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