compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs

   1 use crate::astconv::{
   2     AstConv, CreateSubstsForGenericArgsCtxt, ExplicitLateBound, GenericArgCountMismatch,
   3     GenericArgCountResult, IsMethodCall, PathSeg,
   4 };
   5 use crate::check::callee::{self, DeferredCallResolution};
   6 use crate::check::method::{self, MethodCallee, SelfSource};
   7 use crate::check::{BreakableCtxt, Diverges, Expectation, FnCtxt, LocalTy};
   8
   9 use rustc_data_structures::captures::Captures;
  10 use rustc_data_structures::fx::FxHashSet;
  11 use rustc_errors::{Applicability, Diagnostic, ErrorReported};
  12 use rustc_hir as hir;
  13 use rustc_hir::def::{CtorOf, DefKind, Res};
  14 use rustc_hir::def_id::DefId;
  15 use rustc_hir::lang_items::LangItem;
  16 use rustc_hir::{ExprKind, GenericArg, Node, QPath};
  17 use rustc_infer::infer::canonical::{Canonical, OriginalQueryValues, QueryResponse};
  18 use rustc_infer::infer::error_reporting::TypeAnnotationNeeded::E0282;
  19 use rustc_infer::infer::{InferOk, InferResult};
  20 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
  21 use rustc_middle::ty::fold::TypeFoldable;
  22 use rustc_middle::ty::subst::{
  23     self, GenericArgKind, InternalSubsts, Subst, SubstsRef, UserSelfTy, UserSubsts,
  24 };
  25 use rustc_middle::ty::{
  26     self, AdtKind, CanonicalUserType, DefIdTree, GenericParamDefKind, ToPolyTraitRef, ToPredicate,
  27     Ty, UserType,
  28 };
  29 use rustc_session::lint;
  30 use rustc_span::hygiene::DesugaringKind;
  31 use rustc_span::source_map::{original_sp, DUMMY_SP};
  32 use rustc_span::symbol::{kw, sym, Ident};
  33 use rustc_span::{self, BytePos, MultiSpan, Span};
  34 use rustc_trait_selection::infer::InferCtxtExt as _;
  35 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
  36 use rustc_trait_selection::traits::{
  37     self, ObligationCause, ObligationCauseCode, StatementAsExpression, TraitEngine, TraitEngineExt,
  38     WellFormedLoc,
  39 };
  40
  41 use std::collections::hash_map::Entry;
  42 use std::iter;
  43 use std::slice;
  44
  45 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  46     /// Produces warning on the given node, if the current point in the
  47     /// function is unreachable, and there hasn't been another warning.
  48     pub(in super::super) fn warn_if_unreachable(&self, id: hir::HirId, span: Span, kind: &str) {
  49         // FIXME: Combine these two 'if' expressions into one once
  50         // let chains are implemented
  51         if let Diverges::Always { span: orig_span, custom_note } = self.diverges.get() {
  52             // If span arose from a desugaring of `if` or `while`, then it is the condition itself,
  53             // which diverges, that we are about to lint on. This gives suboptimal diagnostics.
  54             // Instead, stop here so that the `if`- or `while`-expression's block is linted instead.
  55             if !span.is_desugaring(DesugaringKind::CondTemporary)
  56                 && !span.is_desugaring(DesugaringKind::Async)
  57                 && !orig_span.is_desugaring(DesugaringKind::Await)
  58             {
  59                 self.diverges.set(Diverges::WarnedAlways);
  60
  61                 debug!("warn_if_unreachable: id={:?} span={:?} kind={}", id, span, kind);
  62
  63                 self.tcx().struct_span_lint_hir(lint::builtin::UNREACHABLE_CODE, id, span, |lint| {
  64                     let msg = format!("unreachable {}", kind);
  65                     lint.build(&msg)
  66                         .span_label(span, &msg)
  67                         .span_label(
  68                             orig_span,
  69                             custom_note
  70                                 .unwrap_or("any code following this expression is unreachable"),
  71                         )
  72                         .emit();
  73                 })
  74             }
  75         }
  76     }
  77
  78     /// Resolves type and const variables in `ty` if possible. Unlike the infcx
  79     /// version (resolve_vars_if_possible), this version will
  80     /// also select obligations if it seems useful, in an effort
  81     /// to get more type information.
  82     pub(in super::super) fn resolve_vars_with_obligations(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
  83         self.resolve_vars_with_obligations_and_mutate_fulfillment(ty, |_| {})
  84     }
  85
  86     #[instrument(skip(self, mutate_fulfillment_errors), level = "debug")]
  87     pub(in super::super) fn resolve_vars_with_obligations_and_mutate_fulfillment(
  88         &self,
  89         mut ty: Ty<'tcx>,
  90         mutate_fulfillment_errors: impl Fn(&mut Vec<traits::FulfillmentError<'tcx>>),
  91     ) -> Ty<'tcx> {
  92         // No Infer()? Nothing needs doing.
  93         if !ty.has_infer_types_or_consts() {
  94             debug!("no inference var, nothing needs doing");
  95             return ty;
  96         }
  97
  98         // If `ty` is a type variable, see whether we already know what it is.
  99         ty = self.resolve_vars_if_possible(ty);
 100         if !ty.has_infer_types_or_consts() {
 101             debug!(?ty);
 102             return ty;
 103         }
 104
 105         // If not, try resolving pending obligations as much as
 106         // possible. This can help substantially when there are
 107         // indirect dependencies that don't seem worth tracking
 108         // precisely.
 109         self.select_obligations_where_possible(false, mutate_fulfillment_errors);
 110         ty = self.resolve_vars_if_possible(ty);
 111
 112         debug!(?ty);
 113         ty
 114     }
 115
 116     pub(in super::super) fn record_deferred_call_resolution(
 117         &self,
 118         closure_def_id: DefId,
 119         r: DeferredCallResolution<'tcx>,
 120     ) {
 121         let mut deferred_call_resolutions = self.deferred_call_resolutions.borrow_mut();
 122         deferred_call_resolutions.entry(closure_def_id).or_default().push(r);
 123     }
 124
 125     pub(in super::super) fn remove_deferred_call_resolutions(
 126         &self,
 127         closure_def_id: DefId,
 128     ) -> Vec<DeferredCallResolution<'tcx>> {
 129         let mut deferred_call_resolutions = self.deferred_call_resolutions.borrow_mut();
 130         deferred_call_resolutions.remove(&closure_def_id).unwrap_or_default()
 131     }
 132
 133     pub fn tag(&self) -> String {
 134         format!("{:p}", self)
 135     }
 136
 137     pub fn local_ty(&self, span: Span, nid: hir::HirId) -> LocalTy<'tcx> {
 138         self.locals.borrow().get(&nid).cloned().unwrap_or_else(|| {
 139             span_bug!(span, "no type for local variable {}", self.tcx.hir().node_to_string(nid))
 140         })
 141     }
 142
 143     #[inline]
 144     pub fn write_ty(&self, id: hir::HirId, ty: Ty<'tcx>) {
 145         debug!("write_ty({:?}, {:?}) in fcx {}", id, self.resolve_vars_if_possible(ty), self.tag());
 146         self.typeck_results.borrow_mut().node_types_mut().insert(id, ty);
 147
 148         if ty.references_error() {
 149             self.has_errors.set(true);
 150             self.set_tainted_by_errors();
 151         }
 152     }
 153
 154     pub fn write_field_index(&self, hir_id: hir::HirId, index: usize) {
 155         self.typeck_results.borrow_mut().field_indices_mut().insert(hir_id, index);
 156     }
 157
 158     pub(in super::super) fn write_resolution(
 159         &self,
 160         hir_id: hir::HirId,
 161         r: Result<(DefKind, DefId), ErrorReported>,
 162     ) {
 163         self.typeck_results.borrow_mut().type_dependent_defs_mut().insert(hir_id, r);
 164     }
 165
 166     pub fn write_method_call(&self, hir_id: hir::HirId, method: MethodCallee<'tcx>) {
 167         debug!("write_method_call(hir_id={:?}, method={:?})", hir_id, method);
 168         self.write_resolution(hir_id, Ok((DefKind::AssocFn, method.def_id)));
 169         self.write_substs(hir_id, method.substs);
 170
 171         // When the method is confirmed, the `method.substs` includes
 172         // parameters from not just the method, but also the impl of
 173         // the method -- in particular, the `Self` type will be fully
 174         // resolved. However, those are not something that the "user
 175         // specified" -- i.e., those types come from the inferred type
 176         // of the receiver, not something the user wrote. So when we
 177         // create the user-substs, we want to replace those earlier
 178         // types with just the types that the user actually wrote --
 179         // that is, those that appear on the *method itself*.
 180         //
 181         // As an example, if the user wrote something like
 182         // `foo.bar::<u32>(...)` -- the `Self` type here will be the
 183         // type of `foo` (possibly adjusted), but we don't want to
 184         // include that. We want just the `[_, u32]` part.
 185         if !method.substs.is_empty() {
 186             let method_generics = self.tcx.generics_of(method.def_id);
 187             if !method_generics.params.is_empty() {
 188                 let user_type_annotation = self.infcx.probe(|_| {
 189                     let user_substs = UserSubsts {
 190                         substs: InternalSubsts::for_item(self.tcx, method.def_id, |param, _| {
 191                             let i = param.index as usize;
 192                             if i < method_generics.parent_count {
 193                                 self.infcx.var_for_def(DUMMY_SP, param)
 194                             } else {
 195                                 method.substs[i]
 196                             }
 197                         }),
 198                         user_self_ty: None, // not relevant here
 199                     };
 200
 201                     self.infcx.canonicalize_user_type_annotation(UserType::TypeOf(
 202                         method.def_id,
 203                         user_substs,
 204                     ))
 205                 });
 206
 207                 debug!("write_method_call: user_type_annotation={:?}", user_type_annotation);
 208                 self.write_user_type_annotation(hir_id, user_type_annotation);
 209             }
 210         }
 211     }
 212
 213     pub fn write_substs(&self, node_id: hir::HirId, substs: SubstsRef<'tcx>) {
 214         if !substs.is_empty() {
 215             debug!("write_substs({:?}, {:?}) in fcx {}", node_id, substs, self.tag());
 216
 217             self.typeck_results.borrow_mut().node_substs_mut().insert(node_id, substs);
 218         }
 219     }
 220
 221     /// Given the substs that we just converted from the HIR, try to
 222     /// canonicalize them and store them as user-given substitutions
 223     /// (i.e., substitutions that must be respected by the NLL check).
 224     ///
 225     /// This should be invoked **before any unifications have
 226     /// occurred**, so that annotations like `Vec<_>` are preserved
 227     /// properly.
 228     #[instrument(skip(self), level = "debug")]
 229     pub fn write_user_type_annotation_from_substs(
 230         &self,
 231         hir_id: hir::HirId,
 232         def_id: DefId,
 233         substs: SubstsRef<'tcx>,
 234         user_self_ty: Option<UserSelfTy<'tcx>>,
 235     ) {
 236         debug!("fcx {}", self.tag());
 237
 238         if Self::can_contain_user_lifetime_bounds((substs, user_self_ty)) {
 239             let canonicalized = self.infcx.canonicalize_user_type_annotation(UserType::TypeOf(
 240                 def_id,
 241                 UserSubsts { substs, user_self_ty },
 242             ));
 243             debug!(?canonicalized);
 244             self.write_user_type_annotation(hir_id, canonicalized);
 245         }
 246     }
 247
 248     #[instrument(skip(self), level = "debug")]
 249     pub fn write_user_type_annotation(
 250         &self,
 251         hir_id: hir::HirId,
 252         canonical_user_type_annotation: CanonicalUserType<'tcx>,
 253     ) {
 254         debug!("fcx {}", self.tag());
 255
 256         if !canonical_user_type_annotation.is_identity() {
 257             self.typeck_results
 258                 .borrow_mut()
 259                 .user_provided_types_mut()
 260                 .insert(hir_id, canonical_user_type_annotation);
 261         } else {
 262             debug!("skipping identity substs");
 263         }
 264     }
 265
 266     #[instrument(skip(self, expr), level = "debug")]
 267     pub fn apply_adjustments(&self, expr: &hir::Expr<'_>, adj: Vec<Adjustment<'tcx>>) {
 268         debug!("expr = {:#?}", expr);
 269
 270         if adj.is_empty() {
 271             return;
 272         }
 273
 274         for a in &adj {
 275             if let Adjust::NeverToAny = a.kind {
 276                 if a.target.is_ty_var() {
 277                     self.diverging_type_vars.borrow_mut().insert(a.target);
 278                     debug!("apply_adjustments: adding `{:?}` as diverging type var", a.target);
 279                 }
 280             }
 281         }
 282
 283         let autoborrow_mut = adj.iter().any(|adj| {
 284             matches!(
 285                 adj,
 286                 &Adjustment {
 287                     kind: Adjust::Borrow(AutoBorrow::Ref(_, AutoBorrowMutability::Mut { .. })),
 288                     ..
 289                 }
 290             )
 291         });
 292
 293         match self.typeck_results.borrow_mut().adjustments_mut().entry(expr.hir_id) {
 294             Entry::Vacant(entry) => {
 295                 entry.insert(adj);
 296             }
 297             Entry::Occupied(mut entry) => {
 298                 debug!(" - composing on top of {:?}", entry.get());
 299                 match (&entry.get()[..], &adj[..]) {
 300                     // Applying any adjustment on top of a NeverToAny
 301                     // is a valid NeverToAny adjustment, because it can't
 302                     // be reached.
 303                     (&[Adjustment { kind: Adjust::NeverToAny, .. }], _) => return,
 304                     (
 305                         &[
 306                             Adjustment { kind: Adjust::Deref(_), .. },
 307                             Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(..)), .. },
 308                         ],
 309                         &[
 310                             Adjustment { kind: Adjust::Deref(_), .. },
 311                             .., // Any following adjustments are allowed.
 312                         ],
 313                     ) => {
 314                         // A reborrow has no effect before a dereference.
 315                     }
 316                     // FIXME: currently we never try to compose autoderefs
 317                     // and ReifyFnPointer/UnsafeFnPointer, but we could.
 318                     _ => bug!(
 319                         "while adjusting {:?}, can't compose {:?} and {:?}",
 320                         expr,
 321                         entry.get(),
 322                         adj
 323                     ),
 324                 };
 325                 *entry.get_mut() = adj;
 326             }
 327         }
 328
 329         // If there is an mutable auto-borrow, it is equivalent to `&mut <expr>`.
 330         // In this case implicit use of `Deref` and `Index` within `<expr>` should
 331         // instead be `DerefMut` and `IndexMut`, so fix those up.
 332         if autoborrow_mut {
 333             self.convert_place_derefs_to_mutable(expr);
 334         }
 335     }
 336
 337     /// Basically whenever we are converting from a type scheme into
 338     /// the fn body space, we always want to normalize associated
 339     /// types as well. This function combines the two.
 340     fn instantiate_type_scheme<T>(&self, span: Span, substs: SubstsRef<'tcx>, value: T) -> T
 341     where
 342         T: TypeFoldable<'tcx>,
 343     {
 344         debug!("instantiate_type_scheme(value={:?}, substs={:?})", value, substs);
 345         let value = value.subst(self.tcx, substs);
 346         let result = self.normalize_associated_types_in(span, value);
 347         debug!("instantiate_type_scheme = {:?}", result);
 348         result
 349     }
 350
 351     /// As `instantiate_type_scheme`, but for the bounds found in a
 352     /// generic type scheme.
 353     pub(in super::super) fn instantiate_bounds(
 354         &self,
 355         span: Span,
 356         def_id: DefId,
 357         substs: SubstsRef<'tcx>,
 358     ) -> (ty::InstantiatedPredicates<'tcx>, Vec<Span>) {
 359         let bounds = self.tcx.predicates_of(def_id);
 360         let spans: Vec<Span> = bounds.predicates.iter().map(|(_, span)| *span).collect();
 361         let result = bounds.instantiate(self.tcx, substs);
 362         let result = self.normalize_associated_types_in(span, result);
 363         debug!(
 364             "instantiate_bounds(bounds={:?}, substs={:?}) = {:?}, {:?}",
 365             bounds, substs, result, spans,
 366         );
 367         (result, spans)
 368     }
 369
 370     /// Replaces the opaque types from the given value with type variables,
 371     /// and records the `OpaqueTypeMap` for later use during writeback. See
 372     /// `InferCtxt::instantiate_opaque_types` for more details.
 373     #[instrument(skip(self, value_span), level = "debug")]
 374     pub(in super::super) fn instantiate_opaque_types_from_value<T: TypeFoldable<'tcx>>(
 375         &self,
 376         value: T,
 377         value_span: Span,
 378     ) -> T {
 379         self.register_infer_ok_obligations(self.instantiate_opaque_types(
 380             self.body_id,
 381             self.param_env,
 382             value,
 383             value_span,
 384         ))
 385     }
 386
 387     /// Convenience method which tracks extra diagnostic information for normalization
 388     /// that occurs as a result of WF checking. The `hir_id` is the `HirId` of the hir item
 389     /// whose type is being wf-checked - this is used to construct a more precise span if
 390     /// an error occurs.
 391     ///
 392     /// It is never necessary to call this method - calling `normalize_associated_types_in` will
 393     /// just result in a slightly worse diagnostic span, and will still be sound.
 394     pub(in super::super) fn normalize_associated_types_in_wf<T>(
 395         &self,
 396         span: Span,
 397         value: T,
 398         loc: WellFormedLoc,
 399     ) -> T
 400     where
 401         T: TypeFoldable<'tcx>,
 402     {
 403         self.inh.normalize_associated_types_in_with_cause(
 404             ObligationCause::new(span, self.body_id, ObligationCauseCode::WellFormed(Some(loc))),
 405             self.param_env,
 406             value,
 407         )
 408     }
 409
 410     pub(in super::super) fn normalize_associated_types_in<T>(&self, span: Span, value: T) -> T
 411     where
 412         T: TypeFoldable<'tcx>,
 413     {
 414         self.inh.normalize_associated_types_in(span, self.body_id, self.param_env, value)
 415     }
 416
 417     pub(in super::super) fn normalize_associated_types_in_as_infer_ok<T>(
 418         &self,
 419         span: Span,
 420         value: T,
 421     ) -> InferOk<'tcx, T>
 422     where
 423         T: TypeFoldable<'tcx>,
 424     {
 425         self.inh.partially_normalize_associated_types_in(
 426             ObligationCause::misc(span, self.body_id),
 427             self.param_env,
 428             value,
 429         )
 430     }
 431
 432     pub fn require_type_meets(
 433         &self,
 434         ty: Ty<'tcx>,
 435         span: Span,
 436         code: traits::ObligationCauseCode<'tcx>,
 437         def_id: DefId,
 438     ) {
 439         self.register_bound(ty, def_id, traits::ObligationCause::new(span, self.body_id, code));
 440     }
 441
 442     pub fn require_type_is_sized(
 443         &self,
 444         ty: Ty<'tcx>,
 445         span: Span,
 446         code: traits::ObligationCauseCode<'tcx>,
 447     ) {
 448         if !ty.references_error() {
 449             let lang_item = self.tcx.require_lang_item(LangItem::Sized, None);
 450             self.require_type_meets(ty, span, code, lang_item);
 451         }
 452     }
 453
 454     pub fn require_type_is_sized_deferred(
 455         &self,
 456         ty: Ty<'tcx>,
 457         span: Span,
 458         code: traits::ObligationCauseCode<'tcx>,
 459     ) {
 460         if !ty.references_error() {
 461             self.deferred_sized_obligations.borrow_mut().push((ty, span, code));
 462         }
 463     }
 464
 465     pub fn register_bound(
 466         &self,
 467         ty: Ty<'tcx>,
 468         def_id: DefId,
 469         cause: traits::ObligationCause<'tcx>,
 470     ) {
 471         if !ty.references_error() {
 472             self.fulfillment_cx.borrow_mut().register_bound(
 473                 self,
 474                 self.param_env,
 475                 ty,
 476                 def_id,
 477                 cause,
 478             );
 479         }
 480     }
 481
 482     pub fn to_ty(&self, ast_t: &hir::Ty<'_>) -> Ty<'tcx> {
 483         let t = <dyn AstConv<'_>>::ast_ty_to_ty(self, ast_t);
 484         self.register_wf_obligation(t.into(), ast_t.span, traits::MiscObligation);
 485         t
 486     }
 487
 488     pub fn to_ty_saving_user_provided_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
 489         let ty = self.to_ty(ast_ty);
 490         debug!("to_ty_saving_user_provided_ty: ty={:?}", ty);
 491
 492         if Self::can_contain_user_lifetime_bounds(ty) {
 493             let c_ty = self.infcx.canonicalize_response(UserType::Ty(ty));
 494             debug!("to_ty_saving_user_provided_ty: c_ty={:?}", c_ty);
 495             self.typeck_results.borrow_mut().user_provided_types_mut().insert(ast_ty.hir_id, c_ty);
 496         }
 497
 498         ty
 499     }
 500
 501     pub fn array_length_to_const(&self, length: &hir::ArrayLen) -> ty::Const<'tcx> {
 502         match length {
 503             &hir::ArrayLen::Infer(_, span) => self.ct_infer(self.tcx.types.usize, None, span),
 504             hir::ArrayLen::Body(anon_const) => self.to_const(anon_const),
 505         }
 506     }
 507
 508     pub fn to_const(&self, ast_c: &hir::AnonConst) -> ty::Const<'tcx> {
 509         let const_def_id = self.tcx.hir().local_def_id(ast_c.hir_id);
 510         let c = ty::Const::from_anon_const(self.tcx, const_def_id);
 511         self.register_wf_obligation(
 512             c.into(),
 513             self.tcx.hir().span(ast_c.hir_id),
 514             ObligationCauseCode::MiscObligation,
 515         );
 516         c
 517     }
 518
 519     pub fn const_arg_to_const(
 520         &self,
 521         ast_c: &hir::AnonConst,
 522         param_def_id: DefId,
 523     ) -> ty::Const<'tcx> {
 524         let const_def = ty::WithOptConstParam {
 525             did: self.tcx.hir().local_def_id(ast_c.hir_id),
 526             const_param_did: Some(param_def_id),
 527         };
 528         let c = ty::Const::from_opt_const_arg_anon_const(self.tcx, const_def);
 529         self.register_wf_obligation(
 530             c.into(),
 531             self.tcx.hir().span(ast_c.hir_id),
 532             ObligationCauseCode::MiscObligation,
 533         );
 534         c
 535     }
 536
 537     // If the type given by the user has free regions, save it for later, since
 538     // NLL would like to enforce those. Also pass in types that involve
 539     // projections, since those can resolve to `'static` bounds (modulo #54940,
 540     // which hopefully will be fixed by the time you see this comment, dear
 541     // reader, although I have my doubts). Also pass in types with inference
 542     // types, because they may be repeated. Other sorts of things are already
 543     // sufficiently enforced with erased regions. =)
 544     fn can_contain_user_lifetime_bounds<T>(t: T) -> bool
 545     where
 546         T: TypeFoldable<'tcx>,
 547     {
 548         t.has_free_regions() || t.has_projections() || t.has_infer_types()
 549     }
 550
 551     pub fn node_ty(&self, id: hir::HirId) -> Ty<'tcx> {
 552         match self.typeck_results.borrow().node_types().get(id) {
 553             Some(&t) => t,
 554             None if self.is_tainted_by_errors() => self.tcx.ty_error(),
 555             None => {
 556                 bug!(
 557                     "no type for node {}: {} in fcx {}",
 558                     id,
 559                     self.tcx.hir().node_to_string(id),
 560                     self.tag()
 561                 );
 562             }
 563         }
 564     }
 565
 566     pub fn node_ty_opt(&self, id: hir::HirId) -> Option<Ty<'tcx>> {
 567         match self.typeck_results.borrow().node_types().get(id) {
 568             Some(&t) => Some(t),
 569             None if self.is_tainted_by_errors() => Some(self.tcx.ty_error()),
 570             None => None,
 571         }
 572     }
 573
 574     /// Registers an obligation for checking later, during regionck, that `arg` is well-formed.
 575     pub fn register_wf_obligation(
 576         &self,
 577         arg: subst::GenericArg<'tcx>,
 578         span: Span,
 579         code: traits::ObligationCauseCode<'tcx>,
 580     ) {
 581         // WF obligations never themselves fail, so no real need to give a detailed cause:
 582         let cause = traits::ObligationCause::new(span, self.body_id, code);
 583         self.register_predicate(traits::Obligation::new(
 584             cause,
 585             self.param_env,
 586             ty::Binder::dummy(ty::PredicateKind::WellFormed(arg)).to_predicate(self.tcx),
 587         ));
 588     }
 589
 590     /// Registers obligations that all `substs` are well-formed.
 591     pub fn add_wf_bounds(&self, substs: SubstsRef<'tcx>, expr: &hir::Expr<'_>) {
 592         for arg in substs.iter().filter(|arg| {
 593             matches!(arg.unpack(), GenericArgKind::Type(..) | GenericArgKind::Const(..))
 594         }) {
 595             self.register_wf_obligation(arg, expr.span, traits::MiscObligation);
 596         }
 597     }
 598
 599     // FIXME(arielb1): use this instead of field.ty everywhere
 600     // Only for fields! Returns <none> for methods>
 601     // Indifferent to privacy flags
 602     pub fn field_ty(
 603         &self,
 604         span: Span,
 605         field: &'tcx ty::FieldDef,
 606         substs: SubstsRef<'tcx>,
 607     ) -> Ty<'tcx> {
 608         self.normalize_associated_types_in(span, field.ty(self.tcx, substs))
 609     }
 610
 611     pub(in super::super) fn resolve_generator_interiors(&self, def_id: DefId) {
 612         let mut generators = self.deferred_generator_interiors.borrow_mut();
 613         for (body_id, interior, kind) in generators.drain(..) {
 614             self.select_obligations_where_possible(false, |_| {});
 615             crate::check::generator_interior::resolve_interior(
 616                 self, def_id, body_id, interior, kind,
 617             );
 618         }
 619     }
 620
 621     #[instrument(skip(self), level = "debug")]
 622     pub(in super::super) fn select_all_obligations_or_error(&self) {
 623         let errors = self.fulfillment_cx.borrow_mut().select_all_or_error(&self);
 624
 625         if !errors.is_empty() {
 626             self.report_fulfillment_errors(&errors, self.inh.body_id, false);
 627         }
 628     }
 629
 630     /// Select as many obligations as we can at present.
 631     pub(in super::super) fn select_obligations_where_possible(
 632         &self,
 633         fallback_has_occurred: bool,
 634         mutate_fulfillment_errors: impl Fn(&mut Vec<traits::FulfillmentError<'tcx>>),
 635     ) {
 636         let mut result = self.fulfillment_cx.borrow_mut().select_where_possible(self);
 637         if !result.is_empty() {
 638             mutate_fulfillment_errors(&mut result);
 639             self.report_fulfillment_errors(&result, self.inh.body_id, fallback_has_occurred);
 640         }
 641     }
 642
 643     /// For the overloaded place expressions (`*x`, `x[3]`), the trait
 644     /// returns a type of `&T`, but the actual type we assign to the
 645     /// *expression* is `T`. So this function just peels off the return
 646     /// type by one layer to yield `T`.
 647     pub(in super::super) fn make_overloaded_place_return_type(
 648         &self,
 649         method: MethodCallee<'tcx>,
 650     ) -> ty::TypeAndMut<'tcx> {
 651         // extract method return type, which will be &T;
 652         let ret_ty = method.sig.output();
 653
 654         // method returns &T, but the type as visible to user is T, so deref
 655         ret_ty.builtin_deref(true).unwrap()
 656     }
 657
 658     #[instrument(skip(self), level = "debug")]
 659     fn self_type_matches_expected_vid(
 660         &self,
 661         trait_ref: ty::PolyTraitRef<'tcx>,
 662         expected_vid: ty::TyVid,
 663     ) -> bool {
 664         let self_ty = self.shallow_resolve(trait_ref.skip_binder().self_ty());
 665         debug!(?self_ty);
 666
 667         match *self_ty.kind() {
 668             ty::Infer(ty::TyVar(found_vid)) => {
 669                 // FIXME: consider using `sub_root_var` here so we
 670                 // can see through subtyping.
 671                 let found_vid = self.root_var(found_vid);
 672                 debug!("self_type_matches_expected_vid - found_vid={:?}", found_vid);
 673                 expected_vid == found_vid
 674             }
 675             _ => false,
 676         }
 677     }
 678
 679     #[instrument(skip(self), level = "debug")]
 680     pub(in super::super) fn obligations_for_self_ty<'b>(
 681         &'b self,
 682         self_ty: ty::TyVid,
 683     ) -> impl Iterator<Item = (ty::PolyTraitRef<'tcx>, traits::PredicateObligation<'tcx>)>
 684     + Captures<'tcx>
 685     + 'b {
 686         // FIXME: consider using `sub_root_var` here so we
 687         // can see through subtyping.
 688         let ty_var_root = self.root_var(self_ty);
 689         trace!("pending_obligations = {:#?}", self.fulfillment_cx.borrow().pending_obligations());
 690
 691         self.fulfillment_cx
 692             .borrow()
 693             .pending_obligations()
 694             .into_iter()
 695             .filter_map(move |obligation| {
 696                 let bound_predicate = obligation.predicate.kind();
 697                 match bound_predicate.skip_binder() {
 698                     ty::PredicateKind::Projection(data) => Some((
 699                         bound_predicate.rebind(data).required_poly_trait_ref(self.tcx),
 700                         obligation,
 701                     )),
 702                     ty::PredicateKind::Trait(data) => {
 703                         Some((bound_predicate.rebind(data).to_poly_trait_ref(), obligation))
 704                     }
 705                     ty::PredicateKind::Subtype(..) => None,
 706                     ty::PredicateKind::Coerce(..) => None,
 707                     ty::PredicateKind::RegionOutlives(..) => None,
 708                     ty::PredicateKind::TypeOutlives(..) => None,
 709                     ty::PredicateKind::WellFormed(..) => None,
 710                     ty::PredicateKind::ObjectSafe(..) => None,
 711                     ty::PredicateKind::ConstEvaluatable(..) => None,
 712                     ty::PredicateKind::ConstEquate(..) => None,
 713                     // N.B., this predicate is created by breaking down a
 714                     // `ClosureType: FnFoo()` predicate, where
 715                     // `ClosureType` represents some `Closure`. It can't
 716                     // possibly be referring to the current closure,
 717                     // because we haven't produced the `Closure` for
 718                     // this closure yet; this is exactly why the other
 719                     // code is looking for a self type of an unresolved
 720                     // inference variable.
 721                     ty::PredicateKind::ClosureKind(..) => None,
 722                     ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
 723                 }
 724             })
 725             .filter(move |(tr, _)| self.self_type_matches_expected_vid(*tr, ty_var_root))
 726     }
 727
 728     pub(in super::super) fn type_var_is_sized(&self, self_ty: ty::TyVid) -> bool {
 729         self.obligations_for_self_ty(self_ty)
 730             .any(|(tr, _)| Some(tr.def_id()) == self.tcx.lang_items().sized_trait())
 731     }
 732
 733     pub(in super::super) fn err_args(&self, len: usize) -> Vec<Ty<'tcx>> {
 734         vec![self.tcx.ty_error(); len]
 735     }
 736
 737     /// Unifies the output type with the expected type early, for more coercions
 738     /// and forward type information on the input expressions.
 739     #[instrument(skip(self, call_span), level = "debug")]
 740     pub(in super::super) fn expected_inputs_for_expected_output(
 741         &self,
 742         call_span: Span,
 743         expected_ret: Expectation<'tcx>,
 744         formal_ret: Ty<'tcx>,
 745         formal_args: &[Ty<'tcx>],
 746     ) -> Vec<Ty<'tcx>> {
 747         let formal_ret = self.resolve_vars_with_obligations(formal_ret);
 748         let Some(ret_ty) = expected_ret.only_has_type(self) else { return Vec::new() };
 749         let expect_args = self
 750             .fudge_inference_if_ok(|| {
 751                 // Attempt to apply a subtyping relationship between the formal
 752                 // return type (likely containing type variables if the function
 753                 // is polymorphic) and the expected return type.
 754                 // No argument expectations are produced if unification fails.
 755                 let origin = self.misc(call_span);
 756                 let ures = self.at(&origin, self.param_env).sup(ret_ty, formal_ret);
 757
 758                 // FIXME(#27336) can't use ? here, Try::from_error doesn't default
 759                 // to identity so the resulting type is not constrained.
 760                 match ures {
 761                     Ok(ok) => {
 762                         // Process any obligations locally as much as
 763                         // we can.  We don't care if some things turn
 764                         // out unconstrained or ambiguous, as we're
 765                         // just trying to get hints here.
 766                         let errors = self.save_and_restore_in_snapshot_flag(|_| {
 767                             let mut fulfill = <dyn TraitEngine<'_>>::new(self.tcx);
 768                             for obligation in ok.obligations {
 769                                 fulfill.register_predicate_obligation(self, obligation);
 770                             }
 771                             fulfill.select_where_possible(self)
 772                         });
 773
 774                         if !errors.is_empty() {
 775                             return Err(());
 776                         }
 777                     }
 778                     Err(_) => return Err(()),
 779                 }
 780
 781                 // Record all the argument types, with the substitutions
 782                 // produced from the above subtyping unification.
 783                 Ok(formal_args.iter().map(|&ty| self.resolve_vars_if_possible(ty)).collect())
 784             })
 785             .unwrap_or_default();
 786         debug!(?formal_args, ?formal_ret, ?expect_args, ?expected_ret);
 787         expect_args
 788     }
 789
 790     pub(in super::super) fn resolve_lang_item_path(
 791         &self,
 792         lang_item: hir::LangItem,
 793         span: Span,
 794         hir_id: hir::HirId,
 795         expr_hir_id: Option<hir::HirId>,
 796     ) -> (Res, Ty<'tcx>) {
 797         let def_id = self.tcx.require_lang_item(lang_item, Some(span));
 798         let def_kind = self.tcx.def_kind(def_id);
 799
 800         let item_ty = if let DefKind::Variant = def_kind {
 801             self.tcx.type_of(self.tcx.parent(def_id).expect("variant w/out parent"))
 802         } else {
 803             self.tcx.type_of(def_id)
 804         };
 805         let substs = self.infcx.fresh_substs_for_item(span, def_id);
 806         let ty = item_ty.subst(self.tcx, substs);
 807
 808         self.write_resolution(hir_id, Ok((def_kind, def_id)));
 809         self.add_required_obligations_with_code(
 810             span,
 811             def_id,
 812             &substs,
 813             match lang_item {
 814                 hir::LangItem::IntoFutureIntoFuture => {
 815                     ObligationCauseCode::AwaitableExpr(expr_hir_id)
 816                 }
 817                 hir::LangItem::IteratorNext | hir::LangItem::IntoIterIntoIter => {
 818                     ObligationCauseCode::ForLoopIterator
 819                 }
 820                 hir::LangItem::TryTraitFromOutput
 821                 | hir::LangItem::TryTraitFromResidual
 822                 | hir::LangItem::TryTraitBranch => ObligationCauseCode::QuestionMark,
 823                 _ => traits::ItemObligation(def_id),
 824             },
 825         );
 826         (Res::Def(def_kind, def_id), ty)
 827     }
 828
 829     /// Resolves an associated value path into a base type and associated constant, or method
 830     /// resolution. The newly resolved definition is written into `type_dependent_defs`.
 831     pub fn resolve_ty_and_res_fully_qualified_call(
 832         &self,
 833         qpath: &'tcx QPath<'tcx>,
 834         hir_id: hir::HirId,
 835         span: Span,
 836     ) -> (Res, Option<Ty<'tcx>>, &'tcx [hir::PathSegment<'tcx>]) {
 837         debug!(
 838             "resolve_ty_and_res_fully_qualified_call: qpath={:?} hir_id={:?} span={:?}",
 839             qpath, hir_id, span
 840         );
 841         let (ty, qself, item_segment) = match *qpath {
 842             QPath::Resolved(ref opt_qself, ref path) => {
 843                 return (
 844                     path.res,
 845                     opt_qself.as_ref().map(|qself| self.to_ty(qself)),
 846                     path.segments,
 847                 );
 848             }
 849             QPath::TypeRelative(ref qself, ref segment) => {
 850                 // Don't use `self.to_ty`, since this will register a WF obligation.
 851                 // If we're trying to call a non-existent method on a trait
 852                 // (e.g. `MyTrait::missing_method`), then resolution will
 853                 // give us a `QPath::TypeRelative` with a trait object as
 854                 // `qself`. In that case, we want to avoid registering a WF obligation
 855                 // for `dyn MyTrait`, since we don't actually need the trait
 856                 // to be object-safe.
 857                 // We manually call `register_wf_obligation` in the success path
 858                 // below.
 859                 (<dyn AstConv<'_>>::ast_ty_to_ty_in_path(self, qself), qself, segment)
 860             }
 861             QPath::LangItem(..) => {
 862                 bug!("`resolve_ty_and_res_fully_qualified_call` called on `LangItem`")
 863             }
 864         };
 865         if let Some(&cached_result) = self.typeck_results.borrow().type_dependent_defs().get(hir_id)
 866         {
 867             self.register_wf_obligation(ty.into(), qself.span, traits::WellFormed(None));
 868             // Return directly on cache hit. This is useful to avoid doubly reporting
 869             // errors with default match binding modes. See #44614.
 870             let def = cached_result.map_or(Res::Err, |(kind, def_id)| Res::Def(kind, def_id));
 871             return (def, Some(ty), slice::from_ref(&**item_segment));
 872         }
 873         let item_name = item_segment.ident;
 874         let result = self
 875             .resolve_fully_qualified_call(span, item_name, ty, qself.span, hir_id)
 876             .or_else(|error| {
 877                 let result = match error {
 878                     method::MethodError::PrivateMatch(kind, def_id, _) => Ok((kind, def_id)),
 879                     _ => Err(ErrorReported),
 880                 };
 881
 882                 // If we have a path like `MyTrait::missing_method`, then don't register
 883                 // a WF obligation for `dyn MyTrait` when method lookup fails. Otherwise,
 884                 // register a WF obligation so that we can detect any additional
 885                 // errors in the self type.
 886                 if !(matches!(error, method::MethodError::NoMatch(_)) && ty.is_trait()) {
 887                     self.register_wf_obligation(ty.into(), qself.span, traits::WellFormed(None));
 888                 }
 889                 if item_name.name != kw::Empty {
 890                     if let Some(mut e) = self.report_method_error(
 891                         span,
 892                         ty,
 893                         item_name,
 894                         SelfSource::QPath(qself),
 895                         error,
 896                         None,
 897                     ) {
 898                         e.emit();
 899                     }
 900                 }
 901                 result
 902             });
 903
 904         if result.is_ok() {
 905             self.register_wf_obligation(ty.into(), qself.span, traits::WellFormed(None));
 906         }
 907
 908         // Write back the new resolution.
 909         self.write_resolution(hir_id, result);
 910         (
 911             result.map_or(Res::Err, |(kind, def_id)| Res::Def(kind, def_id)),
 912             Some(ty),
 913             slice::from_ref(&**item_segment),
 914         )
 915     }
 916
 917     /// Given a function `Node`, return its `FnDecl` if it exists, or `None` otherwise.
 918     pub(in super::super) fn get_node_fn_decl(
 919         &self,
 920         node: Node<'tcx>,
 921     ) -> Option<(&'tcx hir::FnDecl<'tcx>, Ident, bool)> {
 922         match node {
 923             Node::Item(&hir::Item { ident, kind: hir::ItemKind::Fn(ref sig, ..), .. }) => {
 924                 // This is less than ideal, it will not suggest a return type span on any
 925                 // method called `main`, regardless of whether it is actually the entry point,
 926                 // but it will still present it as the reason for the expected type.
 927                 Some((&sig.decl, ident, ident.name != sym::main))
 928             }
 929             Node::TraitItem(&hir::TraitItem {
 930                 ident,
 931                 kind: hir::TraitItemKind::Fn(ref sig, ..),
 932                 ..
 933             }) => Some((&sig.decl, ident, true)),
 934             Node::ImplItem(&hir::ImplItem {
 935                 ident,
 936                 kind: hir::ImplItemKind::Fn(ref sig, ..),
 937                 ..
 938             }) => Some((&sig.decl, ident, false)),
 939             _ => None,
 940         }
 941     }
 942
 943     /// Given a `HirId`, return the `FnDecl` of the method it is enclosed by and whether a
 944     /// suggestion can be made, `None` otherwise.
 945     pub fn get_fn_decl(&self, blk_id: hir::HirId) -> Option<(&'tcx hir::FnDecl<'tcx>, bool)> {
 946         // Get enclosing Fn, if it is a function or a trait method, unless there's a `loop` or
 947         // `while` before reaching it, as block tail returns are not available in them.
 948         self.tcx.hir().get_return_block(blk_id).and_then(|blk_id| {
 949             let parent = self.tcx.hir().get(blk_id);
 950             self.get_node_fn_decl(parent).map(|(fn_decl, _, is_main)| (fn_decl, is_main))
 951         })
 952     }
 953
 954     pub(in super::super) fn note_internal_mutation_in_method(
 955         &self,
 956         err: &mut Diagnostic,
 957         expr: &hir::Expr<'_>,
 958         expected: Ty<'tcx>,
 959         found: Ty<'tcx>,
 960     ) {
 961         if found != self.tcx.types.unit {
 962             return;
 963         }
 964         if let ExprKind::MethodCall(path_segment, [rcvr, ..], _) = expr.kind {
 965             if self
 966                 .typeck_results
 967                 .borrow()
 968                 .expr_ty_adjusted_opt(rcvr)
 969                 .map_or(true, |ty| expected.peel_refs() != ty.peel_refs())
 970             {
 971                 return;
 972             }
 973             let mut sp = MultiSpan::from_span(path_segment.ident.span);
 974             sp.push_span_label(
 975                 path_segment.ident.span,
 976                 format!(
 977                     "this call modifies {} in-place",
 978                     match rcvr.kind {
 979                         ExprKind::Path(QPath::Resolved(
 980                             None,
 981                             hir::Path { segments: [segment], .. },
 982                         )) => format!("`{}`", segment.ident),
 983                         _ => "its receiver".to_string(),
 984                     }
 985                 ),
 986             );
 987             sp.push_span_label(
 988                 rcvr.span,
 989                 "you probably want to use this value after calling the method...".to_string(),
 990             );
 991             err.span_note(
 992                 sp,
 993                 &format!("method `{}` modifies its receiver in-place", path_segment.ident),
 994             );
 995             err.note(&format!("...instead of the `()` output of method `{}`", path_segment.ident));
 996         }
 997     }
 998
 999     pub(in super::super) fn note_need_for_fn_pointer(
1000         &self,
1001         err: &mut Diagnostic,
1002         expected: Ty<'tcx>,
1003         found: Ty<'tcx>,
1004     ) {
1005         let (sig, did, substs) = match (&expected.kind(), &found.kind()) {
1006             (ty::FnDef(did1, substs1), ty::FnDef(did2, substs2)) => {
1007                 let sig1 = self.tcx.fn_sig(*did1).subst(self.tcx, substs1);
1008                 let sig2 = self.tcx.fn_sig(*did2).subst(self.tcx, substs2);
1009                 if sig1 != sig2 {
1010                     return;
1011                 }
1012                 err.note(
1013                     "different `fn` items always have unique types, even if their signatures are \
1014                      the same",
1015                 );
1016                 (sig1, *did1, substs1)
1017             }
1018             (ty::FnDef(did, substs), ty::FnPtr(sig2)) => {
1019                 let sig1 = self.tcx.fn_sig(*did).subst(self.tcx, substs);
1020                 if sig1 != *sig2 {
1021                     return;
1022                 }
1023                 (sig1, *did, substs)
1024             }
1025             _ => return,
1026         };
1027         err.help(&format!("change the expected type to be function pointer `{}`", sig));
1028         err.help(&format!(
1029             "if the expected type is due to type inference, cast the expected `fn` to a function \
1030              pointer: `{} as {}`",
1031             self.tcx.def_path_str_with_substs(did, substs),
1032             sig
1033         ));
1034     }
1035
1036     pub(in super::super) fn could_remove_semicolon(
1037         &self,
1038         blk: &'tcx hir::Block<'tcx>,
1039         expected_ty: Ty<'tcx>,
1040     ) -> Option<(Span, StatementAsExpression)> {
1041         // Be helpful when the user wrote `{... expr;}` and
1042         // taking the `;` off is enough to fix the error.
1043         let last_stmt = blk.stmts.last()?;
1044         let hir::StmtKind::Semi(ref last_expr) = last_stmt.kind else {
1045             return None;
1046         };
1047         let last_expr_ty = self.node_ty(last_expr.hir_id);
1048         let needs_box = match (last_expr_ty.kind(), expected_ty.kind()) {
1049             (ty::Opaque(last_def_id, _), ty::Opaque(exp_def_id, _))
1050                 if last_def_id == exp_def_id =>
1051             {
1052                 StatementAsExpression::CorrectType
1053             }
1054             (ty::Opaque(last_def_id, last_bounds), ty::Opaque(exp_def_id, exp_bounds)) => {
1055                 debug!(
1056                     "both opaque, likely future {:?} {:?} {:?} {:?}",
1057                     last_def_id, last_bounds, exp_def_id, exp_bounds
1058                 );
1059
1060                 let last_local_id = last_def_id.as_local()?;
1061                 let exp_local_id = exp_def_id.as_local()?;
1062
1063                 match (
1064                     &self.tcx.hir().expect_item(last_local_id).kind,
1065                     &self.tcx.hir().expect_item(exp_local_id).kind,
1066                 ) {
1067                     (
1068                         hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds: last_bounds, .. }),
1069                         hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds: exp_bounds, .. }),
1070                     ) if iter::zip(*last_bounds, *exp_bounds).all(|(left, right)| {
1071                         match (left, right) {
1072                             (
1073                                 hir::GenericBound::Trait(tl, ml),
1074                                 hir::GenericBound::Trait(tr, mr),
1075                             ) if tl.trait_ref.trait_def_id() == tr.trait_ref.trait_def_id()
1076                                 && ml == mr =>
1077                             {
1078                                 true
1079                             }
1080                             (
1081                                 hir::GenericBound::LangItemTrait(langl, _, _, argsl),
1082                                 hir::GenericBound::LangItemTrait(langr, _, _, argsr),
1083                             ) if langl == langr => {
1084                                 // FIXME: consider the bounds!
1085                                 debug!("{:?} {:?}", argsl, argsr);
1086                                 true
1087                             }
1088                             _ => false,
1089                         }
1090                     }) =>
1091                     {
1092                         StatementAsExpression::NeedsBoxing
1093                     }
1094                     _ => StatementAsExpression::CorrectType,
1095                 }
1096             }
1097             _ => StatementAsExpression::CorrectType,
1098         };
1099         if (matches!(last_expr_ty.kind(), ty::Error(_))
1100             || self.can_sub(self.param_env, last_expr_ty, expected_ty).is_err())
1101             && matches!(needs_box, StatementAsExpression::CorrectType)
1102         {
1103             return None;
1104         }
1105         let span = if last_stmt.span.from_expansion() {
1106             let mac_call = original_sp(last_stmt.span, blk.span);
1107             self.tcx.sess.source_map().mac_call_stmt_semi_span(mac_call)?
1108         } else {
1109             last_stmt.span.with_lo(last_stmt.span.hi() - BytePos(1))
1110         };
1111         Some((span, needs_box))
1112     }
1113
1114     // Instantiates the given path, which must refer to an item with the given
1115     // number of type parameters and type.
1116     #[instrument(skip(self, span), level = "debug")]
1117     pub fn instantiate_value_path(
1118         &self,
1119         segments: &[hir::PathSegment<'_>],
1120         self_ty: Option<Ty<'tcx>>,
1121         res: Res,
1122         span: Span,
1123         hir_id: hir::HirId,
1124     ) -> (Ty<'tcx>, Res) {
1125         let tcx = self.tcx;
1126
1127         let path_segs = match res {
1128             Res::Local(_) | Res::SelfCtor(_) => vec![],
1129             Res::Def(kind, def_id) => <dyn AstConv<'_>>::def_ids_for_value_path_segments(
1130                 self, segments, self_ty, kind, def_id,
1131             ),
1132             _ => bug!("instantiate_value_path on {:?}", res),
1133         };
1134
1135         let mut user_self_ty = None;
1136         let mut is_alias_variant_ctor = false;
1137         match res {
1138             Res::Def(DefKind::Ctor(CtorOf::Variant, _), _)
1139                 if let Some(self_ty) = self_ty =>
1140             {
1141                 let adt_def = self_ty.ty_adt_def().unwrap();
1142                 user_self_ty = Some(UserSelfTy { impl_def_id: adt_def.did, self_ty });
1143                 is_alias_variant_ctor = true;
1144             }
1145             Res::Def(DefKind::AssocFn | DefKind::AssocConst, def_id) => {
1146                 let container = tcx.associated_item(def_id).container;
1147                 debug!(?def_id, ?container);
1148                 match container {
1149                     ty::TraitContainer(trait_did) => {
1150                         callee::check_legal_trait_for_method_call(tcx, span, None, span, trait_did)
1151                     }
1152                     ty::ImplContainer(impl_def_id) => {
1153                         if segments.len() == 1 {
1154                             // `<T>::assoc` will end up here, and so
1155                             // can `T::assoc`. It this came from an
1156                             // inherent impl, we need to record the
1157                             // `T` for posterity (see `UserSelfTy` for
1158                             // details).
1159                             let self_ty = self_ty.expect("UFCS sugared assoc missing Self");
1160                             user_self_ty = Some(UserSelfTy { impl_def_id, self_ty });
1161                         }
1162                     }
1163                 }
1164             }
1165             _ => {}
1166         }
1167
1168         // Now that we have categorized what space the parameters for each
1169         // segment belong to, let's sort out the parameters that the user
1170         // provided (if any) into their appropriate spaces. We'll also report
1171         // errors if type parameters are provided in an inappropriate place.
1172
1173         let generic_segs: FxHashSet<_> = path_segs.iter().map(|PathSeg(_, index)| index).collect();
1174         let generics_has_err = <dyn AstConv<'_>>::prohibit_generics(
1175             self,
1176             segments.iter().enumerate().filter_map(|(index, seg)| {
1177                 if !generic_segs.contains(&index) || is_alias_variant_ctor {
1178                     Some(seg)
1179                 } else {
1180                     None
1181                 }
1182             }),
1183         );
1184
1185         if let Res::Local(hid) = res {
1186             let ty = self.local_ty(span, hid).decl_ty;
1187             let ty = self.normalize_associated_types_in(span, ty);
1188             self.write_ty(hir_id, ty);
1189             return (ty, res);
1190         }
1191
1192         if generics_has_err {
1193             // Don't try to infer type parameters when prohibited generic arguments were given.
1194             user_self_ty = None;
1195         }
1196
1197         // Now we have to compare the types that the user *actually*
1198         // provided against the types that were *expected*. If the user
1199         // did not provide any types, then we want to substitute inference
1200         // variables. If the user provided some types, we may still need
1201         // to add defaults. If the user provided *too many* types, that's
1202         // a problem.
1203
1204         let mut infer_args_for_err = FxHashSet::default();
1205
1206         let mut explicit_late_bound = ExplicitLateBound::No;
1207         for &PathSeg(def_id, index) in &path_segs {
1208             let seg = &segments[index];
1209             let generics = tcx.generics_of(def_id);
1210
1211             // Argument-position `impl Trait` is treated as a normal generic
1212             // parameter internally, but we don't allow users to specify the
1213             // parameter's value explicitly, so we have to do some error-
1214             // checking here.
1215             let arg_count = <dyn AstConv<'_>>::check_generic_arg_count_for_call(
1216                 tcx,
1217                 span,
1218                 def_id,
1219                 &generics,
1220                 seg,
1221                 IsMethodCall::No,
1222             );
1223
1224             if let ExplicitLateBound::Yes = arg_count.explicit_late_bound {
1225                 explicit_late_bound = ExplicitLateBound::Yes;
1226             }
1227
1228             if let Err(GenericArgCountMismatch { reported: Some(_), .. }) = arg_count.correct {
1229                 infer_args_for_err.insert(index);
1230                 self.set_tainted_by_errors(); // See issue #53251.
1231             }
1232         }
1233
1234         let has_self = path_segs
1235             .last()
1236             .map(|PathSeg(def_id, _)| tcx.generics_of(*def_id).has_self)
1237             .unwrap_or(false);
1238
1239         let (res, self_ctor_substs) = if let Res::SelfCtor(impl_def_id) = res {
1240             let ty = self.normalize_ty(span, tcx.at(span).type_of(impl_def_id));
1241             match *ty.kind() {
1242                 ty::Adt(adt_def, substs) if adt_def.has_ctor() => {
1243                     let variant = adt_def.non_enum_variant();
1244                     let ctor_def_id = variant.ctor_def_id.unwrap();
1245                     (
1246                         Res::Def(DefKind::Ctor(CtorOf::Struct, variant.ctor_kind), ctor_def_id),
1247                         Some(substs),
1248                     )
1249                 }
1250                 _ => {
1251                     let mut err = tcx.sess.struct_span_err(
1252                         span,
1253                         "the `Self` constructor can only be used with tuple or unit structs",
1254                     );
1255                     if let Some(adt_def) = ty.ty_adt_def() {
1256                         match adt_def.adt_kind() {
1257                             AdtKind::Enum => {
1258                                 err.help("did you mean to use one of the enum's variants?");
1259                             }
1260                             AdtKind::Struct | AdtKind::Union => {
1261                                 err.span_suggestion(
1262                                     span,
1263                                     "use curly brackets",
1264                                     String::from("Self { /* fields */ }"),
1265                                     Applicability::HasPlaceholders,
1266                                 );
1267                             }
1268                         }
1269                     }
1270                     err.emit();
1271
1272                     return (tcx.ty_error(), res);
1273                 }
1274             }
1275         } else {
1276             (res, None)
1277         };
1278         let def_id = res.def_id();
1279
1280         // The things we are substituting into the type should not contain
1281         // escaping late-bound regions, and nor should the base type scheme.
1282         let ty = tcx.type_of(def_id);
1283
1284         let arg_count = GenericArgCountResult {
1285             explicit_late_bound,
1286             correct: if infer_args_for_err.is_empty() {
1287                 Ok(())
1288             } else {
1289                 Err(GenericArgCountMismatch::default())
1290             },
1291         };
1292
1293         struct CreateCtorSubstsContext<'a, 'tcx> {
1294             fcx: &'a FnCtxt<'a, 'tcx>,
1295             span: Span,
1296             path_segs: &'a [PathSeg],
1297             infer_args_for_err: &'a FxHashSet<usize>,
1298             segments: &'a [hir::PathSegment<'a>],
1299         }
1300         impl<'tcx, 'a> CreateSubstsForGenericArgsCtxt<'a, 'tcx> for CreateCtorSubstsContext<'a, 'tcx> {
1301             fn args_for_def_id(
1302                 &mut self,
1303                 def_id: DefId,
1304             ) -> (Option<&'a hir::GenericArgs<'a>>, bool) {
1305                 if let Some(&PathSeg(_, index)) =
1306                     self.path_segs.iter().find(|&PathSeg(did, _)| *did == def_id)
1307                 {
1308                     // If we've encountered an `impl Trait`-related error, we're just
1309                     // going to infer the arguments for better error messages.
1310                     if !self.infer_args_for_err.contains(&index) {
1311                         // Check whether the user has provided generic arguments.
1312                         if let Some(ref data) = self.segments[index].args {
1313                             return (Some(data), self.segments[index].infer_args);
1314                         }
1315                     }
1316                     return (None, self.segments[index].infer_args);
1317                 }
1318
1319                 (None, true)
1320             }
1321
1322             fn provided_kind(
1323                 &mut self,
1324                 param: &ty::GenericParamDef,
1325                 arg: &GenericArg<'_>,
1326             ) -> subst::GenericArg<'tcx> {
1327                 match (&param.kind, arg) {
1328                     (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
1329                         <dyn AstConv<'_>>::ast_region_to_region(self.fcx, lt, Some(param)).into()
1330                     }
1331                     (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
1332                         self.fcx.to_ty(ty).into()
1333                     }
1334                     (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
1335                         self.fcx.const_arg_to_const(&ct.value, param.def_id).into()
1336                     }
1337                     (GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => {
1338                         self.fcx.ty_infer(Some(param), inf.span).into()
1339                     }
1340                     (GenericParamDefKind::Const { .. }, GenericArg::Infer(inf)) => {
1341                         let tcx = self.fcx.tcx();
1342                         self.fcx.ct_infer(tcx.type_of(param.def_id), Some(param), inf.span).into()
1343                     }
1344                     _ => unreachable!(),
1345                 }
1346             }
1347
1348             fn inferred_kind(
1349                 &mut self,
1350                 substs: Option<&[subst::GenericArg<'tcx>]>,
1351                 param: &ty::GenericParamDef,
1352                 infer_args: bool,
1353             ) -> subst::GenericArg<'tcx> {
1354                 let tcx = self.fcx.tcx();
1355                 match param.kind {
1356                     GenericParamDefKind::Lifetime => {
1357                         self.fcx.re_infer(Some(param), self.span).unwrap().into()
1358                     }
1359                     GenericParamDefKind::Type { has_default, .. } => {
1360                         if !infer_args && has_default {
1361                             // If we have a default, then we it doesn't matter that we're not
1362                             // inferring the type arguments: we provide the default where any
1363                             // is missing.
1364                             let default = tcx.type_of(param.def_id);
1365                             self.fcx
1366                                 .normalize_ty(
1367                                     self.span,
1368                                     default.subst_spanned(tcx, substs.unwrap(), Some(self.span)),
1369                                 )
1370                                 .into()
1371                         } else {
1372                             // If no type arguments were provided, we have to infer them.
1373                             // This case also occurs as a result of some malformed input, e.g.
1374                             // a lifetime argument being given instead of a type parameter.
1375                             // Using inference instead of `Error` gives better error messages.
1376                             self.fcx.var_for_def(self.span, param)
1377                         }
1378                     }
1379                     GenericParamDefKind::Const { has_default, .. } => {
1380                         if !infer_args && has_default {
1381                             tcx.const_param_default(param.def_id)
1382                                 .subst_spanned(tcx, substs.unwrap(), Some(self.span))
1383                                 .into()
1384                         } else {
1385                             self.fcx.var_for_def(self.span, param)
1386                         }
1387                     }
1388                 }
1389             }
1390         }
1391
1392         let substs = self_ctor_substs.unwrap_or_else(|| {
1393             <dyn AstConv<'_>>::create_substs_for_generic_args(
1394                 tcx,
1395                 def_id,
1396                 &[],
1397                 has_self,
1398                 self_ty,
1399                 &arg_count,
1400                 &mut CreateCtorSubstsContext {
1401                     fcx: self,
1402                     span,
1403                     path_segs: &path_segs,
1404                     infer_args_for_err: &infer_args_for_err,
1405                     segments,
1406                 },
1407             )
1408         });
1409         assert!(!substs.has_escaping_bound_vars());
1410         assert!(!ty.has_escaping_bound_vars());
1411
1412         // First, store the "user substs" for later.
1413         self.write_user_type_annotation_from_substs(hir_id, def_id, substs, user_self_ty);
1414
1415         self.add_required_obligations(span, def_id, &substs);
1416
1417         // Substitute the values for the type parameters into the type of
1418         // the referenced item.
1419         let ty_substituted = self.instantiate_type_scheme(span, &substs, ty);
1420
1421         if let Some(UserSelfTy { impl_def_id, self_ty }) = user_self_ty {
1422             // In the case of `Foo<T>::method` and `<Foo<T>>::method`, if `method`
1423             // is inherent, there is no `Self` parameter; instead, the impl needs
1424             // type parameters, which we can infer by unifying the provided `Self`
1425             // with the substituted impl type.
1426             // This also occurs for an enum variant on a type alias.
1427             let ty = tcx.type_of(impl_def_id);
1428
1429             let impl_ty = self.instantiate_type_scheme(span, &substs, ty);
1430             match self.at(&self.misc(span), self.param_env).eq(impl_ty, self_ty) {
1431                 Ok(ok) => self.register_infer_ok_obligations(ok),
1432                 Err(_) => {
1433                     self.tcx.sess.delay_span_bug(
1434                         span,
1435                         &format!(
1436                         "instantiate_value_path: (UFCS) {:?} was a subtype of {:?} but now is not?",
1437                         self_ty,
1438                         impl_ty,
1439                     ),
1440                     );
1441                 }
1442             }
1443         }
1444
1445         debug!("instantiate_value_path: type of {:?} is {:?}", hir_id, ty_substituted);
1446         self.write_substs(hir_id, substs);
1447
1448         (ty_substituted, res)
1449     }
1450
1451     /// Add all the obligations that are required, substituting and normalized appropriately.
1452     crate fn add_required_obligations(&self, span: Span, def_id: DefId, substs: &SubstsRef<'tcx>) {
1453         self.add_required_obligations_with_code(
1454             span,
1455             def_id,
1456             substs,
1457             traits::ItemObligation(def_id),
1458         )
1459     }
1460
1461     #[tracing::instrument(level = "debug", skip(self, span, def_id, substs))]
1462     fn add_required_obligations_with_code(
1463         &self,
1464         span: Span,
1465         def_id: DefId,
1466         substs: &SubstsRef<'tcx>,
1467         code: ObligationCauseCode<'tcx>,
1468     ) {
1469         let (bounds, _) = self.instantiate_bounds(span, def_id, &substs);
1470
1471         for obligation in traits::predicates_for_generics(
1472             traits::ObligationCause::new(span, self.body_id, code),
1473             self.param_env,
1474             bounds,
1475         ) {
1476             self.register_predicate(obligation);
1477         }
1478     }
1479
1480     /// Resolves `typ` by a single level if `typ` is a type variable.
1481     /// If no resolution is possible, then an error is reported.
1482     /// Numeric inference variables may be left unresolved.
1483     pub fn structurally_resolved_type(&self, sp: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
1484         let ty = self.resolve_vars_with_obligations(ty);
1485         if !ty.is_ty_var() {
1486             ty
1487         } else {
1488             if !self.is_tainted_by_errors() {
1489                 self.emit_inference_failure_err((**self).body_id, sp, ty.into(), vec![], E0282)
1490                     .note("type must be known at this point")
1491                     .emit();
1492             }
1493             let err = self.tcx.ty_error();
1494             self.demand_suptype(sp, err, ty);
1495             err
1496         }
1497     }
1498
1499     pub(in super::super) fn with_breakable_ctxt<F: FnOnce() -> R, R>(
1500         &self,
1501         id: hir::HirId,
1502         ctxt: BreakableCtxt<'tcx>,
1503         f: F,
1504     ) -> (BreakableCtxt<'tcx>, R) {
1505         let index;
1506         {
1507             let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
1508             index = enclosing_breakables.stack.len();
1509             enclosing_breakables.by_id.insert(id, index);
1510             enclosing_breakables.stack.push(ctxt);
1511         }
1512         let result = f();
1513         let ctxt = {
1514             let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
1515             debug_assert!(enclosing_breakables.stack.len() == index + 1);
1516             enclosing_breakables.by_id.remove(&id).expect("missing breakable context");
1517             enclosing_breakables.stack.pop().expect("missing breakable context")
1518         };
1519         (ctxt, result)
1520     }
1521
1522     /// Instantiate a QueryResponse in a probe context, without a
1523     /// good ObligationCause.
1524     pub(in super::super) fn probe_instantiate_query_response(
1525         &self,
1526         span: Span,
1527         original_values: &OriginalQueryValues<'tcx>,
1528         query_result: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>,
1529     ) -> InferResult<'tcx, Ty<'tcx>> {
1530         self.instantiate_query_response_and_region_obligations(
1531             &traits::ObligationCause::misc(span, self.body_id),
1532             self.param_env,
1533             original_values,
1534             query_result,
1535         )
1536     }
1537
1538     /// Returns `true` if an expression is contained inside the LHS of an assignment expression.
1539     pub(in super::super) fn expr_in_place(&self, mut expr_id: hir::HirId) -> bool {
1540         let mut contained_in_place = false;
1541
1542         while let hir::Node::Expr(parent_expr) =
1543             self.tcx.hir().get(self.tcx.hir().get_parent_node(expr_id))
1544         {
1545             match &parent_expr.kind {
1546                 hir::ExprKind::Assign(lhs, ..) | hir::ExprKind::AssignOp(_, lhs, ..) => {
1547                     if lhs.hir_id == expr_id {
1548                         contained_in_place = true;
1549                         break;
1550                     }
1551                 }
1552                 _ => (),
1553             }
1554             expr_id = parent_expr.hir_id;
1555         }
1556
1557         contained_in_place
1558     }
1559 }