src/librustc_resolve/diagnostics.rs

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