compiler/rustc_hir_typeck/src/method/probe.rs

   1 use super::suggest;
   2 use super::CandidateSource;
   3 use super::MethodError;
   4 use super::NoMatchData;
   5
   6 use crate::errors::MethodCallOnUnknownType;
   7 use crate::FnCtxt;
   8 use rustc_data_structures::fx::FxHashSet;
   9 use rustc_errors::Applicability;
  10 use rustc_hir as hir;
  11 use rustc_hir::def::DefKind;
  12 use rustc_hir_analysis::autoderef::{self, Autoderef};
  13 use rustc_infer::infer::canonical::OriginalQueryValues;
  14 use rustc_infer::infer::canonical::{Canonical, QueryResponse};
  15 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  16 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
  17 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
  18 use rustc_middle::middle::stability;
  19 use rustc_middle::ty::fast_reject::{simplify_type, TreatParams};
  20 use rustc_middle::ty::AssocItem;
  21 use rustc_middle::ty::GenericParamDefKind;
  22 use rustc_middle::ty::ToPredicate;
  23 use rustc_middle::ty::{self, ParamEnvAnd, Ty, TyCtxt, TypeFoldable, TypeVisitable};
  24 use rustc_middle::ty::{InternalSubsts, SubstsRef};
  25 use rustc_session::lint;
  26 use rustc_span::def_id::DefId;
  27 use rustc_span::def_id::LocalDefId;
  28 use rustc_span::lev_distance::{
  29     find_best_match_for_name_with_substrings, lev_distance_with_substrings,
  30 };
  31 use rustc_span::symbol::sym;
  32 use rustc_span::{symbol::Ident, Span, Symbol, DUMMY_SP};
  33 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
  34 use rustc_trait_selection::traits::query::method_autoderef::MethodAutoderefBadTy;
  35 use rustc_trait_selection::traits::query::method_autoderef::{
  36     CandidateStep, MethodAutoderefStepsResult,
  37 };
  38 use rustc_trait_selection::traits::query::CanonicalTyGoal;
  39 use rustc_trait_selection::traits::NormalizeExt;
  40 use rustc_trait_selection::traits::{self, ObligationCause};
  41 use std::cell::RefCell;
  42 use std::cmp::max;
  43 use std::iter;
  44 use std::ops::Deref;
  45
  46 use smallvec::{smallvec, SmallVec};
  47
  48 use self::CandidateKind::*;
  49 pub use self::PickKind::*;
  50
  51 /// Boolean flag used to indicate if this search is for a suggestion
  52 /// or not. If true, we can allow ambiguity and so forth.
  53 #[derive(Clone, Copy, Debug)]
  54 pub struct IsSuggestion(pub bool);
  55
  56 struct ProbeContext<'a, 'tcx> {
  57     fcx: &'a FnCtxt<'a, 'tcx>,
  58     span: Span,
  59     mode: Mode,
  60     method_name: Option<Ident>,
  61     return_type: Option<Ty<'tcx>>,
  62
  63     /// This is the OriginalQueryValues for the steps queries
  64     /// that are answered in steps.
  65     orig_steps_var_values: &'a OriginalQueryValues<'tcx>,
  66     steps: &'tcx [CandidateStep<'tcx>],
  67
  68     inherent_candidates: Vec<Candidate<'tcx>>,
  69     extension_candidates: Vec<Candidate<'tcx>>,
  70     impl_dups: FxHashSet<DefId>,
  71
  72     /// When probing for names, include names that are close to the
  73     /// requested name (by Levenshtein distance)
  74     allow_similar_names: bool,
  75
  76     /// Some(candidate) if there is a private candidate
  77     private_candidate: Option<(DefKind, DefId)>,
  78
  79     /// Collects near misses when the candidate functions are missing a `self` keyword and is only
  80     /// used for error reporting
  81     static_candidates: RefCell<Vec<CandidateSource>>,
  82
  83     /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
  84     /// for error reporting
  85     unsatisfied_predicates: RefCell<
  86         Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>, Option<ObligationCause<'tcx>>)>,
  87     >,
  88
  89     scope_expr_id: hir::HirId,
  90 }
  91
  92 impl<'a, 'tcx> Deref for ProbeContext<'a, 'tcx> {
  93     type Target = FnCtxt<'a, 'tcx>;
  94     fn deref(&self) -> &Self::Target {
  95         self.fcx
  96     }
  97 }
  98
  99 #[derive(Debug, Clone)]
 100 pub(crate) struct Candidate<'tcx> {
 101     // Candidates are (I'm not quite sure, but they are mostly) basically
 102     // some metadata on top of a `ty::AssocItem` (without substs).
 103     //
 104     // However, method probing wants to be able to evaluate the predicates
 105     // for a function with the substs applied - for example, if a function
 106     // has `where Self: Sized`, we don't want to consider it unless `Self`
 107     // is actually `Sized`, and similarly, return-type suggestions want
 108     // to consider the "actual" return type.
 109     //
 110     // The way this is handled is through `xform_self_ty`. It contains
 111     // the receiver type of this candidate, but `xform_self_ty`,
 112     // `xform_ret_ty` and `kind` (which contains the predicates) have the
 113     // generic parameters of this candidate substituted with the *same set*
 114     // of inference variables, which acts as some weird sort of "query".
 115     //
 116     // When we check out a candidate, we require `xform_self_ty` to be
 117     // a subtype of the passed-in self-type, and this equates the type
 118     // variables in the rest of the fields.
 119     //
 120     // For example, if we have this candidate:
 121     // ```
 122     //    trait Foo {
 123     //        fn foo(&self) where Self: Sized;
 124     //    }
 125     // ```
 126     //
 127     // Then `xform_self_ty` will be `&'erased ?X` and `kind` will contain
 128     // the predicate `?X: Sized`, so if we are evaluating `Foo` for a
 129     // the receiver `&T`, we'll do the subtyping which will make `?X`
 130     // get the right value, then when we evaluate the predicate we'll check
 131     // if `T: Sized`.
 132     xform_self_ty: Ty<'tcx>,
 133     xform_ret_ty: Option<Ty<'tcx>>,
 134     pub(crate) item: ty::AssocItem,
 135     pub(crate) kind: CandidateKind<'tcx>,
 136     pub(crate) import_ids: SmallVec<[LocalDefId; 1]>,
 137 }
 138
 139 #[derive(Debug, Clone)]
 140 pub(crate) enum CandidateKind<'tcx> {
 141     InherentImplCandidate(
 142         SubstsRef<'tcx>,
 143         // Normalize obligations
 144         Vec<traits::PredicateObligation<'tcx>>,
 145     ),
 146     ObjectCandidate,
 147     TraitCandidate(ty::TraitRef<'tcx>),
 148     WhereClauseCandidate(
 149         // Trait
 150         ty::PolyTraitRef<'tcx>,
 151     ),
 152 }
 153
 154 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
 155 enum ProbeResult {
 156     NoMatch,
 157     BadReturnType,
 158     Match,
 159 }
 160
 161 /// When adjusting a receiver we often want to do one of
 162 ///
 163 /// - Add a `&` (or `&mut`), converting the receiver from `T` to `&T` (or `&mut T`)
 164 /// - If the receiver has type `*mut T`, convert it to `*const T`
 165 ///
 166 /// This type tells us which one to do.
 167 ///
 168 /// Note that in principle we could do both at the same time. For example, when the receiver has
 169 /// type `T`, we could autoref it to `&T`, then convert to `*const T`. Or, when it has type `*mut
 170 /// T`, we could convert it to `*const T`, then autoref to `&*const T`. However, currently we do
 171 /// (at most) one of these. Either the receiver has type `T` and we convert it to `&T` (or with
 172 /// `mut`), or it has type `*mut T` and we convert it to `*const T`.
 173 #[derive(Debug, PartialEq, Copy, Clone)]
 174 pub enum AutorefOrPtrAdjustment {
 175     /// Receiver has type `T`, add `&` or `&mut` (it `T` is `mut`), and maybe also "unsize" it.
 176     /// Unsizing is used to convert a `[T; N]` to `[T]`, which only makes sense when autorefing.
 177     Autoref {
 178         mutbl: hir::Mutability,
 179
 180         /// Indicates that the source expression should be "unsized" to a target type.
 181         /// This is special-cased for just arrays unsizing to slices.
 182         unsize: bool,
 183     },
 184     /// Receiver has type `*mut T`, convert to `*const T`
 185     ToConstPtr,
 186 }
 187
 188 impl AutorefOrPtrAdjustment {
 189     fn get_unsize(&self) -> bool {
 190         match self {
 191             AutorefOrPtrAdjustment::Autoref { mutbl: _, unsize } => *unsize,
 192             AutorefOrPtrAdjustment::ToConstPtr => false,
 193         }
 194     }
 195 }
 196
 197 #[derive(Debug, Clone)]
 198 pub struct Pick<'tcx> {
 199     pub item: ty::AssocItem,
 200     pub kind: PickKind<'tcx>,
 201     pub import_ids: SmallVec<[LocalDefId; 1]>,
 202
 203     /// Indicates that the source expression should be autoderef'd N times
 204     /// ```ignore (not-rust)
 205     /// A = expr | *expr | **expr | ...
 206     /// ```
 207     pub autoderefs: usize,
 208
 209     /// Indicates that we want to add an autoref (and maybe also unsize it), or if the receiver is
 210     /// `*mut T`, convert it to `*const T`.
 211     pub autoref_or_ptr_adjustment: Option<AutorefOrPtrAdjustment>,
 212     pub self_ty: Ty<'tcx>,
 213
 214     /// Unstable candidates alongside the stable ones.
 215     unstable_candidates: Vec<(Candidate<'tcx>, Symbol)>,
 216 }
 217
 218 #[derive(Clone, Debug, PartialEq, Eq)]
 219 pub enum PickKind<'tcx> {
 220     InherentImplPick,
 221     ObjectPick,
 222     TraitPick,
 223     WhereClausePick(
 224         // Trait
 225         ty::PolyTraitRef<'tcx>,
 226     ),
 227 }
 228
 229 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
 230
 231 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
 232 pub enum Mode {
 233     // An expression of the form `receiver.method_name(...)`.
 234     // Autoderefs are performed on `receiver`, lookup is done based on the
 235     // `self` argument of the method, and static methods aren't considered.
 236     MethodCall,
 237     // An expression of the form `Type::item` or `<T>::item`.
 238     // No autoderefs are performed, lookup is done based on the type each
 239     // implementation is for, and static methods are included.
 240     Path,
 241 }
 242
 243 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
 244 pub enum ProbeScope {
 245     // Assemble candidates coming only from traits in scope.
 246     TraitsInScope,
 247
 248     // Assemble candidates coming from all traits.
 249     AllTraits,
 250 }
 251
 252 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 253     /// This is used to offer suggestions to users. It returns methods
 254     /// that could have been called which have the desired return
 255     /// type. Some effort is made to rule out methods that, if called,
 256     /// would result in an error (basically, the same criteria we
 257     /// would use to decide if a method is a plausible fit for
 258     /// ambiguity purposes).
 259     #[instrument(level = "debug", skip(self, candidate_filter))]
 260     pub fn probe_for_return_type(
 261         &self,
 262         span: Span,
 263         mode: Mode,
 264         return_type: Ty<'tcx>,
 265         self_ty: Ty<'tcx>,
 266         scope_expr_id: hir::HirId,
 267         candidate_filter: impl Fn(&ty::AssocItem) -> bool,
 268     ) -> Vec<ty::AssocItem> {
 269         let method_names = self
 270             .probe_op(
 271                 span,
 272                 mode,
 273                 None,
 274                 Some(return_type),
 275                 IsSuggestion(true),
 276                 self_ty,
 277                 scope_expr_id,
 278                 ProbeScope::AllTraits,
 279                 |probe_cx| Ok(probe_cx.candidate_method_names(candidate_filter)),
 280             )
 281             .unwrap_or_default();
 282         method_names
 283             .iter()
 284             .flat_map(|&method_name| {
 285                 self.probe_op(
 286                     span,
 287                     mode,
 288                     Some(method_name),
 289                     Some(return_type),
 290                     IsSuggestion(true),
 291                     self_ty,
 292                     scope_expr_id,
 293                     ProbeScope::AllTraits,
 294                     |probe_cx| probe_cx.pick(),
 295                 )
 296                 .ok()
 297                 .map(|pick| pick.item)
 298             })
 299             .collect()
 300     }
 301
 302     #[instrument(level = "debug", skip(self))]
 303     pub fn probe_for_name(
 304         &self,
 305         mode: Mode,
 306         item_name: Ident,
 307         return_type: Option<Ty<'tcx>>,
 308         is_suggestion: IsSuggestion,
 309         self_ty: Ty<'tcx>,
 310         scope_expr_id: hir::HirId,
 311         scope: ProbeScope,
 312     ) -> PickResult<'tcx> {
 313         self.probe_op(
 314             item_name.span,
 315             mode,
 316             Some(item_name),
 317             return_type,
 318             is_suggestion,
 319             self_ty,
 320             scope_expr_id,
 321             scope,
 322             |probe_cx| probe_cx.pick(),
 323         )
 324     }
 325
 326     #[instrument(level = "debug", skip(self))]
 327     pub(crate) fn probe_for_name_many(
 328         &self,
 329         mode: Mode,
 330         item_name: Ident,
 331         return_type: Option<Ty<'tcx>>,
 332         is_suggestion: IsSuggestion,
 333         self_ty: Ty<'tcx>,
 334         scope_expr_id: hir::HirId,
 335         scope: ProbeScope,
 336     ) -> Vec<Candidate<'tcx>> {
 337         self.probe_op(
 338             item_name.span,
 339             mode,
 340             Some(item_name),
 341             return_type,
 342             is_suggestion,
 343             self_ty,
 344             scope_expr_id,
 345             scope,
 346             |probe_cx| {
 347                 Ok(probe_cx
 348                     .inherent_candidates
 349                     .into_iter()
 350                     .chain(probe_cx.extension_candidates)
 351                     .collect())
 352             },
 353         )
 354         .unwrap()
 355     }
 356
 357     fn probe_op<OP, R>(
 358         &'a self,
 359         span: Span,
 360         mode: Mode,
 361         method_name: Option<Ident>,
 362         return_type: Option<Ty<'tcx>>,
 363         is_suggestion: IsSuggestion,
 364         self_ty: Ty<'tcx>,
 365         scope_expr_id: hir::HirId,
 366         scope: ProbeScope,
 367         op: OP,
 368     ) -> Result<R, MethodError<'tcx>>
 369     where
 370         OP: FnOnce(ProbeContext<'_, 'tcx>) -> Result<R, MethodError<'tcx>>,
 371     {
 372         let mut orig_values = OriginalQueryValues::default();
 373         let param_env_and_self_ty = self.canonicalize_query(
 374             ParamEnvAnd { param_env: self.param_env, value: self_ty },
 375             &mut orig_values,
 376         );
 377
 378         let steps = match mode {
 379             Mode::MethodCall => self.tcx.method_autoderef_steps(param_env_and_self_ty),
 380             Mode::Path => self.probe(|_| {
 381                 // Mode::Path - the deref steps is "trivial". This turns
 382                 // our CanonicalQuery into a "trivial" QueryResponse. This
 383                 // is a bit inefficient, but I don't think that writing
 384                 // special handling for this "trivial case" is a good idea.
 385
 386                 let infcx = &self.infcx;
 387                 let (ParamEnvAnd { param_env: _, value: self_ty }, canonical_inference_vars) =
 388                     infcx.instantiate_canonical_with_fresh_inference_vars(
 389                         span,
 390                         &param_env_and_self_ty,
 391                     );
 392                 debug!(
 393                     "probe_op: Mode::Path, param_env_and_self_ty={:?} self_ty={:?}",
 394                     param_env_and_self_ty, self_ty
 395                 );
 396                 MethodAutoderefStepsResult {
 397                     steps: infcx.tcx.arena.alloc_from_iter([CandidateStep {
 398                         self_ty: self.make_query_response_ignoring_pending_obligations(
 399                             canonical_inference_vars,
 400                             self_ty,
 401                         ),
 402                         autoderefs: 0,
 403                         from_unsafe_deref: false,
 404                         unsize: false,
 405                     }]),
 406                     opt_bad_ty: None,
 407                     reached_recursion_limit: false,
 408                 }
 409             }),
 410         };
 411
 412         // If our autoderef loop had reached the recursion limit,
 413         // report an overflow error, but continue going on with
 414         // the truncated autoderef list.
 415         if steps.reached_recursion_limit {
 416             self.probe(|_| {
 417                 let ty = &steps
 418                     .steps
 419                     .last()
 420                     .unwrap_or_else(|| span_bug!(span, "reached the recursion limit in 0 steps?"))
 421                     .self_ty;
 422                 let ty = self
 423                     .probe_instantiate_query_response(span, &orig_values, ty)
 424                     .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
 425                 autoderef::report_autoderef_recursion_limit_error(self.tcx, span, ty.value);
 426             });
 427         }
 428
 429         // If we encountered an `_` type or an error type during autoderef, this is
 430         // ambiguous.
 431         if let Some(bad_ty) = &steps.opt_bad_ty {
 432             if is_suggestion.0 {
 433                 // Ambiguity was encountered during a suggestion. Just keep going.
 434                 debug!("ProbeContext: encountered ambiguity in suggestion");
 435             } else if bad_ty.reached_raw_pointer && !self.tcx.features().arbitrary_self_types {
 436                 // this case used to be allowed by the compiler,
 437                 // so we do a future-compat lint here for the 2015 edition
 438                 // (see https://github.com/rust-lang/rust/issues/46906)
 439                 if self.tcx.sess.rust_2018() {
 440                     self.tcx.sess.emit_err(MethodCallOnUnknownType { span });
 441                 } else {
 442                     self.tcx.struct_span_lint_hir(
 443                         lint::builtin::TYVAR_BEHIND_RAW_POINTER,
 444                         scope_expr_id,
 445                         span,
 446                         "type annotations needed",
 447                         |lint| lint,
 448                     );
 449                 }
 450             } else {
 451                 // Encountered a real ambiguity, so abort the lookup. If `ty` is not
 452                 // an `Err`, report the right "type annotations needed" error pointing
 453                 // to it.
 454                 let ty = &bad_ty.ty;
 455                 let ty = self
 456                     .probe_instantiate_query_response(span, &orig_values, ty)
 457                     .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
 458                 let ty = self.structurally_resolved_type(span, ty.value);
 459                 assert!(matches!(ty.kind(), ty::Error(_)));
 460                 return Err(MethodError::NoMatch(NoMatchData {
 461                     static_candidates: Vec::new(),
 462                     unsatisfied_predicates: Vec::new(),
 463                     out_of_scope_traits: Vec::new(),
 464                     similar_candidate: None,
 465                     mode,
 466                 }));
 467             }
 468         }
 469
 470         debug!("ProbeContext: steps for self_ty={:?} are {:?}", self_ty, steps);
 471
 472         // this creates one big transaction so that all type variables etc
 473         // that we create during the probe process are removed later
 474         self.probe(|_| {
 475             let mut probe_cx = ProbeContext::new(
 476                 self,
 477                 span,
 478                 mode,
 479                 method_name,
 480                 return_type,
 481                 &orig_values,
 482                 steps.steps,
 483                 scope_expr_id,
 484             );
 485
 486             probe_cx.assemble_inherent_candidates();
 487             match scope {
 488                 ProbeScope::TraitsInScope => {
 489                     probe_cx.assemble_extension_candidates_for_traits_in_scope()
 490                 }
 491                 ProbeScope::AllTraits => probe_cx.assemble_extension_candidates_for_all_traits(),
 492             };
 493             op(probe_cx)
 494         })
 495     }
 496 }
 497
 498 pub fn provide(providers: &mut ty::query::Providers) {
 499     providers.method_autoderef_steps = method_autoderef_steps;
 500 }
 501
 502 fn method_autoderef_steps<'tcx>(
 503     tcx: TyCtxt<'tcx>,
 504     goal: CanonicalTyGoal<'tcx>,
 505 ) -> MethodAutoderefStepsResult<'tcx> {
 506     debug!("method_autoderef_steps({:?})", goal);
 507
 508     let (ref infcx, goal, inference_vars) = tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &goal);
 509     let ParamEnvAnd { param_env, value: self_ty } = goal;
 510
 511     let mut autoderef =
 512         Autoderef::new(infcx, param_env, hir::def_id::CRATE_DEF_ID, DUMMY_SP, self_ty)
 513             .include_raw_pointers()
 514             .silence_errors();
 515     let mut reached_raw_pointer = false;
 516     let mut steps: Vec<_> = autoderef
 517         .by_ref()
 518         .map(|(ty, d)| {
 519             let step = CandidateStep {
 520                 self_ty: infcx
 521                     .make_query_response_ignoring_pending_obligations(inference_vars.clone(), ty),
 522                 autoderefs: d,
 523                 from_unsafe_deref: reached_raw_pointer,
 524                 unsize: false,
 525             };
 526             if let ty::RawPtr(_) = ty.kind() {
 527                 // all the subsequent steps will be from_unsafe_deref
 528                 reached_raw_pointer = true;
 529             }
 530             step
 531         })
 532         .collect();
 533
 534     let final_ty = autoderef.final_ty(true);
 535     let opt_bad_ty = match final_ty.kind() {
 536         ty::Infer(ty::TyVar(_)) | ty::Error(_) => Some(MethodAutoderefBadTy {
 537             reached_raw_pointer,
 538             ty: infcx.make_query_response_ignoring_pending_obligations(inference_vars, final_ty),
 539         }),
 540         ty::Array(elem_ty, _) => {
 541             let dereferences = steps.len() - 1;
 542
 543             steps.push(CandidateStep {
 544                 self_ty: infcx.make_query_response_ignoring_pending_obligations(
 545                     inference_vars,
 546                     infcx.tcx.mk_slice(*elem_ty),
 547                 ),
 548                 autoderefs: dereferences,
 549                 // this could be from an unsafe deref if we had
 550                 // a *mut/const [T; N]
 551                 from_unsafe_deref: reached_raw_pointer,
 552                 unsize: true,
 553             });
 554
 555             None
 556         }
 557         _ => None,
 558     };
 559
 560     debug!("method_autoderef_steps: steps={:?} opt_bad_ty={:?}", steps, opt_bad_ty);
 561
 562     MethodAutoderefStepsResult {
 563         steps: tcx.arena.alloc_from_iter(steps),
 564         opt_bad_ty: opt_bad_ty.map(|ty| &*tcx.arena.alloc(ty)),
 565         reached_recursion_limit: autoderef.reached_recursion_limit(),
 566     }
 567 }
 568
 569 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
 570     fn new(
 571         fcx: &'a FnCtxt<'a, 'tcx>,
 572         span: Span,
 573         mode: Mode,
 574         method_name: Option<Ident>,
 575         return_type: Option<Ty<'tcx>>,
 576         orig_steps_var_values: &'a OriginalQueryValues<'tcx>,
 577         steps: &'tcx [CandidateStep<'tcx>],
 578         scope_expr_id: hir::HirId,
 579     ) -> ProbeContext<'a, 'tcx> {
 580         ProbeContext {
 581             fcx,
 582             span,
 583             mode,
 584             method_name,
 585             return_type,
 586             inherent_candidates: Vec::new(),
 587             extension_candidates: Vec::new(),
 588             impl_dups: FxHashSet::default(),
 589             orig_steps_var_values,
 590             steps,
 591             allow_similar_names: false,
 592             private_candidate: None,
 593             static_candidates: RefCell::new(Vec::new()),
 594             unsatisfied_predicates: RefCell::new(Vec::new()),
 595             scope_expr_id,
 596         }
 597     }
 598
 599     fn reset(&mut self) {
 600         self.inherent_candidates.clear();
 601         self.extension_candidates.clear();
 602         self.impl_dups.clear();
 603         self.private_candidate = None;
 604         self.static_candidates.borrow_mut().clear();
 605         self.unsatisfied_predicates.borrow_mut().clear();
 606     }
 607
 608     ///////////////////////////////////////////////////////////////////////////
 609     // CANDIDATE ASSEMBLY
 610
 611     fn push_candidate(&mut self, candidate: Candidate<'tcx>, is_inherent: bool) {
 612         let is_accessible = if let Some(name) = self.method_name {
 613             let item = candidate.item;
 614             let hir_id = self.tcx.hir().local_def_id_to_hir_id(self.body_id);
 615             let def_scope =
 616                 self.tcx.adjust_ident_and_get_scope(name, item.container_id(self.tcx), hir_id).1;
 617             item.visibility(self.tcx).is_accessible_from(def_scope, self.tcx)
 618         } else {
 619             true
 620         };
 621         if is_accessible {
 622             if is_inherent {
 623                 self.inherent_candidates.push(candidate);
 624             } else {
 625                 self.extension_candidates.push(candidate);
 626             }
 627         } else if self.private_candidate.is_none() {
 628             self.private_candidate =
 629                 Some((candidate.item.kind.as_def_kind(), candidate.item.def_id));
 630         }
 631     }
 632
 633     fn assemble_inherent_candidates(&mut self) {
 634         for step in self.steps.iter() {
 635             self.assemble_probe(&step.self_ty);
 636         }
 637     }
 638
 639     fn assemble_probe(&mut self, self_ty: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>) {
 640         debug!("assemble_probe: self_ty={:?}", self_ty);
 641         let raw_self_ty = self_ty.value.value;
 642         match *raw_self_ty.kind() {
 643             ty::Dynamic(data, ..) if let Some(p) = data.principal() => {
 644                 // Subtle: we can't use `instantiate_query_response` here: using it will
 645                 // commit to all of the type equalities assumed by inference going through
 646                 // autoderef (see the `method-probe-no-guessing` test).
 647                 //
 648                 // However, in this code, it is OK if we end up with an object type that is
 649                 // "more general" than the object type that we are evaluating. For *every*
 650                 // object type `MY_OBJECT`, a function call that goes through a trait-ref
 651                 // of the form `<MY_OBJECT as SuperTraitOf(MY_OBJECT)>::func` is a valid
 652                 // `ObjectCandidate`, and it should be discoverable "exactly" through one
 653                 // of the iterations in the autoderef loop, so there is no problem with it
 654                 // being discoverable in another one of these iterations.
 655                 //
 656                 // Using `instantiate_canonical_with_fresh_inference_vars` on our
 657                 // `Canonical<QueryResponse<Ty<'tcx>>>` and then *throwing away* the
 658                 // `CanonicalVarValues` will exactly give us such a generalization - it
 659                 // will still match the original object type, but it won't pollute our
 660                 // type variables in any form, so just do that!
 661                 let (QueryResponse { value: generalized_self_ty, .. }, _ignored_var_values) =
 662                     self.fcx
 663                         .instantiate_canonical_with_fresh_inference_vars(self.span, self_ty);
 664
 665                 self.assemble_inherent_candidates_from_object(generalized_self_ty);
 666                 self.assemble_inherent_impl_candidates_for_type(p.def_id());
 667                 if self.tcx.has_attr(p.def_id(), sym::rustc_has_incoherent_inherent_impls) {
 668                     self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
 669                 }
 670             }
 671             ty::Adt(def, _) => {
 672                 let def_id = def.did();
 673                 self.assemble_inherent_impl_candidates_for_type(def_id);
 674                 if self.tcx.has_attr(def_id, sym::rustc_has_incoherent_inherent_impls) {
 675                     self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
 676                 }
 677             }
 678             ty::Foreign(did) => {
 679                 self.assemble_inherent_impl_candidates_for_type(did);
 680                 if self.tcx.has_attr(did, sym::rustc_has_incoherent_inherent_impls) {
 681                     self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
 682                 }
 683             }
 684             ty::Param(p) => {
 685                 self.assemble_inherent_candidates_from_param(p);
 686             }
 687             ty::Bool
 688             | ty::Char
 689             | ty::Int(_)
 690             | ty::Uint(_)
 691             | ty::Float(_)
 692             | ty::Str
 693             | ty::Array(..)
 694             | ty::Slice(_)
 695             | ty::RawPtr(_)
 696             | ty::Ref(..)
 697             | ty::Never
 698             | ty::Tuple(..) => self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty),
 699             _ => {}
 700         }
 701     }
 702
 703     fn assemble_inherent_candidates_for_incoherent_ty(&mut self, self_ty: Ty<'tcx>) {
 704         let Some(simp) = simplify_type(self.tcx, self_ty, TreatParams::AsInfer) else {
 705             bug!("unexpected incoherent type: {:?}", self_ty)
 706         };
 707         for &impl_def_id in self.tcx.incoherent_impls(simp) {
 708             self.assemble_inherent_impl_probe(impl_def_id);
 709         }
 710     }
 711
 712     fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
 713         let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id);
 714         for &impl_def_id in impl_def_ids.iter() {
 715             self.assemble_inherent_impl_probe(impl_def_id);
 716         }
 717     }
 718
 719     fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
 720         if !self.impl_dups.insert(impl_def_id) {
 721             return; // already visited
 722         }
 723
 724         debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
 725
 726         for item in self.impl_or_trait_item(impl_def_id) {
 727             if !self.has_applicable_self(&item) {
 728                 // No receiver declared. Not a candidate.
 729                 self.record_static_candidate(CandidateSource::Impl(impl_def_id));
 730                 continue;
 731             }
 732
 733             let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
 734             let impl_ty = impl_ty.subst(self.tcx, impl_substs);
 735
 736             debug!("impl_ty: {:?}", impl_ty);
 737
 738             // Determine the receiver type that the method itself expects.
 739             let (xform_self_ty, xform_ret_ty) = self.xform_self_ty(&item, impl_ty, impl_substs);
 740             debug!("xform_self_ty: {:?}, xform_ret_ty: {:?}", xform_self_ty, xform_ret_ty);
 741
 742             // We can't use normalize_associated_types_in as it will pollute the
 743             // fcx's fulfillment context after this probe is over.
 744             // Note: we only normalize `xform_self_ty` here since the normalization
 745             // of the return type can lead to inference results that prohibit
 746             // valid candidates from being found, see issue #85671
 747             // FIXME Postponing the normalization of the return type likely only hides a deeper bug,
 748             // which might be caused by the `param_env` itself. The clauses of the `param_env`
 749             // maybe shouldn't include `Param`s, but rather fresh variables or be canonicalized,
 750             // see issue #89650
 751             let cause = traits::ObligationCause::misc(self.span, self.body_id);
 752             let InferOk { value: xform_self_ty, obligations } =
 753                 self.fcx.at(&cause, self.param_env).normalize(xform_self_ty);
 754
 755             debug!(
 756                 "assemble_inherent_impl_probe after normalization: xform_self_ty = {:?}/{:?}",
 757                 xform_self_ty, xform_ret_ty
 758             );
 759
 760             self.push_candidate(
 761                 Candidate {
 762                     xform_self_ty,
 763                     xform_ret_ty,
 764                     item,
 765                     kind: InherentImplCandidate(impl_substs, obligations),
 766                     import_ids: smallvec![],
 767                 },
 768                 true,
 769             );
 770         }
 771     }
 772
 773     fn assemble_inherent_candidates_from_object(&mut self, self_ty: Ty<'tcx>) {
 774         debug!("assemble_inherent_candidates_from_object(self_ty={:?})", self_ty);
 775
 776         let principal = match self_ty.kind() {
 777             ty::Dynamic(ref data, ..) => Some(data),
 778             _ => None,
 779         }
 780         .and_then(|data| data.principal())
 781         .unwrap_or_else(|| {
 782             span_bug!(
 783                 self.span,
 784                 "non-object {:?} in assemble_inherent_candidates_from_object",
 785                 self_ty
 786             )
 787         });
 788
 789         // It is illegal to invoke a method on a trait instance that refers to
 790         // the `Self` type. An [`ObjectSafetyViolation::SupertraitSelf`] error
 791         // will be reported by `object_safety.rs` if the method refers to the
 792         // `Self` type anywhere other than the receiver. Here, we use a
 793         // substitution that replaces `Self` with the object type itself. Hence,
 794         // a `&self` method will wind up with an argument type like `&dyn Trait`.
 795         let trait_ref = principal.with_self_ty(self.tcx, self_ty);
 796         self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
 797             let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
 798
 799             let (xform_self_ty, xform_ret_ty) =
 800                 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
 801             this.push_candidate(
 802                 Candidate {
 803                     xform_self_ty,
 804                     xform_ret_ty,
 805                     item,
 806                     kind: ObjectCandidate,
 807                     import_ids: smallvec![],
 808                 },
 809                 true,
 810             );
 811         });
 812     }
 813
 814     fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) {
 815         // FIXME: do we want to commit to this behavior for param bounds?
 816         debug!("assemble_inherent_candidates_from_param(param_ty={:?})", param_ty);
 817
 818         let bounds = self.param_env.caller_bounds().iter().filter_map(|predicate| {
 819             let bound_predicate = predicate.kind();
 820             match bound_predicate.skip_binder() {
 821                 ty::PredicateKind::Clause(ty::Clause::Trait(trait_predicate)) => {
 822                     match *trait_predicate.trait_ref.self_ty().kind() {
 823                         ty::Param(p) if p == param_ty => {
 824                             Some(bound_predicate.rebind(trait_predicate.trait_ref))
 825                         }
 826                         _ => None,
 827                     }
 828                 }
 829                 ty::PredicateKind::Subtype(..)
 830                 | ty::PredicateKind::Coerce(..)
 831                 | ty::PredicateKind::Clause(ty::Clause::Projection(..))
 832                 | ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
 833                 | ty::PredicateKind::WellFormed(..)
 834                 | ty::PredicateKind::ObjectSafe(..)
 835                 | ty::PredicateKind::ClosureKind(..)
 836                 | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..))
 837                 | ty::PredicateKind::ConstEvaluatable(..)
 838                 | ty::PredicateKind::ConstEquate(..)
 839                 | ty::PredicateKind::Ambiguous
 840                 | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
 841             }
 842         });
 843
 844         self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
 845             let trait_ref = this.erase_late_bound_regions(poly_trait_ref);
 846
 847             let (xform_self_ty, xform_ret_ty) =
 848                 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
 849
 850             // Because this trait derives from a where-clause, it
 851             // should not contain any inference variables or other
 852             // artifacts. This means it is safe to put into the
 853             // `WhereClauseCandidate` and (eventually) into the
 854             // `WhereClausePick`.
 855             assert!(!trait_ref.substs.needs_infer());
 856
 857             this.push_candidate(
 858                 Candidate {
 859                     xform_self_ty,
 860                     xform_ret_ty,
 861                     item,
 862                     kind: WhereClauseCandidate(poly_trait_ref),
 863                     import_ids: smallvec![],
 864                 },
 865                 true,
 866             );
 867         });
 868     }
 869
 870     // Do a search through a list of bounds, using a callback to actually
 871     // create the candidates.
 872     fn elaborate_bounds<F>(
 873         &mut self,
 874         bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
 875         mut mk_cand: F,
 876     ) where
 877         F: for<'b> FnMut(&mut ProbeContext<'b, 'tcx>, ty::PolyTraitRef<'tcx>, ty::AssocItem),
 878     {
 879         let tcx = self.tcx;
 880         for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
 881             debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
 882             for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
 883                 if !self.has_applicable_self(&item) {
 884                     self.record_static_candidate(CandidateSource::Trait(bound_trait_ref.def_id()));
 885                 } else {
 886                     mk_cand(self, bound_trait_ref, item);
 887                 }
 888             }
 889         }
 890     }
 891
 892     fn assemble_extension_candidates_for_traits_in_scope(&mut self) {
 893         let mut duplicates = FxHashSet::default();
 894         let opt_applicable_traits = self.tcx.in_scope_traits(self.scope_expr_id);
 895         if let Some(applicable_traits) = opt_applicable_traits {
 896             for trait_candidate in applicable_traits.iter() {
 897                 let trait_did = trait_candidate.def_id;
 898                 if duplicates.insert(trait_did) {
 899                     self.assemble_extension_candidates_for_trait(
 900                         &trait_candidate.import_ids,
 901                         trait_did,
 902                     );
 903                 }
 904             }
 905         }
 906     }
 907
 908     fn assemble_extension_candidates_for_all_traits(&mut self) {
 909         let mut duplicates = FxHashSet::default();
 910         for trait_info in suggest::all_traits(self.tcx) {
 911             if duplicates.insert(trait_info.def_id) {
 912                 self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id);
 913             }
 914         }
 915     }
 916
 917     fn matches_return_type(
 918         &self,
 919         method: &ty::AssocItem,
 920         self_ty: Option<Ty<'tcx>>,
 921         expected: Ty<'tcx>,
 922     ) -> bool {
 923         match method.kind {
 924             ty::AssocKind::Fn => {
 925                 let fty = self.tcx.bound_fn_sig(method.def_id);
 926                 self.probe(|_| {
 927                     let substs = self.fresh_substs_for_item(self.span, method.def_id);
 928                     let fty = fty.subst(self.tcx, substs);
 929                     let fty =
 930                         self.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, fty);
 931
 932                     if let Some(self_ty) = self_ty {
 933                         if self
 934                             .at(&ObligationCause::dummy(), self.param_env)
 935                             .sup(fty.inputs()[0], self_ty)
 936                             .is_err()
 937                         {
 938                             return false;
 939                         }
 940                     }
 941                     self.can_sub(self.param_env, fty.output(), expected).is_ok()
 942                 })
 943             }
 944             _ => false,
 945         }
 946     }
 947
 948     fn assemble_extension_candidates_for_trait(
 949         &mut self,
 950         import_ids: &SmallVec<[LocalDefId; 1]>,
 951         trait_def_id: DefId,
 952     ) {
 953         debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
 954         let trait_substs = self.fresh_item_substs(trait_def_id);
 955         let trait_ref = self.tcx.mk_trait_ref(trait_def_id, trait_substs);
 956
 957         if self.tcx.is_trait_alias(trait_def_id) {
 958             // For trait aliases, assume all supertraits are relevant.
 959             let bounds = iter::once(ty::Binder::dummy(trait_ref));
 960             self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
 961                 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
 962
 963                 let (xform_self_ty, xform_ret_ty) =
 964                     this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
 965                 this.push_candidate(
 966                     Candidate {
 967                         xform_self_ty,
 968                         xform_ret_ty,
 969                         item,
 970                         import_ids: import_ids.clone(),
 971                         kind: TraitCandidate(new_trait_ref),
 972                     },
 973                     false,
 974                 );
 975             });
 976         } else {
 977             debug_assert!(self.tcx.is_trait(trait_def_id));
 978             if self.tcx.trait_is_auto(trait_def_id) {
 979                 return;
 980             }
 981             for item in self.impl_or_trait_item(trait_def_id) {
 982                 // Check whether `trait_def_id` defines a method with suitable name.
 983                 if !self.has_applicable_self(&item) {
 984                     debug!("method has inapplicable self");
 985                     self.record_static_candidate(CandidateSource::Trait(trait_def_id));
 986                     continue;
 987                 }
 988
 989                 let (xform_self_ty, xform_ret_ty) =
 990                     self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
 991                 self.push_candidate(
 992                     Candidate {
 993                         xform_self_ty,
 994                         xform_ret_ty,
 995                         item,
 996                         import_ids: import_ids.clone(),
 997                         kind: TraitCandidate(trait_ref),
 998                     },
 999                     false,
1000                 );
1001             }
1002         }
1003     }
1004
1005     fn candidate_method_names(
1006         &self,
1007         candidate_filter: impl Fn(&ty::AssocItem) -> bool,
1008     ) -> Vec<Ident> {
1009         let mut set = FxHashSet::default();
1010         let mut names: Vec<_> = self
1011             .inherent_candidates
1012             .iter()
1013             .chain(&self.extension_candidates)
1014             .filter(|candidate| candidate_filter(&candidate.item))
1015             .filter(|candidate| {
1016                 if let Some(return_ty) = self.return_type {
1017                     self.matches_return_type(&candidate.item, None, return_ty)
1018                 } else {
1019                     true
1020                 }
1021             })
1022             .map(|candidate| candidate.item.ident(self.tcx))
1023             .filter(|&name| set.insert(name))
1024             .collect();
1025
1026         // Sort them by the name so we have a stable result.
1027         names.sort_by(|a, b| a.as_str().partial_cmp(b.as_str()).unwrap());
1028         names
1029     }
1030
1031     ///////////////////////////////////////////////////////////////////////////
1032     // THE ACTUAL SEARCH
1033
1034     fn pick(mut self) -> PickResult<'tcx> {
1035         assert!(self.method_name.is_some());
1036
1037         if let Some(r) = self.pick_core() {
1038             return r;
1039         }
1040
1041         debug!("pick: actual search failed, assemble diagnostics");
1042
1043         let static_candidates = std::mem::take(self.static_candidates.get_mut());
1044         let private_candidate = self.private_candidate.take();
1045         let unsatisfied_predicates = std::mem::take(self.unsatisfied_predicates.get_mut());
1046
1047         // things failed, so lets look at all traits, for diagnostic purposes now:
1048         self.reset();
1049
1050         let span = self.span;
1051         let tcx = self.tcx;
1052
1053         self.assemble_extension_candidates_for_all_traits();
1054
1055         let out_of_scope_traits = match self.pick_core() {
1056             Some(Ok(p)) => vec![p.item.container_id(self.tcx)],
1057             Some(Err(MethodError::Ambiguity(v))) => v
1058                 .into_iter()
1059                 .map(|source| match source {
1060                     CandidateSource::Trait(id) => id,
1061                     CandidateSource::Impl(impl_id) => match tcx.trait_id_of_impl(impl_id) {
1062                         Some(id) => id,
1063                         None => span_bug!(span, "found inherent method when looking at traits"),
1064                     },
1065                 })
1066                 .collect(),
1067             Some(Err(MethodError::NoMatch(NoMatchData {
1068                 out_of_scope_traits: others, ..
1069             }))) => {
1070                 assert!(others.is_empty());
1071                 vec![]
1072             }
1073             _ => vec![],
1074         };
1075
1076         if let Some((kind, def_id)) = private_candidate {
1077             return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
1078         }
1079         let similar_candidate = self.probe_for_similar_candidate()?;
1080
1081         Err(MethodError::NoMatch(NoMatchData {
1082             static_candidates,
1083             unsatisfied_predicates,
1084             out_of_scope_traits,
1085             similar_candidate,
1086             mode: self.mode,
1087         }))
1088     }
1089
1090     fn pick_core(&self) -> Option<PickResult<'tcx>> {
1091         let pick = self.pick_all_method(Some(&mut vec![]));
1092
1093         // In this case unstable picking is done by `pick_method`.
1094         if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1095             return pick;
1096         }
1097
1098         if pick.is_none() {
1099             return self.pick_all_method(None);
1100         }
1101         pick
1102     }
1103
1104     fn pick_all_method(
1105         &self,
1106         mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1107     ) -> Option<PickResult<'tcx>> {
1108         self.steps
1109             .iter()
1110             .filter(|step| {
1111                 debug!("pick_all_method: step={:?}", step);
1112                 // skip types that are from a type error or that would require dereferencing
1113                 // a raw pointer
1114                 !step.self_ty.references_error() && !step.from_unsafe_deref
1115             })
1116             .find_map(|step| {
1117                 let InferOk { value: self_ty, obligations: _ } = self
1118                     .fcx
1119                     .probe_instantiate_query_response(
1120                         self.span,
1121                         &self.orig_steps_var_values,
1122                         &step.self_ty,
1123                     )
1124                     .unwrap_or_else(|_| {
1125                         span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1126                     });
1127                 self.pick_by_value_method(step, self_ty, unstable_candidates.as_deref_mut())
1128                     .or_else(|| {
1129                         self.pick_autorefd_method(
1130                             step,
1131                             self_ty,
1132                             hir::Mutability::Not,
1133                             unstable_candidates.as_deref_mut(),
1134                         )
1135                         .or_else(|| {
1136                             self.pick_autorefd_method(
1137                                 step,
1138                                 self_ty,
1139                                 hir::Mutability::Mut,
1140                                 unstable_candidates.as_deref_mut(),
1141                             )
1142                         })
1143                         .or_else(|| {
1144                             self.pick_const_ptr_method(
1145                                 step,
1146                                 self_ty,
1147                                 unstable_candidates.as_deref_mut(),
1148                             )
1149                         })
1150                     })
1151             })
1152     }
1153
1154     /// For each type `T` in the step list, this attempts to find a method where
1155     /// the (transformed) self type is exactly `T`. We do however do one
1156     /// transformation on the adjustment: if we are passing a region pointer in,
1157     /// we will potentially *reborrow* it to a shorter lifetime. This allows us
1158     /// to transparently pass `&mut` pointers, in particular, without consuming
1159     /// them for their entire lifetime.
1160     fn pick_by_value_method(
1161         &self,
1162         step: &CandidateStep<'tcx>,
1163         self_ty: Ty<'tcx>,
1164         unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1165     ) -> Option<PickResult<'tcx>> {
1166         if step.unsize {
1167             return None;
1168         }
1169
1170         self.pick_method(self_ty, unstable_candidates).map(|r| {
1171             r.map(|mut pick| {
1172                 pick.autoderefs = step.autoderefs;
1173
1174                 // Insert a `&*` or `&mut *` if this is a reference type:
1175                 if let ty::Ref(_, _, mutbl) = *step.self_ty.value.value.kind() {
1176                     pick.autoderefs += 1;
1177                     pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
1178                         mutbl,
1179                         unsize: pick.autoref_or_ptr_adjustment.map_or(false, |a| a.get_unsize()),
1180                     })
1181                 }
1182
1183                 pick
1184             })
1185         })
1186     }
1187
1188     fn pick_autorefd_method(
1189         &self,
1190         step: &CandidateStep<'tcx>,
1191         self_ty: Ty<'tcx>,
1192         mutbl: hir::Mutability,
1193         unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1194     ) -> Option<PickResult<'tcx>> {
1195         let tcx = self.tcx;
1196
1197         // In general, during probing we erase regions.
1198         let region = tcx.lifetimes.re_erased;
1199
1200         let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: self_ty, mutbl });
1201         self.pick_method(autoref_ty, unstable_candidates).map(|r| {
1202             r.map(|mut pick| {
1203                 pick.autoderefs = step.autoderefs;
1204                 pick.autoref_or_ptr_adjustment =
1205                     Some(AutorefOrPtrAdjustment::Autoref { mutbl, unsize: step.unsize });
1206                 pick
1207             })
1208         })
1209     }
1210
1211     /// If `self_ty` is `*mut T` then this picks `*const T` methods. The reason why we have a
1212     /// special case for this is because going from `*mut T` to `*const T` with autoderefs and
1213     /// autorefs would require dereferencing the pointer, which is not safe.
1214     fn pick_const_ptr_method(
1215         &self,
1216         step: &CandidateStep<'tcx>,
1217         self_ty: Ty<'tcx>,
1218         unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1219     ) -> Option<PickResult<'tcx>> {
1220         // Don't convert an unsized reference to ptr
1221         if step.unsize {
1222             return None;
1223         }
1224
1225         let &ty::RawPtr(ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut }) = self_ty.kind() else {
1226             return None;
1227         };
1228
1229         let const_self_ty = ty::TypeAndMut { ty, mutbl: hir::Mutability::Not };
1230         let const_ptr_ty = self.tcx.mk_ptr(const_self_ty);
1231         self.pick_method(const_ptr_ty, unstable_candidates).map(|r| {
1232             r.map(|mut pick| {
1233                 pick.autoderefs = step.autoderefs;
1234                 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::ToConstPtr);
1235                 pick
1236             })
1237         })
1238     }
1239
1240     fn pick_method_with_unstable(&self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1241         debug!("pick_method_with_unstable(self_ty={})", self.ty_to_string(self_ty));
1242
1243         let mut possibly_unsatisfied_predicates = Vec::new();
1244
1245         for (kind, candidates) in
1246             &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1247         {
1248             debug!("searching {} candidates", kind);
1249             let res = self.consider_candidates(
1250                 self_ty,
1251                 candidates,
1252                 &mut possibly_unsatisfied_predicates,
1253                 Some(&mut vec![]),
1254             );
1255             if res.is_some() {
1256                 return res;
1257             }
1258         }
1259
1260         for (kind, candidates) in
1261             &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1262         {
1263             debug!("searching unstable {kind} candidates");
1264             let res = self.consider_candidates(
1265                 self_ty,
1266                 candidates,
1267                 &mut possibly_unsatisfied_predicates,
1268                 None,
1269             );
1270             if res.is_some() {
1271                 return res;
1272             }
1273         }
1274
1275         self.unsatisfied_predicates.borrow_mut().extend(possibly_unsatisfied_predicates);
1276         None
1277     }
1278
1279     fn pick_method(
1280         &self,
1281         self_ty: Ty<'tcx>,
1282         mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1283     ) -> Option<PickResult<'tcx>> {
1284         if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1285             return self.pick_method_with_unstable(self_ty);
1286         }
1287
1288         debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1289
1290         let mut possibly_unsatisfied_predicates = Vec::new();
1291
1292         for (kind, candidates) in
1293             &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1294         {
1295             debug!("searching {} candidates", kind);
1296             let res = self.consider_candidates(
1297                 self_ty,
1298                 candidates,
1299                 &mut possibly_unsatisfied_predicates,
1300                 unstable_candidates.as_deref_mut(),
1301             );
1302             if let Some(pick) = res {
1303                 return Some(pick);
1304             }
1305         }
1306
1307         // `pick_method` may be called twice for the same self_ty if no stable methods
1308         // match. Only extend once.
1309         if unstable_candidates.is_some() {
1310             self.unsatisfied_predicates.borrow_mut().extend(possibly_unsatisfied_predicates);
1311         }
1312         None
1313     }
1314
1315     fn consider_candidates(
1316         &self,
1317         self_ty: Ty<'tcx>,
1318         candidates: &[Candidate<'tcx>],
1319         possibly_unsatisfied_predicates: &mut Vec<(
1320             ty::Predicate<'tcx>,
1321             Option<ty::Predicate<'tcx>>,
1322             Option<ObligationCause<'tcx>>,
1323         )>,
1324         mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1325     ) -> Option<PickResult<'tcx>> {
1326         let mut applicable_candidates: Vec<_> = candidates
1327             .iter()
1328             .map(|probe| {
1329                 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1330             })
1331             .filter(|&(_, status)| status != ProbeResult::NoMatch)
1332             .collect();
1333
1334         debug!("applicable_candidates: {:?}", applicable_candidates);
1335
1336         if applicable_candidates.len() > 1 {
1337             if let Some(pick) =
1338                 self.collapse_candidates_to_trait_pick(self_ty, &applicable_candidates)
1339             {
1340                 return Some(Ok(pick));
1341             }
1342         }
1343
1344         if let Some(uc) = &mut unstable_candidates {
1345             applicable_candidates.retain(|&(candidate, _)| {
1346                 if let stability::EvalResult::Deny { feature, .. } =
1347                     self.tcx.eval_stability(candidate.item.def_id, None, self.span, None)
1348                 {
1349                     uc.push((candidate.clone(), feature));
1350                     return false;
1351                 }
1352                 true
1353             });
1354         }
1355
1356         if applicable_candidates.len() > 1 {
1357             let sources = candidates.iter().map(|p| self.candidate_source(p, self_ty)).collect();
1358             return Some(Err(MethodError::Ambiguity(sources)));
1359         }
1360
1361         applicable_candidates.pop().map(|(probe, status)| {
1362             if status == ProbeResult::Match {
1363                 Ok(probe
1364                     .to_unadjusted_pick(self_ty, unstable_candidates.cloned().unwrap_or_default()))
1365             } else {
1366                 Err(MethodError::BadReturnType)
1367             }
1368         })
1369     }
1370 }
1371
1372 impl<'tcx> Pick<'tcx> {
1373     /// In case there were unstable name collisions, emit them as a lint.
1374     /// Checks whether two picks do not refer to the same trait item for the same `Self` type.
1375     /// Only useful for comparisons of picks in order to improve diagnostics.
1376     /// Do not use for type checking.
1377     pub fn differs_from(&self, other: &Self) -> bool {
1378         let Self {
1379             item:
1380                 AssocItem {
1381                     def_id,
1382                     name: _,
1383                     kind: _,
1384                     container: _,
1385                     trait_item_def_id: _,
1386                     fn_has_self_parameter: _,
1387                 },
1388             kind: _,
1389             import_ids: _,
1390             autoderefs: _,
1391             autoref_or_ptr_adjustment: _,
1392             self_ty,
1393             unstable_candidates: _,
1394         } = *self;
1395         self_ty != other.self_ty || def_id != other.item.def_id
1396     }
1397
1398     /// In case there were unstable name collisions, emit them as a lint.
1399     pub fn maybe_emit_unstable_name_collision_hint(
1400         &self,
1401         tcx: TyCtxt<'tcx>,
1402         span: Span,
1403         scope_expr_id: hir::HirId,
1404     ) {
1405         if self.unstable_candidates.is_empty() {
1406             return;
1407         }
1408         let def_kind = self.item.kind.as_def_kind();
1409         tcx.struct_span_lint_hir(
1410             lint::builtin::UNSTABLE_NAME_COLLISIONS,
1411             scope_expr_id,
1412             span,
1413             format!(
1414                 "{} {} with this name may be added to the standard library in the future",
1415                 def_kind.article(),
1416                 def_kind.descr(self.item.def_id),
1417             ),
1418             |lint| {
1419                 match (self.item.kind, self.item.container) {
1420                     (ty::AssocKind::Fn, _) => {
1421                         // FIXME: This should be a `span_suggestion` instead of `help`
1422                         // However `self.span` only
1423                         // highlights the method name, so we can't use it. Also consider reusing
1424                         // the code from `report_method_error()`.
1425                         lint.help(&format!(
1426                             "call with fully qualified syntax `{}(...)` to keep using the current \
1427                              method",
1428                             tcx.def_path_str(self.item.def_id),
1429                         ));
1430                     }
1431                     (ty::AssocKind::Const, ty::AssocItemContainer::TraitContainer) => {
1432                         let def_id = self.item.container_id(tcx);
1433                         lint.span_suggestion(
1434                             span,
1435                             "use the fully qualified path to the associated const",
1436                             format!(
1437                                 "<{} as {}>::{}",
1438                                 self.self_ty,
1439                                 tcx.def_path_str(def_id),
1440                                 self.item.name
1441                             ),
1442                             Applicability::MachineApplicable,
1443                         );
1444                     }
1445                     _ => {}
1446                 }
1447                 if tcx.sess.is_nightly_build() {
1448                     for (candidate, feature) in &self.unstable_candidates {
1449                         lint.help(&format!(
1450                             "add `#![feature({})]` to the crate attributes to enable `{}`",
1451                             feature,
1452                             tcx.def_path_str(candidate.item.def_id),
1453                         ));
1454                     }
1455                 }
1456
1457                 lint
1458             },
1459         );
1460     }
1461 }
1462
1463 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
1464     fn select_trait_candidate(
1465         &self,
1466         trait_ref: ty::TraitRef<'tcx>,
1467     ) -> traits::SelectionResult<'tcx, traits::Selection<'tcx>> {
1468         let cause = traits::ObligationCause::misc(self.span, self.body_id);
1469         let predicate = ty::Binder::dummy(trait_ref);
1470         let obligation = traits::Obligation::new(self.tcx, cause, self.param_env, predicate);
1471         traits::SelectionContext::new(self).select(&obligation)
1472     }
1473
1474     fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>) -> CandidateSource {
1475         match candidate.kind {
1476             InherentImplCandidate(..) => {
1477                 CandidateSource::Impl(candidate.item.container_id(self.tcx))
1478             }
1479             ObjectCandidate | WhereClauseCandidate(_) => {
1480                 CandidateSource::Trait(candidate.item.container_id(self.tcx))
1481             }
1482             TraitCandidate(trait_ref) => self.probe(|_| {
1483                 let _ = self
1484                     .at(&ObligationCause::dummy(), self.param_env)
1485                     .define_opaque_types(false)
1486                     .sup(candidate.xform_self_ty, self_ty);
1487                 match self.select_trait_candidate(trait_ref) {
1488                     Ok(Some(traits::ImplSource::UserDefined(ref impl_data))) => {
1489                         // If only a single impl matches, make the error message point
1490                         // to that impl.
1491                         CandidateSource::Impl(impl_data.impl_def_id)
1492                     }
1493                     _ => CandidateSource::Trait(candidate.item.container_id(self.tcx)),
1494                 }
1495             }),
1496         }
1497     }
1498
1499     fn consider_probe(
1500         &self,
1501         self_ty: Ty<'tcx>,
1502         probe: &Candidate<'tcx>,
1503         possibly_unsatisfied_predicates: &mut Vec<(
1504             ty::Predicate<'tcx>,
1505             Option<ty::Predicate<'tcx>>,
1506             Option<ObligationCause<'tcx>>,
1507         )>,
1508     ) -> ProbeResult {
1509         debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1510
1511         self.probe(|_| {
1512             // First check that the self type can be related.
1513             let sub_obligations = match self
1514                 .at(&ObligationCause::dummy(), self.param_env)
1515                 .define_opaque_types(false)
1516                 .sup(probe.xform_self_ty, self_ty)
1517             {
1518                 Ok(InferOk { obligations, value: () }) => obligations,
1519                 Err(err) => {
1520                     debug!("--> cannot relate self-types {:?}", err);
1521                     return ProbeResult::NoMatch;
1522                 }
1523             };
1524
1525             let mut result = ProbeResult::Match;
1526             let mut xform_ret_ty = probe.xform_ret_ty;
1527             debug!(?xform_ret_ty);
1528
1529             let cause = traits::ObligationCause::misc(self.span, self.body_id);
1530
1531             let mut parent_pred = None;
1532
1533             // If so, impls may carry other conditions (e.g., where
1534             // clauses) that must be considered. Make sure that those
1535             // match as well (or at least may match, sometimes we
1536             // don't have enough information to fully evaluate).
1537             match probe.kind {
1538                 InherentImplCandidate(ref substs, ref ref_obligations) => {
1539                     // `xform_ret_ty` hasn't been normalized yet, only `xform_self_ty`,
1540                     // see the reasons mentioned in the comments in `assemble_inherent_impl_probe`
1541                     // for why this is necessary
1542                     let InferOk {
1543                         value: normalized_xform_ret_ty,
1544                         obligations: normalization_obligations,
1545                     } = self.fcx.at(&cause, self.param_env).normalize(xform_ret_ty);
1546                     xform_ret_ty = normalized_xform_ret_ty;
1547                     debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty);
1548
1549                     // Check whether the impl imposes obligations we have to worry about.
1550                     let impl_def_id = probe.item.container_id(self.tcx);
1551                     let impl_bounds = self.tcx.predicates_of(impl_def_id);
1552                     let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1553
1554                     let InferOk { value: impl_bounds, obligations: norm_obligations } =
1555                         self.fcx.at(&cause, self.param_env).normalize(impl_bounds);
1556
1557                     // Convert the bounds into obligations.
1558                     let impl_obligations = traits::predicates_for_generics(
1559                         |_idx, span| {
1560                             let misc = traits::ObligationCause::misc(span, self.body_id);
1561                             let parent_trait_pred = ty::Binder::dummy(ty::TraitPredicate {
1562                                 trait_ref: ty::TraitRef::from_method(self.tcx, impl_def_id, substs),
1563                                 constness: ty::BoundConstness::NotConst,
1564                                 polarity: ty::ImplPolarity::Positive,
1565                             });
1566                             misc.derived_cause(parent_trait_pred, |derived| {
1567                                 traits::ImplDerivedObligation(Box::new(
1568                                     traits::ImplDerivedObligationCause {
1569                                         derived,
1570                                         impl_def_id,
1571                                         span,
1572                                     },
1573                                 ))
1574                             })
1575                         },
1576                         self.param_env,
1577                         impl_bounds,
1578                     );
1579
1580                     let candidate_obligations = impl_obligations
1581                         .chain(norm_obligations.into_iter())
1582                         .chain(ref_obligations.iter().cloned())
1583                         .chain(normalization_obligations.into_iter());
1584
1585                     // Evaluate those obligations to see if they might possibly hold.
1586                     for o in candidate_obligations {
1587                         let o = self.resolve_vars_if_possible(o);
1588                         if !self.predicate_may_hold(&o) {
1589                             result = ProbeResult::NoMatch;
1590                             let parent_o = o.clone();
1591                             let implied_obligations =
1592                                 traits::elaborate_obligations(self.tcx, vec![o]);
1593                             for o in implied_obligations {
1594                                 let parent = if o == parent_o {
1595                                     None
1596                                 } else {
1597                                     if o.predicate.to_opt_poly_trait_pred().map(|p| p.def_id())
1598                                         == self.tcx.lang_items().sized_trait()
1599                                     {
1600                                         // We don't care to talk about implicit `Sized` bounds.
1601                                         continue;
1602                                     }
1603                                     Some(parent_o.predicate)
1604                                 };
1605                                 if !self.predicate_may_hold(&o) {
1606                                     possibly_unsatisfied_predicates.push((
1607                                         o.predicate,
1608                                         parent,
1609                                         Some(o.cause),
1610                                     ));
1611                                 }
1612                             }
1613                         }
1614                     }
1615                 }
1616
1617                 ObjectCandidate | WhereClauseCandidate(..) => {
1618                     // These have no additional conditions to check.
1619                 }
1620
1621                 TraitCandidate(trait_ref) => {
1622                     if let Some(method_name) = self.method_name {
1623                         // Some trait methods are excluded for arrays before 2021.
1624                         // (`array.into_iter()` wants a slice iterator for compatibility.)
1625                         if self_ty.is_array() && !method_name.span.rust_2021() {
1626                             let trait_def = self.tcx.trait_def(trait_ref.def_id);
1627                             if trait_def.skip_array_during_method_dispatch {
1628                                 return ProbeResult::NoMatch;
1629                             }
1630                         }
1631                     }
1632                     let predicate =
1633                         ty::Binder::dummy(trait_ref).without_const().to_predicate(self.tcx);
1634                     parent_pred = Some(predicate);
1635                     let obligation =
1636                         traits::Obligation::new(self.tcx, cause.clone(), self.param_env, predicate);
1637                     if !self.predicate_may_hold(&obligation) {
1638                         result = ProbeResult::NoMatch;
1639                         if self.probe(|_| {
1640                             match self.select_trait_candidate(trait_ref) {
1641                                 Err(_) => return true,
1642                                 Ok(Some(impl_source))
1643                                     if !impl_source.borrow_nested_obligations().is_empty() =>
1644                                 {
1645                                     for obligation in impl_source.borrow_nested_obligations() {
1646                                         // Determine exactly which obligation wasn't met, so
1647                                         // that we can give more context in the error.
1648                                         if !self.predicate_may_hold(obligation) {
1649                                             let nested_predicate =
1650                                                 self.resolve_vars_if_possible(obligation.predicate);
1651                                             let predicate =
1652                                                 self.resolve_vars_if_possible(predicate);
1653                                             let p = if predicate == nested_predicate {
1654                                                 // Avoid "`MyStruct: Foo` which is required by
1655                                                 // `MyStruct: Foo`" in E0599.
1656                                                 None
1657                                             } else {
1658                                                 Some(predicate)
1659                                             };
1660                                             possibly_unsatisfied_predicates.push((
1661                                                 nested_predicate,
1662                                                 p,
1663                                                 Some(obligation.cause.clone()),
1664                                             ));
1665                                         }
1666                                     }
1667                                 }
1668                                 _ => {
1669                                     // Some nested subobligation of this predicate
1670                                     // failed.
1671                                     let predicate = self.resolve_vars_if_possible(predicate);
1672                                     possibly_unsatisfied_predicates.push((predicate, None, None));
1673                                 }
1674                             }
1675                             false
1676                         }) {
1677                             // This candidate's primary obligation doesn't even
1678                             // select - don't bother registering anything in
1679                             // `potentially_unsatisfied_predicates`.
1680                             return ProbeResult::NoMatch;
1681                         }
1682                     }
1683                 }
1684             }
1685
1686             // Evaluate those obligations to see if they might possibly hold.
1687             for o in sub_obligations {
1688                 let o = self.resolve_vars_if_possible(o);
1689                 if !self.predicate_may_hold(&o) {
1690                     result = ProbeResult::NoMatch;
1691                     possibly_unsatisfied_predicates.push((o.predicate, parent_pred, Some(o.cause)));
1692                 }
1693             }
1694
1695             if let ProbeResult::Match = result
1696                 && let Some(return_ty) = self.return_type
1697                 && let Some(mut xform_ret_ty) = xform_ret_ty
1698             {
1699                 // `xform_ret_ty` has only been normalized for `InherentImplCandidate`.
1700                 // We don't normalize the other candidates for perf/backwards-compat reasons...
1701                 // but `self.return_type` is only set on the diagnostic-path, so we
1702                 // should be okay doing it here.
1703                 if !matches!(probe.kind, InherentImplCandidate(..)) {
1704                     let InferOk {
1705                         value: normalized_xform_ret_ty,
1706                         obligations: normalization_obligations,
1707                     } = self.fcx.at(&cause, self.param_env).normalize(xform_ret_ty);
1708                     xform_ret_ty = normalized_xform_ret_ty;
1709                     debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty);
1710                     // Evaluate those obligations to see if they might possibly hold.
1711                     for o in normalization_obligations {
1712                         let o = self.resolve_vars_if_possible(o);
1713                         if !self.predicate_may_hold(&o) {
1714                             result = ProbeResult::NoMatch;
1715                             possibly_unsatisfied_predicates.push((
1716                                 o.predicate,
1717                                 None,
1718                                 Some(o.cause),
1719                             ));
1720                         }
1721                     }
1722                 }
1723
1724                 debug!(
1725                     "comparing return_ty {:?} with xform ret ty {:?}",
1726                     return_ty, xform_ret_ty
1727                 );
1728                 if let ProbeResult::Match = result
1729                     && self
1730                     .at(&ObligationCause::dummy(), self.param_env)
1731                     .define_opaque_types(false)
1732                     .sup(return_ty, xform_ret_ty)
1733                     .is_err()
1734                 {
1735                     result = ProbeResult::BadReturnType;
1736                 }
1737             }
1738
1739             result
1740         })
1741     }
1742
1743     /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1744     /// same trait, but we don't know which impl to use. In this case, since in all cases the
1745     /// external interface of the method can be determined from the trait, it's ok not to decide.
1746     /// We can basically just collapse all of the probes for various impls into one where-clause
1747     /// probe. This will result in a pending obligation so when more type-info is available we can
1748     /// make the final decision.
1749     ///
1750     /// Example (`tests/ui/method-two-trait-defer-resolution-1.rs`):
1751     ///
1752     /// ```ignore (illustrative)
1753     /// trait Foo { ... }
1754     /// impl Foo for Vec<i32> { ... }
1755     /// impl Foo for Vec<usize> { ... }
1756     /// ```
1757     ///
1758     /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1759     /// use, so it's ok to just commit to "using the method from the trait Foo".
1760     fn collapse_candidates_to_trait_pick(
1761         &self,
1762         self_ty: Ty<'tcx>,
1763         probes: &[(&Candidate<'tcx>, ProbeResult)],
1764     ) -> Option<Pick<'tcx>> {
1765         // Do all probes correspond to the same trait?
1766         let container = probes[0].0.item.trait_container(self.tcx)?;
1767         for (p, _) in &probes[1..] {
1768             let p_container = p.item.trait_container(self.tcx)?;
1769             if p_container != container {
1770                 return None;
1771             }
1772         }
1773
1774         // FIXME: check the return type here somehow.
1775         // If so, just use this trait and call it a day.
1776         Some(Pick {
1777             item: probes[0].0.item,
1778             kind: TraitPick,
1779             import_ids: probes[0].0.import_ids.clone(),
1780             autoderefs: 0,
1781             autoref_or_ptr_adjustment: None,
1782             self_ty,
1783             unstable_candidates: vec![],
1784         })
1785     }
1786
1787     /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1788     /// candidate method where the method name may have been misspelled. Similarly to other
1789     /// Levenshtein based suggestions, we provide at most one such suggestion.
1790     fn probe_for_similar_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
1791         debug!("probing for method names similar to {:?}", self.method_name);
1792
1793         let steps = self.steps.clone();
1794         self.probe(|_| {
1795             let mut pcx = ProbeContext::new(
1796                 self.fcx,
1797                 self.span,
1798                 self.mode,
1799                 self.method_name,
1800                 self.return_type,
1801                 &self.orig_steps_var_values,
1802                 steps,
1803                 self.scope_expr_id,
1804             );
1805             pcx.allow_similar_names = true;
1806             pcx.assemble_inherent_candidates();
1807
1808             let method_names = pcx.candidate_method_names(|_| true);
1809             pcx.allow_similar_names = false;
1810             let applicable_close_candidates: Vec<ty::AssocItem> = method_names
1811                 .iter()
1812                 .filter_map(|&method_name| {
1813                     pcx.reset();
1814                     pcx.method_name = Some(method_name);
1815                     pcx.assemble_inherent_candidates();
1816                     pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
1817                 })
1818                 .collect();
1819
1820             if applicable_close_candidates.is_empty() {
1821                 Ok(None)
1822             } else {
1823                 let best_name = {
1824                     let names = applicable_close_candidates
1825                         .iter()
1826                         .map(|cand| cand.name)
1827                         .collect::<Vec<Symbol>>();
1828                     find_best_match_for_name_with_substrings(
1829                         &names,
1830                         self.method_name.unwrap().name,
1831                         None,
1832                     )
1833                 }
1834                 .or_else(|| {
1835                     applicable_close_candidates
1836                         .iter()
1837                         .find(|cand| self.matches_by_doc_alias(cand.def_id))
1838                         .map(|cand| cand.name)
1839                 })
1840                 .unwrap();
1841                 Ok(applicable_close_candidates.into_iter().find(|method| method.name == best_name))
1842             }
1843         })
1844     }
1845
1846     ///////////////////////////////////////////////////////////////////////////
1847     // MISCELLANY
1848     fn has_applicable_self(&self, item: &ty::AssocItem) -> bool {
1849         // "Fast track" -- check for usage of sugar when in method call
1850         // mode.
1851         //
1852         // In Path mode (i.e., resolving a value like `T::next`), consider any
1853         // associated value (i.e., methods, constants) but not types.
1854         match self.mode {
1855             Mode::MethodCall => item.fn_has_self_parameter,
1856             Mode::Path => match item.kind {
1857                 ty::AssocKind::Type => false,
1858                 ty::AssocKind::Fn | ty::AssocKind::Const => true,
1859             },
1860         }
1861         // FIXME -- check for types that deref to `Self`,
1862         // like `Rc<Self>` and so on.
1863         //
1864         // Note also that the current code will break if this type
1865         // includes any of the type parameters defined on the method
1866         // -- but this could be overcome.
1867     }
1868
1869     fn record_static_candidate(&self, source: CandidateSource) {
1870         self.static_candidates.borrow_mut().push(source);
1871     }
1872
1873     #[instrument(level = "debug", skip(self))]
1874     fn xform_self_ty(
1875         &self,
1876         item: &ty::AssocItem,
1877         impl_ty: Ty<'tcx>,
1878         substs: SubstsRef<'tcx>,
1879     ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1880         if item.kind == ty::AssocKind::Fn && self.mode == Mode::MethodCall {
1881             let sig = self.xform_method_sig(item.def_id, substs);
1882             (sig.inputs()[0], Some(sig.output()))
1883         } else {
1884             (impl_ty, None)
1885         }
1886     }
1887
1888     #[instrument(level = "debug", skip(self))]
1889     fn xform_method_sig(&self, method: DefId, substs: SubstsRef<'tcx>) -> ty::FnSig<'tcx> {
1890         let fn_sig = self.tcx.bound_fn_sig(method);
1891         debug!(?fn_sig);
1892
1893         assert!(!substs.has_escaping_bound_vars());
1894
1895         // It is possible for type parameters or early-bound lifetimes
1896         // to appear in the signature of `self`. The substitutions we
1897         // are given do not include type/lifetime parameters for the
1898         // method yet. So create fresh variables here for those too,
1899         // if there are any.
1900         let generics = self.tcx.generics_of(method);
1901         assert_eq!(substs.len(), generics.parent_count as usize);
1902
1903         let xform_fn_sig = if generics.params.is_empty() {
1904             fn_sig.subst(self.tcx, substs)
1905         } else {
1906             let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1907                 let i = param.index as usize;
1908                 if i < substs.len() {
1909                     substs[i]
1910                 } else {
1911                     match param.kind {
1912                         GenericParamDefKind::Lifetime => {
1913                             // In general, during probe we erase regions.
1914                             self.tcx.lifetimes.re_erased.into()
1915                         }
1916                         GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
1917                             self.var_for_def(self.span, param)
1918                         }
1919                     }
1920                 }
1921             });
1922             fn_sig.subst(self.tcx, substs)
1923         };
1924
1925         self.erase_late_bound_regions(xform_fn_sig)
1926     }
1927
1928     /// Gets the type of an impl and generate substitutions with inference vars.
1929     fn impl_ty_and_substs(
1930         &self,
1931         impl_def_id: DefId,
1932     ) -> (ty::EarlyBinder<Ty<'tcx>>, SubstsRef<'tcx>) {
1933         (self.tcx.bound_type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1934     }
1935
1936     fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1937         InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind {
1938             GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1939             GenericParamDefKind::Type { .. } => self
1940                 .next_ty_var(TypeVariableOrigin {
1941                     kind: TypeVariableOriginKind::SubstitutionPlaceholder,
1942                     span: self.tcx.def_span(def_id),
1943                 })
1944                 .into(),
1945             GenericParamDefKind::Const { .. } => {
1946                 let span = self.tcx.def_span(def_id);
1947                 let origin = ConstVariableOrigin {
1948                     kind: ConstVariableOriginKind::SubstitutionPlaceholder,
1949                     span,
1950                 };
1951                 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1952             }
1953         })
1954     }
1955
1956     /// Replaces late-bound-regions bound by `value` with `'static` using
1957     /// `ty::erase_late_bound_regions`.
1958     ///
1959     /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1960     /// method matching. It is reasonable during the probe phase because we don't consider region
1961     /// relationships at all. Therefore, we can just replace all the region variables with 'static
1962     /// rather than creating fresh region variables. This is nice for two reasons:
1963     ///
1964     /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1965     ///    particular method call, it winds up creating fewer types overall, which helps for memory
1966     ///    usage. (Admittedly, this is a rather small effect, though measurable.)
1967     ///
1968     /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1969     ///    late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1970     ///    regions with actual region variables as is proper, we'd have to ensure that the same
1971     ///    region got replaced with the same variable, which requires a bit more coordination
1972     ///    and/or tracking the substitution and
1973     ///    so forth.
1974     fn erase_late_bound_regions<T>(&self, value: ty::Binder<'tcx, T>) -> T
1975     where
1976         T: TypeFoldable<'tcx>,
1977     {
1978         self.tcx.erase_late_bound_regions(value)
1979     }
1980
1981     /// Determine if the given associated item type is relevant in the current context.
1982     fn is_relevant_kind_for_mode(&self, kind: ty::AssocKind) -> bool {
1983         match (self.mode, kind) {
1984             (Mode::MethodCall, ty::AssocKind::Fn) => true,
1985             (Mode::Path, ty::AssocKind::Const | ty::AssocKind::Fn) => true,
1986             _ => false,
1987         }
1988     }
1989
1990     /// Determine if the associated item withe the given DefId matches
1991     /// the desired name via a doc alias.
1992     fn matches_by_doc_alias(&self, def_id: DefId) -> bool {
1993         let Some(name) = self.method_name else { return false; };
1994         let Some(local_def_id) = def_id.as_local() else { return false; };
1995         let hir_id = self.fcx.tcx.hir().local_def_id_to_hir_id(local_def_id);
1996         let attrs = self.fcx.tcx.hir().attrs(hir_id);
1997         for attr in attrs {
1998             let sym::doc = attr.name_or_empty() else { continue; };
1999             let Some(values) = attr.meta_item_list() else { continue; };
2000             for v in values {
2001                 if v.name_or_empty() != sym::alias {
2002                     continue;
2003                 }
2004                 if let Some(nested) = v.meta_item_list() {
2005                     // #[doc(alias("foo", "bar"))]
2006                     for n in nested {
2007                         if let Some(lit) = n.lit() && name.as_str() == lit.symbol.as_str() {
2008                             return true;
2009                         }
2010                     }
2011                 } else if let Some(meta) = v.meta_item()
2012                     && let Some(lit) = meta.name_value_literal()
2013                     && name.as_str() == lit.symbol.as_str() {
2014                         // #[doc(alias = "foo")]
2015                         return true;
2016                 }
2017             }
2018         }
2019         false
2020     }
2021
2022     /// Finds the method with the appropriate name (or return type, as the case may be). If
2023     /// `allow_similar_names` is set, find methods with close-matching names.
2024     // The length of the returned iterator is nearly always 0 or 1 and this
2025     // method is fairly hot.
2026     fn impl_or_trait_item(&self, def_id: DefId) -> SmallVec<[ty::AssocItem; 1]> {
2027         if let Some(name) = self.method_name {
2028             if self.allow_similar_names {
2029                 let max_dist = max(name.as_str().len(), 3) / 3;
2030                 self.tcx
2031                     .associated_items(def_id)
2032                     .in_definition_order()
2033                     .filter(|x| {
2034                         if !self.is_relevant_kind_for_mode(x.kind) {
2035                             return false;
2036                         }
2037                         if self.matches_by_doc_alias(x.def_id) {
2038                             return true;
2039                         }
2040                         match lev_distance_with_substrings(name.as_str(), x.name.as_str(), max_dist)
2041                         {
2042                             Some(d) => d > 0,
2043                             None => false,
2044                         }
2045                     })
2046                     .copied()
2047                     .collect()
2048             } else {
2049                 self.fcx
2050                     .associated_value(def_id, name)
2051                     .filter(|x| self.is_relevant_kind_for_mode(x.kind))
2052                     .map_or_else(SmallVec::new, |x| SmallVec::from_buf([x]))
2053             }
2054         } else {
2055             self.tcx
2056                 .associated_items(def_id)
2057                 .in_definition_order()
2058                 .filter(|x| self.is_relevant_kind_for_mode(x.kind))
2059                 .copied()
2060                 .collect()
2061         }
2062     }
2063 }
2064
2065 impl<'tcx> Candidate<'tcx> {
2066     fn to_unadjusted_pick(
2067         &self,
2068         self_ty: Ty<'tcx>,
2069         unstable_candidates: Vec<(Candidate<'tcx>, Symbol)>,
2070     ) -> Pick<'tcx> {
2071         Pick {
2072             item: self.item,
2073             kind: match self.kind {
2074                 InherentImplCandidate(..) => InherentImplPick,
2075                 ObjectCandidate => ObjectPick,
2076                 TraitCandidate(_) => TraitPick,
2077                 WhereClauseCandidate(ref trait_ref) => {
2078                     // Only trait derived from where-clauses should
2079                     // appear here, so they should not contain any
2080                     // inference variables or other artifacts. This
2081                     // means they are safe to put into the
2082                     // `WhereClausePick`.
2083                     assert!(
2084                         !trait_ref.skip_binder().substs.needs_infer()
2085                             && !trait_ref.skip_binder().substs.has_placeholders()
2086                     );
2087
2088                     WhereClausePick(*trait_ref)
2089                 }
2090             },
2091             import_ids: self.import_ids.clone(),
2092             autoderefs: 0,
2093             autoref_or_ptr_adjustment: None,
2094             self_ty,
2095             unstable_candidates,
2096         }
2097     }
2098 }