src/librustc_typeck/check/method/suggest.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Give useful errors and suggestions to users when an item can't be
  12 //! found or is otherwise invalid.
  13
  14 use check::FnCtxt;
  15 use rustc::hir::map as hir_map;
  16 use hir::Node;
  17 use rustc_data_structures::sync::Lrc;
  18 use rustc::ty::{self, Ty, TyCtxt, ToPolyTraitRef, ToPredicate, TypeFoldable};
  19 use rustc::ty::item_path::with_crate_prefix;
  20 use hir::def::Def;
  21 use hir::def_id::{CRATE_DEF_INDEX, DefId};
  22 use middle::lang_items::FnOnceTraitLangItem;
  23 use namespace::Namespace;
  24 use rustc::traits::Obligation;
  25 use util::nodemap::FxHashSet;
  26
  27 use syntax::ast;
  28 use syntax::util::lev_distance::find_best_match_for_name;
  29 use errors::{Applicability, DiagnosticBuilder};
  30 use syntax_pos::{Span, FileName};
  31
  32
  33 use rustc::hir::def_id::LOCAL_CRATE;
  34 use rustc::hir;
  35 use rustc::hir::print;
  36 use rustc::infer::type_variable::TypeVariableOrigin;
  37 use rustc::ty::Adt;
  38
  39 use std::cmp::Ordering;
  40
  41 use super::{MethodError, NoMatchData, CandidateSource};
  42 use super::probe::Mode;
  43
  44 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
  45     fn is_fn_ty(&self, ty: &Ty<'tcx>, span: Span) -> bool {
  46         let tcx = self.tcx;
  47         match ty.sty {
  48             // Not all of these (e.g. unsafe fns) implement FnOnce
  49             // so we look for these beforehand
  50             ty::Closure(..) |
  51             ty::FnDef(..) |
  52             ty::FnPtr(_) => true,
  53             // If it's not a simple function, look for things which implement FnOnce
  54             _ => {
  55                 let fn_once = match tcx.lang_items().require(FnOnceTraitLangItem) {
  56                     Ok(fn_once) => fn_once,
  57                     Err(..) => return false,
  58                 };
  59
  60                 self.autoderef(span, ty).any(|(ty, _)| {
  61                     self.probe(|_| {
  62                         let fn_once_substs = tcx.mk_substs_trait(ty, &[
  63                             self.next_ty_var(TypeVariableOrigin::MiscVariable(span)).into()
  64                         ]);
  65                         let trait_ref = ty::TraitRef::new(fn_once, fn_once_substs);
  66                         let poly_trait_ref = trait_ref.to_poly_trait_ref();
  67                         let obligation =
  68                             Obligation::misc(span,
  69                                              self.body_id,
  70                                              self.param_env,
  71                                              poly_trait_ref.to_predicate());
  72                         self.predicate_may_hold(&obligation)
  73                     })
  74                 })
  75             }
  76         }
  77     }
  78
  79     pub fn report_method_error(&self,
  80                                span: Span,
  81                                rcvr_ty: Ty<'tcx>,
  82                                item_name: ast::Ident,
  83                                rcvr_expr: Option<&hir::Expr>,
  84                                error: MethodError<'tcx>,
  85                                args: Option<&'gcx [hir::Expr]>) {
  86         // avoid suggestions when we don't know what's going on.
  87         if rcvr_ty.references_error() {
  88             return;
  89         }
  90
  91         let report_candidates = |err: &mut DiagnosticBuilder, mut sources: Vec<CandidateSource>| {
  92             sources.sort();
  93             sources.dedup();
  94             // Dynamic limit to avoid hiding just one candidate, which is silly.
  95             let limit = if sources.len() == 5 { 5 } else { 4 };
  96
  97             for (idx, source) in sources.iter().take(limit).enumerate() {
  98                 match *source {
  99                     CandidateSource::ImplSource(impl_did) => {
 100                         // Provide the best span we can. Use the item, if local to crate, else
 101                         // the impl, if local to crate (item may be defaulted), else nothing.
 102                         let item = self.associated_item(impl_did, item_name, Namespace::Value)
 103                             .or_else(|| {
 104                                 self.associated_item(
 105                                     self.tcx.impl_trait_ref(impl_did).unwrap().def_id,
 106                                     item_name,
 107                                     Namespace::Value,
 108                                 )
 109                             }).unwrap();
 110                         let note_span = self.tcx.hir.span_if_local(item.def_id).or_else(|| {
 111                             self.tcx.hir.span_if_local(impl_did)
 112                         });
 113
 114                         let impl_ty = self.impl_self_ty(span, impl_did).ty;
 115
 116                         let insertion = match self.tcx.impl_trait_ref(impl_did) {
 117                             None => String::new(),
 118                             Some(trait_ref) => {
 119                                 format!(" of the trait `{}`",
 120                                         self.tcx.item_path_str(trait_ref.def_id))
 121                             }
 122                         };
 123
 124                         let note_str = if sources.len() > 1 {
 125                             format!("candidate #{} is defined in an impl{} for the type `{}`",
 126                                     idx + 1,
 127                                     insertion,
 128                                     impl_ty)
 129                         } else {
 130                             format!("the candidate is defined in an impl{} for the type `{}`",
 131                                     insertion,
 132                                     impl_ty)
 133                         };
 134                         if let Some(note_span) = note_span {
 135                             // We have a span pointing to the method. Show note with snippet.
 136                             err.span_note(self.tcx.sess.source_map().def_span(note_span),
 137                                           &note_str);
 138                         } else {
 139                             err.note(&note_str);
 140                         }
 141                     }
 142                     CandidateSource::TraitSource(trait_did) => {
 143                         let item = self
 144                             .associated_item(trait_did, item_name, Namespace::Value)
 145                             .unwrap();
 146                         let item_span = self.tcx.sess.source_map()
 147                             .def_span(self.tcx.def_span(item.def_id));
 148                         if sources.len() > 1 {
 149                             span_note!(err,
 150                                        item_span,
 151                                        "candidate #{} is defined in the trait `{}`",
 152                                        idx + 1,
 153                                        self.tcx.item_path_str(trait_did));
 154                         } else {
 155                             span_note!(err,
 156                                        item_span,
 157                                        "the candidate is defined in the trait `{}`",
 158                                        self.tcx.item_path_str(trait_did));
 159                         }
 160                         err.help(&format!("to disambiguate the method call, write `{}::{}({}{})` \
 161                                           instead",
 162                                           self.tcx.item_path_str(trait_did),
 163                                           item_name,
 164                                           if rcvr_ty.is_region_ptr() && args.is_some() {
 165                                               if rcvr_ty.is_mutable_pointer() {
 166                                                   "&mut "
 167                                               } else {
 168                                                   "&"
 169                                               }
 170                                           } else {
 171                                               ""
 172                                           },
 173                                           args.map(|arg| arg.iter()
 174                                               .map(|arg| print::to_string(print::NO_ANN,
 175                                                                           |s| s.print_expr(arg)))
 176                                               .collect::<Vec<_>>()
 177                                               .join(", ")).unwrap_or_else(|| "...".to_owned())));
 178                     }
 179                 }
 180             }
 181             if sources.len() > limit {
 182                 err.note(&format!("and {} others", sources.len() - limit));
 183             }
 184         };
 185
 186         match error {
 187             MethodError::NoMatch(NoMatchData {
 188                 static_candidates: static_sources,
 189                 unsatisfied_predicates,
 190                 out_of_scope_traits,
 191                 lev_candidate,
 192                 mode,
 193             }) => {
 194                 let tcx = self.tcx;
 195
 196                 let actual = self.resolve_type_vars_if_possible(&rcvr_ty);
 197                 let ty_string = self.ty_to_string(actual);
 198                 let is_method = mode == Mode::MethodCall;
 199                 let mut suggestion = None;
 200                 let item_kind = if is_method {
 201                     "method"
 202                 } else if actual.is_enum() {
 203                     if let Adt(ref adt_def, _) = actual.sty {
 204                         let names = adt_def.variants.iter().map(|s| &s.name);
 205                         suggestion = find_best_match_for_name(names,
 206                                                               &item_name.as_str(),
 207                                                               None);
 208                     }
 209                     "variant"
 210                 } else {
 211                     match (item_name.as_str().chars().next(), actual.is_fresh_ty()) {
 212                         (Some(name), false) if name.is_lowercase() => {
 213                             "function or associated item"
 214                         }
 215                         (Some(_), false) => "associated item",
 216                         (Some(_), true) | (None, false) => {
 217                             "variant or associated item"
 218                         }
 219                         (None, true) => "variant",
 220                     }
 221                 };
 222                 let mut err = if !actual.references_error() {
 223                     // Suggest clamping down the type if the method that is being attempted to
 224                     // be used exists at all, and the type is an ambiuous numeric type
 225                     // ({integer}/{float}).
 226                     let mut candidates = all_traits(self.tcx)
 227                         .into_iter()
 228                         .filter_map(|info|
 229                             self.associated_item(info.def_id, item_name, Namespace::Value)
 230                         );
 231                     if let (true, false, Some(expr), Some(_)) = (actual.is_numeric(),
 232                                                                  actual.has_concrete_skeleton(),
 233                                                                  rcvr_expr,
 234                                                                  candidates.next()) {
 235                         let mut err = struct_span_err!(
 236                             tcx.sess,
 237                             span,
 238                             E0689,
 239                             "can't call {} `{}` on ambiguous numeric type `{}`",
 240                             item_kind,
 241                             item_name,
 242                             ty_string
 243                         );
 244                         let concrete_type = if actual.is_integral() {
 245                             "i32"
 246                         } else {
 247                             "f32"
 248                         };
 249                         match expr.node {
 250                             hir::ExprKind::Lit(ref lit) => { // numeric literal
 251                                 let snippet = tcx.sess.source_map().span_to_snippet(lit.span)
 252                                     .unwrap_or_else(|_| "<numeric literal>".to_owned());
 253
 254                                 err.span_suggestion_with_applicability(
 255                                                     lit.span,
 256                                                     &format!("you must specify a concrete type for \
 257                                                               this numeric value, like `{}`",
 258                                                              concrete_type),
 259                                                     format!("{}_{}",
 260                                                             snippet,
 261                                                             concrete_type),
 262                                                     Applicability::MaybeIncorrect,
 263                                 );
 264                             }
 265                             hir::ExprKind::Path(ref qpath) => {  // local binding
 266                                 if let &hir::QPath::Resolved(_, ref path) = &qpath {
 267                                     if let hir::def::Def::Local(node_id) = path.def {
 268                                         let span = tcx.hir.span(node_id);
 269                                         let snippet = tcx.sess.source_map().span_to_snippet(span)
 270                                             .unwrap();
 271                                         let filename = tcx.sess.source_map().span_to_filename(span);
 272
 273                                         let parent_node = self.tcx.hir.get(
 274                                             self.tcx.hir.get_parent_node(node_id),
 275                                         );
 276                                         let msg = format!(
 277                                             "you must specify a type for this binding, like `{}`",
 278                                             concrete_type,
 279                                         );
 280
 281                                         match (filename, parent_node) {
 282                                             (FileName::Real(_), Node::Local(hir::Local {
 283                                                 source: hir::LocalSource::Normal,
 284                                                 ty,
 285                                                 ..
 286                                             })) => {
 287                                                 err.span_suggestion_with_applicability(
 288                                                     // account for `let x: _ = 42;`
 289                                                     //                  ^^^^
 290                                                     span.to(ty.as_ref().map(|ty| ty.span)
 291                                                         .unwrap_or(span)),
 292                                                     &msg,
 293                                                     format!("{}: {}", snippet, concrete_type),
 294                                                     Applicability::MaybeIncorrect,
 295                                                 );
 296                                             }
 297                                             _ => {
 298                                                 err.span_label(span, msg);
 299                                             }
 300                                         }
 301                                     }
 302                                 }
 303                             }
 304                             _ => {}
 305                         }
 306                         err.emit();
 307                         return;
 308                     } else {
 309                         let mut err = struct_span_err!(
 310                             tcx.sess,
 311                             span,
 312                             E0599,
 313                             "no {} named `{}` found for type `{}` in the current scope",
 314                             item_kind,
 315                             item_name,
 316                             ty_string
 317                         );
 318                         if let Some(suggestion) = suggestion {
 319                             err.note(&format!("did you mean `{}::{}`?", ty_string, suggestion));
 320                         }
 321                         err
 322                     }
 323                 } else {
 324                     tcx.sess.diagnostic().struct_dummy()
 325                 };
 326
 327                 if let Some(def) = actual.ty_adt_def() {
 328                     if let Some(full_sp) = tcx.hir.span_if_local(def.did) {
 329                         let def_sp = tcx.sess.source_map().def_span(full_sp);
 330                         err.span_label(def_sp, format!("{} `{}` not found {}",
 331                                                        item_kind,
 332                                                        item_name,
 333                                                        if def.is_enum() && !is_method {
 334                                                            "here"
 335                                                        } else {
 336                                                            "for this"
 337                                                        }));
 338                     }
 339                 }
 340
 341                 // If the method name is the name of a field with a function or closure type,
 342                 // give a helping note that it has to be called as (x.f)(...).
 343                 if let Some(expr) = rcvr_expr {
 344                     for (ty, _) in self.autoderef(span, rcvr_ty) {
 345                         if let ty::Adt(def, substs) = ty.sty {
 346                             if !def.is_enum() {
 347                                 let variant = &def.non_enum_variant();
 348                                 if let Some(index) = self.tcx.find_field_index(item_name, variant) {
 349                                     let field = &variant.fields[index];
 350                                     let snippet = tcx.sess.source_map().span_to_snippet(expr.span);
 351                                     let expr_string = match snippet {
 352                                         Ok(expr_string) => expr_string,
 353                                         _ => "s".into(), // Default to a generic placeholder for the
 354                                         // expression when we can't generate a
 355                                         // string snippet
 356                                     };
 357
 358                                     let field_ty = field.ty(tcx, substs);
 359                                     let scope = self.tcx.hir.get_module_parent(self.body_id);
 360                                     if field.vis.is_accessible_from(scope, self.tcx) {
 361                                         if self.is_fn_ty(&field_ty, span) {
 362                                             err.help(&format!("use `({0}.{1})(...)` if you \
 363                                                                meant to call the function \
 364                                                                stored in the `{1}` field",
 365                                                               expr_string,
 366                                                               item_name));
 367                                         } else {
 368                                             err.help(&format!("did you mean to write `{0}.{1}` \
 369                                                                instead of `{0}.{1}(...)`?",
 370                                                               expr_string,
 371                                                               item_name));
 372                                         }
 373                                         err.span_label(span, "field, not a method");
 374                                     } else {
 375                                         err.span_label(span, "private field, not a method");
 376                                     }
 377                                     break;
 378                                 }
 379                             }
 380                         }
 381                     }
 382                 } else {
 383                     err.span_label(span, format!("{} not found in `{}`", item_kind, ty_string));
 384                 }
 385
 386                 if self.is_fn_ty(&rcvr_ty, span) {
 387                     macro_rules! report_function {
 388                         ($span:expr, $name:expr) => {
 389                             err.note(&format!("{} is a function, perhaps you wish to call it",
 390                                               $name));
 391                         }
 392                     }
 393
 394                     if let Some(expr) = rcvr_expr {
 395                         if let Ok(expr_string) = tcx.sess.source_map().span_to_snippet(expr.span) {
 396                             report_function!(expr.span, expr_string);
 397                         } else if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) =
 398                             expr.node
 399                         {
 400                             if let Some(segment) = path.segments.last() {
 401                                 report_function!(expr.span, segment.ident);
 402                             }
 403                         }
 404                     }
 405                 }
 406
 407                 if !static_sources.is_empty() {
 408                     err.note("found the following associated functions; to be used as methods, \
 409                               functions must have a `self` parameter");
 410                     err.span_label(span, "this is an associated function, not a method");
 411                 }
 412                 if static_sources.len() == 1 {
 413                     if let Some(expr) = rcvr_expr {
 414                         err.span_suggestion_with_applicability(expr.span.to(span),
 415                                             "use associated function syntax instead",
 416                                             format!("{}::{}",
 417                                                     self.ty_to_string(actual),
 418                                                     item_name),
 419                                             Applicability::MachineApplicable);
 420                     } else {
 421                         err.help(&format!("try with `{}::{}`",
 422                                           self.ty_to_string(actual), item_name));
 423                     }
 424
 425                     report_candidates(&mut err, static_sources);
 426                 } else if static_sources.len() > 1 {
 427
 428                     report_candidates(&mut err, static_sources);
 429                 }
 430
 431                 if !unsatisfied_predicates.is_empty() {
 432                     let bound_list = unsatisfied_predicates.iter()
 433                         .map(|p| format!("`{} : {}`", p.self_ty(), p))
 434                         .collect::<Vec<_>>()
 435                         .join("\n");
 436                     err.note(&format!("the method `{}` exists but the following trait bounds \
 437                                        were not satisfied:\n{}",
 438                                       item_name,
 439                                       bound_list));
 440                 }
 441
 442                 if actual.is_numeric() && actual.is_fresh() {
 443
 444                 } else {
 445                     self.suggest_traits_to_import(&mut err,
 446                                                   span,
 447                                                   rcvr_ty,
 448                                                   item_name,
 449                                                   rcvr_expr,
 450                                                   out_of_scope_traits);
 451                 }
 452
 453                 if let Some(lev_candidate) = lev_candidate {
 454                     err.help(&format!("did you mean `{}`?", lev_candidate.ident));
 455                 }
 456                 err.emit();
 457             }
 458
 459             MethodError::Ambiguity(sources) => {
 460                 let mut err = struct_span_err!(self.sess(),
 461                                                span,
 462                                                E0034,
 463                                                "multiple applicable items in scope");
 464                 err.span_label(span, format!("multiple `{}` found", item_name));
 465
 466                 report_candidates(&mut err, sources);
 467                 err.emit();
 468             }
 469
 470             MethodError::PrivateMatch(def, out_of_scope_traits) => {
 471                 let mut err = struct_span_err!(self.tcx.sess, span, E0624,
 472                                                "{} `{}` is private", def.kind_name(), item_name);
 473                 self.suggest_valid_traits(&mut err, out_of_scope_traits);
 474                 err.emit();
 475             }
 476
 477             MethodError::IllegalSizedBound(candidates) => {
 478                 let msg = format!("the `{}` method cannot be invoked on a trait object", item_name);
 479                 let mut err = self.sess().struct_span_err(span, &msg);
 480                 if !candidates.is_empty() {
 481                     let help = format!("{an}other candidate{s} {were} found in the following \
 482                                         trait{s}, perhaps add a `use` for {one_of_them}:",
 483                                     an = if candidates.len() == 1 {"an" } else { "" },
 484                                     s = if candidates.len() == 1 { "" } else { "s" },
 485                                     were = if candidates.len() == 1 { "was" } else { "were" },
 486                                     one_of_them = if candidates.len() == 1 {
 487                                         "it"
 488                                     } else {
 489                                         "one_of_them"
 490                                     });
 491                     self.suggest_use_candidates(&mut err, help, candidates);
 492                 }
 493                 err.emit();
 494             }
 495
 496             MethodError::BadReturnType => {
 497                 bug!("no return type expectations but got BadReturnType")
 498             }
 499         }
 500     }
 501
 502     fn suggest_use_candidates(&self,
 503                               err: &mut DiagnosticBuilder,
 504                               mut msg: String,
 505                               candidates: Vec<DefId>) {
 506         let module_did = self.tcx.hir.get_module_parent(self.body_id);
 507         let module_id = self.tcx.hir.as_local_node_id(module_did).unwrap();
 508         let krate = self.tcx.hir.krate();
 509         let (span, found_use) = UsePlacementFinder::check(self.tcx, krate, module_id);
 510         if let Some(span) = span {
 511             let path_strings = candidates.iter().map(|did| {
 512                 // produce an additional newline to separate the new use statement
 513                 // from the directly following item.
 514                 let additional_newline = if found_use {
 515                     ""
 516                 } else {
 517                     "\n"
 518                 };
 519                 format!(
 520                     "use {};\n{}",
 521                     with_crate_prefix(|| self.tcx.item_path_str(*did)),
 522                     additional_newline
 523                 )
 524             }).collect();
 525
 526             err.span_suggestions_with_applicability(
 527                                                     span,
 528                                                     &msg,
 529                                                     path_strings,
 530                                                     Applicability::MaybeIncorrect,
 531             );
 532         } else {
 533             let limit = if candidates.len() == 5 { 5 } else { 4 };
 534             for (i, trait_did) in candidates.iter().take(limit).enumerate() {
 535                 if candidates.len() > 1 {
 536                     msg.push_str(
 537                         &format!(
 538                             "\ncandidate #{}: `use {};`",
 539                             i + 1,
 540                             with_crate_prefix(|| self.tcx.item_path_str(*trait_did))
 541                         )
 542                     );
 543                 } else {
 544                     msg.push_str(
 545                         &format!(
 546                             "\n`use {};`",
 547                             with_crate_prefix(|| self.tcx.item_path_str(*trait_did))
 548                         )
 549                     );
 550                 }
 551             }
 552             if candidates.len() > limit {
 553                 msg.push_str(&format!("\nand {} others", candidates.len() - limit));
 554             }
 555             err.note(&msg[..]);
 556         }
 557     }
 558
 559     fn suggest_valid_traits(&self,
 560                             err: &mut DiagnosticBuilder,
 561                             valid_out_of_scope_traits: Vec<DefId>) -> bool {
 562         if !valid_out_of_scope_traits.is_empty() {
 563             let mut candidates = valid_out_of_scope_traits;
 564             candidates.sort();
 565             candidates.dedup();
 566             err.help("items from traits can only be used if the trait is in scope");
 567             let msg = format!("the following {traits_are} implemented but not in scope, \
 568                                perhaps add a `use` for {one_of_them}:",
 569                             traits_are = if candidates.len() == 1 {
 570                                 "trait is"
 571                             } else {
 572                                 "traits are"
 573                             },
 574                             one_of_them = if candidates.len() == 1 {
 575                                 "it"
 576                             } else {
 577                                 "one of them"
 578                             });
 579
 580             self.suggest_use_candidates(err, msg, candidates);
 581             true
 582         } else {
 583             false
 584         }
 585     }
 586
 587     fn suggest_traits_to_import(&self,
 588                                 err: &mut DiagnosticBuilder,
 589                                 span: Span,
 590                                 rcvr_ty: Ty<'tcx>,
 591                                 item_name: ast::Ident,
 592                                 rcvr_expr: Option<&hir::Expr>,
 593                                 valid_out_of_scope_traits: Vec<DefId>) {
 594         if self.suggest_valid_traits(err, valid_out_of_scope_traits) {
 595             return;
 596         }
 597
 598         let type_is_local = self.type_derefs_to_local(span, rcvr_ty, rcvr_expr);
 599
 600         // there's no implemented traits, so lets suggest some traits to
 601         // implement, by finding ones that have the item name, and are
 602         // legal to implement.
 603         let mut candidates = all_traits(self.tcx)
 604             .into_iter()
 605             .filter(|info| {
 606                 // we approximate the coherence rules to only suggest
 607                 // traits that are legal to implement by requiring that
 608                 // either the type or trait is local. Multidispatch means
 609                 // this isn't perfect (that is, there are cases when
 610                 // implementing a trait would be legal but is rejected
 611                 // here).
 612                 (type_is_local || info.def_id.is_local()) &&
 613                     self.associated_item(info.def_id, item_name, Namespace::Value)
 614                         .filter(|item| {
 615                             // We only want to suggest public or local traits (#45781).
 616                             item.vis == ty::Visibility::Public || info.def_id.is_local()
 617                         })
 618                         .is_some()
 619             })
 620             .collect::<Vec<_>>();
 621
 622         if !candidates.is_empty() {
 623             // sort from most relevant to least relevant
 624             candidates.sort_by(|a, b| a.cmp(b).reverse());
 625             candidates.dedup();
 626
 627             // FIXME #21673 this help message could be tuned to the case
 628             // of a type parameter: suggest adding a trait bound rather
 629             // than implementing.
 630             err.help("items from traits can only be used if the trait is implemented and in scope");
 631             let mut msg = format!("the following {traits_define} an item `{name}`, \
 632                                    perhaps you need to implement {one_of_them}:",
 633                                   traits_define = if candidates.len() == 1 {
 634                                       "trait defines"
 635                                   } else {
 636                                       "traits define"
 637                                   },
 638                                   one_of_them = if candidates.len() == 1 {
 639                                       "it"
 640                                   } else {
 641                                       "one of them"
 642                                   },
 643                                   name = item_name);
 644
 645             for (i, trait_info) in candidates.iter().enumerate() {
 646                 msg.push_str(&format!("\ncandidate #{}: `{}`",
 647                                       i + 1,
 648                                       self.tcx.item_path_str(trait_info.def_id)));
 649             }
 650             err.note(&msg[..]);
 651         }
 652     }
 653
 654     /// Checks whether there is a local type somewhere in the chain of
 655     /// autoderefs of `rcvr_ty`.
 656     fn type_derefs_to_local(&self,
 657                             span: Span,
 658                             rcvr_ty: Ty<'tcx>,
 659                             rcvr_expr: Option<&hir::Expr>)
 660                             -> bool {
 661         fn is_local(ty: Ty) -> bool {
 662             match ty.sty {
 663                 ty::Adt(def, _) => def.did.is_local(),
 664                 ty::Foreign(did) => did.is_local(),
 665
 666                 ty::Dynamic(ref tr, ..) => tr.principal().def_id().is_local(),
 667
 668                 ty::Param(_) => true,
 669
 670                 // everything else (primitive types etc.) is effectively
 671                 // non-local (there are "edge" cases, e.g. (LocalType,), but
 672                 // the noise from these sort of types is usually just really
 673                 // annoying, rather than any sort of help).
 674                 _ => false,
 675             }
 676         }
 677
 678         // This occurs for UFCS desugaring of `T::method`, where there is no
 679         // receiver expression for the method call, and thus no autoderef.
 680         if rcvr_expr.is_none() {
 681             return is_local(self.resolve_type_vars_with_obligations(rcvr_ty));
 682         }
 683
 684         self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))
 685     }
 686 }
 687
 688 #[derive(Copy, Clone)]
 689 pub struct TraitInfo {
 690     pub def_id: DefId,
 691 }
 692
 693 impl PartialEq for TraitInfo {
 694     fn eq(&self, other: &TraitInfo) -> bool {
 695         self.cmp(other) == Ordering::Equal
 696     }
 697 }
 698 impl Eq for TraitInfo {}
 699 impl PartialOrd for TraitInfo {
 700     fn partial_cmp(&self, other: &TraitInfo) -> Option<Ordering> {
 701         Some(self.cmp(other))
 702     }
 703 }
 704 impl Ord for TraitInfo {
 705     fn cmp(&self, other: &TraitInfo) -> Ordering {
 706         // local crates are more important than remote ones (local:
 707         // cnum == 0), and otherwise we throw in the defid for totality
 708
 709         let lhs = (other.def_id.krate, other.def_id);
 710         let rhs = (self.def_id.krate, self.def_id);
 711         lhs.cmp(&rhs)
 712     }
 713 }
 714
 715 /// Retrieve all traits in this crate and any dependent crates.
 716 pub fn all_traits<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Vec<TraitInfo> {
 717     tcx.all_traits(LOCAL_CRATE).iter().map(|&def_id| TraitInfo { def_id }).collect()
 718 }
 719
 720 /// Compute all traits in this crate and any dependent crates.
 721 fn compute_all_traits<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Vec<DefId> {
 722         use rustc::hir::itemlikevisit;
 723
 724         let mut traits = vec![];
 725
 726         // Crate-local:
 727         //
 728         // meh.
 729         struct Visitor<'a, 'tcx: 'a> {
 730             map: &'a hir_map::Map<'tcx>,
 731             traits: &'a mut Vec<DefId>,
 732         }
 733         impl<'v, 'a, 'tcx> itemlikevisit::ItemLikeVisitor<'v> for Visitor<'a, 'tcx> {
 734             fn visit_item(&mut self, i: &'v hir::Item) {
 735                 if let hir::ItemKind::Trait(..) = i.node {
 736                     let def_id = self.map.local_def_id(i.id);
 737                     self.traits.push(def_id);
 738                 }
 739             }
 740
 741             fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem) {
 742             }
 743
 744             fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem) {
 745             }
 746         }
 747         tcx.hir.krate().visit_all_item_likes(&mut Visitor {
 748             map: &tcx.hir,
 749             traits: &mut traits,
 750         });
 751
 752         // Cross-crate:
 753         let mut external_mods = FxHashSet::default();
 754         fn handle_external_def(tcx: TyCtxt,
 755                                traits: &mut Vec<DefId>,
 756                                external_mods: &mut FxHashSet<DefId>,
 757                                def: Def) {
 758             let def_id = def.def_id();
 759             match def {
 760                 Def::Trait(..) => {
 761                     traits.push(def_id);
 762                 }
 763                 Def::Mod(..) => {
 764                     if !external_mods.insert(def_id) {
 765                         return;
 766                     }
 767                     for child in tcx.item_children(def_id).iter() {
 768                         handle_external_def(tcx, traits, external_mods, child.def)
 769                     }
 770                 }
 771                 _ => {}
 772             }
 773         }
 774         for &cnum in tcx.crates().iter() {
 775             let def_id = DefId {
 776                 krate: cnum,
 777                 index: CRATE_DEF_INDEX,
 778             };
 779             handle_external_def(tcx, &mut traits, &mut external_mods, Def::Mod(def_id));
 780         }
 781
 782     traits
 783 }
 784
 785 pub fn provide(providers: &mut ty::query::Providers) {
 786     providers.all_traits = |tcx, cnum| {
 787         assert_eq!(cnum, LOCAL_CRATE);
 788         Lrc::new(compute_all_traits(tcx))
 789     }
 790 }
 791
 792 struct UsePlacementFinder<'a, 'tcx: 'a, 'gcx: 'tcx> {
 793     target_module: ast::NodeId,
 794     span: Option<Span>,
 795     found_use: bool,
 796     tcx: TyCtxt<'a, 'gcx, 'tcx>
 797 }
 798
 799 impl<'a, 'tcx, 'gcx> UsePlacementFinder<'a, 'tcx, 'gcx> {
 800     fn check(
 801         tcx: TyCtxt<'a, 'gcx, 'tcx>,
 802         krate: &'tcx hir::Crate,
 803         target_module: ast::NodeId,
 804     ) -> (Option<Span>, bool) {
 805         let mut finder = UsePlacementFinder {
 806             target_module,
 807             span: None,
 808             found_use: false,
 809             tcx,
 810         };
 811         hir::intravisit::walk_crate(&mut finder, krate);
 812         (finder.span, finder.found_use)
 813     }
 814 }
 815
 816 impl<'a, 'tcx, 'gcx> hir::intravisit::Visitor<'tcx> for UsePlacementFinder<'a, 'tcx, 'gcx> {
 817     fn visit_mod(
 818         &mut self,
 819         module: &'tcx hir::Mod,
 820         _: Span,
 821         node_id: ast::NodeId,
 822     ) {
 823         if self.span.is_some() {
 824             return;
 825         }
 826         if node_id != self.target_module {
 827             hir::intravisit::walk_mod(self, module, node_id);
 828             return;
 829         }
 830         // find a use statement
 831         for item_id in &module.item_ids {
 832             let item = self.tcx.hir.expect_item(item_id.id);
 833             match item.node {
 834                 hir::ItemKind::Use(..) => {
 835                     // don't suggest placing a use before the prelude
 836                     // import or other generated ones
 837                     if item.span.ctxt().outer().expn_info().is_none() {
 838                         self.span = Some(item.span.shrink_to_lo());
 839                         self.found_use = true;
 840                         return;
 841                     }
 842                 },
 843                 // don't place use before extern crate
 844                 hir::ItemKind::ExternCrate(_) => {}
 845                 // but place them before the first other item
 846                 _ => if self.span.map_or(true, |span| item.span < span ) {
 847                     if item.span.ctxt().outer().expn_info().is_none() {
 848                         // don't insert between attributes and an item
 849                         if item.attrs.is_empty() {
 850                             self.span = Some(item.span.shrink_to_lo());
 851                         } else {
 852                             // find the first attribute on the item
 853                             for attr in &item.attrs {
 854                                 if self.span.map_or(true, |span| attr.span < span) {
 855                                     self.span = Some(attr.span.shrink_to_lo());
 856                                 }
 857                             }
 858                         }
 859                     }
 860                 },
 861             }
 862         }
 863     }
 864     fn nested_visit_map<'this>(
 865         &'this mut self
 866     ) -> hir::intravisit::NestedVisitorMap<'this, 'tcx> {
 867         hir::intravisit::NestedVisitorMap::None
 868     }
 869 }