res::Err, |d| d.res());
 480                 self.r.record_partial_res(ty.id, PartialRes::new(res));
 481             }
 482             TyKind::TraitObject(ref bounds, ..) => {
 483                 self.diagnostic_metadata.current_trait_object = Some(&bounds[..]);
 484             }
 485             _ => (),
 486         }
 487         visit::walk_ty(self, ty);
 488         self.diagnostic_metadata.current_trait_object = prev;
 489     }
 490     fn visit_poly_trait_ref(&mut self, tref: &'ast PolyTraitRef, m: &'ast TraitBoundModifier) {
 491         self.smart_resolve_path(
 492             tref.trait_ref.ref_id,
 493             None,
 494             &tref.trait_ref.path,
 495             PathSource::Trait(AliasPossibility::Maybe),
 496         );
 497         visit::walk_poly_trait_ref(self, tref, m);
 498     }
 499     fn visit_foreign_item(&mut self, foreign_item: &'ast ForeignItem) {
 500         match foreign_item.kind {
 501             ForeignItemKind::Fn(box Fn { ref generics, .. })
 502             | ForeignItemKind::TyAlias(box TyAlias { ref generics, .. }) => {
 503                 self.with_generic_param_rib(generics, ItemRibKind(HasGenericParams::Yes), |this| {
 504                     visit::walk_foreign_item(this, foreign_item);
 505                 });
 506             }
 507             ForeignItemKind::Static(..) => {
 508                 self.with_item_rib(HasGenericParams::No, |this| {
 509                     visit::walk_foreign_item(this, foreign_item);
 510                 });
 511             }
 512             ForeignItemKind::MacCall(..) => {
 513                 visit::walk_foreign_item(self, foreign_item);
 514             }
 515         }
 516     }
 517     fn visit_fn(&mut self, fn_kind: FnKind<'ast>, sp: Span, _: NodeId) {
 518         let rib_kind = match fn_kind {
 519             // Bail if there's no body.
 520             FnKind::Fn(.., None) => return visit::walk_fn(self, fn_kind, sp),
 521             FnKind::Fn(FnCtxt::Free | FnCtxt::Foreign, ..) => FnItemRibKind,
 522             FnKind::Fn(FnCtxt::Assoc(_), ..) => NormalRibKind,
 523             FnKind::Closure(..) => ClosureOrAsyncRibKind,
 524         };
 525         let previous_value = self.diagnostic_metadata.current_function;
 526         if matches!(fn_kind, FnKind::Fn(..)) {
 527             self.diagnostic_metadata.current_function = Some((fn_kind, sp));
 528         }
 529         debug!("(resolving function) entering function");
 530         let declaration = fn_kind.decl();
 531
 532         // Create a value rib for the function.
 533         self.with_rib(ValueNS, rib_kind, |this| {
 534             // Create a label rib for the function.
 535             this.with_label_rib(rib_kind, |this| {
 536                 // Add each argument to the rib.
 537                 this.resolve_params(&declaration.inputs);
 538
 539                 visit::walk_fn_ret_ty(this, &declaration.output);
 540
 541                 // Ignore errors in function bodies if this is rustdoc
 542                 // Be sure not to set this until the function signature has been resolved.
 543                 let previous_state = replace(&mut this.in_func_body, true);
 544                 // Resolve the function body, potentially inside the body of an async closure
 545                 match fn_kind {
 546                     FnKind::Fn(.., body) => walk_list!(this, visit_block, body),
 547                     FnKind::Closure(_, body) => this.visit_expr(body),
 548                 };
 549
 550                 debug!("(resolving function) leaving function");
 551                 this.in_func_body = previous_state;
 552             })
 553         });
 554         self.diagnostic_metadata.current_function = previous_value;
 555     }
 556
 557     fn visit_generics(&mut self, generics: &'ast Generics) {
 558         // For type parameter defaults, we have to ban access
 559         // to following type parameters, as the InternalSubsts can only
 560         // provide previous type parameters as they're built. We
 561         // put all the parameters on the ban list and then remove
 562         // them one by one as they are processed and become available.
 563         let mut forward_ty_ban_rib = Rib::new(ForwardGenericParamBanRibKind);
 564         let mut forward_const_ban_rib = Rib::new(ForwardGenericParamBanRibKind);
 565         for param in generics.params.iter() {
 566             match param.kind {
 567                 GenericParamKind::Type { .. } => {
 568                     forward_ty_ban_rib
 569                         .bindings
 570                         .insert(Ident::with_dummy_span(param.ident.name), Res::Err);
 571                 }
 572                 GenericParamKind::Const { .. } => {
 573                     forward_const_ban_rib
 574                         .bindings
 575                         .insert(Ident::with_dummy_span(param.ident.name), Res::Err);
 576                 }
 577                 GenericParamKind::Lifetime => {}
 578             }
 579         }
 580
 581         // rust-lang/rust#61631: The type `Self` is essentially
 582         // another type parameter. For ADTs, we consider it
 583         // well-defined only after all of the ADT type parameters have
 584         // been provided. Therefore, we do not allow use of `Self`
 585         // anywhere in ADT type parameter defaults.
 586         //
 587         // (We however cannot ban `Self` for defaults on *all* generic
 588         // lists; e.g. trait generics can usefully refer to `Self`,
 589         // such as in the case of `trait Add<Rhs = Self>`.)
 590         if self.diagnostic_metadata.current_self_item.is_some() {
 591             // (`Some` if + only if we are in ADT's generics.)
 592             forward_ty_ban_rib.bindings.insert(Ident::with_dummy_span(kw::SelfUpper), Res::Err);
 593         }
 594
 595         for param in &generics.params {
 596             match param.kind {
 597                 GenericParamKind::Lifetime => self.visit_generic_param(param),
 598                 GenericParamKind::Type { ref default } => {
 599                     for bound in &param.bounds {
 600                         self.visit_param_bound(bound);
 601                     }
 602
 603                     if let Some(ref ty) = default {
 604                         self.ribs[TypeNS].push(forward_ty_ban_rib);
 605                         self.ribs[ValueNS].push(forward_const_ban_rib);
 606                         self.visit_ty(ty);
 607                         forward_const_ban_rib = self.ribs[ValueNS].pop().unwrap();
 608                         forward_ty_ban_rib = self.ribs[TypeNS].pop().unwrap();
 609                     }
 610
 611                     // Allow all following defaults to refer to this type parameter.
 612                     forward_ty_ban_rib.bindings.remove(&Ident::with_dummy_span(param.ident.name));
 613                 }
 614                 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
 615                     // Const parameters can't have param bounds.
 616                     assert!(param.bounds.is_empty());
 617
 618                     self.ribs[TypeNS].push(Rib::new(ConstParamTyRibKind));
 619                     self.ribs[ValueNS].push(Rib::new(ConstParamTyRibKind));
 620                     self.visit_ty(ty);
 621                     self.ribs[TypeNS].pop().unwrap();
 622                     self.ribs[ValueNS].pop().unwrap();
 623
 624                     if let Some(ref expr) = default {
 625                         self.ribs[TypeNS].push(forward_ty_ban_rib);
 626                         self.ribs[ValueNS].push(forward_const_ban_rib);
 627                         self.visit_anon_const(expr);
 628                         forward_const_ban_rib = self.ribs[ValueNS].pop().unwrap();
 629                         forward_ty_ban_rib = self.ribs[TypeNS].pop().unwrap();
 630                     }
 631
 632                     // Allow all following defaults to refer to this const parameter.
 633                     forward_const_ban_rib
 634                         .bindings
 635                         .remove(&Ident::with_dummy_span(param.ident.name));
 636                 }
 637             }
 638         }
 639         for p in &generics.where_clause.predicates {
 640             self.visit_where_predicate(p);
 641         }
 642     }
 643
 644     fn visit_generic_arg(&mut self, arg: &'ast GenericArg) {
 645         debug!("visit_generic_arg({:?})", arg);
 646         let prev = replace(&mut self.diagnostic_metadata.currently_processing_generics, true);
 647         match arg {
 648             GenericArg::Type(ref ty) => {
 649                 // We parse const arguments as path types as we cannot distinguish them during
 650                 // parsing. We try to resolve that ambiguity by attempting resolution the type
 651                 // namespace first, and if that fails we try again in the value namespace. If
 652                 // resolution in the value namespace succeeds, we have an generic const argument on
 653                 // our hands.
 654                 if let TyKind::Path(ref qself, ref path) = ty.kind {
 655                     // We cannot disambiguate multi-segment paths right now as that requires type
 656                     // checking.
 657                     if path.segments.len() == 1 && path.segments[0].args.is_none() {
 658                         let mut check_ns = |ns| {
 659                             self.resolve_ident_in_lexical_scope(
 660                                 path.segments[0].ident,
 661                                 ns,
 662                                 None,
 663                                 path.span,
 664                             )
 665                             .is_some()
 666                         };
 667                         if !check_ns(TypeNS) && check_ns(ValueNS) {
 668                             // This must be equivalent to `visit_anon_const`, but we cannot call it
 669                             // directly due to visitor lifetimes so we have to copy-paste some code.
 670                             //
 671                             // Note that we might not be inside of an repeat expression here,
 672                             // but considering that `IsRepeatExpr` is only relevant for
 673                             // non-trivial constants this is doesn't matter.
 674                             self.with_constant_rib(IsRepeatExpr::No, true, None, |this| {
 675                                 this.smart_resolve_path(
 676                                     ty.id,
 677                                     qself.as_ref(),
 678                                     path,
 679                                     PathSource::Expr(None),
 680                                 );
 681
 682                                 if let Some(ref qself) = *qself {
 683                                     this.visit_ty(&qself.ty);
 684                                 }
 685                                 this.visit_path(path, ty.id);
 686                             });
 687
 688                             self.diagnostic_metadata.currently_processing_generics = prev;
 689                             return;
 690                         }
 691                     }
 692                 }
 693
 694                 self.visit_ty(ty);
 695             }
 696             GenericArg::Lifetime(lt) => self.visit_lifetime(lt),
 697             GenericArg::Const(ct) => self.visit_anon_const(ct),
 698         }
 699         self.diagnostic_metadata.currently_processing_generics = prev;
 700     }
 701
 702     fn visit_where_predicate(&mut self, p: &'ast WherePredicate) {
 703         debug!("visit_where_predicate {:?}", p);
 704         let previous_value =
 705             replace(&mut self.diagnostic_metadata.current_where_predicate, Some(p));
 706         visit::walk_where_predicate(self, p);
 707         self.diagnostic_metadata.current_where_predicate = previous_value;
 708     }
 709 }
 710
 711 impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
 712     fn new(resolver: &'b mut Resolver<'a>) -> LateResolutionVisitor<'a, 'b, 'ast> {
 713         // During late resolution we only track the module component of the parent scope,
 714         // although it may be useful to track other components as well for diagnostics.
 715         let graph_root = resolver.graph_root;
 716         let parent_scope = ParentScope::module(graph_root, resolver);
 717         let start_rib_kind = ModuleRibKind(graph_root);
 718         LateResolutionVisitor {
 719             r: resolver,
 720             parent_scope,
 721             ribs: PerNS {
 722                 value_ns: vec![Rib::new(start_rib_kind)],
 723                 type_ns: vec![Rib::new(start_rib_kind)],
 724                 macro_ns: vec![Rib::new(start_rib_kind)],
 725             },
 726             label_ribs: Vec::new(),
 727             current_trait_ref: None,
 728             diagnostic_metadata: DiagnosticMetadata::default(),
 729             // errors at module scope should always be reported
 730             in_func_body: false,
 731         }
 732     }
 733
 734     fn resolve_ident_in_lexical_scope(
 735         &mut self,
 736         ident: Ident,
 737         ns: Namespace,
 738         record_used_id: Option<NodeId>,
 739         path_span: Span,
 740     ) -> Option<LexicalScopeBinding<'a>> {
 741         self.r.resolve_ident_in_lexical_scope(
 742             ident,
 743             ns,
 744             &self.parent_scope,
 745             record_used_id,
 746             path_span,
 747             &self.ribs[ns],
 748         )
 749     }
 750
 751     fn resolve_path(
 752         &mut self,
 753         path: &[Segment],
 754         opt_ns: Option<Namespace>, // `None` indicates a module path in import
 755         record_used: bool,
 756         path_span: Span,
 757         crate_lint: CrateLint,
 758     ) -> PathResult<'a> {
 759         self.r.resolve_path_with_ribs(
 760             path,
 761             opt_ns,
 762             &self.parent_scope,
 763             record_used,
 764             path_span,
 765             crate_lint,
 766             Some(&self.ribs),
 767         )
 768     }
 769
 770     // AST resolution
 771     //
 772     // We maintain a list of value ribs and type ribs.
 773     //
 774     // Simultaneously, we keep track of the current position in the module
 775     // graph in the `parent_scope.module` pointer. When we go to resolve a name in
 776     // the value or type namespaces, we first look through all the ribs and
 777     // then query the module graph. When we resolve a name in the module
 778     // namespace, we can skip all the ribs (since nested modules are not
 779     // allowed within blocks in Rust) and jump straight to the current module
 780     // graph node.
 781     //
 782     // Named implementations are handled separately. When we find a method
 783     // call, we consult the module node to find all of the implementations in
 784     // scope. This information is lazily cached in the module node. We then
 785     // generate a fake "implementation scope" containing all the
 786     // implementations thus found, for compatibility with old resolve pass.
 787
 788     /// Do some `work` within a new innermost rib of the given `kind` in the given namespace (`ns`).
 789     fn with_rib<T>(
 790         &mut self,
 791         ns: Namespace,
 792         kind: RibKind<'a>,
 793         work: impl FnOnce(&mut Self) -> T,
 794     ) -> T {
 795         self.ribs[ns].push(Rib::new(kind));
 796         let ret = work(self);
 797         self.ribs[ns].pop();
 798         ret
 799     }
 800
 801     fn with_scope<T>(&mut self, id: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
 802         if let Some(module) = self.r.get_module(self.r.local_def_id(id).to_def_id()) {
 803             // Move down in the graph.
 804             let orig_module = replace(&mut self.parent_scope.module, module);
 805             self.with_rib(ValueNS, ModuleRibKind(module), |this| {
 806                 this.with_rib(TypeNS, ModuleRibKind(module), |this| {
 807                     let ret = f(this);
 808                     this.parent_scope.module = orig_module;
 809                     ret
 810                 })
 811             })
 812         } else {
 813             f(self)
 814         }
 815     }
 816
 817     /// Searches the current set of local scopes for labels. Returns the `NodeId` of the resolved
 818     /// label and reports an error if the label is not found or is unreachable.
 819     fn resolve_label(&self, mut label: Ident) -> Option<NodeId> {
 820         let mut suggestion = None;
 821
 822         // Preserve the original span so that errors contain "in this macro invocation"
 823         // information.
 824         let original_span = label.span;
 825
 826         for i in (0..self.label_ribs.len()).rev() {
 827             let rib = &self.label_ribs[i];
 828
 829             if let MacroDefinition(def) = rib.kind {
 830                 // If an invocation of this macro created `ident`, give up on `ident`
 831                 // and switch to `ident`'s source from the macro definition.
 832                 if def == self.r.macro_def(label.span.ctxt()) {
 833                     label.span.remove_mark();
 834                 }
 835             }
 836
 837             let ident = label.normalize_to_macro_rules();
 838             if let Some((ident, id)) = rib.bindings.get_key_value(&ident) {
 839                 return if self.is_label_valid_from_rib(i) {
 840                     Some(*id)
 841                 } else {
 842                     self.report_error(
 843                         original_span,
 844                         ResolutionError::UnreachableLabel {
 845                             name: label.name,
 846                             definition_span: ident.span,
 847                             suggestion,
 848                         },
 849                     );
 850
 851                     None
 852                 };
 853             }
 854
 855             // Diagnostics: Check if this rib contains a label with a similar name, keep track of
 856             // the first such label that is encountered.
 857             suggestion = suggestion.or_else(|| self.suggestion_for_label_in_rib(i, label));
 858         }
 859
 860         self.report_error(
 861             original_span,
 862             ResolutionError::UndeclaredLabel { name: label.name, suggestion },
 863         );
 864         None
 865     }
 866
 867     /// Determine whether or not a label from the `rib_index`th label rib is reachable.
 868     fn is_label_valid_from_rib(&self, rib_index: usize) -> bool {
 869         let ribs = &self.label_ribs[rib_index + 1..];
 870
 871         for rib in ribs {
 872             match rib.kind {
 873                 NormalRibKind | MacroDefinition(..) => {
 874                     // Nothing to do. Continue.
 875                 }
 876
 877                 AssocItemRibKind
 878                 | ClosureOrAsyncRibKind
 879                 | FnItemRibKind
 880                 | ItemRibKind(..)
 881                 | ConstantItemRibKind(..)
 882                 | ModuleRibKind(..)
 883                 | ForwardGenericParamBanRibKind
 884                 | ConstParamTyRibKind => {
 885                     return false;
 886                 }
 887             }
 888         }
 889
 890         true
 891     }
 892
 893     fn resolve_adt(&mut self, item: &'ast Item, generics: &'ast Generics) {
 894         debug!("resolve_adt");
 895         self.with_current_self_item(item, |this| {
 896             this.with_generic_param_rib(generics, ItemRibKind(HasGenericParams::Yes), |this| {
 897                 let item_def_id = this.r.local_def_id(item.id).to_def_id();
 898                 this.with_self_rib(Res::SelfTy(None, Some((item_def_id, false))), |this| {
 899                     visit::walk_item(this, item);
 900                 });
 901             });
 902         });
 903     }
 904
 905     fn future_proof_import(&mut self, use_tree: &UseTree) {
 906         let segments = &use_tree.prefix.segments;
 907         if !segments.is_empty() {
 908             let ident = segments[0].ident;
 909             if ident.is_path_segment_keyword() || ident.span.rust_2015() {
 910                 return;
 911             }
 912
 913             let nss = match use_tree.kind {
 914                 UseTreeKind::Simple(..) if segments.len() == 1 => &[TypeNS, ValueNS][..],
 915                 _ => &[TypeNS],
 916             };
 917             let report_error = |this: &Self, ns| {
 918                 let what = if ns == TypeNS { "type parameters" } else { "local variables" };
 919                 if this.should_report_errs() {
 920                     this.r
 921                         .session
 922                         .span_err(ident.span, &format!("imports cannot refer to {}", what));
 923                 }
 924             };
 925
 926             for &ns in nss {
 927                 match self.resolve_ident_in_lexical_scope(ident, ns, None, use_tree.prefix.span) {
 928                     Some(LexicalScopeBinding::Res(..)) => {
 929                         report_error(self, ns);
 930                     }
 931                     Some(LexicalScopeBinding::Item(binding)) => {
 932                         let orig_unusable_binding =
 933                             replace(&mut self.r.unusable_binding, Some(binding));
 934                         if let Some(LexicalScopeBinding::Res(..)) = self
 935                             .resolve_ident_in_lexical_scope(ident, ns, None, use_tree.prefix.span)
 936                         {
 937                             report_error(self, ns);
 938                         }
 939                         self.r.unusable_binding = orig_unusable_binding;
 940                     }
 941                     None => {}
 942                 }
 943             }
 944         } else if let UseTreeKind::Nested(use_trees) = &use_tree.kind {
 945             for (use_tree, _) in use_trees {
 946                 self.future_proof_import(use_tree);
 947             }
 948         }
 949     }
 950
 951     fn resolve_item(&mut self, item: &'ast Item) {
 952         let name = item.ident.name;
 953         debug!("(resolving item) resolving {} ({:?})", name, item.kind);
 954
 955         match item.kind {
 956             ItemKind::TyAlias(box TyAlias { ref generics, .. })
 957             | ItemKind::Fn(box Fn { ref generics, .. }) => {
 958                 self.compute_num_lifetime_params(item.id, generics);
 959                 self.with_generic_param_rib(generics, ItemRibKind(HasGenericParams::Yes), |this| {
 960                     visit::walk_item(this, item)
 961                 });
 962             }
 963
 964             ItemKind::Enum(_, ref generics)
 965             | ItemKind::Struct(_, ref generics)
 966             | ItemKind::Union(_, ref generics) => {
 967                 self.compute_num_lifetime_params(item.id, generics);
 968                 self.resolve_adt(item, generics);
 969             }
 970
 971             ItemKind::Impl(box Impl {
 972                 ref generics,
 973                 ref of_trait,
 974                 ref self_ty,
 975                 items: ref impl_items,
 976                 ..
 977             }) => {
 978                 self.compute_num_lifetime_params(item.id, generics);
 979                 self.resolve_implementation(generics, of_trait, &self_ty, item.id, impl_items);
 980             }
 981
 982             ItemKind::Trait(box Trait { ref generics, ref bounds, ref items, .. }) => {
 983                 self.compute_num_lifetime_params(item.id, generics);
 984                 // Create a new rib for the trait-wide type parameters.
 985                 self.with_generic_param_rib(generics, ItemRibKind(HasGenericParams::Yes), |this| {
 986                     let local_def_id = this.r.local_def_id(item.id).to_def_id();
 987                     this.with_self_rib(Res::SelfTy(Some(local_def_id), None), |this| {
 988                         this.visit_generics(generics);
 989                         walk_list!(this, visit_param_bound, bounds);
 990
 991                         let walk_assoc_item = |this: &mut Self, generics, item| {
 992                             this.with_generic_param_rib(generics, AssocItemRibKind, |this| {
 993                                 visit::walk_assoc_item(this, item, AssocCtxt::Trait)
 994                             });
 995                         };
 996
 997                         this.with_trait_items(items, |this| {
 998                             for item in items {
 999                                 match &item.kind {
1000                                     AssocItemKind::Const(_, ty, default) => {
1001                                         this.visit_ty(ty);
1002                                         // Only impose the restrictions of `ConstRibKind` for an
1003                                         // actual constant expression in a provided default.
1004                                         if let Some(expr) = default {
1005                                             // We allow arbitrary const expressions inside of associated consts,
1006                                             // even if they are potentially not const evaluatable.
1007                                             //
1008                                             // Type parameters can already be used and as associated consts are
1009                                             // not used as part of the type system, this is far less surprising.
1010                                             this.with_constant_rib(
1011                                                 IsRepeatExpr::No,
1012                                                 true,
1013                                                 None,
1014                                                 |this| this.visit_expr(expr),
1015                                             );
1016                                         }
1017                                     }
1018                                     AssocItemKind::Fn(box Fn { generics, .. }) => {
1019                                         walk_assoc_item(this, generics, item);
1020                                     }
1021                                     AssocItemKind::TyAlias(box TyAlias { generics, .. }) => {
1022                                         walk_assoc_item(this, generics, item);
1023                                     }
1024                                     AssocItemKind::MacCall(_) => {
1025                                         panic!("unexpanded macro in resolve!")
1026                                     }
1027                                 };
1028                             }
1029                         });
1030                     });
1031                 });
1032             }
1033
1034             ItemKind::TraitAlias(ref generics, ref bounds) => {
1035                 self.compute_num_lifetime_params(item.id, generics);
1036                 // Create a new rib for the trait-wide type parameters.
1037                 self.with_generic_param_rib(generics, ItemRibKind(HasGenericParams::Yes), |this| {
1038                     let local_def_id = this.r.local_def_id(item.id).to_def_id();
1039                     this.with_self_rib(Res::SelfTy(Some(local_def_id), None), |this| {
1040                         this.visit_generics(generics);
1041                         walk_list!(this, visit_param_bound, bounds);
1042                     });
1043                 });
1044             }
1045
1046             ItemKind::Mod(..) | ItemKind::ForeignMod(_) => {
1047                 self.with_scope(item.id, |this| {
1048                     visit::walk_item(this, item);
1049                 });
1050             }
1051
1052             ItemKind::Static(ref ty, _, ref expr) | ItemKind::Const(_, ref ty, ref expr) => {
1053                 self.with_item_rib(HasGenericParams::No, |this| {
1054                     this.visit_ty(ty);
1055                     if let Some(expr) = expr {
1056                         let constant_item_kind = match item.kind {
1057                             ItemKind::Const(..) => ConstantItemKind::Const,
1058                             ItemKind::Static(..) => ConstantItemKind::Static,
1059                             _ => unreachable!(),
1060                         };
1061                         // We already forbid generic params because of the above item rib,
1062                         // so it doesn't matter whether this is a trivial constant.
1063                         this.with_constant_rib(
1064                             IsRepeatExpr::No,
1065                             true,
1066                             Some((item.ident, constant_item_kind)),
1067                             |this| this.visit_expr(expr),
1068                         );
1069                     }
1070                 });
1071             }
1072
1073             ItemKind::Use(ref use_tree) => {
1074                 self.future_proof_import(use_tree);
1075             }
1076
1077             ItemKind::ExternCrate(..) | ItemKind::MacroDef(..) => {
1078                 // do nothing, these are just around to be encoded
1079             }
1080
1081             ItemKind::GlobalAsm(_) => {
1082                 visit::walk_item(self, item);
1083             }
1084
1085             ItemKind::MacCall(_) => panic!("unexpanded macro in resolve!"),
1086         }
1087     }
1088
1089     fn with_generic_param_rib<'c, F>(&'c mut self, generics: &'c Generics, kind: RibKind<'a>, f: F)
1090     where
1091         F: FnOnce(&mut Self),
1092     {
1093         debug!("with_generic_param_rib");
1094         let mut function_type_rib = Rib::new(kind);
1095         let mut function_value_rib = Rib::new(kind);
1096         let mut seen_bindings = FxHashMap::default();
1097
1098         // We also can't shadow bindings from the parent item
1099         if let AssocItemRibKind = kind {
1100             let mut add_bindings_for_ns = |ns| {
1101                 let parent_rib = self.ribs[ns]
1102                     .iter()
1103                     .rfind(|r| matches!(r.kind, ItemRibKind(_)))
1104                     .expect("associated item outside of an item");
1105                 seen_bindings
1106                     .extend(parent_rib.bindings.iter().map(|(ident, _)| (*ident, ident.span)));
1107             };
1108             add_bindings_for_ns(ValueNS);
1109             add_bindings_for_ns(TypeNS);
1110         }
1111
1112         for param in &generics.params {
1113             if let GenericParamKind::Lifetime { .. } = param.kind {
1114                 continue;
1115             }
1116
1117             let ident = param.ident.normalize_to_macros_2_0();
1118             debug!("with_generic_param_rib: {}", param.id);
1119
1120             match seen_bindings.entry(ident) {
1121                 Entry::Occupied(entry) => {
1122                     let span = *entry.get();
1123                     let err = ResolutionError::NameAlreadyUsedInParameterList(ident.name, span);
1124                     self.report_error(param.ident.span, err);
1125                 }
1126                 Entry::Vacant(entry) => {
1127                     entry.insert(param.ident.span);
1128                 }
1129             }
1130
1131             // Plain insert (no renaming).
1132             let (rib, def_kind) = match param.kind {
1133                 GenericParamKind::Type { .. } => (&mut function_type_rib, DefKind::TyParam),
1134                 GenericParamKind::Const { .. } => (&mut function_value_rib, DefKind::ConstParam),
1135                 _ => unreachable!(),
1136             };
1137             let res = Res::Def(def_kind, self.r.local_def_id(param.id).to_def_id());
1138             self.r.record_partial_res(param.id, PartialRes::new(res));
1139             rib.bindings.insert(ident, res);
1140         }
1141
1142         self.ribs[ValueNS].push(function_value_rib);
1143         self.ribs[TypeNS].push(function_type_rib);
1144
1145         f(self);
1146
1147         self.ribs[TypeNS].pop();
1148         self.ribs[ValueNS].pop();
1149     }
1150
1151     fn with_label_rib(&mut self, kind: RibKind<'a>, f: impl FnOnce(&mut Self)) {
1152         self.label_ribs.push(Rib::new(kind));
1153         f(self);
1154         self.label_ribs.pop();
1155     }
1156
1157     fn with_item_rib(&mut self, has_generic_params: HasGenericParams, f: impl FnOnce(&mut Self)) {
1158         let kind = ItemRibKind(has_generic_params);
1159         self.with_rib(ValueNS, kind, |this| this.with_rib(TypeNS, kind, f))
1160     }
1161
1162     // HACK(min_const_generics,const_evaluatable_unchecked): We
1163     // want to keep allowing `[0; std::mem::size_of::<*mut T>()]`
1164     // with a future compat lint for now. We do this by adding an
1165     // additional special case for repeat expressions.
1166     //
1167     // Note that we intentionally still forbid `[0; N + 1]` during
1168     // name resolution so that we don't extend the future
1169     // compat lint to new cases.
1170     fn with_constant_rib(
1171         &mut self,
1172         is_repeat: IsRepeatExpr,
1173         is_trivial: bool,
1174         item: Option<(Ident, ConstantItemKind)>,
1175         f: impl FnOnce(&mut Self),
1176     ) {
1177         debug!("with_constant_rib: is_repeat={:?} is_trivial={}", is_repeat, is_trivial);
1178         self.with_rib(ValueNS, ConstantItemRibKind(is_trivial, item), |this| {
1179             this.with_rib(
1180                 TypeNS,
1181                 ConstantItemRibKind(is_repeat == IsRepeatExpr::Yes || is_trivial, item),
1182                 |this| {
1183                     this.with_label_rib(ConstantItemRibKind(is_trivial, item), f);
1184                 },
1185             )
1186         });
1187     }
1188
1189     fn with_current_self_type<T>(&mut self, self_type: &Ty, f: impl FnOnce(&mut Self) -> T) -> T {
1190         // Handle nested impls (inside fn bodies)
1191         let previous_value =
1192             replace(&mut self.diagnostic_metadata.current_self_type, Some(self_type.clone()));
1193         let result = f(self);
1194         self.diagnostic_metadata.current_self_type = previous_value;
1195         result
1196     }
1197
1198     fn with_current_self_item<T>(&mut self, self_item: &Item, f: impl FnOnce(&mut Self) -> T) -> T {
1199         let previous_value =
1200             replace(&mut self.diagnostic_metadata.current_self_item, Some(self_item.id));
1201         let result = f(self);
1202         self.diagnostic_metadata.current_self_item = previous_value;
1203         result
1204     }
1205
1206     /// When evaluating a `trait` use its associated types' idents for suggestions in E0412.
1207     fn with_trait_items<T>(
1208         &mut self,
1209         trait_items: &'ast [P<AssocItem>],
1210         f: impl FnOnce(&mut Self) -> T,
1211     ) -> T {
1212         let trait_assoc_items =
1213             replace(&mut self.diagnostic_metadata.current_trait_assoc_items, Some(&trait_items));
1214         let result = f(self);
1215         self.diagnostic_metadata.current_trait_assoc_items = trait_assoc_items;
1216         result
1217     }
1218
1219     /// This is called to resolve a trait reference from an `impl` (i.e., `impl Trait for Foo`).
1220     fn with_optional_trait_ref<T>(
1221         &mut self,
1222         opt_trait_ref: Option<&TraitRef>,
1223         f: impl FnOnce(&mut Self, Option<DefId>) -> T,
1224     ) -> T {
1225         let mut new_val = None;
1226         let mut new_id = None;
1227         if let Some(trait_ref) = opt_trait_ref {
1228             let path: Vec<_> = Segment::from_path(&trait_ref.path);
1229             let res = self.smart_resolve_path_fragment(
1230                 trait_ref.ref_id,
1231                 None,
1232                 &path,
1233                 trait_ref.path.span,
1234                 PathSource::Trait(AliasPossibility::No),
1235                 CrateLint::SimplePath(trait_ref.ref_id),
1236             );
1237             let res = res.base_res();
1238             if res != Res::Err {
1239                 new_id = Some(res.def_id());
1240                 let span = trait_ref.path.span;
1241                 if let PathResult::Module(ModuleOrUniformRoot::Module(module)) = self.resolve_path(
1242                     &path,
1243                     Some(TypeNS),
1244                     false,
1245                     span,
1246                     CrateLint::SimplePath(trait_ref.ref_id),
1247                 ) {
1248                     new_val = Some((module, trait_ref.clone()));
1249                 }
1250             }
1251         }
1252         let original_trait_ref = replace(&mut self.current_trait_ref, new_val);
1253         let result = f(self, new_id);
1254         self.current_trait_ref = original_trait_ref;
1255         result
1256     }
1257
1258     fn with_self_rib_ns(&mut self, ns: Namespace, self_res: Res, f: impl FnOnce(&mut Self)) {
1259         let mut self_type_rib = Rib::new(NormalRibKind);
1260
1261         // Plain insert (no renaming, since types are not currently hygienic)
1262         self_type_rib.bindings.insert(Ident::with_dummy_span(kw::SelfUpper), self_res);
1263         self.ribs[ns].push(self_type_rib);
1264         f(self);
1265         self.ribs[ns].pop();
1266     }
1267
1268     fn with_self_rib(&mut self, self_res: Res, f: impl FnOnce(&mut Self)) {
1269         self.with_self_rib_ns(TypeNS, self_res, f)
1270     }
1271
1272     fn resolve_implementation(
1273         &mut self,
1274         generics: &'ast Generics,
1275         opt_trait_reference: &'ast Option<TraitRef>,
1276         self_type: &'ast Ty,
1277         item_id: NodeId,
1278         impl_items: &'ast [P<AssocItem>],
1279     ) {
1280         debug!("resolve_implementation");
1281         // If applicable, create a rib for the type parameters.
1282         self.with_generic_param_rib(generics, ItemRibKind(HasGenericParams::Yes), |this| {
1283             // Dummy self type for better errors if `Self` is used in the trait path.
1284             this.with_self_rib(Res::SelfTy(None, None), |this| {
1285                 // Resolve the trait reference, if necessary.
1286                 this.with_optional_trait_ref(opt_trait_reference.as_ref(), |this, trait_id| {
1287                     let item_def_id = this.r.local_def_id(item_id);
1288
1289                     // Register the trait definitions from here.
1290                     if let Some(trait_id) = trait_id {
1291                         this.r.trait_impls.entry(trait_id).or_default().push(item_def_id);
1292                     }
1293
1294                     let item_def_id = item_def_id.to_def_id();
1295                     this.with_self_rib(Res::SelfTy(trait_id, Some((item_def_id, false))), |this| {
1296                         if let Some(trait_ref) = opt_trait_reference.as_ref() {
1297                             // Resolve type arguments in the trait path.
1298                             visit::walk_trait_ref(this, trait_ref);
1299                         }
1300                         // Resolve the self type.
1301                         this.visit_ty(self_type);
1302                         // Resolve the generic parameters.
1303                         this.visit_generics(generics);
1304                         // Resolve the items within the impl.
1305                         this.with_current_self_type(self_type, |this| {
1306                             this.with_self_rib_ns(ValueNS, Res::SelfCtor(item_def_id), |this| {
1307                                 debug!("resolve_implementation with_self_rib_ns(ValueNS, ...)");
1308                                 for item in impl_items {
1309                                     use crate::ResolutionError::*;
1310                                     match &item.kind {
1311                                         AssocItemKind::Const(_default, _ty, _expr) => {
1312                                             debug!("resolve_implementation AssocItemKind::Const");
1313                                             // If this is a trait impl, ensure the const
1314                                             // exists in trait
1315                                             this.check_trait_item(
1316                                                 item.ident,
1317                                                 &item.kind,
1318                                                 ValueNS,
1319                                                 item.span,
1320                                                 |i, s, c| ConstNotMemberOfTrait(i, s, c),
1321                                             );
1322
1323                                             // We allow arbitrary const expressions inside of associated consts,
1324                                             // even if they are potentially not const evaluatable.
1325                                             //
1326                                             // Type parameters can already be used and as associated consts are
1327                                             // not used as part of the type system, this is far less surprising.
1328                                             this.with_constant_rib(
1329                                                 IsRepeatExpr::No,
1330                                                 true,
1331                                                 None,
1332                                                 |this| {
1333                                                     visit::walk_assoc_item(
1334                                                         this,
1335                                                         item,
1336                                                         AssocCtxt::Impl,
1337                                                     )
1338                                                 },
1339                                             );
1340                                         }
1341                                         AssocItemKind::Fn(box Fn { generics, .. }) => {
1342                                             debug!("resolve_implementation AssocItemKind::Fn");
1343                                             // We also need a new scope for the impl item type parameters.
1344                                             this.with_generic_param_rib(
1345                                                 generics,
1346                                                 AssocItemRibKind,
1347                                                 |this| {
1348                                                     // If this is a trait impl, ensure the method
1349                                                     // exists in trait
1350                                                     this.check_trait_item(
1351                                                         item.ident,
1352                                                         &item.kind,
1353                                                         ValueNS,
1354                                                         item.span,
1355                                                         |i, s, c| MethodNotMemberOfTrait(i, s, c),
1356                                                     );
1357
1358                                                     visit::walk_assoc_item(
1359                                                         this,
1360                                                         item,
1361                                                         AssocCtxt::Impl,
1362                                                     )
1363                                                 },
1364                                             );
1365                                         }
1366                                         AssocItemKind::TyAlias(box TyAlias {
1367                                             generics, ..
1368                                         }) => {
1369                                             debug!("resolve_implementation AssocItemKind::TyAlias");
1370                                             // We also need a new scope for the impl item type parameters.
1371                                             this.with_generic_param_rib(
1372                                                 generics,
1373                                                 AssocItemRibKind,
1374                                                 |this| {
1375                                                     // If this is a trait impl, ensure the type
1376                                                     // exists in trait
1377                                                     this.check_trait_item(
1378                                                         item.ident,
1379                                                         &item.kind,
1380                                                         TypeNS,
1381                                                         item.span,
1382                                                         |i, s, c| TypeNotMemberOfTrait(i, s, c),
1383                                                     );
1384
1385                                                     visit::walk_assoc_item(
1386                                                         this,
1387                                                         item,
1388                                                         AssocCtxt::Impl,
1389                                                     )
1390                                                 },
1391                                             );
1392                                         }
1393                                         AssocItemKind::MacCall(_) => {
1394                                             panic!("unexpanded macro in resolve!")
1395                                         }
1396                                     }
1397                                 }
1398                             });
1399                         });
1400                     });
1401                 });
1402             });
1403         });
1404     }
1405
1406     fn check_trait_item<F>(
1407         &mut self,
1408         ident: Ident,
1409         kind: &AssocItemKind,
1410         ns: Namespace,
1411         span: Span,
1412         err: F,
1413     ) where
1414         F: FnOnce(Ident, &str, Option<Symbol>) -> ResolutionError<'_>,
1415     {
1416         // If there is a TraitRef in scope for an impl, then the method must be in the
1417         // trait.
1418         if let Some((module, _)) = self.current_trait_ref {
1419             if self
1420                 .r
1421                 .resolve_ident_in_module(
1422                     ModuleOrUniformRoot::Module(module),
1423                     ident,
1424                     ns,
1425                     &self.parent_scope,
1426                     false,
1427                     span,
1428                 )
1429                 .is_err()
1430             {
1431                 let candidate = self.find_similarly_named_assoc_item(ident.name, kind);
1432                 let path = &self.current_trait_ref.as_ref().unwrap().1.path;
1433                 self.report_error(span, err(ident, &path_names_to_string(path), candidate));
1434             }
1435         }
1436     }
1437
1438     fn resolve_params(&mut self, params: &'ast [Param]) {
1439         let mut bindings = smallvec![(PatBoundCtx::Product, Default::default())];
1440         for Param { pat, ty, .. } in params {
1441             self.resolve_pattern(pat, PatternSource::FnParam, &mut bindings);
1442             self.visit_ty(ty);
1443             debug!("(resolving function / closure) recorded parameter");
1444         }
1445     }
1446
1447     fn resolve_local(&mut self, local: &'ast Local) {
1448         debug!("resolving local ({:?})", local);
1449         // Resolve the type.
1450         walk_list!(self, visit_ty, &local.ty);
1451
1452         // Resolve the initializer.
1453         if let Some((init, els)) = local.kind.init_else_opt() {
1454             self.visit_expr(init);
1455
1456             // Resolve the `else` block
1457             if let Some(els) = els {
1458                 self.visit_block(els);
1459             }
1460         }
1461
1462         // Resolve the pattern.
1463         self.resolve_pattern_top(&local.pat, PatternSource::Let);
1464     }
1465
1466     /// build a map from pattern identifiers to binding-info's.
1467     /// this is done hygienically. This could arise for a macro
1468     /// that expands into an or-pattern where one 'x' was from the
1469     /// user and one 'x' came from the macro.
1470     fn binding_mode_map(&mut self, pat: &Pat) -> BindingMap {
1471         let mut binding_map = FxHashMap::default();
1472
1473         pat.walk(&mut |pat| {
1474             match pat.kind {
1475                 PatKind::Ident(binding_mode, ident, ref sub_pat)
1476                     if sub_pat.is_some() || self.is_base_res_local(pat.id) =>
1477                 {
1478                     binding_map.insert(ident, BindingInfo { span: ident.span, binding_mode });
1479                 }
1480                 PatKind::Or(ref ps) => {
1481                     // Check the consistency of this or-pattern and
1482                     // then add all bindings to the larger map.
1483                     for bm in self.check_consistent_bindings(ps) {
1484                         binding_map.extend(bm);
1485                     }
1486                     return false;
1487                 }
1488                 _ => {}
1489             }
1490
1491             true
1492         });
1493
1494         binding_map
1495     }
1496
1497     fn is_base_res_local(&self, nid: NodeId) -> bool {
1498         matches!(self.r.partial_res_map.get(&nid).map(|res| res.base_res()), Some(Res::Local(..)))
1499     }
1500
1501     /// Checks that all of the arms in an or-pattern have exactly the
1502     /// same set of bindings, with the same binding modes for each.
1503     fn check_consistent_bindings(&mut self, pats: &[P<Pat>]) -> Vec<BindingMap> {
1504         let mut missing_vars = FxHashMap::default();
1505         let mut inconsistent_vars = FxHashMap::default();
1506
1507         // 1) Compute the binding maps of all arms.
1508         let maps = pats.iter().map(|pat| self.binding_mode_map(pat)).collect::<Vec<_>>();
1509
1510         // 2) Record any missing bindings or binding mode inconsistencies.
1511         for (map_outer, pat_outer) in pats.iter().enumerate().map(|(idx, pat)| (&maps[idx], pat)) {
1512             // Check against all arms except for the same pattern which is always self-consistent.
1513             let inners = pats
1514                 .iter()
1515                 .enumerate()
1516                 .filter(|(_, pat)| pat.id != pat_outer.id)
1517                 .flat_map(|(idx, _)| maps[idx].iter())
1518                 .map(|(key, binding)| (key.name, map_outer.get(&key), binding));
1519
1520             for (name, info, &binding_inner) in inners {
1521                 match info {
1522                     None => {
1523                         // The inner binding is missing in the outer.
1524                         let binding_error =
1525                             missing_vars.entry(name).or_insert_with(|| BindingError {
1526                                 name,
1527                                 origin: BTreeSet::new(),
1528                                 target: BTreeSet::new(),
1529                                 could_be_path: name.as_str().starts_with(char::is_uppercase),
1530                             });
1531                         binding_error.origin.insert(binding_inner.span);
1532                         binding_error.target.insert(pat_outer.span);
1533                     }
1534                     Some(binding_outer) => {
1535                         if binding_outer.binding_mode != binding_inner.binding_mode {
1536                             // The binding modes in the outer and inner bindings differ.
1537                             inconsistent_vars
1538                                 .entry(name)
1539                                 .or_insert((binding_inner.span, binding_outer.span));
1540                         }
1541                     }
1542                 }
1543             }
1544         }
1545
1546         // 3) Report all missing variables we found.
1547         let mut missing_vars = missing_vars.iter_mut().collect::<Vec<_>>();
1548         missing_vars.sort_by_key(|(sym, _err)| sym.as_str());
1549
1550         for (name, mut v) in missing_vars {
1551             if inconsistent_vars.contains_key(name) {
1552                 v.could_be_path = false;
1553             }
1554             self.report_error(
1555                 *v.origin.iter().next().unwrap(),
1556                 ResolutionError::VariableNotBoundInPattern(v),
1557             );
1558         }
1559
1560         // 4) Report all inconsistencies in binding modes we found.
1561         let mut inconsistent_vars = inconsistent_vars.iter().collect::<Vec<_>>();
1562         inconsistent_vars.sort();
1563         for (name, v) in inconsistent_vars {
1564             self.report_error(v.0, ResolutionError::VariableBoundWithDifferentMode(*name, v.1));
1565         }
1566
1567         // 5) Finally bubble up all the binding maps.
1568         maps
1569     }
1570
1571     /// Check the consistency of the outermost or-patterns.
1572     fn check_consistent_bindings_top(&mut self, pat: &'ast Pat) {
1573         pat.walk(&mut |pat| match pat.kind {
1574             PatKind::Or(ref ps) => {
1575                 self.check_consistent_bindings(ps);
1576                 false
1577             }
1578             _ => true,
1579         })
1580     }
1581
1582     fn resolve_arm(&mut self, arm: &'ast Arm) {
1583         self.with_rib(ValueNS, NormalRibKind, |this| {
1584             this.resolve_pattern_top(&arm.pat, PatternSource::Match);
1585             walk_list!(this, visit_expr, &arm.guard);
1586             this.visit_expr(&arm.body);
1587         });
1588     }
1589
1590     /// Arising from `source`, resolve a top level pattern.
1591     fn resolve_pattern_top(&mut self, pat: &'ast Pat, pat_src: PatternSource) {
1592         let mut bindings = smallvec![(PatBoundCtx::Product, Default::default())];
1593         self.resolve_pattern(pat, pat_src, &mut bindings);
1594     }
1595
1596     fn resolve_pattern(
1597         &mut self,
1598         pat: &'ast Pat,
1599         pat_src: PatternSource,
1600         bindings: &mut SmallVec<[(PatBoundCtx, FxHashSet<Ident>); 1]>,
1601     ) {
1602         self.resolve_pattern_inner(pat, pat_src, bindings);
1603         // This has to happen *after* we determine which pat_idents are variants:
1604         self.check_consistent_bindings_top(pat);
1605         visit::walk_pat(self, pat);
1606     }
1607
1608     /// Resolve bindings in a pattern. This is a helper to `resolve_pattern`.
1609     ///
1610     /// ### `bindings`
1611     ///
1612     /// A stack of sets of bindings accumulated.
1613     ///
1614     /// In each set, `PatBoundCtx::Product` denotes that a found binding in it should
1615     /// be interpreted as re-binding an already bound binding. This results in an error.
1616     /// Meanwhile, `PatBound::Or` denotes that a found binding in the set should result
1617     /// in reusing this binding rather than creating a fresh one.
1618     ///
1619     /// When called at the top level, the stack must have a single element
1620     /// with `PatBound::Product`. Otherwise, pushing to the stack happens as
1621     /// or-patterns (`p_0 | ... | p_n`) are encountered and the context needs
1622     /// to be switched to `PatBoundCtx::Or` and then `PatBoundCtx::Product` for each `p_i`.
1623     /// When each `p_i` has been dealt with, the top set is merged with its parent.
1624     /// When a whole or-pattern has been dealt with, the thing happens.
1625     ///
1626     /// See the implementation and `fresh_binding` for more details.
1627     fn resolve_pattern_inner(
1628         &mut self,
1629         pat: &Pat,
1630         pat_src: PatternSource,
1631         bindings: &mut SmallVec<[(PatBoundCtx, FxHashSet<Ident>); 1]>,
1632     ) {
1633         // Visit all direct subpatterns of this pattern.
1634         pat.walk(&mut |pat| {
1635             debug!("resolve_pattern pat={:?} node={:?}", pat, pat.kind);
1636             match pat.kind {
1637                 PatKind::Ident(bmode, ident, ref sub) => {
1638                     // First try to resolve the identifier as some existing entity,
1639                     // then fall back to a fresh binding.
1640                     let has_sub = sub.is_some();
1641                     let res = self
1642                         .try_resolve_as_non_binding(pat_src, pat, bmode, ident, has_sub)
1643                         .unwrap_or_else(|| self.fresh_binding(ident, pat.id, pat_src, bindings));
1644                     self.r.record_partial_res(pat.id, PartialRes::new(res));
1645                     self.r.record_pat_span(pat.id, pat.span);
1646                 }
1647                 PatKind::TupleStruct(ref qself, ref path, ref sub_patterns) => {
1648                     self.smart_resolve_path(
1649                         pat.id,
1650                         qself.as_ref(),
1651                         path,
1652                         PathSource::TupleStruct(
1653                             pat.span,
1654                             self.r.arenas.alloc_pattern_spans(sub_patterns.iter().map(|p| p.span)),
1655                         ),
1656                     );
1657                 }
1658                 PatKind::Path(ref qself, ref path) => {
1659                     self.smart_resolve_path(pat.id, qself.as_ref(), path, PathSource::Pat);
1660                 }
1661                 PatKind::Struct(ref qself, ref path, ..) => {
1662                     self.smart_resolve_path(pat.id, qself.as_ref(), path, PathSource::Struct);
1663                 }
1664                 PatKind::Or(ref ps) => {
1665                     // Add a new set of bindings to the stack. `Or` here records that when a
1666                     // binding already exists in this set, it should not result in an error because
1667                     // `V1(a) | V2(a)` must be allowed and are checked for consistency later.
1668                     bindings.push((PatBoundCtx::Or, Default::default()));
1669                     for p in ps {
1670                         // Now we need to switch back to a product context so that each
1671                         // part of the or-pattern internally rejects already bound names.
1672                         // For example, `V1(a) | V2(a, a)` and `V1(a, a) | V2(a)` are bad.
1673                         bindings.push((PatBoundCtx::Product, Default::default()));
1674                         self.resolve_pattern_inner(p, pat_src, bindings);
1675                         // Move up the non-overlapping bindings to the or-pattern.
1676                         // Existing bindings just get "merged".
1677                         let collected = bindings.pop().unwrap().1;
1678                         bindings.last_mut().unwrap().1.extend(collected);
1679                     }
1680                     // This or-pattern itself can itself be part of a product,
1681                     // e.g. `(V1(a) | V2(a), a)` or `(a, V1(a) | V2(a))`.
1682                     // Both cases bind `a` again in a product pattern and must be rejected.
1683                     let collected = bindings.pop().unwrap().1;
1684                     bindings.last_mut().unwrap().1.extend(collected);
1685
1686                     // Prevent visiting `ps` as we've already done so above.
1687                     return false;
1688                 }
1689                 _ => {}
1690             }
1691             true
1692         });
1693     }
1694
1695     fn fresh_binding(
1696         &mut self,
1697         ident: Ident,
1698         pat_id: NodeId,
1699         pat_src: PatternSource,
1700         bindings: &mut SmallVec<[(PatBoundCtx, FxHashSet<Ident>); 1]>,
1701     ) -> Res {
1702         // Add the binding to the local ribs, if it doesn't already exist in the bindings map.
1703         // (We must not add it if it's in the bindings map because that breaks the assumptions
1704         // later passes make about or-patterns.)
1705         let ident = ident.normalize_to_macro_rules();
1706
1707         let mut bound_iter = bindings.iter().filter(|(_, set)| set.contains(&ident));
1708         // Already bound in a product pattern? e.g. `(a, a)` which is not allowed.
1709         let already_bound_and = bound_iter.clone().any(|(ctx, _)| *ctx == PatBoundCtx::Product);
1710         // Already bound in an or-pattern? e.g. `V1(a) | V2(a)`.
1711         // This is *required* for consistency which is checked later.
1712         let already_bound_or = bound_iter.any(|(ctx, _)| *ctx == PatBoundCtx::Or);
1713
1714         if already_bound_and {
1715             // Overlap in a product pattern somewhere; report an error.
1716             use ResolutionError::*;
1717             let error = match pat_src {
1718                 // `fn f(a: u8, a: u8)`:
1719                 PatternSource::FnParam => IdentifierBoundMoreThanOnceInParameterList,
1720                 // `Variant(a, a)`:
1721                 _ => IdentifierBoundMoreThanOnceInSamePattern,
1722             };
1723             self.report_error(ident.span, error(ident.name));
1724         }
1725
1726         // Record as bound if it's valid:
1727         let ident_valid = ident.name != kw::Empty;
1728         if ident_valid {
1729             bindings.last_mut().unwrap().1.insert(ident);
1730         }
1731
1732         if already_bound_or {
1733             // `Variant1(a) | Variant2(a)`, ok
1734             // Reuse definition from the first `a`.
1735             self.innermost_rib_bindings(ValueNS)[&ident]
1736         } else {
1737             let res = Res::Local(pat_id);
1738             if ident_valid {
1739                 // A completely fresh binding add to the set if it's valid.
1740                 self.innermost_rib_bindings(ValueNS).insert(ident, res);
1741             }
1742             res
1743         }
1744     }
1745
1746     fn innermost_rib_bindings(&mut self, ns: Namespace) -> &mut IdentMap<Res> {
1747         &mut self.ribs[ns].last_mut().unwrap().bindings
1748     }
1749
1750     fn try_resolve_as_non_binding(
1751         &mut self,
1752         pat_src: PatternSource,
1753         pat: &Pat,
1754         bm: BindingMode,
1755         ident: Ident,
1756         has_sub: bool,
1757     ) -> Option<Res> {
1758         // An immutable (no `mut`) by-value (no `ref`) binding pattern without
1759         // a sub pattern (no `@ $pat`) is syntactically ambiguous as it could
1760         // also be interpreted as a path to e.g. a constant, variant, etc.
1761         let is_syntactic_ambiguity = !has_sub && bm == BindingMode::ByValue(Mutability::Not);
1762
1763         let ls_binding = self.resolve_ident_in_lexical_scope(ident, ValueNS, None, pat.span)?;
1764         let (res, binding) = match ls_binding {
1765             LexicalScopeBinding::Item(binding)
1766                 if is_syntactic_ambiguity && binding.is_ambiguity() =>
1767             {
1768                 // For ambiguous bindings we don't know all their definitions and cannot check
1769                 // whether they can be shadowed by fresh bindings or not, so force an error.
1770                 // issues/33118#issuecomment-233962221 (see below) still applies here,
1771                 // but we have to ignore it for backward compatibility.
1772                 self.r.record_use(ident, binding, false);
1773                 return None;
1774             }
1775             LexicalScopeBinding::Item(binding) => (binding.res(), Some(binding)),
1776             LexicalScopeBinding::Res(res) => (res, None),
1777         };
1778
1779         match res {
1780             Res::SelfCtor(_) // See #70549.
1781             | Res::Def(
1782                 DefKind::Ctor(_, CtorKind::Const) | DefKind::Const | DefKind::ConstParam,
1783                 _,
1784             ) if is_syntactic_ambiguity => {
1785                 // Disambiguate in favor of a unit struct/variant or constant pattern.
1786                 if let Some(binding) = binding {
1787                     self.r.record_use(ident, binding, false);
1788                 }
1789                 Some(res)
1790             }
1791             Res::Def(DefKind::Ctor(..) | DefKind::Const | DefKind::Static, _) => {
1792                 // This is unambiguously a fresh binding, either syntactically
1793                 // (e.g., `IDENT @ PAT` or `ref IDENT`) or because `IDENT` resolves
1794                 // to something unusable as a pattern (e.g., constructor function),
1795                 // but we still conservatively report an error, see
1796                 // issues/33118#issuecomment-233962221 for one reason why.
1797                 let binding = binding.expect("no binding for a ctor or static");
1798                 self.report_error(
1799                     ident.span,
1800                     ResolutionError::BindingShadowsSomethingUnacceptable {
1801                         shadowing_binding_descr: pat_src.descr(),
1802                         name: ident.name,
1803                         participle: if binding.is_import() { "imported" } else { "defined" },
1804                         article: binding.res().article(),
1805                         shadowed_binding_descr: binding.res().descr(),
1806                         shadowed_binding_span: binding.span,
1807                     },
1808                 );
1809                 None
1810             }
1811             Res::Def(DefKind::ConstParam, def_id) => {
1812                 // Same as for DefKind::Const above, but here, `binding` is `None`, so we
1813                 // have to construct the error differently
1814                 self.report_error(
1815                     ident.span,
1816                     ResolutionError::BindingShadowsSomethingUnacceptable {
1817                         shadowing_binding_descr: pat_src.descr(),
1818                         name: ident.name,
1819                         participle: "defined",
1820                         article: res.article(),
1821                         shadowed_binding_descr: res.descr(),
1822                         shadowed_binding_span: self.r.opt_span(def_id).expect("const parameter defined outside of local crate"),
1823                     }
1824                 );
1825                 None
1826             }
1827             Res::Def(DefKind::Fn, _) | Res::Local(..) | Res::Err => {
1828                 // These entities are explicitly allowed to be shadowed by fresh bindings.
1829                 None
1830             }
1831             _ => span_bug!(
1832                 ident.span,
1833                 "unexpected resolution for an identifier in pattern: {:?}",
1834                 res,
1835             ),
1836         }
1837     }
1838
1839     // High-level and context dependent path resolution routine.
1840     // Resolves the path and records the resolution into definition map.
1841     // If resolution fails tries several techniques to find likely
1842     // resolution candidates, suggest imports or other help, and report
1843     // errors in user friendly way.
1844     fn smart_resolve_path(
1845         &mut self,
1846         id: NodeId,
1847         qself: Option<&QSelf>,
1848         path: &Path,
1849         source: PathSource<'ast>,
1850     ) {
1851         self.smart_resolve_path_fragment(
1852             id,
1853             qself,
1854             &Segment::from_path(path),
1855             path.span,
1856             source,
1857             CrateLint::SimplePath(id),
1858         );
1859     }
1860
1861     fn smart_resolve_path_fragment(
1862         &mut self,
1863         id: NodeId,
1864         qself: Option<&QSelf>,
1865         path: &[Segment],
1866         span: Span,
1867         source: PathSource<'ast>,
1868         crate_lint: CrateLint,
1869     ) -> PartialRes {
1870         tracing::debug!(
1871             "smart_resolve_path_fragment(id={:?}, qself={:?}, path={:?})",
1872             id,
1873             qself,
1874             path
1875         );
1876         let ns = source.namespace();
1877
1878         let report_errors = |this: &mut Self, res: Option<Res>| {
1879             if this.should_report_errs() {
1880                 let (err, candidates) = this.smart_resolve_report_errors(path, span, source, res);
1881
1882                 let def_id = this.parent_scope.module.nearest_parent_mod();
1883                 let instead = res.is_some();
1884                 let suggestion =
1885                     if res.is_none() { this.report_missing_type_error(path) } else { None };
1886                 // get_from_node_id
1887
1888                 this.r.use_injections.push(UseError {
1889                     err,
1890                     candidates,
1891                     def_id,
1892                     instead,
1893                     suggestion,
1894                 });
1895             }
1896
1897             PartialRes::new(Res::Err)
1898         };
1899
1900         // For paths originating from calls (like in `HashMap::new()`), tries
1901         // to enrich the plain `failed to resolve: ...` message with hints
1902         // about possible missing imports.
1903         //
1904         // Similar thing, for types, happens in `report_errors` above.
1905         let report_errors_for_call = |this: &mut Self, parent_err: Spanned<ResolutionError<'a>>| {
1906             if !source.is_call() {
1907                 return Some(parent_err);
1908             }
1909
1910             // Before we start looking for candidates, we have to get our hands
1911             // on the type user is trying to perform invocation on; basically:
1912             // we're transforming `HashMap::new` into just `HashMap`.
1913             let path = match path.split_last() {
1914                 Some((_, path)) if !path.is_empty() => path,
1915                 _ => return Some(parent_err),
1916             };
1917
1918             let (mut err, candidates) =
1919                 this.smart_resolve_report_errors(path, span, PathSource::Type, None);
1920
1921             if candidates.is_empty() {
1922                 err.cancel();
1923                 return Some(parent_err);
1924             }
1925
1926             // There are two different error messages user might receive at
1927             // this point:
1928             // - E0412 cannot find type `{}` in this scope
1929             // - E0433 failed to resolve: use of undeclared type or module `{}`
1930             //
1931             // The first one is emitted for paths in type-position, and the
1932             // latter one - for paths in expression-position.
1933             //
1934             // Thus (since we're in expression-position at this point), not to
1935             // confuse the user, we want to keep the *message* from E0432 (so
1936             // `parent_err`), but we want *hints* from E0412 (so `err`).
1937             //
1938             // And that's what happens below - we're just mixing both messages
1939             // into a single one.
1940             let mut parent_err = this.r.into_struct_error(parent_err.span, parent_err.node);
1941
1942             parent_err.cancel();
1943
1944             err.message = take(&mut parent_err.message);
1945             err.code = take(&mut parent_err.code);
1946             err.children = take(&mut parent_err.children);
1947
1948             drop(parent_err);
1949
1950             let def_id = this.parent_scope.module.nearest_parent_mod();
1951
1952             if this.should_report_errs() {
1953                 this.r.use_injections.push(UseError {
1954                     err,
1955                     candidates,
1956                     def_id,
1957                     instead: false,
1958                     suggestion: None,
1959                 });
1960             } else {
1961                 err.cancel();
1962             }
1963
1964             // We don't return `Some(parent_err)` here, because the error will
1965             // be already printed as part of the `use` injections
1966             None
1967         };
1968
1969         let partial_res = match self.resolve_qpath_anywhere(
1970             id,
1971             qself,
1972             path,
1973             ns,
1974             span,
1975             source.defer_to_typeck(),
1976             crate_lint,
1977         ) {
1978             Ok(Some(partial_res)) if partial_res.unresolved_segments() == 0 => {
1979                 if source.is_expected(partial_res.base_res()) || partial_res.base_res() == Res::Err
1980                 {
1981                     partial_res
1982                 } else {
1983                     report_errors(self, Some(partial_res.base_res()))
1984                 }
1985             }
1986
1987             Ok(Some(partial_res)) if source.defer_to_typeck() => {
1988                 // Not fully resolved associated item `T::A::B` or `<T as Tr>::A::B`
1989                 // or `<T>::A::B`. If `B` should be resolved in value namespace then
1990                 // it needs to be added to the trait map.
1991                 if ns == ValueNS {
1992                     let item_name = path.last().unwrap().ident;
1993                     let traits = self.traits_in_scope(item_name, ns);
1994                     self.r.trait_map.insert(id, traits);
1995                 }
1996
1997                 if PrimTy::from_name(path[0].ident.name).is_some() {
1998                     let mut std_path = Vec::with_capacity(1 + path.len());
1999
2000                     std_path.push(Segment::from_ident(Ident::with_dummy_span(sym::std)));
2001                     std_path.extend(path);
2002                     if let PathResult::Module(_) | PathResult::NonModule(_) =
2003                         self.resolve_path(&std_path, Some(ns), false, span, CrateLint::No)
2004                     {
2005                         // Check if we wrote `str::from_utf8` instead of `std::str::from_utf8`
2006                         let item_span =
2007                             path.iter().last().map_or(span, |segment| segment.ident.span);
2008
2009                         self.r.confused_type_with_std_module.insert(item_span, span);
2010                         self.r.confused_type_with_std_module.insert(span, span);
2011                     }
2012                 }
2013
2014                 partial_res
2015             }
2016
2017             Err(err) => {
2018                 if let Some(err) = report_errors_for_call(self, err) {
2019                     self.report_error(err.span, err.node);
2020                 }
2021
2022                 PartialRes::new(Res::Err)
2023             }
2024
2025             _ => report_errors(self, None),
2026         };
2027
2028         if !matches!(source, PathSource::TraitItem(..)) {
2029             // Avoid recording definition of `A::B` in `<T as A>::B::C`.
2030             self.r.record_partial_res(id, partial_res);
2031         }
2032
2033         partial_res
2034     }
2035
2036     fn self_type_is_available(&mut self, span: Span) -> bool {
2037         let binding = self.resolve_ident_in_lexical_scope(
2038             Ident::with_dummy_span(kw::SelfUpper),
2039             TypeNS,
2040             None,
2041             span,
2042         );
2043         if let Some(LexicalScopeBinding::Res(res)) = binding { res != Res::Err } else { false }
2044     }
2045
2046     fn self_value_is_available(&mut self, self_span: Span, path_span: Span) -> bool {
2047         let ident = Ident::new(kw::SelfLower, self_span);
2048         let binding = self.resolve_ident_in_lexical_scope(ident, ValueNS, None, path_span);
2049         if let Some(LexicalScopeBinding::Res(res)) = binding { res != Res::Err } else { false }
2050     }
2051
2052     /// A wrapper around [`Resolver::report_error`].
2053     ///
2054     /// This doesn't emit errors for function bodies if this is rustdoc.
2055     fn report_error(&self, span: Span, resolution_error: ResolutionError<'_>) {
2056         if self.should_report_errs() {
2057             self.r.report_error(span, resolution_error);
2058         }
2059     }
2060
2061     #[inline]
2062     /// If we're actually rustdoc then avoid giving a name resolution error for `cfg()` items.
2063     fn should_report_errs(&self) -> bool {
2064         !(self.r.session.opts.actually_rustdoc && self.in_func_body)
2065     }
2066
2067     // Resolve in alternative namespaces if resolution in the primary namespace fails.
2068     fn resolve_qpath_anywhere(
2069         &mut self,
2070         id: NodeId,
2071         qself: Option<&QSelf>,
2072         path: &[Segment],
2073         primary_ns: Namespace,
2074         span: Span,
2075         defer_to_typeck: bool,
2076         crate_lint: CrateLint,
2077     ) -> Result<Option<PartialRes>, Spanned<ResolutionError<'a>>> {
2078         let mut fin_res = None;
2079
2080         for (i, &ns) in [primary_ns, TypeNS, ValueNS].iter().enumerate() {
2081             if i == 0 || ns != primary_ns {
2082                 match self.resolve_qpath(id, qself, path, ns, span, crate_lint)? {
2083                     Some(partial_res)
2084                         if partial_res.unresolved_segments() == 0 || defer_to_typeck =>
2085                     {
2086                         return Ok(Some(partial_res));
2087                     }
2088                     partial_res => {
2089                         if fin_res.is_none() {
2090                             fin_res = partial_res;
2091                         }
2092                     }
2093                 }
2094             }
2095         }
2096
2097         assert!(primary_ns != MacroNS);
2098
2099         if qself.is_none() {
2100             let path_seg = |seg: &Segment| PathSegment::from_ident(seg.ident);
2101             let path = Path { segments: path.iter().map(path_seg).collect(), span, tokens: None };
2102             if let Ok((_, res)) =
2103                 self.r.resolve_macro_path(&path, None, &self.parent_scope, false, false)
2104             {
2105                 return Ok(Some(PartialRes::new(res)));
2106             }
2107         }
2108
2109         Ok(fin_res)
2110     }
2111
2112     /// Handles paths that may refer to associated items.
2113     fn resolve_qpath(
2114         &mut self,
2115         id: NodeId,
2116         qself: Option<&QSelf>,
2117         path: &[Segment],
2118         ns: Namespace,
2119         span: Span,
2120         crate_lint: CrateLint,
2121     ) -> Result<Option<PartialRes>, Spanned<ResolutionError<'a>>> {
2122         debug!(
2123             "resolve_qpath(id={:?}, qself={:?}, path={:?}, ns={:?}, span={:?})",
2124             id, qself, path, ns, span,
2125         );
2126
2127         if let Some(qself) = qself {
2128             if qself.position == 0 {
2129                 // This is a case like `<T>::B`, where there is no
2130                 // trait to resolve.  In that case, we leave the `B`
2131                 // segment to be resolved by type-check.
2132                 return Ok(Some(PartialRes::with_unresolved_segments(
2133                     Res::Def(DefKind::Mod, DefId::local(CRATE_DEF_INDEX)),
2134                     path.len(),
2135                 )));
2136             }
2137
2138             // Make sure `A::B` in `<T as A::B>::C` is a trait item.
2139             //
2140             // Currently, `path` names the full item (`A::B::C`, in
2141             // our example).  so we extract the prefix of that that is
2142             // the trait (the slice upto and including
2143             // `qself.position`). And then we recursively resolve that,
2144             // but with `qself` set to `None`.
2145             //
2146             // However, setting `qself` to none (but not changing the
2147             // span) loses the information about where this path
2148             // *actually* appears, so for the purposes of the crate
2149             // lint we pass along information that this is the trait
2150             // name from a fully qualified path, and this also
2151             // contains the full span (the `CrateLint::QPathTrait`).
2152             let ns = if qself.position + 1 == path.len() { ns } else { TypeNS };
2153             let partial_res = self.smart_resolve_path_fragment(
2154                 id,
2155                 None,
2156                 &path[..=qself.position],
2157                 span,
2158                 PathSource::TraitItem(ns),
2159                 CrateLint::QPathTrait { qpath_id: id, qpath_span: qself.path_span },
2160             );
2161
2162             // The remaining segments (the `C` in our example) will
2163             // have to be resolved by type-check, since that requires doing
2164             // trait resolution.
2165             return Ok(Some(PartialRes::with_unresolved_segments(
2166                 partial_res.base_res(),
2167                 partial_res.unresolved_segments() + path.len() - qself.position - 1,
2168             )));
2169         }
2170
2171         let result = match self.resolve_path(&path, Some(ns), true, span, crate_lint) {
2172             PathResult::NonModule(path_res) => path_res,
2173             PathResult::Module(ModuleOrUniformRoot::Module(module)) if !module.is_normal() => {
2174                 PartialRes::new(module.res().unwrap())
2175             }
2176             // In `a(::assoc_item)*` `a` cannot be a module. If `a` does resolve to a module we
2177             // don't report an error right away, but try to fallback to a primitive type.
2178             // So, we are still able to successfully resolve something like
2179             //
2180             // use std::u8; // bring module u8 in scope
2181             // fn f() -> u8 { // OK, resolves to primitive u8, not to std::u8
2182             //     u8::max_value() // OK, resolves to associated function <u8>::max_value,
2183             //                     // not to non-existent std::u8::max_value
2184             // }
2185             //
2186             // Such behavior is required for backward compatibility.
2187             // The same fallback is used when `a` resolves to nothing.
2188             PathResult::Module(ModuleOrUniformRoot::Module(_)) | PathResult::Failed { .. }
2189                 if (ns == TypeNS || path.len() > 1)
2190                     && PrimTy::from_name(path[0].ident.name).is_some() =>
2191             {
2192                 let prim = PrimTy::from_name(path[0].ident.name).unwrap();
2193                 PartialRes::with_unresolved_segments(Res::PrimTy(prim), path.len() - 1)
2194             }
2195             PathResult::Module(ModuleOrUniformRoot::Module(module)) => {
2196                 PartialRes::new(module.res().unwrap())
2197             }
2198             PathResult::Failed { is_error_from_last_segment: false, span, label, suggestion } => {
2199                 return Err(respan(span, ResolutionError::FailedToResolve { label, suggestion }));
2200             }
2201             PathResult::Module(..) | PathResult::Failed { .. } => return Ok(None),
2202             PathResult::Indeterminate => bug!("indeterminate path result in resolve_qpath"),
2203         };
2204
2205         if path.len() > 1
2206             && result.base_res() != Res::Err
2207             && path[0].ident.name != kw::PathRoot
2208             && path[0].ident.name != kw::DollarCrate
2209         {
2210             let unqualified_result = {
2211                 match self.resolve_path(
2212                     &[*path.last().unwrap()],
2213                     Some(ns),
2214                     false,
2215                     span,
2216                     CrateLint::No,
2217                 ) {
2218                     PathResult::NonModule(path_res) => path_res.base_res(),
2219                     PathResult::Module(ModuleOrUniformRoot::Module(module)) => {
2220                         module.res().unwrap()
2221                     }
2222                     _ => return Ok(Some(result)),
2223                 }
2224             };
2225             if result.base_res() == unqualified_result {
2226                 let lint = lint::builtin::UNUSED_QUALIFICATIONS;
2227                 self.r.lint_buffer.buffer_lint(lint, id, span, "unnecessary qualification")
2228             }
2229         }
2230
2231         Ok(Some(result))
2232     }
2233
2234     fn with_resolved_label(&mut self, label: Option<Label>, id: NodeId, f: impl FnOnce(&mut Self)) {
2235         if let Some(label) = label {
2236             if label.ident.as_str().as_bytes()[1] != b'_' {
2237                 self.diagnostic_metadata.unused_labels.insert(id, label.ident.span);
2238             }
2239             self.with_label_rib(NormalRibKind, |this| {
2240                 let ident = label.ident.normalize_to_macro_rules();
2241                 this.label_ribs.last_mut().unwrap().bindings.insert(ident, id);
2242                 f(this);
2243             });
2244         } else {
2245             f(self);
2246         }
2247     }
2248
2249     fn resolve_labeled_block(&mut self, label: Option<Label>, id: NodeId, block: &'ast Block) {
2250         self.with_resolved_label(label, id, |this| this.visit_block(block));
2251     }
2252
2253     fn resolve_block(&mut self, block: &'ast Block) {
2254         debug!("(resolving block) entering block");
2255         // Move down in the graph, if there's an anonymous module rooted here.
2256         let orig_module = self.parent_scope.module;
2257         let anonymous_module = self.r.block_map.get(&block.id).cloned(); // clones a reference
2258
2259         let mut num_macro_definition_ribs = 0;
2260         if let Some(anonymous_module) = anonymous_module {
2261             debug!("(resolving block) found anonymous module, moving down");
2262             self.ribs[ValueNS].push(Rib::new(ModuleRibKind(anonymous_module)));
2263             self.ribs[TypeNS].push(Rib::new(ModuleRibKind(anonymous_module)));
2264             self.parent_scope.module = anonymous_module;
2265         } else {
2266             self.ribs[ValueNS].push(Rib::new(NormalRibKind));
2267         }
2268
2269         let prev = self.diagnostic_metadata.current_block_could_be_bare_struct_literal.take();
2270         if let (true, [Stmt { kind: StmtKind::Expr(expr), .. }]) =
2271             (block.could_be_bare_literal, &block.stmts[..])
2272         {
2273             if let ExprKind::Type(..) = expr.kind {
2274                 self.diagnostic_metadata.current_block_could_be_bare_struct_literal =
2275                     Some(block.span);
2276             }
2277         }
2278         // Descend into the block.
2279         for stmt in &block.stmts {
2280             if let StmtKind::Item(ref item) = stmt.kind {
2281                 if let ItemKind::MacroDef(..) = item.kind {
2282                     num_macro_definition_ribs += 1;
2283                     let res = self.r.local_def_id(item.id).to_def_id();
2284                     self.ribs[ValueNS].push(Rib::new(MacroDefinition(res)));
2285                     self.label_ribs.push(Rib::new(MacroDefinition(res)));
2286                 }
2287             }
2288
2289             self.visit_stmt(stmt);
2290         }
2291         self.diagnostic_metadata.current_block_could_be_bare_struct_literal = prev;
2292
2293         // Move back up.
2294         self.parent_scope.module = orig_module;
2295         for _ in 0..num_macro_definition_ribs {
2296             self.ribs[ValueNS].pop();
2297             self.label_ribs.pop();
2298         }
2299         self.ribs[ValueNS].pop();
2300         if anonymous_module.is_some() {
2301             self.ribs[TypeNS].pop();
2302         }
2303         debug!("(resolving block) leaving block");
2304     }
2305
2306     fn resolve_anon_const(&mut self, constant: &'ast AnonConst, is_repeat: IsRepeatExpr) {
2307         debug!("resolve_anon_const {:?} is_repeat: {:?}", constant, is_repeat);
2308         self.with_constant_rib(
2309             is_repeat,
2310             constant.value.is_potential_trivial_const_param(),
2311             None,
2312             |this| {
2313                 visit::walk_anon_const(this, constant);
2314             },
2315         );
2316     }
2317
2318     fn resolve_expr(&mut self, expr: &'ast Expr, parent: Option<&'ast Expr>) {
2319         // First, record candidate traits for this expression if it could
2320         // result in the invocation of a method call.
2321
2322         self.record_candidate_traits_for_expr_if_necessary(expr);
2323
2324         // Next, resolve the node.
2325         match expr.kind {
2326             ExprKind::Path(ref qself, ref path) => {
2327                 self.smart_resolve_path(expr.id, qself.as_ref(), path, PathSource::Expr(parent));
2328                 visit::walk_expr(self, expr);
2329             }
2330
2331             ExprKind::Struct(ref se) => {
2332                 self.smart_resolve_path(expr.id, se.qself.as_ref(), &se.path, PathSource::Struct);
2333                 visit::walk_expr(self, expr);
2334             }
2335
2336             ExprKind::Break(Some(label), _) | ExprKind::Continue(Some(label)) => {
2337                 if let Some(node_id) = self.resolve_label(label.ident) {
2338                     // Since this res is a label, it is never read.
2339                     self.r.label_res_map.insert(expr.id, node_id);
2340                     self.diagnostic_metadata.unused_labels.remove(&node_id);
2341                 }
2342
2343                 // visit `break` argument if any
2344                 visit::walk_expr(self, expr);
2345             }
2346
2347             ExprKind::Break(None, Some(ref e)) => {
2348                 // We use this instead of `visit::walk_expr` to keep the parent expr around for
2349                 // better diagnostics.
2350                 self.resolve_expr(e, Some(&expr));
2351             }
2352
2353             ExprKind::Let(ref pat, ref scrutinee, _) => {
2354                 self.visit_expr(scrutinee);
2355                 self.resolve_pattern_top(pat, PatternSource::Let);
2356             }
2357
2358             ExprKind::If(ref cond, ref then, ref opt_else) => {
2359                 self.with_rib(ValueNS, NormalRibKind, |this| {
2360                     let old = this.diagnostic_metadata.in_if_condition.replace(cond);
2361                     this.visit_expr(cond);
2362                     this.diagnostic_metadata.in_if_condition = old;
2363                     this.visit_block(then);
2364                 });
2365                 if let Some(expr) = opt_else {
2366                     self.visit_expr(expr);
2367                 }
2368             }
2369
2370             ExprKind::Loop(ref block, label) => self.resolve_labeled_block(label, expr.id, &block),
2371
2372             ExprKind::While(ref cond, ref block, label) => {
2373                 self.with_resolved_label(label, expr.id, |this| {
2374                     this.with_rib(ValueNS, NormalRibKind, |this| {
2375                         this.visit_expr(cond);
2376                         this.visit_block(block);
2377                     })
2378                 });
2379             }
2380
2381             ExprKind::ForLoop(ref pat, ref iter_expr, ref block, label) => {
2382                 self.visit_expr(iter_expr);
2383                 self.with_rib(ValueNS, NormalRibKind, |this| {
2384                     this.resolve_pattern_top(pat, PatternSource::For);
2385                     this.resolve_labeled_block(label, expr.id, block);
2386                 });
2387             }
2388
2389             ExprKind::Block(ref block, label) => self.resolve_labeled_block(label, block.id, block),
2390
2391             // Equivalent to `visit::walk_expr` + passing some context to children.
2392             ExprKind::Field(ref subexpression, _) => {
2393                 self.resolve_expr(subexpression, Some(expr));
2394             }
2395             ExprKind::MethodCall(ref segment, ref arguments, _) => {
2396                 let mut arguments = arguments.iter();
2397                 self.resolve_expr(arguments.next().unwrap(), Some(expr));
2398                 for argument in arguments {
2399                     self.resolve_expr(argument, None);
2400                 }
2401                 self.visit_path_segment(expr.span, segment);
2402             }
2403
2404             ExprKind::Call(ref callee, ref arguments) => {
2405                 self.resolve_expr(callee, Some(expr));
2406                 let const_args = self.r.legacy_const_generic_args(callee).unwrap_or_default();
2407                 for (idx, argument) in arguments.iter().enumerate() {
2408                     // Constant arguments need to be treated as AnonConst since
2409                     // that is how they will be later lowered to HIR.
2410                     if const_args.contains(&idx) {
2411                         self.with_constant_rib(
2412                             IsRepeatExpr::No,
2413                             argument.is_potential_trivial_const_param(),
2414                             None,
2415                             |this| {
2416                                 this.resolve_expr(argument, None);
2417                             },
2418                         );
2419                     } else {
2420                         self.resolve_expr(argument, None);
2421                     }
2422                 }
2423             }
2424             ExprKind::Type(ref type_expr, ref ty) => {
2425                 // `ParseSess::type_ascription_path_suggestions` keeps spans of colon tokens in
2426                 // type ascription. Here we are trying to retrieve the span of the colon token as
2427                 // well, but only if it's written without spaces `expr:Ty` and therefore confusable
2428                 // with `expr::Ty`, only in this case it will match the span from
2429                 // `type_ascription_path_suggestions`.
2430                 self.diagnostic_metadata
2431                     .current_type_ascription
2432                     .push(type_expr.span.between(ty.span));
2433                 visit::walk_expr(self, expr);
2434                 self.diagnostic_metadata.current_type_ascription.pop();
2435             }
2436             // `async |x| ...` gets desugared to `|x| future_from_generator(|| ...)`, so we need to
2437             // resolve the arguments within the proper scopes so that usages of them inside the
2438             // closure are detected as upvars rather than normal closure arg usages.
2439             ExprKind::Closure(_, Async::Yes { .. }, _, ref fn_decl, ref body, _span) => {
2440                 self.with_rib(ValueNS, NormalRibKind, |this| {
2441                     this.with_label_rib(ClosureOrAsyncRibKind, |this| {
2442                         // Resolve arguments:
2443                         this.resolve_params(&fn_decl.inputs);
2444                         // No need to resolve return type --
2445                         // the outer closure return type is `FnRetTy::Default`.
2446
2447                         // Now resolve the inner closure
2448                         {
2449                             // No need to resolve arguments: the inner closure has none.
2450                             // Resolve the return type:
2451                             visit::walk_fn_ret_ty(this, &fn_decl.output);
2452                             // Resolve the body
2453                             this.visit_expr(body);
2454                         }
2455                     })
2456                 });
2457             }
2458             ExprKind::Async(..) | ExprKind::Closure(..) => {
2459                 self.with_label_rib(ClosureOrAsyncRibKind, |this| visit::walk_expr(this, expr));
2460             }
2461             ExprKind::Repeat(ref elem, ref ct) => {
2462                 self.visit_expr(elem);
2463                 self.resolve_anon_const(ct, IsRepeatExpr::Yes);
2464             }
2465             _ => {
2466                 visit::walk_expr(self, expr);
2467             }
2468         }
2469     }
2470
2471     fn record_candidate_traits_for_expr_if_necessary(&mut self, expr: &'ast Expr) {
2472         match expr.kind {
2473             ExprKind::Field(_, ident) => {
2474                 // FIXME(#6890): Even though you can't treat a method like a
2475                 // field, we need to add any trait methods we find that match
2476                 // the field name so that we can do some nice error reporting
2477                 // later on in typeck.
2478                 let traits = self.traits_in_scope(ident, ValueNS);
2479                 self.r.trait_map.insert(expr.id, traits);
2480             }
2481             ExprKind::MethodCall(ref segment, ..) => {
2482                 debug!("(recording candidate traits for expr) recording traits for {}", expr.id);
2483                 let traits = self.traits_in_scope(segment.ident, ValueNS);
2484                 self.r.trait_map.insert(expr.id, traits);
2485             }
2486             _ => {
2487                 // Nothing to do.
2488             }
2489         }
2490     }
2491
2492     fn traits_in_scope(&mut self, ident: Ident, ns: Namespace) -> Vec<TraitCandidate> {
2493         self.r.traits_in_scope(
2494             self.current_trait_ref.as_ref().map(|(module, _)| *module),
2495             &self.parent_scope,
2496             ident.span.ctxt(),
2497             Some((ident.name, ns)),
2498         )
2499     }
2500
2501     fn compute_num_lifetime_params(&mut self, id: NodeId, generics: &Generics) {
2502         let def_id = self.r.local_def_id(id);
2503         let count = generics
2504             .params
2505             .iter()
2506             .filter(|param| matches!(param.kind, ast::GenericParamKind::Lifetime { .. }))
2507             .count();
2508         self.r.item_generics_num_lifetimes.insert(def_id, count);
2509     }
2510 }
2511
2512 impl<'a> Resolver<'a> {
2513     pub(crate) fn late_resolve_crate(&mut self, krate: &Crate) {
2514         let mut late_resolution_visitor = LateResolutionVisitor::new(self);
2515         visit::walk_crate(&mut late_resolution_visitor, krate);
2516         for (id, span) in late_resolution_visitor.diagnostic_metadata.unused_labels.iter() {
2517             self.lint_buffer.buffer_lint(lint::builtin::UNUSED_LABELS, *id, *span, "unused label");
2518         }
2519     }
2520 }