src/librustc_typeck/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_ast::util::lev_distance;
   6 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
   7 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
   8 use rustc_hir as hir;
   9 use rustc_hir::def::{DefKind, Namespace, Res};
  10 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
  11 use rustc_hir::intravisit;
  12 use rustc_hir::lang_items::FnOnceTraitLangItem;
  13 use rustc_hir::{ExprKind, Node, QPath};
  14 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  15 use rustc_middle::hir::map as hir_map;
  16 use rustc_middle::ty::print::with_crate_prefix;
  17 use rustc_middle::ty::{
  18     self, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
  19 };
  20 use rustc_span::symbol::{kw, 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(FnOnceTraitLangItem) {
  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(),
  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
 162                                 | ty::AssocKind::Type
 163                                 | ty::AssocKind::OpaqueTy => rcvr_ty,
 164                                 ty::AssocKind::Fn => self
 165                                     .tcx
 166                                     .fn_sig(item.def_id)
 167                                     .inputs()
 168                                     .skip_binder()
 169                                     .get(0)
 170                                     .filter(|ty| ty.is_region_ptr() && !rcvr_ty.is_region_ptr())
 171                                     .copied()
 172                                     .unwrap_or(rcvr_ty),
 173                             };
 174                             print_disambiguation_help(
 175                                 item_name,
 176                                 args,
 177                                 err,
 178                                 path,
 179                                 ty,
 180                                 item.kind,
 181                                 item.def_id,
 182                                 sugg_span,
 183                                 idx,
 184                                 self.tcx.sess.source_map(),
 185                             );
 186                         }
 187                     }
 188                     CandidateSource::TraitSource(trait_did) => {
 189                         let item =
 190                             match self.associated_item(trait_did, item_name, Namespace::ValueNS) {
 191                                 Some(item) => item,
 192                                 None => continue,
 193                             };
 194                         let item_span = self
 195                             .tcx
 196                             .sess
 197                             .source_map()
 198                             .guess_head_span(self.tcx.def_span(item.def_id));
 199                         let idx = if sources.len() > 1 {
 200                             let msg = &format!(
 201                                 "candidate #{} is defined in the trait `{}`",
 202                                 idx + 1,
 203                                 self.tcx.def_path_str(trait_did)
 204                             );
 205                             err.span_note(item_span, msg);
 206                             Some(idx + 1)
 207                         } else {
 208                             let msg = &format!(
 209                                 "the candidate is defined in the trait `{}`",
 210                                 self.tcx.def_path_str(trait_did)
 211                             );
 212                             err.span_note(item_span, msg);
 213                             None
 214                         };
 215                         let path = self.tcx.def_path_str(trait_did);
 216                         print_disambiguation_help(
 217                             item_name,
 218                             args,
 219                             err,
 220                             path,
 221                             rcvr_ty,
 222                             item.kind,
 223                             item.def_id,
 224                             sugg_span,
 225                             idx,
 226                             self.tcx.sess.source_map(),
 227                         );
 228                     }
 229                 }
 230             }
 231             if sources.len() > limit {
 232                 err.note(&format!("and {} others", sources.len() - limit));
 233             }
 234         };
 235
 236         let sugg_span = if let SelfSource::MethodCall(expr) = source {
 237             // Given `foo.bar(baz)`, `expr` is `bar`, but we want to point to the whole thing.
 238             self.tcx.hir().expect_expr(self.tcx.hir().get_parent_node(expr.hir_id)).span
 239         } else {
 240             span
 241         };
 242
 243         match error {
 244             MethodError::NoMatch(NoMatchData {
 245                 static_candidates: static_sources,
 246                 unsatisfied_predicates,
 247                 out_of_scope_traits,
 248                 lev_candidate,
 249                 mode,
 250             }) => {
 251                 let tcx = self.tcx;
 252
 253                 let actual = self.resolve_vars_if_possible(&rcvr_ty);
 254                 let ty_str = self.ty_to_string(actual);
 255                 let is_method = mode == Mode::MethodCall;
 256                 let item_kind = if is_method {
 257                     "method"
 258                 } else if actual.is_enum() {
 259                     "variant or associated item"
 260                 } else {
 261                     match (item_name.as_str().chars().next(), actual.is_fresh_ty()) {
 262                         (Some(name), false) if name.is_lowercase() => "function or associated item",
 263                         (Some(_), false) => "associated item",
 264                         (Some(_), true) | (None, false) => "variant or associated item",
 265                         (None, true) => "variant",
 266                     }
 267                 };
 268                 let mut err = if !actual.references_error() {
 269                     // Suggest clamping down the type if the method that is being attempted to
 270                     // be used exists at all, and the type is an ambiguous numeric type
 271                     // ({integer}/{float}).
 272                     let mut candidates = all_traits(self.tcx).into_iter().filter_map(|info| {
 273                         self.associated_item(info.def_id, item_name, Namespace::ValueNS)
 274                     });
 275                     // There are methods that are defined on the primitive types and won't be
 276                     // found when exploring `all_traits`, but we also need them to be acurate on
 277                     // our suggestions (#47759).
 278                     let fund_assoc = |opt_def_id: Option<DefId>| {
 279                         opt_def_id
 280                             .and_then(|id| self.associated_item(id, item_name, Namespace::ValueNS))
 281                             .is_some()
 282                     };
 283                     let lang_items = tcx.lang_items();
 284                     let found_candidate = candidates.next().is_some()
 285                         || fund_assoc(lang_items.i8_impl())
 286                         || fund_assoc(lang_items.i16_impl())
 287                         || fund_assoc(lang_items.i32_impl())
 288                         || fund_assoc(lang_items.i64_impl())
 289                         || fund_assoc(lang_items.i128_impl())
 290                         || fund_assoc(lang_items.u8_impl())
 291                         || fund_assoc(lang_items.u16_impl())
 292                         || fund_assoc(lang_items.u32_impl())
 293                         || fund_assoc(lang_items.u64_impl())
 294                         || fund_assoc(lang_items.u128_impl())
 295                         || fund_assoc(lang_items.f32_impl())
 296                         || fund_assoc(lang_items.f32_runtime_impl())
 297                         || fund_assoc(lang_items.f64_impl())
 298                         || fund_assoc(lang_items.f64_runtime_impl());
 299                     if let (true, false, SelfSource::MethodCall(expr), true) = (
 300                         actual.is_numeric(),
 301                         actual.has_concrete_skeleton(),
 302                         source,
 303                         found_candidate,
 304                     ) {
 305                         let mut err = struct_span_err!(
 306                             tcx.sess,
 307                             span,
 308                             E0689,
 309                             "can't call {} `{}` on ambiguous numeric type `{}`",
 310                             item_kind,
 311                             item_name,
 312                             ty_str
 313                         );
 314                         let concrete_type = if actual.is_integral() { "i32" } else { "f32" };
 315                         match expr.kind {
 316                             ExprKind::Lit(ref lit) => {
 317                                 // numeric literal
 318                                 let snippet = tcx
 319                                     .sess
 320                                     .source_map()
 321                                     .span_to_snippet(lit.span)
 322                                     .unwrap_or_else(|_| "<numeric literal>".to_owned());
 323
 324                                 err.span_suggestion(
 325                                     lit.span,
 326                                     &format!(
 327                                         "you must specify a concrete type for \
 328                                               this numeric value, like `{}`",
 329                                         concrete_type
 330                                     ),
 331                                     format!("{}_{}", snippet, concrete_type),
 332                                     Applicability::MaybeIncorrect,
 333                                 );
 334                             }
 335                             ExprKind::Path(ref qpath) => {
 336                                 // local binding
 337                                 if let &QPath::Resolved(_, ref path) = &qpath {
 338                                     if let hir::def::Res::Local(hir_id) = path.res {
 339                                         let span = tcx.hir().span(hir_id);
 340                                         let snippet = tcx.sess.source_map().span_to_snippet(span);
 341                                         let filename = tcx.sess.source_map().span_to_filename(span);
 342
 343                                         let parent_node = self
 344                                             .tcx
 345                                             .hir()
 346                                             .get(self.tcx.hir().get_parent_node(hir_id));
 347                                         let msg = format!(
 348                                             "you must specify a type for this binding, like `{}`",
 349                                             concrete_type,
 350                                         );
 351
 352                                         match (filename, parent_node, snippet) {
 353                                             (
 354                                                 FileName::Real(_),
 355                                                 Node::Local(hir::Local {
 356                                                     source: hir::LocalSource::Normal,
 357                                                     ty,
 358                                                     ..
 359                                                 }),
 360                                                 Ok(ref snippet),
 361                                             ) => {
 362                                                 err.span_suggestion(
 363                                                     // account for `let x: _ = 42;`
 364                                                     //                  ^^^^
 365                                                     span.to(ty
 366                                                         .as_ref()
 367                                                         .map(|ty| ty.span)
 368                                                         .unwrap_or(span)),
 369                                                     &msg,
 370                                                     format!("{}: {}", snippet, concrete_type),
 371                                                     Applicability::MaybeIncorrect,
 372                                                 );
 373                                             }
 374                                             _ => {
 375                                                 err.span_label(span, msg);
 376                                             }
 377                                         }
 378                                     }
 379                                 }
 380                             }
 381                             _ => {}
 382                         }
 383                         err.emit();
 384                         return None;
 385                     } else {
 386                         span = item_name.span;
 387                         let mut err = struct_span_err!(
 388                             tcx.sess,
 389                             span,
 390                             E0599,
 391                             "no {} named `{}` found for {} `{}` in the current scope",
 392                             item_kind,
 393                             item_name,
 394                             actual.prefix_string(),
 395                             ty_str,
 396                         );
 397                         if let Some(span) =
 398                             tcx.sess.confused_type_with_std_module.borrow().get(&span)
 399                         {
 400                             if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*span) {
 401                                 err.span_suggestion(
 402                                     *span,
 403                                     "you are looking for the module in `std`, \
 404                                      not the primitive type",
 405                                     format!("std::{}", snippet),
 406                                     Applicability::MachineApplicable,
 407                                 );
 408                             }
 409                         }
 410                         if let ty::RawPtr(_) = &actual.kind {
 411                             err.note(
 412                                 "try using `<*const T>::as_ref()` to get a reference to the \
 413                                       type behind the pointer: https://doc.rust-lang.org/std/\
 414                                       primitive.pointer.html#method.as_ref",
 415                             );
 416                             err.note(
 417                                 "using `<*const T>::as_ref()` on a pointer \
 418                                       which is unaligned or points to invalid \
 419                                       or uninitialized memory is undefined behavior",
 420                             );
 421                         }
 422                         err
 423                     }
 424                 } else {
 425                     tcx.sess.diagnostic().struct_dummy()
 426                 };
 427
 428                 if let Some(def) = actual.ty_adt_def() {
 429                     if let Some(full_sp) = tcx.hir().span_if_local(def.did) {
 430                         let def_sp = tcx.sess.source_map().guess_head_span(full_sp);
 431                         err.span_label(
 432                             def_sp,
 433                             format!(
 434                                 "{} `{}` not found {}",
 435                                 item_kind,
 436                                 item_name,
 437                                 if def.is_enum() && !is_method { "here" } else { "for this" }
 438                             ),
 439                         );
 440                     }
 441                 }
 442
 443                 // If the method name is the name of a field with a function or closure type,
 444                 // give a helping note that it has to be called as `(x.f)(...)`.
 445                 if let SelfSource::MethodCall(expr) = source {
 446                     let field_receiver =
 447                         self.autoderef(span, rcvr_ty).find_map(|(ty, _)| match ty.kind {
 448                             ty::Adt(def, substs) if !def.is_enum() => {
 449                                 let variant = &def.non_enum_variant();
 450                                 self.tcx.find_field_index(item_name, variant).map(|index| {
 451                                     let field = &variant.fields[index];
 452                                     let field_ty = field.ty(tcx, substs);
 453                                     (field, field_ty)
 454                                 })
 455                             }
 456                             _ => None,
 457                         });
 458
 459                     if let Some((field, field_ty)) = field_receiver {
 460                         let scope = self.tcx.parent_module(self.body_id).to_def_id();
 461                         let is_accessible = field.vis.is_accessible_from(scope, self.tcx);
 462
 463                         if is_accessible {
 464                             if self.is_fn_ty(&field_ty, span) {
 465                                 let expr_span = expr.span.to(item_name.span);
 466                                 err.multipart_suggestion(
 467                                     &format!(
 468                                         "to call the function stored in `{}`, \
 469                                          surround the field access with parentheses",
 470                                         item_name,
 471                                     ),
 472                                     vec![
 473                                         (expr_span.shrink_to_lo(), '('.to_string()),
 474                                         (expr_span.shrink_to_hi(), ')'.to_string()),
 475                                     ],
 476                                     Applicability::MachineApplicable,
 477                                 );
 478                             } else {
 479                                 let call_expr = self
 480                                     .tcx
 481                                     .hir()
 482                                     .expect_expr(self.tcx.hir().get_parent_node(expr.hir_id));
 483
 484                                 if let Some(span) = call_expr.span.trim_start(item_name.span) {
 485                                     err.span_suggestion(
 486                                         span,
 487                                         "remove the arguments",
 488                                         String::new(),
 489                                         Applicability::MaybeIncorrect,
 490                                     );
 491                                 }
 492                             }
 493                         }
 494
 495                         let field_kind = if is_accessible { "field" } else { "private field" };
 496                         err.span_label(item_name.span, format!("{}, not a method", field_kind));
 497                     } else if lev_candidate.is_none() && static_sources.is_empty() {
 498                         err.span_label(span, format!("{} not found in `{}`", item_kind, ty_str));
 499                         self.tcx.sess.trait_methods_not_found.borrow_mut().insert(orig_span);
 500                     }
 501                 } else {
 502                     err.span_label(span, format!("{} not found in `{}`", item_kind, ty_str));
 503                     self.tcx.sess.trait_methods_not_found.borrow_mut().insert(orig_span);
 504                 }
 505
 506                 if self.is_fn_ty(&rcvr_ty, span) {
 507                     macro_rules! report_function {
 508                         ($span:expr, $name:expr) => {
 509                             err.note(&format!(
 510                                 "`{}` is a function, perhaps you wish to call it",
 511                                 $name
 512                             ));
 513                         };
 514                     }
 515
 516                     if let SelfSource::MethodCall(expr) = source {
 517                         if let Ok(expr_string) = tcx.sess.source_map().span_to_snippet(expr.span) {
 518                             report_function!(expr.span, expr_string);
 519                         } else if let ExprKind::Path(QPath::Resolved(_, ref path)) = expr.kind {
 520                             if let Some(segment) = path.segments.last() {
 521                                 report_function!(expr.span, segment.ident);
 522                             }
 523                         }
 524                     }
 525                 }
 526
 527                 if !static_sources.is_empty() {
 528                     err.note(
 529                         "found the following associated functions; to be used as methods, \
 530                          functions must have a `self` parameter",
 531                     );
 532                     err.span_label(span, "this is an associated function, not a method");
 533                 }
 534                 if static_sources.len() == 1 {
 535                     let ty_str = if let Some(CandidateSource::ImplSource(impl_did)) =
 536                         static_sources.get(0)
 537                     {
 538                         // When the "method" is resolved through dereferencing, we really want the
 539                         // original type that has the associated function for accurate suggestions.
 540                         // (#61411)
 541                         let ty = tcx.at(span).type_of(*impl_did);
 542                         match (&ty.peel_refs().kind, &actual.peel_refs().kind) {
 543                             (ty::Adt(def, _), ty::Adt(def_actual, _)) if def == def_actual => {
 544                                 // Use `actual` as it will have more `substs` filled in.
 545                                 self.ty_to_value_string(actual.peel_refs())
 546                             }
 547                             _ => self.ty_to_value_string(ty.peel_refs()),
 548                         }
 549                     } else {
 550                         self.ty_to_value_string(actual.peel_refs())
 551                     };
 552                     if let SelfSource::MethodCall(expr) = source {
 553                         err.span_suggestion(
 554                             expr.span.to(span),
 555                             "use associated function syntax instead",
 556                             format!("{}::{}", ty_str, item_name),
 557                             Applicability::MachineApplicable,
 558                         );
 559                     } else {
 560                         err.help(&format!("try with `{}::{}`", ty_str, item_name,));
 561                     }
 562
 563                     report_candidates(span, &mut err, static_sources, sugg_span);
 564                 } else if static_sources.len() > 1 {
 565                     report_candidates(span, &mut err, static_sources, sugg_span);
 566                 }
 567
 568                 let mut restrict_type_params = false;
 569                 if !unsatisfied_predicates.is_empty() {
 570                     let def_span = |def_id| {
 571                         self.tcx.sess.source_map().guess_head_span(self.tcx.def_span(def_id))
 572                     };
 573                     let mut type_params = FxHashMap::default();
 574                     let mut bound_spans = vec![];
 575                     let mut collect_type_param_suggestions =
 576                         |self_ty: Ty<'_>, parent_pred: &ty::Predicate<'_>, obligation: &str| {
 577                             if let (ty::Param(_), ty::PredicateKind::Trait(p, _)) =
 578                                 (&self_ty.kind, parent_pred)
 579                             {
 580                                 if let ty::Adt(def, _) = p.skip_binder().trait_ref.self_ty().kind {
 581                                     let node = def.did.as_local().map(|def_id| {
 582                                         self.tcx.hir().get(self.tcx.hir().as_local_hir_id(def_id))
 583                                     });
 584                                     if let Some(hir::Node::Item(hir::Item { kind, .. })) = node {
 585                                         if let Some(g) = kind.generics() {
 586                                             let key = match &g.where_clause.predicates[..] {
 587                                                 [.., pred] => (pred.span().shrink_to_hi(), false),
 588                                                 [] => (
 589                                                     g.where_clause
 590                                                         .span_for_predicates_or_empty_place(),
 591                                                     true,
 592                                                 ),
 593                                             };
 594                                             type_params
 595                                                 .entry(key)
 596                                                 .or_insert_with(FxHashSet::default)
 597                                                 .insert(obligation.to_owned());
 598                                         }
 599                                     }
 600                                 }
 601                             }
 602                         };
 603                     let mut bound_span_label = |self_ty: Ty<'_>, obligation: &str, quiet: &str| {
 604                         let msg = format!(
 605                             "doesn't satisfy `{}`",
 606                             if obligation.len() > 50 { quiet } else { obligation }
 607                         );
 608                         match &self_ty.kind {
 609                             // Point at the type that couldn't satisfy the bound.
 610                             ty::Adt(def, _) => bound_spans.push((def_span(def.did), msg)),
 611                             // Point at the trait object that couldn't satisfy the bound.
 612                             ty::Dynamic(preds, _) => {
 613                                 for pred in *preds.skip_binder() {
 614                                     match pred {
 615                                         ty::ExistentialPredicate::Trait(tr) => {
 616                                             bound_spans.push((def_span(tr.def_id), msg.clone()))
 617                                         }
 618                                         ty::ExistentialPredicate::Projection(_)
 619                                         | ty::ExistentialPredicate::AutoTrait(_) => {}
 620                                     }
 621                                 }
 622                             }
 623                             // Point at the closure that couldn't satisfy the bound.
 624                             ty::Closure(def_id, _) => bound_spans
 625                                 .push((def_span(*def_id), format!("doesn't satisfy `{}`", quiet))),
 626                             _ => {}
 627                         }
 628                     };
 629                     let mut format_pred = |pred| {
 630                         match pred {
 631                             ty::PredicateKind::Projection(pred) => {
 632                                 // `<Foo as Iterator>::Item = String`.
 633                                 let trait_ref =
 634                                     pred.skip_binder().projection_ty.trait_ref(self.tcx);
 635                                 let assoc = self
 636                                     .tcx
 637                                     .associated_item(pred.skip_binder().projection_ty.item_def_id);
 638                                 let ty = pred.skip_binder().ty;
 639                                 let obligation = format!("{}::{} = {}", trait_ref, assoc.ident, ty);
 640                                 let quiet = format!(
 641                                     "<_ as {}>::{} = {}",
 642                                     trait_ref.print_only_trait_path(),
 643                                     assoc.ident,
 644                                     ty
 645                                 );
 646                                 bound_span_label(trait_ref.self_ty(), &obligation, &quiet);
 647                                 Some((obligation, trait_ref.self_ty()))
 648                             }
 649                             ty::PredicateKind::Trait(poly_trait_ref, _) => {
 650                                 let p = poly_trait_ref.skip_binder().trait_ref;
 651                                 let self_ty = p.self_ty();
 652                                 let path = p.print_only_trait_path();
 653                                 let obligation = format!("{}: {}", self_ty, path);
 654                                 let quiet = format!("_: {}", path);
 655                                 bound_span_label(self_ty, &obligation, &quiet);
 656                                 Some((obligation, self_ty))
 657                             }
 658                             _ => None,
 659                         }
 660                     };
 661                     let mut bound_list = unsatisfied_predicates
 662                         .iter()
 663                         .filter_map(|(pred, parent_pred)| {
 664                             format_pred(*pred).map(|(p, self_ty)| match parent_pred {
 665                                 None => format!("`{}`", p),
 666                                 Some(parent_pred) => match format_pred(*parent_pred) {
 667                                     None => format!("`{}`", p),
 668                                     Some((parent_p, _)) => {
 669                                         collect_type_param_suggestions(self_ty, parent_pred, &p);
 670                                         format!("`{}`\nwhich is required by `{}`", p, parent_p)
 671                                     }
 672                                 },
 673                             })
 674                         })
 675                         .enumerate()
 676                         .collect::<Vec<(usize, String)>>();
 677                     for ((span, empty_where), obligations) in type_params.into_iter() {
 678                         restrict_type_params = true;
 679                         err.span_suggestion_verbose(
 680                             span,
 681                             &format!(
 682                                 "consider restricting the type parameter{s} to satisfy the \
 683                                  trait bound{s}",
 684                                 s = pluralize!(obligations.len())
 685                             ),
 686                             format!(
 687                                 "{} {}",
 688                                 if empty_where { " where" } else { "," },
 689                                 obligations.into_iter().collect::<Vec<_>>().join(", ")
 690                             ),
 691                             Applicability::MaybeIncorrect,
 692                         );
 693                     }
 694
 695                     bound_list.sort_by(|(_, a), (_, b)| a.cmp(&b)); // Sort alphabetically.
 696                     bound_list.dedup_by(|(_, a), (_, b)| a == b); // #35677
 697                     bound_list.sort_by_key(|(pos, _)| *pos); // Keep the original predicate order.
 698                     bound_spans.sort();
 699                     bound_spans.dedup();
 700                     for (span, msg) in bound_spans.into_iter() {
 701                         err.span_label(span, &msg);
 702                     }
 703                     if !bound_list.is_empty() {
 704                         let bound_list = bound_list
 705                             .into_iter()
 706                             .map(|(_, path)| path)
 707                             .collect::<Vec<_>>()
 708                             .join("\n");
 709                         err.note(&format!(
 710                             "the method `{}` exists but the following trait bounds were not \
 711                              satisfied:\n{}",
 712                             item_name, bound_list
 713                         ));
 714                     }
 715                 }
 716
 717                 if actual.is_numeric() && actual.is_fresh() || restrict_type_params {
 718                 } else {
 719                     self.suggest_traits_to_import(
 720                         &mut err,
 721                         span,
 722                         rcvr_ty,
 723                         item_name,
 724                         source,
 725                         out_of_scope_traits,
 726                         &unsatisfied_predicates,
 727                     );
 728                 }
 729
 730                 if actual.is_enum() {
 731                     let adt_def = actual.ty_adt_def().expect("enum is not an ADT");
 732                     if let Some(suggestion) = lev_distance::find_best_match_for_name(
 733                         adt_def.variants.iter().map(|s| &s.ident.name),
 734                         &item_name.as_str(),
 735                         None,
 736                     ) {
 737                         err.span_suggestion(
 738                             span,
 739                             "there is a variant with a similar name",
 740                             suggestion.to_string(),
 741                             Applicability::MaybeIncorrect,
 742                         );
 743                     }
 744                 }
 745
 746                 let mut fallback_span = true;
 747                 let msg = "remove this method call";
 748                 if item_name.as_str() == "as_str" && actual.peel_refs().is_str() {
 749                     if let SelfSource::MethodCall(expr) = source {
 750                         let call_expr =
 751                             self.tcx.hir().expect_expr(self.tcx.hir().get_parent_node(expr.hir_id));
 752                         if let Some(span) = call_expr.span.trim_start(expr.span) {
 753                             err.span_suggestion(
 754                                 span,
 755                                 msg,
 756                                 String::new(),
 757                                 Applicability::MachineApplicable,
 758                             );
 759                             fallback_span = false;
 760                         }
 761                     }
 762                     if fallback_span {
 763                         err.span_label(span, msg);
 764                     }
 765                 } else if let Some(lev_candidate) = lev_candidate {
 766                     let def_kind = lev_candidate.kind.as_def_kind();
 767                     err.span_suggestion(
 768                         span,
 769                         &format!(
 770                             "there is {} {} with a similar name",
 771                             def_kind.article(),
 772                             def_kind.descr(lev_candidate.def_id),
 773                         ),
 774                         lev_candidate.ident.to_string(),
 775                         Applicability::MaybeIncorrect,
 776                     );
 777                 }
 778
 779                 return Some(err);
 780             }
 781
 782             MethodError::Ambiguity(sources) => {
 783                 let mut err = struct_span_err!(
 784                     self.sess(),
 785                     item_name.span,
 786                     E0034,
 787                     "multiple applicable items in scope"
 788                 );
 789                 err.span_label(item_name.span, format!("multiple `{}` found", item_name));
 790
 791                 report_candidates(span, &mut err, sources, sugg_span);
 792                 err.emit();
 793             }
 794
 795             MethodError::PrivateMatch(kind, def_id, out_of_scope_traits) => {
 796                 let kind = kind.descr(def_id);
 797                 let mut err = struct_span_err!(
 798                     self.tcx.sess,
 799                     item_name.span,
 800                     E0624,
 801                     "{} `{}` is private",
 802                     kind,
 803                     item_name
 804                 );
 805                 err.span_label(item_name.span, &format!("private {}", kind));
 806                 self.suggest_valid_traits(&mut err, out_of_scope_traits);
 807                 err.emit();
 808             }
 809
 810             MethodError::IllegalSizedBound(candidates, needs_mut, bound_span) => {
 811                 let msg = format!("the `{}` method cannot be invoked on a trait object", item_name);
 812                 let mut err = self.sess().struct_span_err(span, &msg);
 813                 err.span_label(bound_span, "this has a `Sized` requirement");
 814                 if !candidates.is_empty() {
 815                     let help = format!(
 816                         "{an}other candidate{s} {were} found in the following trait{s}, perhaps \
 817                          add a `use` for {one_of_them}:",
 818                         an = if candidates.len() == 1 { "an" } else { "" },
 819                         s = pluralize!(candidates.len()),
 820                         were = if candidates.len() == 1 { "was" } else { "were" },
 821                         one_of_them = if candidates.len() == 1 { "it" } else { "one_of_them" },
 822                     );
 823                     self.suggest_use_candidates(&mut err, help, candidates);
 824                 }
 825                 if let ty::Ref(region, t_type, mutability) = rcvr_ty.kind {
 826                     if needs_mut {
 827                         let trait_type = self.tcx.mk_ref(
 828                             region,
 829                             ty::TypeAndMut { ty: t_type, mutbl: mutability.invert() },
 830                         );
 831                         err.note(&format!("you need `{}` instead of `{}`", trait_type, rcvr_ty));
 832                     }
 833                 }
 834                 err.emit();
 835             }
 836
 837             MethodError::BadReturnType => bug!("no return type expectations but got BadReturnType"),
 838         }
 839         None
 840     }
 841
 842     /// Print out the type for use in value namespace.
 843     fn ty_to_value_string(&self, ty: Ty<'tcx>) -> String {
 844         match ty.kind {
 845             ty::Adt(def, substs) => format!("{}", ty::Instance::new(def.did, substs)),
 846             _ => self.ty_to_string(ty),
 847         }
 848     }
 849
 850     fn suggest_use_candidates(
 851         &self,
 852         err: &mut DiagnosticBuilder<'_>,
 853         mut msg: String,
 854         candidates: Vec<DefId>,
 855     ) {
 856         let module_did = self.tcx.parent_module(self.body_id);
 857         let module_id = self.tcx.hir().as_local_hir_id(module_did);
 858         let krate = self.tcx.hir().krate();
 859         let (span, found_use) = UsePlacementFinder::check(self.tcx, krate, module_id);
 860         if let Some(span) = span {
 861             let path_strings = candidates.iter().map(|did| {
 862                 // Produce an additional newline to separate the new use statement
 863                 // from the directly following item.
 864                 let additional_newline = if found_use { "" } else { "\n" };
 865                 format!(
 866                     "use {};\n{}",
 867                     with_crate_prefix(|| self.tcx.def_path_str(*did)),
 868                     additional_newline
 869                 )
 870             });
 871
 872             err.span_suggestions(span, &msg, path_strings, Applicability::MaybeIncorrect);
 873         } else {
 874             let limit = if candidates.len() == 5 { 5 } else { 4 };
 875             for (i, trait_did) in candidates.iter().take(limit).enumerate() {
 876                 if candidates.len() > 1 {
 877                     msg.push_str(&format!(
 878                         "\ncandidate #{}: `use {};`",
 879                         i + 1,
 880                         with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
 881                     ));
 882                 } else {
 883                     msg.push_str(&format!(
 884                         "\n`use {};`",
 885                         with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
 886                     ));
 887                 }
 888             }
 889             if candidates.len() > limit {
 890                 msg.push_str(&format!("\nand {} others", candidates.len() - limit));
 891             }
 892             err.note(&msg[..]);
 893         }
 894     }
 895
 896     fn suggest_valid_traits(
 897         &self,
 898         err: &mut DiagnosticBuilder<'_>,
 899         valid_out_of_scope_traits: Vec<DefId>,
 900     ) -> bool {
 901         if !valid_out_of_scope_traits.is_empty() {
 902             let mut candidates = valid_out_of_scope_traits;
 903             candidates.sort();
 904             candidates.dedup();
 905             err.help("items from traits can only be used if the trait is in scope");
 906             let msg = format!(
 907                 "the following {traits_are} implemented but not in scope; \
 908                  perhaps add a `use` for {one_of_them}:",
 909                 traits_are = if candidates.len() == 1 { "trait is" } else { "traits are" },
 910                 one_of_them = if candidates.len() == 1 { "it" } else { "one of them" },
 911             );
 912
 913             self.suggest_use_candidates(err, msg, candidates);
 914             true
 915         } else {
 916             false
 917         }
 918     }
 919
 920     fn suggest_traits_to_import<'b>(
 921         &self,
 922         err: &mut DiagnosticBuilder<'_>,
 923         span: Span,
 924         rcvr_ty: Ty<'tcx>,
 925         item_name: Ident,
 926         source: SelfSource<'b>,
 927         valid_out_of_scope_traits: Vec<DefId>,
 928         unsatisfied_predicates: &[(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>)],
 929     ) {
 930         if self.suggest_valid_traits(err, valid_out_of_scope_traits) {
 931             return;
 932         }
 933
 934         let type_is_local = self.type_derefs_to_local(span, rcvr_ty, source);
 935
 936         let mut arbitrary_rcvr = vec![];
 937         // There are no traits implemented, so lets suggest some traits to
 938         // implement, by finding ones that have the item name, and are
 939         // legal to implement.
 940         let mut candidates = all_traits(self.tcx)
 941             .into_iter()
 942             .filter(|info| {
 943                 // We approximate the coherence rules to only suggest
 944                 // traits that are legal to implement by requiring that
 945                 // either the type or trait is local. Multi-dispatch means
 946                 // this isn't perfect (that is, there are cases when
 947                 // implementing a trait would be legal but is rejected
 948                 // here).
 949                 unsatisfied_predicates.iter().all(|(p, _)| match p {
 950                     // Hide traits if they are present in predicates as they can be fixed without
 951                     // having to implement them.
 952                     ty::PredicateKind::Trait(t, _) => t.def_id() == info.def_id,
 953                     ty::PredicateKind::Projection(p) => p.item_def_id() == info.def_id,
 954                     _ => false,
 955                 }) && (type_is_local || info.def_id.is_local())
 956                     && self
 957                         .associated_item(info.def_id, item_name, Namespace::ValueNS)
 958                         .filter(|item| {
 959                             if let ty::AssocKind::Fn = item.kind {
 960                                 let id = item
 961                                     .def_id
 962                                     .as_local()
 963                                     .map(|def_id| self.tcx.hir().as_local_hir_id(def_id));
 964                                 if let Some(hir::Node::TraitItem(hir::TraitItem {
 965                                     kind: hir::TraitItemKind::Fn(fn_sig, method),
 966                                     ..
 967                                 })) = id.map(|id| self.tcx.hir().get(id))
 968                                 {
 969                                     let self_first_arg = match method {
 970                                         hir::TraitFn::Required([ident, ..]) => {
 971                                             ident.name == kw::SelfLower
 972                                         }
 973                                         hir::TraitFn::Provided(body_id) => {
 974                                             self.tcx.hir().body(*body_id).params.first().map_or(
 975                                                 false,
 976                                                 |param| {
 977                                                     matches!(
 978                                                         param.pat.kind,
 979                                                         hir::PatKind::Binding(_, _, ident, _)
 980                                                             if ident.name == kw::SelfLower
 981                                                     )
 982                                                 },
 983                                             )
 984                                         }
 985                                         _ => false,
 986                                     };
 987
 988                                     if !fn_sig.decl.implicit_self.has_implicit_self()
 989                                         && self_first_arg
 990                                     {
 991                                         if let Some(ty) = fn_sig.decl.inputs.get(0) {
 992                                             arbitrary_rcvr.push(ty.span);
 993                                         }
 994                                         return false;
 995                                     }
 996                                 }
 997                             }
 998                             // We only want to suggest public or local traits (#45781).
 999                             item.vis == ty::Visibility::Public || info.def_id.is_local()
1000                         })
1001                         .is_some()
1002             })
1003             .collect::<Vec<_>>();
1004         for span in &arbitrary_rcvr {
1005             err.span_label(
1006                 *span,
1007                 "the method might not be found because of this arbitrary self type",
1008             );
1009         }
1010
1011         if !candidates.is_empty() {
1012             // Sort from most relevant to least relevant.
1013             candidates.sort_by(|a, b| a.cmp(b).reverse());
1014             candidates.dedup();
1015
1016             let param_type = match rcvr_ty.kind {
1017                 ty::Param(param) => Some(param),
1018                 ty::Ref(_, ty, _) => match ty.kind {
1019                     ty::Param(param) => Some(param),
1020                     _ => None,
1021                 },
1022                 _ => None,
1023             };
1024             err.help(if param_type.is_some() {
1025                 "items from traits can only be used if the type parameter is bounded by the trait"
1026             } else {
1027                 "items from traits can only be used if the trait is implemented and in scope"
1028             });
1029             let message = |action| {
1030                 format!(
1031                     "the following {traits_define} an item `{name}`, perhaps you need to {action} \
1032                      {one_of_them}:",
1033                     traits_define =
1034                         if candidates.len() == 1 { "trait defines" } else { "traits define" },
1035                     action = action,
1036                     one_of_them = if candidates.len() == 1 { "it" } else { "one of them" },
1037                     name = item_name,
1038                 )
1039             };
1040             // Obtain the span for `param` and use it for a structured suggestion.
1041             let mut suggested = false;
1042             if let (Some(ref param), Some(ref table)) = (param_type, self.in_progress_tables) {
1043                 let table_owner = table.borrow().hir_owner;
1044                 if let Some(table_owner) = table_owner {
1045                     let generics = self.tcx.generics_of(table_owner.to_def_id());
1046                     let type_param = generics.type_param(param, self.tcx);
1047                     let hir = &self.tcx.hir();
1048                     if let Some(def_id) = type_param.def_id.as_local() {
1049                         let id = hir.as_local_hir_id(def_id);
1050                         // Get the `hir::Param` to verify whether it already has any bounds.
1051                         // We do this to avoid suggesting code that ends up as `T: FooBar`,
1052                         // instead we suggest `T: Foo + Bar` in that case.
1053                         match hir.get(id) {
1054                             Node::GenericParam(ref param) => {
1055                                 let mut impl_trait = false;
1056                                 let has_bounds = if let hir::GenericParamKind::Type {
1057                                     synthetic: Some(_),
1058                                     ..
1059                                 } = &param.kind
1060                                 {
1061                                     // We've found `fn foo(x: impl Trait)` instead of
1062                                     // `fn foo<T>(x: T)`. We want to suggest the correct
1063                                     // `fn foo(x: impl Trait + TraitBound)` instead of
1064                                     // `fn foo<T: TraitBound>(x: T)`. (#63706)
1065                                     impl_trait = true;
1066                                     param.bounds.get(1)
1067                                 } else {
1068                                     param.bounds.get(0)
1069                                 };
1070                                 let sp = hir.span(id);
1071                                 let sp = if let Some(first_bound) = has_bounds {
1072                                     // `sp` only covers `T`, change it so that it covers
1073                                     // `T:` when appropriate
1074                                     sp.until(first_bound.span())
1075                                 } else {
1076                                     sp
1077                                 };
1078                                 let trait_def_ids: FxHashSet<DefId> = param
1079                                     .bounds
1080                                     .iter()
1081                                     .filter_map(|bound| Some(bound.trait_ref()?.trait_def_id()?))
1082                                     .collect();
1083                                 if !candidates.iter().any(|t| trait_def_ids.contains(&t.def_id)) {
1084                                     err.span_suggestions(
1085                                         sp,
1086                                         &message(format!(
1087                                             "restrict type parameter `{}` with",
1088                                             param.name.ident(),
1089                                         )),
1090                                         candidates.iter().map(|t| {
1091                                             format!(
1092                                                 "{}{} {}{}",
1093                                                 param.name.ident(),
1094                                                 if impl_trait { " +" } else { ":" },
1095                                                 self.tcx.def_path_str(t.def_id),
1096                                                 if has_bounds.is_some() { " + " } else { "" },
1097                                             )
1098                                         }),
1099                                         Applicability::MaybeIncorrect,
1100                                     );
1101                                 }
1102                                 suggested = true;
1103                             }
1104                             Node::Item(hir::Item {
1105                                 kind: hir::ItemKind::Trait(.., bounds, _),
1106                                 ident,
1107                                 ..
1108                             }) => {
1109                                 let (sp, sep, article) = if bounds.is_empty() {
1110                                     (ident.span.shrink_to_hi(), ":", "a")
1111                                 } else {
1112                                     (bounds.last().unwrap().span().shrink_to_hi(), " +", "another")
1113                                 };
1114                                 err.span_suggestions(
1115                                     sp,
1116                                     &message(format!("add {} supertrait for", article)),
1117                                     candidates.iter().map(|t| {
1118                                         format!("{} {}", sep, self.tcx.def_path_str(t.def_id),)
1119                                     }),
1120                                     Applicability::MaybeIncorrect,
1121                                 );
1122                                 suggested = true;
1123                             }
1124                             _ => {}
1125                         }
1126                     }
1127                 };
1128             }
1129
1130             if !suggested {
1131                 let action = if let Some(param) = param_type {
1132                     format!("restrict type parameter `{}` with", param)
1133                 } else {
1134                     // FIXME: it might only need to be imported into scope, not implemented.
1135                     "implement".to_string()
1136                 };
1137                 let mut use_note = true;
1138                 if let [trait_info] = &candidates[..] {
1139                     if let Some(span) = self.tcx.hir().span_if_local(trait_info.def_id) {
1140                         err.span_note(
1141                             self.tcx.sess.source_map().guess_head_span(span),
1142                             &format!(
1143                                 "`{}` defines an item `{}`, perhaps you need to {} it",
1144                                 self.tcx.def_path_str(trait_info.def_id),
1145                                 item_name,
1146                                 action
1147                             ),
1148                         );
1149                         use_note = false
1150                     }
1151                 }
1152                 if use_note {
1153                     let mut msg = message(action);
1154                     for (i, trait_info) in candidates.iter().enumerate() {
1155                         msg.push_str(&format!(
1156                             "\ncandidate #{}: `{}`",
1157                             i + 1,
1158                             self.tcx.def_path_str(trait_info.def_id),
1159                         ));
1160                     }
1161                     err.note(&msg[..]);
1162                 }
1163             }
1164         }
1165     }
1166
1167     /// Checks whether there is a local type somewhere in the chain of
1168     /// autoderefs of `rcvr_ty`.
1169     fn type_derefs_to_local(&self, span: Span, rcvr_ty: Ty<'tcx>, source: SelfSource<'_>) -> bool {
1170         fn is_local(ty: Ty<'_>) -> bool {
1171             match ty.kind {
1172                 ty::Adt(def, _) => def.did.is_local(),
1173                 ty::Foreign(did) => did.is_local(),
1174
1175                 ty::Dynamic(ref tr, ..) => {
1176                     tr.principal().map(|d| d.def_id().is_local()).unwrap_or(false)
1177                 }
1178
1179                 ty::Param(_) => true,
1180
1181                 // Everything else (primitive types, etc.) is effectively
1182                 // non-local (there are "edge" cases, e.g., `(LocalType,)`, but
1183                 // the noise from these sort of types is usually just really
1184                 // annoying, rather than any sort of help).
1185                 _ => false,
1186             }
1187         }
1188
1189         // This occurs for UFCS desugaring of `T::method`, where there is no
1190         // receiver expression for the method call, and thus no autoderef.
1191         if let SelfSource::QPath(_) = source {
1192             return is_local(self.resolve_vars_with_obligations(rcvr_ty));
1193         }
1194
1195         self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))
1196     }
1197 }
1198
1199 #[derive(Copy, Clone)]
1200 pub enum SelfSource<'a> {
1201     QPath(&'a hir::Ty<'a>),
1202     MethodCall(&'a hir::Expr<'a> /* rcvr */),
1203 }
1204
1205 #[derive(Copy, Clone)]
1206 pub struct TraitInfo {
1207     pub def_id: DefId,
1208 }
1209
1210 impl PartialEq for TraitInfo {
1211     fn eq(&self, other: &TraitInfo) -> bool {
1212         self.cmp(other) == Ordering::Equal
1213     }
1214 }
1215 impl Eq for TraitInfo {}
1216 impl PartialOrd for TraitInfo {
1217     fn partial_cmp(&self, other: &TraitInfo) -> Option<Ordering> {
1218         Some(self.cmp(other))
1219     }
1220 }
1221 impl Ord for TraitInfo {
1222     fn cmp(&self, other: &TraitInfo) -> Ordering {
1223         // Local crates are more important than remote ones (local:
1224         // `cnum == 0`), and otherwise we throw in the defid for totality.
1225
1226         let lhs = (other.def_id.krate, other.def_id);
1227         let rhs = (self.def_id.krate, self.def_id);
1228         lhs.cmp(&rhs)
1229     }
1230 }
1231
1232 /// Retrieves all traits in this crate and any dependent crates.
1233 pub fn all_traits(tcx: TyCtxt<'_>) -> Vec<TraitInfo> {
1234     tcx.all_traits(LOCAL_CRATE).iter().map(|&def_id| TraitInfo { def_id }).collect()
1235 }
1236
1237 /// Computes all traits in this crate and any dependent crates.
1238 fn compute_all_traits(tcx: TyCtxt<'_>) -> Vec<DefId> {
1239     use hir::itemlikevisit;
1240
1241     let mut traits = vec![];
1242
1243     // Crate-local:
1244
1245     struct Visitor<'a, 'tcx> {
1246         map: &'a hir_map::Map<'tcx>,
1247         traits: &'a mut Vec<DefId>,
1248     }
1249
1250     impl<'v, 'a, 'tcx> itemlikevisit::ItemLikeVisitor<'v> for Visitor<'a, 'tcx> {
1251         fn visit_item(&mut self, i: &'v hir::Item<'v>) {
1252             match i.kind {
1253                 hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..) => {
1254                     let def_id = self.map.local_def_id(i.hir_id);
1255                     self.traits.push(def_id.to_def_id());
1256                 }
1257                 _ => (),
1258             }
1259         }
1260
1261         fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
1262
1263         fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {}
1264     }
1265
1266     tcx.hir().krate().visit_all_item_likes(&mut Visitor { map: &tcx.hir(), traits: &mut traits });
1267
1268     // Cross-crate:
1269
1270     let mut external_mods = FxHashSet::default();
1271     fn handle_external_res(
1272         tcx: TyCtxt<'_>,
1273         traits: &mut Vec<DefId>,
1274         external_mods: &mut FxHashSet<DefId>,
1275         res: Res,
1276     ) {
1277         match res {
1278             Res::Def(DefKind::Trait | DefKind::TraitAlias, def_id) => {
1279                 traits.push(def_id);
1280             }
1281             Res::Def(DefKind::Mod, def_id) => {
1282                 if !external_mods.insert(def_id) {
1283                     return;
1284                 }
1285                 for child in tcx.item_children(def_id).iter() {
1286                     handle_external_res(tcx, traits, external_mods, child.res)
1287                 }
1288             }
1289             _ => {}
1290         }
1291     }
1292     for &cnum in tcx.crates().iter() {
1293         let def_id = DefId { krate: cnum, index: CRATE_DEF_INDEX };
1294         handle_external_res(tcx, &mut traits, &mut external_mods, Res::Def(DefKind::Mod, def_id));
1295     }
1296
1297     traits
1298 }
1299
1300 pub fn provide(providers: &mut ty::query::Providers<'_>) {
1301     providers.all_traits = |tcx, cnum| {
1302         assert_eq!(cnum, LOCAL_CRATE);
1303         &tcx.arena.alloc(compute_all_traits(tcx))[..]
1304     }
1305 }
1306
1307 struct UsePlacementFinder<'tcx> {
1308     target_module: hir::HirId,
1309     span: Option<Span>,
1310     found_use: bool,
1311     tcx: TyCtxt<'tcx>,
1312 }
1313
1314 impl UsePlacementFinder<'tcx> {
1315     fn check(
1316         tcx: TyCtxt<'tcx>,
1317         krate: &'tcx hir::Crate<'tcx>,
1318         target_module: hir::HirId,
1319     ) -> (Option<Span>, bool) {
1320         let mut finder = UsePlacementFinder { target_module, span: None, found_use: false, tcx };
1321         intravisit::walk_crate(&mut finder, krate);
1322         (finder.span, finder.found_use)
1323     }
1324 }
1325
1326 impl intravisit::Visitor<'tcx> for UsePlacementFinder<'tcx> {
1327     fn visit_mod(&mut self, module: &'tcx hir::Mod<'tcx>, _: Span, hir_id: hir::HirId) {
1328         if self.span.is_some() {
1329             return;
1330         }
1331         if hir_id != self.target_module {
1332             intravisit::walk_mod(self, module, hir_id);
1333             return;
1334         }
1335         // Find a `use` statement.
1336         for item_id in module.item_ids {
1337             let item = self.tcx.hir().expect_item(item_id.id);
1338             match item.kind {
1339                 hir::ItemKind::Use(..) => {
1340                     // Don't suggest placing a `use` before the prelude
1341                     // import or other generated ones.
1342                     if !item.span.from_expansion() {
1343                         self.span = Some(item.span.shrink_to_lo());
1344                         self.found_use = true;
1345                         return;
1346                     }
1347                 }
1348                 // Don't place `use` before `extern crate`...
1349                 hir::ItemKind::ExternCrate(_) => {}
1350                 // ...but do place them before the first other item.
1351                 _ => {
1352                     if self.span.map_or(true, |span| item.span < span) {
1353                         if !item.span.from_expansion() {
1354                             // Don't insert between attributes and an item.
1355                             if item.attrs.is_empty() {
1356                                 self.span = Some(item.span.shrink_to_lo());
1357                             } else {
1358                                 // Find the first attribute on the item.
1359                                 for attr in item.attrs {
1360                                     if self.span.map_or(true, |span| attr.span < span) {
1361                                         self.span = Some(attr.span.shrink_to_lo());
1362                                     }
1363                                 }
1364                             }
1365                         }
1366                     }
1367                 }
1368             }
1369         }
1370     }
1371
1372     type Map = intravisit::ErasedMap<'tcx>;
1373
1374     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1375         intravisit::NestedVisitorMap::None
1376     }
1377 }
1378
1379 fn print_disambiguation_help(
1380     item_name: Ident,
1381     args: Option<&'tcx [hir::Expr<'tcx>]>,
1382     err: &mut DiagnosticBuilder<'_>,
1383     trait_name: String,
1384     rcvr_ty: Ty<'_>,
1385     kind: ty::AssocKind,
1386     def_id: DefId,
1387     span: Span,
1388     candidate: Option<usize>,
1389     source_map: &source_map::SourceMap,
1390 ) {
1391     let mut applicability = Applicability::MachineApplicable;
1392     let sugg_args = if let (ty::AssocKind::Fn, Some(args)) = (kind, args) {
1393         format!(
1394             "({}{})",
1395             if rcvr_ty.is_region_ptr() {
1396                 if rcvr_ty.is_mutable_ptr() { "&mut " } else { "&" }
1397             } else {
1398                 ""
1399             },
1400             args.iter()
1401                 .map(|arg| source_map.span_to_snippet(arg.span).unwrap_or_else(|_| {
1402                     applicability = Applicability::HasPlaceholders;
1403                     "_".to_owned()
1404                 }))
1405                 .collect::<Vec<_>>()
1406                 .join(", "),
1407         )
1408     } else {
1409         String::new()
1410     };
1411     let sugg = format!("{}::{}{}", trait_name, item_name, sugg_args);
1412     err.span_suggestion(
1413         span,
1414         &format!(
1415             "disambiguate the {} for {}",
1416             kind.as_def_kind().descr(def_id),
1417             if let Some(candidate) = candidate {
1418                 format!("candidate #{}", candidate)
1419             } else {
1420                 "the candidate".to_string()
1421             },
1422         ),
1423         sugg,
1424         applicability,
1425     );
1426 }