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