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::ext::base::MacroKind;
  14 use syntax::feature_gate::BUILTIN_ATTRIBUTES;
  15 use syntax::source_map::SourceMap;
  16 use syntax::struct_span_err;
  17 use syntax::symbol::{Symbol, kw};
  18 use syntax::util::lev_distance::find_best_match_for_name;
  19 use syntax_pos::{BytePos, Span, MultiSpan};
  20
  21 use crate::resolve_imports::{ImportDirective, ImportDirectiveSubclass, ImportResolver};
  22 use crate::{path_names_to_string, KNOWN_TOOLS};
  23 use crate::{BindingError, CrateLint, 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 crate fn add_typo_suggestion(
  62     err: &mut DiagnosticBuilder<'_>, suggestion: Option<TypoSuggestion>, span: Span
  63 ) -> bool {
  64     if let Some(suggestion) = suggestion {
  65         let msg = format!(
  66             "{} {} with a similar name exists", suggestion.res.article(), suggestion.res.descr()
  67         );
  68         err.span_suggestion(
  69             span, &msg, suggestion.candidate.to_string(), Applicability::MaybeIncorrect
  70         );
  71         return true;
  72     }
  73     false
  74 }
  75
  76 impl<'a> Resolver<'a> {
  77     crate fn add_module_candidates(
  78         &mut self,
  79         module: Module<'a>,
  80         names: &mut Vec<TypoSuggestion>,
  81         filter_fn: &impl Fn(Res) -> bool,
  82     ) {
  83         for (&(ident, _), resolution) in self.resolutions(module).borrow().iter() {
  84             if let Some(binding) = resolution.borrow().binding {
  85                 let res = binding.res();
  86                 if filter_fn(res) {
  87                     names.push(TypoSuggestion::from_res(ident.name, res));
  88                 }
  89             }
  90         }
  91     }
  92
  93     /// Combines an error with provided span and emits it.
  94     ///
  95     /// This takes the error provided, combines it with the span and any additional spans inside the
  96     /// error and emits it.
  97     crate fn report_error(&self, span: Span, resolution_error: ResolutionError<'_>) {
  98         self.into_struct_error(span, resolution_error).emit();
  99     }
 100
 101     crate fn into_struct_error(
 102         &self, span: Span, resolution_error: ResolutionError<'_>
 103     ) -> DiagnosticBuilder<'_> {
 104         match resolution_error {
 105             ResolutionError::GenericParamsFromOuterFunction(outer_res) => {
 106                 let mut err = struct_span_err!(self.session,
 107                     span,
 108                     E0401,
 109                     "can't use generic parameters from outer function",
 110                 );
 111                 err.span_label(span, format!("use of generic parameter from outer function"));
 112
 113                 let cm = self.session.source_map();
 114                 match outer_res {
 115                     Res::SelfTy(maybe_trait_defid, maybe_impl_defid) => {
 116                         if let Some(impl_span) = maybe_impl_defid.and_then(|def_id| {
 117                             self.definitions.opt_span(def_id)
 118                         }) {
 119                             err.span_label(
 120                                 reduce_impl_span_to_impl_keyword(cm, impl_span),
 121                                 "`Self` type implicitly declared here, by this `impl`",
 122                             );
 123                         }
 124                         match (maybe_trait_defid, maybe_impl_defid) {
 125                             (Some(_), None) => {
 126                                 err.span_label(span, "can't use `Self` here");
 127                             }
 128                             (_, Some(_)) => {
 129                                 err.span_label(span, "use a type here instead");
 130                             }
 131                             (None, None) => bug!("`impl` without trait nor type?"),
 132                         }
 133                         return err;
 134                     },
 135                     Res::Def(DefKind::TyParam, def_id) => {
 136                         if let Some(span) = self.definitions.opt_span(def_id) {
 137                             err.span_label(span, "type parameter from outer function");
 138                         }
 139                     }
 140                     Res::Def(DefKind::ConstParam, def_id) => {
 141                         if let Some(span) = self.definitions.opt_span(def_id) {
 142                             err.span_label(span, "const parameter from outer function");
 143                         }
 144                     }
 145                     _ => {
 146                         bug!("GenericParamsFromOuterFunction should only be used with Res::SelfTy, \
 147                             DefKind::TyParam");
 148                     }
 149                 }
 150
 151                 // Try to retrieve the span of the function signature and generate a new message
 152                 // with a local type or const parameter.
 153                 let sugg_msg = &format!("try using a local generic parameter instead");
 154                 if let Some((sugg_span, new_snippet)) = cm.generate_local_type_param_snippet(span) {
 155                     // Suggest the modification to the user
 156                     err.span_suggestion(
 157                         sugg_span,
 158                         sugg_msg,
 159                         new_snippet,
 160                         Applicability::MachineApplicable,
 161                     );
 162                 } else if let Some(sp) = cm.generate_fn_name_span(span) {
 163                     err.span_label(sp,
 164                         format!("try adding a local generic parameter in this method instead"));
 165                 } else {
 166                     err.help(&format!("try using a local generic parameter instead"));
 167                 }
 168
 169                 err
 170             }
 171             ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => {
 172                 let mut err = struct_span_err!(
 173                     self.session,
 174                     span,
 175                     E0403,
 176                     "the name `{}` is already used for a generic \
 177                      parameter in this item's generic parameters",
 178                     name,
 179                 );
 180                 err.span_label(span, "already used");
 181                 err.span_label(first_use_span, format!("first use of `{}`", name));
 182                 err
 183             }
 184             ResolutionError::MethodNotMemberOfTrait(method, trait_) => {
 185                 let mut err = struct_span_err!(self.session,
 186                                             span,
 187                                             E0407,
 188                                             "method `{}` is not a member of trait `{}`",
 189                                             method,
 190                                             trait_);
 191                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 192                 err
 193             }
 194             ResolutionError::TypeNotMemberOfTrait(type_, trait_) => {
 195                 let mut err = struct_span_err!(self.session,
 196                                 span,
 197                                 E0437,
 198                                 "type `{}` is not a member of trait `{}`",
 199                                 type_,
 200                                 trait_);
 201                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 202                 err
 203             }
 204             ResolutionError::ConstNotMemberOfTrait(const_, trait_) => {
 205                 let mut err = struct_span_err!(self.session,
 206                                 span,
 207                                 E0438,
 208                                 "const `{}` is not a member of trait `{}`",
 209                                 const_,
 210                                 trait_);
 211                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 212                 err
 213             }
 214             ResolutionError::VariableNotBoundInPattern(binding_error) => {
 215                 let BindingError { name, target, origin, could_be_path } = binding_error;
 216
 217                 let target_sp = target.iter().copied().collect::<Vec<_>>();
 218                 let origin_sp = origin.iter().copied().collect::<Vec<_>>();
 219
 220                 let msp = MultiSpan::from_spans(target_sp.clone());
 221                 let msg = format!("variable `{}` is not bound in all patterns", name);
 222                 let mut err = self.session.struct_span_err_with_code(
 223                     msp,
 224                     &msg,
 225                     DiagnosticId::Error("E0408".into()),
 226                 );
 227                 for sp in target_sp {
 228                     err.span_label(sp, format!("pattern doesn't bind `{}`", name));
 229                 }
 230                 for sp in origin_sp {
 231                     err.span_label(sp, "variable not in all patterns");
 232                 }
 233                 if *could_be_path {
 234                     let help_msg = format!(
 235                         "if you meant to match on a variant or a `const` item, consider \
 236                          making the path in the pattern qualified: `?::{}`",
 237                          name,
 238                      );
 239                     err.span_help(span, &help_msg);
 240                 }
 241                 err
 242             }
 243             ResolutionError::VariableBoundWithDifferentMode(variable_name,
 244                                                             first_binding_span) => {
 245                 let mut err = struct_span_err!(self.session,
 246                                 span,
 247                                 E0409,
 248                                 "variable `{}` is bound in inconsistent \
 249                                 ways within the same match arm",
 250                                 variable_name);
 251                 err.span_label(span, "bound in different ways");
 252                 err.span_label(first_binding_span, "first binding");
 253                 err
 254             }
 255             ResolutionError::IdentifierBoundMoreThanOnceInParameterList(identifier) => {
 256                 let mut err = struct_span_err!(self.session,
 257                                 span,
 258                                 E0415,
 259                                 "identifier `{}` is bound more than once in this parameter list",
 260                                 identifier);
 261                 err.span_label(span, "used as parameter more than once");
 262                 err
 263             }
 264             ResolutionError::IdentifierBoundMoreThanOnceInSamePattern(identifier) => {
 265                 let mut err = struct_span_err!(self.session,
 266                                 span,
 267                                 E0416,
 268                                 "identifier `{}` is bound more than once in the same pattern",
 269                                 identifier);
 270                 err.span_label(span, "used in a pattern more than once");
 271                 err
 272             }
 273             ResolutionError::UndeclaredLabel(name, lev_candidate) => {
 274                 let mut err = struct_span_err!(self.session,
 275                                             span,
 276                                             E0426,
 277                                             "use of undeclared label `{}`",
 278                                             name);
 279                 if let Some(lev_candidate) = lev_candidate {
 280                     err.span_suggestion(
 281                         span,
 282                         "a label with a similar name exists in this scope",
 283                         lev_candidate.to_string(),
 284                         Applicability::MaybeIncorrect,
 285                     );
 286                 } else {
 287                     err.span_label(span, format!("undeclared label `{}`", name));
 288                 }
 289                 err
 290             }
 291             ResolutionError::SelfImportsOnlyAllowedWithin => {
 292                 struct_span_err!(self.session,
 293                                 span,
 294                                 E0429,
 295                                 "{}",
 296                                 "`self` imports are only allowed within a { } list")
 297             }
 298             ResolutionError::SelfImportCanOnlyAppearOnceInTheList => {
 299                 let mut err = struct_span_err!(self.session, span, E0430,
 300                                             "`self` import can only appear once in an import list");
 301                 err.span_label(span, "can only appear once in an import list");
 302                 err
 303             }
 304             ResolutionError::SelfImportOnlyInImportListWithNonEmptyPrefix => {
 305                 let mut err = struct_span_err!(self.session, span, E0431,
 306                                             "`self` import can only appear in an import list with \
 307                                                 a non-empty prefix");
 308                 err.span_label(span, "can only appear in an import list with a non-empty prefix");
 309                 err
 310             }
 311             ResolutionError::FailedToResolve { label, suggestion } => {
 312                 let mut err = struct_span_err!(self.session, span, E0433,
 313                                             "failed to resolve: {}", &label);
 314                 err.span_label(span, label);
 315
 316                 if let Some((suggestions, msg, applicability)) = suggestion {
 317                     err.multipart_suggestion(&msg, suggestions, applicability);
 318                 }
 319
 320                 err
 321             }
 322             ResolutionError::CannotCaptureDynamicEnvironmentInFnItem => {
 323                 let mut err = struct_span_err!(self.session,
 324                                             span,
 325                                             E0434,
 326                                             "{}",
 327                                             "can't capture dynamic environment in a fn item");
 328                 err.help("use the `|| { ... }` closure form instead");
 329                 err
 330             }
 331             ResolutionError::AttemptToUseNonConstantValueInConstant => {
 332                 let mut err = struct_span_err!(self.session, span, E0435,
 333                                             "attempt to use a non-constant value in a constant");
 334                 err.span_label(span, "non-constant value");
 335                 err
 336             }
 337             ResolutionError::BindingShadowsSomethingUnacceptable(what_binding, name, binding) => {
 338                 let res = binding.res();
 339                 let shadows_what = res.descr();
 340                 let mut err = struct_span_err!(self.session, span, E0530, "{}s cannot shadow {}s",
 341                                             what_binding, shadows_what);
 342                 err.span_label(span, format!("cannot be named the same as {} {}",
 343                                             res.article(), shadows_what));
 344                 let participle = if binding.is_import() { "imported" } else { "defined" };
 345                 let msg = format!("the {} `{}` is {} here", shadows_what, name, participle);
 346                 err.span_label(binding.span, msg);
 347                 err
 348             }
 349             ResolutionError::ForwardDeclaredTyParam => {
 350                 let mut err = struct_span_err!(self.session, span, E0128,
 351                                             "type parameters with a default cannot use \
 352                                                 forward declared identifiers");
 353                 err.span_label(
 354                     span, "defaulted type parameters cannot be forward declared".to_string());
 355                 err
 356             }
 357             ResolutionError::SelfInTyParamDefault => {
 358                 let mut err = struct_span_err!(
 359                     self.session,
 360                     span,
 361                     E0735,
 362                     "type parameters cannot use `Self` in their defaults"
 363                 );
 364                 err.span_label(
 365                     span, "`Self` in type parameter default".to_string());
 366                 err
 367             }
 368             ResolutionError::ConstParamDependentOnTypeParam => {
 369                 let mut err = struct_span_err!(
 370                     self.session,
 371                     span,
 372                     E0671,
 373                     "const parameters cannot depend on type parameters"
 374                 );
 375                 err.span_label(span, format!("const parameter depends on type parameter"));
 376                 err
 377             }
 378         }
 379     }
 380
 381     /// Lookup typo candidate in scope for a macro or import.
 382     fn early_lookup_typo_candidate(
 383         &mut self,
 384         scope_set: ScopeSet,
 385         parent_scope: &ParentScope<'a>,
 386         ident: Ident,
 387         filter_fn: &impl Fn(Res) -> bool,
 388     ) -> Option<TypoSuggestion> {
 389         let mut suggestions = Vec::new();
 390         self.visit_scopes(scope_set, parent_scope, ident, |this, scope, use_prelude, _| {
 391             match scope {
 392                 Scope::DeriveHelpers => {
 393                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 394                     if filter_fn(res) {
 395                         for derive in parent_scope.derives {
 396                             let parent_scope =
 397                                 &ParentScope { derives: &[], ..*parent_scope };
 398                             if let Ok((Some(ext), _)) = this.resolve_macro_path(
 399                                 derive, Some(MacroKind::Derive), parent_scope, false, false
 400                             ) {
 401                                 suggestions.extend(ext.helper_attrs.iter().map(|name| {
 402                                     TypoSuggestion::from_res(*name, res)
 403                                 }));
 404                             }
 405                         }
 406                     }
 407                 }
 408                 Scope::MacroRules(legacy_scope) => {
 409                     if let LegacyScope::Binding(legacy_binding) = legacy_scope {
 410                         let res = legacy_binding.binding.res();
 411                         if filter_fn(res) {
 412                             suggestions.push(
 413                                 TypoSuggestion::from_res(legacy_binding.ident.name, res)
 414                             )
 415                         }
 416                     }
 417                 }
 418                 Scope::CrateRoot => {
 419                     let root_ident = Ident::new(kw::PathRoot, ident.span);
 420                     let root_module = this.resolve_crate_root(root_ident);
 421                     this.add_module_candidates(root_module, &mut suggestions, filter_fn);
 422                 }
 423                 Scope::Module(module) => {
 424                     this.add_module_candidates(module, &mut suggestions, filter_fn);
 425                 }
 426                 Scope::MacroUsePrelude => {
 427                     suggestions.extend(this.macro_use_prelude.iter().filter_map(|(name, binding)| {
 428                         let res = binding.res();
 429                         if filter_fn(res) {
 430                             Some(TypoSuggestion::from_res(*name, res))
 431                         } else {
 432                             None
 433                         }
 434                     }));
 435                 }
 436                 Scope::BuiltinAttrs => {
 437                     let res = Res::NonMacroAttr(NonMacroAttrKind::Builtin);
 438                     if filter_fn(res) {
 439                         suggestions.extend(BUILTIN_ATTRIBUTES.iter().map(|(name, ..)| {
 440                             TypoSuggestion::from_res(*name, res)
 441                         }));
 442                     }
 443                 }
 444                 Scope::LegacyPluginHelpers => {
 445                     let res = Res::NonMacroAttr(NonMacroAttrKind::LegacyPluginHelper);
 446                     if filter_fn(res) {
 447                         let plugin_attributes = this.session.plugin_attributes.borrow();
 448                         suggestions.extend(plugin_attributes.iter().map(|(name, _)| {
 449                             TypoSuggestion::from_res(*name, res)
 450                         }));
 451                     }
 452                 }
 453                 Scope::ExternPrelude => {
 454                     suggestions.extend(this.extern_prelude.iter().filter_map(|(ident, _)| {
 455                         let res = Res::Def(DefKind::Mod, DefId::local(CRATE_DEF_INDEX));
 456                         if filter_fn(res) {
 457                             Some(TypoSuggestion::from_res(ident.name, res))
 458                         } else {
 459                             None
 460                         }
 461                     }));
 462                 }
 463                 Scope::ToolPrelude => {
 464                     let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
 465                     suggestions.extend(KNOWN_TOOLS.iter().map(|name| {
 466                         TypoSuggestion::from_res(*name, res)
 467                     }));
 468                 }
 469                 Scope::StdLibPrelude => {
 470                     if let Some(prelude) = this.prelude {
 471                         let mut tmp_suggestions = Vec::new();
 472                         this.add_module_candidates(prelude, &mut tmp_suggestions, filter_fn);
 473                         suggestions.extend(tmp_suggestions.into_iter().filter(|s| {
 474                             use_prelude || this.is_builtin_macro(s.res)
 475                         }));
 476                     }
 477                 }
 478                 Scope::BuiltinTypes => {
 479                     let primitive_types = &this.primitive_type_table.primitive_types;
 480                     suggestions.extend(
 481                         primitive_types.iter().flat_map(|(name, prim_ty)| {
 482                             let res = Res::PrimTy(*prim_ty);
 483                             if filter_fn(res) {
 484                                 Some(TypoSuggestion::from_res(*name, res))
 485                             } else {
 486                                 None
 487                             }
 488                         })
 489                     )
 490                 }
 491             }
 492
 493             None::<()>
 494         });
 495
 496         // Make sure error reporting is deterministic.
 497         suggestions.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
 498
 499         match find_best_match_for_name(
 500             suggestions.iter().map(|suggestion| &suggestion.candidate),
 501             &ident.as_str(),
 502             None,
 503         ) {
 504             Some(found) if found != ident.name => suggestions
 505                 .into_iter()
 506                 .find(|suggestion| suggestion.candidate == found),
 507             _ => None,
 508         }
 509     }
 510
 511     fn lookup_import_candidates_from_module<FilterFn>(&mut self,
 512                                           lookup_ident: Ident,
 513                                           namespace: Namespace,
 514                                           start_module: Module<'a>,
 515                                           crate_name: Ident,
 516                                           filter_fn: FilterFn)
 517                                           -> Vec<ImportSuggestion>
 518         where FilterFn: Fn(Res) -> bool
 519     {
 520         let mut candidates = Vec::new();
 521         let mut seen_modules = FxHashSet::default();
 522         let not_local_module = crate_name.name != kw::Crate;
 523         let mut worklist = vec![(start_module, Vec::<ast::PathSegment>::new(), not_local_module)];
 524
 525         while let Some((in_module,
 526                         path_segments,
 527                         in_module_is_extern)) = worklist.pop() {
 528             // We have to visit module children in deterministic order to avoid
 529             // instabilities in reported imports (#43552).
 530             in_module.for_each_child(self, |this, ident, ns, name_binding| {
 531                 // avoid imports entirely
 532                 if name_binding.is_import() && !name_binding.is_extern_crate() { return; }
 533                 // avoid non-importable candidates as well
 534                 if !name_binding.is_importable() { return; }
 535
 536                 // collect results based on the filter function
 537                 if ident.name == lookup_ident.name && ns == namespace {
 538                     let res = name_binding.res();
 539                     if filter_fn(res) {
 540                         // create the path
 541                         let mut segms = path_segments.clone();
 542                         if lookup_ident.span.rust_2018() {
 543                             // crate-local absolute paths start with `crate::` in edition 2018
 544                             // FIXME: may also be stabilized for Rust 2015 (Issues #45477, #44660)
 545                             segms.insert(
 546                                 0, ast::PathSegment::from_ident(crate_name)
 547                             );
 548                         }
 549
 550                         segms.push(ast::PathSegment::from_ident(ident));
 551                         let path = Path {
 552                             span: name_binding.span,
 553                             segments: segms,
 554                         };
 555                         // the entity is accessible in the following cases:
 556                         // 1. if it's defined in the same crate, it's always
 557                         // accessible (since private entities can be made public)
 558                         // 2. if it's defined in another crate, it's accessible
 559                         // only if both the module is public and the entity is
 560                         // declared as public (due to pruning, we don't explore
 561                         // outside crate private modules => no need to check this)
 562                         if !in_module_is_extern || name_binding.vis == ty::Visibility::Public {
 563                             let did = match res {
 564                                 Res::Def(DefKind::Ctor(..), did) => this.parent(did),
 565                                 _ => res.opt_def_id(),
 566                             };
 567                             candidates.push(ImportSuggestion { did, path });
 568                         }
 569                     }
 570                 }
 571
 572                 // collect submodules to explore
 573                 if let Some(module) = name_binding.module() {
 574                     // form the path
 575                     let mut path_segments = path_segments.clone();
 576                     path_segments.push(ast::PathSegment::from_ident(ident));
 577
 578                     let is_extern_crate_that_also_appears_in_prelude =
 579                         name_binding.is_extern_crate() &&
 580                         lookup_ident.span.rust_2018();
 581
 582                     let is_visible_to_user =
 583                         !in_module_is_extern || name_binding.vis == ty::Visibility::Public;
 584
 585                     if !is_extern_crate_that_also_appears_in_prelude && is_visible_to_user {
 586                         // add the module to the lookup
 587                         let is_extern = in_module_is_extern || name_binding.is_extern_crate();
 588                         if seen_modules.insert(module.def_id().unwrap()) {
 589                             worklist.push((module, path_segments, is_extern));
 590                         }
 591                     }
 592                 }
 593             })
 594         }
 595
 596         candidates
 597     }
 598
 599     /// When name resolution fails, this method can be used to look up candidate
 600     /// entities with the expected name. It allows filtering them using the
 601     /// supplied predicate (which should be used to only accept the types of
 602     /// definitions expected, e.g., traits). The lookup spans across all crates.
 603     ///
 604     /// N.B., the method does not look into imports, but this is not a problem,
 605     /// since we report the definitions (thus, the de-aliased imports).
 606     crate fn lookup_import_candidates<FilterFn>(
 607         &mut self, lookup_ident: Ident, namespace: Namespace, filter_fn: FilterFn
 608     ) -> Vec<ImportSuggestion>
 609         where FilterFn: Fn(Res) -> bool
 610     {
 611         let mut suggestions = self.lookup_import_candidates_from_module(
 612             lookup_ident, namespace, self.graph_root, Ident::with_dummy_span(kw::Crate), &filter_fn
 613         );
 614
 615         if lookup_ident.span.rust_2018() {
 616             let extern_prelude_names = self.extern_prelude.clone();
 617             for (ident, _) in extern_prelude_names.into_iter() {
 618                 if ident.span.from_expansion() {
 619                     // Idents are adjusted to the root context before being
 620                     // resolved in the extern prelude, so reporting this to the
 621                     // user is no help. This skips the injected
 622                     // `extern crate std` in the 2018 edition, which would
 623                     // otherwise cause duplicate suggestions.
 624                     continue;
 625                 }
 626                 if let Some(crate_id) = self.crate_loader.maybe_process_path_extern(ident.name,
 627                                                                                     ident.span) {
 628                     let crate_root = self.get_module(DefId {
 629                         krate: crate_id,
 630                         index: CRATE_DEF_INDEX,
 631                     });
 632                     suggestions.extend(self.lookup_import_candidates_from_module(
 633                         lookup_ident, namespace, crate_root, ident, &filter_fn));
 634                 }
 635             }
 636         }
 637
 638         suggestions
 639     }
 640
 641     crate fn unresolved_macro_suggestions(
 642         &mut self,
 643         err: &mut DiagnosticBuilder<'a>,
 644         macro_kind: MacroKind,
 645         parent_scope: &ParentScope<'a>,
 646         ident: Ident,
 647     ) {
 648         let is_expected = &|res: Res| res.macro_kind() == Some(macro_kind);
 649         let suggestion = self.early_lookup_typo_candidate(
 650             ScopeSet::Macro(macro_kind), parent_scope, ident, is_expected
 651         );
 652         add_typo_suggestion(err, suggestion, ident.span);
 653
 654         if macro_kind == MacroKind::Derive &&
 655            (ident.as_str() == "Send" || ident.as_str() == "Sync") {
 656             let msg = format!("unsafe traits like `{}` should be implemented explicitly", ident);
 657             err.span_note(ident.span, &msg);
 658         }
 659         if self.macro_names.contains(&ident.modern()) {
 660             err.help("have you added the `#[macro_use]` on the module/import?");
 661         }
 662     }
 663 }
 664
 665 impl<'a, 'b> ImportResolver<'a, 'b> {
 666     /// Adds suggestions for a path that cannot be resolved.
 667     pub(crate) fn make_path_suggestion(
 668         &mut self,
 669         span: Span,
 670         mut path: Vec<Segment>,
 671         parent_scope: &ParentScope<'b>,
 672     ) -> Option<(Vec<Segment>, Vec<String>)> {
 673         debug!("make_path_suggestion: span={:?} path={:?}", span, path);
 674
 675         match (path.get(0), path.get(1)) {
 676             // `{{root}}::ident::...` on both editions.
 677             // On 2015 `{{root}}` is usually added implicitly.
 678             (Some(fst), Some(snd)) if fst.ident.name == kw::PathRoot &&
 679                                       !snd.ident.is_path_segment_keyword() => {}
 680             // `ident::...` on 2018.
 681             (Some(fst), _) if fst.ident.span.rust_2018() &&
 682                               !fst.ident.is_path_segment_keyword() => {
 683                 // Insert a placeholder that's later replaced by `self`/`super`/etc.
 684                 path.insert(0, Segment::from_ident(Ident::invalid()));
 685             }
 686             _ => return None,
 687         }
 688
 689         self.make_missing_self_suggestion(span, path.clone(), parent_scope)
 690             .or_else(|| self.make_missing_crate_suggestion(span, path.clone(), parent_scope))
 691             .or_else(|| self.make_missing_super_suggestion(span, path.clone(), parent_scope))
 692             .or_else(|| self.make_external_crate_suggestion(span, path, parent_scope))
 693     }
 694
 695     /// Suggest a missing `self::` if that resolves to an correct module.
 696     ///
 697     /// ```
 698     ///    |
 699     /// LL | use foo::Bar;
 700     ///    |     ^^^ did you mean `self::foo`?
 701     /// ```
 702     fn make_missing_self_suggestion(
 703         &mut self,
 704         span: Span,
 705         mut path: Vec<Segment>,
 706         parent_scope: &ParentScope<'b>,
 707     ) -> Option<(Vec<Segment>, Vec<String>)> {
 708         // Replace first ident with `self` and check if that is valid.
 709         path[0].ident.name = kw::SelfLower;
 710         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 711         debug!("make_missing_self_suggestion: path={:?} result={:?}", path, result);
 712         if let PathResult::Module(..) = result {
 713             Some((path, Vec::new()))
 714         } else {
 715             None
 716         }
 717     }
 718
 719     /// Suggests a missing `crate::` if that resolves to an correct module.
 720     ///
 721     /// ```
 722     ///    |
 723     /// LL | use foo::Bar;
 724     ///    |     ^^^ did you mean `crate::foo`?
 725     /// ```
 726     fn make_missing_crate_suggestion(
 727         &mut self,
 728         span: Span,
 729         mut path: Vec<Segment>,
 730         parent_scope: &ParentScope<'b>,
 731     ) -> Option<(Vec<Segment>, Vec<String>)> {
 732         // Replace first ident with `crate` and check if that is valid.
 733         path[0].ident.name = kw::Crate;
 734         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 735         debug!("make_missing_crate_suggestion:  path={:?} result={:?}", path, result);
 736         if let PathResult::Module(..) = result {
 737             Some((
 738                 path,
 739                 vec![
 740                     "`use` statements changed in Rust 2018; read more at \
 741                      <https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-\
 742                      clarity.html>".to_string()
 743                 ],
 744             ))
 745         } else {
 746             None
 747         }
 748     }
 749
 750     /// Suggests a missing `super::` if that resolves to an correct module.
 751     ///
 752     /// ```
 753     ///    |
 754     /// LL | use foo::Bar;
 755     ///    |     ^^^ did you mean `super::foo`?
 756     /// ```
 757     fn make_missing_super_suggestion(
 758         &mut self,
 759         span: Span,
 760         mut path: Vec<Segment>,
 761         parent_scope: &ParentScope<'b>,
 762     ) -> Option<(Vec<Segment>, Vec<String>)> {
 763         // Replace first ident with `crate` and check if that is valid.
 764         path[0].ident.name = kw::Super;
 765         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 766         debug!("make_missing_super_suggestion:  path={:?} result={:?}", path, result);
 767         if let PathResult::Module(..) = result {
 768             Some((path, Vec::new()))
 769         } else {
 770             None
 771         }
 772     }
 773
 774     /// Suggests a missing external crate name if that resolves to an correct module.
 775     ///
 776     /// ```
 777     ///    |
 778     /// LL | use foobar::Baz;
 779     ///    |     ^^^^^^ did you mean `baz::foobar`?
 780     /// ```
 781     ///
 782     /// Used when importing a submodule of an external crate but missing that crate's
 783     /// name as the first part of path.
 784     fn make_external_crate_suggestion(
 785         &mut self,
 786         span: Span,
 787         mut path: Vec<Segment>,
 788         parent_scope: &ParentScope<'b>,
 789     ) -> Option<(Vec<Segment>, Vec<String>)> {
 790         if path[1].ident.span.rust_2015() {
 791             return None;
 792         }
 793
 794         // Sort extern crate names in reverse order to get
 795         // 1) some consistent ordering for emitted dignostics, and
 796         // 2) `std` suggestions before `core` suggestions.
 797         let mut extern_crate_names =
 798             self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
 799         extern_crate_names.sort_by_key(|name| Reverse(name.as_str()));
 800
 801         for name in extern_crate_names.into_iter() {
 802             // Replace first ident with a crate name and check if that is valid.
 803             path[0].ident.name = name;
 804             let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 805             debug!("make_external_crate_suggestion: name={:?} path={:?} result={:?}",
 806                     name, path, result);
 807             if let PathResult::Module(..) = result {
 808                 return Some((path, Vec::new()));
 809             }
 810         }
 811
 812         None
 813     }
 814
 815     /// Suggests importing a macro from the root of the crate rather than a module within
 816     /// the crate.
 817     ///
 818     /// ```
 819     /// help: a macro with this name exists at the root of the crate
 820     ///    |
 821     /// LL | use issue_59764::makro;
 822     ///    |     ^^^^^^^^^^^^^^^^^^
 823     ///    |
 824     ///    = note: this could be because a macro annotated with `#[macro_export]` will be exported
 825     ///            at the root of the crate instead of the module where it is defined
 826     /// ```
 827     pub(crate) fn check_for_module_export_macro(
 828         &mut self,
 829         directive: &'b ImportDirective<'b>,
 830         module: ModuleOrUniformRoot<'b>,
 831         ident: Ident,
 832     ) -> Option<(Option<Suggestion>, Vec<String>)> {
 833         let mut crate_module = if let ModuleOrUniformRoot::Module(module) = module {
 834             module
 835         } else {
 836             return None;
 837         };
 838
 839         while let Some(parent) = crate_module.parent {
 840             crate_module = parent;
 841         }
 842
 843         if ModuleOrUniformRoot::same_def(ModuleOrUniformRoot::Module(crate_module), module) {
 844             // Don't make a suggestion if the import was already from the root of the
 845             // crate.
 846             return None;
 847         }
 848
 849         let resolutions = self.r.resolutions(crate_module).borrow();
 850         let resolution = resolutions.get(&(ident, MacroNS))?;
 851         let binding = resolution.borrow().binding()?;
 852         if let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() {
 853             let module_name = crate_module.kind.name().unwrap();
 854             let import = match directive.subclass {
 855                 ImportDirectiveSubclass::SingleImport { source, target, .. } if source != target =>
 856                     format!("{} as {}", source, target),
 857                 _ => format!("{}", ident),
 858             };
 859
 860             let mut corrections: Vec<(Span, String)> = Vec::new();
 861             if !directive.is_nested() {
 862                 // Assume this is the easy case of `use issue_59764::foo::makro;` and just remove
 863                 // intermediate segments.
 864                 corrections.push((directive.span, format!("{}::{}", module_name, import)));
 865             } else {
 866                 // Find the binding span (and any trailing commas and spaces).
 867                 //   ie. `use a::b::{c, d, e};`
 868                 //                      ^^^
 869                 let (found_closing_brace, binding_span) = find_span_of_binding_until_next_binding(
 870                     self.r.session, directive.span, directive.use_span,
 871                 );
 872                 debug!("check_for_module_export_macro: found_closing_brace={:?} binding_span={:?}",
 873                        found_closing_brace, binding_span);
 874
 875                 let mut removal_span = binding_span;
 876                 if found_closing_brace {
 877                     // If the binding span ended with a closing brace, as in the below example:
 878                     //   ie. `use a::b::{c, d};`
 879                     //                      ^
 880                     // Then expand the span of characters to remove to include the previous
 881                     // binding's trailing comma.
 882                     //   ie. `use a::b::{c, d};`
 883                     //                    ^^^
 884                     if let Some(previous_span) = extend_span_to_previous_binding(
 885                         self.r.session, binding_span,
 886                     ) {
 887                         debug!("check_for_module_export_macro: previous_span={:?}", previous_span);
 888                         removal_span = removal_span.with_lo(previous_span.lo());
 889                     }
 890                 }
 891                 debug!("check_for_module_export_macro: removal_span={:?}", removal_span);
 892
 893                 // Remove the `removal_span`.
 894                 corrections.push((removal_span, "".to_string()));
 895
 896                 // Find the span after the crate name and if it has nested imports immediatately
 897                 // after the crate name already.
 898                 //   ie. `use a::b::{c, d};`
 899                 //               ^^^^^^^^^
 900                 //   or  `use a::{b, c, d}};`
 901                 //               ^^^^^^^^^^^
 902                 let (has_nested, after_crate_name) = find_span_immediately_after_crate_name(
 903                     self.r.session, module_name, directive.use_span,
 904                 );
 905                 debug!("check_for_module_export_macro: has_nested={:?} after_crate_name={:?}",
 906                        has_nested, after_crate_name);
 907
 908                 let source_map = self.r.session.source_map();
 909
 910                 // Add the import to the start, with a `{` if required.
 911                 let start_point = source_map.start_point(after_crate_name);
 912                 if let Ok(start_snippet) = source_map.span_to_snippet(start_point) {
 913                     corrections.push((
 914                         start_point,
 915                         if has_nested {
 916                             // In this case, `start_snippet` must equal '{'.
 917                             format!("{}{}, ", start_snippet, import)
 918                         } else {
 919                             // In this case, add a `{`, then the moved import, then whatever
 920                             // was there before.
 921                             format!("{{{}, {}", import, start_snippet)
 922                         }
 923                     ));
 924                 }
 925
 926                 // Add a `};` to the end if nested, matching the `{` added at the start.
 927                 if !has_nested {
 928                     corrections.push((source_map.end_point(after_crate_name),
 929                                      "};".to_string()));
 930                 }
 931             }
 932
 933             let suggestion = Some((
 934                 corrections,
 935                 String::from("a macro with this name exists at the root of the crate"),
 936                 Applicability::MaybeIncorrect,
 937             ));
 938             let note = vec![
 939                 "this could be because a macro annotated with `#[macro_export]` will be exported \
 940                  at the root of the crate instead of the module where it is defined".to_string(),
 941             ];
 942             Some((suggestion, note))
 943         } else {
 944             None
 945         }
 946     }
 947 }
 948
 949 /// Given a `binding_span` of a binding within a use statement:
 950 ///
 951 /// ```
 952 /// use foo::{a, b, c};
 953 ///              ^
 954 /// ```
 955 ///
 956 /// then return the span until the next binding or the end of the statement:
 957 ///
 958 /// ```
 959 /// use foo::{a, b, c};
 960 ///              ^^^
 961 /// ```
 962 pub(crate) fn find_span_of_binding_until_next_binding(
 963     sess: &Session,
 964     binding_span: Span,
 965     use_span: Span,
 966 ) -> (bool, Span) {
 967     let source_map = sess.source_map();
 968
 969     // Find the span of everything after the binding.
 970     //   ie. `a, e};` or `a};`
 971     let binding_until_end = binding_span.with_hi(use_span.hi());
 972
 973     // Find everything after the binding but not including the binding.
 974     //   ie. `, e};` or `};`
 975     let after_binding_until_end = binding_until_end.with_lo(binding_span.hi());
 976
 977     // Keep characters in the span until we encounter something that isn't a comma or
 978     // whitespace.
 979     //   ie. `, ` or ``.
 980     //
 981     // Also note whether a closing brace character was encountered. If there
 982     // was, then later go backwards to remove any trailing commas that are left.
 983     let mut found_closing_brace = false;
 984     let after_binding_until_next_binding = source_map.span_take_while(
 985         after_binding_until_end,
 986         |&ch| {
 987             if ch == '}' { found_closing_brace = true; }
 988             ch == ' ' || ch == ','
 989         }
 990     );
 991
 992     // Combine the two spans.
 993     //   ie. `a, ` or `a`.
 994     //
 995     // Removing these would leave `issue_52891::{d, e};` or `issue_52891::{d, e, };`
 996     let span = binding_span.with_hi(after_binding_until_next_binding.hi());
 997
 998     (found_closing_brace, span)
 999 }
1000
1001 /// Given a `binding_span`, return the span through to the comma or opening brace of the previous
1002 /// binding.
1003 ///
1004 /// ```
1005 /// use foo::a::{a, b, c};
1006 ///               ^^--- binding span
1007 ///               |
1008 ///               returned span
1009 ///
1010 /// use foo::{a, b, c};
1011 ///           --- binding span
1012 /// ```
1013 pub(crate) fn extend_span_to_previous_binding(
1014     sess: &Session,
1015     binding_span: Span,
1016 ) -> Option<Span> {
1017     let source_map = sess.source_map();
1018
1019     // `prev_source` will contain all of the source that came before the span.
1020     // Then split based on a command and take the first (ie. closest to our span)
1021     // snippet. In the example, this is a space.
1022     let prev_source = source_map.span_to_prev_source(binding_span).ok()?;
1023
1024     let prev_comma = prev_source.rsplit(',').collect::<Vec<_>>();
1025     let prev_starting_brace = prev_source.rsplit('{').collect::<Vec<_>>();
1026     if prev_comma.len() <= 1 || prev_starting_brace.len() <= 1 {
1027         return None;
1028     }
1029
1030     let prev_comma = prev_comma.first().unwrap();
1031     let prev_starting_brace = prev_starting_brace.first().unwrap();
1032
1033     // If the amount of source code before the comma is greater than
1034     // the amount of source code before the starting brace then we've only
1035     // got one item in the nested item (eg. `issue_52891::{self}`).
1036     if prev_comma.len() > prev_starting_brace.len() {
1037         return None;
1038     }
1039
1040     Some(binding_span.with_lo(BytePos(
1041         // Take away the number of bytes for the characters we've found and an
1042         // extra for the comma.
1043         binding_span.lo().0 - (prev_comma.as_bytes().len() as u32) - 1
1044     )))
1045 }
1046
1047 /// Given a `use_span` of a binding within a use statement, returns the highlighted span and if
1048 /// it is a nested use tree.
1049 ///
1050 /// ```
1051 /// use foo::a::{b, c};
1052 ///          ^^^^^^^^^^ // false
1053 ///
1054 /// use foo::{a, b, c};
1055 ///          ^^^^^^^^^^ // true
1056 ///
1057 /// use foo::{a, b::{c, d}};
1058 ///          ^^^^^^^^^^^^^^^ // true
1059 /// ```
1060 fn find_span_immediately_after_crate_name(
1061     sess: &Session,
1062     module_name: Symbol,
1063     use_span: Span,
1064 ) -> (bool, Span) {
1065     debug!("find_span_immediately_after_crate_name: module_name={:?} use_span={:?}",
1066            module_name, use_span);
1067     let source_map = sess.source_map();
1068
1069     // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
1070     let mut num_colons = 0;
1071     // Find second colon.. `use issue_59764:`
1072     let until_second_colon = source_map.span_take_while(use_span, |c| {
1073         if *c == ':' { num_colons += 1; }
1074         match c {
1075             ':' if num_colons == 2 => false,
1076             _ => true,
1077         }
1078     });
1079     // Find everything after the second colon.. `foo::{baz, makro};`
1080     let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
1081
1082     let mut found_a_non_whitespace_character = false;
1083     // Find the first non-whitespace character in `from_second_colon`.. `f`
1084     let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
1085         if found_a_non_whitespace_character { return false; }
1086         if !c.is_whitespace() { found_a_non_whitespace_character = true; }
1087         true
1088     });
1089
1090     // Find the first `{` in from_second_colon.. `foo::{`
1091     let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
1092
1093     (next_left_bracket == after_second_colon, from_second_colon)
1094 }
1095
1096 /// When an entity with a given name is not available in scope, we search for
1097 /// entities with that name in all crates. This method allows outputting the
1098 /// results of this search in a programmer-friendly way
1099 crate fn show_candidates(
1100     err: &mut DiagnosticBuilder<'_>,
1101     // This is `None` if all placement locations are inside expansions
1102     span: Option<Span>,
1103     candidates: &[ImportSuggestion],
1104     better: bool,
1105     found_use: bool,
1106 ) {
1107     // we want consistent results across executions, but candidates are produced
1108     // by iterating through a hash map, so make sure they are ordered:
1109     let mut path_strings: Vec<_> =
1110         candidates.into_iter().map(|c| path_names_to_string(&c.path)).collect();
1111     path_strings.sort();
1112
1113     let better = if better { "better " } else { "" };
1114     let msg_diff = match path_strings.len() {
1115         1 => " is found in another module, you can import it",
1116         _ => "s are found in other modules, you can import them",
1117     };
1118     let msg = format!("possible {}candidate{} into scope", better, msg_diff);
1119
1120     if let Some(span) = span {
1121         for candidate in &mut path_strings {
1122             // produce an additional newline to separate the new use statement
1123             // from the directly following item.
1124             let additional_newline = if found_use {
1125                 ""
1126             } else {
1127                 "\n"
1128             };
1129             *candidate = format!("use {};\n{}", candidate, additional_newline);
1130         }
1131
1132         err.span_suggestions(
1133             span,
1134             &msg,
1135             path_strings.into_iter(),
1136             Applicability::Unspecified,
1137         );
1138     } else {
1139         let mut msg = msg;
1140         msg.push(':');
1141         for candidate in path_strings {
1142             msg.push('\n');
1143             msg.push_str(&candidate);
1144         }
1145     }
1146 }