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