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