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