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::ast;
   6 use rustc_ast::util::lev_distance;
   7 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
   8 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
   9 use rustc_hir as hir;
  10 use rustc_hir::def::{DefKind, Namespace, Res};
  11 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
  12 use rustc_hir::intravisit;
  13 use rustc_hir::lang_items::FnOnceTraitLangItem;
  14 use rustc_hir::{ExprKind, Node, QPath};
  15 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  16 use rustc_middle::hir::map as hir_map;
  17 use rustc_middle::ty::print::with_crate_prefix;
  18 use rustc_middle::ty::{
  19     self, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
  20 };
  21 use rustc_span::symbol::kw;
  22 use rustc_span::{source_map, FileName, Span};
  23 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
  24 use rustc_trait_selection::traits::Obligation;
  25
  26 use std::cmp::Ordering;
  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(FnOnceTraitLangItem) {
  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(),
  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: ast::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.impl_self_ty(span, impl_did).ty;
 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
 163                                 | ty::AssocKind::Type
 164                                 | ty::AssocKind::OpaqueTy => rcvr_ty,
 165                                 ty::AssocKind::Method => self
 166                                     .tcx
 167                                     .fn_sig(item.def_id)
 168                                     .inputs()
 169                                     .skip_binder()
 170                                     .get(0)
 171                                     .filter(|ty| ty.is_region_ptr() && !rcvr_ty.is_region_ptr())
 172                                     .copied()
 173                                     .unwrap_or(rcvr_ty),
 174                             };
 175                             print_disambiguation_help(
 176                                 item_name,
 177                                 args,
 178                                 err,
 179                                 path,
 180                                 ty,
 181                                 item.kind,
 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                             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                     if let (true, false, SelfSource::MethodCall(expr), Some(_)) = (
 275                         actual.is_numeric(),
 276                         actual.has_concrete_skeleton(),
 277                         source,
 278                         candidates.next(),
 279                     ) {
 280                         let mut err = struct_span_err!(
 281                             tcx.sess,
 282                             span,
 283                             E0689,
 284                             "can't call {} `{}` on ambiguous numeric type `{}`",
 285                             item_kind,
 286                             item_name,
 287                             ty_str
 288                         );
 289                         let concrete_type = if actual.is_integral() { "i32" } else { "f32" };
 290                         match expr.kind {
 291                             ExprKind::Lit(ref lit) => {
 292                                 // numeric literal
 293                                 let snippet = tcx
 294                                     .sess
 295                                     .source_map()
 296                                     .span_to_snippet(lit.span)
 297                                     .unwrap_or_else(|_| "<numeric literal>".to_owned());
 298
 299                                 err.span_suggestion(
 300                                     lit.span,
 301                                     &format!(
 302                                         "you must specify a concrete type for \
 303                                               this numeric value, like `{}`",
 304                                         concrete_type
 305                                     ),
 306                                     format!("{}_{}", snippet, concrete_type),
 307                                     Applicability::MaybeIncorrect,
 308                                 );
 309                             }
 310                             ExprKind::Path(ref qpath) => {
 311                                 // local binding
 312                                 if let &QPath::Resolved(_, ref path) = &qpath {
 313                                     if let hir::def::Res::Local(hir_id) = path.res {
 314                                         let span = tcx.hir().span(hir_id);
 315                                         let snippet = tcx.sess.source_map().span_to_snippet(span);
 316                                         let filename = tcx.sess.source_map().span_to_filename(span);
 317
 318                                         let parent_node = self
 319                                             .tcx
 320                                             .hir()
 321                                             .get(self.tcx.hir().get_parent_node(hir_id));
 322                                         let msg = format!(
 323                                             "you must specify a type for this binding, like `{}`",
 324                                             concrete_type,
 325                                         );
 326
 327                                         match (filename, parent_node, snippet) {
 328                                             (
 329                                                 FileName::Real(_),
 330                                                 Node::Local(hir::Local {
 331                                                     source: hir::LocalSource::Normal,
 332                                                     ty,
 333                                                     ..
 334                                                 }),
 335                                                 Ok(ref snippet),
 336                                             ) => {
 337                                                 err.span_suggestion(
 338                                                     // account for `let x: _ = 42;`
 339                                                     //                  ^^^^
 340                                                     span.to(ty
 341                                                         .as_ref()
 342                                                         .map(|ty| ty.span)
 343                                                         .unwrap_or(span)),
 344                                                     &msg,
 345                                                     format!("{}: {}", snippet, concrete_type),
 346                                                     Applicability::MaybeIncorrect,
 347                                                 );
 348                                             }
 349                                             _ => {
 350                                                 err.span_label(span, msg);
 351                                             }
 352                                         }
 353                                     }
 354                                 }
 355                             }
 356                             _ => {}
 357                         }
 358                         err.emit();
 359                         return None;
 360                     } else {
 361                         span = item_name.span;
 362                         let mut err = struct_span_err!(
 363                             tcx.sess,
 364                             span,
 365                             E0599,
 366                             "no {} named `{}` found for {} `{}` in the current scope",
 367                             item_kind,
 368                             item_name,
 369                             actual.prefix_string(),
 370                             ty_str,
 371                         );
 372                         if let Some(span) =
 373                             tcx.sess.confused_type_with_std_module.borrow().get(&span)
 374                         {
 375                             if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*span) {
 376                                 err.span_suggestion(
 377                                     *span,
 378                                     "you are looking for the module in `std`, \
 379                                      not the primitive type",
 380                                     format!("std::{}", snippet),
 381                                     Applicability::MachineApplicable,
 382                                 );
 383                             }
 384                         }
 385                         if let ty::RawPtr(_) = &actual.kind {
 386                             err.note(
 387                                 "try using `<*const T>::as_ref()` to get a reference to the \
 388                                       type behind the pointer: https://doc.rust-lang.org/std/\
 389                                       primitive.pointer.html#method.as_ref",
 390                             );
 391                             err.note(
 392                                 "using `<*const T>::as_ref()` on a pointer \
 393                                       which is unaligned or points to invalid \
 394                                       or uninitialized memory is undefined behavior",
 395                             );
 396                         }
 397                         err
 398                     }
 399                 } else {
 400                     tcx.sess.diagnostic().struct_dummy()
 401                 };
 402
 403                 if let Some(def) = actual.ty_adt_def() {
 404                     if let Some(full_sp) = tcx.hir().span_if_local(def.did) {
 405                         let def_sp = tcx.sess.source_map().guess_head_span(full_sp);
 406                         err.span_label(
 407                             def_sp,
 408                             format!(
 409                                 "{} `{}` not found {}",
 410                                 item_kind,
 411                                 item_name,
 412                                 if def.is_enum() && !is_method { "here" } else { "for this" }
 413                             ),
 414                         );
 415                     }
 416                 }
 417
 418                 // If the method name is the name of a field with a function or closure type,
 419                 // give a helping note that it has to be called as `(x.f)(...)`.
 420                 if let SelfSource::MethodCall(expr) = source {
 421                     let field_receiver =
 422                         self.autoderef(span, rcvr_ty).find_map(|(ty, _)| match ty.kind {
 423                             ty::Adt(def, substs) if !def.is_enum() => {
 424                                 let variant = &def.non_enum_variant();
 425                                 self.tcx.find_field_index(item_name, variant).map(|index| {
 426                                     let field = &variant.fields[index];
 427                                     let field_ty = field.ty(tcx, substs);
 428                                     (field, field_ty)
 429                                 })
 430                             }
 431                             _ => None,
 432                         });
 433
 434                     if let Some((field, field_ty)) = field_receiver {
 435                         let scope = self.tcx.parent_module(self.body_id).to_def_id();
 436                         let is_accessible = field.vis.is_accessible_from(scope, self.tcx);
 437
 438                         if is_accessible {
 439                             if self.is_fn_ty(&field_ty, span) {
 440                                 let expr_span = expr.span.to(item_name.span);
 441                                 err.multipart_suggestion(
 442                                     &format!(
 443                                         "to call the function stored in `{}`, \
 444                                          surround the field access with parentheses",
 445                                         item_name,
 446                                     ),
 447                                     vec![
 448                                         (expr_span.shrink_to_lo(), '('.to_string()),
 449                                         (expr_span.shrink_to_hi(), ')'.to_string()),
 450                                     ],
 451                                     Applicability::MachineApplicable,
 452                                 );
 453                             } else {
 454                                 let call_expr = self
 455                                     .tcx
 456                                     .hir()
 457                                     .expect_expr(self.tcx.hir().get_parent_node(expr.hir_id));
 458
 459                                 if let Some(span) = call_expr.span.trim_start(item_name.span) {
 460                                     err.span_suggestion(
 461                                         span,
 462                                         "remove the arguments",
 463                                         String::new(),
 464                                         Applicability::MaybeIncorrect,
 465                                     );
 466                                 }
 467                             }
 468                         }
 469
 470                         let field_kind = if is_accessible { "field" } else { "private field" };
 471                         err.span_label(item_name.span, format!("{}, not a method", field_kind));
 472                     } else if lev_candidate.is_none() && static_sources.is_empty() {
 473                         err.span_label(span, format!("{} not found in `{}`", item_kind, ty_str));
 474                         self.tcx.sess.trait_methods_not_found.borrow_mut().insert(orig_span);
 475                     }
 476                 } else {
 477                     err.span_label(span, format!("{} not found in `{}`", item_kind, ty_str));
 478                     self.tcx.sess.trait_methods_not_found.borrow_mut().insert(orig_span);
 479                 }
 480
 481                 if self.is_fn_ty(&rcvr_ty, span) {
 482                     macro_rules! report_function {
 483                         ($span:expr, $name:expr) => {
 484                             err.note(&format!(
 485                                 "`{}` is a function, perhaps you wish to call it",
 486                                 $name
 487                             ));
 488                         };
 489                     }
 490
 491                     if let SelfSource::MethodCall(expr) = source {
 492                         if let Ok(expr_string) = tcx.sess.source_map().span_to_snippet(expr.span) {
 493                             report_function!(expr.span, expr_string);
 494                         } else if let ExprKind::Path(QPath::Resolved(_, ref path)) = expr.kind {
 495                             if let Some(segment) = path.segments.last() {
 496                                 report_function!(expr.span, segment.ident);
 497                             }
 498                         }
 499                     }
 500                 }
 501
 502                 if !static_sources.is_empty() {
 503                     err.note(
 504                         "found the following associated functions; to be used as methods, \
 505                          functions must have a `self` parameter",
 506                     );
 507                     err.span_label(span, "this is an associated function, not a method");
 508                 }
 509                 if static_sources.len() == 1 {
 510                     let ty_str = if let Some(CandidateSource::ImplSource(impl_did)) =
 511                         static_sources.get(0)
 512                     {
 513                         // When the "method" is resolved through dereferencing, we really want the
 514                         // original type that has the associated function for accurate suggestions.
 515                         // (#61411)
 516                         let ty = self.impl_self_ty(span, *impl_did).ty;
 517                         match (&ty.peel_refs().kind, &actual.peel_refs().kind) {
 518                             (ty::Adt(def, _), ty::Adt(def_actual, _)) if def == def_actual => {
 519                                 // Use `actual` as it will have more `substs` filled in.
 520                                 self.ty_to_value_string(actual.peel_refs())
 521                             }
 522                             _ => self.ty_to_value_string(ty.peel_refs()),
 523                         }
 524                     } else {
 525                         self.ty_to_value_string(actual.peel_refs())
 526                     };
 527                     if let SelfSource::MethodCall(expr) = source {
 528                         err.span_suggestion(
 529                             expr.span.to(span),
 530                             "use associated function syntax instead",
 531                             format!("{}::{}", ty_str, item_name),
 532                             Applicability::MachineApplicable,
 533                         );
 534                     } else {
 535                         err.help(&format!("try with `{}::{}`", ty_str, item_name,));
 536                     }
 537
 538                     report_candidates(span, &mut err, static_sources, sugg_span);
 539                 } else if static_sources.len() > 1 {
 540                     report_candidates(span, &mut err, static_sources, sugg_span);
 541                 }
 542
 543                 let mut restrict_type_params = false;
 544                 if !unsatisfied_predicates.is_empty() {
 545                     let def_span = |def_id| {
 546                         self.tcx.sess.source_map().guess_head_span(self.tcx.def_span(def_id))
 547                     };
 548                     let mut type_params = FxHashMap::default();
 549                     let mut bound_spans = vec![];
 550                     let mut collect_type_param_suggestions =
 551                         |self_ty: Ty<'_>, parent_pred: &ty::Predicate<'_>, obligation: &str| {
 552                             if let (ty::Param(_), ty::Predicate::Trait(p, _)) =
 553                                 (&self_ty.kind, parent_pred)
 554                             {
 555                                 if let ty::Adt(def, _) = p.skip_binder().trait_ref.self_ty().kind {
 556                                     let node = self
 557                                         .tcx
 558                                         .hir()
 559                                         .as_local_hir_id(def.did)
 560                                         .map(|id| self.tcx.hir().get(id));
 561                                     if let Some(hir::Node::Item(hir::Item { kind, .. })) = node {
 562                                         if let Some(g) = kind.generics() {
 563                                             let key = match &g.where_clause.predicates[..] {
 564                                                 [.., pred] => (pred.span().shrink_to_hi(), false),
 565                                                 [] => (
 566                                                     g.where_clause
 567                                                         .span_for_predicates_or_empty_place(),
 568                                                     true,
 569                                                 ),
 570                                             };
 571                                             type_params
 572                                                 .entry(key)
 573                                                 .or_insert_with(FxHashSet::default)
 574                                                 .insert(obligation.to_owned());
 575                                         }
 576                                     }
 577                                 }
 578                             }
 579                         };
 580                     let mut bound_span_label = |self_ty: Ty<'_>, obligation: &str, quiet: &str| {
 581                         let msg = format!(
 582                             "doesn't satisfy `{}`",
 583                             if obligation.len() > 50 { quiet } else { obligation }
 584                         );
 585                         match &self_ty.kind {
 586                             // Point at the type that couldn't satisfy the bound.
 587                             ty::Adt(def, _) => bound_spans.push((def_span(def.did), msg)),
 588                             // Point at the trait object that couldn't satisfy the bound.
 589                             ty::Dynamic(preds, _) => {
 590                                 for pred in *preds.skip_binder() {
 591                                     match pred {
 592                                         ty::ExistentialPredicate::Trait(tr) => {
 593                                             bound_spans.push((def_span(tr.def_id), msg.clone()))
 594                                         }
 595                                         ty::ExistentialPredicate::Projection(_)
 596                                         | ty::ExistentialPredicate::AutoTrait(_) => {}
 597                                     }
 598                                 }
 599                             }
 600                             // Point at the closure that couldn't satisfy the bound.
 601                             ty::Closure(def_id, _) => bound_spans
 602                                 .push((def_span(*def_id), format!("doesn't satisfy `{}`", quiet))),
 603                             _ => {}
 604                         }
 605                     };
 606                     let mut format_pred = |pred| {
 607                         match pred {
 608                             ty::Predicate::Projection(pred) => {
 609                                 // `<Foo as Iterator>::Item = String`.
 610                                 let trait_ref =
 611                                     pred.skip_binder().projection_ty.trait_ref(self.tcx);
 612                                 let assoc = self
 613                                     .tcx
 614                                     .associated_item(pred.skip_binder().projection_ty.item_def_id);
 615                                 let ty = pred.skip_binder().ty;
 616                                 let obligation = format!("{}::{} = {}", trait_ref, assoc.ident, ty);
 617                                 let quiet = format!(
 618                                     "<_ as {}>::{} = {}",
 619                                     trait_ref.print_only_trait_path(),
 620                                     assoc.ident,
 621                                     ty
 622                                 );
 623                                 bound_span_label(trait_ref.self_ty(), &obligation, &quiet);
 624                                 Some((obligation, trait_ref.self_ty()))
 625                             }
 626                             ty::Predicate::Trait(poly_trait_ref, _) => {
 627                                 let p = poly_trait_ref.skip_binder().trait_ref;
 628                                 let self_ty = p.self_ty();
 629                                 let path = p.print_only_trait_path();
 630                                 let obligation = format!("{}: {}", self_ty, path);
 631                                 let quiet = format!("_: {}", path);
 632                                 bound_span_label(self_ty, &obligation, &quiet);
 633                                 Some((obligation, self_ty))
 634                             }
 635                             _ => None,
 636                         }
 637                     };
 638                     let mut bound_list = unsatisfied_predicates
 639                         .iter()
 640                         .filter_map(|(pred, parent_pred)| {
 641                             format_pred(*pred).map(|(p, self_ty)| match parent_pred {
 642                                 None => format!("`{}`", p),
 643                                 Some(parent_pred) => match format_pred(*parent_pred) {
 644                                     None => format!("`{}`", p),
 645                                     Some((parent_p, _)) => {
 646                                         collect_type_param_suggestions(self_ty, parent_pred, &p);
 647                                         format!("`{}`\nwhich is required by `{}`", p, parent_p)
 648                                     }
 649                                 },
 650                             })
 651                         })
 652                         .enumerate()
 653                         .collect::<Vec<(usize, String)>>();
 654                     for ((span, empty_where), obligations) in type_params.into_iter() {
 655                         restrict_type_params = true;
 656                         err.span_suggestion_verbose(
 657                             span,
 658                             &format!(
 659                                 "consider restricting the type parameter{s} to satisfy the \
 660                                  trait bound{s}",
 661                                 s = pluralize!(obligations.len())
 662                             ),
 663                             format!(
 664                                 "{} {}",
 665                                 if empty_where { " where" } else { "," },
 666                                 obligations.into_iter().collect::<Vec<_>>().join(", ")
 667                             ),
 668                             Applicability::MaybeIncorrect,
 669                         );
 670                     }
 671
 672                     bound_list.sort_by(|(_, a), (_, b)| a.cmp(&b)); // Sort alphabetically.
 673                     bound_list.dedup_by(|(_, a), (_, b)| a == b); // #35677
 674                     bound_list.sort_by_key(|(pos, _)| *pos); // Keep the original predicate order.
 675                     bound_spans.sort();
 676                     bound_spans.dedup();
 677                     for (span, msg) in bound_spans.into_iter() {
 678                         err.span_label(span, &msg);
 679                     }
 680                     if !bound_list.is_empty() {
 681                         let bound_list = bound_list
 682                             .into_iter()
 683                             .map(|(_, path)| path)
 684                             .collect::<Vec<_>>()
 685                             .join("\n");
 686                         err.note(&format!(
 687                             "the method `{}` exists but the following trait bounds were not \
 688                              satisfied:\n{}",
 689                             item_name, bound_list
 690                         ));
 691                     }
 692                 }
 693
 694                 if actual.is_numeric() && actual.is_fresh() || restrict_type_params {
 695                 } else {
 696                     self.suggest_traits_to_import(
 697                         &mut err,
 698                         span,
 699                         rcvr_ty,
 700                         item_name,
 701                         source,
 702                         out_of_scope_traits,
 703                         &unsatisfied_predicates,
 704                     );
 705                 }
 706
 707                 if actual.is_enum() {
 708                     let adt_def = actual.ty_adt_def().expect("enum is not an ADT");
 709                     if let Some(suggestion) = lev_distance::find_best_match_for_name(
 710                         adt_def.variants.iter().map(|s| &s.ident.name),
 711                         &item_name.as_str(),
 712                         None,
 713                     ) {
 714                         err.span_suggestion(
 715                             span,
 716                             "there is a variant with a similar name",
 717                             suggestion.to_string(),
 718                             Applicability::MaybeIncorrect,
 719                         );
 720                     }
 721                 }
 722
 723                 let mut fallback_span = true;
 724                 let msg = "remove this method call";
 725                 if item_name.as_str() == "as_str" && actual.peel_refs().is_str() {
 726                     if let SelfSource::MethodCall(expr) = source {
 727                         let call_expr =
 728                             self.tcx.hir().expect_expr(self.tcx.hir().get_parent_node(expr.hir_id));
 729                         if let Some(span) = call_expr.span.trim_start(expr.span) {
 730                             err.span_suggestion(
 731                                 span,
 732                                 msg,
 733                                 String::new(),
 734                                 Applicability::MachineApplicable,
 735                             );
 736                             fallback_span = false;
 737                         }
 738                     }
 739                     if fallback_span {
 740                         err.span_label(span, msg);
 741                     }
 742                 } else if let Some(lev_candidate) = lev_candidate {
 743                     let def_kind = lev_candidate.def_kind();
 744                     err.span_suggestion(
 745                         span,
 746                         &format!(
 747                             "there is {} {} with a similar name",
 748                             def_kind.article(),
 749                             def_kind.descr(lev_candidate.def_id),
 750                         ),
 751                         lev_candidate.ident.to_string(),
 752                         Applicability::MaybeIncorrect,
 753                     );
 754                 }
 755
 756                 return Some(err);
 757             }
 758
 759             MethodError::Ambiguity(sources) => {
 760                 let mut err = struct_span_err!(
 761                     self.sess(),
 762                     item_name.span,
 763                     E0034,
 764                     "multiple applicable items in scope"
 765                 );
 766                 err.span_label(item_name.span, format!("multiple `{}` found", item_name));
 767
 768                 report_candidates(span, &mut err, sources, sugg_span);
 769                 err.emit();
 770             }
 771
 772             MethodError::PrivateMatch(kind, def_id, out_of_scope_traits) => {
 773                 let kind = kind.descr(def_id);
 774                 let mut err = struct_span_err!(
 775                     self.tcx.sess,
 776                     item_name.span,
 777                     E0624,
 778                     "{} `{}` is private",
 779                     kind,
 780                     item_name
 781                 );
 782                 err.span_label(item_name.span, &format!("private {}", kind));
 783                 self.suggest_valid_traits(&mut err, out_of_scope_traits);
 784                 err.emit();
 785             }
 786
 787             MethodError::IllegalSizedBound(candidates, needs_mut, bound_span) => {
 788                 let msg = format!("the `{}` method cannot be invoked on a trait object", item_name);
 789                 let mut err = self.sess().struct_span_err(span, &msg);
 790                 err.span_label(bound_span, "this has a `Sized` requirement");
 791                 if !candidates.is_empty() {
 792                     let help = format!(
 793                         "{an}other candidate{s} {were} found in the following trait{s}, perhaps \
 794                          add a `use` for {one_of_them}:",
 795                         an = if candidates.len() == 1 { "an" } else { "" },
 796                         s = pluralize!(candidates.len()),
 797                         were = if candidates.len() == 1 { "was" } else { "were" },
 798                         one_of_them = if candidates.len() == 1 { "it" } else { "one_of_them" },
 799                     );
 800                     self.suggest_use_candidates(&mut err, help, candidates);
 801                 }
 802                 if let ty::Ref(region, t_type, mutability) = rcvr_ty.kind {
 803                     if needs_mut {
 804                         let trait_type = self.tcx.mk_ref(
 805                             region,
 806                             ty::TypeAndMut { ty: t_type, mutbl: mutability.invert() },
 807                         );
 808                         err.note(&format!("you need `{}` instead of `{}`", trait_type, rcvr_ty));
 809                     }
 810                 }
 811                 err.emit();
 812             }
 813
 814             MethodError::BadReturnType => bug!("no return type expectations but got BadReturnType"),
 815         }
 816         None
 817     }
 818
 819     /// Print out the type for use in value namespace.
 820     fn ty_to_value_string(&self, ty: Ty<'tcx>) -> String {
 821         match ty.kind {
 822             ty::Adt(def, substs) => format!("{}", ty::Instance::new(def.did, substs)),
 823             _ => self.ty_to_string(ty),
 824         }
 825     }
 826
 827     fn suggest_use_candidates(
 828         &self,
 829         err: &mut DiagnosticBuilder<'_>,
 830         mut msg: String,
 831         candidates: Vec<DefId>,
 832     ) {
 833         let module_did = self.tcx.parent_module(self.body_id);
 834         let module_id = self.tcx.hir().as_local_hir_id(module_did.to_def_id()).unwrap();
 835         let krate = self.tcx.hir().krate();
 836         let (span, found_use) = UsePlacementFinder::check(self.tcx, krate, module_id);
 837         if let Some(span) = span {
 838             let path_strings = candidates.iter().map(|did| {
 839                 // Produce an additional newline to separate the new use statement
 840                 // from the directly following item.
 841                 let additional_newline = if found_use { "" } else { "\n" };
 842                 format!(
 843                     "use {};\n{}",
 844                     with_crate_prefix(|| self.tcx.def_path_str(*did)),
 845                     additional_newline
 846                 )
 847             });
 848
 849             err.span_suggestions(span, &msg, path_strings, Applicability::MaybeIncorrect);
 850         } else {
 851             let limit = if candidates.len() == 5 { 5 } else { 4 };
 852             for (i, trait_did) in candidates.iter().take(limit).enumerate() {
 853                 if candidates.len() > 1 {
 854                     msg.push_str(&format!(
 855                         "\ncandidate #{}: `use {};`",
 856                         i + 1,
 857                         with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
 858                     ));
 859                 } else {
 860                     msg.push_str(&format!(
 861                         "\n`use {};`",
 862                         with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
 863                     ));
 864                 }
 865             }
 866             if candidates.len() > limit {
 867                 msg.push_str(&format!("\nand {} others", candidates.len() - limit));
 868             }
 869             err.note(&msg[..]);
 870         }
 871     }
 872
 873     fn suggest_valid_traits(
 874         &self,
 875         err: &mut DiagnosticBuilder<'_>,
 876         valid_out_of_scope_traits: Vec<DefId>,
 877     ) -> bool {
 878         if !valid_out_of_scope_traits.is_empty() {
 879             let mut candidates = valid_out_of_scope_traits;
 880             candidates.sort();
 881             candidates.dedup();
 882             err.help("items from traits can only be used if the trait is in scope");
 883             let msg = format!(
 884                 "the following {traits_are} implemented but not in scope; \
 885                  perhaps add a `use` for {one_of_them}:",
 886                 traits_are = if candidates.len() == 1 { "trait is" } else { "traits are" },
 887                 one_of_them = if candidates.len() == 1 { "it" } else { "one of them" },
 888             );
 889
 890             self.suggest_use_candidates(err, msg, candidates);
 891             true
 892         } else {
 893             false
 894         }
 895     }
 896
 897     fn suggest_traits_to_import<'b>(
 898         &self,
 899         err: &mut DiagnosticBuilder<'_>,
 900         span: Span,
 901         rcvr_ty: Ty<'tcx>,
 902         item_name: ast::Ident,
 903         source: SelfSource<'b>,
 904         valid_out_of_scope_traits: Vec<DefId>,
 905         unsatisfied_predicates: &[(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>)],
 906     ) {
 907         if self.suggest_valid_traits(err, valid_out_of_scope_traits) {
 908             return;
 909         }
 910
 911         let type_is_local = self.type_derefs_to_local(span, rcvr_ty, source);
 912
 913         let mut arbitrary_rcvr = vec![];
 914         // There are no traits implemented, so lets suggest some traits to
 915         // implement, by finding ones that have the item name, and are
 916         // legal to implement.
 917         let mut candidates = all_traits(self.tcx)
 918             .into_iter()
 919             .filter(|info| {
 920                 // We approximate the coherence rules to only suggest
 921                 // traits that are legal to implement by requiring that
 922                 // either the type or trait is local. Multi-dispatch means
 923                 // this isn't perfect (that is, there are cases when
 924                 // implementing a trait would be legal but is rejected
 925                 // here).
 926                 !unsatisfied_predicates.iter().any(|(p, _)| match p {
 927                     // Hide traits if they are present in predicates as they can be fixed without
 928                     // having to implement them.
 929                     ty::Predicate::Trait(t, _) => t.def_id() != info.def_id,
 930                     ty::Predicate::Projection(p) => p.item_def_id() != info.def_id,
 931                     _ => true,
 932                 }) && (type_is_local || info.def_id.is_local())
 933                     && self
 934                         .associated_item(info.def_id, item_name, Namespace::ValueNS)
 935                         .filter(|item| {
 936                             if let ty::AssocKind::Method = item.kind {
 937                                 let id = self.tcx.hir().as_local_hir_id(item.def_id);
 938                                 if let Some(hir::Node::TraitItem(hir::TraitItem {
 939                                     kind: hir::TraitItemKind::Fn(fn_sig, method),
 940                                     ..
 941                                 })) = id.map(|id| self.tcx.hir().get(id))
 942                                 {
 943                                     let self_first_arg = match method {
 944                                         hir::TraitFn::Required([ident, ..]) => {
 945                                             ident.name == kw::SelfLower
 946                                         }
 947                                         hir::TraitFn::Provided(body_id) => {
 948                                             match &self.tcx.hir().body(*body_id).params[..] {
 949                                                 [hir::Param {
 950                                                     pat:
 951                                                         hir::Pat {
 952                                                             kind:
 953                                                                 hir::PatKind::Binding(
 954                                                                     _,
 955                                                                     _,
 956                                                                     ident,
 957                                                                     ..,
 958                                                                 ),
 959                                                             ..
 960                                                         },
 961                                                     ..
 962                                                 }, ..] => ident.name == kw::SelfLower,
 963                                                 _ => false,
 964                                             }
 965                                         }
 966                                         _ => false,
 967                                     };
 968
 969                                     if !fn_sig.decl.implicit_self.has_implicit_self()
 970                                         && self_first_arg
 971                                     {
 972                                         if let Some(ty) = fn_sig.decl.inputs.get(0) {
 973                                             arbitrary_rcvr.push(ty.span);
 974                                         }
 975                                         return false;
 976                                     }
 977                                 }
 978                             }
 979                             // We only want to suggest public or local traits (#45781).
 980                             item.vis == ty::Visibility::Public || info.def_id.is_local()
 981                         })
 982                         .is_some()
 983             })
 984             .collect::<Vec<_>>();
 985         for span in &arbitrary_rcvr {
 986             err.span_label(
 987                 *span,
 988                 "the method might not be found because of this arbitrary self type",
 989             );
 990         }
 991
 992         if !candidates.is_empty() {
 993             // Sort from most relevant to least relevant.
 994             candidates.sort_by(|a, b| a.cmp(b).reverse());
 995             candidates.dedup();
 996
 997             let param_type = match rcvr_ty.kind {
 998                 ty::Param(param) => Some(param),
 999                 ty::Ref(_, ty, _) => match ty.kind {
1000                     ty::Param(param) => Some(param),
1001                     _ => None,
1002                 },
1003                 _ => None,
1004             };
1005             err.help(if param_type.is_some() {
1006                 "items from traits can only be used if the type parameter is bounded by the trait"
1007             } else {
1008                 "items from traits can only be used if the trait is implemented and in scope"
1009             });
1010             let message = |action| {
1011                 format!(
1012                     "the following {traits_define} an item `{name}`, perhaps you need to {action} \
1013                      {one_of_them}:",
1014                     traits_define =
1015                         if candidates.len() == 1 { "trait defines" } else { "traits define" },
1016                     action = action,
1017                     one_of_them = if candidates.len() == 1 { "it" } else { "one of them" },
1018                     name = item_name,
1019                 )
1020             };
1021             // Obtain the span for `param` and use it for a structured suggestion.
1022             let mut suggested = false;
1023             if let (Some(ref param), Some(ref table)) = (param_type, self.in_progress_tables) {
1024                 let table_owner = table.borrow().hir_owner;
1025                 if let Some(table_owner) = table_owner {
1026                     let generics = self.tcx.generics_of(table_owner.to_def_id());
1027                     let type_param = generics.type_param(param, self.tcx);
1028                     let hir = &self.tcx.hir();
1029                     if let Some(id) = hir.as_local_hir_id(type_param.def_id) {
1030                         // Get the `hir::Param` to verify whether it already has any bounds.
1031                         // We do this to avoid suggesting code that ends up as `T: FooBar`,
1032                         // instead we suggest `T: Foo + Bar` in that case.
1033                         match hir.get(id) {
1034                             Node::GenericParam(ref param) => {
1035                                 let mut impl_trait = false;
1036                                 let has_bounds = if let hir::GenericParamKind::Type {
1037                                     synthetic: Some(_),
1038                                     ..
1039                                 } = &param.kind
1040                                 {
1041                                     // We've found `fn foo(x: impl Trait)` instead of
1042                                     // `fn foo<T>(x: T)`. We want to suggest the correct
1043                                     // `fn foo(x: impl Trait + TraitBound)` instead of
1044                                     // `fn foo<T: TraitBound>(x: T)`. (#63706)
1045                                     impl_trait = true;
1046                                     param.bounds.get(1)
1047                                 } else {
1048                                     param.bounds.get(0)
1049                                 };
1050                                 let sp = hir.span(id);
1051                                 let sp = if let Some(first_bound) = has_bounds {
1052                                     // `sp` only covers `T`, change it so that it covers
1053                                     // `T:` when appropriate
1054                                     sp.until(first_bound.span())
1055                                 } else {
1056                                     sp
1057                                 };
1058                                 let trait_def_ids: FxHashSet<DefId> = param
1059                                     .bounds
1060                                     .iter()
1061                                     .filter_map(|bound| Some(bound.trait_ref()?.trait_def_id()?))
1062                                     .collect();
1063                                 if !candidates.iter().any(|t| trait_def_ids.contains(&t.def_id)) {
1064                                     err.span_suggestions(
1065                                         sp,
1066                                         &message(format!(
1067                                             "restrict type parameter `{}` with",
1068                                             param.name.ident(),
1069                                         )),
1070                                         candidates.iter().map(|t| {
1071                                             format!(
1072                                                 "{}{} {}{}",
1073                                                 param.name.ident(),
1074                                                 if impl_trait { " +" } else { ":" },
1075                                                 self.tcx.def_path_str(t.def_id),
1076                                                 if has_bounds.is_some() { " + " } else { "" },
1077                                             )
1078                                         }),
1079                                         Applicability::MaybeIncorrect,
1080                                     );
1081                                 }
1082                                 suggested = true;
1083                             }
1084                             Node::Item(hir::Item {
1085                                 kind: hir::ItemKind::Trait(.., bounds, _),
1086                                 ident,
1087                                 ..
1088                             }) => {
1089                                 let (sp, sep, article) = if bounds.is_empty() {
1090                                     (ident.span.shrink_to_hi(), ":", "a")
1091                                 } else {
1092                                     (bounds.last().unwrap().span().shrink_to_hi(), " +", "another")
1093                                 };
1094                                 err.span_suggestions(
1095                                     sp,
1096                                     &message(format!("add {} supertrait for", article)),
1097                                     candidates.iter().map(|t| {
1098                                         format!("{} {}", sep, self.tcx.def_path_str(t.def_id),)
1099                                     }),
1100                                     Applicability::MaybeIncorrect,
1101                                 );
1102                                 suggested = true;
1103                             }
1104                             _ => {}
1105                         }
1106                     }
1107                 };
1108             }
1109
1110             if !suggested {
1111                 let action = if let Some(param) = param_type {
1112                     format!("restrict type parameter `{}` with", param)
1113                 } else {
1114                     // FIXME: it might only need to be imported into scope, not implemented.
1115                     "implement".to_string()
1116                 };
1117                 let mut use_note = true;
1118                 if let [trait_info] = &candidates[..] {
1119                     if let Some(span) = self.tcx.hir().span_if_local(trait_info.def_id) {
1120                         err.span_note(
1121                             self.tcx.sess.source_map().guess_head_span(span),
1122                             &format!(
1123                                 "`{}` defines an item `{}`, perhaps you need to {} it",
1124                                 self.tcx.def_path_str(trait_info.def_id),
1125                                 item_name,
1126                                 action
1127                             ),
1128                         );
1129                         use_note = false
1130                     }
1131                 }
1132                 if use_note {
1133                     let mut msg = message(action);
1134                     for (i, trait_info) in candidates.iter().enumerate() {
1135                         msg.push_str(&format!(
1136                             "\ncandidate #{}: `{}`",
1137                             i + 1,
1138                             self.tcx.def_path_str(trait_info.def_id),
1139                         ));
1140                     }
1141                     err.note(&msg[..]);
1142                 }
1143             }
1144         }
1145     }
1146
1147     /// Checks whether there is a local type somewhere in the chain of
1148     /// autoderefs of `rcvr_ty`.
1149     fn type_derefs_to_local(&self, span: Span, rcvr_ty: Ty<'tcx>, source: SelfSource<'_>) -> bool {
1150         fn is_local(ty: Ty<'_>) -> bool {
1151             match ty.kind {
1152                 ty::Adt(def, _) => def.did.is_local(),
1153                 ty::Foreign(did) => did.is_local(),
1154
1155                 ty::Dynamic(ref tr, ..) => {
1156                     tr.principal().map(|d| d.def_id().is_local()).unwrap_or(false)
1157                 }
1158
1159                 ty::Param(_) => true,
1160
1161                 // Everything else (primitive types, etc.) is effectively
1162                 // non-local (there are "edge" cases, e.g., `(LocalType,)`, but
1163                 // the noise from these sort of types is usually just really
1164                 // annoying, rather than any sort of help).
1165                 _ => false,
1166             }
1167         }
1168
1169         // This occurs for UFCS desugaring of `T::method`, where there is no
1170         // receiver expression for the method call, and thus no autoderef.
1171         if let SelfSource::QPath(_) = source {
1172             return is_local(self.resolve_vars_with_obligations(rcvr_ty));
1173         }
1174
1175         self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))
1176     }
1177 }
1178
1179 #[derive(Copy, Clone)]
1180 pub enum SelfSource<'a> {
1181     QPath(&'a hir::Ty<'a>),
1182     MethodCall(&'a hir::Expr<'a> /* rcvr */),
1183 }
1184
1185 #[derive(Copy, Clone)]
1186 pub struct TraitInfo {
1187     pub def_id: DefId,
1188 }
1189
1190 impl PartialEq for TraitInfo {
1191     fn eq(&self, other: &TraitInfo) -> bool {
1192         self.cmp(other) == Ordering::Equal
1193     }
1194 }
1195 impl Eq for TraitInfo {}
1196 impl PartialOrd for TraitInfo {
1197     fn partial_cmp(&self, other: &TraitInfo) -> Option<Ordering> {
1198         Some(self.cmp(other))
1199     }
1200 }
1201 impl Ord for TraitInfo {
1202     fn cmp(&self, other: &TraitInfo) -> Ordering {
1203         // Local crates are more important than remote ones (local:
1204         // `cnum == 0`), and otherwise we throw in the defid for totality.
1205
1206         let lhs = (other.def_id.krate, other.def_id);
1207         let rhs = (self.def_id.krate, self.def_id);
1208         lhs.cmp(&rhs)
1209     }
1210 }
1211
1212 /// Retrieves all traits in this crate and any dependent crates.
1213 pub fn all_traits(tcx: TyCtxt<'_>) -> Vec<TraitInfo> {
1214     tcx.all_traits(LOCAL_CRATE).iter().map(|&def_id| TraitInfo { def_id }).collect()
1215 }
1216
1217 /// Computes all traits in this crate and any dependent crates.
1218 fn compute_all_traits(tcx: TyCtxt<'_>) -> Vec<DefId> {
1219     use hir::itemlikevisit;
1220
1221     let mut traits = vec![];
1222
1223     // Crate-local:
1224
1225     struct Visitor<'a, 'tcx> {
1226         map: &'a hir_map::Map<'tcx>,
1227         traits: &'a mut Vec<DefId>,
1228     }
1229
1230     impl<'v, 'a, 'tcx> itemlikevisit::ItemLikeVisitor<'v> for Visitor<'a, 'tcx> {
1231         fn visit_item(&mut self, i: &'v hir::Item<'v>) {
1232             match i.kind {
1233                 hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..) => {
1234                     let def_id = self.map.local_def_id(i.hir_id);
1235                     self.traits.push(def_id);
1236                 }
1237                 _ => (),
1238             }
1239         }
1240
1241         fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
1242
1243         fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {}
1244     }
1245
1246     tcx.hir().krate().visit_all_item_likes(&mut Visitor { map: &tcx.hir(), traits: &mut traits });
1247
1248     // Cross-crate:
1249
1250     let mut external_mods = FxHashSet::default();
1251     fn handle_external_res(
1252         tcx: TyCtxt<'_>,
1253         traits: &mut Vec<DefId>,
1254         external_mods: &mut FxHashSet<DefId>,
1255         res: Res,
1256     ) {
1257         match res {
1258             Res::Def(DefKind::Trait, def_id) | Res::Def(DefKind::TraitAlias, def_id) => {
1259                 traits.push(def_id);
1260             }
1261             Res::Def(DefKind::Mod, def_id) => {
1262                 if !external_mods.insert(def_id) {
1263                     return;
1264                 }
1265                 for child in tcx.item_children(def_id).iter() {
1266                     handle_external_res(tcx, traits, external_mods, child.res)
1267                 }
1268             }
1269             _ => {}
1270         }
1271     }
1272     for &cnum in tcx.crates().iter() {
1273         let def_id = DefId { krate: cnum, index: CRATE_DEF_INDEX };
1274         handle_external_res(tcx, &mut traits, &mut external_mods, Res::Def(DefKind::Mod, def_id));
1275     }
1276
1277     traits
1278 }
1279
1280 pub fn provide(providers: &mut ty::query::Providers<'_>) {
1281     providers.all_traits = |tcx, cnum| {
1282         assert_eq!(cnum, LOCAL_CRATE);
1283         &tcx.arena.alloc(compute_all_traits(tcx))[..]
1284     }
1285 }
1286
1287 struct UsePlacementFinder<'tcx> {
1288     target_module: hir::HirId,
1289     span: Option<Span>,
1290     found_use: bool,
1291     tcx: TyCtxt<'tcx>,
1292 }
1293
1294 impl UsePlacementFinder<'tcx> {
1295     fn check(
1296         tcx: TyCtxt<'tcx>,
1297         krate: &'tcx hir::Crate<'tcx>,
1298         target_module: hir::HirId,
1299     ) -> (Option<Span>, bool) {
1300         let mut finder = UsePlacementFinder { target_module, span: None, found_use: false, tcx };
1301         intravisit::walk_crate(&mut finder, krate);
1302         (finder.span, finder.found_use)
1303     }
1304 }
1305
1306 impl intravisit::Visitor<'tcx> for UsePlacementFinder<'tcx> {
1307     fn visit_mod(&mut self, module: &'tcx hir::Mod<'tcx>, _: Span, hir_id: hir::HirId) {
1308         if self.span.is_some() {
1309             return;
1310         }
1311         if hir_id != self.target_module {
1312             intravisit::walk_mod(self, module, hir_id);
1313             return;
1314         }
1315         // Find a `use` statement.
1316         for item_id in module.item_ids {
1317             let item = self.tcx.hir().expect_item(item_id.id);
1318             match item.kind {
1319                 hir::ItemKind::Use(..) => {
1320                     // Don't suggest placing a `use` before the prelude
1321                     // import or other generated ones.
1322                     if !item.span.from_expansion() {
1323                         self.span = Some(item.span.shrink_to_lo());
1324                         self.found_use = true;
1325                         return;
1326                     }
1327                 }
1328                 // Don't place `use` before `extern crate`...
1329                 hir::ItemKind::ExternCrate(_) => {}
1330                 // ...but do place them before the first other item.
1331                 _ => {
1332                     if self.span.map_or(true, |span| item.span < span) {
1333                         if !item.span.from_expansion() {
1334                             // Don't insert between attributes and an item.
1335                             if item.attrs.is_empty() {
1336                                 self.span = Some(item.span.shrink_to_lo());
1337                             } else {
1338                                 // Find the first attribute on the item.
1339                                 for attr in item.attrs {
1340                                     if self.span.map_or(true, |span| attr.span < span) {
1341                                         self.span = Some(attr.span.shrink_to_lo());
1342                                     }
1343                                 }
1344                             }
1345                         }
1346                     }
1347                 }
1348             }
1349         }
1350     }
1351
1352     type Map = intravisit::ErasedMap<'tcx>;
1353
1354     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1355         intravisit::NestedVisitorMap::None
1356     }
1357 }
1358
1359 fn print_disambiguation_help(
1360     item_name: ast::Ident,
1361     args: Option<&'tcx [hir::Expr<'tcx>]>,
1362     err: &mut DiagnosticBuilder<'_>,
1363     trait_name: String,
1364     rcvr_ty: Ty<'_>,
1365     kind: ty::AssocKind,
1366     span: Span,
1367     candidate: Option<usize>,
1368     source_map: &source_map::SourceMap,
1369 ) {
1370     let mut applicability = Applicability::MachineApplicable;
1371     let sugg_args = if let (ty::AssocKind::Method, Some(args)) = (kind, args) {
1372         format!(
1373             "({}{})",
1374             if rcvr_ty.is_region_ptr() {
1375                 if rcvr_ty.is_mutable_ptr() { "&mut " } else { "&" }
1376             } else {
1377                 ""
1378             },
1379             args.iter()
1380                 .map(|arg| source_map.span_to_snippet(arg.span).unwrap_or_else(|_| {
1381                     applicability = Applicability::HasPlaceholders;
1382                     "_".to_owned()
1383                 }))
1384                 .collect::<Vec<_>>()
1385                 .join(", "),
1386         )
1387     } else {
1388         String::new()
1389     };
1390     let sugg = format!("{}::{}{}", trait_name, item_name, sugg_args);
1391     err.span_suggestion(
1392         span,
1393         &format!(
1394             "disambiguate the {} for {}",
1395             kind.suggestion_descr(),
1396             if let Some(candidate) = candidate {
1397                 format!("candidate #{}", candidate)
1398             } else {
1399                 "the candidate".to_string()
1400             },
1401         ),
1402         sugg,
1403         applicability,
1404     );
1405 }