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