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 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<'b>(
  72         &self,
  73         span: Span,
  74         rcvr_ty: Ty<'tcx>,
  75         item_name: Ident,
  76         source: SelfSource<'b>,
  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 \
 327                                               this numeric value, 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                 if !unsatisfied_predicates.is_empty() {
 583                     let def_span = |def_id| {
 584                         self.tcx.sess.source_map().guess_head_span(self.tcx.def_span(def_id))
 585                     };
 586                     let mut type_params = FxHashMap::default();
 587                     let mut bound_spans = vec![];
 588
 589                     let mut collect_type_param_suggestions =
 590                         |self_ty: Ty<'tcx>, parent_pred: &ty::Predicate<'tcx>, obligation: &str| {
 591                             // We don't care about regions here, so it's fine to skip the binder here.
 592                             if let (ty::Param(_), ty::PredicateKind::Trait(p, _)) =
 593                                 (self_ty.kind(), parent_pred.kind().skip_binder())
 594                             {
 595                                 if let ty::Adt(def, _) = p.trait_ref.self_ty().kind() {
 596                                     let node = def.did.as_local().map(|def_id| {
 597                                         self.tcx
 598                                             .hir()
 599                                             .get(self.tcx.hir().local_def_id_to_hir_id(def_id))
 600                                     });
 601                                     if let Some(hir::Node::Item(hir::Item { kind, .. })) = node {
 602                                         if let Some(g) = kind.generics() {
 603                                             let key = match g.where_clause.predicates {
 604                                                 [.., pred] => (pred.span().shrink_to_hi(), false),
 605                                                 [] => (
 606                                                     g.where_clause
 607                                                         .span_for_predicates_or_empty_place(),
 608                                                     true,
 609                                                 ),
 610                                             };
 611                                             type_params
 612                                                 .entry(key)
 613                                                 .or_insert_with(FxHashSet::default)
 614                                                 .insert(obligation.to_owned());
 615                                         }
 616                                     }
 617                                 }
 618                             }
 619                         };
 620                     let mut bound_span_label = |self_ty: Ty<'_>, obligation: &str, quiet: &str| {
 621                         let msg = format!(
 622                             "doesn't satisfy `{}`",
 623                             if obligation.len() > 50 { quiet } else { obligation }
 624                         );
 625                         match &self_ty.kind() {
 626                             // Point at the type that couldn't satisfy the bound.
 627                             ty::Adt(def, _) => bound_spans.push((def_span(def.did), msg)),
 628                             // Point at the trait object that couldn't satisfy the bound.
 629                             ty::Dynamic(preds, _) => {
 630                                 for pred in preds.iter() {
 631                                     match pred.skip_binder() {
 632                                         ty::ExistentialPredicate::Trait(tr) => {
 633                                             bound_spans.push((def_span(tr.def_id), msg.clone()))
 634                                         }
 635                                         ty::ExistentialPredicate::Projection(_)
 636                                         | ty::ExistentialPredicate::AutoTrait(_) => {}
 637                                     }
 638                                 }
 639                             }
 640                             // Point at the closure that couldn't satisfy the bound.
 641                             ty::Closure(def_id, _) => bound_spans
 642                                 .push((def_span(*def_id), format!("doesn't satisfy `{}`", quiet))),
 643                             _ => {}
 644                         }
 645                     };
 646                     let mut format_pred = |pred: ty::Predicate<'tcx>| {
 647                         let bound_predicate = pred.kind();
 648                         match bound_predicate.skip_binder() {
 649                             ty::PredicateKind::Projection(pred) => {
 650                                 let pred = bound_predicate.rebind(pred);
 651                                 // `<Foo as Iterator>::Item = String`.
 652                                 let projection_ty = pred.skip_binder().projection_ty;
 653
 654                                 let substs_with_infer_self = tcx.mk_substs(
 655                                     iter::once(tcx.mk_ty_var(ty::TyVid { index: 0 }).into())
 656                                         .chain(projection_ty.substs.iter().skip(1)),
 657                                 );
 658
 659                                 let quiet_projection_ty = ty::ProjectionTy {
 660                                     substs: substs_with_infer_self,
 661                                     item_def_id: projection_ty.item_def_id,
 662                                 };
 663
 664                                 let ty = pred.skip_binder().ty;
 665
 666                                 let obligation = format!("{} = {}", projection_ty, ty);
 667                                 let quiet = format!("{} = {}", quiet_projection_ty, ty);
 668
 669                                 bound_span_label(projection_ty.self_ty(), &obligation, &quiet);
 670                                 Some((obligation, projection_ty.self_ty()))
 671                             }
 672                             ty::PredicateKind::Trait(poly_trait_ref, _) => {
 673                                 let p = poly_trait_ref.trait_ref;
 674                                 let self_ty = p.self_ty();
 675                                 let path = p.print_only_trait_path();
 676                                 let obligation = format!("{}: {}", self_ty, path);
 677                                 let quiet = format!("_: {}", path);
 678                                 bound_span_label(self_ty, &obligation, &quiet);
 679                                 Some((obligation, self_ty))
 680                             }
 681                             _ => None,
 682                         }
 683                     };
 684                     let mut bound_list = unsatisfied_predicates
 685                         .iter()
 686                         .filter_map(|(pred, parent_pred)| {
 687                             format_pred(*pred).map(|(p, self_ty)| match parent_pred {
 688                                 None => format!("`{}`", &p),
 689                                 Some(parent_pred) => match format_pred(*parent_pred) {
 690                                     None => format!("`{}`", &p),
 691                                     Some((parent_p, _)) => {
 692                                         collect_type_param_suggestions(self_ty, parent_pred, &p);
 693                                         format!("`{}`\nwhich is required by `{}`", p, parent_p)
 694                                     }
 695                                 },
 696                             })
 697                         })
 698                         .enumerate()
 699                         .collect::<Vec<(usize, String)>>();
 700                     for ((span, empty_where), obligations) in type_params.into_iter() {
 701                         restrict_type_params = true;
 702                         // #74886: Sort here so that the output is always the same.
 703                         let mut obligations = obligations.into_iter().collect::<Vec<_>>();
 704                         obligations.sort();
 705                         err.span_suggestion_verbose(
 706                             span,
 707                             &format!(
 708                                 "consider restricting the type parameter{s} to satisfy the \
 709                                  trait bound{s}",
 710                                 s = pluralize!(obligations.len())
 711                             ),
 712                             format!(
 713                                 "{} {}",
 714                                 if empty_where { " where" } else { "," },
 715                                 obligations.join(", ")
 716                             ),
 717                             Applicability::MaybeIncorrect,
 718                         );
 719                     }
 720
 721                     bound_list.sort_by(|(_, a), (_, b)| a.cmp(&b)); // Sort alphabetically.
 722                     bound_list.dedup_by(|(_, a), (_, b)| a == b); // #35677
 723                     bound_list.sort_by_key(|(pos, _)| *pos); // Keep the original predicate order.
 724                     bound_spans.sort();
 725                     bound_spans.dedup();
 726                     for (span, msg) in bound_spans.into_iter() {
 727                         err.span_label(span, &msg);
 728                     }
 729                     if !bound_list.is_empty() {
 730                         let bound_list = bound_list
 731                             .into_iter()
 732                             .map(|(_, path)| path)
 733                             .collect::<Vec<_>>()
 734                             .join("\n");
 735                         let actual_prefix = actual.prefix_string(self.tcx);
 736                         err.set_primary_message(&format!(
 737                             "the {item_kind} `{item_name}` exists for {actual_prefix} `{ty_str}`, but its trait bounds were not satisfied"
 738                         ));
 739                         err.note(&format!(
 740                             "the following trait bounds were not satisfied:\n{bound_list}"
 741                         ));
 742                     }
 743                 }
 744
 745                 if actual.is_numeric() && actual.is_fresh() || restrict_type_params {
 746                 } else {
 747                     self.suggest_traits_to_import(
 748                         &mut err,
 749                         span,
 750                         rcvr_ty,
 751                         item_name,
 752                         source,
 753                         out_of_scope_traits,
 754                         &unsatisfied_predicates,
 755                     );
 756                 }
 757
 758                 // Don't emit a suggestion if we found an actual method
 759                 // that had unsatisfied trait bounds
 760                 if unsatisfied_predicates.is_empty() && actual.is_enum() {
 761                     let adt_def = actual.ty_adt_def().expect("enum is not an ADT");
 762                     if let Some(suggestion) = lev_distance::find_best_match_for_name(
 763                         &adt_def.variants.iter().map(|s| s.ident.name).collect::<Vec<_>>(),
 764                         item_name.name,
 765                         None,
 766                     ) {
 767                         err.span_suggestion(
 768                             span,
 769                             "there is a variant with a similar name",
 770                             suggestion.to_string(),
 771                             Applicability::MaybeIncorrect,
 772                         );
 773                     }
 774                 }
 775
 776                 let mut fallback_span = true;
 777                 let msg = "remove this method call";
 778                 if item_name.name == sym::as_str && actual.peel_refs().is_str() {
 779                     if let SelfSource::MethodCall(expr) = source {
 780                         let call_expr =
 781                             self.tcx.hir().expect_expr(self.tcx.hir().get_parent_node(expr.hir_id));
 782                         if let Some(span) = call_expr.span.trim_start(expr.span) {
 783                             err.span_suggestion(
 784                                 span,
 785                                 msg,
 786                                 String::new(),
 787                                 Applicability::MachineApplicable,
 788                             );
 789                             fallback_span = false;
 790                         }
 791                     }
 792                     if fallback_span {
 793                         err.span_label(span, msg);
 794                     }
 795                 } else if let Some(lev_candidate) = lev_candidate {
 796                     // Don't emit a suggestion if we found an actual method
 797                     // that had unsatisfied trait bounds
 798                     if unsatisfied_predicates.is_empty() {
 799                         let def_kind = lev_candidate.kind.as_def_kind();
 800                         err.span_suggestion(
 801                             span,
 802                             &format!(
 803                                 "there is {} {} with a similar name",
 804                                 def_kind.article(),
 805                                 def_kind.descr(lev_candidate.def_id),
 806                             ),
 807                             lev_candidate.ident.to_string(),
 808                             Applicability::MaybeIncorrect,
 809                         );
 810                     }
 811                 }
 812
 813                 return Some(err);
 814             }
 815
 816             MethodError::Ambiguity(sources) => {
 817                 let mut err = struct_span_err!(
 818                     self.sess(),
 819                     item_name.span,
 820                     E0034,
 821                     "multiple applicable items in scope"
 822                 );
 823                 err.span_label(item_name.span, format!("multiple `{}` found", item_name));
 824
 825                 report_candidates(span, &mut err, sources, sugg_span);
 826                 err.emit();
 827             }
 828
 829             MethodError::PrivateMatch(kind, def_id, out_of_scope_traits) => {
 830                 let kind = kind.descr(def_id);
 831                 let mut err = struct_span_err!(
 832                     self.tcx.sess,
 833                     item_name.span,
 834                     E0624,
 835                     "{} `{}` is private",
 836                     kind,
 837                     item_name
 838                 );
 839                 err.span_label(item_name.span, &format!("private {}", kind));
 840                 self.suggest_valid_traits(&mut err, out_of_scope_traits);
 841                 err.emit();
 842             }
 843
 844             MethodError::IllegalSizedBound(candidates, needs_mut, bound_span) => {
 845                 let msg = format!("the `{}` method cannot be invoked on a trait object", item_name);
 846                 let mut err = self.sess().struct_span_err(span, &msg);
 847                 err.span_label(bound_span, "this has a `Sized` requirement");
 848                 if !candidates.is_empty() {
 849                     let help = format!(
 850                         "{an}other candidate{s} {were} found in the following trait{s}, perhaps \
 851                          add a `use` for {one_of_them}:",
 852                         an = if candidates.len() == 1 { "an" } else { "" },
 853                         s = pluralize!(candidates.len()),
 854                         were = if candidates.len() == 1 { "was" } else { "were" },
 855                         one_of_them = if candidates.len() == 1 { "it" } else { "one_of_them" },
 856                     );
 857                     self.suggest_use_candidates(&mut err, help, candidates);
 858                 }
 859                 if let ty::Ref(region, t_type, mutability) = rcvr_ty.kind() {
 860                     if needs_mut {
 861                         let trait_type = self.tcx.mk_ref(
 862                             region,
 863                             ty::TypeAndMut { ty: t_type, mutbl: mutability.invert() },
 864                         );
 865                         err.note(&format!("you need `{}` instead of `{}`", trait_type, rcvr_ty));
 866                     }
 867                 }
 868                 err.emit();
 869             }
 870
 871             MethodError::BadReturnType => bug!("no return type expectations but got BadReturnType"),
 872         }
 873         None
 874     }
 875
 876     /// Print out the type for use in value namespace.
 877     fn ty_to_value_string(&self, ty: Ty<'tcx>) -> String {
 878         match ty.kind() {
 879             ty::Adt(def, substs) => format!("{}", ty::Instance::new(def.did, substs)),
 880             _ => self.ty_to_string(ty),
 881         }
 882     }
 883
 884     fn suggest_await_before_method(
 885         &self,
 886         err: &mut DiagnosticBuilder<'_>,
 887         item_name: Ident,
 888         ty: Ty<'tcx>,
 889         call: &hir::Expr<'_>,
 890         span: Span,
 891     ) {
 892         let output_ty = match self.infcx.get_impl_future_output_ty(ty) {
 893             Some(output_ty) => self.resolve_vars_if_possible(output_ty),
 894             _ => return,
 895         };
 896         let method_exists = self.method_exists(item_name, output_ty, call.hir_id, true);
 897         debug!("suggest_await_before_method: is_method_exist={}", method_exists);
 898         if method_exists {
 899             err.span_suggestion_verbose(
 900                 span.shrink_to_lo(),
 901                 "consider `await`ing on the `Future` and calling the method on its `Output`",
 902                 "await.".to_string(),
 903                 Applicability::MaybeIncorrect,
 904             );
 905         }
 906     }
 907
 908     fn suggest_use_candidates(
 909         &self,
 910         err: &mut DiagnosticBuilder<'_>,
 911         mut msg: String,
 912         candidates: Vec<DefId>,
 913     ) {
 914         let module_did = self.tcx.parent_module(self.body_id);
 915         let module_id = self.tcx.hir().local_def_id_to_hir_id(module_did);
 916         let krate = self.tcx.hir().krate();
 917         let (span, found_use) = UsePlacementFinder::check(self.tcx, krate, module_id);
 918         if let Some(span) = span {
 919             let path_strings = candidates.iter().map(|did| {
 920                 // Produce an additional newline to separate the new use statement
 921                 // from the directly following item.
 922                 let additional_newline = if found_use { "" } else { "\n" };
 923                 format!(
 924                     "use {};\n{}",
 925                     with_crate_prefix(|| self.tcx.def_path_str(*did)),
 926                     additional_newline
 927                 )
 928             });
 929
 930             err.span_suggestions(span, &msg, path_strings, Applicability::MaybeIncorrect);
 931         } else {
 932             let limit = if candidates.len() == 5 { 5 } else { 4 };
 933             for (i, trait_did) in candidates.iter().take(limit).enumerate() {
 934                 if candidates.len() > 1 {
 935                     msg.push_str(&format!(
 936                         "\ncandidate #{}: `use {};`",
 937                         i + 1,
 938                         with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
 939                     ));
 940                 } else {
 941                     msg.push_str(&format!(
 942                         "\n`use {};`",
 943                         with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
 944                     ));
 945                 }
 946             }
 947             if candidates.len() > limit {
 948                 msg.push_str(&format!("\nand {} others", candidates.len() - limit));
 949             }
 950             err.note(&msg[..]);
 951         }
 952     }
 953
 954     fn suggest_valid_traits(
 955         &self,
 956         err: &mut DiagnosticBuilder<'_>,
 957         valid_out_of_scope_traits: Vec<DefId>,
 958     ) -> bool {
 959         if !valid_out_of_scope_traits.is_empty() {
 960             let mut candidates = valid_out_of_scope_traits;
 961             candidates.sort();
 962             candidates.dedup();
 963             err.help("items from traits can only be used if the trait is in scope");
 964             let msg = format!(
 965                 "the following {traits_are} implemented but not in scope; \
 966                  perhaps add a `use` for {one_of_them}:",
 967                 traits_are = if candidates.len() == 1 { "trait is" } else { "traits are" },
 968                 one_of_them = if candidates.len() == 1 { "it" } else { "one of them" },
 969             );
 970
 971             self.suggest_use_candidates(err, msg, candidates);
 972             true
 973         } else {
 974             false
 975         }
 976     }
 977
 978     fn suggest_traits_to_import<'b>(
 979         &self,
 980         err: &mut DiagnosticBuilder<'_>,
 981         span: Span,
 982         rcvr_ty: Ty<'tcx>,
 983         item_name: Ident,
 984         source: SelfSource<'b>,
 985         valid_out_of_scope_traits: Vec<DefId>,
 986         unsatisfied_predicates: &[(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>)],
 987     ) {
 988         if self.suggest_valid_traits(err, valid_out_of_scope_traits) {
 989             return;
 990         }
 991
 992         let type_is_local = self.type_derefs_to_local(span, rcvr_ty, source);
 993
 994         let mut arbitrary_rcvr = vec![];
 995         // There are no traits implemented, so lets suggest some traits to
 996         // implement, by finding ones that have the item name, and are
 997         // legal to implement.
 998         let mut candidates = all_traits(self.tcx)
 999             .into_iter()
1000             // Don't issue suggestions for unstable traits since they're
1001             // unlikely to be implementable anyway
1002             .filter(|info| match self.tcx.lookup_stability(info.def_id) {
1003                 Some(attr) => attr.level.is_stable(),
1004                 None => true,
1005             })
1006             .filter(|info| {
1007                 // We approximate the coherence rules to only suggest
1008                 // traits that are legal to implement by requiring that
1009                 // either the type or trait is local. Multi-dispatch means
1010                 // this isn't perfect (that is, there are cases when
1011                 // implementing a trait would be legal but is rejected
1012                 // here).
1013                 unsatisfied_predicates.iter().all(|(p, _)| {
1014                     match p.kind().skip_binder() {
1015                         // Hide traits if they are present in predicates as they can be fixed without
1016                         // having to implement them.
1017                         ty::PredicateKind::Trait(t, _) => t.def_id() == info.def_id,
1018                         ty::PredicateKind::Projection(p) => {
1019                             p.projection_ty.item_def_id == info.def_id
1020                         }
1021                         _ => false,
1022                     }
1023                 }) && (type_is_local || info.def_id.is_local())
1024                     && self
1025                         .associated_item(info.def_id, item_name, Namespace::ValueNS)
1026                         .filter(|item| {
1027                             if let ty::AssocKind::Fn = item.kind {
1028                                 let id = item
1029                                     .def_id
1030                                     .as_local()
1031                                     .map(|def_id| self.tcx.hir().local_def_id_to_hir_id(def_id));
1032                                 if let Some(hir::Node::TraitItem(hir::TraitItem {
1033                                     kind: hir::TraitItemKind::Fn(fn_sig, method),
1034                                     ..
1035                                 })) = id.map(|id| self.tcx.hir().get(id))
1036                                 {
1037                                     let self_first_arg = match method {
1038                                         hir::TraitFn::Required([ident, ..]) => {
1039                                             ident.name == kw::SelfLower
1040                                         }
1041                                         hir::TraitFn::Provided(body_id) => {
1042                                             self.tcx.hir().body(*body_id).params.first().map_or(
1043                                                 false,
1044                                                 |param| {
1045                                                     matches!(
1046                                                         param.pat.kind,
1047                                                         hir::PatKind::Binding(_, _, ident, _)
1048                                                             if ident.name == kw::SelfLower
1049                                                     )
1050                                                 },
1051                                             )
1052                                         }
1053                                         _ => false,
1054                                     };
1055
1056                                     if !fn_sig.decl.implicit_self.has_implicit_self()
1057                                         && self_first_arg
1058                                     {
1059                                         if let Some(ty) = fn_sig.decl.inputs.get(0) {
1060                                             arbitrary_rcvr.push(ty.span);
1061                                         }
1062                                         return false;
1063                                     }
1064                                 }
1065                             }
1066                             // We only want to suggest public or local traits (#45781).
1067                             item.vis == ty::Visibility::Public || info.def_id.is_local()
1068                         })
1069                         .is_some()
1070             })
1071             .collect::<Vec<_>>();
1072         for span in &arbitrary_rcvr {
1073             err.span_label(
1074                 *span,
1075                 "the method might not be found because of this arbitrary self type",
1076             );
1077         }
1078
1079         if !candidates.is_empty() {
1080             // Sort from most relevant to least relevant.
1081             candidates.sort_by(|a, b| a.cmp(b).reverse());
1082             candidates.dedup();
1083
1084             let param_type = match rcvr_ty.kind() {
1085                 ty::Param(param) => Some(param),
1086                 ty::Ref(_, ty, _) => match ty.kind() {
1087                     ty::Param(param) => Some(param),
1088                     _ => None,
1089                 },
1090                 _ => None,
1091             };
1092             err.help(if param_type.is_some() {
1093                 "items from traits can only be used if the type parameter is bounded by the trait"
1094             } else {
1095                 "items from traits can only be used if the trait is implemented and in scope"
1096             });
1097             let candidates_len = candidates.len();
1098             let message = |action| {
1099                 format!(
1100                     "the following {traits_define} an item `{name}`, perhaps you need to {action} \
1101                      {one_of_them}:",
1102                     traits_define =
1103                         if candidates_len == 1 { "trait defines" } else { "traits define" },
1104                     action = action,
1105                     one_of_them = if candidates_len == 1 { "it" } else { "one of them" },
1106                     name = item_name,
1107                 )
1108             };
1109             // Obtain the span for `param` and use it for a structured suggestion.
1110             if let (Some(ref param), Some(ref table)) =
1111                 (param_type, self.in_progress_typeck_results)
1112             {
1113                 let table_owner = table.borrow().hir_owner;
1114                 let generics = self.tcx.generics_of(table_owner.to_def_id());
1115                 let type_param = generics.type_param(param, self.tcx);
1116                 let hir = &self.tcx.hir();
1117                 if let Some(def_id) = type_param.def_id.as_local() {
1118                     let id = hir.local_def_id_to_hir_id(def_id);
1119                     // Get the `hir::Param` to verify whether it already has any bounds.
1120                     // We do this to avoid suggesting code that ends up as `T: FooBar`,
1121                     // instead we suggest `T: Foo + Bar` in that case.
1122                     match hir.get(id) {
1123                         Node::GenericParam(ref param) => {
1124                             let mut impl_trait = false;
1125                             let has_bounds =
1126                                 if let hir::GenericParamKind::Type { synthetic: Some(_), .. } =
1127                                     &param.kind
1128                                 {
1129                                     // We've found `fn foo(x: impl Trait)` instead of
1130                                     // `fn foo<T>(x: T)`. We want to suggest the correct
1131                                     // `fn foo(x: impl Trait + TraitBound)` instead of
1132                                     // `fn foo<T: TraitBound>(x: T)`. (#63706)
1133                                     impl_trait = true;
1134                                     param.bounds.get(1)
1135                                 } else {
1136                                     param.bounds.get(0)
1137                                 };
1138                             let sp = hir.span(id);
1139                             let sp = if let Some(first_bound) = has_bounds {
1140                                 // `sp` only covers `T`, change it so that it covers
1141                                 // `T:` when appropriate
1142                                 sp.until(first_bound.span())
1143                             } else {
1144                                 sp
1145                             };
1146                             let trait_def_ids: FxHashSet<DefId> = param
1147                                 .bounds
1148                                 .iter()
1149                                 .filter_map(|bound| bound.trait_ref()?.trait_def_id())
1150                                 .collect();
1151                             if !candidates.iter().any(|t| trait_def_ids.contains(&t.def_id)) {
1152                                 err.span_suggestions(
1153                                     sp,
1154                                     &message(format!(
1155                                         "restrict type parameter `{}` with",
1156                                         param.name.ident(),
1157                                     )),
1158                                     candidates.iter().map(|t| {
1159                                         format!(
1160                                             "{}{} {}{}",
1161                                             param.name.ident(),
1162                                             if impl_trait { " +" } else { ":" },
1163                                             self.tcx.def_path_str(t.def_id),
1164                                             if has_bounds.is_some() { " + " } else { "" },
1165                                         )
1166                                     }),
1167                                     Applicability::MaybeIncorrect,
1168                                 );
1169                             }
1170                             return;
1171                         }
1172                         Node::Item(hir::Item {
1173                             kind: hir::ItemKind::Trait(.., bounds, _),
1174                             ident,
1175                             ..
1176                         }) => {
1177                             let (sp, sep, article) = if bounds.is_empty() {
1178                                 (ident.span.shrink_to_hi(), ":", "a")
1179                             } else {
1180                                 (bounds.last().unwrap().span().shrink_to_hi(), " +", "another")
1181                             };
1182                             err.span_suggestions(
1183                                 sp,
1184                                 &message(format!("add {} supertrait for", article)),
1185                                 candidates.iter().map(|t| {
1186                                     format!("{} {}", sep, self.tcx.def_path_str(t.def_id),)
1187                                 }),
1188                                 Applicability::MaybeIncorrect,
1189                             );
1190                             return;
1191                         }
1192                         _ => {}
1193                     }
1194                 }
1195             }
1196
1197             let (potential_candidates, explicitly_negative) = if param_type.is_some() {
1198                 // FIXME: Even though negative bounds are not implemented, we could maybe handle
1199                 // cases where a positive bound implies a negative impl.
1200                 (candidates, Vec::new())
1201             } else if let Some(simp_rcvr_ty) = simplify_type(self.tcx, rcvr_ty, true) {
1202                 let mut potential_candidates = Vec::new();
1203                 let mut explicitly_negative = Vec::new();
1204                 for candidate in candidates {
1205                     // Check if there's a negative impl of `candidate` for `rcvr_ty`
1206                     if self
1207                         .tcx
1208                         .all_impls(candidate.def_id)
1209                         .filter(|imp_did| {
1210                             self.tcx.impl_polarity(*imp_did) == ty::ImplPolarity::Negative
1211                         })
1212                         .any(|imp_did| {
1213                             let imp = self.tcx.impl_trait_ref(imp_did).unwrap();
1214                             let imp_simp = simplify_type(self.tcx, imp.self_ty(), true);
1215                             imp_simp.map_or(false, |s| s == simp_rcvr_ty)
1216                         })
1217                     {
1218                         explicitly_negative.push(candidate);
1219                     } else {
1220                         potential_candidates.push(candidate);
1221                     }
1222                 }
1223                 (potential_candidates, explicitly_negative)
1224             } else {
1225                 // We don't know enough about `recv_ty` to make proper suggestions.
1226                 (candidates, Vec::new())
1227             };
1228
1229             let action = if let Some(param) = param_type {
1230                 format!("restrict type parameter `{}` with", param)
1231             } else {
1232                 // FIXME: it might only need to be imported into scope, not implemented.
1233                 "implement".to_string()
1234             };
1235             match &potential_candidates[..] {
1236                 [] => {}
1237                 [trait_info] if trait_info.def_id.is_local() => {
1238                     let span = self.tcx.hir().span_if_local(trait_info.def_id).unwrap();
1239                     err.span_note(
1240                         self.tcx.sess.source_map().guess_head_span(span),
1241                         &format!(
1242                             "`{}` defines an item `{}`, perhaps you need to {} it",
1243                             self.tcx.def_path_str(trait_info.def_id),
1244                             item_name,
1245                             action
1246                         ),
1247                     );
1248                 }
1249                 trait_infos => {
1250                     let mut msg = message(action);
1251                     for (i, trait_info) in trait_infos.iter().enumerate() {
1252                         msg.push_str(&format!(
1253                             "\ncandidate #{}: `{}`",
1254                             i + 1,
1255                             self.tcx.def_path_str(trait_info.def_id),
1256                         ));
1257                     }
1258                     err.note(&msg);
1259                 }
1260             }
1261             match &explicitly_negative[..] {
1262                 [] => {}
1263                 [trait_info] => {
1264                     let msg = format!(
1265                         "the trait `{}` defines an item `{}`, but is explicitely unimplemented",
1266                         self.tcx.def_path_str(trait_info.def_id),
1267                         item_name
1268                     );
1269                     err.note(&msg);
1270                 }
1271                 trait_infos => {
1272                     let mut msg = format!(
1273                         "the following traits define an item `{}`, but are explicitely unimplemented:",
1274                         item_name
1275                     );
1276                     for trait_info in trait_infos {
1277                         msg.push_str(&format!("\n{}", self.tcx.def_path_str(trait_info.def_id)));
1278                     }
1279                     err.note(&msg);
1280                 }
1281             }
1282         }
1283     }
1284
1285     /// Checks whether there is a local type somewhere in the chain of
1286     /// autoderefs of `rcvr_ty`.
1287     fn type_derefs_to_local(&self, span: Span, rcvr_ty: Ty<'tcx>, source: SelfSource<'_>) -> bool {
1288         fn is_local(ty: Ty<'_>) -> bool {
1289             match ty.kind() {
1290                 ty::Adt(def, _) => def.did.is_local(),
1291                 ty::Foreign(did) => did.is_local(),
1292                 ty::Dynamic(ref tr, ..) => tr.principal().map_or(false, |d| d.def_id().is_local()),
1293                 ty::Param(_) => true,
1294
1295                 // Everything else (primitive types, etc.) is effectively
1296                 // non-local (there are "edge" cases, e.g., `(LocalType,)`, but
1297                 // the noise from these sort of types is usually just really
1298                 // annoying, rather than any sort of help).
1299                 _ => false,
1300             }
1301         }
1302
1303         // This occurs for UFCS desugaring of `T::method`, where there is no
1304         // receiver expression for the method call, and thus no autoderef.
1305         if let SelfSource::QPath(_) = source {
1306             return is_local(self.resolve_vars_with_obligations(rcvr_ty));
1307         }
1308
1309         self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))
1310     }
1311 }
1312
1313 #[derive(Copy, Clone)]
1314 pub enum SelfSource<'a> {
1315     QPath(&'a hir::Ty<'a>),
1316     MethodCall(&'a hir::Expr<'a> /* rcvr */),
1317 }
1318
1319 #[derive(Copy, Clone)]
1320 pub struct TraitInfo {
1321     pub def_id: DefId,
1322 }
1323
1324 impl PartialEq for TraitInfo {
1325     fn eq(&self, other: &TraitInfo) -> bool {
1326         self.cmp(other) == Ordering::Equal
1327     }
1328 }
1329 impl Eq for TraitInfo {}
1330 impl PartialOrd for TraitInfo {
1331     fn partial_cmp(&self, other: &TraitInfo) -> Option<Ordering> {
1332         Some(self.cmp(other))
1333     }
1334 }
1335 impl Ord for TraitInfo {
1336     fn cmp(&self, other: &TraitInfo) -> Ordering {
1337         // Local crates are more important than remote ones (local:
1338         // `cnum == 0`), and otherwise we throw in the defid for totality.
1339
1340         let lhs = (other.def_id.krate, other.def_id);
1341         let rhs = (self.def_id.krate, self.def_id);
1342         lhs.cmp(&rhs)
1343     }
1344 }
1345
1346 /// Retrieves all traits in this crate and any dependent crates.
1347 pub fn all_traits(tcx: TyCtxt<'_>) -> Vec<TraitInfo> {
1348     tcx.all_traits(LOCAL_CRATE).iter().map(|&def_id| TraitInfo { def_id }).collect()
1349 }
1350
1351 /// Computes all traits in this crate and any dependent crates.
1352 fn compute_all_traits(tcx: TyCtxt<'_>) -> Vec<DefId> {
1353     use hir::itemlikevisit;
1354
1355     let mut traits = vec![];
1356
1357     // Crate-local:
1358
1359     struct Visitor<'a> {
1360         traits: &'a mut Vec<DefId>,
1361     }
1362
1363     impl<'v, 'a> itemlikevisit::ItemLikeVisitor<'v> for Visitor<'a> {
1364         fn visit_item(&mut self, i: &'v hir::Item<'v>) {
1365             match i.kind {
1366                 hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..) => {
1367                     self.traits.push(i.def_id.to_def_id());
1368                 }
1369                 _ => (),
1370             }
1371         }
1372
1373         fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
1374
1375         fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {}
1376
1377         fn visit_foreign_item(&mut self, _foreign_item: &hir::ForeignItem<'_>) {}
1378     }
1379
1380     tcx.hir().krate().visit_all_item_likes(&mut Visitor { traits: &mut traits });
1381
1382     // Cross-crate:
1383
1384     let mut external_mods = FxHashSet::default();
1385     fn handle_external_res(
1386         tcx: TyCtxt<'_>,
1387         traits: &mut Vec<DefId>,
1388         external_mods: &mut FxHashSet<DefId>,
1389         res: Res,
1390     ) {
1391         match res {
1392             Res::Def(DefKind::Trait | DefKind::TraitAlias, def_id) => {
1393                 traits.push(def_id);
1394             }
1395             Res::Def(DefKind::Mod, def_id) => {
1396                 if !external_mods.insert(def_id) {
1397                     return;
1398                 }
1399                 for child in tcx.item_children(def_id).iter() {
1400                     handle_external_res(tcx, traits, external_mods, child.res)
1401                 }
1402             }
1403             _ => {}
1404         }
1405     }
1406     for &cnum in tcx.crates().iter() {
1407         let def_id = DefId { krate: cnum, index: CRATE_DEF_INDEX };
1408         handle_external_res(tcx, &mut traits, &mut external_mods, Res::Def(DefKind::Mod, def_id));
1409     }
1410
1411     traits
1412 }
1413
1414 pub fn provide(providers: &mut ty::query::Providers) {
1415     providers.all_traits = |tcx, cnum| {
1416         assert_eq!(cnum, LOCAL_CRATE);
1417         &tcx.arena.alloc(compute_all_traits(tcx))[..]
1418     }
1419 }
1420
1421 struct UsePlacementFinder<'tcx> {
1422     target_module: hir::HirId,
1423     span: Option<Span>,
1424     found_use: bool,
1425     tcx: TyCtxt<'tcx>,
1426 }
1427
1428 impl UsePlacementFinder<'tcx> {
1429     fn check(
1430         tcx: TyCtxt<'tcx>,
1431         krate: &'tcx hir::Crate<'tcx>,
1432         target_module: hir::HirId,
1433     ) -> (Option<Span>, bool) {
1434         let mut finder = UsePlacementFinder { target_module, span: None, found_use: false, tcx };
1435         intravisit::walk_crate(&mut finder, krate);
1436         (finder.span, finder.found_use)
1437     }
1438 }
1439
1440 impl intravisit::Visitor<'tcx> for UsePlacementFinder<'tcx> {
1441     fn visit_mod(&mut self, module: &'tcx hir::Mod<'tcx>, _: Span, hir_id: hir::HirId) {
1442         if self.span.is_some() {
1443             return;
1444         }
1445         if hir_id != self.target_module {
1446             intravisit::walk_mod(self, module, hir_id);
1447             return;
1448         }
1449         // Find a `use` statement.
1450         for &item_id in module.item_ids {
1451             let item = self.tcx.hir().item(item_id);
1452             match item.kind {
1453                 hir::ItemKind::Use(..) => {
1454                     // Don't suggest placing a `use` before the prelude
1455                     // import or other generated ones.
1456                     if !item.span.from_expansion() {
1457                         self.span = Some(item.span.shrink_to_lo());
1458                         self.found_use = true;
1459                         return;
1460                     }
1461                 }
1462                 // Don't place `use` before `extern crate`...
1463                 hir::ItemKind::ExternCrate(_) => {}
1464                 // ...but do place them before the first other item.
1465                 _ => {
1466                     if self.span.map_or(true, |span| item.span < span) {
1467                         if !item.span.from_expansion() {
1468                             // Don't insert between attributes and an item.
1469                             let attrs = self.tcx.hir().attrs(item.hir_id());
1470                             if attrs.is_empty() {
1471                                 self.span = Some(item.span.shrink_to_lo());
1472                             } else {
1473                                 // Find the first attribute on the item.
1474                                 for attr in attrs {
1475                                     if self.span.map_or(true, |span| attr.span < span) {
1476                                         self.span = Some(attr.span.shrink_to_lo());
1477                                     }
1478                                 }
1479                             }
1480                         }
1481                     }
1482                 }
1483             }
1484         }
1485     }
1486
1487     type Map = intravisit::ErasedMap<'tcx>;
1488
1489     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1490         intravisit::NestedVisitorMap::None
1491     }
1492 }
1493
1494 fn print_disambiguation_help(
1495     item_name: Ident,
1496     args: Option<&'tcx [hir::Expr<'tcx>]>,
1497     err: &mut DiagnosticBuilder<'_>,
1498     trait_name: String,
1499     rcvr_ty: Ty<'_>,
1500     kind: ty::AssocKind,
1501     def_id: DefId,
1502     span: Span,
1503     candidate: Option<usize>,
1504     source_map: &source_map::SourceMap,
1505 ) {
1506     let mut applicability = Applicability::MachineApplicable;
1507     let sugg_args = if let (ty::AssocKind::Fn, Some(args)) = (kind, args) {
1508         format!(
1509             "({}{})",
1510             if rcvr_ty.is_region_ptr() {
1511                 if rcvr_ty.is_mutable_ptr() { "&mut " } else { "&" }
1512             } else {
1513                 ""
1514             },
1515             args.iter()
1516                 .map(|arg| source_map.span_to_snippet(arg.span).unwrap_or_else(|_| {
1517                     applicability = Applicability::HasPlaceholders;
1518                     "_".to_owned()
1519                 }))
1520                 .collect::<Vec<_>>()
1521                 .join(", "),
1522         )
1523     } else {
1524         String::new()
1525     };
1526     let sugg = format!("{}::{}{}", trait_name, item_name, sugg_args);
1527     err.span_suggestion(
1528         span,
1529         &format!(
1530             "disambiguate the {} for {}",
1531             kind.as_def_kind().descr(def_id),
1532             if let Some(candidate) = candidate {
1533                 format!("candidate #{}", candidate)
1534             } else {
1535                 "the candidate".to_string()
1536             },
1537         ),
1538         sugg,
1539         applicability,
1540     );
1541 }