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::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
   7 use rustc_hir as hir;
   8 use rustc_hir::def::{DefKind, Namespace, Res};
   9 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX};
  10 use rustc_hir::intravisit;
  11 use rustc_hir::lang_items::LangItem;
  12 use rustc_hir::{ExprKind, Node, QPath};
  13 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  14 use rustc_middle::ty::fast_reject::simplify_type;
  15 use rustc_middle::ty::print::with_crate_prefix;
  16 use rustc_middle::ty::{
  17     self, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
  18 };
  19 use rustc_span::lev_distance;
  20 use rustc_span::symbol::{kw, sym, Ident};
  21 use rustc_span::{source_map, FileName, Span};
  22 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
  23 use rustc_trait_selection::traits::Obligation;
  24
  25 use std::cmp::Ordering;
  26 use std::iter;
  27
  28 use super::probe::Mode;
  29 use super::{CandidateSource, MethodError, NoMatchData};
  30
  31 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  32     fn is_fn_ty(&self, ty: Ty<'tcx>, span: Span) -> bool {
  33         let tcx = self.tcx;
  34         match ty.kind() {
  35             // Not all of these (e.g., unsafe fns) implement `FnOnce`,
  36             // so we look for these beforehand.
  37             ty::Closure(..) | ty::FnDef(..) | ty::FnPtr(_) => true,
  38             // If it's not a simple function, look for things which implement `FnOnce`.
  39             _ => {
  40                 let fn_once = match tcx.lang_items().require(LangItem::FnOnce) {
  41                     Ok(fn_once) => fn_once,
  42                     Err(..) => return false,
  43                 };
  44
  45                 self.autoderef(span, ty).any(|(ty, _)| {
  46                     self.probe(|_| {
  47                         let fn_once_substs = tcx.mk_substs_trait(
  48                             ty,
  49                             &[self
  50                                 .next_ty_var(TypeVariableOrigin {
  51                                     kind: TypeVariableOriginKind::MiscVariable,
  52                                     span,
  53                                 })
  54                                 .into()],
  55                         );
  56                         let trait_ref = ty::TraitRef::new(fn_once, fn_once_substs);
  57                         let poly_trait_ref = trait_ref.to_poly_trait_ref();
  58                         let obligation = Obligation::misc(
  59                             span,
  60                             self.body_id,
  61                             self.param_env,
  62                             poly_trait_ref.without_const().to_predicate(tcx),
  63                         );
  64                         self.predicate_may_hold(&obligation)
  65                     })
  66                 })
  67             }
  68         }
  69     }
  70
  71     pub fn report_method_error(
  72         &self,
  73         span: Span,
  74         rcvr_ty: Ty<'tcx>,
  75         item_name: Ident,
  76         source: SelfSource<'tcx>,
  77         error: MethodError<'tcx>,
  78         args: Option<&'tcx [hir::Expr<'tcx>]>,
  79     ) -> Option<DiagnosticBuilder<'_>> {
  80         let orig_span = span;
  81         let mut span = span;
  82         // Avoid suggestions when we don't know what's going on.
  83         if rcvr_ty.references_error() {
  84             return None;
  85         }
  86
  87         let report_candidates = |span: Span,
  88                                  err: &mut DiagnosticBuilder<'_>,
  89                                  mut sources: Vec<CandidateSource>,
  90                                  sugg_span: Span| {
  91             sources.sort();
  92             sources.dedup();
  93             // Dynamic limit to avoid hiding just one candidate, which is silly.
  94             let limit = if sources.len() == 5 { 5 } else { 4 };
  95
  96             for (idx, source) in sources.iter().take(limit).enumerate() {
  97                 match *source {
  98                     CandidateSource::ImplSource(impl_did) => {
  99                         // Provide the best span we can. Use the item, if local to crate, else
 100                         // the impl, if local to crate (item may be defaulted), else nothing.
 101                         let item = match self
 102                             .associated_item(impl_did, item_name, Namespace::ValueNS)
 103                             .or_else(|| {
 104                                 let impl_trait_ref = self.tcx.impl_trait_ref(impl_did)?;
 105                                 self.associated_item(
 106                                     impl_trait_ref.def_id,
 107                                     item_name,
 108                                     Namespace::ValueNS,
 109                                 )
 110                             }) {
 111                             Some(item) => item,
 112                             None => continue,
 113                         };
 114                         let note_span = self
 115                             .tcx
 116                             .hir()
 117                             .span_if_local(item.def_id)
 118                             .or_else(|| self.tcx.hir().span_if_local(impl_did));
 119
 120                         let impl_ty = self.tcx.at(span).type_of(impl_did);
 121
 122                         let insertion = match self.tcx.impl_trait_ref(impl_did) {
 123                             None => String::new(),
 124                             Some(trait_ref) => format!(
 125                                 " of the trait `{}`",
 126                                 self.tcx.def_path_str(trait_ref.def_id)
 127                             ),
 128                         };
 129
 130                         let (note_str, idx) = if sources.len() > 1 {
 131                             (
 132                                 format!(
 133                                     "candidate #{} is defined in an impl{} for the type `{}`",
 134                                     idx + 1,
 135                                     insertion,
 136                                     impl_ty,
 137                                 ),
 138                                 Some(idx + 1),
 139                             )
 140                         } else {
 141                             (
 142                                 format!(
 143                                     "the candidate is defined in an impl{} for the type `{}`",
 144                                     insertion, impl_ty,
 145                                 ),
 146                                 None,
 147                             )
 148                         };
 149                         if let Some(note_span) = note_span {
 150                             // We have a span pointing to the method. Show note with snippet.
 151                             err.span_note(
 152                                 self.tcx.sess.source_map().guess_head_span(note_span),
 153                                 &note_str,
 154                             );
 155                         } else {
 156                             err.note(&note_str);
 157                         }
 158                         if let Some(trait_ref) = self.tcx.impl_trait_ref(impl_did) {
 159                             let path = self.tcx.def_path_str(trait_ref.def_id);
 160
 161                             let ty = match item.kind {
 162                                 ty::AssocKind::Const | ty::AssocKind::Type => rcvr_ty,
 163                                 ty::AssocKind::Fn => self
 164                                     .tcx
 165                                     .fn_sig(item.def_id)
 166                                     .inputs()
 167                                     .skip_binder()
 168                                     .get(0)
 169                                     .filter(|ty| ty.is_region_ptr() && !rcvr_ty.is_region_ptr())
 170                                     .copied()
 171                                     .unwrap_or(rcvr_ty),
 172                             };
 173                             print_disambiguation_help(
 174                                 item_name,
 175                                 args,
 176                                 err,
 177                                 path,
 178                                 ty,
 179                                 item.kind,
 180                                 item.def_id,
 181                                 sugg_span,
 182                                 idx,
 183                                 self.tcx.sess.source_map(),
 184                             );
 185                         }
 186                     }
 187                     CandidateSource::TraitSource(trait_did) => {
 188                         let item =
 189                             match self.associated_item(trait_did, item_name, Namespace::ValueNS) {
 190                                 Some(item) => item,
 191                                 None => continue,
 192                             };
 193                         let item_span = self
 194                             .tcx
 195                             .sess
 196                             .source_map()
 197                             .guess_head_span(self.tcx.def_span(item.def_id));
 198                         let idx = if sources.len() > 1 {
 199                             let msg = &format!(
 200                                 "candidate #{} is defined in the trait `{}`",
 201                                 idx + 1,
 202                                 self.tcx.def_path_str(trait_did)
 203                             );
 204                             err.span_note(item_span, msg);
 205                             Some(idx + 1)
 206                         } else {
 207                             let msg = &format!(
 208                                 "the candidate is defined in the trait `{}`",
 209                                 self.tcx.def_path_str(trait_did)
 210                             );
 211                             err.span_note(item_span, msg);
 212                             None
 213                         };
 214                         let path = self.tcx.def_path_str(trait_did);
 215                         print_disambiguation_help(
 216                             item_name,
 217                             args,
 218                             err,
 219                             path,
 220                             rcvr_ty,
 221                             item.kind,
 222                             item.def_id,
 223                             sugg_span,
 224                             idx,
 225                             self.tcx.sess.source_map(),
 226                         );
 227                     }
 228                 }
 229             }
 230             if sources.len() > limit {
 231                 err.note(&format!("and {} others", sources.len() - limit));
 232             }
 233         };
 234
 235         let sugg_span = if let SelfSource::MethodCall(expr) = source {
 236             // Given `foo.bar(baz)`, `expr` is `bar`, but we want to point to the whole thing.
 237             self.tcx.hir().expect_expr(self.tcx.hir().get_parent_node(expr.hir_id)).span
 238         } else {
 239             span
 240         };
 241
 242         match error {
 243             MethodError::NoMatch(NoMatchData {
 244                 static_candidates: static_sources,
 245                 unsatisfied_predicates,
 246                 out_of_scope_traits,
 247                 lev_candidate,
 248                 mode,
 249             }) => {
 250                 let tcx = self.tcx;
 251
 252                 let actual = self.resolve_vars_if_possible(rcvr_ty);
 253                 let ty_str = self.ty_to_string(actual);
 254                 let is_method = mode == Mode::MethodCall;
 255                 let item_kind = if is_method {
 256                     "method"
 257                 } else if actual.is_enum() {
 258                     "variant or associated item"
 259                 } else {
 260                     match (item_name.as_str().chars().next(), actual.is_fresh_ty()) {
 261                         (Some(name), false) if name.is_lowercase() => "function or associated item",
 262                         (Some(_), false) => "associated item",
 263                         (Some(_), true) | (None, false) => "variant or associated item",
 264                         (None, true) => "variant",
 265                     }
 266                 };
 267                 let mut err = if !actual.references_error() {
 268                     // Suggest clamping down the type if the method that is being attempted to
 269                     // be used exists at all, and the type is an ambiguous numeric type
 270                     // ({integer}/{float}).
 271                     let mut candidates = all_traits(self.tcx).into_iter().filter_map(|info| {
 272                         self.associated_item(info.def_id, item_name, Namespace::ValueNS)
 273                     });
 274                     // There are methods that are defined on the primitive types and won't be
 275                     // found when exploring `all_traits`, but we also need them to be acurate on
 276                     // our suggestions (#47759).
 277                     let fund_assoc = |opt_def_id: Option<DefId>| {
 278                         opt_def_id
 279                             .and_then(|id| self.associated_item(id, item_name, Namespace::ValueNS))
 280                             .is_some()
 281                     };
 282                     let lang_items = tcx.lang_items();
 283                     let found_candidate = candidates.next().is_some()
 284                         || fund_assoc(lang_items.i8_impl())
 285                         || fund_assoc(lang_items.i16_impl())
 286                         || fund_assoc(lang_items.i32_impl())
 287                         || fund_assoc(lang_items.i64_impl())
 288                         || fund_assoc(lang_items.i128_impl())
 289                         || fund_assoc(lang_items.u8_impl())
 290                         || fund_assoc(lang_items.u16_impl())
 291                         || fund_assoc(lang_items.u32_impl())
 292                         || fund_assoc(lang_items.u64_impl())
 293                         || fund_assoc(lang_items.u128_impl())
 294                         || fund_assoc(lang_items.f32_impl())
 295                         || fund_assoc(lang_items.f32_runtime_impl())
 296                         || fund_assoc(lang_items.f64_impl())
 297                         || fund_assoc(lang_items.f64_runtime_impl());
 298                     if let (true, false, SelfSource::MethodCall(expr), true) = (
 299                         actual.is_numeric(),
 300                         actual.has_concrete_skeleton(),
 301                         source,
 302                         found_candidate,
 303                     ) {
 304                         let mut err = struct_span_err!(
 305                             tcx.sess,
 306                             span,
 307                             E0689,
 308                             "can't call {} `{}` on ambiguous numeric type `{}`",
 309                             item_kind,
 310                             item_name,
 311                             ty_str
 312                         );
 313                         let concrete_type = if actual.is_integral() { "i32" } else { "f32" };
 314                         match expr.kind {
 315                             ExprKind::Lit(ref lit) => {
 316                                 // numeric literal
 317                                 let snippet = tcx
 318                                     .sess
 319                                     .source_map()
 320                                     .span_to_snippet(lit.span)
 321                                     .unwrap_or_else(|_| "<numeric literal>".to_owned());
 322
 323                                 err.span_suggestion(
 324                                     lit.span,
 325                                     &format!(
 326                                         "you must specify a concrete type for this numeric value, \
 327                                          like `{}`",
 328                                         concrete_type
 329                                     ),
 330                                     format!("{}_{}", snippet, concrete_type),
 331                                     Applicability::MaybeIncorrect,
 332                                 );
 333                             }
 334                             ExprKind::Path(ref qpath) => {
 335                                 // local binding
 336                                 if let QPath::Resolved(_, path) = qpath {
 337                                     if let hir::def::Res::Local(hir_id) = path.res {
 338                                         let span = tcx.hir().span(hir_id);
 339                                         let snippet = tcx.sess.source_map().span_to_snippet(span);
 340                                         let filename = tcx.sess.source_map().span_to_filename(span);
 341
 342                                         let parent_node = self
 343                                             .tcx
 344                                             .hir()
 345                                             .get(self.tcx.hir().get_parent_node(hir_id));
 346                                         let msg = format!(
 347                                             "you must specify a type for this binding, like `{}`",
 348                                             concrete_type,
 349                                         );
 350
 351                                         match (filename, parent_node, snippet) {
 352                                             (
 353                                                 FileName::Real(_),
 354                                                 Node::Local(hir::Local {
 355                                                     source: hir::LocalSource::Normal,
 356                                                     ty,
 357                                                     ..
 358                                                 }),
 359                                                 Ok(ref snippet),
 360                                             ) => {
 361                                                 err.span_suggestion(
 362                                                     // account for `let x: _ = 42;`
 363                                                     //                  ^^^^
 364                                                     span.to(ty
 365                                                         .as_ref()
 366                                                         .map(|ty| ty.span)
 367                                                         .unwrap_or(span)),
 368                                                     &msg,
 369                                                     format!("{}: {}", snippet, concrete_type),
 370                                                     Applicability::MaybeIncorrect,
 371                                                 );
 372                                             }
 373                                             _ => {
 374                                                 err.span_label(span, msg);
 375                                             }
 376                                         }
 377                                     }
 378                                 }
 379                             }
 380                             _ => {}
 381                         }
 382                         err.emit();
 383                         return None;
 384                     } else {
 385                         span = item_name.span;
 386                         let mut err = struct_span_err!(
 387                             tcx.sess,
 388                             span,
 389                             E0599,
 390                             "no {} named `{}` found for {} `{}` in the current scope",
 391                             item_kind,
 392                             item_name,
 393                             actual.prefix_string(self.tcx),
 394                             ty_str,
 395                         );
 396                         if let Mode::MethodCall = mode {
 397                             if let SelfSource::MethodCall(call) = source {
 398                                 self.suggest_await_before_method(
 399                                     &mut err, item_name, actual, call, span,
 400                                 );
 401                             }
 402                         }
 403                         if let Some(span) =
 404                             tcx.sess.confused_type_with_std_module.borrow().get(&span)
 405                         {
 406                             if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*span) {
 407                                 err.span_suggestion(
 408                                     *span,
 409                                     "you are looking for the module in `std`, \
 410                                      not the primitive type",
 411                                     format!("std::{}", snippet),
 412                                     Applicability::MachineApplicable,
 413                                 );
 414                             }
 415                         }
 416                         if let ty::RawPtr(_) = &actual.kind() {
 417                             err.note(
 418                                 "try using `<*const T>::as_ref()` to get a reference to the \
 419                                       type behind the pointer: https://doc.rust-lang.org/std/\
 420                                       primitive.pointer.html#method.as_ref",
 421                             );
 422                             err.note(
 423                                 "using `<*const T>::as_ref()` on a pointer \
 424                                       which is unaligned or points to invalid \
 425                                       or uninitialized memory is undefined behavior",
 426                             );
 427                         }
 428                         err
 429                     }
 430                 } else {
 431                     tcx.sess.diagnostic().struct_dummy()
 432                 };
 433
 434                 if let Some(def) = actual.ty_adt_def() {
 435                     if let Some(full_sp) = tcx.hir().span_if_local(def.did) {
 436                         let def_sp = tcx.sess.source_map().guess_head_span(full_sp);
 437                         err.span_label(
 438                             def_sp,
 439                             format!(
 440                                 "{} `{}` not found {}",
 441                                 item_kind,
 442                                 item_name,
 443                                 if def.is_enum() && !is_method { "here" } else { "for this" }
 444                             ),
 445                         );
 446                     }
 447                 }
 448
 449                 let mut label_span_not_found = || {
 450                     if unsatisfied_predicates.is_empty() {
 451                         err.span_label(span, format!("{item_kind} not found in `{ty_str}`"));
 452                     } else {
 453                         err.span_label(span, format!("{item_kind} cannot be called on `{ty_str}` due to unsatisfied trait bounds"));
 454                     }
 455                     self.tcx.sess.trait_methods_not_found.borrow_mut().insert(orig_span);
 456                 };
 457
 458                 // If the method name is the name of a field with a function or closure type,
 459                 // give a helping note that it has to be called as `(x.f)(...)`.
 460                 if let SelfSource::MethodCall(expr) = source {
 461                     let field_receiver =
 462                         self.autoderef(span, rcvr_ty).find_map(|(ty, _)| match ty.kind() {
 463                             ty::Adt(def, substs) if !def.is_enum() => {
 464                                 let variant = &def.non_enum_variant();
 465                                 self.tcx.find_field_index(item_name, variant).map(|index| {
 466                                     let field = &variant.fields[index];
 467                                     let field_ty = field.ty(tcx, substs);
 468                                     (field, field_ty)
 469                                 })
 470                             }
 471                             _ => None,
 472                         });
 473
 474                     if let Some((field, field_ty)) = field_receiver {
 475                         let scope = self.tcx.parent_module(self.body_id).to_def_id();
 476                         let is_accessible = field.vis.is_accessible_from(scope, self.tcx);
 477
 478                         if is_accessible {
 479                             if self.is_fn_ty(&field_ty, span) {
 480                                 let expr_span = expr.span.to(item_name.span);
 481                                 err.multipart_suggestion(
 482                                     &format!(
 483                                         "to call the function stored in `{}`, \
 484                                          surround the field access with parentheses",
 485                                         item_name,
 486                                     ),
 487                                     vec![
 488                                         (expr_span.shrink_to_lo(), '('.to_string()),
 489                                         (expr_span.shrink_to_hi(), ')'.to_string()),
 490                                     ],
 491                                     Applicability::MachineApplicable,
 492                                 );
 493                             } else {
 494                                 let call_expr = self
 495                                     .tcx
 496                                     .hir()
 497                                     .expect_expr(self.tcx.hir().get_parent_node(expr.hir_id));
 498
 499                                 if let Some(span) = call_expr.span.trim_start(item_name.span) {
 500                                     err.span_suggestion(
 501                                         span,
 502                                         "remove the arguments",
 503                                         String::new(),
 504                                         Applicability::MaybeIncorrect,
 505                                     );
 506                                 }
 507                             }
 508                         }
 509
 510                         let field_kind = if is_accessible { "field" } else { "private field" };
 511                         err.span_label(item_name.span, format!("{}, not a method", field_kind));
 512                     } else if lev_candidate.is_none() && static_sources.is_empty() {
 513                         label_span_not_found();
 514                     }
 515                 } else {
 516                     label_span_not_found();
 517                 }
 518
 519                 if self.is_fn_ty(&rcvr_ty, span) {
 520                     fn report_function<T: std::fmt::Display>(
 521                         err: &mut DiagnosticBuilder<'_>,
 522                         name: T,
 523                     ) {
 524                         err.note(
 525                             &format!("`{}` is a function, perhaps you wish to call it", name,),
 526                         );
 527                     }
 528
 529                     if let SelfSource::MethodCall(expr) = source {
 530                         if let Ok(expr_string) = tcx.sess.source_map().span_to_snippet(expr.span) {
 531                             report_function(&mut err, expr_string);
 532                         } else if let ExprKind::Path(QPath::Resolved(_, ref path)) = expr.kind {
 533                             if let Some(segment) = path.segments.last() {
 534                                 report_function(&mut err, segment.ident);
 535                             }
 536                         }
 537                     }
 538                 }
 539
 540                 if !static_sources.is_empty() {
 541                     err.note(
 542                         "found the following associated functions; to be used as methods, \
 543                          functions must have a `self` parameter",
 544                     );
 545                     err.span_label(span, "this is an associated function, not a method");
 546                 }
 547                 if static_sources.len() == 1 {
 548                     let ty_str = if let Some(CandidateSource::ImplSource(impl_did)) =
 549                         static_sources.get(0)
 550                     {
 551                         // When the "method" is resolved through dereferencing, we really want the
 552                         // original type that has the associated function for accurate suggestions.
 553                         // (#61411)
 554                         let ty = tcx.at(span).type_of(*impl_did);
 555                         match (&ty.peel_refs().kind(), &actual.peel_refs().kind()) {
 556                             (ty::Adt(def, _), ty::Adt(def_actual, _)) if def == def_actual => {
 557                                 // Use `actual` as it will have more `substs` filled in.
 558                                 self.ty_to_value_string(actual.peel_refs())
 559                             }
 560                             _ => self.ty_to_value_string(ty.peel_refs()),
 561                         }
 562                     } else {
 563                         self.ty_to_value_string(actual.peel_refs())
 564                     };
 565                     if let SelfSource::MethodCall(expr) = source {
 566                         err.span_suggestion(
 567                             expr.span.to(span),
 568                             "use associated function syntax instead",
 569                             format!("{}::{}", ty_str, item_name),
 570                             Applicability::MachineApplicable,
 571                         );
 572                     } else {
 573                         err.help(&format!("try with `{}::{}`", ty_str, item_name,));
 574                     }
 575
 576                     report_candidates(span, &mut err, static_sources, sugg_span);
 577                 } else if static_sources.len() > 1 {
 578                     report_candidates(span, &mut err, static_sources, sugg_span);
 579                 }
 580
 581                 let mut restrict_type_params = false;
 582                 let mut unsatisfied_bounds = false;
 583                 if !unsatisfied_predicates.is_empty() {
 584                     let def_span = |def_id| {
 585                         self.tcx.sess.source_map().guess_head_span(self.tcx.def_span(def_id))
 586                     };
 587                     let mut type_params = FxHashMap::default();
 588                     let mut bound_spans = vec![];
 589
 590                     let mut collect_type_param_suggestions =
 591                         |self_ty: Ty<'tcx>, parent_pred: &ty::Predicate<'tcx>, obligation: &str| {
 592                             // We don't care about regions here, so it's fine to skip the binder here.
 593                             if let (ty::Param(_), ty::PredicateKind::Trait(p, _)) =
 594                                 (self_ty.kind(), parent_pred.kind().skip_binder())
 595                             {
 596                                 if let ty::Adt(def, _) = p.trait_ref.self_ty().kind() {
 597                                     let node = def.did.as_local().map(|def_id| {
 598                                         self.tcx
 599                                             .hir()
 600                                             .get(self.tcx.hir().local_def_id_to_hir_id(def_id))
 601                                     });
 602                                     if let Some(hir::Node::Item(hir::Item { kind, .. })) = node {
 603                                         if let Some(g) = kind.generics() {
 604                                             let key = match g.where_clause.predicates {
 605                                                 [.., pred] => (pred.span().shrink_to_hi(), false),
 606                                                 [] => (
 607                                                     g.where_clause
 608                                                         .span_for_predicates_or_empty_place(),
 609                                                     true,
 610                                                 ),
 611                                             };
 612                                             type_params
 613                                                 .entry(key)
 614                                                 .or_insert_with(FxHashSet::default)
 615                                                 .insert(obligation.to_owned());
 616                                         }
 617                                     }
 618                                 }
 619                             }
 620                         };
 621                     let mut bound_span_label = |self_ty: Ty<'_>, obligation: &str, quiet: &str| {
 622                         let msg = format!(
 623                             "doesn't satisfy `{}`",
 624                             if obligation.len() > 50 { quiet } else { obligation }
 625                         );
 626                         match &self_ty.kind() {
 627                             // Point at the type that couldn't satisfy the bound.
 628                             ty::Adt(def, _) => bound_spans.push((def_span(def.did), msg)),
 629                             // Point at the trait object that couldn't satisfy the bound.
 630                             ty::Dynamic(preds, _) => {
 631                                 for pred in preds.iter() {
 632                                     match pred.skip_binder() {
 633                                         ty::ExistentialPredicate::Trait(tr) => {
 634                                             bound_spans.push((def_span(tr.def_id), msg.clone()))
 635                                         }
 636                                         ty::ExistentialPredicate::Projection(_)
 637                                         | ty::ExistentialPredicate::AutoTrait(_) => {}
 638                                     }
 639                                 }
 640                             }
 641                             // Point at the closure that couldn't satisfy the bound.
 642                             ty::Closure(def_id, _) => bound_spans
 643                                 .push((def_span(*def_id), format!("doesn't satisfy `{}`", quiet))),
 644                             _ => {}
 645                         }
 646                     };
 647                     let mut format_pred = |pred: ty::Predicate<'tcx>| {
 648                         let bound_predicate = pred.kind();
 649                         match bound_predicate.skip_binder() {
 650                             ty::PredicateKind::Projection(pred) => {
 651                                 let pred = bound_predicate.rebind(pred);
 652                                 // `<Foo as Iterator>::Item = String`.
 653                                 let projection_ty = pred.skip_binder().projection_ty;
 654
 655                                 let substs_with_infer_self = tcx.mk_substs(
 656                                     iter::once(tcx.mk_ty_var(ty::TyVid { index: 0 }).into())
 657                                         .chain(projection_ty.substs.iter().skip(1)),
 658                                 );
 659
 660                                 let quiet_projection_ty = ty::ProjectionTy {
 661                                     substs: substs_with_infer_self,
 662                                     item_def_id: projection_ty.item_def_id,
 663                                 };
 664
 665                                 let ty = pred.skip_binder().ty;
 666
 667                                 let obligation = format!("{} = {}", projection_ty, ty);
 668                                 let quiet = format!("{} = {}", quiet_projection_ty, ty);
 669
 670                                 bound_span_label(projection_ty.self_ty(), &obligation, &quiet);
 671                                 Some((obligation, projection_ty.self_ty()))
 672                             }
 673                             ty::PredicateKind::Trait(poly_trait_ref, _) => {
 674                                 let p = poly_trait_ref.trait_ref;
 675                                 let self_ty = p.self_ty();
 676                                 let path = p.print_only_trait_path();
 677                                 let obligation = format!("{}: {}", self_ty, path);
 678                                 let quiet = format!("_: {}", path);
 679                                 bound_span_label(self_ty, &obligation, &quiet);
 680                                 Some((obligation, self_ty))
 681                             }
 682                             _ => None,
 683                         }
 684                     };
 685                     let mut bound_list = unsatisfied_predicates
 686                         .iter()
 687                         .filter_map(|(pred, parent_pred)| {
 688                             format_pred(*pred).map(|(p, self_ty)| match parent_pred {
 689                                 None => format!("`{}`", &p),
 690                                 Some(parent_pred) => match format_pred(*parent_pred) {
 691                                     None => format!("`{}`", &p),
 692                                     Some((parent_p, _)) => {
 693                                         collect_type_param_suggestions(self_ty, parent_pred, &p);
 694                                         format!("`{}`\nwhich is required by `{}`", p, parent_p)
 695                                     }
 696                                 },
 697                             })
 698                         })
 699                         .enumerate()
 700                         .collect::<Vec<(usize, String)>>();
 701                     for ((span, empty_where), obligations) in type_params.into_iter() {
 702                         restrict_type_params = true;
 703                         // #74886: Sort here so that the output is always the same.
 704                         let mut obligations = obligations.into_iter().collect::<Vec<_>>();
 705                         obligations.sort();
 706                         err.span_suggestion_verbose(
 707                             span,
 708                             &format!(
 709                                 "consider restricting the type parameter{s} to satisfy the \
 710                                  trait bound{s}",
 711                                 s = pluralize!(obligations.len())
 712                             ),
 713                             format!(
 714                                 "{} {}",
 715                                 if empty_where { " where" } else { "," },
 716                                 obligations.join(", ")
 717                             ),
 718                             Applicability::MaybeIncorrect,
 719                         );
 720                     }
 721
 722                     bound_list.sort_by(|(_, a), (_, b)| a.cmp(&b)); // Sort alphabetically.
 723                     bound_list.dedup_by(|(_, a), (_, b)| a == b); // #35677
 724                     bound_list.sort_by_key(|(pos, _)| *pos); // Keep the original predicate order.
 725                     bound_spans.sort();
 726                     bound_spans.dedup();
 727                     for (span, msg) in bound_spans.into_iter() {
 728                         err.span_label(span, &msg);
 729                     }
 730                     if !bound_list.is_empty() {
 731                         let bound_list = bound_list
 732                             .into_iter()
 733                             .map(|(_, path)| path)
 734                             .collect::<Vec<_>>()
 735                             .join("\n");
 736                         let actual_prefix = actual.prefix_string(self.tcx);
 737                         err.set_primary_message(&format!(
 738                             "the {item_kind} `{item_name}` exists for {actual_prefix} `{ty_str}`, but its trait bounds were not satisfied"
 739                         ));
 740                         err.note(&format!(
 741                             "the following trait bounds were not satisfied:\n{bound_list}"
 742                         ));
 743                         unsatisfied_bounds = true;
 744                     }
 745                 }
 746
 747                 if actual.is_numeric() && actual.is_fresh() || restrict_type_params {
 748                 } else {
 749                     self.suggest_traits_to_import(
 750                         &mut err,
 751                         span,
 752                         rcvr_ty,
 753                         item_name,
 754                         source,
 755                         out_of_scope_traits,
 756                         &unsatisfied_predicates,
 757                         unsatisfied_bounds,
 758                     );
 759                 }
 760
 761                 // Don't emit a suggestion if we found an actual method
 762                 // that had unsatisfied trait bounds
 763                 if unsatisfied_predicates.is_empty() && actual.is_enum() {
 764                     let adt_def = actual.ty_adt_def().expect("enum is not an ADT");
 765                     if let Some(suggestion) = lev_distance::find_best_match_for_name(
 766                         &adt_def.variants.iter().map(|s| s.ident.name).collect::<Vec<_>>(),
 767                         item_name.name,
 768                         None,
 769                     ) {
 770                         err.span_suggestion(
 771                             span,
 772                             "there is a variant with a similar name",
 773                             suggestion.to_string(),
 774                             Applicability::MaybeIncorrect,
 775                         );
 776                     }
 777                 }
 778
 779                 let mut fallback_span = true;
 780                 let msg = "remove this method call";
 781                 if item_name.name == sym::as_str && actual.peel_refs().is_str() {
 782                     if let SelfSource::MethodCall(expr) = source {
 783                         let call_expr =
 784                             self.tcx.hir().expect_expr(self.tcx.hir().get_parent_node(expr.hir_id));
 785                         if let Some(span) = call_expr.span.trim_start(expr.span) {
 786                             err.span_suggestion(
 787                                 span,
 788                                 msg,
 789                                 String::new(),
 790                                 Applicability::MachineApplicable,
 791                             );
 792                             fallback_span = false;
 793                         }
 794                     }
 795                     if fallback_span {
 796                         err.span_label(span, msg);
 797                     }
 798                 } else if let Some(lev_candidate) = lev_candidate {
 799                     // Don't emit a suggestion if we found an actual method
 800                     // that had unsatisfied trait bounds
 801                     if unsatisfied_predicates.is_empty() {
 802                         let def_kind = lev_candidate.kind.as_def_kind();
 803                         err.span_suggestion(
 804                             span,
 805                             &format!(
 806                                 "there is {} {} with a similar name",
 807                                 def_kind.article(),
 808                                 def_kind.descr(lev_candidate.def_id),
 809                             ),
 810                             lev_candidate.ident.to_string(),
 811                             Applicability::MaybeIncorrect,
 812                         );
 813                     }
 814                 }
 815
 816                 return Some(err);
 817             }
 818
 819             MethodError::Ambiguity(sources) => {
 820                 let mut err = struct_span_err!(
 821                     self.sess(),
 822                     item_name.span,
 823                     E0034,
 824                     "multiple applicable items in scope"
 825                 );
 826                 err.span_label(item_name.span, format!("multiple `{}` found", item_name));
 827
 828                 report_candidates(span, &mut err, sources, sugg_span);
 829                 err.emit();
 830             }
 831
 832             MethodError::PrivateMatch(kind, def_id, out_of_scope_traits) => {
 833                 let kind = kind.descr(def_id);
 834                 let mut err = struct_span_err!(
 835                     self.tcx.sess,
 836                     item_name.span,
 837                     E0624,
 838                     "{} `{}` is private",
 839                     kind,
 840                     item_name
 841                 );
 842                 err.span_label(item_name.span, &format!("private {}", kind));
 843                 self.suggest_valid_traits(&mut err, out_of_scope_traits);
 844                 err.emit();
 845             }
 846
 847             MethodError::IllegalSizedBound(candidates, needs_mut, bound_span) => {
 848                 let msg = format!("the `{}` method cannot be invoked on a trait object", item_name);
 849                 let mut err = self.sess().struct_span_err(span, &msg);
 850                 err.span_label(bound_span, "this has a `Sized` requirement");
 851                 if !candidates.is_empty() {
 852                     let help = format!(
 853                         "{an}other candidate{s} {were} found in the following trait{s}, perhaps \
 854                          add a `use` for {one_of_them}:",
 855                         an = if candidates.len() == 1 { "an" } else { "" },
 856                         s = pluralize!(candidates.len()),
 857                         were = if candidates.len() == 1 { "was" } else { "were" },
 858                         one_of_them = if candidates.len() == 1 { "it" } else { "one_of_them" },
 859                     );
 860                     self.suggest_use_candidates(&mut err, help, candidates);
 861                 }
 862                 if let ty::Ref(region, t_type, mutability) = rcvr_ty.kind() {
 863                     if needs_mut {
 864                         let trait_type = self.tcx.mk_ref(
 865                             region,
 866                             ty::TypeAndMut { ty: t_type, mutbl: mutability.invert() },
 867                         );
 868                         err.note(&format!("you need `{}` instead of `{}`", trait_type, rcvr_ty));
 869                     }
 870                 }
 871                 err.emit();
 872             }
 873
 874             MethodError::BadReturnType => bug!("no return type expectations but got BadReturnType"),
 875         }
 876         None
 877     }
 878
 879     /// Print out the type for use in value namespace.
 880     fn ty_to_value_string(&self, ty: Ty<'tcx>) -> String {
 881         match ty.kind() {
 882             ty::Adt(def, substs) => format!("{}", ty::Instance::new(def.did, substs)),
 883             _ => self.ty_to_string(ty),
 884         }
 885     }
 886
 887     fn suggest_await_before_method(
 888         &self,
 889         err: &mut DiagnosticBuilder<'_>,
 890         item_name: Ident,
 891         ty: Ty<'tcx>,
 892         call: &hir::Expr<'_>,
 893         span: Span,
 894     ) {
 895         let output_ty = match self.infcx.get_impl_future_output_ty(ty) {
 896             Some(output_ty) => self.resolve_vars_if_possible(output_ty),
 897             _ => return,
 898         };
 899         let method_exists = self.method_exists(item_name, output_ty, call.hir_id, true);
 900         debug!("suggest_await_before_method: is_method_exist={}", method_exists);
 901         if method_exists {
 902             err.span_suggestion_verbose(
 903                 span.shrink_to_lo(),
 904                 "consider `await`ing on the `Future` and calling the method on its `Output`",
 905                 "await.".to_string(),
 906                 Applicability::MaybeIncorrect,
 907             );
 908         }
 909     }
 910
 911     fn suggest_use_candidates(
 912         &self,
 913         err: &mut DiagnosticBuilder<'_>,
 914         mut msg: String,
 915         candidates: Vec<DefId>,
 916     ) {
 917         let module_did = self.tcx.parent_module(self.body_id);
 918         let module_id = self.tcx.hir().local_def_id_to_hir_id(module_did);
 919         let krate = self.tcx.hir().krate();
 920         let (span, found_use) = UsePlacementFinder::check(self.tcx, krate, module_id);
 921         if let Some(span) = span {
 922             let path_strings = candidates.iter().map(|did| {
 923                 // Produce an additional newline to separate the new use statement
 924                 // from the directly following item.
 925                 let additional_newline = if found_use { "" } else { "\n" };
 926                 format!(
 927                     "use {};\n{}",
 928                     with_crate_prefix(|| self.tcx.def_path_str(*did)),
 929                     additional_newline
 930                 )
 931             });
 932
 933             err.span_suggestions(span, &msg, path_strings, Applicability::MaybeIncorrect);
 934         } else {
 935             let limit = if candidates.len() == 5 { 5 } else { 4 };
 936             for (i, trait_did) in candidates.iter().take(limit).enumerate() {
 937                 if candidates.len() > 1 {
 938                     msg.push_str(&format!(
 939                         "\ncandidate #{}: `use {};`",
 940                         i + 1,
 941                         with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
 942                     ));
 943                 } else {
 944                     msg.push_str(&format!(
 945                         "\n`use {};`",
 946                         with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
 947                     ));
 948                 }
 949             }
 950             if candidates.len() > limit {
 951                 msg.push_str(&format!("\nand {} others", candidates.len() - limit));
 952             }
 953             err.note(&msg[..]);
 954         }
 955     }
 956
 957     fn suggest_valid_traits(
 958         &self,
 959         err: &mut DiagnosticBuilder<'_>,
 960         valid_out_of_scope_traits: Vec<DefId>,
 961     ) -> bool {
 962         if !valid_out_of_scope_traits.is_empty() {
 963             let mut candidates = valid_out_of_scope_traits;
 964             candidates.sort();
 965             candidates.dedup();
 966             err.help("items from traits can only be used if the trait is in scope");
 967             let msg = format!(
 968                 "the following {traits_are} implemented but not in scope; \
 969                  perhaps add a `use` for {one_of_them}:",
 970                 traits_are = if candidates.len() == 1 { "trait is" } else { "traits are" },
 971                 one_of_them = if candidates.len() == 1 { "it" } else { "one of them" },
 972             );
 973
 974             self.suggest_use_candidates(err, msg, candidates);
 975             true
 976         } else {
 977             false
 978         }
 979     }
 980
 981     fn suggest_traits_to_import(
 982         &self,
 983         err: &mut DiagnosticBuilder<'_>,
 984         span: Span,
 985         rcvr_ty: Ty<'tcx>,
 986         item_name: Ident,
 987         source: SelfSource<'tcx>,
 988         valid_out_of_scope_traits: Vec<DefId>,
 989         unsatisfied_predicates: &[(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>)],
 990         unsatisfied_bounds: bool,
 991     ) {
 992         let mut alt_rcvr_sugg = false;
 993         if let (SelfSource::MethodCall(rcvr), false) = (source, unsatisfied_bounds) {
 994             debug!(?span, ?item_name, ?rcvr_ty, ?rcvr);
 995             let skippable = [
 996                 self.tcx.lang_items().clone_trait(),
 997                 self.tcx.lang_items().deref_trait(),
 998                 self.tcx.lang_items().deref_mut_trait(),
 999                 self.tcx.lang_items().drop_trait(),
1000             ];
1001             // Try alternative arbitrary self types that could fulfill this call.
1002             // FIXME: probe for all types that *could* be arbitrary self-types, not
1003             // just this list.
1004             for (rcvr_ty, post) in &[
1005                 (rcvr_ty, ""),
1006                 (self.tcx.mk_mut_ref(&ty::ReErased, rcvr_ty), "&mut "),
1007                 (self.tcx.mk_imm_ref(&ty::ReErased, rcvr_ty), "&"),
1008             ] {
1009                 if let Ok(pick) = self.lookup_probe(
1010                     span,
1011                     item_name,
1012                     rcvr_ty,
1013                     rcvr,
1014                     crate::check::method::probe::ProbeScope::AllTraits,
1015                 ) {
1016                     // If the method is defined for the receiver we have, it likely wasn't `use`d.
1017                     // We point at the method, but we just skip the rest of the check for arbitrary
1018                     // self types and rely on the suggestion to `use` the trait from
1019                     // `suggest_valid_traits`.
1020                     let did = Some(pick.item.container.id());
1021                     let skip = skippable.contains(&did);
1022                     if pick.autoderefs == 0 && !skip {
1023                         err.span_label(
1024                             pick.item.ident.span,
1025                             &format!("the method is available for `{}` here", rcvr_ty),
1026                         );
1027                     }
1028                     break;
1029                 }
1030                 for (rcvr_ty, pre) in &[
1031                     (self.tcx.mk_lang_item(rcvr_ty, LangItem::OwnedBox), "Box::new"),
1032                     (self.tcx.mk_lang_item(rcvr_ty, LangItem::Pin), "Pin::new"),
1033                     (self.tcx.mk_diagnostic_item(rcvr_ty, sym::Arc), "Arc::new"),
1034                     (self.tcx.mk_diagnostic_item(rcvr_ty, sym::Rc), "Rc::new"),
1035                 ] {
1036                     if let Some(new_rcvr_t) = *rcvr_ty {
1037                         if let Ok(pick) = self.lookup_probe(
1038                             span,
1039                             item_name,
1040                             new_rcvr_t,
1041                             rcvr,
1042                             crate::check::method::probe::ProbeScope::AllTraits,
1043                         ) {
1044                             debug!("try_alt_rcvr: pick candidate {:?}", pick);
1045                             let did = Some(pick.item.container.id());
1046                             // We don't want to suggest a container type when the missing
1047                             // method is `.clone()` or `.deref()` otherwise we'd suggest
1048                             // `Arc::new(foo).clone()`, which is far from what the user wants.
1049                             let skip = skippable.contains(&did);
1050                             // Make sure the method is defined for the *actual* receiver: we don't
1051                             // want to treat `Box<Self>` as a receiver if it only works because of
1052                             // an autoderef to `&self`
1053                             if pick.autoderefs == 0 && !skip {
1054                                 err.span_label(
1055                                     pick.item.ident.span,
1056                                     &format!("the method is available for `{}` here", new_rcvr_t),
1057                                 );
1058                                 err.multipart_suggestion(
1059                                     "consider wrapping the receiver expression with the \
1060                                         appropriate type",
1061                                     vec![
1062                                         (rcvr.span.shrink_to_lo(), format!("{}({}", pre, post)),
1063                                         (rcvr.span.shrink_to_hi(), ")".to_string()),
1064                                     ],
1065                                     Applicability::MaybeIncorrect,
1066                                 );
1067                                 // We don't care about the other suggestions.
1068                                 alt_rcvr_sugg = true;
1069                             }
1070                         }
1071                     }
1072                 }
1073             }
1074         }
1075         if self.suggest_valid_traits(err, valid_out_of_scope_traits) {
1076             return;
1077         }
1078
1079         let type_is_local = self.type_derefs_to_local(span, rcvr_ty, source);
1080
1081         let mut arbitrary_rcvr = vec![];
1082         // There are no traits implemented, so lets suggest some traits to
1083         // implement, by finding ones that have the item name, and are
1084         // legal to implement.
1085         let mut candidates = all_traits(self.tcx)
1086             .into_iter()
1087             // Don't issue suggestions for unstable traits since they're
1088             // unlikely to be implementable anyway
1089             .filter(|info| match self.tcx.lookup_stability(info.def_id) {
1090                 Some(attr) => attr.level.is_stable(),
1091                 None => true,
1092             })
1093             .filter(|info| {
1094                 // We approximate the coherence rules to only suggest
1095                 // traits that are legal to implement by requiring that
1096                 // either the type or trait is local. Multi-dispatch means
1097                 // this isn't perfect (that is, there are cases when
1098                 // implementing a trait would be legal but is rejected
1099                 // here).
1100                 unsatisfied_predicates.iter().all(|(p, _)| {
1101                     match p.kind().skip_binder() {
1102                         // Hide traits if they are present in predicates as they can be fixed without
1103                         // having to implement them.
1104                         ty::PredicateKind::Trait(t, _) => t.def_id() == info.def_id,
1105                         ty::PredicateKind::Projection(p) => {
1106                             p.projection_ty.item_def_id == info.def_id
1107                         }
1108                         _ => false,
1109                     }
1110                 }) && (type_is_local || info.def_id.is_local())
1111                     && self
1112                         .associated_item(info.def_id, item_name, Namespace::ValueNS)
1113                         .filter(|item| {
1114                             if let ty::AssocKind::Fn = item.kind {
1115                                 let id = item
1116                                     .def_id
1117                                     .as_local()
1118                                     .map(|def_id| self.tcx.hir().local_def_id_to_hir_id(def_id));
1119                                 if let Some(hir::Node::TraitItem(hir::TraitItem {
1120                                     kind: hir::TraitItemKind::Fn(fn_sig, method),
1121                                     ..
1122                                 })) = id.map(|id| self.tcx.hir().get(id))
1123                                 {
1124                                     let self_first_arg = match method {
1125                                         hir::TraitFn::Required([ident, ..]) => {
1126                                             ident.name == kw::SelfLower
1127                                         }
1128                                         hir::TraitFn::Provided(body_id) => {
1129                                             self.tcx.hir().body(*body_id).params.first().map_or(
1130                                                 false,
1131                                                 |param| {
1132                                                     matches!(
1133                                                         param.pat.kind,
1134                                                         hir::PatKind::Binding(_, _, ident, _)
1135                                                             if ident.name == kw::SelfLower
1136                                                     )
1137                                                 },
1138                                             )
1139                                         }
1140                                         _ => false,
1141                                     };
1142
1143                                     if !fn_sig.decl.implicit_self.has_implicit_self()
1144                                         && self_first_arg
1145                                     {
1146                                         if let Some(ty) = fn_sig.decl.inputs.get(0) {
1147                                             arbitrary_rcvr.push(ty.span);
1148                                         }
1149                                         return false;
1150                                     }
1151                                 }
1152                             }
1153                             // We only want to suggest public or local traits (#45781).
1154                             item.vis == ty::Visibility::Public || info.def_id.is_local()
1155                         })
1156                         .is_some()
1157             })
1158             .collect::<Vec<_>>();
1159         for span in &arbitrary_rcvr {
1160             err.span_label(
1161                 *span,
1162                 "the method might not be found because of this arbitrary self type",
1163             );
1164         }
1165         if alt_rcvr_sugg {
1166             return;
1167         }
1168
1169         if !candidates.is_empty() {
1170             // Sort from most relevant to least relevant.
1171             candidates.sort_by(|a, b| a.cmp(b).reverse());
1172             candidates.dedup();
1173
1174             let param_type = match rcvr_ty.kind() {
1175                 ty::Param(param) => Some(param),
1176                 ty::Ref(_, ty, _) => match ty.kind() {
1177                     ty::Param(param) => Some(param),
1178                     _ => None,
1179                 },
1180                 _ => None,
1181             };
1182             err.help(if param_type.is_some() {
1183                 "items from traits can only be used if the type parameter is bounded by the trait"
1184             } else {
1185                 "items from traits can only be used if the trait is implemented and in scope"
1186             });
1187             let candidates_len = candidates.len();
1188             let message = |action| {
1189                 format!(
1190                     "the following {traits_define} an item `{name}`, perhaps you need to {action} \
1191                      {one_of_them}:",
1192                     traits_define =
1193                         if candidates_len == 1 { "trait defines" } else { "traits define" },
1194                     action = action,
1195                     one_of_them = if candidates_len == 1 { "it" } else { "one of them" },
1196                     name = item_name,
1197                 )
1198             };
1199             // Obtain the span for `param` and use it for a structured suggestion.
1200             if let (Some(ref param), Some(ref table)) =
1201                 (param_type, self.in_progress_typeck_results)
1202             {
1203                 let table_owner = table.borrow().hir_owner;
1204                 let generics = self.tcx.generics_of(table_owner.to_def_id());
1205                 let type_param = generics.type_param(param, self.tcx);
1206                 let hir = &self.tcx.hir();
1207                 if let Some(def_id) = type_param.def_id.as_local() {
1208                     let id = hir.local_def_id_to_hir_id(def_id);
1209                     // Get the `hir::Param` to verify whether it already has any bounds.
1210                     // We do this to avoid suggesting code that ends up as `T: FooBar`,
1211                     // instead we suggest `T: Foo + Bar` in that case.
1212                     match hir.get(id) {
1213                         Node::GenericParam(ref param) => {
1214                             let mut impl_trait = false;
1215                             let has_bounds =
1216                                 if let hir::GenericParamKind::Type { synthetic: Some(_), .. } =
1217                                     &param.kind
1218                                 {
1219                                     // We've found `fn foo(x: impl Trait)` instead of
1220                                     // `fn foo<T>(x: T)`. We want to suggest the correct
1221                                     // `fn foo(x: impl Trait + TraitBound)` instead of
1222                                     // `fn foo<T: TraitBound>(x: T)`. (#63706)
1223                                     impl_trait = true;
1224                                     param.bounds.get(1)
1225                                 } else {
1226                                     param.bounds.get(0)
1227                                 };
1228                             let sp = hir.span(id);
1229                             let sp = if let Some(first_bound) = has_bounds {
1230                                 // `sp` only covers `T`, change it so that it covers
1231                                 // `T:` when appropriate
1232                                 sp.until(first_bound.span())
1233                             } else {
1234                                 sp
1235                             };
1236                             let trait_def_ids: FxHashSet<DefId> = param
1237                                 .bounds
1238                                 .iter()
1239                                 .filter_map(|bound| bound.trait_ref()?.trait_def_id())
1240                                 .collect();
1241                             if !candidates.iter().any(|t| trait_def_ids.contains(&t.def_id)) {
1242                                 err.span_suggestions(
1243                                     sp,
1244                                     &message(format!(
1245                                         "restrict type parameter `{}` with",
1246                                         param.name.ident(),
1247                                     )),
1248                                     candidates.iter().map(|t| {
1249                                         format!(
1250                                             "{}{} {}{}",
1251                                             param.name.ident(),
1252                                             if impl_trait { " +" } else { ":" },
1253                                             self.tcx.def_path_str(t.def_id),
1254                                             if has_bounds.is_some() { " + " } else { "" },
1255                                         )
1256                                     }),
1257                                     Applicability::MaybeIncorrect,
1258                                 );
1259                             }
1260                             return;
1261                         }
1262                         Node::Item(hir::Item {
1263                             kind: hir::ItemKind::Trait(.., bounds, _),
1264                             ident,
1265                             ..
1266                         }) => {
1267                             let (sp, sep, article) = if bounds.is_empty() {
1268                                 (ident.span.shrink_to_hi(), ":", "a")
1269                             } else {
1270                                 (bounds.last().unwrap().span().shrink_to_hi(), " +", "another")
1271                             };
1272                             err.span_suggestions(
1273                                 sp,
1274                                 &message(format!("add {} supertrait for", article)),
1275                                 candidates.iter().map(|t| {
1276                                     format!("{} {}", sep, self.tcx.def_path_str(t.def_id),)
1277                                 }),
1278                                 Applicability::MaybeIncorrect,
1279                             );
1280                             return;
1281                         }
1282                         _ => {}
1283                     }
1284                 }
1285             }
1286
1287             let (potential_candidates, explicitly_negative) = if param_type.is_some() {
1288                 // FIXME: Even though negative bounds are not implemented, we could maybe handle
1289                 // cases where a positive bound implies a negative impl.
1290                 (candidates, Vec::new())
1291             } else if let Some(simp_rcvr_ty) = simplify_type(self.tcx, rcvr_ty, true) {
1292                 let mut potential_candidates = Vec::new();
1293                 let mut explicitly_negative = Vec::new();
1294                 for candidate in candidates {
1295                     // Check if there's a negative impl of `candidate` for `rcvr_ty`
1296                     if self
1297                         .tcx
1298                         .all_impls(candidate.def_id)
1299                         .filter(|imp_did| {
1300                             self.tcx.impl_polarity(*imp_did) == ty::ImplPolarity::Negative
1301                         })
1302                         .any(|imp_did| {
1303                             let imp = self.tcx.impl_trait_ref(imp_did).unwrap();
1304                             let imp_simp = simplify_type(self.tcx, imp.self_ty(), true);
1305                             imp_simp.map_or(false, |s| s == simp_rcvr_ty)
1306                         })
1307                     {
1308                         explicitly_negative.push(candidate);
1309                     } else {
1310                         potential_candidates.push(candidate);
1311                     }
1312                 }
1313                 (potential_candidates, explicitly_negative)
1314             } else {
1315                 // We don't know enough about `recv_ty` to make proper suggestions.
1316                 (candidates, Vec::new())
1317             };
1318
1319             let action = if let Some(param) = param_type {
1320                 format!("restrict type parameter `{}` with", param)
1321             } else {
1322                 // FIXME: it might only need to be imported into scope, not implemented.
1323                 "implement".to_string()
1324             };
1325             match &potential_candidates[..] {
1326                 [] => {}
1327                 [trait_info] if trait_info.def_id.is_local() => {
1328                     let span = self.tcx.hir().span_if_local(trait_info.def_id).unwrap();
1329                     err.span_note(
1330                         self.tcx.sess.source_map().guess_head_span(span),
1331                         &format!(
1332                             "`{}` defines an item `{}`, perhaps you need to {} it",
1333                             self.tcx.def_path_str(trait_info.def_id),
1334                             item_name,
1335                             action
1336                         ),
1337                     );
1338                 }
1339                 trait_infos => {
1340                     let mut msg = message(action);
1341                     for (i, trait_info) in trait_infos.iter().enumerate() {
1342                         msg.push_str(&format!(
1343                             "\ncandidate #{}: `{}`",
1344                             i + 1,
1345                             self.tcx.def_path_str(trait_info.def_id),
1346                         ));
1347                     }
1348                     err.note(&msg);
1349                 }
1350             }
1351             match &explicitly_negative[..] {
1352                 [] => {}
1353                 [trait_info] => {
1354                     let msg = format!(
1355                         "the trait `{}` defines an item `{}`, but is explicitely unimplemented",
1356                         self.tcx.def_path_str(trait_info.def_id),
1357                         item_name
1358                     );
1359                     err.note(&msg);
1360                 }
1361                 trait_infos => {
1362                     let mut msg = format!(
1363                         "the following traits define an item `{}`, but are explicitely unimplemented:",
1364                         item_name
1365                     );
1366                     for trait_info in trait_infos {
1367                         msg.push_str(&format!("\n{}", self.tcx.def_path_str(trait_info.def_id)));
1368                     }
1369                     err.note(&msg);
1370                 }
1371             }
1372         }
1373     }
1374
1375     /// Checks whether there is a local type somewhere in the chain of
1376     /// autoderefs of `rcvr_ty`.
1377     fn type_derefs_to_local(
1378         &self,
1379         span: Span,
1380         rcvr_ty: Ty<'tcx>,
1381         source: SelfSource<'tcx>,
1382     ) -> bool {
1383         fn is_local(ty: Ty<'_>) -> bool {
1384             match ty.kind() {
1385                 ty::Adt(def, _) => def.did.is_local(),
1386                 ty::Foreign(did) => did.is_local(),
1387                 ty::Dynamic(ref tr, ..) => tr.principal().map_or(false, |d| d.def_id().is_local()),
1388                 ty::Param(_) => true,
1389
1390                 // Everything else (primitive types, etc.) is effectively
1391                 // non-local (there are "edge" cases, e.g., `(LocalType,)`, but
1392                 // the noise from these sort of types is usually just really
1393                 // annoying, rather than any sort of help).
1394                 _ => false,
1395             }
1396         }
1397
1398         // This occurs for UFCS desugaring of `T::method`, where there is no
1399         // receiver expression for the method call, and thus no autoderef.
1400         if let SelfSource::QPath(_) = source {
1401             return is_local(self.resolve_vars_with_obligations(rcvr_ty));
1402         }
1403
1404         self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))
1405     }
1406 }
1407
1408 #[derive(Copy, Clone, Debug)]
1409 pub enum SelfSource<'a> {
1410     QPath(&'a hir::Ty<'a>),
1411     MethodCall(&'a hir::Expr<'a> /* rcvr */),
1412 }
1413
1414 #[derive(Copy, Clone)]
1415 pub struct TraitInfo {
1416     pub def_id: DefId,
1417 }
1418
1419 impl PartialEq for TraitInfo {
1420     fn eq(&self, other: &TraitInfo) -> bool {
1421         self.cmp(other) == Ordering::Equal
1422     }
1423 }
1424 impl Eq for TraitInfo {}
1425 impl PartialOrd for TraitInfo {
1426     fn partial_cmp(&self, other: &TraitInfo) -> Option<Ordering> {
1427         Some(self.cmp(other))
1428     }
1429 }
1430 impl Ord for TraitInfo {
1431     fn cmp(&self, other: &TraitInfo) -> Ordering {
1432         // Local crates are more important than remote ones (local:
1433         // `cnum == 0`), and otherwise we throw in the defid for totality.
1434
1435         let lhs = (other.def_id.krate, other.def_id);
1436         let rhs = (self.def_id.krate, self.def_id);
1437         lhs.cmp(&rhs)
1438     }
1439 }
1440
1441 /// Retrieves all traits in this crate and any dependent crates.
1442 pub fn all_traits(tcx: TyCtxt<'_>) -> Vec<TraitInfo> {
1443     tcx.all_traits(()).iter().map(|&def_id| TraitInfo { def_id }).collect()
1444 }
1445
1446 /// Computes all traits in this crate and any dependent crates.
1447 fn compute_all_traits(tcx: TyCtxt<'_>, (): ()) -> &[DefId] {
1448     use hir::itemlikevisit;
1449
1450     let mut traits = vec![];
1451
1452     // Crate-local:
1453
1454     struct Visitor<'a> {
1455         traits: &'a mut Vec<DefId>,
1456     }
1457
1458     impl<'v, 'a> itemlikevisit::ItemLikeVisitor<'v> for Visitor<'a> {
1459         fn visit_item(&mut self, i: &'v hir::Item<'v>) {
1460             match i.kind {
1461                 hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..) => {
1462                     self.traits.push(i.def_id.to_def_id());
1463                 }
1464                 _ => (),
1465             }
1466         }
1467
1468         fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
1469
1470         fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {}
1471
1472         fn visit_foreign_item(&mut self, _foreign_item: &hir::ForeignItem<'_>) {}
1473     }
1474
1475     tcx.hir().krate().visit_all_item_likes(&mut Visitor { traits: &mut traits });
1476
1477     // Cross-crate:
1478
1479     let mut external_mods = FxHashSet::default();
1480     fn handle_external_res(
1481         tcx: TyCtxt<'_>,
1482         traits: &mut Vec<DefId>,
1483         external_mods: &mut FxHashSet<DefId>,
1484         res: Res,
1485     ) {
1486         match res {
1487             Res::Def(DefKind::Trait | DefKind::TraitAlias, def_id) => {
1488                 traits.push(def_id);
1489             }
1490             Res::Def(DefKind::Mod, def_id) => {
1491                 if !external_mods.insert(def_id) {
1492                     return;
1493                 }
1494                 for child in tcx.item_children(def_id).iter() {
1495                     handle_external_res(tcx, traits, external_mods, child.res)
1496                 }
1497             }
1498             _ => {}
1499         }
1500     }
1501     for &cnum in tcx.crates().iter() {
1502         let def_id = DefId { krate: cnum, index: CRATE_DEF_INDEX };
1503         handle_external_res(tcx, &mut traits, &mut external_mods, Res::Def(DefKind::Mod, def_id));
1504     }
1505
1506     tcx.arena.alloc_from_iter(traits)
1507 }
1508
1509 pub fn provide(providers: &mut ty::query::Providers) {
1510     providers.all_traits = compute_all_traits;
1511 }
1512
1513 struct UsePlacementFinder<'tcx> {
1514     target_module: hir::HirId,
1515     span: Option<Span>,
1516     found_use: bool,
1517     tcx: TyCtxt<'tcx>,
1518 }
1519
1520 impl UsePlacementFinder<'tcx> {
1521     fn check(
1522         tcx: TyCtxt<'tcx>,
1523         krate: &'tcx hir::Crate<'tcx>,
1524         target_module: hir::HirId,
1525     ) -> (Option<Span>, bool) {
1526         let mut finder = UsePlacementFinder { target_module, span: None, found_use: false, tcx };
1527         intravisit::walk_crate(&mut finder, krate);
1528         (finder.span, finder.found_use)
1529     }
1530 }
1531
1532 impl intravisit::Visitor<'tcx> for UsePlacementFinder<'tcx> {
1533     fn visit_mod(&mut self, module: &'tcx hir::Mod<'tcx>, _: Span, hir_id: hir::HirId) {
1534         if self.span.is_some() {
1535             return;
1536         }
1537         if hir_id != self.target_module {
1538             intravisit::walk_mod(self, module, hir_id);
1539             return;
1540         }
1541         // Find a `use` statement.
1542         for &item_id in module.item_ids {
1543             let item = self.tcx.hir().item(item_id);
1544             match item.kind {
1545                 hir::ItemKind::Use(..) => {
1546                     // Don't suggest placing a `use` before the prelude
1547                     // import or other generated ones.
1548                     if !item.span.from_expansion() {
1549                         self.span = Some(item.span.shrink_to_lo());
1550                         self.found_use = true;
1551                         return;
1552                     }
1553                 }
1554                 // Don't place `use` before `extern crate`...
1555                 hir::ItemKind::ExternCrate(_) => {}
1556                 // ...but do place them before the first other item.
1557                 _ => {
1558                     if self.span.map_or(true, |span| item.span < span) {
1559                         if !item.span.from_expansion() {
1560                             // Don't insert between attributes and an item.
1561                             let attrs = self.tcx.hir().attrs(item.hir_id());
1562                             if attrs.is_empty() {
1563                                 self.span = Some(item.span.shrink_to_lo());
1564                             } else {
1565                                 // Find the first attribute on the item.
1566                                 for attr in attrs {
1567                                     if self.span.map_or(true, |span| attr.span < span) {
1568                                         self.span = Some(attr.span.shrink_to_lo());
1569                                     }
1570                                 }
1571                             }
1572                         }
1573                     }
1574                 }
1575             }
1576         }
1577     }
1578
1579     type Map = intravisit::ErasedMap<'tcx>;
1580
1581     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1582         intravisit::NestedVisitorMap::None
1583     }
1584 }
1585
1586 fn print_disambiguation_help(
1587     item_name: Ident,
1588     args: Option<&'tcx [hir::Expr<'tcx>]>,
1589     err: &mut DiagnosticBuilder<'_>,
1590     trait_name: String,
1591     rcvr_ty: Ty<'_>,
1592     kind: ty::AssocKind,
1593     def_id: DefId,
1594     span: Span,
1595     candidate: Option<usize>,
1596     source_map: &source_map::SourceMap,
1597 ) {
1598     let mut applicability = Applicability::MachineApplicable;
1599     let sugg_args = if let (ty::AssocKind::Fn, Some(args)) = (kind, args) {
1600         format!(
1601             "({}{})",
1602             if rcvr_ty.is_region_ptr() {
1603                 if rcvr_ty.is_mutable_ptr() { "&mut " } else { "&" }
1604             } else {
1605                 ""
1606             },
1607             args.iter()
1608                 .map(|arg| source_map.span_to_snippet(arg.span).unwrap_or_else(|_| {
1609                     applicability = Applicability::HasPlaceholders;
1610                     "_".to_owned()
1611                 }))
1612                 .collect::<Vec<_>>()
1613                 .join(", "),
1614         )
1615     } else {
1616         String::new()
1617     };
1618     let sugg = format!("{}::{}{}", trait_name, item_name, sugg_args);
1619     err.span_suggestion(
1620         span,
1621         &format!(
1622             "disambiguate the {} for {}",
1623             kind.as_def_kind().descr(def_id),
1624             if let Some(candidate) = candidate {
1625                 format!("candidate #{}", candidate)
1626             } else {
1627                 "the candidate".to_string()
1628             },
1629         ),
1630         sugg,
1631         applicability,
1632     );
1633 }