compiler/rustc_hir_typeck/src/method/suggest.rs

   1 //! Give useful errors and suggestions to users when an item can't be
   2 //! found or is otherwise invalid.
   3
   4 use crate::errors;
   5 use crate::Expectation;
   6 use crate::FnCtxt;
   7 use rustc_ast::ast::Mutability;
   8 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
   9 use rustc_errors::StashKey;
  10 use rustc_errors::{
  11     pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
  12     MultiSpan,
  13 };
  14 use rustc_hir as hir;
  15 use rustc_hir::def::DefKind;
  16 use rustc_hir::def_id::DefId;
  17 use rustc_hir::lang_items::LangItem;
  18 use rustc_hir::PatKind::Binding;
  19 use rustc_hir::PathSegment;
  20 use rustc_hir::{ExprKind, Node, QPath};
  21 use rustc_infer::infer::{
  22     type_variable::{TypeVariableOrigin, TypeVariableOriginKind},
  23     RegionVariableOrigin,
  24 };
  25 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
  26 use rustc_middle::traits::util::supertraits;
  27 use rustc_middle::ty::fast_reject::DeepRejectCtxt;
  28 use rustc_middle::ty::fast_reject::{simplify_type, TreatParams};
  29 use rustc_middle::ty::print::{with_crate_prefix, with_forced_trimmed_paths};
  30 use rustc_middle::ty::{self, DefIdTree, GenericArgKind, Ty, TyCtxt, TypeVisitable};
  31 use rustc_middle::ty::{IsSuggestable, ToPolyTraitRef};
  32 use rustc_span::symbol::{kw, sym, Ident};
  33 use rustc_span::Symbol;
  34 use rustc_span::{lev_distance, source_map, ExpnKind, FileName, MacroKind, Span};
  35 use rustc_trait_selection::traits::error_reporting::on_unimplemented::OnUnimplementedNote;
  36 use rustc_trait_selection::traits::error_reporting::on_unimplemented::TypeErrCtxtExt as _;
  37 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
  38 use rustc_trait_selection::traits::{
  39     FulfillmentError, Obligation, ObligationCause, ObligationCauseCode,
  40 };
  41
  42 use super::probe::{AutorefOrPtrAdjustment, IsSuggestion, Mode, ProbeScope};
  43 use super::{CandidateSource, MethodError, NoMatchData};
  44 use rustc_hir::intravisit::Visitor;
  45 use std::cmp::Ordering;
  46 use std::iter;
  47
  48 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  49     fn is_fn_ty(&self, ty: Ty<'tcx>, span: Span) -> bool {
  50         let tcx = self.tcx;
  51         match ty.kind() {
  52             // Not all of these (e.g., unsafe fns) implement `FnOnce`,
  53             // so we look for these beforehand.
  54             ty::Closure(..) | ty::FnDef(..) | ty::FnPtr(_) => true,
  55             // If it's not a simple function, look for things which implement `FnOnce`.
  56             _ => {
  57                 let Some(fn_once) = tcx.lang_items().fn_once_trait() else {
  58                     return false;
  59                 };
  60
  61                 // This conditional prevents us from asking to call errors and unresolved types.
  62                 // It might seem that we can use `predicate_must_hold_modulo_regions`,
  63                 // but since a Dummy binder is used to fill in the FnOnce trait's arguments,
  64                 // type resolution always gives a "maybe" here.
  65                 if self.autoderef(span, ty).any(|(ty, _)| {
  66                     info!("check deref {:?} error", ty);
  67                     matches!(ty.kind(), ty::Error(_) | ty::Infer(_))
  68                 }) {
  69                     return false;
  70                 }
  71
  72                 self.autoderef(span, ty).any(|(ty, _)| {
  73                     info!("check deref {:?} impl FnOnce", ty);
  74                     self.probe(|_| {
  75                         let trait_ref = tcx.mk_trait_ref(
  76                             fn_once,
  77                             [
  78                                 ty,
  79                                 self.next_ty_var(TypeVariableOrigin {
  80                                     kind: TypeVariableOriginKind::MiscVariable,
  81                                     span,
  82                                 }),
  83                             ],
  84                         );
  85                         let poly_trait_ref = ty::Binder::dummy(trait_ref);
  86                         let obligation = Obligation::misc(
  87                             tcx,
  88                             span,
  89                             self.body_id,
  90                             self.param_env,
  91                             poly_trait_ref.without_const(),
  92                         );
  93                         self.predicate_may_hold(&obligation)
  94                     })
  95                 })
  96             }
  97         }
  98     }
  99
 100     fn is_slice_ty(&self, ty: Ty<'tcx>, span: Span) -> bool {
 101         self.autoderef(span, ty).any(|(ty, _)| matches!(ty.kind(), ty::Slice(..) | ty::Array(..)))
 102     }
 103
 104     #[instrument(level = "debug", skip(self))]
 105     pub fn report_method_error(
 106         &self,
 107         span: Span,
 108         rcvr_ty: Ty<'tcx>,
 109         item_name: Ident,
 110         source: SelfSource<'tcx>,
 111         error: MethodError<'tcx>,
 112         args: Option<(&'tcx hir::Expr<'tcx>, &'tcx [hir::Expr<'tcx>])>,
 113         expected: Expectation<'tcx>,
 114     ) -> Option<DiagnosticBuilder<'_, ErrorGuaranteed>> {
 115         // Avoid suggestions when we don't know what's going on.
 116         if rcvr_ty.references_error() {
 117             return None;
 118         }
 119
 120         let sugg_span = if let SelfSource::MethodCall(expr) = source {
 121             // Given `foo.bar(baz)`, `expr` is `bar`, but we want to point to the whole thing.
 122             self.tcx.hir().expect_expr(self.tcx.hir().parent_id(expr.hir_id)).span
 123         } else {
 124             span
 125         };
 126
 127         match error {
 128             MethodError::NoMatch(mut no_match_data) => {
 129                 return self.report_no_match_method_error(
 130                     span,
 131                     rcvr_ty,
 132                     item_name,
 133                     source,
 134                     args,
 135                     sugg_span,
 136                     &mut no_match_data,
 137                     expected,
 138                 );
 139             }
 140
 141             MethodError::Ambiguity(mut sources) => {
 142                 let mut err = struct_span_err!(
 143                     self.sess(),
 144                     item_name.span,
 145                     E0034,
 146                     "multiple applicable items in scope"
 147                 );
 148                 err.span_label(item_name.span, format!("multiple `{}` found", item_name));
 149
 150                 self.note_candidates_on_method_error(
 151                     rcvr_ty,
 152                     item_name,
 153                     args,
 154                     span,
 155                     &mut err,
 156                     &mut sources,
 157                     Some(sugg_span),
 158                 );
 159                 err.emit();
 160             }
 161
 162             MethodError::PrivateMatch(kind, def_id, out_of_scope_traits) => {
 163                 let kind = kind.descr(def_id);
 164                 let mut err = struct_span_err!(
 165                     self.tcx.sess,
 166                     item_name.span,
 167                     E0624,
 168                     "{} `{}` is private",
 169                     kind,
 170                     item_name
 171                 );
 172                 err.span_label(item_name.span, &format!("private {}", kind));
 173                 let sp = self
 174                     .tcx
 175                     .hir()
 176                     .span_if_local(def_id)
 177                     .unwrap_or_else(|| self.tcx.def_span(def_id));
 178                 err.span_label(sp, &format!("private {} defined here", kind));
 179                 self.suggest_valid_traits(&mut err, out_of_scope_traits);
 180                 err.emit();
 181             }
 182
 183             MethodError::IllegalSizedBound { candidates, needs_mut, bound_span, self_expr } => {
 184                 let msg = if needs_mut {
 185                     with_forced_trimmed_paths!(format!(
 186                         "the `{item_name}` method cannot be invoked on `{rcvr_ty}`"
 187                     ))
 188                 } else {
 189                     format!("the `{item_name}` method cannot be invoked on a trait object")
 190                 };
 191                 let mut err = self.sess().struct_span_err(span, &msg);
 192                 if !needs_mut {
 193                     err.span_label(bound_span, "this has a `Sized` requirement");
 194                 }
 195                 if !candidates.is_empty() {
 196                     let help = format!(
 197                         "{an}other candidate{s} {were} found in the following trait{s}, perhaps \
 198                          add a `use` for {one_of_them}:",
 199                         an = if candidates.len() == 1 { "an" } else { "" },
 200                         s = pluralize!(candidates.len()),
 201                         were = pluralize!("was", candidates.len()),
 202                         one_of_them = if candidates.len() == 1 { "it" } else { "one_of_them" },
 203                     );
 204                     self.suggest_use_candidates(&mut err, help, candidates);
 205                 }
 206                 if let ty::Ref(region, t_type, mutability) = rcvr_ty.kind() {
 207                     if needs_mut {
 208                         let trait_type = self.tcx.mk_ref(
 209                             *region,
 210                             ty::TypeAndMut { ty: *t_type, mutbl: mutability.invert() },
 211                         );
 212                         let msg = format!("you need `{}` instead of `{}`", trait_type, rcvr_ty);
 213                         let mut kind = &self_expr.kind;
 214                         while let hir::ExprKind::AddrOf(_, _, expr)
 215                         | hir::ExprKind::Unary(hir::UnOp::Deref, expr) = kind
 216                         {
 217                             kind = &expr.kind;
 218                         }
 219                         if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = kind
 220                             && let hir::def::Res::Local(hir_id) = path.res
 221                             && let Some(hir::Node::Pat(b)) = self.tcx.hir().find(hir_id)
 222                             && let Some(hir::Node::Param(p)) = self.tcx.hir().find_parent(b.hir_id)
 223                             && let Some(node) = self.tcx.hir().find_parent(p.hir_id)
 224                             && let Some(decl) = node.fn_decl()
 225                             && let Some(ty) = decl.inputs.iter().find(|ty| ty.span == p.ty_span)
 226                             && let hir::TyKind::Ref(_, mut_ty) = &ty.kind
 227                             && let hir::Mutability::Not = mut_ty.mutbl
 228                         {
 229                             err.span_suggestion_verbose(
 230                                 mut_ty.ty.span.shrink_to_lo(),
 231                                 &msg,
 232                                 "mut ",
 233                                 Applicability::MachineApplicable,
 234                             );
 235                         } else {
 236                             err.help(&msg);
 237                         }
 238                     }
 239                 }
 240                 err.emit();
 241             }
 242
 243             MethodError::BadReturnType => bug!("no return type expectations but got BadReturnType"),
 244         }
 245         None
 246     }
 247
 248     pub fn report_no_match_method_error(
 249         &self,
 250         mut span: Span,
 251         rcvr_ty: Ty<'tcx>,
 252         item_name: Ident,
 253         source: SelfSource<'tcx>,
 254         args: Option<(&'tcx hir::Expr<'tcx>, &'tcx [hir::Expr<'tcx>])>,
 255         sugg_span: Span,
 256         no_match_data: &mut NoMatchData<'tcx>,
 257         expected: Expectation<'tcx>,
 258     ) -> Option<DiagnosticBuilder<'_, ErrorGuaranteed>> {
 259         let mode = no_match_data.mode;
 260         let tcx = self.tcx;
 261         let rcvr_ty = self.resolve_vars_if_possible(rcvr_ty);
 262         let ty_str = with_forced_trimmed_paths!(self.ty_to_string(rcvr_ty));
 263         let is_method = mode == Mode::MethodCall;
 264         let unsatisfied_predicates = &no_match_data.unsatisfied_predicates;
 265         let lev_candidate = no_match_data.lev_candidate;
 266         let item_kind = if is_method {
 267             "method"
 268         } else if rcvr_ty.is_enum() {
 269             "variant or associated item"
 270         } else {
 271             match (item_name.as_str().chars().next(), rcvr_ty.is_fresh_ty()) {
 272                 (Some(name), false) if name.is_lowercase() => "function or associated item",
 273                 (Some(_), false) => "associated item",
 274                 (Some(_), true) | (None, false) => "variant or associated item",
 275                 (None, true) => "variant",
 276             }
 277         };
 278
 279         if self.suggest_wrapping_range_with_parens(tcx, rcvr_ty, source, span, item_name, &ty_str)
 280             || self.suggest_constraining_numerical_ty(
 281                 tcx, rcvr_ty, source, span, item_kind, item_name, &ty_str,
 282             )
 283         {
 284             return None;
 285         }
 286         span = item_name.span;
 287
 288         // Don't show generic arguments when the method can't be found in any implementation (#81576).
 289         let mut ty_str_reported = ty_str.clone();
 290         if let ty::Adt(_, generics) = rcvr_ty.kind() {
 291             if generics.len() > 0 {
 292                 let mut autoderef = self.autoderef(span, rcvr_ty);
 293                 let candidate_found = autoderef.any(|(ty, _)| {
 294                     if let ty::Adt(adt_def, _) = ty.kind() {
 295                         self.tcx
 296                             .inherent_impls(adt_def.did())
 297                             .iter()
 298                             .any(|def_id| self.associated_value(*def_id, item_name).is_some())
 299                     } else {
 300                         false
 301                     }
 302                 });
 303                 let has_deref = autoderef.step_count() > 0;
 304                 if !candidate_found && !has_deref && unsatisfied_predicates.is_empty() {
 305                     if let Some((path_string, _)) = ty_str.split_once('<') {
 306                         ty_str_reported = path_string.to_string();
 307                     }
 308                 }
 309             }
 310         }
 311
 312         let mut err = struct_span_err!(
 313             tcx.sess,
 314             span,
 315             E0599,
 316             "no {} named `{}` found for {} `{}` in the current scope",
 317             item_kind,
 318             item_name,
 319             rcvr_ty.prefix_string(self.tcx),
 320             ty_str_reported,
 321         );
 322         if rcvr_ty.references_error() {
 323             err.downgrade_to_delayed_bug();
 324         }
 325
 326         if let Mode::MethodCall = mode && let SelfSource::MethodCall(cal) = source {
 327             self.suggest_await_before_method(
 328                 &mut err, item_name, rcvr_ty, cal, span, expected.only_has_type(self),
 329             );
 330         }
 331         if let Some(span) =
 332             tcx.resolutions(()).confused_type_with_std_module.get(&span.with_parent(None))
 333         {
 334             err.span_suggestion(
 335                 span.shrink_to_lo(),
 336                 "you are looking for the module in `std`, not the primitive type",
 337                 "std::",
 338                 Applicability::MachineApplicable,
 339             );
 340         }
 341         if let ty::RawPtr(_) = &rcvr_ty.kind() {
 342             err.note(
 343                 "try using `<*const T>::as_ref()` to get a reference to the \
 344                  type behind the pointer: https://doc.rust-lang.org/std/\
 345                  primitive.pointer.html#method.as_ref",
 346             );
 347             err.note(
 348                 "using `<*const T>::as_ref()` on a pointer which is unaligned or points \
 349                  to invalid or uninitialized memory is undefined behavior",
 350             );
 351         }
 352
 353         let ty_span = match rcvr_ty.kind() {
 354             ty::Param(param_type) => {
 355                 Some(param_type.span_from_generics(self.tcx, self.body_id.owner.to_def_id()))
 356             }
 357             ty::Adt(def, _) if def.did().is_local() => Some(tcx.def_span(def.did())),
 358             _ => None,
 359         };
 360         if let Some(span) = ty_span {
 361             err.span_label(
 362                 span,
 363                 format!(
 364                     "{item_kind} `{item_name}` not found for this {}",
 365                     rcvr_ty.prefix_string(self.tcx)
 366                 ),
 367             );
 368         }
 369
 370         if let SelfSource::MethodCall(rcvr_expr) = source {
 371             self.suggest_fn_call(&mut err, rcvr_expr, rcvr_ty, |output_ty| {
 372                 let call_expr =
 373                     self.tcx.hir().expect_expr(self.tcx.hir().parent_id(rcvr_expr.hir_id));
 374                 let probe = self.lookup_probe_for_diagnostic(
 375                     item_name,
 376                     output_ty,
 377                     call_expr,
 378                     ProbeScope::AllTraits,
 379                     expected.only_has_type(self),
 380                 );
 381                 probe.is_ok()
 382             });
 383         }
 384
 385         let mut custom_span_label = false;
 386
 387         let static_candidates = &mut no_match_data.static_candidates;
 388         if !static_candidates.is_empty() {
 389             err.note(
 390                 "found the following associated functions; to be used as methods, \
 391                  functions must have a `self` parameter",
 392             );
 393             err.span_label(span, "this is an associated function, not a method");
 394             custom_span_label = true;
 395         }
 396         if static_candidates.len() == 1 {
 397             self.suggest_associated_call_syntax(
 398                 &mut err,
 399                 &static_candidates,
 400                 rcvr_ty,
 401                 source,
 402                 item_name,
 403                 args,
 404                 sugg_span,
 405             );
 406
 407             self.note_candidates_on_method_error(
 408                 rcvr_ty,
 409                 item_name,
 410                 args,
 411                 span,
 412                 &mut err,
 413                 static_candidates,
 414                 None,
 415             );
 416         } else if static_candidates.len() > 1 {
 417             self.note_candidates_on_method_error(
 418                 rcvr_ty,
 419                 item_name,
 420                 args,
 421                 span,
 422                 &mut err,
 423                 static_candidates,
 424                 Some(sugg_span),
 425             );
 426         }
 427
 428         let mut bound_spans = vec![];
 429         let mut restrict_type_params = false;
 430         let mut unsatisfied_bounds = false;
 431         if item_name.name == sym::count && self.is_slice_ty(rcvr_ty, span) {
 432             let msg = "consider using `len` instead";
 433             if let SelfSource::MethodCall(_expr) = source {
 434                 err.span_suggestion_short(span, msg, "len", Applicability::MachineApplicable);
 435             } else {
 436                 err.span_label(span, msg);
 437             }
 438             if let Some(iterator_trait) = self.tcx.get_diagnostic_item(sym::Iterator) {
 439                 let iterator_trait = self.tcx.def_path_str(iterator_trait);
 440                 err.note(&format!(
 441                     "`count` is defined on `{iterator_trait}`, which `{rcvr_ty}` does not implement"
 442                 ));
 443             }
 444         } else if !unsatisfied_predicates.is_empty() {
 445             let mut type_params = FxHashMap::default();
 446
 447             // Pick out the list of unimplemented traits on the receiver.
 448             // This is used for custom error messages with the `#[rustc_on_unimplemented]` attribute.
 449             let mut unimplemented_traits = FxHashMap::default();
 450             let mut unimplemented_traits_only = true;
 451             for (predicate, _parent_pred, cause) in unsatisfied_predicates {
 452                 if let (ty::PredicateKind::Clause(ty::Clause::Trait(p)), Some(cause)) =
 453                     (predicate.kind().skip_binder(), cause.as_ref())
 454                 {
 455                     if p.trait_ref.self_ty() != rcvr_ty {
 456                         // This is necessary, not just to keep the errors clean, but also
 457                         // because our derived obligations can wind up with a trait ref that
 458                         // requires a different param_env to be correctly compared.
 459                         continue;
 460                     }
 461                     unimplemented_traits.entry(p.trait_ref.def_id).or_insert((
 462                         predicate.kind().rebind(p.trait_ref),
 463                         Obligation {
 464                             cause: cause.clone(),
 465                             param_env: self.param_env,
 466                             predicate: *predicate,
 467                             recursion_depth: 0,
 468                         },
 469                     ));
 470                 }
 471             }
 472
 473             // Make sure that, if any traits other than the found ones were involved,
 474             // we don't don't report an unimplemented trait.
 475             // We don't want to say that `iter::Cloned` is not an iterator, just
 476             // because of some non-Clone item being iterated over.
 477             for (predicate, _parent_pred, _cause) in unsatisfied_predicates {
 478                 match predicate.kind().skip_binder() {
 479                     ty::PredicateKind::Clause(ty::Clause::Trait(p))
 480                         if unimplemented_traits.contains_key(&p.trait_ref.def_id) => {}
 481                     _ => {
 482                         unimplemented_traits_only = false;
 483                         break;
 484                     }
 485                 }
 486             }
 487
 488             let mut collect_type_param_suggestions =
 489                 |self_ty: Ty<'tcx>, parent_pred: ty::Predicate<'tcx>, obligation: &str| {
 490                     // We don't care about regions here, so it's fine to skip the binder here.
 491                     if let (ty::Param(_), ty::PredicateKind::Clause(ty::Clause::Trait(p))) =
 492                         (self_ty.kind(), parent_pred.kind().skip_binder())
 493                     {
 494                         let hir = self.tcx.hir();
 495                         let node = match p.trait_ref.self_ty().kind() {
 496                             ty::Param(_) => {
 497                                 // Account for `fn` items like in `issue-35677.rs` to
 498                                 // suggest restricting its type params.
 499                                 let parent_body =
 500                                     hir.body_owner(hir::BodyId { hir_id: self.body_id });
 501                                 Some(hir.get(parent_body))
 502                             }
 503                             ty::Adt(def, _) => {
 504                                 def.did().as_local().map(|def_id| hir.get_by_def_id(def_id))
 505                             }
 506                             _ => None,
 507                         };
 508                         if let Some(hir::Node::Item(hir::Item { kind, .. })) = node
 509                             && let Some(g) = kind.generics()
 510                         {
 511                             let key = (
 512                                 g.tail_span_for_predicate_suggestion(),
 513                                 g.add_where_or_trailing_comma(),
 514                             );
 515                             type_params
 516                                 .entry(key)
 517                                 .or_insert_with(FxHashSet::default)
 518                                 .insert(obligation.to_owned());
 519                             return true;
 520                         }
 521                     }
 522                     false
 523                 };
 524             let mut bound_span_label = |self_ty: Ty<'_>, obligation: &str, quiet: &str| {
 525                 let msg = format!(
 526                     "doesn't satisfy `{}`",
 527                     if obligation.len() > 50 { quiet } else { obligation }
 528                 );
 529                 match &self_ty.kind() {
 530                     // Point at the type that couldn't satisfy the bound.
 531                     ty::Adt(def, _) => bound_spans.push((self.tcx.def_span(def.did()), msg)),
 532                     // Point at the trait object that couldn't satisfy the bound.
 533                     ty::Dynamic(preds, _, _) => {
 534                         for pred in preds.iter() {
 535                             match pred.skip_binder() {
 536                                 ty::ExistentialPredicate::Trait(tr) => {
 537                                     bound_spans.push((self.tcx.def_span(tr.def_id), msg.clone()))
 538                                 }
 539                                 ty::ExistentialPredicate::Projection(_)
 540                                 | ty::ExistentialPredicate::AutoTrait(_) => {}
 541                             }
 542                         }
 543                     }
 544                     // Point at the closure that couldn't satisfy the bound.
 545                     ty::Closure(def_id, _) => bound_spans
 546                         .push((tcx.def_span(*def_id), format!("doesn't satisfy `{}`", quiet))),
 547                     _ => {}
 548                 }
 549             };
 550             let mut format_pred = |pred: ty::Predicate<'tcx>| {
 551                 let bound_predicate = pred.kind();
 552                 match bound_predicate.skip_binder() {
 553                     ty::PredicateKind::Clause(ty::Clause::Projection(pred)) => {
 554                         let pred = bound_predicate.rebind(pred);
 555                         // `<Foo as Iterator>::Item = String`.
 556                         let projection_ty = pred.skip_binder().projection_ty;
 557
 558                         let substs_with_infer_self = tcx.mk_substs(
 559                             iter::once(tcx.mk_ty_var(ty::TyVid::from_u32(0)).into())
 560                                 .chain(projection_ty.substs.iter().skip(1)),
 561                         );
 562
 563                         let quiet_projection_ty =
 564                             tcx.mk_alias_ty(projection_ty.def_id, substs_with_infer_self);
 565
 566                         let term = pred.skip_binder().term;
 567
 568                         let obligation = format!("{} = {}", projection_ty, term);
 569                         let quiet = with_forced_trimmed_paths!(format!(
 570                             "{} = {}",
 571                             quiet_projection_ty, term
 572                         ));
 573
 574                         bound_span_label(projection_ty.self_ty(), &obligation, &quiet);
 575                         Some((obligation, projection_ty.self_ty()))
 576                     }
 577                     ty::PredicateKind::Clause(ty::Clause::Trait(poly_trait_ref)) => {
 578                         let p = poly_trait_ref.trait_ref;
 579                         let self_ty = p.self_ty();
 580                         let path = p.print_only_trait_path();
 581                         let obligation = format!("{}: {}", self_ty, path);
 582                         let quiet = with_forced_trimmed_paths!(format!("_: {}", path));
 583                         bound_span_label(self_ty, &obligation, &quiet);
 584                         Some((obligation, self_ty))
 585                     }
 586                     _ => None,
 587                 }
 588             };
 589
 590             // Find all the requirements that come from a local `impl` block.
 591             let mut skip_list: FxHashSet<_> = Default::default();
 592             let mut spanned_predicates = FxHashMap::default();
 593             for (p, parent_p, impl_def_id, cause) in unsatisfied_predicates
 594                 .iter()
 595                 .filter_map(|(p, parent, c)| c.as_ref().map(|c| (p, parent, c)))
 596                 .filter_map(|(p, parent, c)| match c.code() {
 597                     ObligationCauseCode::ImplDerivedObligation(data)
 598                         if matches!(p.kind().skip_binder(), ty::PredicateKind::Clause(_)) =>
 599                     {
 600                         Some((p, parent, data.impl_def_id, data))
 601                     }
 602                     _ => None,
 603                 })
 604             {
 605                 match self.tcx.hir().get_if_local(impl_def_id) {
 606                     // Unmet obligation comes from a `derive` macro, point at it once to
 607                     // avoid multiple span labels pointing at the same place.
 608                     Some(Node::Item(hir::Item {
 609                         kind: hir::ItemKind::Impl(hir::Impl { of_trait, self_ty, .. }),
 610                         ..
 611                     })) if matches!(
 612                         self_ty.span.ctxt().outer_expn_data().kind,
 613                         ExpnKind::Macro(MacroKind::Derive, _)
 614                     ) || matches!(
 615                         of_trait.as_ref().map(|t| t.path.span.ctxt().outer_expn_data().kind),
 616                         Some(ExpnKind::Macro(MacroKind::Derive, _))
 617                     ) =>
 618                     {
 619                         let span = self_ty.span.ctxt().outer_expn_data().call_site;
 620                         let entry = spanned_predicates.entry(span);
 621                         let entry = entry.or_insert_with(|| {
 622                             (FxHashSet::default(), FxHashSet::default(), Vec::new())
 623                         });
 624                         entry.0.insert(span);
 625                         entry.1.insert((
 626                             span,
 627                             "unsatisfied trait bound introduced in this `derive` macro",
 628                         ));
 629                         entry.2.push(p);
 630                         skip_list.insert(p);
 631                     }
 632
 633                     // Unmet obligation coming from an `impl`.
 634                     Some(Node::Item(hir::Item {
 635                         kind: hir::ItemKind::Impl(hir::Impl { of_trait, self_ty, generics, .. }),
 636                         span: item_span,
 637                         ..
 638                     })) => {
 639                         let sized_pred =
 640                             unsatisfied_predicates.iter().any(|(pred, _, _)| {
 641                                 match pred.kind().skip_binder() {
 642                                     ty::PredicateKind::Clause(ty::Clause::Trait(pred)) => {
 643                                         Some(pred.def_id()) == self.tcx.lang_items().sized_trait()
 644                                             && pred.polarity == ty::ImplPolarity::Positive
 645                                     }
 646                                     _ => false,
 647                                 }
 648                             });
 649                         for param in generics.params {
 650                             if param.span == cause.span && sized_pred {
 651                                 let (sp, sugg) = match param.colon_span {
 652                                     Some(sp) => (sp.shrink_to_hi(), " ?Sized +"),
 653                                     None => (param.span.shrink_to_hi(), ": ?Sized"),
 654                                 };
 655                                 err.span_suggestion_verbose(
 656                                     sp,
 657                                     "consider relaxing the type parameter's implicit `Sized` bound",
 658                                     sugg,
 659                                     Applicability::MachineApplicable,
 660                                 );
 661                             }
 662                         }
 663                         if let Some(pred) = parent_p {
 664                             // Done to add the "doesn't satisfy" `span_label`.
 665                             let _ = format_pred(*pred);
 666                         }
 667                         skip_list.insert(p);
 668                         let entry = spanned_predicates.entry(self_ty.span);
 669                         let entry = entry.or_insert_with(|| {
 670                             (FxHashSet::default(), FxHashSet::default(), Vec::new())
 671                         });
 672                         entry.2.push(p);
 673                         if cause.span != *item_span {
 674                             entry.0.insert(cause.span);
 675                             entry.1.insert((cause.span, "unsatisfied trait bound introduced here"));
 676                         } else {
 677                             if let Some(trait_ref) = of_trait {
 678                                 entry.0.insert(trait_ref.path.span);
 679                             }
 680                             entry.0.insert(self_ty.span);
 681                         };
 682                         if let Some(trait_ref) = of_trait {
 683                             entry.1.insert((trait_ref.path.span, ""));
 684                         }
 685                         entry.1.insert((self_ty.span, ""));
 686                     }
 687                     Some(Node::Item(hir::Item {
 688                         kind: hir::ItemKind::Trait(rustc_ast::ast::IsAuto::Yes, ..),
 689                         span: item_span,
 690                         ..
 691                     })) => {
 692                         tcx.sess.delay_span_bug(
 693                             *item_span,
 694                             "auto trait is invoked with no method error, but no error reported?",
 695                         );
 696                     }
 697                     Some(Node::Item(hir::Item {
 698                         ident, kind: hir::ItemKind::Trait(..), ..
 699                     })) => {
 700                         skip_list.insert(p);
 701                         let entry = spanned_predicates.entry(ident.span);
 702                         let entry = entry.or_insert_with(|| {
 703                             (FxHashSet::default(), FxHashSet::default(), Vec::new())
 704                         });
 705                         entry.0.insert(cause.span);
 706                         entry.1.insert((ident.span, ""));
 707                         entry.1.insert((cause.span, "unsatisfied trait bound introduced here"));
 708                         entry.2.push(p);
 709                     }
 710                     Some(node) => unreachable!("encountered `{node:?}`"),
 711                     None => (),
 712                 }
 713             }
 714             let mut spanned_predicates: Vec<_> = spanned_predicates.into_iter().collect();
 715             spanned_predicates.sort_by_key(|(span, _)| *span);
 716             for (_, (primary_spans, span_labels, predicates)) in spanned_predicates {
 717                 let mut preds: Vec<_> = predicates
 718                     .iter()
 719                     .filter_map(|pred| format_pred(**pred))
 720                     .map(|(p, _)| format!("`{}`", p))
 721                     .collect();
 722                 preds.sort();
 723                 preds.dedup();
 724                 let msg = if let [pred] = &preds[..] {
 725                     format!("trait bound {} was not satisfied", pred)
 726                 } else {
 727                     format!("the following trait bounds were not satisfied:\n{}", preds.join("\n"),)
 728                 };
 729                 let mut span: MultiSpan = primary_spans.into_iter().collect::<Vec<_>>().into();
 730                 for (sp, label) in span_labels {
 731                     span.push_span_label(sp, label);
 732                 }
 733                 err.span_note(span, &msg);
 734                 unsatisfied_bounds = true;
 735             }
 736
 737             let mut suggested_bounds = FxHashSet::default();
 738             // The requirements that didn't have an `impl` span to show.
 739             let mut bound_list = unsatisfied_predicates
 740                 .iter()
 741                 .filter_map(|(pred, parent_pred, _cause)| {
 742                     let mut suggested = false;
 743                     format_pred(*pred).map(|(p, self_ty)| {
 744                         if let Some(parent) = parent_pred && suggested_bounds.contains(parent) {
 745                             // We don't suggest `PartialEq` when we already suggest `Eq`.
 746                         } else if !suggested_bounds.contains(pred) {
 747                             if collect_type_param_suggestions(self_ty, *pred, &p) {
 748                                 suggested = true;
 749                                 suggested_bounds.insert(pred);
 750                             }
 751                         }
 752                         (
 753                             match parent_pred {
 754                                 None => format!("`{}`", &p),
 755                                 Some(parent_pred) => match format_pred(*parent_pred) {
 756                                     None => format!("`{}`", &p),
 757                                     Some((parent_p, _)) => {
 758                                         if !suggested
 759                                             && !suggested_bounds.contains(pred)
 760                                             && !suggested_bounds.contains(parent_pred)
 761                                         {
 762                                             if collect_type_param_suggestions(
 763                                                 self_ty,
 764                                                 *parent_pred,
 765                                                 &p,
 766                                             ) {
 767                                                 suggested_bounds.insert(pred);
 768                                             }
 769                                         }
 770                                         format!("`{}`\nwhich is required by `{}`", p, parent_p)
 771                                     }
 772                                 },
 773                             },
 774                             *pred,
 775                         )
 776                     })
 777                 })
 778                 .filter(|(_, pred)| !skip_list.contains(&pred))
 779                 .map(|(t, _)| t)
 780                 .enumerate()
 781                 .collect::<Vec<(usize, String)>>();
 782
 783             for ((span, add_where_or_comma), obligations) in type_params.into_iter() {
 784                 restrict_type_params = true;
 785                 // #74886: Sort here so that the output is always the same.
 786                 let mut obligations = obligations.into_iter().collect::<Vec<_>>();
 787                 obligations.sort();
 788                 err.span_suggestion_verbose(
 789                     span,
 790                     &format!(
 791                         "consider restricting the type parameter{s} to satisfy the \
 792                          trait bound{s}",
 793                         s = pluralize!(obligations.len())
 794                     ),
 795                     format!("{} {}", add_where_or_comma, obligations.join(", ")),
 796                     Applicability::MaybeIncorrect,
 797                 );
 798             }
 799
 800             bound_list.sort_by(|(_, a), (_, b)| a.cmp(b)); // Sort alphabetically.
 801             bound_list.dedup_by(|(_, a), (_, b)| a == b); // #35677
 802             bound_list.sort_by_key(|(pos, _)| *pos); // Keep the original predicate order.
 803
 804             if !bound_list.is_empty() || !skip_list.is_empty() {
 805                 let bound_list =
 806                     bound_list.into_iter().map(|(_, path)| path).collect::<Vec<_>>().join("\n");
 807                 let actual_prefix = rcvr_ty.prefix_string(self.tcx);
 808                 info!("unimplemented_traits.len() == {}", unimplemented_traits.len());
 809                 let (primary_message, label) = if unimplemented_traits.len() == 1
 810                     && unimplemented_traits_only
 811                 {
 812                     unimplemented_traits
 813                         .into_iter()
 814                         .next()
 815                         .map(|(_, (trait_ref, obligation))| {
 816                             if trait_ref.self_ty().references_error() || rcvr_ty.references_error()
 817                             {
 818                                 // Avoid crashing.
 819                                 return (None, None);
 820                             }
 821                             let OnUnimplementedNote { message, label, .. } =
 822                                 self.err_ctxt().on_unimplemented_note(trait_ref, &obligation);
 823                             (message, label)
 824                         })
 825                         .unwrap()
 826                 } else {
 827                     (None, None)
 828                 };
 829                 let primary_message = primary_message.unwrap_or_else(|| {
 830                     format!(
 831                         "the {item_kind} `{item_name}` exists for {actual_prefix} `{ty_str}`, \
 832                     but its trait bounds were not satisfied"
 833                     )
 834                 });
 835                 err.set_primary_message(&primary_message);
 836                 if let Some(label) = label {
 837                     custom_span_label = true;
 838                     err.span_label(span, label);
 839                 }
 840                 if !bound_list.is_empty() {
 841                     err.note(&format!(
 842                         "the following trait bounds were not satisfied:\n{bound_list}"
 843                     ));
 844                 }
 845                 self.suggest_derive(&mut err, &unsatisfied_predicates);
 846
 847                 unsatisfied_bounds = true;
 848             }
 849         }
 850
 851         let label_span_not_found = |err: &mut Diagnostic| {
 852             if unsatisfied_predicates.is_empty() {
 853                 err.span_label(span, format!("{item_kind} not found in `{ty_str}`"));
 854                 let is_string_or_ref_str = match rcvr_ty.kind() {
 855                     ty::Ref(_, ty, _) => {
 856                         ty.is_str()
 857                             || matches!(
 858                                 ty.kind(),
 859                                 ty::Adt(adt, _) if Some(adt.did()) == self.tcx.lang_items().string()
 860                             )
 861                     }
 862                     ty::Adt(adt, _) => Some(adt.did()) == self.tcx.lang_items().string(),
 863                     _ => false,
 864                 };
 865                 if is_string_or_ref_str && item_name.name == sym::iter {
 866                     err.span_suggestion_verbose(
 867                         item_name.span,
 868                         "because of the in-memory representation of `&str`, to obtain \
 869                          an `Iterator` over each of its codepoint use method `chars`",
 870                         "chars",
 871                         Applicability::MachineApplicable,
 872                     );
 873                 }
 874                 if let ty::Adt(adt, _) = rcvr_ty.kind() {
 875                     let mut inherent_impls_candidate = self
 876                         .tcx
 877                         .inherent_impls(adt.did())
 878                         .iter()
 879                         .copied()
 880                         .filter(|def_id| {
 881                             if let Some(assoc) = self.associated_value(*def_id, item_name) {
 882                                 // Check for both mode is the same so we avoid suggesting
 883                                 // incorrect associated item.
 884                                 match (mode, assoc.fn_has_self_parameter, source) {
 885                                     (Mode::MethodCall, true, SelfSource::MethodCall(_)) => {
 886                                         // We check that the suggest type is actually
 887                                         // different from the received one
 888                                         // So we avoid suggestion method with Box<Self>
 889                                         // for instance
 890                                         self.tcx.at(span).type_of(*def_id) != rcvr_ty
 891                                             && self.tcx.at(span).type_of(*def_id) != rcvr_ty
 892                                     }
 893                                     (Mode::Path, false, _) => true,
 894                                     _ => false,
 895                                 }
 896                             } else {
 897                                 false
 898                             }
 899                         })
 900                         .collect::<Vec<_>>();
 901                     if !inherent_impls_candidate.is_empty() {
 902                         inherent_impls_candidate.sort();
 903                         inherent_impls_candidate.dedup();
 904
 905                         // number of type to shows at most.
 906                         let limit = if inherent_impls_candidate.len() == 5 { 5 } else { 4 };
 907                         let type_candidates = inherent_impls_candidate
 908                             .iter()
 909                             .take(limit)
 910                             .map(|impl_item| {
 911                                 format!("- `{}`", self.tcx.at(span).type_of(*impl_item))
 912                             })
 913                             .collect::<Vec<_>>()
 914                             .join("\n");
 915                         let additional_types = if inherent_impls_candidate.len() > limit {
 916                             format!("\nand {} more types", inherent_impls_candidate.len() - limit)
 917                         } else {
 918                             "".to_string()
 919                         };
 920                         err.note(&format!(
 921                             "the {item_kind} was found for\n{}{}",
 922                             type_candidates, additional_types
 923                         ));
 924                     }
 925                 }
 926             } else {
 927                 let ty_str =
 928                     if ty_str.len() > 50 { String::new() } else { format!("on `{ty_str}` ") };
 929                 err.span_label(
 930                     span,
 931                     format!("{item_kind} cannot be called {ty_str}due to unsatisfied trait bounds"),
 932                 );
 933             }
 934         };
 935
 936         // If the method name is the name of a field with a function or closure type,
 937         // give a helping note that it has to be called as `(x.f)(...)`.
 938         if let SelfSource::MethodCall(expr) = source {
 939             if !self.suggest_calling_field_as_fn(span, rcvr_ty, expr, item_name, &mut err)
 940                 && lev_candidate.is_none()
 941                 && !custom_span_label
 942             {
 943                 label_span_not_found(&mut err);
 944             }
 945         } else if !custom_span_label {
 946             label_span_not_found(&mut err);
 947         }
 948
 949         // Don't suggest (for example) `expr.field.clone()` if `expr.clone()`
 950         // can't be called due to `typeof(expr): Clone` not holding.
 951         if unsatisfied_predicates.is_empty() {
 952             self.suggest_calling_method_on_field(
 953                 &mut err,
 954                 source,
 955                 span,
 956                 rcvr_ty,
 957                 item_name,
 958                 expected.only_has_type(self),
 959             );
 960         }
 961
 962         self.check_for_inner_self(&mut err, source, rcvr_ty, item_name);
 963
 964         bound_spans.sort();
 965         bound_spans.dedup();
 966         for (span, msg) in bound_spans.into_iter() {
 967             err.span_label(span, &msg);
 968         }
 969
 970         if rcvr_ty.is_numeric() && rcvr_ty.is_fresh() || restrict_type_params {
 971         } else {
 972             self.suggest_traits_to_import(
 973                 &mut err,
 974                 span,
 975                 rcvr_ty,
 976                 item_name,
 977                 args.map(|(_, args)| args.len() + 1),
 978                 source,
 979                 no_match_data.out_of_scope_traits.clone(),
 980                 &unsatisfied_predicates,
 981                 &static_candidates,
 982                 unsatisfied_bounds,
 983                 expected.only_has_type(self),
 984             );
 985         }
 986
 987         // Don't emit a suggestion if we found an actual method
 988         // that had unsatisfied trait bounds
 989         if unsatisfied_predicates.is_empty() && rcvr_ty.is_enum() {
 990             let adt_def = rcvr_ty.ty_adt_def().expect("enum is not an ADT");
 991             if let Some(suggestion) = lev_distance::find_best_match_for_name(
 992                 &adt_def.variants().iter().map(|s| s.name).collect::<Vec<_>>(),
 993                 item_name.name,
 994                 None,
 995             ) {
 996                 err.span_suggestion(
 997                     span,
 998                     "there is a variant with a similar name",
 999                     suggestion,
1000                     Applicability::MaybeIncorrect,
1001                 );
1002             }
1003         }
1004
1005         if item_name.name == sym::as_str && rcvr_ty.peel_refs().is_str() {
1006             let msg = "remove this method call";
1007             let mut fallback_span = true;
1008             if let SelfSource::MethodCall(expr) = source {
1009                 let call_expr = self.tcx.hir().expect_expr(self.tcx.hir().parent_id(expr.hir_id));
1010                 if let Some(span) = call_expr.span.trim_start(expr.span) {
1011                     err.span_suggestion(span, msg, "", Applicability::MachineApplicable);
1012                     fallback_span = false;
1013                 }
1014             }
1015             if fallback_span {
1016                 err.span_label(span, msg);
1017             }
1018         } else if let Some(lev_candidate) = lev_candidate {
1019             // Don't emit a suggestion if we found an actual method
1020             // that had unsatisfied trait bounds
1021             if unsatisfied_predicates.is_empty() {
1022                 let def_kind = lev_candidate.kind.as_def_kind();
1023                 // Methods are defined within the context of a struct and their first parameter is always self,
1024                 // which represents the instance of the struct the method is being called on
1025                 // Associated functions don’t take self as a parameter and
1026                 // they are not methods because they don’t have an instance of the struct to work with.
1027                 if def_kind == DefKind::AssocFn && lev_candidate.fn_has_self_parameter {
1028                     err.span_suggestion(
1029                         span,
1030                         "there is a method with a similar name",
1031                         lev_candidate.name,
1032                         Applicability::MaybeIncorrect,
1033                     );
1034                 } else {
1035                     err.span_suggestion(
1036                         span,
1037                         &format!(
1038                             "there is {} {} with a similar name",
1039                             def_kind.article(),
1040                             def_kind.descr(lev_candidate.def_id),
1041                         ),
1042                         lev_candidate.name,
1043                         Applicability::MaybeIncorrect,
1044                     );
1045                 }
1046             }
1047         }
1048
1049         self.check_for_deref_method(&mut err, source, rcvr_ty, item_name, expected);
1050         return Some(err);
1051     }
1052
1053     fn note_candidates_on_method_error(
1054         &self,
1055         rcvr_ty: Ty<'tcx>,
1056         item_name: Ident,
1057         args: Option<(&'tcx hir::Expr<'tcx>, &'tcx [hir::Expr<'tcx>])>,
1058         span: Span,
1059         err: &mut Diagnostic,
1060         sources: &mut Vec<CandidateSource>,
1061         sugg_span: Option<Span>,
1062     ) {
1063         sources.sort();
1064         sources.dedup();
1065         // Dynamic limit to avoid hiding just one candidate, which is silly.
1066         let limit = if sources.len() == 5 { 5 } else { 4 };
1067
1068         for (idx, source) in sources.iter().take(limit).enumerate() {
1069             match *source {
1070                 CandidateSource::Impl(impl_did) => {
1071                     // Provide the best span we can. Use the item, if local to crate, else
1072                     // the impl, if local to crate (item may be defaulted), else nothing.
1073                     let Some(item) = self.associated_value(impl_did, item_name).or_else(|| {
1074                         let impl_trait_ref = self.tcx.impl_trait_ref(impl_did)?;
1075                         self.associated_value(impl_trait_ref.skip_binder().def_id, item_name)
1076                     }) else {
1077                         continue;
1078                     };
1079
1080                     let note_span = if item.def_id.is_local() {
1081                         Some(self.tcx.def_span(item.def_id))
1082                     } else if impl_did.is_local() {
1083                         Some(self.tcx.def_span(impl_did))
1084                     } else {
1085                         None
1086                     };
1087
1088                     let impl_ty = self.tcx.at(span).type_of(impl_did);
1089
1090                     let insertion = match self.tcx.impl_trait_ref(impl_did) {
1091                         None => String::new(),
1092                         Some(trait_ref) => {
1093                             format!(
1094                                 " of the trait `{}`",
1095                                 self.tcx.def_path_str(trait_ref.skip_binder().def_id)
1096                             )
1097                         }
1098                     };
1099
1100                     let (note_str, idx) = if sources.len() > 1 {
1101                         (
1102                             format!(
1103                                 "candidate #{} is defined in an impl{} for the type `{}`",
1104                                 idx + 1,
1105                                 insertion,
1106                                 impl_ty,
1107                             ),
1108                             Some(idx + 1),
1109                         )
1110                     } else {
1111                         (
1112                             format!(
1113                                 "the candidate is defined in an impl{} for the type `{}`",
1114                                 insertion, impl_ty,
1115                             ),
1116                             None,
1117                         )
1118                     };
1119                     if let Some(note_span) = note_span {
1120                         // We have a span pointing to the method. Show note with snippet.
1121                         err.span_note(note_span, &note_str);
1122                     } else {
1123                         err.note(&note_str);
1124                     }
1125                     if let Some(sugg_span) = sugg_span
1126                         && let Some(trait_ref) = self.tcx.impl_trait_ref(impl_did) {
1127                         let path = self.tcx.def_path_str(trait_ref.skip_binder().def_id);
1128
1129                         let ty = match item.kind {
1130                             ty::AssocKind::Const | ty::AssocKind::Type => rcvr_ty,
1131                             ty::AssocKind::Fn => self
1132                                 .tcx
1133                                 .fn_sig(item.def_id)
1134                                 .inputs()
1135                                 .skip_binder()
1136                                 .get(0)
1137                                 .filter(|ty| ty.is_region_ptr() && !rcvr_ty.is_region_ptr())
1138                                 .copied()
1139                                 .unwrap_or(rcvr_ty),
1140                         };
1141                         print_disambiguation_help(
1142                             item_name,
1143                             args,
1144                             err,
1145                             path,
1146                             ty,
1147                             item.kind,
1148                             item.def_id,
1149                             sugg_span,
1150                             idx,
1151                             self.tcx.sess.source_map(),
1152                             item.fn_has_self_parameter,
1153                         );
1154                     }
1155                 }
1156                 CandidateSource::Trait(trait_did) => {
1157                     let Some(item) = self.associated_value(trait_did, item_name) else { continue };
1158                     let item_span = self.tcx.def_span(item.def_id);
1159                     let idx = if sources.len() > 1 {
1160                         let msg = &format!(
1161                             "candidate #{} is defined in the trait `{}`",
1162                             idx + 1,
1163                             self.tcx.def_path_str(trait_did)
1164                         );
1165                         err.span_note(item_span, msg);
1166                         Some(idx + 1)
1167                     } else {
1168                         let msg = &format!(
1169                             "the candidate is defined in the trait `{}`",
1170                             self.tcx.def_path_str(trait_did)
1171                         );
1172                         err.span_note(item_span, msg);
1173                         None
1174                     };
1175                     if let Some(sugg_span) = sugg_span {
1176                         let path = self.tcx.def_path_str(trait_did);
1177                         print_disambiguation_help(
1178                             item_name,
1179                             args,
1180                             err,
1181                             path,
1182                             rcvr_ty,
1183                             item.kind,
1184                             item.def_id,
1185                             sugg_span,
1186                             idx,
1187                             self.tcx.sess.source_map(),
1188                             item.fn_has_self_parameter,
1189                         );
1190                     }
1191                 }
1192             }
1193         }
1194         if sources.len() > limit {
1195             err.note(&format!("and {} others", sources.len() - limit));
1196         }
1197     }
1198
1199     /// Suggest calling `Ty::method` if `.method()` isn't found because the method
1200     /// doesn't take a `self` receiver.
1201     fn suggest_associated_call_syntax(
1202         &self,
1203         err: &mut Diagnostic,
1204         static_candidates: &Vec<CandidateSource>,
1205         rcvr_ty: Ty<'tcx>,
1206         source: SelfSource<'tcx>,
1207         item_name: Ident,
1208         args: Option<(&hir::Expr<'tcx>, &[hir::Expr<'tcx>])>,
1209         sugg_span: Span,
1210     ) {
1211         let mut has_unsuggestable_args = false;
1212         let ty_str = if let Some(CandidateSource::Impl(impl_did)) = static_candidates.get(0) {
1213             // When the "method" is resolved through dereferencing, we really want the
1214             // original type that has the associated function for accurate suggestions.
1215             // (#61411)
1216             let impl_ty = self.tcx.type_of(*impl_did);
1217             let target_ty = self
1218                 .autoderef(sugg_span, rcvr_ty)
1219                 .find(|(rcvr_ty, _)| {
1220                     DeepRejectCtxt { treat_obligation_params: TreatParams::AsInfer }
1221                         .types_may_unify(*rcvr_ty, impl_ty)
1222                 })
1223                 .map_or(impl_ty, |(ty, _)| ty)
1224                 .peel_refs();
1225             if let ty::Adt(def, substs) = target_ty.kind() {
1226                 // If there are any inferred arguments, (`{integer}`), we should replace
1227                 // them with underscores to allow the compiler to infer them
1228                 let infer_substs = self.tcx.mk_substs(substs.into_iter().map(|arg| {
1229                     if !arg.is_suggestable(self.tcx, true) {
1230                         has_unsuggestable_args = true;
1231                         match arg.unpack() {
1232                             GenericArgKind::Lifetime(_) => self
1233                                 .next_region_var(RegionVariableOrigin::MiscVariable(
1234                                     rustc_span::DUMMY_SP,
1235                                 ))
1236                                 .into(),
1237                             GenericArgKind::Type(_) => self
1238                                 .next_ty_var(TypeVariableOrigin {
1239                                     span: rustc_span::DUMMY_SP,
1240                                     kind: TypeVariableOriginKind::MiscVariable,
1241                                 })
1242                                 .into(),
1243                             GenericArgKind::Const(arg) => self
1244                                 .next_const_var(
1245                                     arg.ty(),
1246                                     ConstVariableOrigin {
1247                                         span: rustc_span::DUMMY_SP,
1248                                         kind: ConstVariableOriginKind::MiscVariable,
1249                                     },
1250                                 )
1251                                 .into(),
1252                         }
1253                     } else {
1254                         arg
1255                     }
1256                 }));
1257
1258                 self.tcx.value_path_str_with_substs(def.did(), infer_substs)
1259             } else {
1260                 self.ty_to_value_string(target_ty)
1261             }
1262         } else {
1263             self.ty_to_value_string(rcvr_ty.peel_refs())
1264         };
1265         if let SelfSource::MethodCall(_) = source {
1266             let first_arg = if let Some(CandidateSource::Impl(impl_did)) = static_candidates.get(0)
1267                 && let Some(assoc) = self.associated_value(*impl_did, item_name)
1268                 && assoc.kind == ty::AssocKind::Fn
1269             {
1270                 let sig = self.tcx.fn_sig(assoc.def_id);
1271                 sig.inputs().skip_binder().get(0).and_then(|first| if first.peel_refs() == rcvr_ty.peel_refs() {
1272                     None
1273                 } else {
1274                     Some(first.ref_mutability().map_or("", |mutbl| mutbl.ref_prefix_str()))
1275                 })
1276             } else {
1277                 None
1278             };
1279             let mut applicability = Applicability::MachineApplicable;
1280             let args = if let Some((receiver, args)) = args {
1281                 // The first arg is the same kind as the receiver
1282                 let explicit_args = if first_arg.is_some() {
1283                     std::iter::once(receiver).chain(args.iter()).collect::<Vec<_>>()
1284                 } else {
1285                     // There is no `Self` kind to infer the arguments from
1286                     if has_unsuggestable_args {
1287                         applicability = Applicability::HasPlaceholders;
1288                     }
1289                     args.iter().collect()
1290                 };
1291                 format!(
1292                     "({}{})",
1293                     first_arg.unwrap_or(""),
1294                     explicit_args
1295                         .iter()
1296                         .map(|arg| self
1297                             .tcx
1298                             .sess
1299                             .source_map()
1300                             .span_to_snippet(arg.span)
1301                             .unwrap_or_else(|_| {
1302                                 applicability = Applicability::HasPlaceholders;
1303                                 "_".to_owned()
1304                             }))
1305                         .collect::<Vec<_>>()
1306                         .join(", "),
1307                 )
1308             } else {
1309                 applicability = Applicability::HasPlaceholders;
1310                 "(...)".to_owned()
1311             };
1312             err.span_suggestion(
1313                 sugg_span,
1314                 "use associated function syntax instead",
1315                 format!("{}::{}{}", ty_str, item_name, args),
1316                 applicability,
1317             );
1318         } else {
1319             err.help(&format!("try with `{}::{}`", ty_str, item_name,));
1320         }
1321     }
1322
1323     /// Suggest calling a field with a type that implements the `Fn*` traits instead of a method with
1324     /// the same name as the field i.e. `(a.my_fn_ptr)(10)` instead of `a.my_fn_ptr(10)`.
1325     fn suggest_calling_field_as_fn(
1326         &self,
1327         span: Span,
1328         rcvr_ty: Ty<'tcx>,
1329         expr: &hir::Expr<'_>,
1330         item_name: Ident,
1331         err: &mut Diagnostic,
1332     ) -> bool {
1333         let tcx = self.tcx;
1334         let field_receiver = self.autoderef(span, rcvr_ty).find_map(|(ty, _)| match ty.kind() {
1335             ty::Adt(def, substs) if !def.is_enum() => {
1336                 let variant = &def.non_enum_variant();
1337                 tcx.find_field_index(item_name, variant).map(|index| {
1338                     let field = &variant.fields[index];
1339                     let field_ty = field.ty(tcx, substs);
1340                     (field, field_ty)
1341                 })
1342             }
1343             _ => None,
1344         });
1345         if let Some((field, field_ty)) = field_receiver {
1346             let scope = tcx.parent_module(self.body_id);
1347             let is_accessible = field.vis.is_accessible_from(scope, tcx);
1348
1349             if is_accessible {
1350                 if self.is_fn_ty(field_ty, span) {
1351                     let expr_span = expr.span.to(item_name.span);
1352                     err.multipart_suggestion(
1353                         &format!(
1354                             "to call the function stored in `{}`, \
1355                                          surround the field access with parentheses",
1356                             item_name,
1357                         ),
1358                         vec![
1359                             (expr_span.shrink_to_lo(), '('.to_string()),
1360                             (expr_span.shrink_to_hi(), ')'.to_string()),
1361                         ],
1362                         Applicability::MachineApplicable,
1363                     );
1364                 } else {
1365                     let call_expr = tcx.hir().expect_expr(tcx.hir().parent_id(expr.hir_id));
1366
1367                     if let Some(span) = call_expr.span.trim_start(item_name.span) {
1368                         err.span_suggestion(
1369                             span,
1370                             "remove the arguments",
1371                             "",
1372                             Applicability::MaybeIncorrect,
1373                         );
1374                     }
1375                 }
1376             }
1377
1378             let field_kind = if is_accessible { "field" } else { "private field" };
1379             err.span_label(item_name.span, format!("{}, not a method", field_kind));
1380             return true;
1381         }
1382         false
1383     }
1384
1385     /// Suggest possible range with adding parentheses, for example:
1386     /// when encountering `0..1.map(|i| i + 1)` suggest `(0..1).map(|i| i + 1)`.
1387     fn suggest_wrapping_range_with_parens(
1388         &self,
1389         tcx: TyCtxt<'tcx>,
1390         actual: Ty<'tcx>,
1391         source: SelfSource<'tcx>,
1392         span: Span,
1393         item_name: Ident,
1394         ty_str: &str,
1395     ) -> bool {
1396         if let SelfSource::MethodCall(expr) = source {
1397             for (_, parent) in tcx.hir().parent_iter(expr.hir_id).take(5) {
1398                 if let Node::Expr(parent_expr) = parent {
1399                     let lang_item = match parent_expr.kind {
1400                         ExprKind::Struct(ref qpath, _, _) => match **qpath {
1401                             QPath::LangItem(LangItem::Range, ..) => Some(LangItem::Range),
1402                             QPath::LangItem(LangItem::RangeTo, ..) => Some(LangItem::RangeTo),
1403                             QPath::LangItem(LangItem::RangeToInclusive, ..) => {
1404                                 Some(LangItem::RangeToInclusive)
1405                             }
1406                             _ => None,
1407                         },
1408                         ExprKind::Call(ref func, _) => match func.kind {
1409                             // `..=` desugars into `::std::ops::RangeInclusive::new(...)`.
1410                             ExprKind::Path(QPath::LangItem(LangItem::RangeInclusiveNew, ..)) => {
1411                                 Some(LangItem::RangeInclusiveStruct)
1412                             }
1413                             _ => None,
1414                         },
1415                         _ => None,
1416                     };
1417
1418                     if lang_item.is_none() {
1419                         continue;
1420                     }
1421
1422                     let span_included = match parent_expr.kind {
1423                         hir::ExprKind::Struct(_, eps, _) => {
1424                             eps.len() > 0 && eps.last().map_or(false, |ep| ep.span.contains(span))
1425                         }
1426                         // `..=` desugars into `::std::ops::RangeInclusive::new(...)`.
1427                         hir::ExprKind::Call(ref func, ..) => func.span.contains(span),
1428                         _ => false,
1429                     };
1430
1431                     if !span_included {
1432                         continue;
1433                     }
1434
1435                     let range_def_id = self.tcx.require_lang_item(lang_item.unwrap(), None);
1436                     let range_ty =
1437                         self.tcx.bound_type_of(range_def_id).subst(self.tcx, &[actual.into()]);
1438
1439                     let pick = self.lookup_probe_for_diagnostic(
1440                         item_name,
1441                         range_ty,
1442                         expr,
1443                         ProbeScope::AllTraits,
1444                         None,
1445                     );
1446                     if pick.is_ok() {
1447                         let range_span = parent_expr.span.with_hi(expr.span.hi());
1448                         tcx.sess.emit_err(errors::MissingParentheseInRange {
1449                             span,
1450                             ty_str: ty_str.to_string(),
1451                             method_name: item_name.as_str().to_string(),
1452                             add_missing_parentheses: Some(errors::AddMissingParenthesesInRange {
1453                                 func_name: item_name.name.as_str().to_string(),
1454                                 left: range_span.shrink_to_lo(),
1455                                 right: range_span.shrink_to_hi(),
1456                             }),
1457                         });
1458                         return true;
1459                     }
1460                 }
1461             }
1462         }
1463         false
1464     }
1465
1466     fn suggest_constraining_numerical_ty(
1467         &self,
1468         tcx: TyCtxt<'tcx>,
1469         actual: Ty<'tcx>,
1470         source: SelfSource<'_>,
1471         span: Span,
1472         item_kind: &str,
1473         item_name: Ident,
1474         ty_str: &str,
1475     ) -> bool {
1476         let found_candidate = all_traits(self.tcx)
1477             .into_iter()
1478             .any(|info| self.associated_value(info.def_id, item_name).is_some());
1479         let found_assoc = |ty: Ty<'tcx>| {
1480             simplify_type(tcx, ty, TreatParams::AsInfer)
1481                 .and_then(|simp| {
1482                     tcx.incoherent_impls(simp)
1483                         .iter()
1484                         .find_map(|&id| self.associated_value(id, item_name))
1485                 })
1486                 .is_some()
1487         };
1488         let found_candidate = found_candidate
1489             || found_assoc(tcx.types.i8)
1490             || found_assoc(tcx.types.i16)
1491             || found_assoc(tcx.types.i32)
1492             || found_assoc(tcx.types.i64)
1493             || found_assoc(tcx.types.i128)
1494             || found_assoc(tcx.types.u8)
1495             || found_assoc(tcx.types.u16)
1496             || found_assoc(tcx.types.u32)
1497             || found_assoc(tcx.types.u64)
1498             || found_assoc(tcx.types.u128)
1499             || found_assoc(tcx.types.f32)
1500             || found_assoc(tcx.types.f32);
1501         if found_candidate
1502             && actual.is_numeric()
1503             && !actual.has_concrete_skeleton()
1504             && let SelfSource::MethodCall(expr) = source
1505         {
1506             let mut err = struct_span_err!(
1507                 tcx.sess,
1508                 span,
1509                 E0689,
1510                 "can't call {} `{}` on ambiguous numeric type `{}`",
1511                 item_kind,
1512                 item_name,
1513                 ty_str
1514             );
1515             let concrete_type = if actual.is_integral() { "i32" } else { "f32" };
1516             match expr.kind {
1517                 ExprKind::Lit(ref lit) => {
1518                     // numeric literal
1519                     let snippet = tcx
1520                         .sess
1521                         .source_map()
1522                         .span_to_snippet(lit.span)
1523                         .unwrap_or_else(|_| "<numeric literal>".to_owned());
1524
1525                     // If this is a floating point literal that ends with '.',
1526                     // get rid of it to stop this from becoming a member access.
1527                     let snippet = snippet.strip_suffix('.').unwrap_or(&snippet);
1528                     err.span_suggestion(
1529                         lit.span,
1530                         &format!(
1531                             "you must specify a concrete type for this numeric value, \
1532                                          like `{}`",
1533                             concrete_type
1534                         ),
1535                         format!("{snippet}_{concrete_type}"),
1536                         Applicability::MaybeIncorrect,
1537                     );
1538                 }
1539                 ExprKind::Path(QPath::Resolved(_, path)) => {
1540                     // local binding
1541                     if let hir::def::Res::Local(hir_id) = path.res {
1542                         let span = tcx.hir().span(hir_id);
1543                         let filename = tcx.sess.source_map().span_to_filename(span);
1544
1545                         let parent_node =
1546                             self.tcx.hir().get_parent(hir_id);
1547                         let msg = format!(
1548                             "you must specify a type for this binding, like `{}`",
1549                             concrete_type,
1550                         );
1551
1552                         match (filename, parent_node) {
1553                             (
1554                                 FileName::Real(_),
1555                                 Node::Local(hir::Local {
1556                                     source: hir::LocalSource::Normal,
1557                                     ty,
1558                                     ..
1559                                 }),
1560                             ) => {
1561                                 let type_span = ty.map(|ty| ty.span.with_lo(span.hi())).unwrap_or(span.shrink_to_hi());
1562                                 err.span_suggestion(
1563                                     // account for `let x: _ = 42;`
1564                                     //                   ^^^
1565                                     type_span,
1566                                     &msg,
1567                                     format!(": {concrete_type}"),
1568                                     Applicability::MaybeIncorrect,
1569                                 );
1570                             }
1571                             _ => {
1572                                 err.span_label(span, msg);
1573                             }
1574                         }
1575                     }
1576                 }
1577                 _ => {}
1578             }
1579             err.emit();
1580             return true;
1581         }
1582         false
1583     }
1584
1585     /// For code `rect::area(...)`,
1586     /// if `rect` is a local variable and `area` is a valid assoc method for it,
1587     /// we try to suggest `rect.area()`
1588     pub(crate) fn suggest_assoc_method_call(&self, segs: &[PathSegment<'_>]) {
1589         debug!("suggest_assoc_method_call segs: {:?}", segs);
1590         let [seg1, seg2] = segs else { return; };
1591         let Some(mut diag) =
1592                 self.tcx.sess.diagnostic().steal_diagnostic(seg1.ident.span, StashKey::CallAssocMethod)
1593                 else { return };
1594
1595         let map = self.infcx.tcx.hir();
1596         let body = map.body(rustc_hir::BodyId { hir_id: self.body_id });
1597         struct LetVisitor<'a> {
1598             result: Option<&'a hir::Expr<'a>>,
1599             ident_name: Symbol,
1600         }
1601
1602         // FIXME: This really should be taking scoping, etc into account.
1603         impl<'v> Visitor<'v> for LetVisitor<'v> {
1604             fn visit_stmt(&mut self, ex: &'v hir::Stmt<'v>) {
1605                 if let hir::StmtKind::Local(hir::Local { pat, init, .. }) = &ex.kind
1606                     && let Binding(_, _, ident, ..) = pat.kind
1607                     && ident.name == self.ident_name
1608                 {
1609                     self.result = *init;
1610                 } else {
1611                     hir::intravisit::walk_stmt(self, ex);
1612                 }
1613             }
1614         }
1615
1616         let mut visitor = LetVisitor { result: None, ident_name: seg1.ident.name };
1617         visitor.visit_body(&body);
1618
1619         let parent = self.tcx.hir().parent_id(seg1.hir_id);
1620         if let Some(Node::Expr(call_expr)) = self.tcx.hir().find(parent)
1621             && let Some(expr) = visitor.result
1622             && let Some(self_ty) = self.node_ty_opt(expr.hir_id)
1623         {
1624             let probe = self.lookup_probe_for_diagnostic(
1625                 seg2.ident,
1626                 self_ty,
1627                 call_expr,
1628                 ProbeScope::TraitsInScope,
1629                 None,
1630             );
1631             if probe.is_ok() {
1632                 let sm = self.infcx.tcx.sess.source_map();
1633                 diag.span_suggestion_verbose(
1634                     sm.span_extend_while(seg1.ident.span.shrink_to_hi(), |c| c == ':').unwrap(),
1635                     "you may have meant to call an instance method",
1636                     ".".to_string(),
1637                     Applicability::MaybeIncorrect,
1638                 );
1639             }
1640         }
1641         diag.emit();
1642     }
1643
1644     /// Suggest calling a method on a field i.e. `a.field.bar()` instead of `a.bar()`
1645     fn suggest_calling_method_on_field(
1646         &self,
1647         err: &mut Diagnostic,
1648         source: SelfSource<'tcx>,
1649         span: Span,
1650         actual: Ty<'tcx>,
1651         item_name: Ident,
1652         return_type: Option<Ty<'tcx>>,
1653     ) {
1654         if let SelfSource::MethodCall(expr) = source
1655         && let mod_id = self.tcx.parent_module(expr.hir_id).to_def_id()
1656         && let Some((fields, substs)) =
1657             self.get_field_candidates_considering_privacy(span, actual, mod_id)
1658         {
1659             let call_expr = self.tcx.hir().expect_expr(self.tcx.hir().parent_id(expr.hir_id));
1660
1661             let lang_items = self.tcx.lang_items();
1662             let never_mention_traits = [
1663                 lang_items.clone_trait(),
1664                 lang_items.deref_trait(),
1665                 lang_items.deref_mut_trait(),
1666                 self.tcx.get_diagnostic_item(sym::AsRef),
1667                 self.tcx.get_diagnostic_item(sym::AsMut),
1668                 self.tcx.get_diagnostic_item(sym::Borrow),
1669                 self.tcx.get_diagnostic_item(sym::BorrowMut),
1670             ];
1671             let candidate_fields: Vec<_> = fields
1672                 .filter_map(|candidate_field| {
1673                     self.check_for_nested_field_satisfying(
1674                         span,
1675                         &|_, field_ty| {
1676                             self.lookup_probe_for_diagnostic(
1677                                 item_name,
1678                                 field_ty,
1679                                 call_expr,
1680                                 ProbeScope::TraitsInScope,
1681                                 return_type,
1682                             )
1683                             .map_or(false, |pick| {
1684                                 !never_mention_traits
1685                                     .iter()
1686                                     .flatten()
1687                                     .any(|def_id| self.tcx.parent(pick.item.def_id) == *def_id)
1688                             })
1689                         },
1690                         candidate_field,
1691                         substs,
1692                         vec![],
1693                         mod_id,
1694                     )
1695                 })
1696                 .map(|field_path| {
1697                     field_path
1698                         .iter()
1699                         .map(|id| id.name.to_ident_string())
1700                         .collect::<Vec<String>>()
1701                         .join(".")
1702                 })
1703                 .collect();
1704
1705             let len = candidate_fields.len();
1706             if len > 0 {
1707                 err.span_suggestions(
1708                     item_name.span.shrink_to_lo(),
1709                     format!(
1710                         "{} of the expressions' fields {} a method of the same name",
1711                         if len > 1 { "some" } else { "one" },
1712                         if len > 1 { "have" } else { "has" },
1713                     ),
1714                     candidate_fields.iter().map(|path| format!("{path}.")),
1715                     Applicability::MaybeIncorrect,
1716                 );
1717             }
1718         }
1719     }
1720
1721     fn check_for_inner_self(
1722         &self,
1723         err: &mut Diagnostic,
1724         source: SelfSource<'tcx>,
1725         actual: Ty<'tcx>,
1726         item_name: Ident,
1727     ) {
1728         let tcx = self.tcx;
1729         let SelfSource::MethodCall(expr) = source else { return; };
1730         let call_expr = tcx.hir().expect_expr(tcx.hir().parent_id(expr.hir_id));
1731
1732         let ty::Adt(kind, substs) = actual.kind() else { return; };
1733         match kind.adt_kind() {
1734             ty::AdtKind::Enum => {
1735                 let matching_variants: Vec<_> = kind
1736                     .variants()
1737                     .iter()
1738                     .flat_map(|variant| {
1739                         let [field] = &variant.fields[..] else { return None; };
1740                         let field_ty = field.ty(tcx, substs);
1741
1742                         // Skip `_`, since that'll just lead to ambiguity.
1743                         if self.resolve_vars_if_possible(field_ty).is_ty_var() {
1744                             return None;
1745                         }
1746
1747                         self.lookup_probe_for_diagnostic(
1748                             item_name,
1749                             field_ty,
1750                             call_expr,
1751                             ProbeScope::TraitsInScope,
1752                             None,
1753                         )
1754                         .ok()
1755                         .map(|pick| (variant, field, pick))
1756                     })
1757                     .collect();
1758
1759                 let ret_ty_matches = |diagnostic_item| {
1760                     if let Some(ret_ty) = self
1761                         .ret_coercion
1762                         .as_ref()
1763                         .map(|c| self.resolve_vars_if_possible(c.borrow().expected_ty()))
1764                         && let ty::Adt(kind, _) = ret_ty.kind()
1765                         && tcx.get_diagnostic_item(diagnostic_item) == Some(kind.did())
1766                     {
1767                         true
1768                     } else {
1769                         false
1770                     }
1771                 };
1772
1773                 match &matching_variants[..] {
1774                     [(_, field, pick)] => {
1775                         let self_ty = field.ty(tcx, substs);
1776                         err.span_note(
1777                             tcx.def_span(pick.item.def_id),
1778                             &format!("the method `{item_name}` exists on the type `{self_ty}`"),
1779                         );
1780                         let (article, kind, variant, question) =
1781                             if tcx.is_diagnostic_item(sym::Result, kind.did()) {
1782                                 ("a", "Result", "Err", ret_ty_matches(sym::Result))
1783                             } else if tcx.is_diagnostic_item(sym::Option, kind.did()) {
1784                                 ("an", "Option", "None", ret_ty_matches(sym::Option))
1785                             } else {
1786                                 return;
1787                             };
1788                         if question {
1789                             err.span_suggestion_verbose(
1790                                 expr.span.shrink_to_hi(),
1791                                 format!(
1792                                     "use the `?` operator to extract the `{self_ty}` value, propagating \
1793                                     {article} `{kind}::{variant}` value to the caller"
1794                                 ),
1795                                 "?",
1796                                 Applicability::MachineApplicable,
1797                             );
1798                         } else {
1799                             err.span_suggestion_verbose(
1800                                 expr.span.shrink_to_hi(),
1801                                 format!(
1802                                     "consider using `{kind}::expect` to unwrap the `{self_ty}` value, \
1803                                     panicking if the value is {article} `{kind}::{variant}`"
1804                                 ),
1805                                 ".expect(\"REASON\")",
1806                                 Applicability::HasPlaceholders,
1807                             );
1808                         }
1809                     }
1810                     // FIXME(compiler-errors): Support suggestions for other matching enum variants
1811                     _ => {}
1812                 }
1813             }
1814             // Target wrapper types - types that wrap or pretend to wrap another type,
1815             // perhaps this inner type is meant to be called?
1816             ty::AdtKind::Struct | ty::AdtKind::Union => {
1817                 let [first] = ***substs else { return; };
1818                 let ty::GenericArgKind::Type(ty) = first.unpack() else { return; };
1819                 let Ok(pick) = self.lookup_probe_for_diagnostic(
1820                     item_name,
1821                     ty,
1822                     call_expr,
1823                     ProbeScope::TraitsInScope,
1824                     None,
1825                 )  else { return; };
1826
1827                 let name = self.ty_to_value_string(actual);
1828                 let inner_id = kind.did();
1829                 let mutable = if let Some(AutorefOrPtrAdjustment::Autoref { mutbl, .. }) =
1830                     pick.autoref_or_ptr_adjustment
1831                 {
1832                     Some(mutbl)
1833                 } else {
1834                     None
1835                 };
1836
1837                 if tcx.is_diagnostic_item(sym::LocalKey, inner_id) {
1838                     err.help("use `with` or `try_with` to access thread local storage");
1839                 } else if Some(kind.did()) == tcx.lang_items().maybe_uninit() {
1840                     err.help(format!(
1841                         "if this `{name}` has been initialized, \
1842                         use one of the `assume_init` methods to access the inner value"
1843                     ));
1844                 } else if tcx.is_diagnostic_item(sym::RefCell, inner_id) {
1845                     let (suggestion, borrow_kind, panic_if) = match mutable {
1846                         Some(Mutability::Not) => (".borrow()", "borrow", "a mutable borrow exists"),
1847                         Some(Mutability::Mut) => {
1848                             (".borrow_mut()", "mutably borrow", "any borrows exist")
1849                         }
1850                         None => return,
1851                     };
1852                     err.span_suggestion_verbose(
1853                         expr.span.shrink_to_hi(),
1854                         format!(
1855                             "use `{suggestion}` to {borrow_kind} the `{ty}`, \
1856                             panicking if {panic_if}"
1857                         ),
1858                         suggestion,
1859                         Applicability::MaybeIncorrect,
1860                     );
1861                 } else if tcx.is_diagnostic_item(sym::Mutex, inner_id) {
1862                     err.span_suggestion_verbose(
1863                         expr.span.shrink_to_hi(),
1864                         format!(
1865                             "use `.lock().unwrap()` to borrow the `{ty}`, \
1866                             blocking the current thread until it can be acquired"
1867                         ),
1868                         ".lock().unwrap()",
1869                         Applicability::MaybeIncorrect,
1870                     );
1871                 } else if tcx.is_diagnostic_item(sym::RwLock, inner_id) {
1872                     let (suggestion, borrow_kind) = match mutable {
1873                         Some(Mutability::Not) => (".read().unwrap()", "borrow"),
1874                         Some(Mutability::Mut) => (".write().unwrap()", "mutably borrow"),
1875                         None => return,
1876                     };
1877                     err.span_suggestion_verbose(
1878                         expr.span.shrink_to_hi(),
1879                         format!(
1880                             "use `{suggestion}` to {borrow_kind} the `{ty}`, \
1881                             blocking the current thread until it can be acquired"
1882                         ),
1883                         suggestion,
1884                         Applicability::MaybeIncorrect,
1885                     );
1886                 } else {
1887                     return;
1888                 };
1889
1890                 err.span_note(
1891                     tcx.def_span(pick.item.def_id),
1892                     &format!("the method `{item_name}` exists on the type `{ty}`"),
1893                 );
1894             }
1895         }
1896     }
1897
1898     pub(crate) fn note_unmet_impls_on_type(
1899         &self,
1900         err: &mut Diagnostic,
1901         errors: Vec<FulfillmentError<'tcx>>,
1902     ) {
1903         let all_local_types_needing_impls =
1904             errors.iter().all(|e| match e.obligation.predicate.kind().skip_binder() {
1905                 ty::PredicateKind::Clause(ty::Clause::Trait(pred)) => match pred.self_ty().kind() {
1906                     ty::Adt(def, _) => def.did().is_local(),
1907                     _ => false,
1908                 },
1909                 _ => false,
1910             });
1911         let mut preds: Vec<_> = errors
1912             .iter()
1913             .filter_map(|e| match e.obligation.predicate.kind().skip_binder() {
1914                 ty::PredicateKind::Clause(ty::Clause::Trait(pred)) => Some(pred),
1915                 _ => None,
1916             })
1917             .collect();
1918         preds.sort_by_key(|pred| (pred.def_id(), pred.self_ty()));
1919         let def_ids = preds
1920             .iter()
1921             .filter_map(|pred| match pred.self_ty().kind() {
1922                 ty::Adt(def, _) => Some(def.did()),
1923                 _ => None,
1924             })
1925             .collect::<FxHashSet<_>>();
1926         let mut spans: MultiSpan = def_ids
1927             .iter()
1928             .filter_map(|def_id| {
1929                 let span = self.tcx.def_span(*def_id);
1930                 if span.is_dummy() { None } else { Some(span) }
1931             })
1932             .collect::<Vec<_>>()
1933             .into();
1934
1935         for pred in &preds {
1936             match pred.self_ty().kind() {
1937                 ty::Adt(def, _) if def.did().is_local() => {
1938                     spans.push_span_label(
1939                         self.tcx.def_span(def.did()),
1940                         format!("must implement `{}`", pred.trait_ref.print_only_trait_path()),
1941                     );
1942                 }
1943                 _ => {}
1944             }
1945         }
1946
1947         if all_local_types_needing_impls && spans.primary_span().is_some() {
1948             let msg = if preds.len() == 1 {
1949                 format!(
1950                     "an implementation of `{}` might be missing for `{}`",
1951                     preds[0].trait_ref.print_only_trait_path(),
1952                     preds[0].self_ty()
1953                 )
1954             } else {
1955                 format!(
1956                     "the following type{} would have to `impl` {} required trait{} for this \
1957                      operation to be valid",
1958                     pluralize!(def_ids.len()),
1959                     if def_ids.len() == 1 { "its" } else { "their" },
1960                     pluralize!(preds.len()),
1961                 )
1962             };
1963             err.span_note(spans, &msg);
1964         }
1965
1966         let preds: Vec<_> = errors
1967             .iter()
1968             .map(|e| (e.obligation.predicate, None, Some(e.obligation.cause.clone())))
1969             .collect();
1970         self.suggest_derive(err, &preds);
1971     }
1972
1973     pub fn suggest_derive(
1974         &self,
1975         err: &mut Diagnostic,
1976         unsatisfied_predicates: &[(
1977             ty::Predicate<'tcx>,
1978             Option<ty::Predicate<'tcx>>,
1979             Option<ObligationCause<'tcx>>,
1980         )],
1981     ) {
1982         let mut derives = Vec::<(String, Span, Symbol)>::new();
1983         let mut traits = Vec::new();
1984         for (pred, _, _) in unsatisfied_predicates {
1985             let ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred)) = pred.kind().skip_binder() else { continue };
1986             let adt = match trait_pred.self_ty().ty_adt_def() {
1987                 Some(adt) if adt.did().is_local() => adt,
1988                 _ => continue,
1989             };
1990             if let Some(diagnostic_name) = self.tcx.get_diagnostic_name(trait_pred.def_id()) {
1991                 let can_derive = match diagnostic_name {
1992                     sym::Default => !adt.is_enum(),
1993                     sym::Eq
1994                     | sym::PartialEq
1995                     | sym::Ord
1996                     | sym::PartialOrd
1997                     | sym::Clone
1998                     | sym::Copy
1999                     | sym::Hash
2000                     | sym::Debug => true,
2001                     _ => false,
2002                 };
2003                 if can_derive {
2004                     let self_name = trait_pred.self_ty().to_string();
2005                     let self_span = self.tcx.def_span(adt.did());
2006                     if let Some(poly_trait_ref) = pred.to_opt_poly_trait_pred() {
2007                         for super_trait in supertraits(self.tcx, poly_trait_ref.to_poly_trait_ref())
2008                         {
2009                             if let Some(parent_diagnostic_name) =
2010                                 self.tcx.get_diagnostic_name(super_trait.def_id())
2011                             {
2012                                 derives.push((
2013                                     self_name.clone(),
2014                                     self_span,
2015                                     parent_diagnostic_name,
2016                                 ));
2017                             }
2018                         }
2019                     }
2020                     derives.push((self_name, self_span, diagnostic_name));
2021                 } else {
2022                     traits.push(trait_pred.def_id());
2023                 }
2024             } else {
2025                 traits.push(trait_pred.def_id());
2026             }
2027         }
2028         traits.sort();
2029         traits.dedup();
2030
2031         derives.sort();
2032         derives.dedup();
2033
2034         let mut derives_grouped = Vec::<(String, Span, String)>::new();
2035         for (self_name, self_span, trait_name) in derives.into_iter() {
2036             if let Some((last_self_name, _, ref mut last_trait_names)) = derives_grouped.last_mut()
2037             {
2038                 if last_self_name == &self_name {
2039                     last_trait_names.push_str(format!(", {}", trait_name).as_str());
2040                     continue;
2041                 }
2042             }
2043             derives_grouped.push((self_name, self_span, trait_name.to_string()));
2044         }
2045
2046         let len = traits.len();
2047         if len > 0 {
2048             let span =
2049                 MultiSpan::from_spans(traits.iter().map(|&did| self.tcx.def_span(did)).collect());
2050             let mut names = format!("`{}`", self.tcx.def_path_str(traits[0]));
2051             for (i, &did) in traits.iter().enumerate().skip(1) {
2052                 if len > 2 {
2053                     names.push_str(", ");
2054                 }
2055                 if i == len - 1 {
2056                     names.push_str(" and ");
2057                 }
2058                 names.push('`');
2059                 names.push_str(&self.tcx.def_path_str(did));
2060                 names.push('`');
2061             }
2062             err.span_note(
2063                 span,
2064                 &format!("the trait{} {} must be implemented", pluralize!(len), names),
2065             );
2066         }
2067
2068         for (self_name, self_span, traits) in &derives_grouped {
2069             err.span_suggestion_verbose(
2070                 self_span.shrink_to_lo(),
2071                 &format!("consider annotating `{}` with `#[derive({})]`", self_name, traits),
2072                 format!("#[derive({})]\n", traits),
2073                 Applicability::MaybeIncorrect,
2074             );
2075         }
2076     }
2077
2078     fn check_for_deref_method(
2079         &self,
2080         err: &mut Diagnostic,
2081         self_source: SelfSource<'tcx>,
2082         rcvr_ty: Ty<'tcx>,
2083         item_name: Ident,
2084         expected: Expectation<'tcx>,
2085     ) {
2086         let SelfSource::QPath(ty) = self_source else { return; };
2087         for (deref_ty, _) in self.autoderef(rustc_span::DUMMY_SP, rcvr_ty).skip(1) {
2088             if let Ok(pick) = self.probe_for_name(
2089                 Mode::Path,
2090                 item_name,
2091                 expected.only_has_type(self),
2092                 IsSuggestion(true),
2093                 deref_ty,
2094                 ty.hir_id,
2095                 ProbeScope::TraitsInScope,
2096             ) {
2097                 if deref_ty.is_suggestable(self.tcx, true)
2098                     // If this method receives `&self`, then the provided
2099                     // argument _should_ coerce, so it's valid to suggest
2100                     // just changing the path.
2101                     && pick.item.fn_has_self_parameter
2102                     && let Some(self_ty) =
2103                         self.tcx.fn_sig(pick.item.def_id).inputs().skip_binder().get(0)
2104                     && self_ty.is_ref()
2105                 {
2106                     let suggested_path = match deref_ty.kind() {
2107                         ty::Bool
2108                         | ty::Char
2109                         | ty::Int(_)
2110                         | ty::Uint(_)
2111                         | ty::Float(_)
2112                         | ty::Adt(_, _)
2113                         | ty::Str
2114                         | ty::Alias(ty::Projection, _)
2115                         | ty::Param(_) => format!("{deref_ty}"),
2116                         // we need to test something like  <&[_]>::len or <(&[u32])>::len
2117                         // and Vec::function();
2118                         // <&[_]>::len or <&[u32]>::len doesn't need an extra "<>" between
2119                         // but for Adt type like Vec::function()
2120                         // we would suggest <[_]>::function();
2121                         _ if self.tcx.sess.source_map().span_wrapped_by_angle_or_parentheses(ty.span)  => format!("{deref_ty}"),
2122                         _ => format!("<{deref_ty}>"),
2123                     };
2124                     err.span_suggestion_verbose(
2125                         ty.span,
2126                         format!("the function `{item_name}` is implemented on `{deref_ty}`"),
2127                         suggested_path,
2128                         Applicability::MaybeIncorrect,
2129                     );
2130                 } else {
2131                     err.span_note(
2132                         ty.span,
2133                         format!("the function `{item_name}` is implemented on `{deref_ty}`"),
2134                     );
2135                 }
2136                 return;
2137             }
2138         }
2139     }
2140
2141     /// Print out the type for use in value namespace.
2142     fn ty_to_value_string(&self, ty: Ty<'tcx>) -> String {
2143         match ty.kind() {
2144             ty::Adt(def, substs) => self.tcx.def_path_str_with_substs(def.did(), substs),
2145             _ => self.ty_to_string(ty),
2146         }
2147     }
2148
2149     fn suggest_await_before_method(
2150         &self,
2151         err: &mut Diagnostic,
2152         item_name: Ident,
2153         ty: Ty<'tcx>,
2154         call: &hir::Expr<'_>,
2155         span: Span,
2156         return_type: Option<Ty<'tcx>>,
2157     ) {
2158         let output_ty = match self.get_impl_future_output_ty(ty) {
2159             Some(output_ty) => self.resolve_vars_if_possible(output_ty),
2160             _ => return,
2161         };
2162         let method_exists =
2163             self.method_exists(item_name, output_ty, call.hir_id, true, return_type);
2164         debug!("suggest_await_before_method: is_method_exist={}", method_exists);
2165         if method_exists {
2166             err.span_suggestion_verbose(
2167                 span.shrink_to_lo(),
2168                 "consider `await`ing on the `Future` and calling the method on its `Output`",
2169                 "await.",
2170                 Applicability::MaybeIncorrect,
2171             );
2172         }
2173     }
2174
2175     fn suggest_use_candidates(&self, err: &mut Diagnostic, msg: String, candidates: Vec<DefId>) {
2176         let parent_map = self.tcx.visible_parent_map(());
2177
2178         // Separate out candidates that must be imported with a glob, because they are named `_`
2179         // and cannot be referred with their identifier.
2180         let (candidates, globs): (Vec<_>, Vec<_>) = candidates.into_iter().partition(|trait_did| {
2181             if let Some(parent_did) = parent_map.get(trait_did) {
2182                 // If the item is re-exported as `_`, we should suggest a glob-import instead.
2183                 if *parent_did != self.tcx.parent(*trait_did)
2184                     && self
2185                         .tcx
2186                         .module_children(*parent_did)
2187                         .iter()
2188                         .filter(|child| child.res.opt_def_id() == Some(*trait_did))
2189                         .all(|child| child.ident.name == kw::Underscore)
2190                 {
2191                     return false;
2192                 }
2193             }
2194
2195             true
2196         });
2197
2198         let module_did = self.tcx.parent_module(self.body_id);
2199         let (module, _, _) = self.tcx.hir().get_module(module_did);
2200         let span = module.spans.inject_use_span;
2201
2202         let path_strings = candidates.iter().map(|trait_did| {
2203             format!("use {};\n", with_crate_prefix!(self.tcx.def_path_str(*trait_did)),)
2204         });
2205
2206         let glob_path_strings = globs.iter().map(|trait_did| {
2207             let parent_did = parent_map.get(trait_did).unwrap();
2208             format!(
2209                 "use {}::*; // trait {}\n",
2210                 with_crate_prefix!(self.tcx.def_path_str(*parent_did)),
2211                 self.tcx.item_name(*trait_did),
2212             )
2213         });
2214
2215         err.span_suggestions(
2216             span,
2217             &msg,
2218             path_strings.chain(glob_path_strings),
2219             Applicability::MaybeIncorrect,
2220         );
2221     }
2222
2223     fn suggest_valid_traits(
2224         &self,
2225         err: &mut Diagnostic,
2226         valid_out_of_scope_traits: Vec<DefId>,
2227     ) -> bool {
2228         if !valid_out_of_scope_traits.is_empty() {
2229             let mut candidates = valid_out_of_scope_traits;
2230             candidates.sort();
2231             candidates.dedup();
2232
2233             // `TryFrom` and `FromIterator` have no methods
2234             let edition_fix = candidates
2235                 .iter()
2236                 .find(|did| self.tcx.is_diagnostic_item(sym::TryInto, **did))
2237                 .copied();
2238
2239             err.help("items from traits can only be used if the trait is in scope");
2240             let msg = format!(
2241                 "the following {traits_are} implemented but not in scope; \
2242                  perhaps add a `use` for {one_of_them}:",
2243                 traits_are = if candidates.len() == 1 { "trait is" } else { "traits are" },
2244                 one_of_them = if candidates.len() == 1 { "it" } else { "one of them" },
2245             );
2246
2247             self.suggest_use_candidates(err, msg, candidates);
2248             if let Some(did) = edition_fix {
2249                 err.note(&format!(
2250                     "'{}' is included in the prelude starting in Edition 2021",
2251                     with_crate_prefix!(self.tcx.def_path_str(did))
2252                 ));
2253             }
2254
2255             true
2256         } else {
2257             false
2258         }
2259     }
2260
2261     fn suggest_traits_to_import(
2262         &self,
2263         err: &mut Diagnostic,
2264         span: Span,
2265         rcvr_ty: Ty<'tcx>,
2266         item_name: Ident,
2267         inputs_len: Option<usize>,
2268         source: SelfSource<'tcx>,
2269         valid_out_of_scope_traits: Vec<DefId>,
2270         unsatisfied_predicates: &[(
2271             ty::Predicate<'tcx>,
2272             Option<ty::Predicate<'tcx>>,
2273             Option<ObligationCause<'tcx>>,
2274         )],
2275         static_candidates: &[CandidateSource],
2276         unsatisfied_bounds: bool,
2277         return_type: Option<Ty<'tcx>>,
2278     ) {
2279         let mut alt_rcvr_sugg = false;
2280         if let (SelfSource::MethodCall(rcvr), false) = (source, unsatisfied_bounds) {
2281             debug!(
2282                 "suggest_traits_to_import: span={:?}, item_name={:?}, rcvr_ty={:?}, rcvr={:?}",
2283                 span, item_name, rcvr_ty, rcvr
2284             );
2285             let skippable = [
2286                 self.tcx.lang_items().clone_trait(),
2287                 self.tcx.lang_items().deref_trait(),
2288                 self.tcx.lang_items().deref_mut_trait(),
2289                 self.tcx.lang_items().drop_trait(),
2290                 self.tcx.get_diagnostic_item(sym::AsRef),
2291             ];
2292             // Try alternative arbitrary self types that could fulfill this call.
2293             // FIXME: probe for all types that *could* be arbitrary self-types, not
2294             // just this list.
2295             for (rcvr_ty, post) in &[
2296                 (rcvr_ty, ""),
2297                 (self.tcx.mk_mut_ref(self.tcx.lifetimes.re_erased, rcvr_ty), "&mut "),
2298                 (self.tcx.mk_imm_ref(self.tcx.lifetimes.re_erased, rcvr_ty), "&"),
2299             ] {
2300                 match self.lookup_probe_for_diagnostic(
2301                     item_name,
2302                     *rcvr_ty,
2303                     rcvr,
2304                     ProbeScope::AllTraits,
2305                     return_type,
2306                 ) {
2307                     Ok(pick) => {
2308                         // If the method is defined for the receiver we have, it likely wasn't `use`d.
2309                         // We point at the method, but we just skip the rest of the check for arbitrary
2310                         // self types and rely on the suggestion to `use` the trait from
2311                         // `suggest_valid_traits`.
2312                         let did = Some(pick.item.container_id(self.tcx));
2313                         let skip = skippable.contains(&did);
2314                         if pick.autoderefs == 0 && !skip {
2315                             err.span_label(
2316                                 pick.item.ident(self.tcx).span,
2317                                 &format!("the method is available for `{}` here", rcvr_ty),
2318                             );
2319                         }
2320                         break;
2321                     }
2322                     Err(MethodError::Ambiguity(_)) => {
2323                         // If the method is defined (but ambiguous) for the receiver we have, it is also
2324                         // likely we haven't `use`d it. It may be possible that if we `Box`/`Pin`/etc.
2325                         // the receiver, then it might disambiguate this method, but I think these
2326                         // suggestions are generally misleading (see #94218).
2327                         break;
2328                     }
2329                     Err(_) => (),
2330                 }
2331
2332                 for (rcvr_ty, pre) in &[
2333                     (self.tcx.mk_lang_item(*rcvr_ty, LangItem::OwnedBox), "Box::new"),
2334                     (self.tcx.mk_lang_item(*rcvr_ty, LangItem::Pin), "Pin::new"),
2335                     (self.tcx.mk_diagnostic_item(*rcvr_ty, sym::Arc), "Arc::new"),
2336                     (self.tcx.mk_diagnostic_item(*rcvr_ty, sym::Rc), "Rc::new"),
2337                 ] {
2338                     if let Some(new_rcvr_t) = *rcvr_ty
2339                         && let Ok(pick) = self.lookup_probe_for_diagnostic(
2340                             item_name,
2341                             new_rcvr_t,
2342                             rcvr,
2343                             ProbeScope::AllTraits,
2344                             return_type,
2345                         )
2346                     {
2347                         debug!("try_alt_rcvr: pick candidate {:?}", pick);
2348                         let did = Some(pick.item.container_id(self.tcx));
2349                         // We don't want to suggest a container type when the missing
2350                         // method is `.clone()` or `.deref()` otherwise we'd suggest
2351                         // `Arc::new(foo).clone()`, which is far from what the user wants.
2352                         // Explicitly ignore the `Pin::as_ref()` method as `Pin` does not
2353                         // implement the `AsRef` trait.
2354                         let skip = skippable.contains(&did)
2355                             || (("Pin::new" == *pre) && (sym::as_ref == item_name.name))
2356                             || inputs_len.map_or(false, |inputs_len| pick.item.kind == ty::AssocKind::Fn && self.tcx.fn_sig(pick.item.def_id).skip_binder().inputs().len() != inputs_len);
2357                         // Make sure the method is defined for the *actual* receiver: we don't
2358                         // want to treat `Box<Self>` as a receiver if it only works because of
2359                         // an autoderef to `&self`
2360                         if pick.autoderefs == 0 && !skip {
2361                             err.span_label(
2362                                 pick.item.ident(self.tcx).span,
2363                                 &format!("the method is available for `{}` here", new_rcvr_t),
2364                             );
2365                             err.multipart_suggestion(
2366                                 "consider wrapping the receiver expression with the \
2367                                     appropriate type",
2368                                 vec![
2369                                     (rcvr.span.shrink_to_lo(), format!("{}({}", pre, post)),
2370                                     (rcvr.span.shrink_to_hi(), ")".to_string()),
2371                                 ],
2372                                 Applicability::MaybeIncorrect,
2373                             );
2374                             // We don't care about the other suggestions.
2375                             alt_rcvr_sugg = true;
2376                         }
2377                     }
2378                 }
2379             }
2380         }
2381         if self.suggest_valid_traits(err, valid_out_of_scope_traits) {
2382             return;
2383         }
2384
2385         let type_is_local = self.type_derefs_to_local(span, rcvr_ty, source);
2386
2387         let mut arbitrary_rcvr = vec![];
2388         // There are no traits implemented, so lets suggest some traits to
2389         // implement, by finding ones that have the item name, and are
2390         // legal to implement.
2391         let mut candidates = all_traits(self.tcx)
2392             .into_iter()
2393             // Don't issue suggestions for unstable traits since they're
2394             // unlikely to be implementable anyway
2395             .filter(|info| match self.tcx.lookup_stability(info.def_id) {
2396                 Some(attr) => attr.level.is_stable(),
2397                 None => true,
2398             })
2399             .filter(|info| {
2400                 // Static candidates are already implemented, and known not to work
2401                 // Do not suggest them again
2402                 static_candidates.iter().all(|sc| match *sc {
2403                     CandidateSource::Trait(def_id) => def_id != info.def_id,
2404                     CandidateSource::Impl(def_id) => {
2405                         self.tcx.trait_id_of_impl(def_id) != Some(info.def_id)
2406                     }
2407                 })
2408             })
2409             .filter(|info| {
2410                 // We approximate the coherence rules to only suggest
2411                 // traits that are legal to implement by requiring that
2412                 // either the type or trait is local. Multi-dispatch means
2413                 // this isn't perfect (that is, there are cases when
2414                 // implementing a trait would be legal but is rejected
2415                 // here).
2416                 unsatisfied_predicates.iter().all(|(p, _, _)| {
2417                     match p.kind().skip_binder() {
2418                         // Hide traits if they are present in predicates as they can be fixed without
2419                         // having to implement them.
2420                         ty::PredicateKind::Clause(ty::Clause::Trait(t)) => {
2421                             t.def_id() == info.def_id
2422                         }
2423                         ty::PredicateKind::Clause(ty::Clause::Projection(p)) => {
2424                             p.projection_ty.def_id == info.def_id
2425                         }
2426                         _ => false,
2427                     }
2428                 }) && (type_is_local || info.def_id.is_local())
2429                     && !self.tcx.trait_is_auto(info.def_id)
2430                     && self
2431                         .associated_value(info.def_id, item_name)
2432                         .filter(|item| {
2433                             if let ty::AssocKind::Fn = item.kind {
2434                                 let id = item
2435                                     .def_id
2436                                     .as_local()
2437                                     .map(|def_id| self.tcx.hir().local_def_id_to_hir_id(def_id));
2438                                 if let Some(hir::Node::TraitItem(hir::TraitItem {
2439                                     kind: hir::TraitItemKind::Fn(fn_sig, method),
2440                                     ..
2441                                 })) = id.map(|id| self.tcx.hir().get(id))
2442                                 {
2443                                     let self_first_arg = match method {
2444                                         hir::TraitFn::Required([ident, ..]) => {
2445                                             ident.name == kw::SelfLower
2446                                         }
2447                                         hir::TraitFn::Provided(body_id) => {
2448                                             self.tcx.hir().body(*body_id).params.first().map_or(
2449                                                 false,
2450                                                 |param| {
2451                                                     matches!(
2452                                                         param.pat.kind,
2453                                                         hir::PatKind::Binding(_, _, ident, _)
2454                                                             if ident.name == kw::SelfLower
2455                                                     )
2456                                                 },
2457                                             )
2458                                         }
2459                                         _ => false,
2460                                     };
2461
2462                                     if !fn_sig.decl.implicit_self.has_implicit_self()
2463                                         && self_first_arg
2464                                     {
2465                                         if let Some(ty) = fn_sig.decl.inputs.get(0) {
2466                                             arbitrary_rcvr.push(ty.span);
2467                                         }
2468                                         return false;
2469                                     }
2470                                 }
2471                             }
2472                             // We only want to suggest public or local traits (#45781).
2473                             item.visibility(self.tcx).is_public() || info.def_id.is_local()
2474                         })
2475                         .is_some()
2476             })
2477             .collect::<Vec<_>>();
2478         for span in &arbitrary_rcvr {
2479             err.span_label(
2480                 *span,
2481                 "the method might not be found because of this arbitrary self type",
2482             );
2483         }
2484         if alt_rcvr_sugg {
2485             return;
2486         }
2487
2488         if !candidates.is_empty() {
2489             // Sort from most relevant to least relevant.
2490             candidates.sort_by(|a, b| a.cmp(b).reverse());
2491             candidates.dedup();
2492
2493             let param_type = match rcvr_ty.kind() {
2494                 ty::Param(param) => Some(param),
2495                 ty::Ref(_, ty, _) => match ty.kind() {
2496                     ty::Param(param) => Some(param),
2497                     _ => None,
2498                 },
2499                 _ => None,
2500             };
2501             err.help(if param_type.is_some() {
2502                 "items from traits can only be used if the type parameter is bounded by the trait"
2503             } else {
2504                 "items from traits can only be used if the trait is implemented and in scope"
2505             });
2506             let candidates_len = candidates.len();
2507             let message = |action| {
2508                 format!(
2509                     "the following {traits_define} an item `{name}`, perhaps you need to {action} \
2510                      {one_of_them}:",
2511                     traits_define =
2512                         if candidates_len == 1 { "trait defines" } else { "traits define" },
2513                     action = action,
2514                     one_of_them = if candidates_len == 1 { "it" } else { "one of them" },
2515                     name = item_name,
2516                 )
2517             };
2518             // Obtain the span for `param` and use it for a structured suggestion.
2519             if let Some(param) = param_type {
2520                 let generics = self.tcx.generics_of(self.body_id.owner.to_def_id());
2521                 let type_param = generics.type_param(param, self.tcx);
2522                 let hir = self.tcx.hir();
2523                 if let Some(def_id) = type_param.def_id.as_local() {
2524                     let id = hir.local_def_id_to_hir_id(def_id);
2525                     // Get the `hir::Param` to verify whether it already has any bounds.
2526                     // We do this to avoid suggesting code that ends up as `T: FooBar`,
2527                     // instead we suggest `T: Foo + Bar` in that case.
2528                     match hir.get(id) {
2529                         Node::GenericParam(param) => {
2530                             enum Introducer {
2531                                 Plus,
2532                                 Colon,
2533                                 Nothing,
2534                             }
2535                             let ast_generics = hir.get_generics(id.owner.def_id).unwrap();
2536                             let (sp, mut introducer) = if let Some(span) =
2537                                 ast_generics.bounds_span_for_suggestions(def_id)
2538                             {
2539                                 (span, Introducer::Plus)
2540                             } else if let Some(colon_span) = param.colon_span {
2541                                 (colon_span.shrink_to_hi(), Introducer::Nothing)
2542                             } else {
2543                                 (param.span.shrink_to_hi(), Introducer::Colon)
2544                             };
2545                             if matches!(
2546                                 param.kind,
2547                                 hir::GenericParamKind::Type { synthetic: true, .. },
2548                             ) {
2549                                 introducer = Introducer::Plus
2550                             }
2551                             let trait_def_ids: FxHashSet<DefId> = ast_generics
2552                                 .bounds_for_param(def_id)
2553                                 .flat_map(|bp| bp.bounds.iter())
2554                                 .filter_map(|bound| bound.trait_ref()?.trait_def_id())
2555                                 .collect();
2556                             if !candidates.iter().any(|t| trait_def_ids.contains(&t.def_id)) {
2557                                 err.span_suggestions(
2558                                     sp,
2559                                     &message(format!(
2560                                         "restrict type parameter `{}` with",
2561                                         param.name.ident(),
2562                                     )),
2563                                     candidates.iter().map(|t| {
2564                                         format!(
2565                                             "{} {}",
2566                                             match introducer {
2567                                                 Introducer::Plus => " +",
2568                                                 Introducer::Colon => ":",
2569                                                 Introducer::Nothing => "",
2570                                             },
2571                                             self.tcx.def_path_str(t.def_id),
2572                                         )
2573                                     }),
2574                                     Applicability::MaybeIncorrect,
2575                                 );
2576                             }
2577                             return;
2578                         }
2579                         Node::Item(hir::Item {
2580                             kind: hir::ItemKind::Trait(.., bounds, _),
2581                             ident,
2582                             ..
2583                         }) => {
2584                             let (sp, sep, article) = if bounds.is_empty() {
2585                                 (ident.span.shrink_to_hi(), ":", "a")
2586                             } else {
2587                                 (bounds.last().unwrap().span().shrink_to_hi(), " +", "another")
2588                             };
2589                             err.span_suggestions(
2590                                 sp,
2591                                 &message(format!("add {} supertrait for", article)),
2592                                 candidates.iter().map(|t| {
2593                                     format!("{} {}", sep, self.tcx.def_path_str(t.def_id),)
2594                                 }),
2595                                 Applicability::MaybeIncorrect,
2596                             );
2597                             return;
2598                         }
2599                         _ => {}
2600                     }
2601                 }
2602             }
2603
2604             let (potential_candidates, explicitly_negative) = if param_type.is_some() {
2605                 // FIXME: Even though negative bounds are not implemented, we could maybe handle
2606                 // cases where a positive bound implies a negative impl.
2607                 (candidates, Vec::new())
2608             } else if let Some(simp_rcvr_ty) =
2609                 simplify_type(self.tcx, rcvr_ty, TreatParams::AsPlaceholder)
2610             {
2611                 let mut potential_candidates = Vec::new();
2612                 let mut explicitly_negative = Vec::new();
2613                 for candidate in candidates {
2614                     // Check if there's a negative impl of `candidate` for `rcvr_ty`
2615                     if self
2616                         .tcx
2617                         .all_impls(candidate.def_id)
2618                         .filter(|imp_did| {
2619                             self.tcx.impl_polarity(*imp_did) == ty::ImplPolarity::Negative
2620                         })
2621                         .any(|imp_did| {
2622                             let imp = self.tcx.impl_trait_ref(imp_did).unwrap().subst_identity();
2623                             let imp_simp =
2624                                 simplify_type(self.tcx, imp.self_ty(), TreatParams::AsPlaceholder);
2625                             imp_simp.map_or(false, |s| s == simp_rcvr_ty)
2626                         })
2627                     {
2628                         explicitly_negative.push(candidate);
2629                     } else {
2630                         potential_candidates.push(candidate);
2631                     }
2632                 }
2633                 (potential_candidates, explicitly_negative)
2634             } else {
2635                 // We don't know enough about `recv_ty` to make proper suggestions.
2636                 (candidates, Vec::new())
2637             };
2638
2639             let action = if let Some(param) = param_type {
2640                 format!("restrict type parameter `{}` with", param)
2641             } else {
2642                 // FIXME: it might only need to be imported into scope, not implemented.
2643                 "implement".to_string()
2644             };
2645             match &potential_candidates[..] {
2646                 [] => {}
2647                 [trait_info] if trait_info.def_id.is_local() => {
2648                     err.span_note(
2649                         self.tcx.def_span(trait_info.def_id),
2650                         &format!(
2651                             "`{}` defines an item `{}`, perhaps you need to {} it",
2652                             self.tcx.def_path_str(trait_info.def_id),
2653                             item_name,
2654                             action
2655                         ),
2656                     );
2657                 }
2658                 trait_infos => {
2659                     let mut msg = message(action);
2660                     for (i, trait_info) in trait_infos.iter().enumerate() {
2661                         msg.push_str(&format!(
2662                             "\ncandidate #{}: `{}`",
2663                             i + 1,
2664                             self.tcx.def_path_str(trait_info.def_id),
2665                         ));
2666                     }
2667                     err.note(&msg);
2668                 }
2669             }
2670             match &explicitly_negative[..] {
2671                 [] => {}
2672                 [trait_info] => {
2673                     let msg = format!(
2674                         "the trait `{}` defines an item `{}`, but is explicitly unimplemented",
2675                         self.tcx.def_path_str(trait_info.def_id),
2676                         item_name
2677                     );
2678                     err.note(&msg);
2679                 }
2680                 trait_infos => {
2681                     let mut msg = format!(
2682                         "the following traits define an item `{}`, but are explicitly unimplemented:",
2683                         item_name
2684                     );
2685                     for trait_info in trait_infos {
2686                         msg.push_str(&format!("\n{}", self.tcx.def_path_str(trait_info.def_id)));
2687                     }
2688                     err.note(&msg);
2689                 }
2690             }
2691         }
2692     }
2693
2694     /// issue #102320, for `unwrap_or` with closure as argument, suggest `unwrap_or_else`
2695     /// FIXME: currently not working for suggesting `map_or_else`, see #102408
2696     pub(crate) fn suggest_else_fn_with_closure(
2697         &self,
2698         err: &mut Diagnostic,
2699         expr: &hir::Expr<'_>,
2700         found: Ty<'tcx>,
2701         expected: Ty<'tcx>,
2702     ) -> bool {
2703         let Some((_def_id_or_name, output, _inputs)) =
2704             self.extract_callable_info(found) else {
2705                 return false;
2706         };
2707
2708         if !self.can_coerce(output, expected) {
2709             return false;
2710         }
2711
2712         let parent = self.tcx.hir().parent_id(expr.hir_id);
2713         if  let Some(Node::Expr(call_expr)) = self.tcx.hir().find(parent) &&
2714             let hir::ExprKind::MethodCall(
2715                 hir::PathSegment { ident: method_name, .. },
2716                 self_expr,
2717                 args,
2718                 ..,
2719              ) = call_expr.kind &&
2720             let Some(self_ty) = self.typeck_results.borrow().expr_ty_opt(self_expr) {
2721             let new_name = Ident {
2722                 name: Symbol::intern(&format!("{}_else", method_name.as_str())),
2723                 span: method_name.span,
2724             };
2725             let probe = self.lookup_probe_for_diagnostic(
2726                 new_name,
2727                 self_ty,
2728                 self_expr,
2729                 ProbeScope::TraitsInScope,
2730                 Some(expected),
2731             );
2732
2733             // check the method arguments number
2734             if let Ok(pick) = probe &&
2735                 let fn_sig = self.tcx.fn_sig(pick.item.def_id) &&
2736                 let fn_args = fn_sig.skip_binder().inputs() &&
2737                 fn_args.len() == args.len() + 1 {
2738                 err.span_suggestion_verbose(
2739                     method_name.span.shrink_to_hi(),
2740                     &format!("try calling `{}` instead", new_name.name.as_str()),
2741                     "_else",
2742                     Applicability::MaybeIncorrect,
2743                 );
2744                 return true;
2745             }
2746         }
2747         false
2748     }
2749
2750     /// Checks whether there is a local type somewhere in the chain of
2751     /// autoderefs of `rcvr_ty`.
2752     fn type_derefs_to_local(
2753         &self,
2754         span: Span,
2755         rcvr_ty: Ty<'tcx>,
2756         source: SelfSource<'tcx>,
2757     ) -> bool {
2758         fn is_local(ty: Ty<'_>) -> bool {
2759             match ty.kind() {
2760                 ty::Adt(def, _) => def.did().is_local(),
2761                 ty::Foreign(did) => did.is_local(),
2762                 ty::Dynamic(tr, ..) => tr.principal().map_or(false, |d| d.def_id().is_local()),
2763                 ty::Param(_) => true,
2764
2765                 // Everything else (primitive types, etc.) is effectively
2766                 // non-local (there are "edge" cases, e.g., `(LocalType,)`, but
2767                 // the noise from these sort of types is usually just really
2768                 // annoying, rather than any sort of help).
2769                 _ => false,
2770             }
2771         }
2772
2773         // This occurs for UFCS desugaring of `T::method`, where there is no
2774         // receiver expression for the method call, and thus no autoderef.
2775         if let SelfSource::QPath(_) = source {
2776             return is_local(self.resolve_vars_with_obligations(rcvr_ty));
2777         }
2778
2779         self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))
2780     }
2781 }
2782
2783 #[derive(Copy, Clone, Debug)]
2784 pub enum SelfSource<'a> {
2785     QPath(&'a hir::Ty<'a>),
2786     MethodCall(&'a hir::Expr<'a> /* rcvr */),
2787 }
2788
2789 #[derive(Copy, Clone)]
2790 pub struct TraitInfo {
2791     pub def_id: DefId,
2792 }
2793
2794 impl PartialEq for TraitInfo {
2795     fn eq(&self, other: &TraitInfo) -> bool {
2796         self.cmp(other) == Ordering::Equal
2797     }
2798 }
2799 impl Eq for TraitInfo {}
2800 impl PartialOrd for TraitInfo {
2801     fn partial_cmp(&self, other: &TraitInfo) -> Option<Ordering> {
2802         Some(self.cmp(other))
2803     }
2804 }
2805 impl Ord for TraitInfo {
2806     fn cmp(&self, other: &TraitInfo) -> Ordering {
2807         // Local crates are more important than remote ones (local:
2808         // `cnum == 0`), and otherwise we throw in the defid for totality.
2809
2810         let lhs = (other.def_id.krate, other.def_id);
2811         let rhs = (self.def_id.krate, self.def_id);
2812         lhs.cmp(&rhs)
2813     }
2814 }
2815
2816 /// Retrieves all traits in this crate and any dependent crates,
2817 /// and wraps them into `TraitInfo` for custom sorting.
2818 pub fn all_traits(tcx: TyCtxt<'_>) -> Vec<TraitInfo> {
2819     tcx.all_traits().map(|def_id| TraitInfo { def_id }).collect()
2820 }
2821
2822 fn print_disambiguation_help<'tcx>(
2823     item_name: Ident,
2824     args: Option<(&'tcx hir::Expr<'tcx>, &'tcx [hir::Expr<'tcx>])>,
2825     err: &mut Diagnostic,
2826     trait_name: String,
2827     rcvr_ty: Ty<'_>,
2828     kind: ty::AssocKind,
2829     def_id: DefId,
2830     span: Span,
2831     candidate: Option<usize>,
2832     source_map: &source_map::SourceMap,
2833     fn_has_self_parameter: bool,
2834 ) {
2835     let mut applicability = Applicability::MachineApplicable;
2836     let (span, sugg) = if let (ty::AssocKind::Fn, Some((receiver, args))) = (kind, args) {
2837         let args = format!(
2838             "({}{})",
2839             rcvr_ty.ref_mutability().map_or("", |mutbl| mutbl.ref_prefix_str()),
2840             std::iter::once(receiver)
2841                 .chain(args.iter())
2842                 .map(|arg| source_map.span_to_snippet(arg.span).unwrap_or_else(|_| {
2843                     applicability = Applicability::HasPlaceholders;
2844                     "_".to_owned()
2845                 }))
2846                 .collect::<Vec<_>>()
2847                 .join(", "),
2848         );
2849         let trait_name = if !fn_has_self_parameter {
2850             format!("<{} as {}>", rcvr_ty, trait_name)
2851         } else {
2852             trait_name
2853         };
2854         (span, format!("{}::{}{}", trait_name, item_name, args))
2855     } else {
2856         (span.with_hi(item_name.span.lo()), format!("<{} as {}>::", rcvr_ty, trait_name))
2857     };
2858     err.span_suggestion_verbose(
2859         span,
2860         &format!(
2861             "disambiguate the {} for {}",
2862             kind.as_def_kind().descr(def_id),
2863             if let Some(candidate) = candidate {
2864                 format!("candidate #{}", candidate)
2865             } else {
2866                 "the candidate".to_string()
2867             },
2868         ),
2869         sugg,
2870         applicability,
2871     );
2872 }