compiler/rustc_resolve/src/late.rs

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