src/librustc_resolve/diagnostics.rs

   1 use std::cmp::Reverse;
   2
   3 use errors::{Applicability, DiagnosticBuilder, DiagnosticId};
   4 use log::debug;
   5 use rustc::bug;
   6 use rustc::hir::def::{self, DefKind, NonMacroAttrKind};
   7 use rustc::hir::def::Namespace::{self, *};
   8 use rustc::hir::def_id::{CRATE_DEF_INDEX, DefId};
   9 use rustc::session::Session;
  10 use rustc::ty::{self, DefIdTree};
  11 use rustc::util::nodemap::FxHashSet;
  12 use syntax::ast::{self, Ident, Path};
  13 use syntax::feature_gate::BUILTIN_ATTRIBUTES;
  14 use syntax::source_map::SourceMap;
  15 use syntax::struct_span_err;
  16 use syntax::symbol::{Symbol, kw};
  17 use syntax::util::lev_distance::find_best_match_for_name;
  18 use syntax_pos::hygiene::MacroKind;
  19 use syntax_pos::{BytePos, Span, MultiSpan};
  20
  21 use crate::resolve_imports::{ImportDirective, ImportDirectiveSubclass, ImportResolver};
  22 use crate::path_names_to_string;
  23 use crate::{BindingError, CrateLint, HasGenericParams, LegacyScope, Module, ModuleOrUniformRoot};
  24 use crate::{PathResult, ParentScope, ResolutionError, Resolver, Scope, ScopeSet, Segment};
  25
  26 type Res = def::Res<ast::NodeId>;
  27
  28 /// A vector of spans and replacements, a message and applicability.
  29 crate type Suggestion = (Vec<(Span, String)>, String, Applicability);
  30
  31 crate struct TypoSuggestion {
  32     pub candidate: Symbol,
  33     pub res: Res,
  34 }
  35
  36 impl TypoSuggestion {
  37     crate fn from_res(candidate: Symbol, res: Res) -> TypoSuggestion {
  38         TypoSuggestion { candidate, res }
  39     }
  40 }
  41
  42 /// A free importable items suggested in case of resolution failure.
  43 crate struct ImportSuggestion {
  44     pub did: Option<DefId>,
  45     pub path: Path,
  46 }
  47
  48 /// Adjust the impl span so that just the `impl` keyword is taken by removing
  49 /// everything after `<` (`"impl<T> Iterator for A<T> {}" -> "impl"`) and
  50 /// everything after the first whitespace (`"impl Iterator for A" -> "impl"`).
  51 ///
  52 /// *Attention*: the method used is very fragile since it essentially duplicates the work of the
  53 /// parser. If you need to use this function or something similar, please consider updating the
  54 /// `source_map` functions and this function to something more robust.
  55 fn reduce_impl_span_to_impl_keyword(cm: &SourceMap, impl_span: Span) -> Span {
  56     let impl_span = cm.span_until_char(impl_span, '<');
  57     let impl_span = cm.span_until_whitespace(impl_span);
  58     impl_span
  59 }
  60
  61 impl<'a> Resolver<'a> {
  62     crate fn add_module_candidates(
  63         &mut self,
  64         module: Module<'a>,
  65         names: &mut Vec<TypoSuggestion>,
  66         filter_fn: &impl Fn(Res) -> bool,
  67     ) {
  68         for (key, resolution) in self.resolutions(module).borrow().iter() {
  69             if let Some(binding) = resolution.borrow().binding {
  70                 let res = binding.res();
  71                 if filter_fn(res) {
  72                     names.push(TypoSuggestion::from_res(key.ident.name, res));
  73                 }
  74             }
  75         }
  76     }
  77
  78     /// Combines an error with provided span and emits it.
  79     ///
  80     /// This takes the error provided, combines it with the span and any additional spans inside the
  81     /// error and emits it.
  82     crate fn report_error(&self, span: Span, resolution_error: ResolutionError<'_>) {
  83         self.into_struct_error(span, resolution_error).emit();
  84     }
  85
  86     crate fn into_struct_error(
  87         &self, span: Span, resolution_error: ResolutionError<'_>
  88     ) -> DiagnosticBuilder<'_> {
  89         match resolution_error {
  90             ResolutionError::GenericParamsFromOuterFunction(outer_res, has_generic_params) => {
  91                 let mut err = struct_span_err!(self.session,
  92                     span,
  93                     E0401,
  94                     "can't use generic parameters from outer function",
  95                 );
  96                 err.span_label(span, format!("use of generic parameter from outer function"));
  97
  98                 let cm = self.session.source_map();
  99                 match outer_res {
 100                     Res::SelfTy(maybe_trait_defid, maybe_impl_defid) => {
 101                         if let Some(impl_span) = maybe_impl_defid.and_then(|def_id| {
 102                             self.definitions.opt_span(def_id)
 103                         }) {
 104                             err.span_label(
 105                                 reduce_impl_span_to_impl_keyword(cm, impl_span),
 106                                 "`Self` type implicitly declared here, by this `impl`",
 107                             );
 108                         }
 109                         match (maybe_trait_defid, maybe_impl_defid) {
 110                             (Some(_), None) => {
 111                                 err.span_label(span, "can't use `Self` here");
 112                             }
 113                             (_, Some(_)) => {
 114                                 err.span_label(span, "use a type here instead");
 115                             }
 116                             (None, None) => bug!("`impl` without trait nor type?"),
 117                         }
 118                         return err;
 119                     },
 120                     Res::Def(DefKind::TyParam, def_id) => {
 121                         if let Some(span) = self.definitions.opt_span(def_id) {
 122                             err.span_label(span, "type parameter from outer function");
 123                         }
 124                     }
 125                     Res::Def(DefKind::ConstParam, def_id) => {
 126                         if let Some(span) = self.definitions.opt_span(def_id) {
 127                             err.span_label(span, "const parameter from outer function");
 128                         }
 129                     }
 130                     _ => {
 131                         bug!("GenericParamsFromOuterFunction should only be used with Res::SelfTy, \
 132                             DefKind::TyParam");
 133                     }
 134                 }
 135
 136                 if has_generic_params == HasGenericParams::Yes {
 137                     // Try to retrieve the span of the function signature and generate a new
 138                     // message with a local type or const parameter.
 139                     let sugg_msg = &format!("try using a local generic parameter instead");
 140                     if let Some((sugg_span, snippet)) = cm.generate_local_type_param_snippet(span) {
 141                         // Suggest the modification to the user
 142                         err.span_suggestion(
 143                             sugg_span,
 144                             sugg_msg,
 145                             snippet,
 146                             Applicability::MachineApplicable,
 147                         );
 148                     } else if let Some(sp) = cm.generate_fn_name_span(span) {
 149                         err.span_label(sp,
 150                             format!("try adding a local generic parameter in this method instead"));
 151                     } else {
 152                         err.help(&format!("try using a local generic parameter instead"));
 153                     }
 154                 }
 155
 156                 err
 157             }
 158             ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => {
 159                 let mut err = struct_span_err!(
 160                     self.session,
 161                     span,
 162                     E0403,
 163                     "the name `{}` is already used for a generic \
 164                      parameter in this item's generic parameters",
 165                     name,
 166                 );
 167                 err.span_label(span, "already used");
 168                 err.span_label(first_use_span, format!("first use of `{}`", name));
 169                 err
 170             }
 171             ResolutionError::MethodNotMemberOfTrait(method, trait_) => {
 172                 let mut err = struct_span_err!(self.session,
 173                                             span,
 174                                             E0407,
 175                                             "method `{}` is not a member of trait `{}`",
 176                                             method,
 177                                             trait_);
 178                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 179                 err
 180             }
 181             ResolutionError::TypeNotMemberOfTrait(type_, trait_) => {
 182                 let mut err = struct_span_err!(self.session,
 183                                 span,
 184                                 E0437,
 185                                 "type `{}` is not a member of trait `{}`",
 186                                 type_,
 187                                 trait_);
 188                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 189                 err
 190             }
 191             ResolutionError::ConstNotMemberOfTrait(const_, trait_) => {
 192                 let mut err = struct_span_err!(self.session,
 193                                 span,
 194                                 E0438,
 195                                 "const `{}` is not a member of trait `{}`",
 196                                 const_,
 197                                 trait_);
 198                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 199                 err
 200             }
 201             ResolutionError::VariableNotBoundInPattern(binding_error) => {
 202                 let BindingError { name, target, origin, could_be_path } = binding_error;
 203
 204                 let target_sp = target.iter().copied().collect::<Vec<_>>();
 205                 let origin_sp = origin.iter().copied().collect::<Vec<_>>();
 206
 207                 let msp = MultiSpan::from_spans(target_sp.clone());
 208                 let msg = format!("variable `{}` is not bound in all patterns", name);
 209                 let mut err = self.session.struct_span_err_with_code(
 210                     msp,
 211                     &msg,
 212                     DiagnosticId::Error("E0408".into()),
 213                 );
 214                 for sp in target_sp {
 215                     err.span_label(sp, format!("pattern doesn't bind `{}`", name));
 216                 }
 217                 for sp in origin_sp {
 218                     err.span_label(sp, "variable not in all patterns");
 219                 }
 220                 if *could_be_path {
 221                     let help_msg = format!(
 222                         "if you meant to match on a variant or a `const` item, consider \
 223                          making the path in the pattern qualified: `?::{}`",
 224                          name,
 225                      );
 226                     err.span_help(span, &help_msg);
 227                 }
 228                 err
 229             }
 230             ResolutionError::VariableBoundWithDifferentMode(variable_name,
 231                                                             first_binding_span) => {
 232                 let mut err = struct_span_err!(self.session,
 233                                 span,
 234                                 E0409,
 235                                 "variable `{}` is bound in inconsistent \
 236                                 ways within the same match arm",
 237                                 variable_name);
 238                 err.span_label(span, "bound in different ways");
 239                 err.span_label(first_binding_span, "first binding");
 240                 err
 241             }
 242             ResolutionError::IdentifierBoundMoreThanOnceInParameterList(identifier) => {
 243                 let mut err = struct_span_err!(self.session,
 244                                 span,
 245                                 E0415,
 246                                 "identifier `{}` is bound more than once in this parameter list",
 247                                 identifier);
 248                 err.span_label(span, "used as parameter more than once");
 249                 err
 250             }
 251             ResolutionError::IdentifierBoundMoreThanOnceInSamePattern(identifier) => {
 252                 let mut err = struct_span_err!(self.session,
 253                                 span,
 254                                 E0416,
 255                                 "identifier `{}` is bound more than once in the same pattern",
 256                                 identifier);
 257                 err.span_label(span, "used in a pattern more than once");
 258                 err
 259             }
 260             ResolutionError::UndeclaredLabel(name, lev_candidate) => {
 261                 let mut err = struct_span_err!(self.session,
 262                                             span,
 263                                             E0426,
 264                                             "use of undeclared label `{}`",
 265                                             name);
 266                 if let Some(lev_candidate) = lev_candidate {
 267                     err.span_suggestion(
 268                         span,
 269                         "a label with a similar name exists in this scope",
 270                         lev_candidate.to_string(),
 271                         Applicability::MaybeIncorrect,
 272                     );
 273                 } else {
 274                     err.span_label(span, format!("undeclared label `{}`", name));
 275                 }
 276                 err
 277             }
 278             ResolutionError::SelfImportsOnlyAllowedWithin => {
 279                 struct_span_err!(self.session,
 280                                 span,
 281                                 E0429,
 282                                 "{}",
 283                                 "`self` imports are only allowed within a { } list")
 284             }
 285             ResolutionError::SelfImportCanOnlyAppearOnceInTheList => {
 286                 let mut err = struct_span_err!(self.session, span, E0430,
 287                                             "`self` import can only appear once in an import list");
 288                 err.span_label(span, "can only appear once in an import list");
 289                 err
 290             }
 291             ResolutionError::SelfImportOnlyInImportListWithNonEmptyPrefix => {
 292                 let mut err = struct_span_err!(self.session, span, E0431,
 293                                             "`self` import can only appear in an import list with \
 294                                                 a non-empty prefix");
 295                 err.span_label(span, "can only appear in an import list with a non-empty prefix");
 296                 err
 297             }
 298             ResolutionError::FailedToResolve { label, suggestion } => {
 299                 let mut err = struct_span_err!(self.session, span, E0433,
 300                                             "failed to resolve: {}", &label);
 301                 err.span_label(span, label);
 302
 303                 if let Some((suggestions, msg, applicability)) = suggestion {
 304                     err.multipart_suggestion(&msg, suggestions, applicability);
 305                 }
 306
 307                 err
 308             }
 309             ResolutionError::CannotCaptureDynamicEnvironmentInFnItem => {
 310                 let mut err = struct_span_err!(self.session,
 311                                             span,
 312                                             E0434,
 313                                             "{}",
 314                                             "can't capture dynamic environment in a fn item");
 315                 err.help("use the `|| { ... }` closure form instead");
 316                 err
 317             }
 318             ResolutionError::AttemptToUseNonConstantValueInConstant => {
 319                 let mut err = struct_span_err!(self.session, span, E0435,
 320                                             "attempt to use a non-constant value in a constant");
 321                 err.span_label(span, "non-constant value");
 322                 err
 323             }
 324             ResolutionError::BindingShadowsSomethingUnacceptable(what_binding, name, binding) => {
 325                 let res = binding.res();
 326                 let shadows_what = res.descr();
 327                 let mut err = struct_span_err!(self.session, span, E0530, "{}s cannot shadow {}s",
 328                                             what_binding, shadows_what);
 329                 err.span_label(span, format!("cannot be named the same as {} {}",
 330                                             res.article(), shadows_what));
 331                 let participle = if binding.is_import() { "imported" } else { "defined" };
 332                 let msg = format!("the {} `{}` is {} here", shadows_what, name, participle);
 333                 err.span_label(binding.span, msg);
 334                 err
 335             }
 336             ResolutionError::ForwardDeclaredTyParam => {
 337                 let mut err = struct_span_err!(self.session, span, E0128,
 338                                             "type parameters with a default cannot use \
 339                                                 forward declared identifiers");
 340                 err.span_label(
 341                     span, "defaulted type parameters cannot be forward declared".to_string());
 342                 err
 343             }
 344             ResolutionError::SelfInTyParamDefault => {
 345                 let mut err = struct_span_err!(
 346                     self.session,
 347                     span,
 348                     E0735,
 349                     "type parameters cannot use `Self` in their defaults"
 350                 );
 351                 err.span_label(
 352                     span, "`Self` in type parameter default".to_string());
 353                 err
 354             }
 355         }
 356     }
 357
 358     /// Lookup typo candidate in scope for a macro or import.
 359     fn early_lookup_typo_candidate(
 360         &mut self,
 361         scope_set: ScopeSet,
 362         parent_scope: &ParentScope<'a>,
 363         ident: Ident,
 364         filter_fn: &impl Fn(Res) -> bool,
 365     ) -> Option<TypoSuggestion> {
 366         let mut suggestions = Vec::new();
 367         self.visit_scopes(scope_set, parent_scope, ident, |this, scope, use_prelude, _| {
 368             match scope {
 369                 Scope::DeriveHelpers => {
 370                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 371                     if filter_fn(res) {
 372                         for derive in parent_scope.derives {
 373                             let parent_scope =
 374                                 &ParentScope { derives: &[], ..*parent_scope };
 375                             if let Ok((Some(ext), _)) = this.resolve_macro_path(
 376                                 derive, Some(MacroKind::Derive), parent_scope, false, false
 377                             ) {
 378                                 suggestions.extend(ext.helper_attrs.iter().map(|name| {
 379                                     TypoSuggestion::from_res(*name, res)
 380                                 }));
 381                             }
 382                         }
 383                     }
 384                 }
 385                 Scope::MacroRules(legacy_scope) => {
 386                     if let LegacyScope::Binding(legacy_binding) = legacy_scope {
 387                         let res = legacy_binding.binding.res();
 388                         if filter_fn(res) {
 389                             suggestions.push(
 390                                 TypoSuggestion::from_res(legacy_binding.ident.name, res)
 391                             )
 392                         }
 393                     }
 394                 }
 395                 Scope::CrateRoot => {
 396                     let root_ident = Ident::new(kw::PathRoot, ident.span);
 397                     let root_module = this.resolve_crate_root(root_ident);
 398                     this.add_module_candidates(root_module, &mut suggestions, filter_fn);
 399                 }
 400                 Scope::Module(module) => {
 401                     this.add_module_candidates(module, &mut suggestions, filter_fn);
 402                 }
 403                 Scope::RegisteredAttrs => {
 404                     let res = Res::NonMacroAttr(NonMacroAttrKind::Registered);
 405                     if filter_fn(res) {
 406                         suggestions.extend(this.registered_attrs.iter().map(|ident| {
 407                             TypoSuggestion::from_res(ident.name, res)
 408                         }));
 409                     }
 410                 }
 411                 Scope::MacroUsePrelude => {
 412                     suggestions.extend(this.macro_use_prelude.iter().filter_map(|(name, binding)| {
 413                         let res = binding.res();
 414                         if filter_fn(res) {
 415                             Some(TypoSuggestion::from_res(*name, res))
 416                         } else {
 417                             None
 418                         }
 419                     }));
 420                 }
 421                 Scope::BuiltinAttrs => {
 422                     let res = Res::NonMacroAttr(NonMacroAttrKind::Builtin);
 423                     if filter_fn(res) {
 424                         suggestions.extend(BUILTIN_ATTRIBUTES.iter().map(|(name, ..)| {
 425                             TypoSuggestion::from_res(*name, res)
 426                         }));
 427                     }
 428                 }
 429                 Scope::LegacyPluginHelpers => {
 430                     let res = Res::NonMacroAttr(NonMacroAttrKind::LegacyPluginHelper);
 431                     if filter_fn(res) {
 432                         let plugin_attributes = this.session.plugin_attributes.borrow();
 433                         suggestions.extend(plugin_attributes.iter().map(|(name, _)| {
 434                             TypoSuggestion::from_res(*name, res)
 435                         }));
 436                     }
 437                 }
 438                 Scope::ExternPrelude => {
 439                     suggestions.extend(this.extern_prelude.iter().filter_map(|(ident, _)| {
 440                         let res = Res::Def(DefKind::Mod, DefId::local(CRATE_DEF_INDEX));
 441                         if filter_fn(res) {
 442                             Some(TypoSuggestion::from_res(ident.name, res))
 443                         } else {
 444                             None
 445                         }
 446                     }));
 447                 }
 448                 Scope::ToolPrelude => {
 449                     let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
 450                     suggestions.extend(this.registered_tools.iter().map(|ident| {
 451                         TypoSuggestion::from_res(ident.name, res)
 452                     }));
 453                 }
 454                 Scope::StdLibPrelude => {
 455                     if let Some(prelude) = this.prelude {
 456                         let mut tmp_suggestions = Vec::new();
 457                         this.add_module_candidates(prelude, &mut tmp_suggestions, filter_fn);
 458                         suggestions.extend(tmp_suggestions.into_iter().filter(|s| {
 459                             use_prelude || this.is_builtin_macro(s.res)
 460                         }));
 461                     }
 462                 }
 463                 Scope::BuiltinTypes => {
 464                     let primitive_types = &this.primitive_type_table.primitive_types;
 465                     suggestions.extend(
 466                         primitive_types.iter().flat_map(|(name, prim_ty)| {
 467                             let res = Res::PrimTy(*prim_ty);
 468                             if filter_fn(res) {
 469                                 Some(TypoSuggestion::from_res(*name, res))
 470                             } else {
 471                                 None
 472                             }
 473                         })
 474                     )
 475                 }
 476             }
 477
 478             None::<()>
 479         });
 480
 481         // Make sure error reporting is deterministic.
 482         suggestions.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
 483
 484         match find_best_match_for_name(
 485             suggestions.iter().map(|suggestion| &suggestion.candidate),
 486             &ident.as_str(),
 487             None,
 488         ) {
 489             Some(found) if found != ident.name => suggestions
 490                 .into_iter()
 491                 .find(|suggestion| suggestion.candidate == found),
 492             _ => None,
 493         }
 494     }
 495
 496     fn lookup_import_candidates_from_module<FilterFn>(&mut self,
 497                                           lookup_ident: Ident,
 498                                           namespace: Namespace,
 499                                           start_module: Module<'a>,
 500                                           crate_name: Ident,
 501                                           filter_fn: FilterFn)
 502                                           -> Vec<ImportSuggestion>
 503         where FilterFn: Fn(Res) -> bool
 504     {
 505         let mut candidates = Vec::new();
 506         let mut seen_modules = FxHashSet::default();
 507         let not_local_module = crate_name.name != kw::Crate;
 508         let mut worklist = vec![(start_module, Vec::<ast::PathSegment>::new(), not_local_module)];
 509
 510         while let Some((in_module,
 511                         path_segments,
 512                         in_module_is_extern)) = worklist.pop() {
 513             // We have to visit module children in deterministic order to avoid
 514             // instabilities in reported imports (#43552).
 515             in_module.for_each_child(self, |this, ident, ns, name_binding| {
 516                 // avoid imports entirely
 517                 if name_binding.is_import() && !name_binding.is_extern_crate() { return; }
 518                 // avoid non-importable candidates as well
 519                 if !name_binding.is_importable() { return; }
 520
 521                 // collect results based on the filter function
 522                 if ident.name == lookup_ident.name && ns == namespace {
 523                     let res = name_binding.res();
 524                     if filter_fn(res) {
 525                         // create the path
 526                         let mut segms = path_segments.clone();
 527                         if lookup_ident.span.rust_2018() {
 528                             // crate-local absolute paths start with `crate::` in edition 2018
 529                             // FIXME: may also be stabilized for Rust 2015 (Issues #45477, #44660)
 530                             segms.insert(
 531                                 0, ast::PathSegment::from_ident(crate_name)
 532                             );
 533                         }
 534
 535                         segms.push(ast::PathSegment::from_ident(ident));
 536                         let path = Path {
 537                             span: name_binding.span,
 538                             segments: segms,
 539                         };
 540                         // the entity is accessible in the following cases:
 541                         // 1. if it's defined in the same crate, it's always
 542                         // accessible (since private entities can be made public)
 543                         // 2. if it's defined in another crate, it's accessible
 544                         // only if both the module is public and the entity is
 545                         // declared as public (due to pruning, we don't explore
 546                         // outside crate private modules => no need to check this)
 547                         if !in_module_is_extern || name_binding.vis == ty::Visibility::Public {
 548                             let did = match res {
 549                                 Res::Def(DefKind::Ctor(..), did) => this.parent(did),
 550                                 _ => res.opt_def_id(),
 551                             };
 552                             candidates.push(ImportSuggestion { did, path });
 553                         }
 554                     }
 555                 }
 556
 557                 // collect submodules to explore
 558                 if let Some(module) = name_binding.module() {
 559                     // form the path
 560                     let mut path_segments = path_segments.clone();
 561                     path_segments.push(ast::PathSegment::from_ident(ident));
 562
 563                     let is_extern_crate_that_also_appears_in_prelude =
 564                         name_binding.is_extern_crate() &&
 565                         lookup_ident.span.rust_2018();
 566
 567                     let is_visible_to_user =
 568                         !in_module_is_extern || name_binding.vis == ty::Visibility::Public;
 569
 570                     if !is_extern_crate_that_also_appears_in_prelude && is_visible_to_user {
 571                         // add the module to the lookup
 572                         let is_extern = in_module_is_extern || name_binding.is_extern_crate();
 573                         if seen_modules.insert(module.def_id().unwrap()) {
 574                             worklist.push((module, path_segments, is_extern));
 575                         }
 576                     }
 577                 }
 578             })
 579         }
 580
 581         candidates
 582     }
 583
 584     /// When name resolution fails, this method can be used to look up candidate
 585     /// entities with the expected name. It allows filtering them using the
 586     /// supplied predicate (which should be used to only accept the types of
 587     /// definitions expected, e.g., traits). The lookup spans across all crates.
 588     ///
 589     /// N.B., the method does not look into imports, but this is not a problem,
 590     /// since we report the definitions (thus, the de-aliased imports).
 591     crate fn lookup_import_candidates<FilterFn>(
 592         &mut self, lookup_ident: Ident, namespace: Namespace, filter_fn: FilterFn
 593     ) -> Vec<ImportSuggestion>
 594         where FilterFn: Fn(Res) -> bool
 595     {
 596         let mut suggestions = self.lookup_import_candidates_from_module(
 597             lookup_ident, namespace, self.graph_root, Ident::with_dummy_span(kw::Crate), &filter_fn
 598         );
 599
 600         if lookup_ident.span.rust_2018() {
 601             let extern_prelude_names = self.extern_prelude.clone();
 602             for (ident, _) in extern_prelude_names.into_iter() {
 603                 if ident.span.from_expansion() {
 604                     // Idents are adjusted to the root context before being
 605                     // resolved in the extern prelude, so reporting this to the
 606                     // user is no help. This skips the injected
 607                     // `extern crate std` in the 2018 edition, which would
 608                     // otherwise cause duplicate suggestions.
 609                     continue;
 610                 }
 611                 if let Some(crate_id) = self.crate_loader.maybe_process_path_extern(ident.name,
 612                                                                                     ident.span) {
 613                     let crate_root = self.get_module(DefId {
 614                         krate: crate_id,
 615                         index: CRATE_DEF_INDEX,
 616                     });
 617                     suggestions.extend(self.lookup_import_candidates_from_module(
 618                         lookup_ident, namespace, crate_root, ident, &filter_fn));
 619                 }
 620             }
 621         }
 622
 623         suggestions
 624     }
 625
 626     crate fn unresolved_macro_suggestions(
 627         &mut self,
 628         err: &mut DiagnosticBuilder<'a>,
 629         macro_kind: MacroKind,
 630         parent_scope: &ParentScope<'a>,
 631         ident: Ident,
 632     ) {
 633         let is_expected = &|res: Res| res.macro_kind() == Some(macro_kind);
 634         let suggestion = self.early_lookup_typo_candidate(
 635             ScopeSet::Macro(macro_kind), parent_scope, ident, is_expected
 636         );
 637         self.add_typo_suggestion(err, suggestion, ident.span);
 638
 639         if macro_kind == MacroKind::Derive &&
 640            (ident.as_str() == "Send" || ident.as_str() == "Sync") {
 641             let msg = format!("unsafe traits like `{}` should be implemented explicitly", ident);
 642             err.span_note(ident.span, &msg);
 643         }
 644         if self.macro_names.contains(&ident.modern()) {
 645             err.help("have you added the `#[macro_use]` on the module/import?");
 646         }
 647     }
 648
 649     crate fn add_typo_suggestion(
 650         &self,
 651         err: &mut DiagnosticBuilder<'_>,
 652         suggestion: Option<TypoSuggestion>,
 653         span: Span,
 654     ) -> bool {
 655         if let Some(suggestion) = suggestion {
 656             let msg = format!(
 657                 "{} {} with a similar name exists", suggestion.res.article(), suggestion.res.descr()
 658             );
 659             err.span_suggestion(
 660                 span, &msg, suggestion.candidate.to_string(), Applicability::MaybeIncorrect
 661             );
 662             let def_span = suggestion.res.opt_def_id()
 663                 .and_then(|def_id| self.definitions.opt_span(def_id));
 664             if let Some(span) = def_span {
 665                 err.span_label(span, &format!(
 666                     "similarly named {} `{}` defined here",
 667                     suggestion.res.descr(),
 668                     suggestion.candidate.as_str(),
 669                 ));
 670             }
 671             return true;
 672         }
 673         false
 674     }
 675 }
 676
 677 impl<'a, 'b> ImportResolver<'a, 'b> {
 678     /// Adds suggestions for a path that cannot be resolved.
 679     pub(crate) fn make_path_suggestion(
 680         &mut self,
 681         span: Span,
 682         mut path: Vec<Segment>,
 683         parent_scope: &ParentScope<'b>,
 684     ) -> Option<(Vec<Segment>, Vec<String>)> {
 685         debug!("make_path_suggestion: span={:?} path={:?}", span, path);
 686
 687         match (path.get(0), path.get(1)) {
 688             // `{{root}}::ident::...` on both editions.
 689             // On 2015 `{{root}}` is usually added implicitly.
 690             (Some(fst), Some(snd)) if fst.ident.name == kw::PathRoot &&
 691                                       !snd.ident.is_path_segment_keyword() => {}
 692             // `ident::...` on 2018.
 693             (Some(fst), _) if fst.ident.span.rust_2018() &&
 694                               !fst.ident.is_path_segment_keyword() => {
 695                 // Insert a placeholder that's later replaced by `self`/`super`/etc.
 696                 path.insert(0, Segment::from_ident(Ident::invalid()));
 697             }
 698             _ => return None,
 699         }
 700
 701         self.make_missing_self_suggestion(span, path.clone(), parent_scope)
 702             .or_else(|| self.make_missing_crate_suggestion(span, path.clone(), parent_scope))
 703             .or_else(|| self.make_missing_super_suggestion(span, path.clone(), parent_scope))
 704             .or_else(|| self.make_external_crate_suggestion(span, path, parent_scope))
 705     }
 706
 707     /// Suggest a missing `self::` if that resolves to an correct module.
 708     ///
 709     /// ```
 710     ///    |
 711     /// LL | use foo::Bar;
 712     ///    |     ^^^ did you mean `self::foo`?
 713     /// ```
 714     fn make_missing_self_suggestion(
 715         &mut self,
 716         span: Span,
 717         mut path: Vec<Segment>,
 718         parent_scope: &ParentScope<'b>,
 719     ) -> Option<(Vec<Segment>, Vec<String>)> {
 720         // Replace first ident with `self` and check if that is valid.
 721         path[0].ident.name = kw::SelfLower;
 722         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 723         debug!("make_missing_self_suggestion: path={:?} result={:?}", path, result);
 724         if let PathResult::Module(..) = result {
 725             Some((path, Vec::new()))
 726         } else {
 727             None
 728         }
 729     }
 730
 731     /// Suggests a missing `crate::` if that resolves to an correct module.
 732     ///
 733     /// ```
 734     ///    |
 735     /// LL | use foo::Bar;
 736     ///    |     ^^^ did you mean `crate::foo`?
 737     /// ```
 738     fn make_missing_crate_suggestion(
 739         &mut self,
 740         span: Span,
 741         mut path: Vec<Segment>,
 742         parent_scope: &ParentScope<'b>,
 743     ) -> Option<(Vec<Segment>, Vec<String>)> {
 744         // Replace first ident with `crate` and check if that is valid.
 745         path[0].ident.name = kw::Crate;
 746         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 747         debug!("make_missing_crate_suggestion:  path={:?} result={:?}", path, result);
 748         if let PathResult::Module(..) = result {
 749             Some((
 750                 path,
 751                 vec![
 752                     "`use` statements changed in Rust 2018; read more at \
 753                      <https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-\
 754                      clarity.html>".to_string()
 755                 ],
 756             ))
 757         } else {
 758             None
 759         }
 760     }
 761
 762     /// Suggests a missing `super::` if that resolves to an correct module.
 763     ///
 764     /// ```
 765     ///    |
 766     /// LL | use foo::Bar;
 767     ///    |     ^^^ did you mean `super::foo`?
 768     /// ```
 769     fn make_missing_super_suggestion(
 770         &mut self,
 771         span: Span,
 772         mut path: Vec<Segment>,
 773         parent_scope: &ParentScope<'b>,
 774     ) -> Option<(Vec<Segment>, Vec<String>)> {
 775         // Replace first ident with `crate` and check if that is valid.
 776         path[0].ident.name = kw::Super;
 777         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 778         debug!("make_missing_super_suggestion:  path={:?} result={:?}", path, result);
 779         if let PathResult::Module(..) = result {
 780             Some((path, Vec::new()))
 781         } else {
 782             None
 783         }
 784     }
 785
 786     /// Suggests a missing external crate name if that resolves to an correct module.
 787     ///
 788     /// ```
 789     ///    |
 790     /// LL | use foobar::Baz;
 791     ///    |     ^^^^^^ did you mean `baz::foobar`?
 792     /// ```
 793     ///
 794     /// Used when importing a submodule of an external crate but missing that crate's
 795     /// name as the first part of path.
 796     fn make_external_crate_suggestion(
 797         &mut self,
 798         span: Span,
 799         mut path: Vec<Segment>,
 800         parent_scope: &ParentScope<'b>,
 801     ) -> Option<(Vec<Segment>, Vec<String>)> {
 802         if path[1].ident.span.rust_2015() {
 803             return None;
 804         }
 805
 806         // Sort extern crate names in reverse order to get
 807         // 1) some consistent ordering for emitted dignostics, and
 808         // 2) `std` suggestions before `core` suggestions.
 809         let mut extern_crate_names =
 810             self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
 811         extern_crate_names.sort_by_key(|name| Reverse(name.as_str()));
 812
 813         for name in extern_crate_names.into_iter() {
 814             // Replace first ident with a crate name and check if that is valid.
 815             path[0].ident.name = name;
 816             let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 817             debug!("make_external_crate_suggestion: name={:?} path={:?} result={:?}",
 818                     name, path, result);
 819             if let PathResult::Module(..) = result {
 820                 return Some((path, Vec::new()));
 821             }
 822         }
 823
 824         None
 825     }
 826
 827     /// Suggests importing a macro from the root of the crate rather than a module within
 828     /// the crate.
 829     ///
 830     /// ```
 831     /// help: a macro with this name exists at the root of the crate
 832     ///    |
 833     /// LL | use issue_59764::makro;
 834     ///    |     ^^^^^^^^^^^^^^^^^^
 835     ///    |
 836     ///    = note: this could be because a macro annotated with `#[macro_export]` will be exported
 837     ///            at the root of the crate instead of the module where it is defined
 838     /// ```
 839     pub(crate) fn check_for_module_export_macro(
 840         &mut self,
 841         directive: &'b ImportDirective<'b>,
 842         module: ModuleOrUniformRoot<'b>,
 843         ident: Ident,
 844     ) -> Option<(Option<Suggestion>, Vec<String>)> {
 845         let mut crate_module = if let ModuleOrUniformRoot::Module(module) = module {
 846             module
 847         } else {
 848             return None;
 849         };
 850
 851         while let Some(parent) = crate_module.parent {
 852             crate_module = parent;
 853         }
 854
 855         if ModuleOrUniformRoot::same_def(ModuleOrUniformRoot::Module(crate_module), module) {
 856             // Don't make a suggestion if the import was already from the root of the
 857             // crate.
 858             return None;
 859         }
 860
 861         let resolutions = self.r.resolutions(crate_module).borrow();
 862         let resolution = resolutions.get(&self.r.new_key(ident, MacroNS))?;
 863         let binding = resolution.borrow().binding()?;
 864         if let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() {
 865             let module_name = crate_module.kind.name().unwrap();
 866             let import = match directive.subclass {
 867                 ImportDirectiveSubclass::SingleImport { source, target, .. } if source != target =>
 868                     format!("{} as {}", source, target),
 869                 _ => format!("{}", ident),
 870             };
 871
 872             let mut corrections: Vec<(Span, String)> = Vec::new();
 873             if !directive.is_nested() {
 874                 // Assume this is the easy case of `use issue_59764::foo::makro;` and just remove
 875                 // intermediate segments.
 876                 corrections.push((directive.span, format!("{}::{}", module_name, import)));
 877             } else {
 878                 // Find the binding span (and any trailing commas and spaces).
 879                 //   ie. `use a::b::{c, d, e};`
 880                 //                      ^^^
 881                 let (found_closing_brace, binding_span) = find_span_of_binding_until_next_binding(
 882                     self.r.session, directive.span, directive.use_span,
 883                 );
 884                 debug!("check_for_module_export_macro: found_closing_brace={:?} binding_span={:?}",
 885                        found_closing_brace, binding_span);
 886
 887                 let mut removal_span = binding_span;
 888                 if found_closing_brace {
 889                     // If the binding span ended with a closing brace, as in the below example:
 890                     //   ie. `use a::b::{c, d};`
 891                     //                      ^
 892                     // Then expand the span of characters to remove to include the previous
 893                     // binding's trailing comma.
 894                     //   ie. `use a::b::{c, d};`
 895                     //                    ^^^
 896                     if let Some(previous_span) = extend_span_to_previous_binding(
 897                         self.r.session, binding_span,
 898                     ) {
 899                         debug!("check_for_module_export_macro: previous_span={:?}", previous_span);
 900                         removal_span = removal_span.with_lo(previous_span.lo());
 901                     }
 902                 }
 903                 debug!("check_for_module_export_macro: removal_span={:?}", removal_span);
 904
 905                 // Remove the `removal_span`.
 906                 corrections.push((removal_span, "".to_string()));
 907
 908                 // Find the span after the crate name and if it has nested imports immediatately
 909                 // after the crate name already.
 910                 //   ie. `use a::b::{c, d};`
 911                 //               ^^^^^^^^^
 912                 //   or  `use a::{b, c, d}};`
 913                 //               ^^^^^^^^^^^
 914                 let (has_nested, after_crate_name) = find_span_immediately_after_crate_name(
 915                     self.r.session, module_name, directive.use_span,
 916                 );
 917                 debug!("check_for_module_export_macro: has_nested={:?} after_crate_name={:?}",
 918                        has_nested, after_crate_name);
 919
 920                 let source_map = self.r.session.source_map();
 921
 922                 // Add the import to the start, with a `{` if required.
 923                 let start_point = source_map.start_point(after_crate_name);
 924                 if let Ok(start_snippet) = source_map.span_to_snippet(start_point) {
 925                     corrections.push((
 926                         start_point,
 927                         if has_nested {
 928                             // In this case, `start_snippet` must equal '{'.
 929                             format!("{}{}, ", start_snippet, import)
 930                         } else {
 931                             // In this case, add a `{`, then the moved import, then whatever
 932                             // was there before.
 933                             format!("{{{}, {}", import, start_snippet)
 934                         }
 935                     ));
 936                 }
 937
 938                 // Add a `};` to the end if nested, matching the `{` added at the start.
 939                 if !has_nested {
 940                     corrections.push((source_map.end_point(after_crate_name),
 941                                      "};".to_string()));
 942                 }
 943             }
 944
 945             let suggestion = Some((
 946                 corrections,
 947                 String::from("a macro with this name exists at the root of the crate"),
 948                 Applicability::MaybeIncorrect,
 949             ));
 950             let note = vec![
 951                 "this could be because a macro annotated with `#[macro_export]` will be exported \
 952                  at the root of the crate instead of the module where it is defined".to_string(),
 953             ];
 954             Some((suggestion, note))
 955         } else {
 956             None
 957         }
 958     }
 959 }
 960
 961 /// Given a `binding_span` of a binding within a use statement:
 962 ///
 963 /// ```
 964 /// use foo::{a, b, c};
 965 ///              ^
 966 /// ```
 967 ///
 968 /// then return the span until the next binding or the end of the statement:
 969 ///
 970 /// ```
 971 /// use foo::{a, b, c};
 972 ///              ^^^
 973 /// ```
 974 pub(crate) fn find_span_of_binding_until_next_binding(
 975     sess: &Session,
 976     binding_span: Span,
 977     use_span: Span,
 978 ) -> (bool, Span) {
 979     let source_map = sess.source_map();
 980
 981     // Find the span of everything after the binding.
 982     //   ie. `a, e};` or `a};`
 983     let binding_until_end = binding_span.with_hi(use_span.hi());
 984
 985     // Find everything after the binding but not including the binding.
 986     //   ie. `, e};` or `};`
 987     let after_binding_until_end = binding_until_end.with_lo(binding_span.hi());
 988
 989     // Keep characters in the span until we encounter something that isn't a comma or
 990     // whitespace.
 991     //   ie. `, ` or ``.
 992     //
 993     // Also note whether a closing brace character was encountered. If there
 994     // was, then later go backwards to remove any trailing commas that are left.
 995     let mut found_closing_brace = false;
 996     let after_binding_until_next_binding = source_map.span_take_while(
 997         after_binding_until_end,
 998         |&ch| {
 999             if ch == '}' { found_closing_brace = true; }
1000             ch == ' ' || ch == ','
1001         }
1002     );
1003
1004     // Combine the two spans.
1005     //   ie. `a, ` or `a`.
1006     //
1007     // Removing these would leave `issue_52891::{d, e};` or `issue_52891::{d, e, };`
1008     let span = binding_span.with_hi(after_binding_until_next_binding.hi());
1009
1010     (found_closing_brace, span)
1011 }
1012
1013 /// Given a `binding_span`, return the span through to the comma or opening brace of the previous
1014 /// binding.
1015 ///
1016 /// ```
1017 /// use foo::a::{a, b, c};
1018 ///               ^^--- binding span
1019 ///               |
1020 ///               returned span
1021 ///
1022 /// use foo::{a, b, c};
1023 ///           --- binding span
1024 /// ```
1025 pub(crate) fn extend_span_to_previous_binding(
1026     sess: &Session,
1027     binding_span: Span,
1028 ) -> Option<Span> {
1029     let source_map = sess.source_map();
1030
1031     // `prev_source` will contain all of the source that came before the span.
1032     // Then split based on a command and take the first (ie. closest to our span)
1033     // snippet. In the example, this is a space.
1034     let prev_source = source_map.span_to_prev_source(binding_span).ok()?;
1035
1036     let prev_comma = prev_source.rsplit(',').collect::<Vec<_>>();
1037     let prev_starting_brace = prev_source.rsplit('{').collect::<Vec<_>>();
1038     if prev_comma.len() <= 1 || prev_starting_brace.len() <= 1 {
1039         return None;
1040     }
1041
1042     let prev_comma = prev_comma.first().unwrap();
1043     let prev_starting_brace = prev_starting_brace.first().unwrap();
1044
1045     // If the amount of source code before the comma is greater than
1046     // the amount of source code before the starting brace then we've only
1047     // got one item in the nested item (eg. `issue_52891::{self}`).
1048     if prev_comma.len() > prev_starting_brace.len() {
1049         return None;
1050     }
1051
1052     Some(binding_span.with_lo(BytePos(
1053         // Take away the number of bytes for the characters we've found and an
1054         // extra for the comma.
1055         binding_span.lo().0 - (prev_comma.as_bytes().len() as u32) - 1
1056     )))
1057 }
1058
1059 /// Given a `use_span` of a binding within a use statement, returns the highlighted span and if
1060 /// it is a nested use tree.
1061 ///
1062 /// ```
1063 /// use foo::a::{b, c};
1064 ///          ^^^^^^^^^^ // false
1065 ///
1066 /// use foo::{a, b, c};
1067 ///          ^^^^^^^^^^ // true
1068 ///
1069 /// use foo::{a, b::{c, d}};
1070 ///          ^^^^^^^^^^^^^^^ // true
1071 /// ```
1072 fn find_span_immediately_after_crate_name(
1073     sess: &Session,
1074     module_name: Symbol,
1075     use_span: Span,
1076 ) -> (bool, Span) {
1077     debug!("find_span_immediately_after_crate_name: module_name={:?} use_span={:?}",
1078            module_name, use_span);
1079     let source_map = sess.source_map();
1080
1081     // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
1082     let mut num_colons = 0;
1083     // Find second colon.. `use issue_59764:`
1084     let until_second_colon = source_map.span_take_while(use_span, |c| {
1085         if *c == ':' { num_colons += 1; }
1086         match c {
1087             ':' if num_colons == 2 => false,
1088             _ => true,
1089         }
1090     });
1091     // Find everything after the second colon.. `foo::{baz, makro};`
1092     let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
1093
1094     let mut found_a_non_whitespace_character = false;
1095     // Find the first non-whitespace character in `from_second_colon`.. `f`
1096     let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
1097         if found_a_non_whitespace_character { return false; }
1098         if !c.is_whitespace() { found_a_non_whitespace_character = true; }
1099         true
1100     });
1101
1102     // Find the first `{` in from_second_colon.. `foo::{`
1103     let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
1104
1105     (next_left_bracket == after_second_colon, from_second_colon)
1106 }
1107
1108 /// When an entity with a given name is not available in scope, we search for
1109 /// entities with that name in all crates. This method allows outputting the
1110 /// results of this search in a programmer-friendly way
1111 crate fn show_candidates(
1112     err: &mut DiagnosticBuilder<'_>,
1113     // This is `None` if all placement locations are inside expansions
1114     span: Option<Span>,
1115     candidates: &[ImportSuggestion],
1116     better: bool,
1117     found_use: bool,
1118 ) {
1119     // we want consistent results across executions, but candidates are produced
1120     // by iterating through a hash map, so make sure they are ordered:
1121     let mut path_strings: Vec<_> =
1122         candidates.into_iter().map(|c| path_names_to_string(&c.path)).collect();
1123     path_strings.sort();
1124
1125     let better = if better { "better " } else { "" };
1126     let msg_diff = match path_strings.len() {
1127         1 => " is found in another module, you can import it",
1128         _ => "s are found in other modules, you can import them",
1129     };
1130     let msg = format!("possible {}candidate{} into scope", better, msg_diff);
1131
1132     if let Some(span) = span {
1133         for candidate in &mut path_strings {
1134             // produce an additional newline to separate the new use statement
1135             // from the directly following item.
1136             let additional_newline = if found_use {
1137                 ""
1138             } else {
1139                 "\n"
1140             };
1141             *candidate = format!("use {};\n{}", candidate, additional_newline);
1142         }
1143
1144         err.span_suggestions(
1145             span,
1146             &msg,
1147             path_strings.into_iter(),
1148             Applicability::Unspecified,
1149         );
1150     } else {
1151         let mut msg = msg;
1152         msg.push(':');
1153         for candidate in path_strings {
1154             msg.push('\n');
1155             msg.push_str(&candidate);
1156         }
1157     }
1158 }