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 => self.probe(|_| {
 925                 let substs = self.fresh_substs_for_item(self.span, method.def_id);
 926                 let fty = self.tcx.fn_sig(method.def_id).subst(self.tcx, substs);
 927                 let fty = self.instantiate_binder_with_fresh_vars(self.span, infer::FnCall, fty);
 928
 929                 if let Some(self_ty) = self_ty {
 930                     if self
 931                         .at(&ObligationCause::dummy(), self.param_env)
 932                         .sup(fty.inputs()[0], self_ty)
 933                         .is_err()
 934                     {
 935                         return false;
 936                     }
 937                 }
 938                 self.can_sub(self.param_env, fty.output(), expected).is_ok()
 939             }),
 940             _ => false,
 941         }
 942     }
 943
 944     fn assemble_extension_candidates_for_trait(
 945         &mut self,
 946         import_ids: &SmallVec<[LocalDefId; 1]>,
 947         trait_def_id: DefId,
 948     ) {
 949         debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
 950         let trait_substs = self.fresh_item_substs(trait_def_id);
 951         let trait_ref = self.tcx.mk_trait_ref(trait_def_id, trait_substs);
 952
 953         if self.tcx.is_trait_alias(trait_def_id) {
 954             // For trait aliases, assume all supertraits are relevant.
 955             let bounds = iter::once(ty::Binder::dummy(trait_ref));
 956             self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
 957                 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
 958
 959                 let (xform_self_ty, xform_ret_ty) =
 960                     this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
 961                 this.push_candidate(
 962                     Candidate {
 963                         xform_self_ty,
 964                         xform_ret_ty,
 965                         item,
 966                         import_ids: import_ids.clone(),
 967                         kind: TraitCandidate(new_trait_ref),
 968                     },
 969                     false,
 970                 );
 971             });
 972         } else {
 973             debug_assert!(self.tcx.is_trait(trait_def_id));
 974             if self.tcx.trait_is_auto(trait_def_id) {
 975                 return;
 976             }
 977             for item in self.impl_or_trait_item(trait_def_id) {
 978                 // Check whether `trait_def_id` defines a method with suitable name.
 979                 if !self.has_applicable_self(&item) {
 980                     debug!("method has inapplicable self");
 981                     self.record_static_candidate(CandidateSource::Trait(trait_def_id));
 982                     continue;
 983                 }
 984
 985                 let (xform_self_ty, xform_ret_ty) =
 986                     self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
 987                 self.push_candidate(
 988                     Candidate {
 989                         xform_self_ty,
 990                         xform_ret_ty,
 991                         item,
 992                         import_ids: import_ids.clone(),
 993                         kind: TraitCandidate(trait_ref),
 994                     },
 995                     false,
 996                 );
 997             }
 998         }
 999     }
1000
1001     fn candidate_method_names(
1002         &self,
1003         candidate_filter: impl Fn(&ty::AssocItem) -> bool,
1004     ) -> Vec<Ident> {
1005         let mut set = FxHashSet::default();
1006         let mut names: Vec<_> = self
1007             .inherent_candidates
1008             .iter()
1009             .chain(&self.extension_candidates)
1010             .filter(|candidate| candidate_filter(&candidate.item))
1011             .filter(|candidate| {
1012                 if let Some(return_ty) = self.return_type {
1013                     self.matches_return_type(&candidate.item, None, return_ty)
1014                 } else {
1015                     true
1016                 }
1017             })
1018             .map(|candidate| candidate.item.ident(self.tcx))
1019             .filter(|&name| set.insert(name))
1020             .collect();
1021
1022         // Sort them by the name so we have a stable result.
1023         names.sort_by(|a, b| a.as_str().partial_cmp(b.as_str()).unwrap());
1024         names
1025     }
1026
1027     ///////////////////////////////////////////////////////////////////////////
1028     // THE ACTUAL SEARCH
1029
1030     fn pick(mut self) -> PickResult<'tcx> {
1031         assert!(self.method_name.is_some());
1032
1033         if let Some(r) = self.pick_core() {
1034             return r;
1035         }
1036
1037         debug!("pick: actual search failed, assemble diagnostics");
1038
1039         let static_candidates = std::mem::take(self.static_candidates.get_mut());
1040         let private_candidate = self.private_candidate.take();
1041         let unsatisfied_predicates = std::mem::take(self.unsatisfied_predicates.get_mut());
1042
1043         // things failed, so lets look at all traits, for diagnostic purposes now:
1044         self.reset();
1045
1046         let span = self.span;
1047         let tcx = self.tcx;
1048
1049         self.assemble_extension_candidates_for_all_traits();
1050
1051         let out_of_scope_traits = match self.pick_core() {
1052             Some(Ok(p)) => vec![p.item.container_id(self.tcx)],
1053             Some(Err(MethodError::Ambiguity(v))) => v
1054                 .into_iter()
1055                 .map(|source| match source {
1056                     CandidateSource::Trait(id) => id,
1057                     CandidateSource::Impl(impl_id) => match tcx.trait_id_of_impl(impl_id) {
1058                         Some(id) => id,
1059                         None => span_bug!(span, "found inherent method when looking at traits"),
1060                     },
1061                 })
1062                 .collect(),
1063             Some(Err(MethodError::NoMatch(NoMatchData {
1064                 out_of_scope_traits: others, ..
1065             }))) => {
1066                 assert!(others.is_empty());
1067                 vec![]
1068             }
1069             _ => vec![],
1070         };
1071
1072         if let Some((kind, def_id)) = private_candidate {
1073             return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
1074         }
1075         let similar_candidate = self.probe_for_similar_candidate()?;
1076
1077         Err(MethodError::NoMatch(NoMatchData {
1078             static_candidates,
1079             unsatisfied_predicates,
1080             out_of_scope_traits,
1081             similar_candidate,
1082             mode: self.mode,
1083         }))
1084     }
1085
1086     fn pick_core(&self) -> Option<PickResult<'tcx>> {
1087         let pick = self.pick_all_method(Some(&mut vec![]));
1088
1089         // In this case unstable picking is done by `pick_method`.
1090         if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1091             return pick;
1092         }
1093
1094         if pick.is_none() {
1095             return self.pick_all_method(None);
1096         }
1097         pick
1098     }
1099
1100     fn pick_all_method(
1101         &self,
1102         mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1103     ) -> Option<PickResult<'tcx>> {
1104         self.steps
1105             .iter()
1106             .filter(|step| {
1107                 debug!("pick_all_method: step={:?}", step);
1108                 // skip types that are from a type error or that would require dereferencing
1109                 // a raw pointer
1110                 !step.self_ty.references_error() && !step.from_unsafe_deref
1111             })
1112             .find_map(|step| {
1113                 let InferOk { value: self_ty, obligations: _ } = self
1114                     .fcx
1115                     .probe_instantiate_query_response(
1116                         self.span,
1117                         &self.orig_steps_var_values,
1118                         &step.self_ty,
1119                     )
1120                     .unwrap_or_else(|_| {
1121                         span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1122                     });
1123                 self.pick_by_value_method(step, self_ty, unstable_candidates.as_deref_mut())
1124                     .or_else(|| {
1125                         self.pick_autorefd_method(
1126                             step,
1127                             self_ty,
1128                             hir::Mutability::Not,
1129                             unstable_candidates.as_deref_mut(),
1130                         )
1131                         .or_else(|| {
1132                             self.pick_autorefd_method(
1133                                 step,
1134                                 self_ty,
1135                                 hir::Mutability::Mut,
1136                                 unstable_candidates.as_deref_mut(),
1137                             )
1138                         })
1139                         .or_else(|| {
1140                             self.pick_const_ptr_method(
1141                                 step,
1142                                 self_ty,
1143                                 unstable_candidates.as_deref_mut(),
1144                             )
1145                         })
1146                     })
1147             })
1148     }
1149
1150     /// For each type `T` in the step list, this attempts to find a method where
1151     /// the (transformed) self type is exactly `T`. We do however do one
1152     /// transformation on the adjustment: if we are passing a region pointer in,
1153     /// we will potentially *reborrow* it to a shorter lifetime. This allows us
1154     /// to transparently pass `&mut` pointers, in particular, without consuming
1155     /// them for their entire lifetime.
1156     fn pick_by_value_method(
1157         &self,
1158         step: &CandidateStep<'tcx>,
1159         self_ty: Ty<'tcx>,
1160         unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1161     ) -> Option<PickResult<'tcx>> {
1162         if step.unsize {
1163             return None;
1164         }
1165
1166         self.pick_method(self_ty, unstable_candidates).map(|r| {
1167             r.map(|mut pick| {
1168                 pick.autoderefs = step.autoderefs;
1169
1170                 // Insert a `&*` or `&mut *` if this is a reference type:
1171                 if let ty::Ref(_, _, mutbl) = *step.self_ty.value.value.kind() {
1172                     pick.autoderefs += 1;
1173                     pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
1174                         mutbl,
1175                         unsize: pick.autoref_or_ptr_adjustment.map_or(false, |a| a.get_unsize()),
1176                     })
1177                 }
1178
1179                 pick
1180             })
1181         })
1182     }
1183
1184     fn pick_autorefd_method(
1185         &self,
1186         step: &CandidateStep<'tcx>,
1187         self_ty: Ty<'tcx>,
1188         mutbl: hir::Mutability,
1189         unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1190     ) -> Option<PickResult<'tcx>> {
1191         let tcx = self.tcx;
1192
1193         // In general, during probing we erase regions.
1194         let region = tcx.lifetimes.re_erased;
1195
1196         let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: self_ty, mutbl });
1197         self.pick_method(autoref_ty, unstable_candidates).map(|r| {
1198             r.map(|mut pick| {
1199                 pick.autoderefs = step.autoderefs;
1200                 pick.autoref_or_ptr_adjustment =
1201                     Some(AutorefOrPtrAdjustment::Autoref { mutbl, unsize: step.unsize });
1202                 pick
1203             })
1204         })
1205     }
1206
1207     /// If `self_ty` is `*mut T` then this picks `*const T` methods. The reason why we have a
1208     /// special case for this is because going from `*mut T` to `*const T` with autoderefs and
1209     /// autorefs would require dereferencing the pointer, which is not safe.
1210     fn pick_const_ptr_method(
1211         &self,
1212         step: &CandidateStep<'tcx>,
1213         self_ty: Ty<'tcx>,
1214         unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1215     ) -> Option<PickResult<'tcx>> {
1216         // Don't convert an unsized reference to ptr
1217         if step.unsize {
1218             return None;
1219         }
1220
1221         let &ty::RawPtr(ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut }) = self_ty.kind() else {
1222             return None;
1223         };
1224
1225         let const_self_ty = ty::TypeAndMut { ty, mutbl: hir::Mutability::Not };
1226         let const_ptr_ty = self.tcx.mk_ptr(const_self_ty);
1227         self.pick_method(const_ptr_ty, unstable_candidates).map(|r| {
1228             r.map(|mut pick| {
1229                 pick.autoderefs = step.autoderefs;
1230                 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::ToConstPtr);
1231                 pick
1232             })
1233         })
1234     }
1235
1236     fn pick_method_with_unstable(&self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1237         debug!("pick_method_with_unstable(self_ty={})", self.ty_to_string(self_ty));
1238
1239         let mut possibly_unsatisfied_predicates = Vec::new();
1240
1241         for (kind, candidates) in
1242             &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1243         {
1244             debug!("searching {} candidates", kind);
1245             let res = self.consider_candidates(
1246                 self_ty,
1247                 candidates,
1248                 &mut possibly_unsatisfied_predicates,
1249                 Some(&mut vec![]),
1250             );
1251             if res.is_some() {
1252                 return res;
1253             }
1254         }
1255
1256         for (kind, candidates) in
1257             &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1258         {
1259             debug!("searching unstable {kind} candidates");
1260             let res = self.consider_candidates(
1261                 self_ty,
1262                 candidates,
1263                 &mut possibly_unsatisfied_predicates,
1264                 None,
1265             );
1266             if res.is_some() {
1267                 return res;
1268             }
1269         }
1270
1271         self.unsatisfied_predicates.borrow_mut().extend(possibly_unsatisfied_predicates);
1272         None
1273     }
1274
1275     fn pick_method(
1276         &self,
1277         self_ty: Ty<'tcx>,
1278         mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1279     ) -> Option<PickResult<'tcx>> {
1280         if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1281             return self.pick_method_with_unstable(self_ty);
1282         }
1283
1284         debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1285
1286         let mut possibly_unsatisfied_predicates = Vec::new();
1287
1288         for (kind, candidates) in
1289             &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1290         {
1291             debug!("searching {} candidates", kind);
1292             let res = self.consider_candidates(
1293                 self_ty,
1294                 candidates,
1295                 &mut possibly_unsatisfied_predicates,
1296                 unstable_candidates.as_deref_mut(),
1297             );
1298             if let Some(pick) = res {
1299                 return Some(pick);
1300             }
1301         }
1302
1303         // `pick_method` may be called twice for the same self_ty if no stable methods
1304         // match. Only extend once.
1305         if unstable_candidates.is_some() {
1306             self.unsatisfied_predicates.borrow_mut().extend(possibly_unsatisfied_predicates);
1307         }
1308         None
1309     }
1310
1311     fn consider_candidates(
1312         &self,
1313         self_ty: Ty<'tcx>,
1314         candidates: &[Candidate<'tcx>],
1315         possibly_unsatisfied_predicates: &mut Vec<(
1316             ty::Predicate<'tcx>,
1317             Option<ty::Predicate<'tcx>>,
1318             Option<ObligationCause<'tcx>>,
1319         )>,
1320         mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1321     ) -> Option<PickResult<'tcx>> {
1322         let mut applicable_candidates: Vec<_> = candidates
1323             .iter()
1324             .map(|probe| {
1325                 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1326             })
1327             .filter(|&(_, status)| status != ProbeResult::NoMatch)
1328             .collect();
1329
1330         debug!("applicable_candidates: {:?}", applicable_candidates);
1331
1332         if applicable_candidates.len() > 1 {
1333             if let Some(pick) =
1334                 self.collapse_candidates_to_trait_pick(self_ty, &applicable_candidates)
1335             {
1336                 return Some(Ok(pick));
1337             }
1338         }
1339
1340         if let Some(uc) = &mut unstable_candidates {
1341             applicable_candidates.retain(|&(candidate, _)| {
1342                 if let stability::EvalResult::Deny { feature, .. } =
1343                     self.tcx.eval_stability(candidate.item.def_id, None, self.span, None)
1344                 {
1345                     uc.push((candidate.clone(), feature));
1346                     return false;
1347                 }
1348                 true
1349             });
1350         }
1351
1352         if applicable_candidates.len() > 1 {
1353             let sources = candidates.iter().map(|p| self.candidate_source(p, self_ty)).collect();
1354             return Some(Err(MethodError::Ambiguity(sources)));
1355         }
1356
1357         applicable_candidates.pop().map(|(probe, status)| match status {
1358             ProbeResult::Match => {
1359                 Ok(probe
1360                     .to_unadjusted_pick(self_ty, unstable_candidates.cloned().unwrap_or_default()))
1361             }
1362             ProbeResult::NoMatch | ProbeResult::BadReturnType => Err(MethodError::BadReturnType),
1363         })
1364     }
1365 }
1366
1367 impl<'tcx> Pick<'tcx> {
1368     /// In case there were unstable name collisions, emit them as a lint.
1369     /// Checks whether two picks do not refer to the same trait item for the same `Self` type.
1370     /// Only useful for comparisons of picks in order to improve diagnostics.
1371     /// Do not use for type checking.
1372     pub fn differs_from(&self, other: &Self) -> bool {
1373         let Self {
1374             item:
1375                 AssocItem {
1376                     def_id,
1377                     name: _,
1378                     kind: _,
1379                     container: _,
1380                     trait_item_def_id: _,
1381                     fn_has_self_parameter: _,
1382                 },
1383             kind: _,
1384             import_ids: _,
1385             autoderefs: _,
1386             autoref_or_ptr_adjustment: _,
1387             self_ty,
1388             unstable_candidates: _,
1389         } = *self;
1390         self_ty != other.self_ty || def_id != other.item.def_id
1391     }
1392
1393     /// In case there were unstable name collisions, emit them as a lint.
1394     pub fn maybe_emit_unstable_name_collision_hint(
1395         &self,
1396         tcx: TyCtxt<'tcx>,
1397         span: Span,
1398         scope_expr_id: hir::HirId,
1399     ) {
1400         if self.unstable_candidates.is_empty() {
1401             return;
1402         }
1403         let def_kind = self.item.kind.as_def_kind();
1404         tcx.struct_span_lint_hir(
1405             lint::builtin::UNSTABLE_NAME_COLLISIONS,
1406             scope_expr_id,
1407             span,
1408             format!(
1409                 "{} {} with this name may be added to the standard library in the future",
1410                 def_kind.article(),
1411                 def_kind.descr(self.item.def_id),
1412             ),
1413             |lint| {
1414                 match (self.item.kind, self.item.container) {
1415                     (ty::AssocKind::Fn, _) => {
1416                         // FIXME: This should be a `span_suggestion` instead of `help`
1417                         // However `self.span` only
1418                         // highlights the method name, so we can't use it. Also consider reusing
1419                         // the code from `report_method_error()`.
1420                         lint.help(&format!(
1421                             "call with fully qualified syntax `{}(...)` to keep using the current \
1422                              method",
1423                             tcx.def_path_str(self.item.def_id),
1424                         ));
1425                     }
1426                     (ty::AssocKind::Const, ty::AssocItemContainer::TraitContainer) => {
1427                         let def_id = self.item.container_id(tcx);
1428                         lint.span_suggestion(
1429                             span,
1430                             "use the fully qualified path to the associated const",
1431                             format!(
1432                                 "<{} as {}>::{}",
1433                                 self.self_ty,
1434                                 tcx.def_path_str(def_id),
1435                                 self.item.name
1436                             ),
1437                             Applicability::MachineApplicable,
1438                         );
1439                     }
1440                     _ => {}
1441                 }
1442                 if tcx.sess.is_nightly_build() {
1443                     for (candidate, feature) in &self.unstable_candidates {
1444                         lint.help(&format!(
1445                             "add `#![feature({})]` to the crate attributes to enable `{}`",
1446                             feature,
1447                             tcx.def_path_str(candidate.item.def_id),
1448                         ));
1449                     }
1450                 }
1451
1452                 lint
1453             },
1454         );
1455     }
1456 }
1457
1458 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
1459     fn select_trait_candidate(
1460         &self,
1461         trait_ref: ty::TraitRef<'tcx>,
1462     ) -> traits::SelectionResult<'tcx, traits::Selection<'tcx>> {
1463         let cause = traits::ObligationCause::misc(self.span, self.body_id);
1464         let predicate = ty::Binder::dummy(trait_ref);
1465         let obligation = traits::Obligation::new(self.tcx, cause, self.param_env, predicate);
1466         traits::SelectionContext::new(self).select(&obligation)
1467     }
1468
1469     fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>) -> CandidateSource {
1470         match candidate.kind {
1471             InherentImplCandidate(..) => {
1472                 CandidateSource::Impl(candidate.item.container_id(self.tcx))
1473             }
1474             ObjectCandidate | WhereClauseCandidate(_) => {
1475                 CandidateSource::Trait(candidate.item.container_id(self.tcx))
1476             }
1477             TraitCandidate(trait_ref) => self.probe(|_| {
1478                 let _ = self
1479                     .at(&ObligationCause::dummy(), self.param_env)
1480                     .define_opaque_types(false)
1481                     .sup(candidate.xform_self_ty, self_ty);
1482                 match self.select_trait_candidate(trait_ref) {
1483                     Ok(Some(traits::ImplSource::UserDefined(ref impl_data))) => {
1484                         // If only a single impl matches, make the error message point
1485                         // to that impl.
1486                         CandidateSource::Impl(impl_data.impl_def_id)
1487                     }
1488                     _ => CandidateSource::Trait(candidate.item.container_id(self.tcx)),
1489                 }
1490             }),
1491         }
1492     }
1493
1494     fn consider_probe(
1495         &self,
1496         self_ty: Ty<'tcx>,
1497         probe: &Candidate<'tcx>,
1498         possibly_unsatisfied_predicates: &mut Vec<(
1499             ty::Predicate<'tcx>,
1500             Option<ty::Predicate<'tcx>>,
1501             Option<ObligationCause<'tcx>>,
1502         )>,
1503     ) -> ProbeResult {
1504         debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1505
1506         self.probe(|_| {
1507             // First check that the self type can be related.
1508             let sub_obligations = match self
1509                 .at(&ObligationCause::dummy(), self.param_env)
1510                 .define_opaque_types(false)
1511                 .sup(probe.xform_self_ty, self_ty)
1512             {
1513                 Ok(InferOk { obligations, value: () }) => obligations,
1514                 Err(err) => {
1515                     debug!("--> cannot relate self-types {:?}", err);
1516                     return ProbeResult::NoMatch;
1517                 }
1518             };
1519
1520             let mut result = ProbeResult::Match;
1521             let mut xform_ret_ty = probe.xform_ret_ty;
1522             debug!(?xform_ret_ty);
1523
1524             let cause = traits::ObligationCause::misc(self.span, self.body_id);
1525
1526             let mut parent_pred = None;
1527
1528             // If so, impls may carry other conditions (e.g., where
1529             // clauses) that must be considered. Make sure that those
1530             // match as well (or at least may match, sometimes we
1531             // don't have enough information to fully evaluate).
1532             match probe.kind {
1533                 InherentImplCandidate(ref substs, ref ref_obligations) => {
1534                     // `xform_ret_ty` hasn't been normalized yet, only `xform_self_ty`,
1535                     // see the reasons mentioned in the comments in `assemble_inherent_impl_probe`
1536                     // for why this is necessary
1537                     let InferOk {
1538                         value: normalized_xform_ret_ty,
1539                         obligations: normalization_obligations,
1540                     } = self.fcx.at(&cause, self.param_env).normalize(xform_ret_ty);
1541                     xform_ret_ty = normalized_xform_ret_ty;
1542                     debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty);
1543
1544                     // Check whether the impl imposes obligations we have to worry about.
1545                     let impl_def_id = probe.item.container_id(self.tcx);
1546                     let impl_bounds = self.tcx.predicates_of(impl_def_id);
1547                     let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1548
1549                     let InferOk { value: impl_bounds, obligations: norm_obligations } =
1550                         self.fcx.at(&cause, self.param_env).normalize(impl_bounds);
1551
1552                     // Convert the bounds into obligations.
1553                     let impl_obligations = traits::predicates_for_generics(
1554                         |_idx, span| {
1555                             let misc = traits::ObligationCause::misc(span, self.body_id);
1556                             let parent_trait_pred = ty::Binder::dummy(ty::TraitPredicate {
1557                                 trait_ref: ty::TraitRef::from_method(self.tcx, impl_def_id, substs),
1558                                 constness: ty::BoundConstness::NotConst,
1559                                 polarity: ty::ImplPolarity::Positive,
1560                             });
1561                             misc.derived_cause(parent_trait_pred, |derived| {
1562                                 traits::ImplDerivedObligation(Box::new(
1563                                     traits::ImplDerivedObligationCause {
1564                                         derived,
1565                                         impl_def_id,
1566                                         impl_def_predicate_index: None,
1567                                         span,
1568                                     },
1569                                 ))
1570                             })
1571                         },
1572                         self.param_env,
1573                         impl_bounds,
1574                     );
1575
1576                     let candidate_obligations = impl_obligations
1577                         .chain(norm_obligations.into_iter())
1578                         .chain(ref_obligations.iter().cloned())
1579                         .chain(normalization_obligations.into_iter());
1580
1581                     // Evaluate those obligations to see if they might possibly hold.
1582                     for o in candidate_obligations {
1583                         let o = self.resolve_vars_if_possible(o);
1584                         if !self.predicate_may_hold(&o) {
1585                             result = ProbeResult::NoMatch;
1586                             let parent_o = o.clone();
1587                             let implied_obligations =
1588                                 traits::elaborate_obligations(self.tcx, vec![o]);
1589                             for o in implied_obligations {
1590                                 let parent = if o == parent_o {
1591                                     None
1592                                 } else {
1593                                     if o.predicate.to_opt_poly_trait_pred().map(|p| p.def_id())
1594                                         == self.tcx.lang_items().sized_trait()
1595                                     {
1596                                         // We don't care to talk about implicit `Sized` bounds.
1597                                         continue;
1598                                     }
1599                                     Some(parent_o.predicate)
1600                                 };
1601                                 if !self.predicate_may_hold(&o) {
1602                                     possibly_unsatisfied_predicates.push((
1603                                         o.predicate,
1604                                         parent,
1605                                         Some(o.cause),
1606                                     ));
1607                                 }
1608                             }
1609                         }
1610                     }
1611                 }
1612
1613                 ObjectCandidate | WhereClauseCandidate(..) => {
1614                     // These have no additional conditions to check.
1615                 }
1616
1617                 TraitCandidate(trait_ref) => {
1618                     if let Some(method_name) = self.method_name {
1619                         // Some trait methods are excluded for arrays before 2021.
1620                         // (`array.into_iter()` wants a slice iterator for compatibility.)
1621                         if self_ty.is_array() && !method_name.span.rust_2021() {
1622                             let trait_def = self.tcx.trait_def(trait_ref.def_id);
1623                             if trait_def.skip_array_during_method_dispatch {
1624                                 return ProbeResult::NoMatch;
1625                             }
1626                         }
1627                     }
1628                     let predicate =
1629                         ty::Binder::dummy(trait_ref).without_const().to_predicate(self.tcx);
1630                     parent_pred = Some(predicate);
1631                     let obligation =
1632                         traits::Obligation::new(self.tcx, cause.clone(), self.param_env, predicate);
1633                     if !self.predicate_may_hold(&obligation) {
1634                         result = ProbeResult::NoMatch;
1635                         if self.probe(|_| {
1636                             match self.select_trait_candidate(trait_ref) {
1637                                 Err(_) => return true,
1638                                 Ok(Some(impl_source))
1639                                     if !impl_source.borrow_nested_obligations().is_empty() =>
1640                                 {
1641                                     for obligation in impl_source.borrow_nested_obligations() {
1642                                         // Determine exactly which obligation wasn't met, so
1643                                         // that we can give more context in the error.
1644                                         if !self.predicate_may_hold(obligation) {
1645                                             let nested_predicate =
1646                                                 self.resolve_vars_if_possible(obligation.predicate);
1647                                             let predicate =
1648                                                 self.resolve_vars_if_possible(predicate);
1649                                             let p = if predicate == nested_predicate {
1650                                                 // Avoid "`MyStruct: Foo` which is required by
1651                                                 // `MyStruct: Foo`" in E0599.
1652                                                 None
1653                                             } else {
1654                                                 Some(predicate)
1655                                             };
1656                                             possibly_unsatisfied_predicates.push((
1657                                                 nested_predicate,
1658                                                 p,
1659                                                 Some(obligation.cause.clone()),
1660                                             ));
1661                                         }
1662                                     }
1663                                 }
1664                                 _ => {
1665                                     // Some nested subobligation of this predicate
1666                                     // failed.
1667                                     let predicate = self.resolve_vars_if_possible(predicate);
1668                                     possibly_unsatisfied_predicates.push((predicate, None, None));
1669                                 }
1670                             }
1671                             false
1672                         }) {
1673                             // This candidate's primary obligation doesn't even
1674                             // select - don't bother registering anything in
1675                             // `potentially_unsatisfied_predicates`.
1676                             return ProbeResult::NoMatch;
1677                         }
1678                     }
1679                 }
1680             }
1681
1682             // Evaluate those obligations to see if they might possibly hold.
1683             for o in sub_obligations {
1684                 let o = self.resolve_vars_if_possible(o);
1685                 if !self.predicate_may_hold(&o) {
1686                     result = ProbeResult::NoMatch;
1687                     possibly_unsatisfied_predicates.push((o.predicate, parent_pred, Some(o.cause)));
1688                 }
1689             }
1690
1691             if let ProbeResult::Match = result
1692                 && let Some(return_ty) = self.return_type
1693                 && let Some(mut xform_ret_ty) = xform_ret_ty
1694             {
1695                 // `xform_ret_ty` has only been normalized for `InherentImplCandidate`.
1696                 // We don't normalize the other candidates for perf/backwards-compat reasons...
1697                 // but `self.return_type` is only set on the diagnostic-path, so we
1698                 // should be okay doing it here.
1699                 if !matches!(probe.kind, InherentImplCandidate(..)) {
1700                     let InferOk {
1701                         value: normalized_xform_ret_ty,
1702                         obligations: normalization_obligations,
1703                     } = self.fcx.at(&cause, self.param_env).normalize(xform_ret_ty);
1704                     xform_ret_ty = normalized_xform_ret_ty;
1705                     debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty);
1706                     // Evaluate those obligations to see if they might possibly hold.
1707                     for o in normalization_obligations {
1708                         let o = self.resolve_vars_if_possible(o);
1709                         if !self.predicate_may_hold(&o) {
1710                             result = ProbeResult::NoMatch;
1711                             possibly_unsatisfied_predicates.push((
1712                                 o.predicate,
1713                                 None,
1714                                 Some(o.cause),
1715                             ));
1716                         }
1717                     }
1718                 }
1719
1720                 debug!(
1721                     "comparing return_ty {:?} with xform ret ty {:?}",
1722                     return_ty, xform_ret_ty
1723                 );
1724                 if let ProbeResult::Match = result
1725                     && self
1726                     .at(&ObligationCause::dummy(), self.param_env)
1727                     .define_opaque_types(false)
1728                     .sup(return_ty, xform_ret_ty)
1729                     .is_err()
1730                 {
1731                     result = ProbeResult::BadReturnType;
1732                 }
1733             }
1734
1735             result
1736         })
1737     }
1738
1739     /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1740     /// same trait, but we don't know which impl to use. In this case, since in all cases the
1741     /// external interface of the method can be determined from the trait, it's ok not to decide.
1742     /// We can basically just collapse all of the probes for various impls into one where-clause
1743     /// probe. This will result in a pending obligation so when more type-info is available we can
1744     /// make the final decision.
1745     ///
1746     /// Example (`tests/ui/method-two-trait-defer-resolution-1.rs`):
1747     ///
1748     /// ```ignore (illustrative)
1749     /// trait Foo { ... }
1750     /// impl Foo for Vec<i32> { ... }
1751     /// impl Foo for Vec<usize> { ... }
1752     /// ```
1753     ///
1754     /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1755     /// use, so it's ok to just commit to "using the method from the trait Foo".
1756     fn collapse_candidates_to_trait_pick(
1757         &self,
1758         self_ty: Ty<'tcx>,
1759         probes: &[(&Candidate<'tcx>, ProbeResult)],
1760     ) -> Option<Pick<'tcx>> {
1761         // Do all probes correspond to the same trait?
1762         let container = probes[0].0.item.trait_container(self.tcx)?;
1763         for (p, _) in &probes[1..] {
1764             let p_container = p.item.trait_container(self.tcx)?;
1765             if p_container != container {
1766                 return None;
1767             }
1768         }
1769
1770         // FIXME: check the return type here somehow.
1771         // If so, just use this trait and call it a day.
1772         Some(Pick {
1773             item: probes[0].0.item,
1774             kind: TraitPick,
1775             import_ids: probes[0].0.import_ids.clone(),
1776             autoderefs: 0,
1777             autoref_or_ptr_adjustment: None,
1778             self_ty,
1779             unstable_candidates: vec![],
1780         })
1781     }
1782
1783     /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1784     /// candidate method where the method name may have been misspelled. Similarly to other
1785     /// Levenshtein based suggestions, we provide at most one such suggestion.
1786     fn probe_for_similar_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
1787         debug!("probing for method names similar to {:?}", self.method_name);
1788
1789         let steps = self.steps.clone();
1790         self.probe(|_| {
1791             let mut pcx = ProbeContext::new(
1792                 self.fcx,
1793                 self.span,
1794                 self.mode,
1795                 self.method_name,
1796                 self.return_type,
1797                 &self.orig_steps_var_values,
1798                 steps,
1799                 self.scope_expr_id,
1800             );
1801             pcx.allow_similar_names = true;
1802             pcx.assemble_inherent_candidates();
1803
1804             let method_names = pcx.candidate_method_names(|_| true);
1805             pcx.allow_similar_names = false;
1806             let applicable_close_candidates: Vec<ty::AssocItem> = method_names
1807                 .iter()
1808                 .filter_map(|&method_name| {
1809                     pcx.reset();
1810                     pcx.method_name = Some(method_name);
1811                     pcx.assemble_inherent_candidates();
1812                     pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
1813                 })
1814                 .collect();
1815
1816             if applicable_close_candidates.is_empty() {
1817                 Ok(None)
1818             } else {
1819                 let best_name = {
1820                     let names = applicable_close_candidates
1821                         .iter()
1822                         .map(|cand| cand.name)
1823                         .collect::<Vec<Symbol>>();
1824                     find_best_match_for_name_with_substrings(
1825                         &names,
1826                         self.method_name.unwrap().name,
1827                         None,
1828                     )
1829                 }
1830                 .or_else(|| {
1831                     applicable_close_candidates
1832                         .iter()
1833                         .find(|cand| self.matches_by_doc_alias(cand.def_id))
1834                         .map(|cand| cand.name)
1835                 })
1836                 .unwrap();
1837                 Ok(applicable_close_candidates.into_iter().find(|method| method.name == best_name))
1838             }
1839         })
1840     }
1841
1842     ///////////////////////////////////////////////////////////////////////////
1843     // MISCELLANY
1844     fn has_applicable_self(&self, item: &ty::AssocItem) -> bool {
1845         // "Fast track" -- check for usage of sugar when in method call
1846         // mode.
1847         //
1848         // In Path mode (i.e., resolving a value like `T::next`), consider any
1849         // associated value (i.e., methods, constants) but not types.
1850         match self.mode {
1851             Mode::MethodCall => item.fn_has_self_parameter,
1852             Mode::Path => match item.kind {
1853                 ty::AssocKind::Type => false,
1854                 ty::AssocKind::Fn | ty::AssocKind::Const => true,
1855             },
1856         }
1857         // FIXME -- check for types that deref to `Self`,
1858         // like `Rc<Self>` and so on.
1859         //
1860         // Note also that the current code will break if this type
1861         // includes any of the type parameters defined on the method
1862         // -- but this could be overcome.
1863     }
1864
1865     fn record_static_candidate(&self, source: CandidateSource) {
1866         self.static_candidates.borrow_mut().push(source);
1867     }
1868
1869     #[instrument(level = "debug", skip(self))]
1870     fn xform_self_ty(
1871         &self,
1872         item: &ty::AssocItem,
1873         impl_ty: Ty<'tcx>,
1874         substs: SubstsRef<'tcx>,
1875     ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1876         if item.kind == ty::AssocKind::Fn && self.mode == Mode::MethodCall {
1877             let sig = self.xform_method_sig(item.def_id, substs);
1878             (sig.inputs()[0], Some(sig.output()))
1879         } else {
1880             (impl_ty, None)
1881         }
1882     }
1883
1884     #[instrument(level = "debug", skip(self))]
1885     fn xform_method_sig(&self, method: DefId, substs: SubstsRef<'tcx>) -> ty::FnSig<'tcx> {
1886         let fn_sig = self.tcx.fn_sig(method);
1887         debug!(?fn_sig);
1888
1889         assert!(!substs.has_escaping_bound_vars());
1890
1891         // It is possible for type parameters or early-bound lifetimes
1892         // to appear in the signature of `self`. The substitutions we
1893         // are given do not include type/lifetime parameters for the
1894         // method yet. So create fresh variables here for those too,
1895         // if there are any.
1896         let generics = self.tcx.generics_of(method);
1897         assert_eq!(substs.len(), generics.parent_count as usize);
1898
1899         let xform_fn_sig = if generics.params.is_empty() {
1900             fn_sig.subst(self.tcx, substs)
1901         } else {
1902             let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1903                 let i = param.index as usize;
1904                 if i < substs.len() {
1905                     substs[i]
1906                 } else {
1907                     match param.kind {
1908                         GenericParamDefKind::Lifetime => {
1909                             // In general, during probe we erase regions.
1910                             self.tcx.lifetimes.re_erased.into()
1911                         }
1912                         GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
1913                             self.var_for_def(self.span, param)
1914                         }
1915                     }
1916                 }
1917             });
1918             fn_sig.subst(self.tcx, substs)
1919         };
1920
1921         self.erase_late_bound_regions(xform_fn_sig)
1922     }
1923
1924     /// Gets the type of an impl and generate substitutions with inference vars.
1925     fn impl_ty_and_substs(
1926         &self,
1927         impl_def_id: DefId,
1928     ) -> (ty::EarlyBinder<Ty<'tcx>>, SubstsRef<'tcx>) {
1929         (self.tcx.bound_type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1930     }
1931
1932     fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1933         InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind {
1934             GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1935             GenericParamDefKind::Type { .. } => self
1936                 .next_ty_var(TypeVariableOrigin {
1937                     kind: TypeVariableOriginKind::SubstitutionPlaceholder,
1938                     span: self.tcx.def_span(def_id),
1939                 })
1940                 .into(),
1941             GenericParamDefKind::Const { .. } => {
1942                 let span = self.tcx.def_span(def_id);
1943                 let origin = ConstVariableOrigin {
1944                     kind: ConstVariableOriginKind::SubstitutionPlaceholder,
1945                     span,
1946                 };
1947                 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1948             }
1949         })
1950     }
1951
1952     /// Replaces late-bound-regions bound by `value` with `'static` using
1953     /// `ty::erase_late_bound_regions`.
1954     ///
1955     /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1956     /// method matching. It is reasonable during the probe phase because we don't consider region
1957     /// relationships at all. Therefore, we can just replace all the region variables with 'static
1958     /// rather than creating fresh region variables. This is nice for two reasons:
1959     ///
1960     /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1961     ///    particular method call, it winds up creating fewer types overall, which helps for memory
1962     ///    usage. (Admittedly, this is a rather small effect, though measurable.)
1963     ///
1964     /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1965     ///    late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1966     ///    regions with actual region variables as is proper, we'd have to ensure that the same
1967     ///    region got replaced with the same variable, which requires a bit more coordination
1968     ///    and/or tracking the substitution and
1969     ///    so forth.
1970     fn erase_late_bound_regions<T>(&self, value: ty::Binder<'tcx, T>) -> T
1971     where
1972         T: TypeFoldable<'tcx>,
1973     {
1974         self.tcx.erase_late_bound_regions(value)
1975     }
1976
1977     /// Determine if the given associated item type is relevant in the current context.
1978     fn is_relevant_kind_for_mode(&self, kind: ty::AssocKind) -> bool {
1979         match (self.mode, kind) {
1980             (Mode::MethodCall, ty::AssocKind::Fn) => true,
1981             (Mode::Path, ty::AssocKind::Const | ty::AssocKind::Fn) => true,
1982             _ => false,
1983         }
1984     }
1985
1986     /// Determine if the associated item withe the given DefId matches
1987     /// the desired name via a doc alias.
1988     fn matches_by_doc_alias(&self, def_id: DefId) -> bool {
1989         let Some(name) = self.method_name else { return false; };
1990         let Some(local_def_id) = def_id.as_local() else { return false; };
1991         let hir_id = self.fcx.tcx.hir().local_def_id_to_hir_id(local_def_id);
1992         let attrs = self.fcx.tcx.hir().attrs(hir_id);
1993         for attr in attrs {
1994             let sym::doc = attr.name_or_empty() else { continue; };
1995             let Some(values) = attr.meta_item_list() else { continue; };
1996             for v in values {
1997                 if v.name_or_empty() != sym::alias {
1998                     continue;
1999                 }
2000                 if let Some(nested) = v.meta_item_list() {
2001                     // #[doc(alias("foo", "bar"))]
2002                     for n in nested {
2003                         if let Some(lit) = n.lit() && name.as_str() == lit.symbol.as_str() {
2004                             return true;
2005                         }
2006                     }
2007                 } else if let Some(meta) = v.meta_item()
2008                     && let Some(lit) = meta.name_value_literal()
2009                     && name.as_str() == lit.symbol.as_str() {
2010                         // #[doc(alias = "foo")]
2011                         return true;
2012                 }
2013             }
2014         }
2015         false
2016     }
2017
2018     /// Finds the method with the appropriate name (or return type, as the case may be). If
2019     /// `allow_similar_names` is set, find methods with close-matching names.
2020     // The length of the returned iterator is nearly always 0 or 1 and this
2021     // method is fairly hot.
2022     fn impl_or_trait_item(&self, def_id: DefId) -> SmallVec<[ty::AssocItem; 1]> {
2023         if let Some(name) = self.method_name {
2024             if self.allow_similar_names {
2025                 let max_dist = max(name.as_str().len(), 3) / 3;
2026                 self.tcx
2027                     .associated_items(def_id)
2028                     .in_definition_order()
2029                     .filter(|x| {
2030                         if !self.is_relevant_kind_for_mode(x.kind) {
2031                             return false;
2032                         }
2033                         if self.matches_by_doc_alias(x.def_id) {
2034                             return true;
2035                         }
2036                         match lev_distance_with_substrings(name.as_str(), x.name.as_str(), max_dist)
2037                         {
2038                             Some(d) => d > 0,
2039                             None => false,
2040                         }
2041                     })
2042                     .copied()
2043                     .collect()
2044             } else {
2045                 self.fcx
2046                     .associated_value(def_id, name)
2047                     .filter(|x| self.is_relevant_kind_for_mode(x.kind))
2048                     .map_or_else(SmallVec::new, |x| SmallVec::from_buf([x]))
2049             }
2050         } else {
2051             self.tcx
2052                 .associated_items(def_id)
2053                 .in_definition_order()
2054                 .filter(|x| self.is_relevant_kind_for_mode(x.kind))
2055                 .copied()
2056                 .collect()
2057         }
2058     }
2059 }
2060
2061 impl<'tcx> Candidate<'tcx> {
2062     fn to_unadjusted_pick(
2063         &self,
2064         self_ty: Ty<'tcx>,
2065         unstable_candidates: Vec<(Candidate<'tcx>, Symbol)>,
2066     ) -> Pick<'tcx> {
2067         Pick {
2068             item: self.item,
2069             kind: match self.kind {
2070                 InherentImplCandidate(..) => InherentImplPick,
2071                 ObjectCandidate => ObjectPick,
2072                 TraitCandidate(_) => TraitPick,
2073                 WhereClauseCandidate(ref trait_ref) => {
2074                     // Only trait derived from where-clauses should
2075                     // appear here, so they should not contain any
2076                     // inference variables or other artifacts. This
2077                     // means they are safe to put into the
2078                     // `WhereClausePick`.
2079                     assert!(
2080                         !trait_ref.skip_binder().substs.needs_infer()
2081                             && !trait_ref.skip_binder().substs.has_placeholders()
2082                     );
2083
2084                     WhereClausePick(*trait_ref)
2085                 }
2086             },
2087             import_ids: self.import_ids.clone(),
2088             autoderefs: 0,
2089             autoref_or_ptr_adjustment: None,
2090             self_ty,
2091             unstable_candidates,
2092         }
2093     }
2094 }