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