src/librustc_resolve/diagnostics.rs

   1 use std::cmp::Reverse;
   2
   3 use log::debug;
   4 use rustc::bug;
   5 use rustc::session::Session;
   6 use rustc::ty::{self, DefIdTree};
   7 use rustc_ast::ast::{self, Ident, Path};
   8 use rustc_ast::util::lev_distance::find_best_match_for_name;
   9 use rustc_ast_pretty::pprust;
  10 use rustc_data_structures::fx::FxHashSet;
  11 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
  12 use rustc_feature::BUILTIN_ATTRIBUTES;
  13 use rustc_hir::def::Namespace::{self, *};
  14 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind, NonMacroAttrKind};
  15 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
  16 use rustc_span::hygiene::MacroKind;
  17 use rustc_span::source_map::SourceMap;
  18 use rustc_span::symbol::{kw, Symbol};
  19 use rustc_span::{BytePos, MultiSpan, Span};
  20
  21 use crate::imports::{ImportDirective, ImportDirectiveSubclass, ImportResolver};
  22 use crate::path_names_to_string;
  23 use crate::{AmbiguityError, AmbiguityErrorMisc, AmbiguityKind};
  24 use crate::{BindingError, CrateLint, HasGenericParams, LegacyScope, Module, ModuleOrUniformRoot};
  25 use crate::{NameBinding, NameBindingKind, PrivacyError, VisResolutionError};
  26 use crate::{ParentScope, PathResult, ResolutionError, Resolver, Scope, ScopeSet, Segment};
  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(sm: &SourceMap, impl_span: Span) -> Span {
  58     let impl_span = sm.span_until_char(impl_span, '<');
  59     let impl_span = sm.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,
  90         span: Span,
  91         resolution_error: ResolutionError<'_>,
  92     ) -> DiagnosticBuilder<'_> {
  93         match resolution_error {
  94             ResolutionError::GenericParamsFromOuterFunction(outer_res, has_generic_params) => {
  95                 let mut err = struct_span_err!(
  96                     self.session,
  97                     span,
  98                     E0401,
  99                     "can't use generic parameters from outer function",
 100                 );
 101                 err.span_label(span, "use of generic parameter from outer function".to_string());
 102
 103                 let sm = self.session.source_map();
 104                 match outer_res {
 105                     Res::SelfTy(maybe_trait_defid, maybe_impl_defid) => {
 106                         if let Some(impl_span) =
 107                             maybe_impl_defid.and_then(|def_id| self.definitions.opt_span(def_id))
 108                         {
 109                             err.span_label(
 110                                 reduce_impl_span_to_impl_keyword(sm, impl_span),
 111                                 "`Self` type implicitly declared here, by this `impl`",
 112                             );
 113                         }
 114                         match (maybe_trait_defid, maybe_impl_defid) {
 115                             (Some(_), None) => {
 116                                 err.span_label(span, "can't use `Self` here");
 117                             }
 118                             (_, Some(_)) => {
 119                                 err.span_label(span, "use a type here instead");
 120                             }
 121                             (None, None) => bug!("`impl` without trait nor type?"),
 122                         }
 123                         return err;
 124                     }
 125                     Res::Def(DefKind::TyParam, def_id) => {
 126                         if let Some(span) = self.definitions.opt_span(def_id) {
 127                             err.span_label(span, "type parameter from outer function");
 128                         }
 129                     }
 130                     Res::Def(DefKind::ConstParam, def_id) => {
 131                         if let Some(span) = self.definitions.opt_span(def_id) {
 132                             err.span_label(span, "const parameter from outer function");
 133                         }
 134                     }
 135                     _ => {
 136                         bug!(
 137                             "GenericParamsFromOuterFunction should only be used with Res::SelfTy, \
 138                             DefKind::TyParam"
 139                         );
 140                     }
 141                 }
 142
 143                 if has_generic_params == HasGenericParams::Yes {
 144                     // Try to retrieve the span of the function signature and generate a new
 145                     // message with a local type or const parameter.
 146                     let sugg_msg = "try using a local generic parameter instead";
 147                     if let Some((sugg_span, snippet)) = sm.generate_local_type_param_snippet(span) {
 148                         // Suggest the modification to the user
 149                         err.span_suggestion(
 150                             sugg_span,
 151                             sugg_msg,
 152                             snippet,
 153                             Applicability::MachineApplicable,
 154                         );
 155                     } else if let Some(sp) = sm.generate_fn_name_span(span) {
 156                         err.span_label(
 157                             sp,
 158                             "try adding a local generic parameter in this method instead"
 159                                 .to_string(),
 160                         );
 161                     } else {
 162                         err.help("try using a local generic parameter instead");
 163                     }
 164                 }
 165
 166                 err
 167             }
 168             ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => {
 169                 let mut err = struct_span_err!(
 170                     self.session,
 171                     span,
 172                     E0403,
 173                     "the name `{}` is already used for a generic \
 174                      parameter in this item's generic parameters",
 175                     name,
 176                 );
 177                 err.span_label(span, "already used");
 178                 err.span_label(first_use_span, format!("first use of `{}`", name));
 179                 err
 180             }
 181             ResolutionError::MethodNotMemberOfTrait(method, trait_) => {
 182                 let mut err = struct_span_err!(
 183                     self.session,
 184                     span,
 185                     E0407,
 186                     "method `{}` is not a member of trait `{}`",
 187                     method,
 188                     trait_
 189                 );
 190                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 191                 err
 192             }
 193             ResolutionError::TypeNotMemberOfTrait(type_, trait_) => {
 194                 let mut err = struct_span_err!(
 195                     self.session,
 196                     span,
 197                     E0437,
 198                     "type `{}` is not a member of trait `{}`",
 199                     type_,
 200                     trait_
 201                 );
 202                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 203                 err
 204             }
 205             ResolutionError::ConstNotMemberOfTrait(const_, trait_) => {
 206                 let mut err = struct_span_err!(
 207                     self.session,
 208                     span,
 209                     E0438,
 210                     "const `{}` is not a member of trait `{}`",
 211                     const_,
 212                     trait_
 213                 );
 214                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 215                 err
 216             }
 217             ResolutionError::VariableNotBoundInPattern(binding_error) => {
 218                 let BindingError { name, target, origin, could_be_path } = binding_error;
 219
 220                 let target_sp = target.iter().copied().collect::<Vec<_>>();
 221                 let origin_sp = origin.iter().copied().collect::<Vec<_>>();
 222
 223                 let msp = MultiSpan::from_spans(target_sp.clone());
 224                 let mut err = struct_span_err!(
 225                     self.session,
 226                     msp,
 227                     E0408,
 228                     "variable `{}` is not bound in all patterns",
 229                     name,
 230                 );
 231                 for sp in target_sp {
 232                     err.span_label(sp, format!("pattern doesn't bind `{}`", name));
 233                 }
 234                 for sp in origin_sp {
 235                     err.span_label(sp, "variable not in all patterns");
 236                 }
 237                 if *could_be_path {
 238                     let help_msg = format!(
 239                         "if you meant to match on a variant or a `const` item, consider \
 240                          making the path in the pattern qualified: `?::{}`",
 241                         name,
 242                     );
 243                     err.span_help(span, &help_msg);
 244                 }
 245                 err
 246             }
 247             ResolutionError::VariableBoundWithDifferentMode(variable_name, first_binding_span) => {
 248                 let mut err = struct_span_err!(
 249                     self.session,
 250                     span,
 251                     E0409,
 252                     "variable `{}` is bound in inconsistent \
 253                                 ways within the same match arm",
 254                     variable_name
 255                 );
 256                 err.span_label(span, "bound in different ways");
 257                 err.span_label(first_binding_span, "first binding");
 258                 err
 259             }
 260             ResolutionError::IdentifierBoundMoreThanOnceInParameterList(identifier) => {
 261                 let mut err = struct_span_err!(
 262                     self.session,
 263                     span,
 264                     E0415,
 265                     "identifier `{}` is bound more than once in this parameter list",
 266                     identifier
 267                 );
 268                 err.span_label(span, "used as parameter more than once");
 269                 err
 270             }
 271             ResolutionError::IdentifierBoundMoreThanOnceInSamePattern(identifier) => {
 272                 let mut err = struct_span_err!(
 273                     self.session,
 274                     span,
 275                     E0416,
 276                     "identifier `{}` is bound more than once in the same pattern",
 277                     identifier
 278                 );
 279                 err.span_label(span, "used in a pattern more than once");
 280                 err
 281             }
 282             ResolutionError::UndeclaredLabel(name, lev_candidate) => {
 283                 let mut err = struct_span_err!(
 284                     self.session,
 285                     span,
 286                     E0426,
 287                     "use of undeclared label `{}`",
 288                     name
 289                 );
 290                 if let Some(lev_candidate) = lev_candidate {
 291                     err.span_suggestion(
 292                         span,
 293                         "a label with a similar name exists in this scope",
 294                         lev_candidate.to_string(),
 295                         Applicability::MaybeIncorrect,
 296                     );
 297                 } else {
 298                     err.span_label(span, format!("undeclared label `{}`", name));
 299                 }
 300                 err
 301             }
 302             ResolutionError::SelfImportsOnlyAllowedWithin => struct_span_err!(
 303                 self.session,
 304                 span,
 305                 E0429,
 306                 "{}",
 307                 "`self` imports are only allowed within a { } list"
 308             ),
 309             ResolutionError::SelfImportCanOnlyAppearOnceInTheList => {
 310                 let mut err = struct_span_err!(
 311                     self.session,
 312                     span,
 313                     E0430,
 314                     "`self` import can only appear once in an import list"
 315                 );
 316                 err.span_label(span, "can only appear once in an import list");
 317                 err
 318             }
 319             ResolutionError::SelfImportOnlyInImportListWithNonEmptyPrefix => {
 320                 let mut err = struct_span_err!(
 321                     self.session,
 322                     span,
 323                     E0431,
 324                     "`self` import can only appear in an import list with \
 325                                                 a non-empty prefix"
 326                 );
 327                 err.span_label(span, "can only appear in an import list with a non-empty prefix");
 328                 err
 329             }
 330             ResolutionError::FailedToResolve { label, suggestion } => {
 331                 let mut err =
 332                     struct_span_err!(self.session, span, E0433, "failed to resolve: {}", &label);
 333                 err.span_label(span, label);
 334
 335                 if let Some((suggestions, msg, applicability)) = suggestion {
 336                     err.multipart_suggestion(&msg, suggestions, applicability);
 337                 }
 338
 339                 err
 340             }
 341             ResolutionError::CannotCaptureDynamicEnvironmentInFnItem => {
 342                 let mut err = struct_span_err!(
 343                     self.session,
 344                     span,
 345                     E0434,
 346                     "{}",
 347                     "can't capture dynamic environment in a fn item"
 348                 );
 349                 err.help("use the `|| { ... }` closure form instead");
 350                 err
 351             }
 352             ResolutionError::AttemptToUseNonConstantValueInConstant => {
 353                 let mut err = struct_span_err!(
 354                     self.session,
 355                     span,
 356                     E0435,
 357                     "attempt to use a non-constant value in a constant"
 358                 );
 359                 err.span_label(span, "non-constant value");
 360                 err
 361             }
 362             ResolutionError::BindingShadowsSomethingUnacceptable(what_binding, name, binding) => {
 363                 let res = binding.res();
 364                 let shadows_what = res.descr();
 365                 let mut err = struct_span_err!(
 366                     self.session,
 367                     span,
 368                     E0530,
 369                     "{}s cannot shadow {}s",
 370                     what_binding,
 371                     shadows_what
 372                 );
 373                 err.span_label(
 374                     span,
 375                     format!("cannot be named the same as {} {}", res.article(), shadows_what),
 376                 );
 377                 let participle = if binding.is_import() { "imported" } else { "defined" };
 378                 let msg = format!("the {} `{}` is {} here", shadows_what, name, participle);
 379                 err.span_label(binding.span, msg);
 380                 err
 381             }
 382             ResolutionError::ForwardDeclaredTyParam => {
 383                 let mut err = struct_span_err!(
 384                     self.session,
 385                     span,
 386                     E0128,
 387                     "type parameters with a default cannot use \
 388                                                 forward declared identifiers"
 389                 );
 390                 err.span_label(
 391                     span,
 392                     "defaulted type parameters cannot be forward declared".to_string(),
 393                 );
 394                 err
 395             }
 396             ResolutionError::SelfInTyParamDefault => {
 397                 let mut err = struct_span_err!(
 398                     self.session,
 399                     span,
 400                     E0735,
 401                     "type parameters cannot use `Self` in their defaults"
 402                 );
 403                 err.span_label(span, "`Self` in type parameter default".to_string());
 404                 err
 405             }
 406         }
 407     }
 408
 409     crate fn report_vis_error(&self, vis_resolution_error: VisResolutionError<'_>) {
 410         match vis_resolution_error {
 411             VisResolutionError::Relative2018(span, path) => {
 412                 let mut err = self.session.struct_span_err(
 413                     span,
 414                     "relative paths are not supported in visibilities on 2018 edition",
 415                 );
 416                 err.span_suggestion(
 417                     path.span,
 418                     "try",
 419                     format!("crate::{}", pprust::path_to_string(&path)),
 420                     Applicability::MaybeIncorrect,
 421                 );
 422                 err
 423             }
 424             VisResolutionError::AncestorOnly(span) => struct_span_err!(
 425                 self.session,
 426                 span,
 427                 E0742,
 428                 "visibilities can only be restricted to ancestor modules"
 429             ),
 430             VisResolutionError::FailedToResolve(span, label, suggestion) => {
 431                 self.into_struct_error(span, ResolutionError::FailedToResolve { label, suggestion })
 432             }
 433             VisResolutionError::ExpectedFound(span, path_str, res) => {
 434                 let mut err = struct_span_err!(
 435                     self.session,
 436                     span,
 437                     E0577,
 438                     "expected module, found {} `{}`",
 439                     res.descr(),
 440                     path_str
 441                 );
 442                 err.span_label(span, "not a module");
 443                 err
 444             }
 445             VisResolutionError::Indeterminate(span) => struct_span_err!(
 446                 self.session,
 447                 span,
 448                 E0578,
 449                 "cannot determine resolution for the visibility"
 450             ),
 451             VisResolutionError::ModuleOnly(span) => {
 452                 self.session.struct_span_err(span, "visibility must resolve to a module")
 453             }
 454         }
 455         .emit()
 456     }
 457
 458     /// Lookup typo candidate in scope for a macro or import.
 459     fn early_lookup_typo_candidate(
 460         &mut self,
 461         scope_set: ScopeSet,
 462         parent_scope: &ParentScope<'a>,
 463         ident: Ident,
 464         filter_fn: &impl Fn(Res) -> bool,
 465     ) -> Option<TypoSuggestion> {
 466         let mut suggestions = Vec::new();
 467         self.visit_scopes(scope_set, parent_scope, ident, |this, scope, use_prelude, _| {
 468             match scope {
 469                 Scope::DeriveHelpers(expn_id) => {
 470                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 471                     if filter_fn(res) {
 472                         suggestions.extend(
 473                             this.helper_attrs
 474                                 .get(&expn_id)
 475                                 .into_iter()
 476                                 .flatten()
 477                                 .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 478                         );
 479                     }
 480                 }
 481                 Scope::DeriveHelpersCompat => {
 482                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 483                     if filter_fn(res) {
 484                         for derive in parent_scope.derives {
 485                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
 486                             if let Ok((Some(ext), _)) = this.resolve_macro_path(
 487                                 derive,
 488                                 Some(MacroKind::Derive),
 489                                 parent_scope,
 490                                 false,
 491                                 false,
 492                             ) {
 493                                 suggestions.extend(
 494                                     ext.helper_attrs
 495                                         .iter()
 496                                         .map(|name| TypoSuggestion::from_res(*name, res)),
 497                                 );
 498                             }
 499                         }
 500                     }
 501                 }
 502                 Scope::MacroRules(legacy_scope) => {
 503                     if let LegacyScope::Binding(legacy_binding) = legacy_scope {
 504                         let res = legacy_binding.binding.res();
 505                         if filter_fn(res) {
 506                             suggestions
 507                                 .push(TypoSuggestion::from_res(legacy_binding.ident.name, res))
 508                         }
 509                     }
 510                 }
 511                 Scope::CrateRoot => {
 512                     let root_ident = Ident::new(kw::PathRoot, ident.span);
 513                     let root_module = this.resolve_crate_root(root_ident);
 514                     this.add_module_candidates(root_module, &mut suggestions, filter_fn);
 515                 }
 516                 Scope::Module(module) => {
 517                     this.add_module_candidates(module, &mut suggestions, filter_fn);
 518                 }
 519                 Scope::RegisteredAttrs => {
 520                     let res = Res::NonMacroAttr(NonMacroAttrKind::Registered);
 521                     if filter_fn(res) {
 522                         suggestions.extend(
 523                             this.registered_attrs
 524                                 .iter()
 525                                 .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 526                         );
 527                     }
 528                 }
 529                 Scope::MacroUsePrelude => {
 530                     suggestions.extend(this.macro_use_prelude.iter().filter_map(
 531                         |(name, binding)| {
 532                             let res = binding.res();
 533                             filter_fn(res).then_some(TypoSuggestion::from_res(*name, res))
 534                         },
 535                     ));
 536                 }
 537                 Scope::BuiltinAttrs => {
 538                     let res = Res::NonMacroAttr(NonMacroAttrKind::Builtin);
 539                     if filter_fn(res) {
 540                         suggestions.extend(
 541                             BUILTIN_ATTRIBUTES
 542                                 .iter()
 543                                 .map(|(name, ..)| TypoSuggestion::from_res(*name, res)),
 544                         );
 545                     }
 546                 }
 547                 Scope::ExternPrelude => {
 548                     suggestions.extend(this.extern_prelude.iter().filter_map(|(ident, _)| {
 549                         let res = Res::Def(DefKind::Mod, DefId::local(CRATE_DEF_INDEX));
 550                         filter_fn(res).then_some(TypoSuggestion::from_res(ident.name, res))
 551                     }));
 552                 }
 553                 Scope::ToolPrelude => {
 554                     let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
 555                     suggestions.extend(
 556                         this.registered_tools
 557                             .iter()
 558                             .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 559                     );
 560                 }
 561                 Scope::StdLibPrelude => {
 562                     if let Some(prelude) = this.prelude {
 563                         let mut tmp_suggestions = Vec::new();
 564                         this.add_module_candidates(prelude, &mut tmp_suggestions, filter_fn);
 565                         suggestions.extend(
 566                             tmp_suggestions
 567                                 .into_iter()
 568                                 .filter(|s| use_prelude || this.is_builtin_macro(s.res)),
 569                         );
 570                     }
 571                 }
 572                 Scope::BuiltinTypes => {
 573                     let primitive_types = &this.primitive_type_table.primitive_types;
 574                     suggestions.extend(primitive_types.iter().flat_map(|(name, prim_ty)| {
 575                         let res = Res::PrimTy(*prim_ty);
 576                         filter_fn(res).then_some(TypoSuggestion::from_res(*name, res))
 577                     }))
 578                 }
 579             }
 580
 581             None::<()>
 582         });
 583
 584         // Make sure error reporting is deterministic.
 585         suggestions.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
 586
 587         match find_best_match_for_name(
 588             suggestions.iter().map(|suggestion| &suggestion.candidate),
 589             &ident.as_str(),
 590             None,
 591         ) {
 592             Some(found) if found != ident.name => {
 593                 suggestions.into_iter().find(|suggestion| suggestion.candidate == found)
 594             }
 595             _ => None,
 596         }
 597     }
 598
 599     fn lookup_import_candidates_from_module<FilterFn>(
 600         &mut self,
 601         lookup_ident: Ident,
 602         namespace: Namespace,
 603         start_module: Module<'a>,
 604         crate_name: Ident,
 605         filter_fn: FilterFn,
 606     ) -> Vec<ImportSuggestion>
 607     where
 608         FilterFn: Fn(Res) -> bool,
 609     {
 610         let mut candidates = Vec::new();
 611         let mut seen_modules = FxHashSet::default();
 612         let not_local_module = crate_name.name != kw::Crate;
 613         let mut worklist = vec![(start_module, Vec::<ast::PathSegment>::new(), not_local_module)];
 614
 615         while let Some((in_module, path_segments, in_module_is_extern)) = worklist.pop() {
 616             // We have to visit module children in deterministic order to avoid
 617             // instabilities in reported imports (#43552).
 618             in_module.for_each_child(self, |this, ident, ns, name_binding| {
 619                 // avoid imports entirely
 620                 if name_binding.is_import() && !name_binding.is_extern_crate() {
 621                     return;
 622                 }
 623                 // avoid non-importable candidates as well
 624                 if !name_binding.is_importable() {
 625                     return;
 626                 }
 627
 628                 // collect results based on the filter function
 629                 if ident.name == lookup_ident.name && ns == namespace {
 630                     let res = name_binding.res();
 631                     if filter_fn(res) {
 632                         // create the path
 633                         let mut segms = path_segments.clone();
 634                         if lookup_ident.span.rust_2018() {
 635                             // crate-local absolute paths start with `crate::` in edition 2018
 636                             // FIXME: may also be stabilized for Rust 2015 (Issues #45477, #44660)
 637                             segms.insert(0, ast::PathSegment::from_ident(crate_name));
 638                         }
 639
 640                         segms.push(ast::PathSegment::from_ident(ident));
 641                         let path = Path { span: name_binding.span, segments: segms };
 642                         // the entity is accessible in the following cases:
 643                         // 1. if it's defined in the same crate, it's always
 644                         // accessible (since private entities can be made public)
 645                         // 2. if it's defined in another crate, it's accessible
 646                         // only if both the module is public and the entity is
 647                         // declared as public (due to pruning, we don't explore
 648                         // outside crate private modules => no need to check this)
 649                         if !in_module_is_extern || name_binding.vis == ty::Visibility::Public {
 650                             let did = match res {
 651                                 Res::Def(DefKind::Ctor(..), did) => this.parent(did),
 652                                 _ => res.opt_def_id(),
 653                             };
 654                             candidates.push(ImportSuggestion { did, path });
 655                         }
 656                     }
 657                 }
 658
 659                 // collect submodules to explore
 660                 if let Some(module) = name_binding.module() {
 661                     // form the path
 662                     let mut path_segments = path_segments.clone();
 663                     path_segments.push(ast::PathSegment::from_ident(ident));
 664
 665                     let is_extern_crate_that_also_appears_in_prelude =
 666                         name_binding.is_extern_crate() && lookup_ident.span.rust_2018();
 667
 668                     let is_visible_to_user =
 669                         !in_module_is_extern || name_binding.vis == ty::Visibility::Public;
 670
 671                     if !is_extern_crate_that_also_appears_in_prelude && is_visible_to_user {
 672                         // add the module to the lookup
 673                         let is_extern = in_module_is_extern || name_binding.is_extern_crate();
 674                         if seen_modules.insert(module.def_id().unwrap()) {
 675                             worklist.push((module, path_segments, is_extern));
 676                         }
 677                     }
 678                 }
 679             })
 680         }
 681
 682         candidates
 683     }
 684
 685     /// When name resolution fails, this method can be used to look up candidate
 686     /// entities with the expected name. It allows filtering them using the
 687     /// supplied predicate (which should be used to only accept the types of
 688     /// definitions expected, e.g., traits). The lookup spans across all crates.
 689     ///
 690     /// N.B., the method does not look into imports, but this is not a problem,
 691     /// since we report the definitions (thus, the de-aliased imports).
 692     crate fn lookup_import_candidates<FilterFn>(
 693         &mut self,
 694         lookup_ident: Ident,
 695         namespace: Namespace,
 696         filter_fn: FilterFn,
 697     ) -> Vec<ImportSuggestion>
 698     where
 699         FilterFn: Fn(Res) -> bool,
 700     {
 701         let mut suggestions = self.lookup_import_candidates_from_module(
 702             lookup_ident,
 703             namespace,
 704             self.graph_root,
 705             Ident::with_dummy_span(kw::Crate),
 706             &filter_fn,
 707         );
 708
 709         if lookup_ident.span.rust_2018() {
 710             let extern_prelude_names = self.extern_prelude.clone();
 711             for (ident, _) in extern_prelude_names.into_iter() {
 712                 if ident.span.from_expansion() {
 713                     // Idents are adjusted to the root context before being
 714                     // resolved in the extern prelude, so reporting this to the
 715                     // user is no help. This skips the injected
 716                     // `extern crate std` in the 2018 edition, which would
 717                     // otherwise cause duplicate suggestions.
 718                     continue;
 719                 }
 720                 if let Some(crate_id) =
 721                     self.crate_loader.maybe_process_path_extern(ident.name, ident.span)
 722                 {
 723                     let crate_root =
 724                         self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
 725                     suggestions.extend(self.lookup_import_candidates_from_module(
 726                         lookup_ident,
 727                         namespace,
 728                         crate_root,
 729                         ident,
 730                         &filter_fn,
 731                     ));
 732                 }
 733             }
 734         }
 735
 736         suggestions
 737     }
 738
 739     crate fn unresolved_macro_suggestions(
 740         &mut self,
 741         err: &mut DiagnosticBuilder<'a>,
 742         macro_kind: MacroKind,
 743         parent_scope: &ParentScope<'a>,
 744         ident: Ident,
 745     ) {
 746         let is_expected = &|res: Res| res.macro_kind() == Some(macro_kind);
 747         let suggestion = self.early_lookup_typo_candidate(
 748             ScopeSet::Macro(macro_kind),
 749             parent_scope,
 750             ident,
 751             is_expected,
 752         );
 753         self.add_typo_suggestion(err, suggestion, ident.span);
 754
 755         if macro_kind == MacroKind::Derive && (ident.as_str() == "Send" || ident.as_str() == "Sync")
 756         {
 757             let msg = format!("unsafe traits like `{}` should be implemented explicitly", ident);
 758             err.span_note(ident.span, &msg);
 759         }
 760         if self.macro_names.contains(&ident.modern()) {
 761             err.help("have you added the `#[macro_use]` on the module/import?");
 762         }
 763     }
 764
 765     crate fn add_typo_suggestion(
 766         &self,
 767         err: &mut DiagnosticBuilder<'_>,
 768         suggestion: Option<TypoSuggestion>,
 769         span: Span,
 770     ) -> bool {
 771         if let Some(suggestion) = suggestion {
 772             // We shouldn't suggest underscore.
 773             if suggestion.candidate == kw::Underscore {
 774                 return false;
 775             }
 776
 777             let msg = format!(
 778                 "{} {} with a similar name exists",
 779                 suggestion.res.article(),
 780                 suggestion.res.descr()
 781             );
 782             err.span_suggestion(
 783                 span,
 784                 &msg,
 785                 suggestion.candidate.to_string(),
 786                 Applicability::MaybeIncorrect,
 787             );
 788             let def_span = suggestion.res.opt_def_id().and_then(|def_id| match def_id.krate {
 789                 LOCAL_CRATE => self.definitions.opt_span(def_id),
 790                 _ => Some(
 791                     self.session
 792                         .source_map()
 793                         .def_span(self.cstore().get_span_untracked(def_id, self.session)),
 794                 ),
 795             });
 796             if let Some(span) = def_span {
 797                 err.span_label(
 798                     span,
 799                     &format!(
 800                         "similarly named {} `{}` defined here",
 801                         suggestion.res.descr(),
 802                         suggestion.candidate.as_str(),
 803                     ),
 804                 );
 805             }
 806             return true;
 807         }
 808         false
 809     }
 810
 811     fn binding_description(&self, b: &NameBinding<'_>, ident: Ident, from_prelude: bool) -> String {
 812         let res = b.res();
 813         if b.span.is_dummy() {
 814             let add_built_in = match b.res() {
 815                 // These already contain the "built-in" prefix or look bad with it.
 816                 Res::NonMacroAttr(..) | Res::PrimTy(..) | Res::ToolMod => false,
 817                 _ => true,
 818             };
 819             let (built_in, from) = if from_prelude {
 820                 ("", " from prelude")
 821             } else if b.is_extern_crate()
 822                 && !b.is_import()
 823                 && self.session.opts.externs.get(&ident.as_str()).is_some()
 824             {
 825                 ("", " passed with `--extern`")
 826             } else if add_built_in {
 827                 (" built-in", "")
 828             } else {
 829                 ("", "")
 830             };
 831
 832             let article = if built_in.is_empty() { res.article() } else { "a" };
 833             format!(
 834                 "{a}{built_in} {thing}{from}",
 835                 a = article,
 836                 thing = res.descr(),
 837                 built_in = built_in,
 838                 from = from
 839             )
 840         } else {
 841             let introduced = if b.is_import() { "imported" } else { "defined" };
 842             format!("the {thing} {introduced} here", thing = res.descr(), introduced = introduced)
 843         }
 844     }
 845
 846     crate fn report_ambiguity_error(&self, ambiguity_error: &AmbiguityError<'_>) {
 847         let AmbiguityError { kind, ident, b1, b2, misc1, misc2 } = *ambiguity_error;
 848         let (b1, b2, misc1, misc2, swapped) = if b2.span.is_dummy() && !b1.span.is_dummy() {
 849             // We have to print the span-less alternative first, otherwise formatting looks bad.
 850             (b2, b1, misc2, misc1, true)
 851         } else {
 852             (b1, b2, misc1, misc2, false)
 853         };
 854
 855         let mut err = struct_span_err!(
 856             self.session,
 857             ident.span,
 858             E0659,
 859             "`{ident}` is ambiguous ({why})",
 860             ident = ident,
 861             why = kind.descr()
 862         );
 863         err.span_label(ident.span, "ambiguous name");
 864
 865         let mut could_refer_to = |b: &NameBinding<'_>, misc: AmbiguityErrorMisc, also: &str| {
 866             let what = self.binding_description(b, ident, misc == AmbiguityErrorMisc::FromPrelude);
 867             let note_msg = format!(
 868                 "`{ident}` could{also} refer to {what}",
 869                 ident = ident,
 870                 also = also,
 871                 what = what
 872             );
 873
 874             let thing = b.res().descr();
 875             let mut help_msgs = Vec::new();
 876             if b.is_glob_import()
 877                 && (kind == AmbiguityKind::GlobVsGlob
 878                     || kind == AmbiguityKind::GlobVsExpanded
 879                     || kind == AmbiguityKind::GlobVsOuter && swapped != also.is_empty())
 880             {
 881                 help_msgs.push(format!(
 882                     "consider adding an explicit import of \
 883                      `{ident}` to disambiguate",
 884                     ident = ident
 885                 ))
 886             }
 887             if b.is_extern_crate() && ident.span.rust_2018() {
 888                 help_msgs.push(format!(
 889                     "use `::{ident}` to refer to this {thing} unambiguously",
 890                     ident = ident,
 891                     thing = thing,
 892                 ))
 893             }
 894             if misc == AmbiguityErrorMisc::SuggestCrate {
 895                 help_msgs.push(format!(
 896                     "use `crate::{ident}` to refer to this {thing} unambiguously",
 897                     ident = ident,
 898                     thing = thing,
 899                 ))
 900             } else if misc == AmbiguityErrorMisc::SuggestSelf {
 901                 help_msgs.push(format!(
 902                     "use `self::{ident}` to refer to this {thing} unambiguously",
 903                     ident = ident,
 904                     thing = thing,
 905                 ))
 906             }
 907
 908             err.span_note(b.span, &note_msg);
 909             for (i, help_msg) in help_msgs.iter().enumerate() {
 910                 let or = if i == 0 { "" } else { "or " };
 911                 err.help(&format!("{}{}", or, help_msg));
 912             }
 913         };
 914
 915         could_refer_to(b1, misc1, "");
 916         could_refer_to(b2, misc2, " also");
 917         err.emit();
 918     }
 919
 920     crate fn report_privacy_error(&self, privacy_error: &PrivacyError<'_>) {
 921         let PrivacyError { ident, binding, .. } = *privacy_error;
 922         let session = &self.session;
 923         let mk_struct_span_error = |is_constructor| {
 924             let mut descr = binding.res().descr().to_string();
 925             if is_constructor {
 926                 descr += " constructor";
 927             }
 928             if binding.is_import() {
 929                 descr += " import";
 930             }
 931
 932             let mut err =
 933                 struct_span_err!(session, ident.span, E0603, "{} `{}` is private", descr, ident);
 934
 935             err.span_label(ident.span, &format!("this {} is private", descr));
 936             err.span_note(
 937                 session.source_map().def_span(binding.span),
 938                 &format!("the {} `{}` is defined here", descr, ident),
 939             );
 940
 941             err
 942         };
 943
 944         let mut err = if let NameBindingKind::Res(
 945             Res::Def(DefKind::Ctor(CtorOf::Struct, CtorKind::Fn), ctor_def_id),
 946             _,
 947         ) = binding.kind
 948         {
 949             let def_id = (&*self).parent(ctor_def_id).expect("no parent for a constructor");
 950             if let Some(fields) = self.field_names.get(&def_id) {
 951                 let mut err = mk_struct_span_error(true);
 952                 let first_field = fields.first().expect("empty field list in the map");
 953                 err.span_label(
 954                     fields.iter().fold(first_field.span, |acc, field| acc.to(field.span)),
 955                     "a constructor is private if any of the fields is private",
 956                 );
 957                 err
 958             } else {
 959                 mk_struct_span_error(false)
 960             }
 961         } else {
 962             mk_struct_span_error(false)
 963         };
 964
 965         err.emit();
 966     }
 967 }
 968
 969 impl<'a, 'b> ImportResolver<'a, 'b> {
 970     /// Adds suggestions for a path that cannot be resolved.
 971     pub(crate) fn make_path_suggestion(
 972         &mut self,
 973         span: Span,
 974         mut path: Vec<Segment>,
 975         parent_scope: &ParentScope<'b>,
 976     ) -> Option<(Vec<Segment>, Vec<String>)> {
 977         debug!("make_path_suggestion: span={:?} path={:?}", span, path);
 978
 979         match (path.get(0), path.get(1)) {
 980             // `{{root}}::ident::...` on both editions.
 981             // On 2015 `{{root}}` is usually added implicitly.
 982             (Some(fst), Some(snd))
 983                 if fst.ident.name == kw::PathRoot && !snd.ident.is_path_segment_keyword() => {}
 984             // `ident::...` on 2018.
 985             (Some(fst), _)
 986                 if fst.ident.span.rust_2018() && !fst.ident.is_path_segment_keyword() =>
 987             {
 988                 // Insert a placeholder that's later replaced by `self`/`super`/etc.
 989                 path.insert(0, Segment::from_ident(Ident::invalid()));
 990             }
 991             _ => return None,
 992         }
 993
 994         self.make_missing_self_suggestion(span, path.clone(), parent_scope)
 995             .or_else(|| self.make_missing_crate_suggestion(span, path.clone(), parent_scope))
 996             .or_else(|| self.make_missing_super_suggestion(span, path.clone(), parent_scope))
 997             .or_else(|| self.make_external_crate_suggestion(span, path, parent_scope))
 998     }
 999
1000     /// Suggest a missing `self::` if that resolves to an correct module.
1001     ///
1002     /// ```
1003     ///    |
1004     /// LL | use foo::Bar;
1005     ///    |     ^^^ did you mean `self::foo`?
1006     /// ```
1007     fn make_missing_self_suggestion(
1008         &mut self,
1009         span: Span,
1010         mut path: Vec<Segment>,
1011         parent_scope: &ParentScope<'b>,
1012     ) -> Option<(Vec<Segment>, Vec<String>)> {
1013         // Replace first ident with `self` and check if that is valid.
1014         path[0].ident.name = kw::SelfLower;
1015         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1016         debug!("make_missing_self_suggestion: path={:?} result={:?}", path, result);
1017         if let PathResult::Module(..) = result { Some((path, Vec::new())) } else { None }
1018     }
1019
1020     /// Suggests a missing `crate::` if that resolves to an correct module.
1021     ///
1022     /// ```
1023     ///    |
1024     /// LL | use foo::Bar;
1025     ///    |     ^^^ did you mean `crate::foo`?
1026     /// ```
1027     fn make_missing_crate_suggestion(
1028         &mut self,
1029         span: Span,
1030         mut path: Vec<Segment>,
1031         parent_scope: &ParentScope<'b>,
1032     ) -> Option<(Vec<Segment>, Vec<String>)> {
1033         // Replace first ident with `crate` and check if that is valid.
1034         path[0].ident.name = kw::Crate;
1035         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1036         debug!("make_missing_crate_suggestion:  path={:?} result={:?}", path, result);
1037         if let PathResult::Module(..) = result {
1038             Some((
1039                 path,
1040                 vec![
1041                     "`use` statements changed in Rust 2018; read more at \
1042                      <https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-\
1043                      clarity.html>"
1044                         .to_string(),
1045                 ],
1046             ))
1047         } else {
1048             None
1049         }
1050     }
1051
1052     /// Suggests a missing `super::` if that resolves to an correct module.
1053     ///
1054     /// ```
1055     ///    |
1056     /// LL | use foo::Bar;
1057     ///    |     ^^^ did you mean `super::foo`?
1058     /// ```
1059     fn make_missing_super_suggestion(
1060         &mut self,
1061         span: Span,
1062         mut path: Vec<Segment>,
1063         parent_scope: &ParentScope<'b>,
1064     ) -> Option<(Vec<Segment>, Vec<String>)> {
1065         // Replace first ident with `crate` and check if that is valid.
1066         path[0].ident.name = kw::Super;
1067         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1068         debug!("make_missing_super_suggestion:  path={:?} result={:?}", path, result);
1069         if let PathResult::Module(..) = result { Some((path, Vec::new())) } else { None }
1070     }
1071
1072     /// Suggests a missing external crate name if that resolves to an correct module.
1073     ///
1074     /// ```
1075     ///    |
1076     /// LL | use foobar::Baz;
1077     ///    |     ^^^^^^ did you mean `baz::foobar`?
1078     /// ```
1079     ///
1080     /// Used when importing a submodule of an external crate but missing that crate's
1081     /// name as the first part of path.
1082     fn make_external_crate_suggestion(
1083         &mut self,
1084         span: Span,
1085         mut path: Vec<Segment>,
1086         parent_scope: &ParentScope<'b>,
1087     ) -> Option<(Vec<Segment>, Vec<String>)> {
1088         if path[1].ident.span.rust_2015() {
1089             return None;
1090         }
1091
1092         // Sort extern crate names in reverse order to get
1093         // 1) some consistent ordering for emitted dignostics, and
1094         // 2) `std` suggestions before `core` suggestions.
1095         let mut extern_crate_names =
1096             self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
1097         extern_crate_names.sort_by_key(|name| Reverse(name.as_str()));
1098
1099         for name in extern_crate_names.into_iter() {
1100             // Replace first ident with a crate name and check if that is valid.
1101             path[0].ident.name = name;
1102             let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1103             debug!(
1104                 "make_external_crate_suggestion: name={:?} path={:?} result={:?}",
1105                 name, path, result
1106             );
1107             if let PathResult::Module(..) = result {
1108                 return Some((path, Vec::new()));
1109             }
1110         }
1111
1112         None
1113     }
1114
1115     /// Suggests importing a macro from the root of the crate rather than a module within
1116     /// the crate.
1117     ///
1118     /// ```
1119     /// help: a macro with this name exists at the root of the crate
1120     ///    |
1121     /// LL | use issue_59764::makro;
1122     ///    |     ^^^^^^^^^^^^^^^^^^
1123     ///    |
1124     ///    = note: this could be because a macro annotated with `#[macro_export]` will be exported
1125     ///            at the root of the crate instead of the module where it is defined
1126     /// ```
1127     pub(crate) fn check_for_module_export_macro(
1128         &mut self,
1129         directive: &'b ImportDirective<'b>,
1130         module: ModuleOrUniformRoot<'b>,
1131         ident: Ident,
1132     ) -> Option<(Option<Suggestion>, Vec<String>)> {
1133         let mut crate_module = if let ModuleOrUniformRoot::Module(module) = module {
1134             module
1135         } else {
1136             return None;
1137         };
1138
1139         while let Some(parent) = crate_module.parent {
1140             crate_module = parent;
1141         }
1142
1143         if ModuleOrUniformRoot::same_def(ModuleOrUniformRoot::Module(crate_module), module) {
1144             // Don't make a suggestion if the import was already from the root of the
1145             // crate.
1146             return None;
1147         }
1148
1149         let resolutions = self.r.resolutions(crate_module).borrow();
1150         let resolution = resolutions.get(&self.r.new_key(ident, MacroNS))?;
1151         let binding = resolution.borrow().binding()?;
1152         if let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() {
1153             let module_name = crate_module.kind.name().unwrap();
1154             let import = match directive.subclass {
1155                 ImportDirectiveSubclass::SingleImport { source, target, .. }
1156                     if source != target =>
1157                 {
1158                     format!("{} as {}", source, target)
1159                 }
1160                 _ => format!("{}", ident),
1161             };
1162
1163             let mut corrections: Vec<(Span, String)> = Vec::new();
1164             if !directive.is_nested() {
1165                 // Assume this is the easy case of `use issue_59764::foo::makro;` and just remove
1166                 // intermediate segments.
1167                 corrections.push((directive.span, format!("{}::{}", module_name, import)));
1168             } else {
1169                 // Find the binding span (and any trailing commas and spaces).
1170                 //   ie. `use a::b::{c, d, e};`
1171                 //                      ^^^
1172                 let (found_closing_brace, binding_span) = find_span_of_binding_until_next_binding(
1173                     self.r.session,
1174                     directive.span,
1175                     directive.use_span,
1176                 );
1177                 debug!(
1178                     "check_for_module_export_macro: found_closing_brace={:?} binding_span={:?}",
1179                     found_closing_brace, binding_span
1180                 );
1181
1182                 let mut removal_span = binding_span;
1183                 if found_closing_brace {
1184                     // If the binding span ended with a closing brace, as in the below example:
1185                     //   ie. `use a::b::{c, d};`
1186                     //                      ^
1187                     // Then expand the span of characters to remove to include the previous
1188                     // binding's trailing comma.
1189                     //   ie. `use a::b::{c, d};`
1190                     //                    ^^^
1191                     if let Some(previous_span) =
1192                         extend_span_to_previous_binding(self.r.session, binding_span)
1193                     {
1194                         debug!("check_for_module_export_macro: previous_span={:?}", previous_span);
1195                         removal_span = removal_span.with_lo(previous_span.lo());
1196                     }
1197                 }
1198                 debug!("check_for_module_export_macro: removal_span={:?}", removal_span);
1199
1200                 // Remove the `removal_span`.
1201                 corrections.push((removal_span, "".to_string()));
1202
1203                 // Find the span after the crate name and if it has nested imports immediatately
1204                 // after the crate name already.
1205                 //   ie. `use a::b::{c, d};`
1206                 //               ^^^^^^^^^
1207                 //   or  `use a::{b, c, d}};`
1208                 //               ^^^^^^^^^^^
1209                 let (has_nested, after_crate_name) = find_span_immediately_after_crate_name(
1210                     self.r.session,
1211                     module_name,
1212                     directive.use_span,
1213                 );
1214                 debug!(
1215                     "check_for_module_export_macro: has_nested={:?} after_crate_name={:?}",
1216                     has_nested, after_crate_name
1217                 );
1218
1219                 let source_map = self.r.session.source_map();
1220
1221                 // Add the import to the start, with a `{` if required.
1222                 let start_point = source_map.start_point(after_crate_name);
1223                 if let Ok(start_snippet) = source_map.span_to_snippet(start_point) {
1224                     corrections.push((
1225                         start_point,
1226                         if has_nested {
1227                             // In this case, `start_snippet` must equal '{'.
1228                             format!("{}{}, ", start_snippet, import)
1229                         } else {
1230                             // In this case, add a `{`, then the moved import, then whatever
1231                             // was there before.
1232                             format!("{{{}, {}", import, start_snippet)
1233                         },
1234                     ));
1235                 }
1236
1237                 // Add a `};` to the end if nested, matching the `{` added at the start.
1238                 if !has_nested {
1239                     corrections.push((source_map.end_point(after_crate_name), "};".to_string()));
1240                 }
1241             }
1242
1243             let suggestion = Some((
1244                 corrections,
1245                 String::from("a macro with this name exists at the root of the crate"),
1246                 Applicability::MaybeIncorrect,
1247             ));
1248             let note = vec![
1249                 "this could be because a macro annotated with `#[macro_export]` will be exported \
1250                  at the root of the crate instead of the module where it is defined"
1251                     .to_string(),
1252             ];
1253             Some((suggestion, note))
1254         } else {
1255             None
1256         }
1257     }
1258 }
1259
1260 /// Given a `binding_span` of a binding within a use statement:
1261 ///
1262 /// ```
1263 /// use foo::{a, b, c};
1264 ///              ^
1265 /// ```
1266 ///
1267 /// then return the span until the next binding or the end of the statement:
1268 ///
1269 /// ```
1270 /// use foo::{a, b, c};
1271 ///              ^^^
1272 /// ```
1273 pub(crate) fn find_span_of_binding_until_next_binding(
1274     sess: &Session,
1275     binding_span: Span,
1276     use_span: Span,
1277 ) -> (bool, Span) {
1278     let source_map = sess.source_map();
1279
1280     // Find the span of everything after the binding.
1281     //   ie. `a, e};` or `a};`
1282     let binding_until_end = binding_span.with_hi(use_span.hi());
1283
1284     // Find everything after the binding but not including the binding.
1285     //   ie. `, e};` or `};`
1286     let after_binding_until_end = binding_until_end.with_lo(binding_span.hi());
1287
1288     // Keep characters in the span until we encounter something that isn't a comma or
1289     // whitespace.
1290     //   ie. `, ` or ``.
1291     //
1292     // Also note whether a closing brace character was encountered. If there
1293     // was, then later go backwards to remove any trailing commas that are left.
1294     let mut found_closing_brace = false;
1295     let after_binding_until_next_binding =
1296         source_map.span_take_while(after_binding_until_end, |&ch| {
1297             if ch == '}' {
1298                 found_closing_brace = true;
1299             }
1300             ch == ' ' || ch == ','
1301         });
1302
1303     // Combine the two spans.
1304     //   ie. `a, ` or `a`.
1305     //
1306     // Removing these would leave `issue_52891::{d, e};` or `issue_52891::{d, e, };`
1307     let span = binding_span.with_hi(after_binding_until_next_binding.hi());
1308
1309     (found_closing_brace, span)
1310 }
1311
1312 /// Given a `binding_span`, return the span through to the comma or opening brace of the previous
1313 /// binding.
1314 ///
1315 /// ```
1316 /// use foo::a::{a, b, c};
1317 ///               ^^--- binding span
1318 ///               |
1319 ///               returned span
1320 ///
1321 /// use foo::{a, b, c};
1322 ///           --- binding span
1323 /// ```
1324 pub(crate) fn extend_span_to_previous_binding(sess: &Session, binding_span: Span) -> Option<Span> {
1325     let source_map = sess.source_map();
1326
1327     // `prev_source` will contain all of the source that came before the span.
1328     // Then split based on a command and take the first (ie. closest to our span)
1329     // snippet. In the example, this is a space.
1330     let prev_source = source_map.span_to_prev_source(binding_span).ok()?;
1331
1332     let prev_comma = prev_source.rsplit(',').collect::<Vec<_>>();
1333     let prev_starting_brace = prev_source.rsplit('{').collect::<Vec<_>>();
1334     if prev_comma.len() <= 1 || prev_starting_brace.len() <= 1 {
1335         return None;
1336     }
1337
1338     let prev_comma = prev_comma.first().unwrap();
1339     let prev_starting_brace = prev_starting_brace.first().unwrap();
1340
1341     // If the amount of source code before the comma is greater than
1342     // the amount of source code before the starting brace then we've only
1343     // got one item in the nested item (eg. `issue_52891::{self}`).
1344     if prev_comma.len() > prev_starting_brace.len() {
1345         return None;
1346     }
1347
1348     Some(binding_span.with_lo(BytePos(
1349         // Take away the number of bytes for the characters we've found and an
1350         // extra for the comma.
1351         binding_span.lo().0 - (prev_comma.as_bytes().len() as u32) - 1,
1352     )))
1353 }
1354
1355 /// Given a `use_span` of a binding within a use statement, returns the highlighted span and if
1356 /// it is a nested use tree.
1357 ///
1358 /// ```
1359 /// use foo::a::{b, c};
1360 ///          ^^^^^^^^^^ // false
1361 ///
1362 /// use foo::{a, b, c};
1363 ///          ^^^^^^^^^^ // true
1364 ///
1365 /// use foo::{a, b::{c, d}};
1366 ///          ^^^^^^^^^^^^^^^ // true
1367 /// ```
1368 fn find_span_immediately_after_crate_name(
1369     sess: &Session,
1370     module_name: Symbol,
1371     use_span: Span,
1372 ) -> (bool, Span) {
1373     debug!(
1374         "find_span_immediately_after_crate_name: module_name={:?} use_span={:?}",
1375         module_name, use_span
1376     );
1377     let source_map = sess.source_map();
1378
1379     // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
1380     let mut num_colons = 0;
1381     // Find second colon.. `use issue_59764:`
1382     let until_second_colon = source_map.span_take_while(use_span, |c| {
1383         if *c == ':' {
1384             num_colons += 1;
1385         }
1386         match c {
1387             ':' if num_colons == 2 => false,
1388             _ => true,
1389         }
1390     });
1391     // Find everything after the second colon.. `foo::{baz, makro};`
1392     let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
1393
1394     let mut found_a_non_whitespace_character = false;
1395     // Find the first non-whitespace character in `from_second_colon`.. `f`
1396     let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
1397         if found_a_non_whitespace_character {
1398             return false;
1399         }
1400         if !c.is_whitespace() {
1401             found_a_non_whitespace_character = true;
1402         }
1403         true
1404     });
1405
1406     // Find the first `{` in from_second_colon.. `foo::{`
1407     let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
1408
1409     (next_left_bracket == after_second_colon, from_second_colon)
1410 }
1411
1412 /// When an entity with a given name is not available in scope, we search for
1413 /// entities with that name in all crates. This method allows outputting the
1414 /// results of this search in a programmer-friendly way
1415 crate fn show_candidates(
1416     err: &mut DiagnosticBuilder<'_>,
1417     // This is `None` if all placement locations are inside expansions
1418     span: Option<Span>,
1419     candidates: &[ImportSuggestion],
1420     better: bool,
1421     found_use: bool,
1422 ) {
1423     if candidates.is_empty() {
1424         return;
1425     }
1426     // we want consistent results across executions, but candidates are produced
1427     // by iterating through a hash map, so make sure they are ordered:
1428     let mut path_strings: Vec<_> =
1429         candidates.iter().map(|c| path_names_to_string(&c.path)).collect();
1430     path_strings.sort();
1431     path_strings.dedup();
1432
1433     let better = if better { "better " } else { "" };
1434     let msg_diff = match path_strings.len() {
1435         1 => " is found in another module, you can import it",
1436         _ => "s are found in other modules, you can import them",
1437     };
1438     let msg = format!("possible {}candidate{} into scope", better, msg_diff);
1439
1440     if let Some(span) = span {
1441         for candidate in &mut path_strings {
1442             // produce an additional newline to separate the new use statement
1443             // from the directly following item.
1444             let additional_newline = if found_use { "" } else { "\n" };
1445             *candidate = format!("use {};\n{}", candidate, additional_newline);
1446         }
1447
1448         err.span_suggestions(span, &msg, path_strings.into_iter(), Applicability::Unspecified);
1449     } else {
1450         let mut msg = msg;
1451         msg.push(':');
1452         for candidate in path_strings {
1453             msg.push('\n');
1454             msg.push_str(&candidate);
1455         }
1456         err.note(&msg);
1457     }
1458 }