src/librustc_typeck/check/method/suggest.rs

   1 //! Give useful errors and suggestions to users when an item can't be
   2 //! found or is otherwise invalid.
   3
   4 use crate::check::FnCtxt;
   5 use rustc_ast::util::lev_distance;
   6 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
   7 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
   8 use rustc_hir as hir;
   9 use rustc_hir::def::{DefKind, Namespace, Res};
  10 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
  11 use rustc_hir::intravisit;
  12 use rustc_hir::lang_items::FnOnceTraitLangItem;
  13 use rustc_hir::{ExprKind, Node, QPath};
  14 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  15 use rustc_middle::hir::map as hir_map;
  16 use rustc_middle::ty::print::with_crate_prefix;
  17 use rustc_middle::ty::{
  18     self, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
  19 };
  20 use rustc_span::symbol::{kw, sym, Ident};
  21 use rustc_span::{source_map, FileName, Span};
  22 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
  23 use rustc_trait_selection::traits::Obligation;
  24
  25 use std::cmp::Ordering;
  26
  27 use super::probe::Mode;
  28 use super::{CandidateSource, MethodError, NoMatchData};
  29
  30 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  31     fn is_fn_ty(&self, ty: Ty<'tcx>, span: Span) -> bool {
  32         let tcx = self.tcx;
  33         match ty.kind {
  34             // Not all of these (e.g., unsafe fns) implement `FnOnce`,
  35             // so we look for these beforehand.
  36             ty::Closure(..) | ty::FnDef(..) | ty::FnPtr(_) => true,
  37             // If it's not a simple function, look for things which implement `FnOnce`.
  38             _ => {
  39                 let fn_once = match tcx.lang_items().require(FnOnceTraitLangItem) {
  40                     Ok(fn_once) => fn_once,
  41                     Err(..) => return false,
  42                 };
  43
  44                 self.autoderef(span, ty).any(|(ty, _)| {
  45                     self.probe(|_| {
  46                         let fn_once_substs = tcx.mk_substs_trait(
  47                             ty,
  48                             &[self
  49                                 .next_ty_var(TypeVariableOrigin {
  50                                     kind: TypeVariableOriginKind::MiscVariable,
  51                                     span,
  52                                 })
  53                                 .into()],
  54                         );
  55                         let trait_ref = ty::TraitRef::new(fn_once, fn_once_substs);
  56                         let poly_trait_ref = trait_ref.to_poly_trait_ref();
  57                         let obligation = Obligation::misc(
  58                             span,
  59                             self.body_id,
  60                             self.param_env,
  61                             poly_trait_ref.without_const().to_predicate(tcx),
  62                         );
  63                         self.predicate_may_hold(&obligation)
  64                     })
  65                 })
  66             }
  67         }
  68     }
  69
  70     pub fn report_method_error<'b>(
  71         &self,
  72         span: Span,
  73         rcvr_ty: Ty<'tcx>,
  74         item_name: Ident,
  75         source: SelfSource<'b>,
  76         error: MethodError<'tcx>,
  77         args: Option<&'tcx [hir::Expr<'tcx>]>,
  78     ) -> Option<DiagnosticBuilder<'_>> {
  79         let orig_span = span;
  80         let mut span = span;
  81         // Avoid suggestions when we don't know what's going on.
  82         if rcvr_ty.references_error() {
  83             return None;
  84         }
  85
  86         let report_candidates = |span: Span,
  87                                  err: &mut DiagnosticBuilder<'_>,
  88                                  mut sources: Vec<CandidateSource>,
  89                                  sugg_span: Span| {
  90             sources.sort();
  91             sources.dedup();
  92             // Dynamic limit to avoid hiding just one candidate, which is silly.
  93             let limit = if sources.len() == 5 { 5 } else { 4 };
  94
  95             for (idx, source) in sources.iter().take(limit).enumerate() {
  96                 match *source {
  97                     CandidateSource::ImplSource(impl_did) => {
  98                         // Provide the best span we can. Use the item, if local to crate, else
  99                         // the impl, if local to crate (item may be defaulted), else nothing.
 100                         let item = match self
 101                             .associated_item(impl_did, item_name, Namespace::ValueNS)
 102                             .or_else(|| {
 103                                 let impl_trait_ref = self.tcx.impl_trait_ref(impl_did)?;
 104                                 self.associated_item(
 105                                     impl_trait_ref.def_id,
 106                                     item_name,
 107                                     Namespace::ValueNS,
 108                                 )
 109                             }) {
 110                             Some(item) => item,
 111                             None => continue,
 112                         };
 113                         let note_span = self
 114                             .tcx
 115                             .hir()
 116                             .span_if_local(item.def_id)
 117                             .or_else(|| self.tcx.hir().span_if_local(impl_did));
 118
 119                         let impl_ty = self.tcx.at(span).type_of(impl_did);
 120
 121                         let insertion = match self.tcx.impl_trait_ref(impl_did) {
 122                             None => String::new(),
 123                             Some(trait_ref) => format!(
 124                                 " of the trait `{}`",
 125                                 self.tcx.def_path_str(trait_ref.def_id)
 126                             ),
 127                         };
 128
 129                         let (note_str, idx) = if sources.len() > 1 {
 130                             (
 131                                 format!(
 132                                     "candidate #{} is defined in an impl{} for the type `{}`",
 133                                     idx + 1,
 134                                     insertion,
 135                                     impl_ty,
 136                                 ),
 137                                 Some(idx + 1),
 138                             )
 139                         } else {
 140                             (
 141                                 format!(
 142                                     "the candidate is defined in an impl{} for the type `{}`",
 143                                     insertion, impl_ty,
 144                                 ),
 145                                 None,
 146                             )
 147                         };
 148                         if let Some(note_span) = note_span {
 149                             // We have a span pointing to the method. Show note with snippet.
 150                             err.span_note(
 151                                 self.tcx.sess.source_map().guess_head_span(note_span),
 152                                 &note_str,
 153                             );
 154                         } else {
 155                             err.note(&note_str);
 156                         }
 157                         if let Some(trait_ref) = self.tcx.impl_trait_ref(impl_did) {
 158                             let path = self.tcx.def_path_str(trait_ref.def_id);
 159
 160                             let ty = match item.kind {
 161                                 ty::AssocKind::Const | ty::AssocKind::Type => rcvr_ty,
 162                                 ty::AssocKind::Fn => self
 163                                     .tcx
 164                                     .fn_sig(item.def_id)
 165                                     .inputs()
 166                                     .skip_binder()
 167                                     .get(0)
 168                                     .filter(|ty| ty.is_region_ptr() && !rcvr_ty.is_region_ptr())
 169                                     .copied()
 170                                     .unwrap_or(rcvr_ty),
 171                             };
 172                             print_disambiguation_help(
 173                                 item_name,
 174                                 args,
 175                                 err,
 176                                 path,
 177                                 ty,
 178                                 item.kind,
 179                                 item.def_id,
 180                                 sugg_span,
 181                                 idx,
 182                                 self.tcx.sess.source_map(),
 183                             );
 184                         }
 185                     }
 186                     CandidateSource::TraitSource(trait_did) => {
 187                         let item =
 188                             match self.associated_item(trait_did, item_name, Namespace::ValueNS) {
 189                                 Some(item) => item,
 190                                 None => continue,
 191                             };
 192                         let item_span = self
 193                             .tcx
 194                             .sess
 195                             .source_map()
 196                             .guess_head_span(self.tcx.def_span(item.def_id));
 197                         let idx = if sources.len() > 1 {
 198                             let msg = &format!(
 199                                 "candidate #{} is defined in the trait `{}`",
 200                                 idx + 1,
 201                                 self.tcx.def_path_str(trait_did)
 202                             );
 203                             err.span_note(item_span, msg);
 204                             Some(idx + 1)
 205                         } else {
 206                             let msg = &format!(
 207                                 "the candidate is defined in the trait `{}`",
 208                                 self.tcx.def_path_str(trait_did)
 209                             );
 210                             err.span_note(item_span, msg);
 211                             None
 212                         };
 213                         let path = self.tcx.def_path_str(trait_did);
 214                         print_disambiguation_help(
 215                             item_name,
 216                             args,
 217                             err,
 218                             path,
 219                             rcvr_ty,
 220                             item.kind,
 221                             item.def_id,
 222                             sugg_span,
 223                             idx,
 224                             self.tcx.sess.source_map(),
 225                         );
 226                     }
 227                 }
 228             }
 229             if sources.len() > limit {
 230                 err.note(&format!("and {} others", sources.len() - limit));
 231             }
 232         };
 233
 234         let sugg_span = if let SelfSource::MethodCall(expr) = source {
 235             // Given `foo.bar(baz)`, `expr` is `bar`, but we want to point to the whole thing.
 236             self.tcx.hir().expect_expr(self.tcx.hir().get_parent_node(expr.hir_id)).span
 237         } else {
 238             span
 239         };
 240
 241         match error {
 242             MethodError::NoMatch(NoMatchData {
 243                 static_candidates: static_sources,
 244                 unsatisfied_predicates,
 245                 out_of_scope_traits,
 246                 lev_candidate,
 247                 mode,
 248             }) => {
 249                 let tcx = self.tcx;
 250
 251                 let actual = self.resolve_vars_if_possible(&rcvr_ty);
 252                 let ty_str = self.ty_to_string(actual);
 253                 let is_method = mode == Mode::MethodCall;
 254                 let item_kind = if is_method {
 255                     "method"
 256                 } else if actual.is_enum() {
 257                     "variant or associated item"
 258                 } else {
 259                     match (item_name.as_str().chars().next(), actual.is_fresh_ty()) {
 260                         (Some(name), false) if name.is_lowercase() => "function or associated item",
 261                         (Some(_), false) => "associated item",
 262                         (Some(_), true) | (None, false) => "variant or associated item",
 263                         (None, true) => "variant",
 264                     }
 265                 };
 266                 let mut err = if !actual.references_error() {
 267                     // Suggest clamping down the type if the method that is being attempted to
 268                     // be used exists at all, and the type is an ambiguous numeric type
 269                     // ({integer}/{float}).
 270                     let mut candidates = all_traits(self.tcx).into_iter().filter_map(|info| {
 271                         self.associated_item(info.def_id, item_name, Namespace::ValueNS)
 272                     });
 273                     // There are methods that are defined on the primitive types and won't be
 274                     // found when exploring `all_traits`, but we also need them to be acurate on
 275                     // our suggestions (#47759).
 276                     let fund_assoc = |opt_def_id: Option<DefId>| {
 277                         opt_def_id
 278                             .and_then(|id| self.associated_item(id, item_name, Namespace::ValueNS))
 279                             .is_some()
 280                     };
 281                     let lang_items = tcx.lang_items();
 282                     let found_candidate = candidates.next().is_some()
 283                         || fund_assoc(lang_items.i8_impl())
 284                         || fund_assoc(lang_items.i16_impl())
 285                         || fund_assoc(lang_items.i32_impl())
 286                         || fund_assoc(lang_items.i64_impl())
 287                         || fund_assoc(lang_items.i128_impl())
 288                         || fund_assoc(lang_items.u8_impl())
 289                         || fund_assoc(lang_items.u16_impl())
 290                         || fund_assoc(lang_items.u32_impl())
 291                         || fund_assoc(lang_items.u64_impl())
 292                         || fund_assoc(lang_items.u128_impl())
 293                         || fund_assoc(lang_items.f32_impl())
 294                         || fund_assoc(lang_items.f32_runtime_impl())
 295                         || fund_assoc(lang_items.f64_impl())
 296                         || fund_assoc(lang_items.f64_runtime_impl());
 297                     if let (true, false, SelfSource::MethodCall(expr), true) = (
 298                         actual.is_numeric(),
 299                         actual.has_concrete_skeleton(),
 300                         source,
 301                         found_candidate,
 302                     ) {
 303                         let mut err = struct_span_err!(
 304                             tcx.sess,
 305                             span,
 306                             E0689,
 307                             "can't call {} `{}` on ambiguous numeric type `{}`",
 308                             item_kind,
 309                             item_name,
 310                             ty_str
 311                         );
 312                         let concrete_type = if actual.is_integral() { "i32" } else { "f32" };
 313                         match expr.kind {
 314                             ExprKind::Lit(ref lit) => {
 315                                 // numeric literal
 316                                 let snippet = tcx
 317                                     .sess
 318                                     .source_map()
 319                                     .span_to_snippet(lit.span)
 320                                     .unwrap_or_else(|_| "<numeric literal>".to_owned());
 321
 322                                 err.span_suggestion(
 323                                     lit.span,
 324                                     &format!(
 325                                         "you must specify a concrete type for \
 326                                               this numeric value, like `{}`",
 327                                         concrete_type
 328                                     ),
 329                                     format!("{}_{}", snippet, concrete_type),
 330                                     Applicability::MaybeIncorrect,
 331                                 );
 332                             }
 333                             ExprKind::Path(ref qpath) => {
 334                                 // local binding
 335                                 if let &QPath::Resolved(_, ref path) = &qpath {
 336                                     if let hir::def::Res::Local(hir_id) = path.res {
 337                                         let span = tcx.hir().span(hir_id);
 338                                         let snippet = tcx.sess.source_map().span_to_snippet(span);
 339                                         let filename = tcx.sess.source_map().span_to_filename(span);
 340
 341                                         let parent_node = self
 342                                             .tcx
 343                                             .hir()
 344                                             .get(self.tcx.hir().get_parent_node(hir_id));
 345                                         let msg = format!(
 346                                             "you must specify a type for this binding, like `{}`",
 347                                             concrete_type,
 348                                         );
 349
 350                                         match (filename, parent_node, snippet) {
 351                                             (
 352                                                 FileName::Real(_),
 353                                                 Node::Local(hir::Local {
 354                                                     source: hir::LocalSource::Normal,
 355                                                     ty,
 356                                                     ..
 357                                                 }),
 358                                                 Ok(ref snippet),
 359                                             ) => {
 360                                                 err.span_suggestion(
 361                                                     // account for `let x: _ = 42;`
 362                                                     //                  ^^^^
 363                                                     span.to(ty
 364                                                         .as_ref()
 365                                                         .map(|ty| ty.span)
 366                                                         .unwrap_or(span)),
 367                                                     &msg,
 368                                                     format!("{}: {}", snippet, concrete_type),
 369                                                     Applicability::MaybeIncorrect,
 370                                                 );
 371                                             }
 372                                             _ => {
 373                                                 err.span_label(span, msg);
 374                                             }
 375                                         }
 376                                     }
 377                                 }
 378                             }
 379                             _ => {}
 380                         }
 381                         err.emit();
 382                         return None;
 383                     } else {
 384                         span = item_name.span;
 385                         let mut err = struct_span_err!(
 386                             tcx.sess,
 387                             span,
 388                             E0599,
 389                             "no {} named `{}` found for {} `{}` in the current scope",
 390                             item_kind,
 391                             item_name,
 392                             actual.prefix_string(),
 393                             ty_str,
 394                         );
 395                         if let Some(span) =
 396                             tcx.sess.confused_type_with_std_module.borrow().get(&span)
 397                         {
 398                             if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*span) {
 399                                 err.span_suggestion(
 400                                     *span,
 401                                     "you are looking for the module in `std`, \
 402                                      not the primitive type",
 403                                     format!("std::{}", snippet),
 404                                     Applicability::MachineApplicable,
 405                                 );
 406                             }
 407                         }
 408                         if let ty::RawPtr(_) = &actual.kind {
 409                             err.note(
 410                                 "try using `<*const T>::as_ref()` to get a reference to the \
 411                                       type behind the pointer: https://doc.rust-lang.org/std/\
 412                                       primitive.pointer.html#method.as_ref",
 413                             );
 414                             err.note(
 415                                 "using `<*const T>::as_ref()` on a pointer \
 416                                       which is unaligned or points to invalid \
 417                                       or uninitialized memory is undefined behavior",
 418                             );
 419                         }
 420                         err
 421                     }
 422                 } else {
 423                     tcx.sess.diagnostic().struct_dummy()
 424                 };
 425
 426                 if let Some(def) = actual.ty_adt_def() {
 427                     if let Some(full_sp) = tcx.hir().span_if_local(def.did) {
 428                         let def_sp = tcx.sess.source_map().guess_head_span(full_sp);
 429                         err.span_label(
 430                             def_sp,
 431                             format!(
 432                                 "{} `{}` not found {}",
 433                                 item_kind,
 434                                 item_name,
 435                                 if def.is_enum() && !is_method { "here" } else { "for this" }
 436                             ),
 437                         );
 438                     }
 439                 }
 440
 441                 // If the method name is the name of a field with a function or closure type,
 442                 // give a helping note that it has to be called as `(x.f)(...)`.
 443                 if let SelfSource::MethodCall(expr) = source {
 444                     let field_receiver =
 445                         self.autoderef(span, rcvr_ty).find_map(|(ty, _)| match ty.kind {
 446                             ty::Adt(def, substs) if !def.is_enum() => {
 447                                 let variant = &def.non_enum_variant();
 448                                 self.tcx.find_field_index(item_name, variant).map(|index| {
 449                                     let field = &variant.fields[index];
 450                                     let field_ty = field.ty(tcx, substs);
 451                                     (field, field_ty)
 452                                 })
 453                             }
 454                             _ => None,
 455                         });
 456
 457                     if let Some((field, field_ty)) = field_receiver {
 458                         let scope = self.tcx.parent_module(self.body_id).to_def_id();
 459                         let is_accessible = field.vis.is_accessible_from(scope, self.tcx);
 460
 461                         if is_accessible {
 462                             if self.is_fn_ty(&field_ty, span) {
 463                                 let expr_span = expr.span.to(item_name.span);
 464                                 err.multipart_suggestion(
 465                                     &format!(
 466                                         "to call the function stored in `{}`, \
 467                                          surround the field access with parentheses",
 468                                         item_name,
 469                                     ),
 470                                     vec![
 471                                         (expr_span.shrink_to_lo(), '('.to_string()),
 472                                         (expr_span.shrink_to_hi(), ')'.to_string()),
 473                                     ],
 474                                     Applicability::MachineApplicable,
 475                                 );
 476                             } else {
 477                                 let call_expr = self
 478                                     .tcx
 479                                     .hir()
 480                                     .expect_expr(self.tcx.hir().get_parent_node(expr.hir_id));
 481
 482                                 if let Some(span) = call_expr.span.trim_start(item_name.span) {
 483                                     err.span_suggestion(
 484                                         span,
 485                                         "remove the arguments",
 486                                         String::new(),
 487                                         Applicability::MaybeIncorrect,
 488                                     );
 489                                 }
 490                             }
 491                         }
 492
 493                         let field_kind = if is_accessible { "field" } else { "private field" };
 494                         err.span_label(item_name.span, format!("{}, not a method", field_kind));
 495                     } else if lev_candidate.is_none() && static_sources.is_empty() {
 496                         err.span_label(span, format!("{} not found in `{}`", item_kind, ty_str));
 497                         self.tcx.sess.trait_methods_not_found.borrow_mut().insert(orig_span);
 498                     }
 499                 } else {
 500                     err.span_label(span, format!("{} not found in `{}`", item_kind, ty_str));
 501                     self.tcx.sess.trait_methods_not_found.borrow_mut().insert(orig_span);
 502                 }
 503
 504                 if self.is_fn_ty(&rcvr_ty, span) {
 505                     macro_rules! report_function {
 506                         ($span:expr, $name:expr) => {
 507                             err.note(&format!(
 508                                 "`{}` is a function, perhaps you wish to call it",
 509                                 $name
 510                             ));
 511                         };
 512                     }
 513
 514                     if let SelfSource::MethodCall(expr) = source {
 515                         if let Ok(expr_string) = tcx.sess.source_map().span_to_snippet(expr.span) {
 516                             report_function!(expr.span, expr_string);
 517                         } else if let ExprKind::Path(QPath::Resolved(_, ref path)) = expr.kind {
 518                             if let Some(segment) = path.segments.last() {
 519                                 report_function!(expr.span, segment.ident);
 520                             }
 521                         }
 522                     }
 523                 }
 524
 525                 if !static_sources.is_empty() {
 526                     err.note(
 527                         "found the following associated functions; to be used as methods, \
 528                          functions must have a `self` parameter",
 529                     );
 530                     err.span_label(span, "this is an associated function, not a method");
 531                 }
 532                 if static_sources.len() == 1 {
 533                     let ty_str = if let Some(CandidateSource::ImplSource(impl_did)) =
 534                         static_sources.get(0)
 535                     {
 536                         // When the "method" is resolved through dereferencing, we really want the
 537                         // original type that has the associated function for accurate suggestions.
 538                         // (#61411)
 539                         let ty = tcx.at(span).type_of(*impl_did);
 540                         match (&ty.peel_refs().kind, &actual.peel_refs().kind) {
 541                             (ty::Adt(def, _), ty::Adt(def_actual, _)) if def == def_actual => {
 542                                 // Use `actual` as it will have more `substs` filled in.
 543                                 self.ty_to_value_string(actual.peel_refs())
 544                             }
 545                             _ => self.ty_to_value_string(ty.peel_refs()),
 546                         }
 547                     } else {
 548                         self.ty_to_value_string(actual.peel_refs())
 549                     };
 550                     if let SelfSource::MethodCall(expr) = source {
 551                         err.span_suggestion(
 552                             expr.span.to(span),
 553                             "use associated function syntax instead",
 554                             format!("{}::{}", ty_str, item_name),
 555                             Applicability::MachineApplicable,
 556                         );
 557                     } else {
 558                         err.help(&format!("try with `{}::{}`", ty_str, item_name,));
 559                     }
 560
 561                     report_candidates(span, &mut err, static_sources, sugg_span);
 562                 } else if static_sources.len() > 1 {
 563                     report_candidates(span, &mut err, static_sources, sugg_span);
 564                 }
 565
 566                 let mut restrict_type_params = false;
 567                 if !unsatisfied_predicates.is_empty() {
 568                     let def_span = |def_id| {
 569                         self.tcx.sess.source_map().guess_head_span(self.tcx.def_span(def_id))
 570                     };
 571                     let mut type_params = FxHashMap::default();
 572                     let mut bound_spans = vec![];
 573                     let mut collect_type_param_suggestions =
 574                         |self_ty: Ty<'_>, parent_pred: &ty::Predicate<'_>, obligation: &str| {
 575                             if let (ty::Param(_), ty::PredicateKind::Trait(p, _)) =
 576                                 (&self_ty.kind, parent_pred.kind())
 577                             {
 578                                 if let ty::Adt(def, _) = p.skip_binder().trait_ref.self_ty().kind {
 579                                     let node = def.did.as_local().map(|def_id| {
 580                                         self.tcx.hir().get(self.tcx.hir().as_local_hir_id(def_id))
 581                                     });
 582                                     if let Some(hir::Node::Item(hir::Item { kind, .. })) = node {
 583                                         if let Some(g) = kind.generics() {
 584                                             let key = match &g.where_clause.predicates[..] {
 585                                                 [.., pred] => (pred.span().shrink_to_hi(), false),
 586                                                 [] => (
 587                                                     g.where_clause
 588                                                         .span_for_predicates_or_empty_place(),
 589                                                     true,
 590                                                 ),
 591                                             };
 592                                             type_params
 593                                                 .entry(key)
 594                                                 .or_insert_with(FxHashSet::default)
 595                                                 .insert(obligation.to_owned());
 596                                         }
 597                                     }
 598                                 }
 599                             }
 600                         };
 601                     let mut bound_span_label = |self_ty: Ty<'_>, obligation: &str, quiet: &str| {
 602                         let msg = format!(
 603                             "doesn't satisfy `{}`",
 604                             if obligation.len() > 50 { quiet } else { obligation }
 605                         );
 606                         match &self_ty.kind {
 607                             // Point at the type that couldn't satisfy the bound.
 608                             ty::Adt(def, _) => bound_spans.push((def_span(def.did), msg)),
 609                             // Point at the trait object that couldn't satisfy the bound.
 610                             ty::Dynamic(preds, _) => {
 611                                 for pred in preds.skip_binder() {
 612                                     match pred {
 613                                         ty::ExistentialPredicate::Trait(tr) => {
 614                                             bound_spans.push((def_span(tr.def_id), msg.clone()))
 615                                         }
 616                                         ty::ExistentialPredicate::Projection(_)
 617                                         | ty::ExistentialPredicate::AutoTrait(_) => {}
 618                                     }
 619                                 }
 620                             }
 621                             // Point at the closure that couldn't satisfy the bound.
 622                             ty::Closure(def_id, _) => bound_spans
 623                                 .push((def_span(*def_id), format!("doesn't satisfy `{}`", quiet))),
 624                             _ => {}
 625                         }
 626                     };
 627                     let mut format_pred = |pred: ty::Predicate<'tcx>| {
 628                         match pred.kind() {
 629                             ty::PredicateKind::Projection(pred) => {
 630                                 // `<Foo as Iterator>::Item = String`.
 631                                 let trait_ref =
 632                                     pred.skip_binder().projection_ty.trait_ref(self.tcx);
 633                                 let assoc = self
 634                                     .tcx
 635                                     .associated_item(pred.skip_binder().projection_ty.item_def_id);
 636                                 let ty = pred.skip_binder().ty;
 637                                 let obligation = format!("{}::{} = {}", trait_ref, assoc.ident, ty);
 638                                 let quiet = format!(
 639                                     "<_ as {}>::{} = {}",
 640                                     trait_ref.print_only_trait_path(),
 641                                     assoc.ident,
 642                                     ty
 643                                 );
 644                                 bound_span_label(trait_ref.self_ty(), &obligation, &quiet);
 645                                 Some((obligation, trait_ref.self_ty()))
 646                             }
 647                             ty::PredicateKind::Trait(poly_trait_ref, _) => {
 648                                 let p = poly_trait_ref.skip_binder().trait_ref;
 649                                 let self_ty = p.self_ty();
 650                                 let path = p.print_only_trait_path();
 651                                 let obligation = format!("{}: {}", self_ty, path);
 652                                 let quiet = format!("_: {}", path);
 653                                 bound_span_label(self_ty, &obligation, &quiet);
 654                                 Some((obligation, self_ty))
 655                             }
 656                             _ => None,
 657                         }
 658                     };
 659                     let mut bound_list = unsatisfied_predicates
 660                         .iter()
 661                         .filter_map(|(pred, parent_pred)| {
 662                             format_pred(*pred).map(|(p, self_ty)| match parent_pred {
 663                                 None => format!("`{}`", p),
 664                                 Some(parent_pred) => match format_pred(*parent_pred) {
 665                                     None => format!("`{}`", p),
 666                                     Some((parent_p, _)) => {
 667                                         collect_type_param_suggestions(self_ty, parent_pred, &p);
 668                                         format!("`{}`\nwhich is required by `{}`", p, parent_p)
 669                                     }
 670                                 },
 671                             })
 672                         })
 673                         .enumerate()
 674                         .collect::<Vec<(usize, String)>>();
 675                     for ((span, empty_where), obligations) in type_params.into_iter() {
 676                         restrict_type_params = true;
 677                         err.span_suggestion_verbose(
 678                             span,
 679                             &format!(
 680                                 "consider restricting the type parameter{s} to satisfy the \
 681                                  trait bound{s}",
 682                                 s = pluralize!(obligations.len())
 683                             ),
 684                             format!(
 685                                 "{} {}",
 686                                 if empty_where { " where" } else { "," },
 687                                 obligations.into_iter().collect::<Vec<_>>().join(", ")
 688                             ),
 689                             Applicability::MaybeIncorrect,
 690                         );
 691                     }
 692
 693                     bound_list.sort_by(|(_, a), (_, b)| a.cmp(&b)); // Sort alphabetically.
 694                     bound_list.dedup_by(|(_, a), (_, b)| a == b); // #35677
 695                     bound_list.sort_by_key(|(pos, _)| *pos); // Keep the original predicate order.
 696                     bound_spans.sort();
 697                     bound_spans.dedup();
 698                     for (span, msg) in bound_spans.into_iter() {
 699                         err.span_label(span, &msg);
 700                     }
 701                     if !bound_list.is_empty() {
 702                         let bound_list = bound_list
 703                             .into_iter()
 704                             .map(|(_, path)| path)
 705                             .collect::<Vec<_>>()
 706                             .join("\n");
 707                         err.note(&format!(
 708                             "the method `{}` exists but the following trait bounds were not \
 709                              satisfied:\n{}",
 710                             item_name, bound_list
 711                         ));
 712                     }
 713                 }
 714
 715                 if actual.is_numeric() && actual.is_fresh() || restrict_type_params {
 716                 } else {
 717                     self.suggest_traits_to_import(
 718                         &mut err,
 719                         span,
 720                         rcvr_ty,
 721                         item_name,
 722                         source,
 723                         out_of_scope_traits,
 724                         &unsatisfied_predicates,
 725                     );
 726                 }
 727
 728                 if actual.is_enum() {
 729                     let adt_def = actual.ty_adt_def().expect("enum is not an ADT");
 730                     if let Some(suggestion) = lev_distance::find_best_match_for_name(
 731                         adt_def.variants.iter().map(|s| &s.ident.name),
 732                         item_name.name,
 733                         None,
 734                     ) {
 735                         err.span_suggestion(
 736                             span,
 737                             "there is a variant with a similar name",
 738                             suggestion.to_string(),
 739                             Applicability::MaybeIncorrect,
 740                         );
 741                     }
 742                 }
 743
 744                 let mut fallback_span = true;
 745                 let msg = "remove this method call";
 746                 if item_name.name == sym::as_str && actual.peel_refs().is_str() {
 747                     if let SelfSource::MethodCall(expr) = source {
 748                         let call_expr =
 749                             self.tcx.hir().expect_expr(self.tcx.hir().get_parent_node(expr.hir_id));
 750                         if let Some(span) = call_expr.span.trim_start(expr.span) {
 751                             err.span_suggestion(
 752                                 span,
 753                                 msg,
 754                                 String::new(),
 755                                 Applicability::MachineApplicable,
 756                             );
 757                             fallback_span = false;
 758                         }
 759                     }
 760                     if fallback_span {
 761                         err.span_label(span, msg);
 762                     }
 763                 } else if let Some(lev_candidate) = lev_candidate {
 764                     let def_kind = lev_candidate.kind.as_def_kind();
 765                     err.span_suggestion(
 766                         span,
 767                         &format!(
 768                             "there is {} {} with a similar name",
 769                             def_kind.article(),
 770                             def_kind.descr(lev_candidate.def_id),
 771                         ),
 772                         lev_candidate.ident.to_string(),
 773                         Applicability::MaybeIncorrect,
 774                     );
 775                 }
 776
 777                 return Some(err);
 778             }
 779
 780             MethodError::Ambiguity(sources) => {
 781                 let mut err = struct_span_err!(
 782                     self.sess(),
 783                     item_name.span,
 784                     E0034,
 785                     "multiple applicable items in scope"
 786                 );
 787                 err.span_label(item_name.span, format!("multiple `{}` found", item_name));
 788
 789                 report_candidates(span, &mut err, sources, sugg_span);
 790                 err.emit();
 791             }
 792
 793             MethodError::PrivateMatch(kind, def_id, out_of_scope_traits) => {
 794                 let kind = kind.descr(def_id);
 795                 let mut err = struct_span_err!(
 796                     self.tcx.sess,
 797                     item_name.span,
 798                     E0624,
 799                     "{} `{}` is private",
 800                     kind,
 801                     item_name
 802                 );
 803                 err.span_label(item_name.span, &format!("private {}", kind));
 804                 self.suggest_valid_traits(&mut err, out_of_scope_traits);
 805                 err.emit();
 806             }
 807
 808             MethodError::IllegalSizedBound(candidates, needs_mut, bound_span) => {
 809                 let msg = format!("the `{}` method cannot be invoked on a trait object", item_name);
 810                 let mut err = self.sess().struct_span_err(span, &msg);
 811                 err.span_label(bound_span, "this has a `Sized` requirement");
 812                 if !candidates.is_empty() {
 813                     let help = format!(
 814                         "{an}other candidate{s} {were} found in the following trait{s}, perhaps \
 815                          add a `use` for {one_of_them}:",
 816                         an = if candidates.len() == 1 { "an" } else { "" },
 817                         s = pluralize!(candidates.len()),
 818                         were = if candidates.len() == 1 { "was" } else { "were" },
 819                         one_of_them = if candidates.len() == 1 { "it" } else { "one_of_them" },
 820                     );
 821                     self.suggest_use_candidates(&mut err, help, candidates);
 822                 }
 823                 if let ty::Ref(region, t_type, mutability) = rcvr_ty.kind {
 824                     if needs_mut {
 825                         let trait_type = self.tcx.mk_ref(
 826                             region,
 827                             ty::TypeAndMut { ty: t_type, mutbl: mutability.invert() },
 828                         );
 829                         err.note(&format!("you need `{}` instead of `{}`", trait_type, rcvr_ty));
 830                     }
 831                 }
 832                 err.emit();
 833             }
 834
 835             MethodError::BadReturnType => bug!("no return type expectations but got BadReturnType"),
 836         }
 837         None
 838     }
 839
 840     /// Print out the type for use in value namespace.
 841     fn ty_to_value_string(&self, ty: Ty<'tcx>) -> String {
 842         match ty.kind {
 843             ty::Adt(def, substs) => format!("{}", ty::Instance::new(def.did, substs)),
 844             _ => self.ty_to_string(ty),
 845         }
 846     }
 847
 848     fn suggest_use_candidates(
 849         &self,
 850         err: &mut DiagnosticBuilder<'_>,
 851         mut msg: String,
 852         candidates: Vec<DefId>,
 853     ) {
 854         let module_did = self.tcx.parent_module(self.body_id);
 855         let module_id = self.tcx.hir().as_local_hir_id(module_did);
 856         let krate = self.tcx.hir().krate();
 857         let (span, found_use) = UsePlacementFinder::check(self.tcx, krate, module_id);
 858         if let Some(span) = span {
 859             let path_strings = candidates.iter().map(|did| {
 860                 // Produce an additional newline to separate the new use statement
 861                 // from the directly following item.
 862                 let additional_newline = if found_use { "" } else { "\n" };
 863                 format!(
 864                     "use {};\n{}",
 865                     with_crate_prefix(|| self.tcx.def_path_str(*did)),
 866                     additional_newline
 867                 )
 868             });
 869
 870             err.span_suggestions(span, &msg, path_strings, Applicability::MaybeIncorrect);
 871         } else {
 872             let limit = if candidates.len() == 5 { 5 } else { 4 };
 873             for (i, trait_did) in candidates.iter().take(limit).enumerate() {
 874                 if candidates.len() > 1 {
 875                     msg.push_str(&format!(
 876                         "\ncandidate #{}: `use {};`",
 877                         i + 1,
 878                         with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
 879                     ));
 880                 } else {
 881                     msg.push_str(&format!(
 882                         "\n`use {};`",
 883                         with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
 884                     ));
 885                 }
 886             }
 887             if candidates.len() > limit {
 888                 msg.push_str(&format!("\nand {} others", candidates.len() - limit));
 889             }
 890             err.note(&msg[..]);
 891         }
 892     }
 893
 894     fn suggest_valid_traits(
 895         &self,
 896         err: &mut DiagnosticBuilder<'_>,
 897         valid_out_of_scope_traits: Vec<DefId>,
 898     ) -> bool {
 899         if !valid_out_of_scope_traits.is_empty() {
 900             let mut candidates = valid_out_of_scope_traits;
 901             candidates.sort();
 902             candidates.dedup();
 903             err.help("items from traits can only be used if the trait is in scope");
 904             let msg = format!(
 905                 "the following {traits_are} implemented but not in scope; \
 906                  perhaps add a `use` for {one_of_them}:",
 907                 traits_are = if candidates.len() == 1 { "trait is" } else { "traits are" },
 908                 one_of_them = if candidates.len() == 1 { "it" } else { "one of them" },
 909             );
 910
 911             self.suggest_use_candidates(err, msg, candidates);
 912             true
 913         } else {
 914             false
 915         }
 916     }
 917
 918     fn suggest_traits_to_import<'b>(
 919         &self,
 920         err: &mut DiagnosticBuilder<'_>,
 921         span: Span,
 922         rcvr_ty: Ty<'tcx>,
 923         item_name: Ident,
 924         source: SelfSource<'b>,
 925         valid_out_of_scope_traits: Vec<DefId>,
 926         unsatisfied_predicates: &[(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>)],
 927     ) {
 928         if self.suggest_valid_traits(err, valid_out_of_scope_traits) {
 929             return;
 930         }
 931
 932         let type_is_local = self.type_derefs_to_local(span, rcvr_ty, source);
 933
 934         let mut arbitrary_rcvr = vec![];
 935         // There are no traits implemented, so lets suggest some traits to
 936         // implement, by finding ones that have the item name, and are
 937         // legal to implement.
 938         let mut candidates = all_traits(self.tcx)
 939             .into_iter()
 940             // Don't issue suggestions for unstable traits since they're
 941             // unlikely to be implementable anyway
 942             .filter(|info| match self.tcx.lookup_stability(info.def_id) {
 943                 Some(attr) => attr.level.is_stable(),
 944                 None => true,
 945             })
 946             .filter(|info| {
 947                 // We approximate the coherence rules to only suggest
 948                 // traits that are legal to implement by requiring that
 949                 // either the type or trait is local. Multi-dispatch means
 950                 // this isn't perfect (that is, there are cases when
 951                 // implementing a trait would be legal but is rejected
 952                 // here).
 953                 unsatisfied_predicates.iter().all(|(p, _)| match p.kind() {
 954                     // Hide traits if they are present in predicates as they can be fixed without
 955                     // having to implement them.
 956                     ty::PredicateKind::Trait(t, _) => t.def_id() == info.def_id,
 957                     ty::PredicateKind::Projection(p) => p.item_def_id() == info.def_id,
 958                     _ => false,
 959                 }) && (type_is_local || info.def_id.is_local())
 960                     && self
 961                         .associated_item(info.def_id, item_name, Namespace::ValueNS)
 962                         .filter(|item| {
 963                             if let ty::AssocKind::Fn = item.kind {
 964                                 let id = item
 965                                     .def_id
 966                                     .as_local()
 967                                     .map(|def_id| self.tcx.hir().as_local_hir_id(def_id));
 968                                 if let Some(hir::Node::TraitItem(hir::TraitItem {
 969                                     kind: hir::TraitItemKind::Fn(fn_sig, method),
 970                                     ..
 971                                 })) = id.map(|id| self.tcx.hir().get(id))
 972                                 {
 973                                     let self_first_arg = match method {
 974                                         hir::TraitFn::Required([ident, ..]) => {
 975                                             ident.name == kw::SelfLower
 976                                         }
 977                                         hir::TraitFn::Provided(body_id) => {
 978                                             self.tcx.hir().body(*body_id).params.first().map_or(
 979                                                 false,
 980                                                 |param| {
 981                                                     matches!(
 982                                                         param.pat.kind,
 983                                                         hir::PatKind::Binding(_, _, ident, _)
 984                                                             if ident.name == kw::SelfLower
 985                                                     )
 986                                                 },
 987                                             )
 988                                         }
 989                                         _ => false,
 990                                     };
 991
 992                                     if !fn_sig.decl.implicit_self.has_implicit_self()
 993                                         && self_first_arg
 994                                     {
 995                                         if let Some(ty) = fn_sig.decl.inputs.get(0) {
 996                                             arbitrary_rcvr.push(ty.span);
 997                                         }
 998                                         return false;
 999                                     }
1000                                 }
1001                             }
1002                             // We only want to suggest public or local traits (#45781).
1003                             item.vis == ty::Visibility::Public || info.def_id.is_local()
1004                         })
1005                         .is_some()
1006             })
1007             .collect::<Vec<_>>();
1008         for span in &arbitrary_rcvr {
1009             err.span_label(
1010                 *span,
1011                 "the method might not be found because of this arbitrary self type",
1012             );
1013         }
1014
1015         if !candidates.is_empty() {
1016             // Sort from most relevant to least relevant.
1017             candidates.sort_by(|a, b| a.cmp(b).reverse());
1018             candidates.dedup();
1019
1020             let param_type = match rcvr_ty.kind {
1021                 ty::Param(param) => Some(param),
1022                 ty::Ref(_, ty, _) => match ty.kind {
1023                     ty::Param(param) => Some(param),
1024                     _ => None,
1025                 },
1026                 _ => None,
1027             };
1028             err.help(if param_type.is_some() {
1029                 "items from traits can only be used if the type parameter is bounded by the trait"
1030             } else {
1031                 "items from traits can only be used if the trait is implemented and in scope"
1032             });
1033             let message = |action| {
1034                 format!(
1035                     "the following {traits_define} an item `{name}`, perhaps you need to {action} \
1036                      {one_of_them}:",
1037                     traits_define =
1038                         if candidates.len() == 1 { "trait defines" } else { "traits define" },
1039                     action = action,
1040                     one_of_them = if candidates.len() == 1 { "it" } else { "one of them" },
1041                     name = item_name,
1042                 )
1043             };
1044             // Obtain the span for `param` and use it for a structured suggestion.
1045             let mut suggested = false;
1046             if let (Some(ref param), Some(ref table)) =
1047                 (param_type, self.in_progress_typeck_results)
1048             {
1049                 let table_owner = table.borrow().hir_owner;
1050                 let generics = self.tcx.generics_of(table_owner.to_def_id());
1051                 let type_param = generics.type_param(param, self.tcx);
1052                 let hir = &self.tcx.hir();
1053                 if let Some(def_id) = type_param.def_id.as_local() {
1054                     let id = hir.as_local_hir_id(def_id);
1055                     // Get the `hir::Param` to verify whether it already has any bounds.
1056                     // We do this to avoid suggesting code that ends up as `T: FooBar`,
1057                     // instead we suggest `T: Foo + Bar` in that case.
1058                     match hir.get(id) {
1059                         Node::GenericParam(ref param) => {
1060                             let mut impl_trait = false;
1061                             let has_bounds =
1062                                 if let hir::GenericParamKind::Type { synthetic: Some(_), .. } =
1063                                     &param.kind
1064                                 {
1065                                     // We've found `fn foo(x: impl Trait)` instead of
1066                                     // `fn foo<T>(x: T)`. We want to suggest the correct
1067                                     // `fn foo(x: impl Trait + TraitBound)` instead of
1068                                     // `fn foo<T: TraitBound>(x: T)`. (#63706)
1069                                     impl_trait = true;
1070                                     param.bounds.get(1)
1071                                 } else {
1072                                     param.bounds.get(0)
1073                                 };
1074                             let sp = hir.span(id);
1075                             let sp = if let Some(first_bound) = has_bounds {
1076                                 // `sp` only covers `T`, change it so that it covers
1077                                 // `T:` when appropriate
1078                                 sp.until(first_bound.span())
1079                             } else {
1080                                 sp
1081                             };
1082                             let trait_def_ids: FxHashSet<DefId> = param
1083                                 .bounds
1084                                 .iter()
1085                                 .filter_map(|bound| Some(bound.trait_ref()?.trait_def_id()?))
1086                                 .collect();
1087                             if !candidates.iter().any(|t| trait_def_ids.contains(&t.def_id)) {
1088                                 err.span_suggestions(
1089                                     sp,
1090                                     &message(format!(
1091                                         "restrict type parameter `{}` with",
1092                                         param.name.ident(),
1093                                     )),
1094                                     candidates.iter().map(|t| {
1095                                         format!(
1096                                             "{}{} {}{}",
1097                                             param.name.ident(),
1098                                             if impl_trait { " +" } else { ":" },
1099                                             self.tcx.def_path_str(t.def_id),
1100                                             if has_bounds.is_some() { " + " } else { "" },
1101                                         )
1102                                     }),
1103                                     Applicability::MaybeIncorrect,
1104                                 );
1105                             }
1106                             suggested = true;
1107                         }
1108                         Node::Item(hir::Item {
1109                             kind: hir::ItemKind::Trait(.., bounds, _),
1110                             ident,
1111                             ..
1112                         }) => {
1113                             let (sp, sep, article) = if bounds.is_empty() {
1114                                 (ident.span.shrink_to_hi(), ":", "a")
1115                             } else {
1116                                 (bounds.last().unwrap().span().shrink_to_hi(), " +", "another")
1117                             };
1118                             err.span_suggestions(
1119                                 sp,
1120                                 &message(format!("add {} supertrait for", article)),
1121                                 candidates.iter().map(|t| {
1122                                     format!("{} {}", sep, self.tcx.def_path_str(t.def_id),)
1123                                 }),
1124                                 Applicability::MaybeIncorrect,
1125                             );
1126                             suggested = true;
1127                         }
1128                         _ => {}
1129                     }
1130                 }
1131             }
1132
1133             if !suggested {
1134                 let action = if let Some(param) = param_type {
1135                     format!("restrict type parameter `{}` with", param)
1136                 } else {
1137                     // FIXME: it might only need to be imported into scope, not implemented.
1138                     "implement".to_string()
1139                 };
1140                 let mut use_note = true;
1141                 if let [trait_info] = &candidates[..] {
1142                     if let Some(span) = self.tcx.hir().span_if_local(trait_info.def_id) {
1143                         err.span_note(
1144                             self.tcx.sess.source_map().guess_head_span(span),
1145                             &format!(
1146                                 "`{}` defines an item `{}`, perhaps you need to {} it",
1147                                 self.tcx.def_path_str(trait_info.def_id),
1148                                 item_name,
1149                                 action
1150                             ),
1151                         );
1152                         use_note = false
1153                     }
1154                 }
1155                 if use_note {
1156                     let mut msg = message(action);
1157                     for (i, trait_info) in candidates.iter().enumerate() {
1158                         msg.push_str(&format!(
1159                             "\ncandidate #{}: `{}`",
1160                             i + 1,
1161                             self.tcx.def_path_str(trait_info.def_id),
1162                         ));
1163                     }
1164                     err.note(&msg[..]);
1165                 }
1166             }
1167         }
1168     }
1169
1170     /// Checks whether there is a local type somewhere in the chain of
1171     /// autoderefs of `rcvr_ty`.
1172     fn type_derefs_to_local(&self, span: Span, rcvr_ty: Ty<'tcx>, source: SelfSource<'_>) -> bool {
1173         fn is_local(ty: Ty<'_>) -> bool {
1174             match ty.kind {
1175                 ty::Adt(def, _) => def.did.is_local(),
1176                 ty::Foreign(did) => did.is_local(),
1177
1178                 ty::Dynamic(ref tr, ..) => {
1179                     tr.principal().map(|d| d.def_id().is_local()).unwrap_or(false)
1180                 }
1181
1182                 ty::Param(_) => true,
1183
1184                 // Everything else (primitive types, etc.) is effectively
1185                 // non-local (there are "edge" cases, e.g., `(LocalType,)`, but
1186                 // the noise from these sort of types is usually just really
1187                 // annoying, rather than any sort of help).
1188                 _ => false,
1189             }
1190         }
1191
1192         // This occurs for UFCS desugaring of `T::method`, where there is no
1193         // receiver expression for the method call, and thus no autoderef.
1194         if let SelfSource::QPath(_) = source {
1195             return is_local(self.resolve_vars_with_obligations(rcvr_ty));
1196         }
1197
1198         self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))
1199     }
1200 }
1201
1202 #[derive(Copy, Clone)]
1203 pub enum SelfSource<'a> {
1204     QPath(&'a hir::Ty<'a>),
1205     MethodCall(&'a hir::Expr<'a> /* rcvr */),
1206 }
1207
1208 #[derive(Copy, Clone)]
1209 pub struct TraitInfo {
1210     pub def_id: DefId,
1211 }
1212
1213 impl PartialEq for TraitInfo {
1214     fn eq(&self, other: &TraitInfo) -> bool {
1215         self.cmp(other) == Ordering::Equal
1216     }
1217 }
1218 impl Eq for TraitInfo {}
1219 impl PartialOrd for TraitInfo {
1220     fn partial_cmp(&self, other: &TraitInfo) -> Option<Ordering> {
1221         Some(self.cmp(other))
1222     }
1223 }
1224 impl Ord for TraitInfo {
1225     fn cmp(&self, other: &TraitInfo) -> Ordering {
1226         // Local crates are more important than remote ones (local:
1227         // `cnum == 0`), and otherwise we throw in the defid for totality.
1228
1229         let lhs = (other.def_id.krate, other.def_id);
1230         let rhs = (self.def_id.krate, self.def_id);
1231         lhs.cmp(&rhs)
1232     }
1233 }
1234
1235 /// Retrieves all traits in this crate and any dependent crates.
1236 pub fn all_traits(tcx: TyCtxt<'_>) -> Vec<TraitInfo> {
1237     tcx.all_traits(LOCAL_CRATE).iter().map(|&def_id| TraitInfo { def_id }).collect()
1238 }
1239
1240 /// Computes all traits in this crate and any dependent crates.
1241 fn compute_all_traits(tcx: TyCtxt<'_>) -> Vec<DefId> {
1242     use hir::itemlikevisit;
1243
1244     let mut traits = vec![];
1245
1246     // Crate-local:
1247
1248     struct Visitor<'a, 'tcx> {
1249         map: &'a hir_map::Map<'tcx>,
1250         traits: &'a mut Vec<DefId>,
1251     }
1252
1253     impl<'v, 'a, 'tcx> itemlikevisit::ItemLikeVisitor<'v> for Visitor<'a, 'tcx> {
1254         fn visit_item(&mut self, i: &'v hir::Item<'v>) {
1255             match i.kind {
1256                 hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..) => {
1257                     let def_id = self.map.local_def_id(i.hir_id);
1258                     self.traits.push(def_id.to_def_id());
1259                 }
1260                 _ => (),
1261             }
1262         }
1263
1264         fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {}
1265
1266         fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {}
1267     }
1268
1269     tcx.hir().krate().visit_all_item_likes(&mut Visitor { map: &tcx.hir(), traits: &mut traits });
1270
1271     // Cross-crate:
1272
1273     let mut external_mods = FxHashSet::default();
1274     fn handle_external_res(
1275         tcx: TyCtxt<'_>,
1276         traits: &mut Vec<DefId>,
1277         external_mods: &mut FxHashSet<DefId>,
1278         res: Res,
1279     ) {
1280         match res {
1281             Res::Def(DefKind::Trait | DefKind::TraitAlias, def_id) => {
1282                 traits.push(def_id);
1283             }
1284             Res::Def(DefKind::Mod, def_id) => {
1285                 if !external_mods.insert(def_id) {
1286                     return;
1287                 }
1288                 for child in tcx.item_children(def_id).iter() {
1289                     handle_external_res(tcx, traits, external_mods, child.res)
1290                 }
1291             }
1292             _ => {}
1293         }
1294     }
1295     for &cnum in tcx.crates().iter() {
1296         let def_id = DefId { krate: cnum, index: CRATE_DEF_INDEX };
1297         handle_external_res(tcx, &mut traits, &mut external_mods, Res::Def(DefKind::Mod, def_id));
1298     }
1299
1300     traits
1301 }
1302
1303 pub fn provide(providers: &mut ty::query::Providers) {
1304     providers.all_traits = |tcx, cnum| {
1305         assert_eq!(cnum, LOCAL_CRATE);
1306         &tcx.arena.alloc(compute_all_traits(tcx))[..]
1307     }
1308 }
1309
1310 struct UsePlacementFinder<'tcx> {
1311     target_module: hir::HirId,
1312     span: Option<Span>,
1313     found_use: bool,
1314     tcx: TyCtxt<'tcx>,
1315 }
1316
1317 impl UsePlacementFinder<'tcx> {
1318     fn check(
1319         tcx: TyCtxt<'tcx>,
1320         krate: &'tcx hir::Crate<'tcx>,
1321         target_module: hir::HirId,
1322     ) -> (Option<Span>, bool) {
1323         let mut finder = UsePlacementFinder { target_module, span: None, found_use: false, tcx };
1324         intravisit::walk_crate(&mut finder, krate);
1325         (finder.span, finder.found_use)
1326     }
1327 }
1328
1329 impl intravisit::Visitor<'tcx> for UsePlacementFinder<'tcx> {
1330     fn visit_mod(&mut self, module: &'tcx hir::Mod<'tcx>, _: Span, hir_id: hir::HirId) {
1331         if self.span.is_some() {
1332             return;
1333         }
1334         if hir_id != self.target_module {
1335             intravisit::walk_mod(self, module, hir_id);
1336             return;
1337         }
1338         // Find a `use` statement.
1339         for item_id in module.item_ids {
1340             let item = self.tcx.hir().expect_item(item_id.id);
1341             match item.kind {
1342                 hir::ItemKind::Use(..) => {
1343                     // Don't suggest placing a `use` before the prelude
1344                     // import or other generated ones.
1345                     if !item.span.from_expansion() {
1346                         self.span = Some(item.span.shrink_to_lo());
1347                         self.found_use = true;
1348                         return;
1349                     }
1350                 }
1351                 // Don't place `use` before `extern crate`...
1352                 hir::ItemKind::ExternCrate(_) => {}
1353                 // ...but do place them before the first other item.
1354                 _ => {
1355                     if self.span.map_or(true, |span| item.span < span) {
1356                         if !item.span.from_expansion() {
1357                             // Don't insert between attributes and an item.
1358                             if item.attrs.is_empty() {
1359                                 self.span = Some(item.span.shrink_to_lo());
1360                             } else {
1361                                 // Find the first attribute on the item.
1362                                 for attr in item.attrs {
1363                                     if self.span.map_or(true, |span| attr.span < span) {
1364                                         self.span = Some(attr.span.shrink_to_lo());
1365                                     }
1366                                 }
1367                             }
1368                         }
1369                     }
1370                 }
1371             }
1372         }
1373     }
1374
1375     type Map = intravisit::ErasedMap<'tcx>;
1376
1377     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1378         intravisit::NestedVisitorMap::None
1379     }
1380 }
1381
1382 fn print_disambiguation_help(
1383     item_name: Ident,
1384     args: Option<&'tcx [hir::Expr<'tcx>]>,
1385     err: &mut DiagnosticBuilder<'_>,
1386     trait_name: String,
1387     rcvr_ty: Ty<'_>,
1388     kind: ty::AssocKind,
1389     def_id: DefId,
1390     span: Span,
1391     candidate: Option<usize>,
1392     source_map: &source_map::SourceMap,
1393 ) {
1394     let mut applicability = Applicability::MachineApplicable;
1395     let sugg_args = if let (ty::AssocKind::Fn, Some(args)) = (kind, args) {
1396         format!(
1397             "({}{})",
1398             if rcvr_ty.is_region_ptr() {
1399                 if rcvr_ty.is_mutable_ptr() { "&mut " } else { "&" }
1400             } else {
1401                 ""
1402             },
1403             args.iter()
1404                 .map(|arg| source_map.span_to_snippet(arg.span).unwrap_or_else(|_| {
1405                     applicability = Applicability::HasPlaceholders;
1406                     "_".to_owned()
1407                 }))
1408                 .collect::<Vec<_>>()
1409                 .join(", "),
1410         )
1411     } else {
1412         String::new()
1413     };
1414     let sugg = format!("{}::{}{}", trait_name, item_name, sugg_args);
1415     err.span_suggestion(
1416         span,
1417         &format!(
1418             "disambiguate the {} for {}",
1419             kind.as_def_kind().descr(def_id),
1420             if let Some(candidate) = candidate {
1421                 format!("candidate #{}", candidate)
1422             } else {
1423                 "the candidate".to_string()
1424             },
1425         ),
1426         sugg,
1427         applicability,
1428     );
1429 }