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