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