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 crate::namespace::Namespace;
   7 use crate::util::nodemap::FxHashSet;
   8 use errors::{Applicability, DiagnosticBuilder};
   9 use rustc_data_structures::sync::Lrc;
  10 use rustc::hir::{self, ExprKind, Node, QPath};
  11 use rustc::hir::def::Def;
  12 use rustc::hir::def_id::{CRATE_DEF_INDEX, LOCAL_CRATE, DefId};
  13 use rustc::hir::map as hir_map;
  14 use rustc::hir::print;
  15 use rustc::infer::type_variable::TypeVariableOrigin;
  16 use rustc::traits::Obligation;
  17 use rustc::ty::{self, Adt, Ty, TyCtxt, ToPolyTraitRef, ToPredicate, TypeFoldable};
  18 use rustc::ty::print::with_crate_prefix;
  19 use syntax_pos::{Span, FileName};
  20 use syntax::ast;
  21 use syntax::util::lev_distance::find_best_match_for_name;
  22
  23 use std::cmp::Ordering;
  24
  25 use super::{MethodError, NoMatchData, CandidateSource};
  26 use super::probe::Mode;
  27
  28 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
  29     fn is_fn_ty(&self, ty: &Ty<'tcx>, span: Span) -> bool {
  30         let tcx = self.tcx;
  31         match ty.sty {
  32             // Not all of these (e.g., unsafe fns) implement `FnOnce`,
  33             // so we look for these beforehand.
  34             ty::Closure(..) |
  35             ty::FnDef(..) |
  36             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(ty, &[
  47                             self.next_ty_var(TypeVariableOrigin::MiscVariable(span)).into()
  48                         ]);
  49                         let trait_ref = ty::TraitRef::new(fn_once, fn_once_substs);
  50                         let poly_trait_ref = trait_ref.to_poly_trait_ref();
  51                         let obligation =
  52                             Obligation::misc(span,
  53                                              self.body_id,
  54                                              self.param_env,
  55                                              poly_trait_ref.to_predicate());
  56                         self.predicate_may_hold(&obligation)
  57                     })
  58                 })
  59             }
  60         }
  61     }
  62
  63     pub fn report_method_error<'b>(&self,
  64                                    span: Span,
  65                                    rcvr_ty: Ty<'tcx>,
  66                                    item_name: ast::Ident,
  67                                    source: SelfSource<'b>,
  68                                    error: MethodError<'tcx>,
  69                                    args: Option<&'gcx [hir::Expr]>) {
  70         // Avoid suggestions when we don't know what's going on.
  71         if rcvr_ty.references_error() {
  72             return;
  73         }
  74
  75         let report_candidates = |err: &mut DiagnosticBuilder<'_>,
  76                                  mut sources: Vec<CandidateSource>| {
  77             sources.sort();
  78             sources.dedup();
  79             // Dynamic limit to avoid hiding just one candidate, which is silly.
  80             let limit = if sources.len() == 5 { 5 } else { 4 };
  81
  82             for (idx, source) in sources.iter().take(limit).enumerate() {
  83                 match *source {
  84                     CandidateSource::ImplSource(impl_did) => {
  85                         // Provide the best span we can. Use the item, if local to crate, else
  86                         // the impl, if local to crate (item may be defaulted), else nothing.
  87                         let item = self.associated_item(impl_did, item_name, Namespace::Value)
  88                             .or_else(|| {
  89                                 self.associated_item(
  90                                     self.tcx.impl_trait_ref(impl_did).unwrap().def_id,
  91                                     item_name,
  92                                     Namespace::Value,
  93                                 )
  94                             }).unwrap();
  95                         let note_span = self.tcx.hir().span_if_local(item.def_id).or_else(|| {
  96                             self.tcx.hir().span_if_local(impl_did)
  97                         });
  98
  99                         let impl_ty = self.impl_self_ty(span, impl_did).ty;
 100
 101                         let insertion = match self.tcx.impl_trait_ref(impl_did) {
 102                             None => String::new(),
 103                             Some(trait_ref) => {
 104                                 format!(" of the trait `{}`",
 105                                         self.tcx.def_path_str(trait_ref.def_id))
 106                             }
 107                         };
 108
 109                         let note_str = if sources.len() > 1 {
 110                             format!("candidate #{} is defined in an impl{} for the type `{}`",
 111                                     idx + 1,
 112                                     insertion,
 113                                     impl_ty)
 114                         } else {
 115                             format!("the candidate is defined in an impl{} for the type `{}`",
 116                                     insertion,
 117                                     impl_ty)
 118                         };
 119                         if let Some(note_span) = note_span {
 120                             // We have a span pointing to the method. Show note with snippet.
 121                             err.span_note(self.tcx.sess.source_map().def_span(note_span),
 122                                           &note_str);
 123                         } else {
 124                             err.note(&note_str);
 125                         }
 126                     }
 127                     CandidateSource::TraitSource(trait_did) => {
 128                         let item = self
 129                             .associated_item(trait_did, item_name, Namespace::Value)
 130                             .unwrap();
 131                         let item_span = self.tcx.sess.source_map()
 132                             .def_span(self.tcx.def_span(item.def_id));
 133                         if sources.len() > 1 {
 134                             span_note!(err,
 135                                        item_span,
 136                                        "candidate #{} is defined in the trait `{}`",
 137                                        idx + 1,
 138                                        self.tcx.def_path_str(trait_did));
 139                         } else {
 140                             span_note!(err,
 141                                        item_span,
 142                                        "the candidate is defined in the trait `{}`",
 143                                        self.tcx.def_path_str(trait_did));
 144                         }
 145                         err.help(&format!("to disambiguate the method call, write `{}::{}({}{})` \
 146                                           instead",
 147                                           self.tcx.def_path_str(trait_did),
 148                                           item_name,
 149                                           if rcvr_ty.is_region_ptr() && args.is_some() {
 150                                               if rcvr_ty.is_mutable_pointer() {
 151                                                   "&mut "
 152                                               } else {
 153                                                   "&"
 154                                               }
 155                                           } else {
 156                                               ""
 157                                           },
 158                                           args.map(|arg| arg.iter()
 159                                               .map(|arg| print::to_string(print::NO_ANN,
 160                                                                           |s| s.print_expr(arg)))
 161                                               .collect::<Vec<_>>()
 162                                               .join(", ")).unwrap_or_else(|| "...".to_owned())));
 163                     }
 164                 }
 165             }
 166             if sources.len() > limit {
 167                 err.note(&format!("and {} others", sources.len() - limit));
 168             }
 169         };
 170
 171         match error {
 172             MethodError::NoMatch(NoMatchData {
 173                 static_candidates: static_sources,
 174                 unsatisfied_predicates,
 175                 out_of_scope_traits,
 176                 lev_candidate,
 177                 mode,
 178             }) => {
 179                 let tcx = self.tcx;
 180
 181                 let actual = self.resolve_type_vars_if_possible(&rcvr_ty);
 182                 let ty_str = self.ty_to_string(actual);
 183                 let is_method = mode == Mode::MethodCall;
 184                 let mut suggestion = None;
 185                 let item_kind = if is_method {
 186                     "method"
 187                 } else if actual.is_enum() {
 188                     if let Adt(ref adt_def, _) = actual.sty {
 189                         let names = adt_def.variants.iter().map(|s| &s.ident.name);
 190                         suggestion = find_best_match_for_name(names,
 191                                                               &item_name.as_str(),
 192                                                               None);
 193                     }
 194                     "variant"
 195                 } else {
 196                     match (item_name.as_str().chars().next(), actual.is_fresh_ty()) {
 197                         (Some(name), false) if name.is_lowercase() => {
 198                             "function or associated item"
 199                         }
 200                         (Some(_), false) => "associated item",
 201                         (Some(_), true) | (None, false) => {
 202                             "variant or associated item"
 203                         }
 204                         (None, true) => "variant",
 205                     }
 206                 };
 207                 let mut err = if !actual.references_error() {
 208                     // Suggest clamping down the type if the method that is being attempted to
 209                     // be used exists at all, and the type is an ambiuous numeric type
 210                     // ({integer}/{float}).
 211                     let mut candidates = all_traits(self.tcx)
 212                         .into_iter()
 213                         .filter_map(|info|
 214                             self.associated_item(info.def_id, item_name, Namespace::Value)
 215                         );
 216                     if let (true, false, SelfSource::MethodCall(expr), Some(_)) =
 217                            (actual.is_numeric(),
 218                             actual.has_concrete_skeleton(),
 219                             source,
 220                             candidates.next()) {
 221                         let mut err = struct_span_err!(
 222                             tcx.sess,
 223                             span,
 224                             E0689,
 225                             "can't call {} `{}` on ambiguous numeric type `{}`",
 226                             item_kind,
 227                             item_name,
 228                             ty_str
 229                         );
 230                         let concrete_type = if actual.is_integral() {
 231                             "i32"
 232                         } else {
 233                             "f32"
 234                         };
 235                         match expr.node {
 236                             ExprKind::Lit(ref lit) => {
 237                                 // numeric literal
 238                                 let snippet = tcx.sess.source_map().span_to_snippet(lit.span)
 239                                     .unwrap_or_else(|_| "<numeric literal>".to_owned());
 240
 241                                 err.span_suggestion(
 242                                     lit.span,
 243                                     &format!("you must specify a concrete type for \
 244                                               this numeric value, like `{}`", concrete_type),
 245                                     format!("{}_{}", snippet, concrete_type),
 246                                     Applicability::MaybeIncorrect,
 247                                 );
 248                             }
 249                             ExprKind::Path(ref qpath) => {
 250                                 // local binding
 251                                 if let &QPath::Resolved(_, ref path) = &qpath {
 252                                     if let hir::def::Def::Local(node_id) = path.def {
 253                                         let span = tcx.hir().span(node_id);
 254                                         let snippet = tcx.sess.source_map().span_to_snippet(span)
 255                                             .unwrap();
 256                                         let filename = tcx.sess.source_map().span_to_filename(span);
 257
 258                                         let parent_node = self.tcx.hir().get(
 259                                             self.tcx.hir().get_parent_node(node_id),
 260                                         );
 261                                         let msg = format!(
 262                                             "you must specify a type for this binding, like `{}`",
 263                                             concrete_type,
 264                                         );
 265
 266                                         match (filename, parent_node) {
 267                                             (FileName::Real(_), Node::Local(hir::Local {
 268                                                 source: hir::LocalSource::Normal,
 269                                                 ty,
 270                                                 ..
 271                                             })) => {
 272                                                 err.span_suggestion(
 273                                                     // account for `let x: _ = 42;`
 274                                                     //                  ^^^^
 275                                                     span.to(ty.as_ref().map(|ty| ty.span)
 276                                                         .unwrap_or(span)),
 277                                                     &msg,
 278                                                     format!("{}: {}", snippet, concrete_type),
 279                                                     Applicability::MaybeIncorrect,
 280                                                 );
 281                                             }
 282                                             _ => {
 283                                                 err.span_label(span, msg);
 284                                             }
 285                                         }
 286                                     }
 287                                 }
 288                             }
 289                             _ => {}
 290                         }
 291                         err.emit();
 292                         return;
 293                     } else {
 294                         let mut err = struct_span_err!(
 295                             tcx.sess,
 296                             item_name.span,
 297                             E0599,
 298                             "no {} named `{}` found for type `{}` in the current scope",
 299                             item_kind,
 300                             item_name,
 301                             ty_str
 302                         );
 303                         if let Some(suggestion) = suggestion {
 304                             // enum variant
 305                             err.span_suggestion(
 306                                 item_name.span,
 307                                 "did you mean",
 308                                 suggestion.to_string(),
 309                                 Applicability::MaybeIncorrect,
 310                             );
 311                         }
 312                         err
 313                     }
 314                 } else {
 315                     tcx.sess.diagnostic().struct_dummy()
 316                 };
 317
 318                 if let Some(def) = actual.ty_adt_def() {
 319                     if let Some(full_sp) = tcx.hir().span_if_local(def.did) {
 320                         let def_sp = tcx.sess.source_map().def_span(full_sp);
 321                         err.span_label(def_sp, format!("{} `{}` not found {}",
 322                                                        item_kind,
 323                                                        item_name,
 324                                                        if def.is_enum() && !is_method {
 325                                                            "here"
 326                                                        } else {
 327                                                            "for this"
 328                                                        }));
 329                     }
 330                 }
 331
 332                 // If the method name is the name of a field with a function or closure type,
 333                 // give a helping note that it has to be called as `(x.f)(...)`.
 334                 if let SelfSource::MethodCall(expr) = source {
 335                     let field_receiver = self
 336                         .autoderef(span, rcvr_ty)
 337                         .find_map(|(ty, _)| match ty.sty {
 338                             ty::Adt(def, substs) if !def.is_enum() => {
 339                                 let variant = &def.non_enum_variant();
 340                                 self.tcx.find_field_index(item_name, variant).map(|index| {
 341                                     let field = &variant.fields[index];
 342                                     let field_ty = field.ty(tcx, substs);
 343                                     (field, field_ty)
 344                                 })
 345                             }
 346                             _ => None,
 347                         });
 348
 349                     if let Some((field, field_ty)) = field_receiver {
 350                         let scope = self.tcx.hir().get_module_parent_by_hir_id(self.body_id);
 351                         let is_accessible = field.vis.is_accessible_from(scope, self.tcx);
 352
 353                         if is_accessible {
 354                             if self.is_fn_ty(&field_ty, span) {
 355                                 let expr_span = expr.span.to(item_name.span);
 356                                 err.multipart_suggestion(
 357                                     &format!(
 358                                         "to call the function stored in `{}`, \
 359                                          surround the field access with parentheses",
 360                                         item_name,
 361                                     ),
 362                                     vec![
 363                                         (expr_span.shrink_to_lo(), '('.to_string()),
 364                                         (expr_span.shrink_to_hi(), ')'.to_string()),
 365                                     ],
 366                                     Applicability::MachineApplicable,
 367                                 );
 368                             } else {
 369                                 let call_expr = self.tcx.hir().expect_expr_by_hir_id(
 370                                     self.tcx.hir().get_parent_node_by_hir_id(expr.hir_id),
 371                                 );
 372
 373                                 let span = call_expr.span.trim_start(item_name.span).unwrap();
 374
 375                                 err.span_suggestion(
 376                                     span,
 377                                     "remove the arguments",
 378                                     String::new(),
 379                                     Applicability::MaybeIncorrect,
 380                                 );
 381                             }
 382                         }
 383
 384                         let field_kind = if is_accessible {
 385                             "field"
 386                         } else {
 387                             "private field"
 388                         };
 389                         err.span_label(item_name.span, format!("{}, not a method", field_kind));
 390                     }
 391                 } else {
 392                     err.span_label(span, format!("{} not found in `{}`", item_kind, ty_str));
 393                 }
 394
 395                 if self.is_fn_ty(&rcvr_ty, span) {
 396                     macro_rules! report_function {
 397                         ($span:expr, $name:expr) => {
 398                             err.note(&format!("{} is a function, perhaps you wish to call it",
 399                                               $name));
 400                         }
 401                     }
 402
 403                     if let SelfSource::MethodCall(expr) = source {
 404                         if let Ok(expr_string) = tcx.sess.source_map().span_to_snippet(expr.span) {
 405                             report_function!(expr.span, expr_string);
 406                         } else if let ExprKind::Path(QPath::Resolved(_, ref path)) =
 407                             expr.node
 408                         {
 409                             if let Some(segment) = path.segments.last() {
 410                                 report_function!(expr.span, segment.ident);
 411                             }
 412                         }
 413                     }
 414                 }
 415
 416                 if !static_sources.is_empty() {
 417                     err.note("found the following associated functions; to be used as methods, \
 418                               functions must have a `self` parameter");
 419                     err.span_label(span, "this is an associated function, not a method");
 420                 }
 421                 if static_sources.len() == 1 {
 422                     if let SelfSource::MethodCall(expr) = source {
 423                         err.span_suggestion(expr.span.to(span),
 424                                             "use associated function syntax instead",
 425                                             format!("{}::{}",
 426                                                     self.ty_to_string(actual),
 427                                                     item_name),
 428                                             Applicability::MachineApplicable);
 429                     } else {
 430                         err.help(&format!("try with `{}::{}`",
 431                                           self.ty_to_string(actual), item_name));
 432                     }
 433
 434                     report_candidates(&mut err, static_sources);
 435                 } else if static_sources.len() > 1 {
 436                     report_candidates(&mut err, static_sources);
 437                 }
 438
 439                 if !unsatisfied_predicates.is_empty() {
 440                     let mut bound_list = unsatisfied_predicates.iter()
 441                         .map(|p| format!("`{} : {}`", p.self_ty(), p))
 442                         .collect::<Vec<_>>();
 443                     bound_list.sort();
 444                     bound_list.dedup();  // #35677
 445                     let bound_list = bound_list.join("\n");
 446                     err.note(&format!("the method `{}` exists but the following trait bounds \
 447                                        were not satisfied:\n{}",
 448                                       item_name,
 449                                       bound_list));
 450                 }
 451
 452                 if actual.is_numeric() && actual.is_fresh() {
 453
 454                 } else {
 455                     self.suggest_traits_to_import(&mut err,
 456                                                   span,
 457                                                   rcvr_ty,
 458                                                   item_name,
 459                                                   source,
 460                                                   out_of_scope_traits);
 461                 }
 462
 463                 if let Some(lev_candidate) = lev_candidate {
 464                     err.span_suggestion(
 465                         span,
 466                         "did you mean",
 467                         lev_candidate.ident.to_string(),
 468                         Applicability::MaybeIncorrect,
 469                     );
 470                 }
 471                 err.emit();
 472             }
 473
 474             MethodError::Ambiguity(sources) => {
 475                 let mut err = struct_span_err!(self.sess(),
 476                                                span,
 477                                                E0034,
 478                                                "multiple applicable items in scope");
 479                 err.span_label(span, format!("multiple `{}` found", item_name));
 480
 481                 report_candidates(&mut err, sources);
 482                 err.emit();
 483             }
 484
 485             MethodError::PrivateMatch(def, out_of_scope_traits) => {
 486                 let mut err = struct_span_err!(self.tcx.sess, span, E0624,
 487                                                "{} `{}` is private", def.kind_name(), item_name);
 488                 self.suggest_valid_traits(&mut err, out_of_scope_traits);
 489                 err.emit();
 490             }
 491
 492             MethodError::IllegalSizedBound(candidates) => {
 493                 let msg = format!("the `{}` method cannot be invoked on a trait object", item_name);
 494                 let mut err = self.sess().struct_span_err(span, &msg);
 495                 if !candidates.is_empty() {
 496                     let help = format!("{an}other candidate{s} {were} found in the following \
 497                                         trait{s}, perhaps add a `use` for {one_of_them}:",
 498                                     an = if candidates.len() == 1 {"an" } else { "" },
 499                                     s = if candidates.len() == 1 { "" } else { "s" },
 500                                     were = if candidates.len() == 1 { "was" } else { "were" },
 501                                     one_of_them = if candidates.len() == 1 {
 502                                         "it"
 503                                     } else {
 504                                         "one_of_them"
 505                                     });
 506                     self.suggest_use_candidates(&mut err, help, candidates);
 507                 }
 508                 err.emit();
 509             }
 510
 511             MethodError::BadReturnType => {
 512                 bug!("no return type expectations but got BadReturnType")
 513             }
 514         }
 515     }
 516
 517     fn suggest_use_candidates(&self,
 518                               err: &mut DiagnosticBuilder<'_>,
 519                               mut msg: String,
 520                               candidates: Vec<DefId>) {
 521         let module_did = self.tcx.hir().get_module_parent_by_hir_id(self.body_id);
 522         let module_id = self.tcx.hir().as_local_hir_id(module_did).unwrap();
 523         let krate = self.tcx.hir().krate();
 524         let (span, found_use) = UsePlacementFinder::check(self.tcx, krate, module_id);
 525         if let Some(span) = span {
 526             let path_strings = candidates.iter().map(|did| {
 527                 // Produce an additional newline to separate the new use statement
 528                 // from the directly following item.
 529                 let additional_newline = if found_use {
 530                     ""
 531                 } else {
 532                     "\n"
 533                 };
 534                 format!(
 535                     "use {};\n{}",
 536                     with_crate_prefix(|| self.tcx.def_path_str(*did)),
 537                     additional_newline
 538                 )
 539             });
 540
 541             err.span_suggestions(span, &msg, path_strings, Applicability::MaybeIncorrect);
 542         } else {
 543             let limit = if candidates.len() == 5 { 5 } else { 4 };
 544             for (i, trait_did) in candidates.iter().take(limit).enumerate() {
 545                 if candidates.len() > 1 {
 546                     msg.push_str(
 547                         &format!(
 548                             "\ncandidate #{}: `use {};`",
 549                             i + 1,
 550                             with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
 551                         )
 552                     );
 553                 } else {
 554                     msg.push_str(
 555                         &format!(
 556                             "\n`use {};`",
 557                             with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
 558                         )
 559                     );
 560                 }
 561             }
 562             if candidates.len() > limit {
 563                 msg.push_str(&format!("\nand {} others", candidates.len() - limit));
 564             }
 565             err.note(&msg[..]);
 566         }
 567     }
 568
 569     fn suggest_valid_traits(&self,
 570                             err: &mut DiagnosticBuilder<'_>,
 571                             valid_out_of_scope_traits: Vec<DefId>) -> bool {
 572         if !valid_out_of_scope_traits.is_empty() {
 573             let mut candidates = valid_out_of_scope_traits;
 574             candidates.sort();
 575             candidates.dedup();
 576             err.help("items from traits can only be used if the trait is in scope");
 577             let msg = format!("the following {traits_are} implemented but not in scope, \
 578                                perhaps add a `use` for {one_of_them}:",
 579                             traits_are = if candidates.len() == 1 {
 580                                 "trait is"
 581                             } else {
 582                                 "traits are"
 583                             },
 584                             one_of_them = if candidates.len() == 1 {
 585                                 "it"
 586                             } else {
 587                                 "one of them"
 588                             });
 589
 590             self.suggest_use_candidates(err, msg, candidates);
 591             true
 592         } else {
 593             false
 594         }
 595     }
 596
 597     fn suggest_traits_to_import<'b>(&self,
 598                                     err: &mut DiagnosticBuilder<'_>,
 599                                     span: Span,
 600                                     rcvr_ty: Ty<'tcx>,
 601                                     item_name: ast::Ident,
 602                                     source: SelfSource<'b>,
 603                                     valid_out_of_scope_traits: Vec<DefId>) {
 604         if self.suggest_valid_traits(err, valid_out_of_scope_traits) {
 605             return;
 606         }
 607
 608         let type_is_local = self.type_derefs_to_local(span, rcvr_ty, source);
 609
 610         // There are no traits implemented, so lets suggest some traits to
 611         // implement, by finding ones that have the item name, and are
 612         // legal to implement.
 613         let mut candidates = all_traits(self.tcx)
 614             .into_iter()
 615             .filter(|info| {
 616                 // We approximate the coherence rules to only suggest
 617                 // traits that are legal to implement by requiring that
 618                 // either the type or trait is local. Multi-dispatch means
 619                 // this isn't perfect (that is, there are cases when
 620                 // implementing a trait would be legal but is rejected
 621                 // here).
 622                 (type_is_local || info.def_id.is_local()) &&
 623                     self.associated_item(info.def_id, item_name, Namespace::Value)
 624                         .filter(|item| {
 625                             // We only want to suggest public or local traits (#45781).
 626                             item.vis == ty::Visibility::Public || info.def_id.is_local()
 627                         })
 628                         .is_some()
 629             })
 630             .collect::<Vec<_>>();
 631
 632         if !candidates.is_empty() {
 633             // Sort from most relevant to least relevant.
 634             candidates.sort_by(|a, b| a.cmp(b).reverse());
 635             candidates.dedup();
 636
 637             // FIXME #21673: this help message could be tuned to the case
 638             // of a type parameter: suggest adding a trait bound rather
 639             // than implementing.
 640             err.help("items from traits can only be used if the trait is implemented and in scope");
 641             let mut msg = format!("the following {traits_define} an item `{name}`, \
 642                                    perhaps you need to implement {one_of_them}:",
 643                                   traits_define = if candidates.len() == 1 {
 644                                       "trait defines"
 645                                   } else {
 646                                       "traits define"
 647                                   },
 648                                   one_of_them = if candidates.len() == 1 {
 649                                       "it"
 650                                   } else {
 651                                       "one of them"
 652                                   },
 653                                   name = item_name);
 654
 655             for (i, trait_info) in candidates.iter().enumerate() {
 656                 msg.push_str(&format!("\ncandidate #{}: `{}`",
 657                                       i + 1,
 658                                       self.tcx.def_path_str(trait_info.def_id)));
 659             }
 660             err.note(&msg[..]);
 661         }
 662     }
 663
 664     /// Checks whether there is a local type somewhere in the chain of
 665     /// autoderefs of `rcvr_ty`.
 666     fn type_derefs_to_local(&self,
 667                             span: Span,
 668                             rcvr_ty: Ty<'tcx>,
 669                             source: SelfSource<'_>) -> bool {
 670         fn is_local(ty: Ty<'_>) -> bool {
 671             match ty.sty {
 672                 ty::Adt(def, _) => def.did.is_local(),
 673                 ty::Foreign(did) => did.is_local(),
 674
 675                 ty::Dynamic(ref tr, ..) =>
 676                     tr.principal().map(|d| d.def_id().is_local()).unwrap_or(false),
 677
 678                 ty::Param(_) => true,
 679
 680                 // Everything else (primitive types, etc.) is effectively
 681                 // non-local (there are "edge" cases, e.g., `(LocalType,)`, but
 682                 // the noise from these sort of types is usually just really
 683                 // annoying, rather than any sort of help).
 684                 _ => false,
 685             }
 686         }
 687
 688         // This occurs for UFCS desugaring of `T::method`, where there is no
 689         // receiver expression for the method call, and thus no autoderef.
 690         if let SelfSource::QPath(_) = source {
 691             return is_local(self.resolve_type_vars_with_obligations(rcvr_ty));
 692         }
 693
 694         self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))
 695     }
 696 }
 697
 698 #[derive(Copy, Clone)]
 699 pub enum SelfSource<'a> {
 700     QPath(&'a hir::Ty),
 701     MethodCall(&'a hir::Expr /* rcvr */),
 702 }
 703
 704 #[derive(Copy, Clone)]
 705 pub struct TraitInfo {
 706     pub def_id: DefId,
 707 }
 708
 709 impl PartialEq for TraitInfo {
 710     fn eq(&self, other: &TraitInfo) -> bool {
 711         self.cmp(other) == Ordering::Equal
 712     }
 713 }
 714 impl Eq for TraitInfo {}
 715 impl PartialOrd for TraitInfo {
 716     fn partial_cmp(&self, other: &TraitInfo) -> Option<Ordering> {
 717         Some(self.cmp(other))
 718     }
 719 }
 720 impl Ord for TraitInfo {
 721     fn cmp(&self, other: &TraitInfo) -> Ordering {
 722         // Local crates are more important than remote ones (local:
 723         // `cnum == 0`), and otherwise we throw in the defid for totality.
 724
 725         let lhs = (other.def_id.krate, other.def_id);
 726         let rhs = (self.def_id.krate, self.def_id);
 727         lhs.cmp(&rhs)
 728     }
 729 }
 730
 731 /// Retrieves all traits in this crate and any dependent crates.
 732 pub fn all_traits<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Vec<TraitInfo> {
 733     tcx.all_traits(LOCAL_CRATE).iter().map(|&def_id| TraitInfo { def_id }).collect()
 734 }
 735
 736 /// Computes all traits in this crate and any dependent crates.
 737 fn compute_all_traits<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Vec<DefId> {
 738     use hir::itemlikevisit;
 739
 740     let mut traits = vec![];
 741
 742     // Crate-local:
 743
 744     struct Visitor<'a, 'tcx: 'a> {
 745         map: &'a hir_map::Map<'tcx>,
 746         traits: &'a mut Vec<DefId>,
 747     }
 748
 749     impl<'v, 'a, 'tcx> itemlikevisit::ItemLikeVisitor<'v> for Visitor<'a, 'tcx> {
 750         fn visit_item(&mut self, i: &'v hir::Item) {
 751             match i.node {
 752                 hir::ItemKind::Trait(..) |
 753                 hir::ItemKind::TraitAlias(..) => {
 754                     let def_id = self.map.local_def_id_from_hir_id(i.hir_id);
 755                     self.traits.push(def_id);
 756                 }
 757                 _ => ()
 758             }
 759         }
 760
 761         fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem) {}
 762
 763         fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem) {}
 764     }
 765
 766     tcx.hir().krate().visit_all_item_likes(&mut Visitor {
 767         map: &tcx.hir(),
 768         traits: &mut traits,
 769     });
 770
 771     // Cross-crate:
 772
 773     let mut external_mods = FxHashSet::default();
 774     fn handle_external_def(tcx: TyCtxt<'_, '_, '_>,
 775                            traits: &mut Vec<DefId>,
 776                            external_mods: &mut FxHashSet<DefId>,
 777                            def: Def) {
 778         match def {
 779             Def::Trait(def_id) |
 780             Def::TraitAlias(def_id) => {
 781                 traits.push(def_id);
 782             }
 783             Def::Mod(def_id) => {
 784                 if !external_mods.insert(def_id) {
 785                     return;
 786                 }
 787                 for child in tcx.item_children(def_id).iter() {
 788                     handle_external_def(tcx, traits, external_mods, child.def)
 789                 }
 790             }
 791             _ => {}
 792         }
 793     }
 794     for &cnum in tcx.crates().iter() {
 795         let def_id = DefId {
 796             krate: cnum,
 797             index: CRATE_DEF_INDEX,
 798         };
 799         handle_external_def(tcx, &mut traits, &mut external_mods, Def::Mod(def_id));
 800     }
 801
 802     traits
 803 }
 804
 805 pub fn provide(providers: &mut ty::query::Providers<'_>) {
 806     providers.all_traits = |tcx, cnum| {
 807         assert_eq!(cnum, LOCAL_CRATE);
 808         Lrc::new(compute_all_traits(tcx))
 809     }
 810 }
 811
 812 struct UsePlacementFinder<'a, 'tcx: 'a, 'gcx: 'tcx> {
 813     target_module: hir::HirId,
 814     span: Option<Span>,
 815     found_use: bool,
 816     tcx: TyCtxt<'a, 'gcx, 'tcx>
 817 }
 818
 819 impl<'a, 'tcx, 'gcx> UsePlacementFinder<'a, 'tcx, 'gcx> {
 820     fn check(
 821         tcx: TyCtxt<'a, 'gcx, 'tcx>,
 822         krate: &'tcx hir::Crate,
 823         target_module: hir::HirId,
 824     ) -> (Option<Span>, bool) {
 825         let mut finder = UsePlacementFinder {
 826             target_module,
 827             span: None,
 828             found_use: false,
 829             tcx,
 830         };
 831         hir::intravisit::walk_crate(&mut finder, krate);
 832         (finder.span, finder.found_use)
 833     }
 834 }
 835
 836 impl<'a, 'tcx, 'gcx> hir::intravisit::Visitor<'tcx> for UsePlacementFinder<'a, 'tcx, 'gcx> {
 837     fn visit_mod(
 838         &mut self,
 839         module: &'tcx hir::Mod,
 840         _: Span,
 841         hir_id: hir::HirId,
 842     ) {
 843         if self.span.is_some() {
 844             return;
 845         }
 846         if hir_id != self.target_module {
 847             hir::intravisit::walk_mod(self, module, hir_id);
 848             return;
 849         }
 850         // Find a `use` statement.
 851         for item_id in &module.item_ids {
 852             let item = self.tcx.hir().expect_item(item_id.id);
 853             match item.node {
 854                 hir::ItemKind::Use(..) => {
 855                     // Don't suggest placing a `use` before the prelude
 856                     // import or other generated ones.
 857                     if item.span.ctxt().outer().expn_info().is_none() {
 858                         self.span = Some(item.span.shrink_to_lo());
 859                         self.found_use = true;
 860                         return;
 861                     }
 862                 },
 863                 // Don't place `use` before `extern crate`...
 864                 hir::ItemKind::ExternCrate(_) => {}
 865                 // ...but do place them before the first other item.
 866                 _ => if self.span.map_or(true, |span| item.span < span ) {
 867                     if item.span.ctxt().outer().expn_info().is_none() {
 868                         // Don't insert between attributes and an item.
 869                         if item.attrs.is_empty() {
 870                             self.span = Some(item.span.shrink_to_lo());
 871                         } else {
 872                             // Find the first attribute on the item.
 873                             for attr in &item.attrs {
 874                                 if self.span.map_or(true, |span| attr.span < span) {
 875                                     self.span = Some(attr.span.shrink_to_lo());
 876                                 }
 877                             }
 878                         }
 879                     }
 880                 },
 881             }
 882         }
 883     }
 884
 885     fn nested_visit_map<'this>(
 886         &'this mut self
 887     ) -> hir::intravisit::NestedVisitorMap<'this, 'tcx> {
 888         hir::intravisit::NestedVisitorMap::None
 889     }
 890 }