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