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_data_structures::fx::FxHashSet;
   8 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
   9 use rustc_feature::BUILTIN_ATTRIBUTES;
  10 use rustc_hir::def::Namespace::{self, *};
  11 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind, NonMacroAttrKind};
  12 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
  13 use rustc_span::hygiene::MacroKind;
  14 use rustc_span::source_map::SourceMap;
  15 use rustc_span::symbol::{kw, Symbol};
  16 use rustc_span::{BytePos, MultiSpan, Span};
  17 use syntax::ast::{self, Ident, Path};
  18 use syntax::print::pprust;
  19 use syntax::util::lev_distance::find_best_match_for_name;
  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 use rustc_error_codes::*;
  29
  30 type Res = def::Res<ast::NodeId>;
  31
  32 /// A vector of spans and replacements, a message and applicability.
  33 crate type Suggestion = (Vec<(Span, String)>, String, Applicability);
  34
  35 crate struct TypoSuggestion {
  36     pub candidate: Symbol,
  37     pub res: Res,
  38 }
  39
  40 impl TypoSuggestion {
  41     crate fn from_res(candidate: Symbol, res: Res) -> TypoSuggestion {
  42         TypoSuggestion { candidate, res }
  43     }
  44 }
  45
  46 /// A free importable items suggested in case of resolution failure.
  47 crate struct ImportSuggestion {
  48     pub did: Option<DefId>,
  49     pub path: Path,
  50 }
  51
  52 /// Adjust the impl span so that just the `impl` keyword is taken by removing
  53 /// everything after `<` (`"impl<T> Iterator for A<T> {}" -> "impl"`) and
  54 /// everything after the first whitespace (`"impl Iterator for A" -> "impl"`).
  55 ///
  56 /// *Attention*: the method used is very fragile since it essentially duplicates the work of the
  57 /// parser. If you need to use this function or something similar, please consider updating the
  58 /// `source_map` functions and this function to something more robust.
  59 fn reduce_impl_span_to_impl_keyword(cm: &SourceMap, impl_span: Span) -> Span {
  60     let impl_span = cm.span_until_char(impl_span, '<');
  61     let impl_span = cm.span_until_whitespace(impl_span);
  62     impl_span
  63 }
  64
  65 impl<'a> Resolver<'a> {
  66     crate fn add_module_candidates(
  67         &mut self,
  68         module: Module<'a>,
  69         names: &mut Vec<TypoSuggestion>,
  70         filter_fn: &impl Fn(Res) -> bool,
  71     ) {
  72         for (key, resolution) in self.resolutions(module).borrow().iter() {
  73             if let Some(binding) = resolution.borrow().binding {
  74                 let res = binding.res();
  75                 if filter_fn(res) {
  76                     names.push(TypoSuggestion::from_res(key.ident.name, res));
  77                 }
  78             }
  79         }
  80     }
  81
  82     /// Combines an error with provided span and emits it.
  83     ///
  84     /// This takes the error provided, combines it with the span and any additional spans inside the
  85     /// error and emits it.
  86     crate fn report_error(&self, span: Span, resolution_error: ResolutionError<'_>) {
  87         self.into_struct_error(span, resolution_error).emit();
  88     }
  89
  90     crate fn into_struct_error(
  91         &self,
  92         span: Span,
  93         resolution_error: ResolutionError<'_>,
  94     ) -> DiagnosticBuilder<'_> {
  95         match resolution_error {
  96             ResolutionError::GenericParamsFromOuterFunction(outer_res, has_generic_params) => {
  97                 let mut err = struct_span_err!(
  98                     self.session,
  99                     span,
 100                     E0401,
 101                     "can't use generic parameters from outer function",
 102                 );
 103                 err.span_label(span, format!("use of generic parameter from outer function"));
 104
 105                 let cm = self.session.source_map();
 106                 match outer_res {
 107                     Res::SelfTy(maybe_trait_defid, maybe_impl_defid) => {
 108                         if let Some(impl_span) =
 109                             maybe_impl_defid.and_then(|def_id| self.definitions.opt_span(def_id))
 110                         {
 111                             err.span_label(
 112                                 reduce_impl_span_to_impl_keyword(cm, impl_span),
 113                                 "`Self` type implicitly declared here, by this `impl`",
 114                             );
 115                         }
 116                         match (maybe_trait_defid, maybe_impl_defid) {
 117                             (Some(_), None) => {
 118                                 err.span_label(span, "can't use `Self` here");
 119                             }
 120                             (_, Some(_)) => {
 121                                 err.span_label(span, "use a type here instead");
 122                             }
 123                             (None, None) => bug!("`impl` without trait nor type?"),
 124                         }
 125                         return err;
 126                     }
 127                     Res::Def(DefKind::TyParam, def_id) => {
 128                         if let Some(span) = self.definitions.opt_span(def_id) {
 129                             err.span_label(span, "type parameter from outer function");
 130                         }
 131                     }
 132                     Res::Def(DefKind::ConstParam, def_id) => {
 133                         if let Some(span) = self.definitions.opt_span(def_id) {
 134                             err.span_label(span, "const parameter from outer function");
 135                         }
 136                     }
 137                     _ => {
 138                         bug!(
 139                             "GenericParamsFromOuterFunction should only be used with Res::SelfTy, \
 140                             DefKind::TyParam"
 141                         );
 142                     }
 143                 }
 144
 145                 if has_generic_params == HasGenericParams::Yes {
 146                     // Try to retrieve the span of the function signature and generate a new
 147                     // message with a local type or const parameter.
 148                     let sugg_msg = &format!("try using a local generic parameter instead");
 149                     if let Some((sugg_span, snippet)) = cm.generate_local_type_param_snippet(span) {
 150                         // Suggest the modification to the user
 151                         err.span_suggestion(
 152                             sugg_span,
 153                             sugg_msg,
 154                             snippet,
 155                             Applicability::MachineApplicable,
 156                         );
 157                     } else if let Some(sp) = cm.generate_fn_name_span(span) {
 158                         err.span_label(
 159                             sp,
 160                             format!("try adding a local generic parameter in this method instead"),
 161                         );
 162                     } else {
 163                         err.help(&format!("try using a local generic parameter instead"));
 164                     }
 165                 }
 166
 167                 err
 168             }
 169             ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => {
 170                 let mut err = struct_span_err!(
 171                     self.session,
 172                     span,
 173                     E0403,
 174                     "the name `{}` is already used for a generic \
 175                      parameter in this item's generic parameters",
 176                     name,
 177                 );
 178                 err.span_label(span, "already used");
 179                 err.span_label(first_use_span, format!("first use of `{}`", name));
 180                 err
 181             }
 182             ResolutionError::MethodNotMemberOfTrait(method, trait_) => {
 183                 let mut err = struct_span_err!(
 184                     self.session,
 185                     span,
 186                     E0407,
 187                     "method `{}` is not a member of trait `{}`",
 188                     method,
 189                     trait_
 190                 );
 191                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 192                 err
 193             }
 194             ResolutionError::TypeNotMemberOfTrait(type_, trait_) => {
 195                 let mut err = struct_span_err!(
 196                     self.session,
 197                     span,
 198                     E0437,
 199                     "type `{}` is not a member of trait `{}`",
 200                     type_,
 201                     trait_
 202                 );
 203                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 204                 err
 205             }
 206             ResolutionError::ConstNotMemberOfTrait(const_, trait_) => {
 207                 let mut err = struct_span_err!(
 208                     self.session,
 209                     span,
 210                     E0438,
 211                     "const `{}` is not a member of trait `{}`",
 212                     const_,
 213                     trait_
 214                 );
 215                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 216                 err
 217             }
 218             ResolutionError::VariableNotBoundInPattern(binding_error) => {
 219                 let BindingError { name, target, origin, could_be_path } = binding_error;
 220
 221                 let target_sp = target.iter().copied().collect::<Vec<_>>();
 222                 let origin_sp = origin.iter().copied().collect::<Vec<_>>();
 223
 224                 let msp = MultiSpan::from_spans(target_sp.clone());
 225                 let mut err = struct_span_err!(
 226                     self.session,
 227                     msp,
 228                     E0408,
 229                     "variable `{}` is not bound in all patterns",
 230                     name,
 231                 );
 232                 for sp in target_sp {
 233                     err.span_label(sp, format!("pattern doesn't bind `{}`", name));
 234                 }
 235                 for sp in origin_sp {
 236                     err.span_label(sp, "variable not in all patterns");
 237                 }
 238                 if *could_be_path {
 239                     let help_msg = format!(
 240                         "if you meant to match on a variant or a `const` item, consider \
 241                          making the path in the pattern qualified: `?::{}`",
 242                         name,
 243                     );
 244                     err.span_help(span, &help_msg);
 245                 }
 246                 err
 247             }
 248             ResolutionError::VariableBoundWithDifferentMode(variable_name, first_binding_span) => {
 249                 let mut err = struct_span_err!(
 250                     self.session,
 251                     span,
 252                     E0409,
 253                     "variable `{}` is bound in inconsistent \
 254                                 ways within the same match arm",
 255                     variable_name
 256                 );
 257                 err.span_label(span, "bound in different ways");
 258                 err.span_label(first_binding_span, "first binding");
 259                 err
 260             }
 261             ResolutionError::IdentifierBoundMoreThanOnceInParameterList(identifier) => {
 262                 let mut err = struct_span_err!(
 263                     self.session,
 264                     span,
 265                     E0415,
 266                     "identifier `{}` is bound more than once in this parameter list",
 267                     identifier
 268                 );
 269                 err.span_label(span, "used as parameter more than once");
 270                 err
 271             }
 272             ResolutionError::IdentifierBoundMoreThanOnceInSamePattern(identifier) => {
 273                 let mut err = struct_span_err!(
 274                     self.session,
 275                     span,
 276                     E0416,
 277                     "identifier `{}` is bound more than once in the same pattern",
 278                     identifier
 279                 );
 280                 err.span_label(span, "used in a pattern more than once");
 281                 err
 282             }
 283             ResolutionError::UndeclaredLabel(name, lev_candidate) => {
 284                 let mut err = struct_span_err!(
 285                     self.session,
 286                     span,
 287                     E0426,
 288                     "use of undeclared label `{}`",
 289                     name
 290                 );
 291                 if let Some(lev_candidate) = lev_candidate {
 292                     err.span_suggestion(
 293                         span,
 294                         "a label with a similar name exists in this scope",
 295                         lev_candidate.to_string(),
 296                         Applicability::MaybeIncorrect,
 297                     );
 298                 } else {
 299                     err.span_label(span, format!("undeclared label `{}`", name));
 300                 }
 301                 err
 302             }
 303             ResolutionError::SelfImportsOnlyAllowedWithin => struct_span_err!(
 304                 self.session,
 305                 span,
 306                 E0429,
 307                 "{}",
 308                 "`self` imports are only allowed within a { } list"
 309             ),
 310             ResolutionError::SelfImportCanOnlyAppearOnceInTheList => {
 311                 let mut err = struct_span_err!(
 312                     self.session,
 313                     span,
 314                     E0430,
 315                     "`self` import can only appear once in an import list"
 316                 );
 317                 err.span_label(span, "can only appear once in an import list");
 318                 err
 319             }
 320             ResolutionError::SelfImportOnlyInImportListWithNonEmptyPrefix => {
 321                 let mut err = struct_span_err!(
 322                     self.session,
 323                     span,
 324                     E0431,
 325                     "`self` import can only appear in an import list with \
 326                                                 a non-empty prefix"
 327                 );
 328                 err.span_label(span, "can only appear in an import list with a non-empty prefix");
 329                 err
 330             }
 331             ResolutionError::FailedToResolve { label, suggestion } => {
 332                 let mut err =
 333                     struct_span_err!(self.session, span, E0433, "failed to resolve: {}", &label);
 334                 err.span_label(span, label);
 335
 336                 if let Some((suggestions, msg, applicability)) = suggestion {
 337                     err.multipart_suggestion(&msg, suggestions, applicability);
 338                 }
 339
 340                 err
 341             }
 342             ResolutionError::CannotCaptureDynamicEnvironmentInFnItem => {
 343                 let mut err = struct_span_err!(
 344                     self.session,
 345                     span,
 346                     E0434,
 347                     "{}",
 348                     "can't capture dynamic environment in a fn item"
 349                 );
 350                 err.help("use the `|| { ... }` closure form instead");
 351                 err
 352             }
 353             ResolutionError::AttemptToUseNonConstantValueInConstant => {
 354                 let mut err = struct_span_err!(
 355                     self.session,
 356                     span,
 357                     E0435,
 358                     "attempt to use a non-constant value in a constant"
 359                 );
 360                 err.span_label(span, "non-constant value");
 361                 err
 362             }
 363             ResolutionError::BindingShadowsSomethingUnacceptable(what_binding, name, binding) => {
 364                 let res = binding.res();
 365                 let shadows_what = res.descr();
 366                 let mut err = struct_span_err!(
 367                     self.session,
 368                     span,
 369                     E0530,
 370                     "{}s cannot shadow {}s",
 371                     what_binding,
 372                     shadows_what
 373                 );
 374                 err.span_label(
 375                     span,
 376                     format!("cannot be named the same as {} {}", res.article(), shadows_what),
 377                 );
 378                 let participle = if binding.is_import() { "imported" } else { "defined" };
 379                 let msg = format!("the {} `{}` is {} here", shadows_what, name, participle);
 380                 err.span_label(binding.span, msg);
 381                 err
 382             }
 383             ResolutionError::ForwardDeclaredTyParam => {
 384                 let mut err = struct_span_err!(
 385                     self.session,
 386                     span,
 387                     E0128,
 388                     "type parameters with a default cannot use \
 389                                                 forward declared identifiers"
 390                 );
 391                 err.span_label(
 392                     span,
 393                     "defaulted type parameters cannot be forward declared".to_string(),
 394                 );
 395                 err
 396             }
 397             ResolutionError::SelfInTyParamDefault => {
 398                 let mut err = struct_span_err!(
 399                     self.session,
 400                     span,
 401                     E0735,
 402                     "type parameters cannot use `Self` in their defaults"
 403                 );
 404                 err.span_label(span, "`Self` in type parameter default".to_string());
 405                 err
 406             }
 407         }
 408     }
 409
 410     crate fn report_vis_error(&self, vis_resolution_error: VisResolutionError<'_>) {
 411         match vis_resolution_error {
 412             VisResolutionError::Relative2018(span, path) => {
 413                 let mut err = self.session.struct_span_err(
 414                     span,
 415                     "relative paths are not supported in visibilities on 2018 edition",
 416                 );
 417                 err.span_suggestion(
 418                     path.span,
 419                     "try",
 420                     format!("crate::{}", pprust::path_to_string(&path)),
 421                     Applicability::MaybeIncorrect,
 422                 );
 423                 err
 424             }
 425             VisResolutionError::AncestorOnly(span) => struct_span_err!(
 426                 self.session,
 427                 span,
 428                 E0742,
 429                 "visibilities can only be restricted to ancestor modules"
 430             ),
 431             VisResolutionError::FailedToResolve(span, label, suggestion) => {
 432                 self.into_struct_error(span, ResolutionError::FailedToResolve { label, suggestion })
 433             }
 434             VisResolutionError::ExpectedFound(span, path_str, res) => {
 435                 let mut err = struct_span_err!(
 436                     self.session,
 437                     span,
 438                     E0577,
 439                     "expected module, found {} `{}`",
 440                     res.descr(),
 441                     path_str
 442                 );
 443                 err.span_label(span, "not a module");
 444                 err
 445             }
 446             VisResolutionError::Indeterminate(span) => struct_span_err!(
 447                 self.session,
 448                 span,
 449                 E0578,
 450                 "cannot determine resolution for the visibility"
 451             ),
 452             VisResolutionError::ModuleOnly(span) => {
 453                 self.session.struct_span_err(span, "visibility must resolve to a module")
 454             }
 455         }
 456         .emit()
 457     }
 458
 459     /// Lookup typo candidate in scope for a macro or import.
 460     fn early_lookup_typo_candidate(
 461         &mut self,
 462         scope_set: ScopeSet,
 463         parent_scope: &ParentScope<'a>,
 464         ident: Ident,
 465         filter_fn: &impl Fn(Res) -> bool,
 466     ) -> Option<TypoSuggestion> {
 467         let mut suggestions = Vec::new();
 468         self.visit_scopes(scope_set, parent_scope, ident, |this, scope, use_prelude, _| {
 469             match scope {
 470                 Scope::DeriveHelpers(expn_id) => {
 471                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 472                     if filter_fn(res) {
 473                         suggestions.extend(
 474                             this.helper_attrs
 475                                 .get(&expn_id)
 476                                 .into_iter()
 477                                 .flatten()
 478                                 .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 479                         );
 480                     }
 481                 }
 482                 Scope::DeriveHelpersCompat => {
 483                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 484                     if filter_fn(res) {
 485                         for derive in parent_scope.derives {
 486                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
 487                             if let Ok((Some(ext), _)) = this.resolve_macro_path(
 488                                 derive,
 489                                 Some(MacroKind::Derive),
 490                                 parent_scope,
 491                                 false,
 492                                 false,
 493                             ) {
 494                                 suggestions.extend(
 495                                     ext.helper_attrs
 496                                         .iter()
 497                                         .map(|name| TypoSuggestion::from_res(*name, res)),
 498                                 );
 499                             }
 500                         }
 501                     }
 502                 }
 503                 Scope::MacroRules(legacy_scope) => {
 504                     if let LegacyScope::Binding(legacy_binding) = legacy_scope {
 505                         let res = legacy_binding.binding.res();
 506                         if filter_fn(res) {
 507                             suggestions
 508                                 .push(TypoSuggestion::from_res(legacy_binding.ident.name, res))
 509                         }
 510                     }
 511                 }
 512                 Scope::CrateRoot => {
 513                     let root_ident = Ident::new(kw::PathRoot, ident.span);
 514                     let root_module = this.resolve_crate_root(root_ident);
 515                     this.add_module_candidates(root_module, &mut suggestions, filter_fn);
 516                 }
 517                 Scope::Module(module) => {
 518                     this.add_module_candidates(module, &mut suggestions, filter_fn);
 519                 }
 520                 Scope::RegisteredAttrs => {
 521                     let res = Res::NonMacroAttr(NonMacroAttrKind::Registered);
 522                     if filter_fn(res) {
 523                         suggestions.extend(
 524                             this.registered_attrs
 525                                 .iter()
 526                                 .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 527                         );
 528                     }
 529                 }
 530                 Scope::MacroUsePrelude => {
 531                     suggestions.extend(this.macro_use_prelude.iter().filter_map(
 532                         |(name, binding)| {
 533                             let res = binding.res();
 534                             filter_fn(res).then_some(TypoSuggestion::from_res(*name, res))
 535                         },
 536                     ));
 537                 }
 538                 Scope::BuiltinAttrs => {
 539                     let res = Res::NonMacroAttr(NonMacroAttrKind::Builtin);
 540                     if filter_fn(res) {
 541                         suggestions.extend(
 542                             BUILTIN_ATTRIBUTES
 543                                 .iter()
 544                                 .map(|(name, ..)| TypoSuggestion::from_res(*name, res)),
 545                         );
 546                     }
 547                 }
 548                 Scope::ExternPrelude => {
 549                     suggestions.extend(this.extern_prelude.iter().filter_map(|(ident, _)| {
 550                         let res = Res::Def(DefKind::Mod, DefId::local(CRATE_DEF_INDEX));
 551                         filter_fn(res).then_some(TypoSuggestion::from_res(ident.name, res))
 552                     }));
 553                 }
 554                 Scope::ToolPrelude => {
 555                     let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
 556                     suggestions.extend(
 557                         this.registered_tools
 558                             .iter()
 559                             .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 560                     );
 561                 }
 562                 Scope::StdLibPrelude => {
 563                     if let Some(prelude) = this.prelude {
 564                         let mut tmp_suggestions = Vec::new();
 565                         this.add_module_candidates(prelude, &mut tmp_suggestions, filter_fn);
 566                         suggestions.extend(
 567                             tmp_suggestions
 568                                 .into_iter()
 569                                 .filter(|s| use_prelude || this.is_builtin_macro(s.res)),
 570                         );
 571                     }
 572                 }
 573                 Scope::BuiltinTypes => {
 574                     let primitive_types = &this.primitive_type_table.primitive_types;
 575                     suggestions.extend(primitive_types.iter().flat_map(|(name, prim_ty)| {
 576                         let res = Res::PrimTy(*prim_ty);
 577                         filter_fn(res).then_some(TypoSuggestion::from_res(*name, res))
 578                     }))
 579                 }
 580             }
 581
 582             None::<()>
 583         });
 584
 585         // Make sure error reporting is deterministic.
 586         suggestions.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
 587
 588         match find_best_match_for_name(
 589             suggestions.iter().map(|suggestion| &suggestion.candidate),
 590             &ident.as_str(),
 591             None,
 592         ) {
 593             Some(found) if found != ident.name => {
 594                 suggestions.into_iter().find(|suggestion| suggestion.candidate == found)
 595             }
 596             _ => None,
 597         }
 598     }
 599
 600     fn lookup_import_candidates_from_module<FilterFn>(
 601         &mut self,
 602         lookup_ident: Ident,
 603         namespace: Namespace,
 604         start_module: Module<'a>,
 605         crate_name: Ident,
 606         filter_fn: FilterFn,
 607     ) -> Vec<ImportSuggestion>
 608     where
 609         FilterFn: Fn(Res) -> bool,
 610     {
 611         let mut candidates = Vec::new();
 612         let mut seen_modules = FxHashSet::default();
 613         let not_local_module = crate_name.name != kw::Crate;
 614         let mut worklist = vec![(start_module, Vec::<ast::PathSegment>::new(), not_local_module)];
 615
 616         while let Some((in_module, path_segments, in_module_is_extern)) = worklist.pop() {
 617             // We have to visit module children in deterministic order to avoid
 618             // instabilities in reported imports (#43552).
 619             in_module.for_each_child(self, |this, ident, ns, name_binding| {
 620                 // avoid imports entirely
 621                 if name_binding.is_import() && !name_binding.is_extern_crate() {
 622                     return;
 623                 }
 624                 // avoid non-importable candidates as well
 625                 if !name_binding.is_importable() {
 626                     return;
 627                 }
 628
 629                 // collect results based on the filter function
 630                 if ident.name == lookup_ident.name && ns == namespace {
 631                     let res = name_binding.res();
 632                     if filter_fn(res) {
 633                         // create the path
 634                         let mut segms = path_segments.clone();
 635                         if lookup_ident.span.rust_2018() {
 636                             // crate-local absolute paths start with `crate::` in edition 2018
 637                             // FIXME: may also be stabilized for Rust 2015 (Issues #45477, #44660)
 638                             segms.insert(0, ast::PathSegment::from_ident(crate_name));
 639                         }
 640
 641                         segms.push(ast::PathSegment::from_ident(ident));
 642                         let path = Path { span: name_binding.span, segments: segms };
 643                         // the entity is accessible in the following cases:
 644                         // 1. if it's defined in the same crate, it's always
 645                         // accessible (since private entities can be made public)
 646                         // 2. if it's defined in another crate, it's accessible
 647                         // only if both the module is public and the entity is
 648                         // declared as public (due to pruning, we don't explore
 649                         // outside crate private modules => no need to check this)
 650                         if !in_module_is_extern || name_binding.vis == ty::Visibility::Public {
 651                             let did = match res {
 652                                 Res::Def(DefKind::Ctor(..), did) => this.parent(did),
 653                                 _ => res.opt_def_id(),
 654                             };
 655                             candidates.push(ImportSuggestion { did, path });
 656                         }
 657                     }
 658                 }
 659
 660                 // collect submodules to explore
 661                 if let Some(module) = name_binding.module() {
 662                     // form the path
 663                     let mut path_segments = path_segments.clone();
 664                     path_segments.push(ast::PathSegment::from_ident(ident));
 665
 666                     let is_extern_crate_that_also_appears_in_prelude =
 667                         name_binding.is_extern_crate() && lookup_ident.span.rust_2018();
 668
 669                     let is_visible_to_user =
 670                         !in_module_is_extern || name_binding.vis == ty::Visibility::Public;
 671
 672                     if !is_extern_crate_that_also_appears_in_prelude && is_visible_to_user {
 673                         // add the module to the lookup
 674                         let is_extern = in_module_is_extern || name_binding.is_extern_crate();
 675                         if seen_modules.insert(module.def_id().unwrap()) {
 676                             worklist.push((module, path_segments, is_extern));
 677                         }
 678                     }
 679                 }
 680             })
 681         }
 682
 683         candidates
 684     }
 685
 686     /// When name resolution fails, this method can be used to look up candidate
 687     /// entities with the expected name. It allows filtering them using the
 688     /// supplied predicate (which should be used to only accept the types of
 689     /// definitions expected, e.g., traits). The lookup spans across all crates.
 690     ///
 691     /// N.B., the method does not look into imports, but this is not a problem,
 692     /// since we report the definitions (thus, the de-aliased imports).
 693     crate fn lookup_import_candidates<FilterFn>(
 694         &mut self,
 695         lookup_ident: Ident,
 696         namespace: Namespace,
 697         filter_fn: FilterFn,
 698     ) -> Vec<ImportSuggestion>
 699     where
 700         FilterFn: Fn(Res) -> bool,
 701     {
 702         let mut suggestions = self.lookup_import_candidates_from_module(
 703             lookup_ident,
 704             namespace,
 705             self.graph_root,
 706             Ident::with_dummy_span(kw::Crate),
 707             &filter_fn,
 708         );
 709
 710         if lookup_ident.span.rust_2018() {
 711             let extern_prelude_names = self.extern_prelude.clone();
 712             for (ident, _) in extern_prelude_names.into_iter() {
 713                 if ident.span.from_expansion() {
 714                     // Idents are adjusted to the root context before being
 715                     // resolved in the extern prelude, so reporting this to the
 716                     // user is no help. This skips the injected
 717                     // `extern crate std` in the 2018 edition, which would
 718                     // otherwise cause duplicate suggestions.
 719                     continue;
 720                 }
 721                 if let Some(crate_id) =
 722                     self.crate_loader.maybe_process_path_extern(ident.name, ident.span)
 723                 {
 724                     let crate_root =
 725                         self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
 726                     suggestions.extend(self.lookup_import_candidates_from_module(
 727                         lookup_ident,
 728                         namespace,
 729                         crate_root,
 730                         ident,
 731                         &filter_fn,
 732                     ));
 733                 }
 734             }
 735         }
 736
 737         suggestions
 738     }
 739
 740     crate fn unresolved_macro_suggestions(
 741         &mut self,
 742         err: &mut DiagnosticBuilder<'a>,
 743         macro_kind: MacroKind,
 744         parent_scope: &ParentScope<'a>,
 745         ident: Ident,
 746     ) {
 747         let is_expected = &|res: Res| res.macro_kind() == Some(macro_kind);
 748         let suggestion = self.early_lookup_typo_candidate(
 749             ScopeSet::Macro(macro_kind),
 750             parent_scope,
 751             ident,
 752             is_expected,
 753         );
 754         self.add_typo_suggestion(err, suggestion, ident.span);
 755
 756         if macro_kind == MacroKind::Derive && (ident.as_str() == "Send" || ident.as_str() == "Sync")
 757         {
 758             let msg = format!("unsafe traits like `{}` should be implemented explicitly", ident);
 759             err.span_note(ident.span, &msg);
 760         }
 761         if self.macro_names.contains(&ident.modern()) {
 762             err.help("have you added the `#[macro_use]` on the module/import?");
 763         }
 764     }
 765
 766     crate fn add_typo_suggestion(
 767         &self,
 768         err: &mut DiagnosticBuilder<'_>,
 769         suggestion: Option<TypoSuggestion>,
 770         span: Span,
 771     ) -> bool {
 772         if let Some(suggestion) = suggestion {
 773             let msg = format!(
 774                 "{} {} with a similar name exists",
 775                 suggestion.res.article(),
 776                 suggestion.res.descr()
 777             );
 778             err.span_suggestion(
 779                 span,
 780                 &msg,
 781                 suggestion.candidate.to_string(),
 782                 Applicability::MaybeIncorrect,
 783             );
 784             let def_span = suggestion.res.opt_def_id().and_then(|def_id| match def_id.krate {
 785                 LOCAL_CRATE => self.definitions.opt_span(def_id),
 786                 _ => Some(
 787                     self.session
 788                         .source_map()
 789                         .def_span(self.cstore().get_span_untracked(def_id, self.session)),
 790                 ),
 791             });
 792             if let Some(span) = def_span {
 793                 err.span_label(
 794                     span,
 795                     &format!(
 796                         "similarly named {} `{}` defined here",
 797                         suggestion.res.descr(),
 798                         suggestion.candidate.as_str(),
 799                     ),
 800                 );
 801             }
 802             return true;
 803         }
 804         false
 805     }
 806
 807     fn binding_description(&self, b: &NameBinding<'_>, ident: Ident, from_prelude: bool) -> String {
 808         let res = b.res();
 809         if b.span.is_dummy() {
 810             let add_built_in = match b.res() {
 811                 // These already contain the "built-in" prefix or look bad with it.
 812                 Res::NonMacroAttr(..) | Res::PrimTy(..) | Res::ToolMod => false,
 813                 _ => true,
 814             };
 815             let (built_in, from) = if from_prelude {
 816                 ("", " from prelude")
 817             } else if b.is_extern_crate()
 818                 && !b.is_import()
 819                 && self.session.opts.externs.get(&ident.as_str()).is_some()
 820             {
 821                 ("", " passed with `--extern`")
 822             } else if add_built_in {
 823                 (" built-in", "")
 824             } else {
 825                 ("", "")
 826             };
 827
 828             let article = if built_in.is_empty() { res.article() } else { "a" };
 829             format!(
 830                 "{a}{built_in} {thing}{from}",
 831                 a = article,
 832                 thing = res.descr(),
 833                 built_in = built_in,
 834                 from = from
 835             )
 836         } else {
 837             let introduced = if b.is_import() { "imported" } else { "defined" };
 838             format!("the {thing} {introduced} here", thing = res.descr(), introduced = introduced)
 839         }
 840     }
 841
 842     crate fn report_ambiguity_error(&self, ambiguity_error: &AmbiguityError<'_>) {
 843         let AmbiguityError { kind, ident, b1, b2, misc1, misc2 } = *ambiguity_error;
 844         let (b1, b2, misc1, misc2, swapped) = if b2.span.is_dummy() && !b1.span.is_dummy() {
 845             // We have to print the span-less alternative first, otherwise formatting looks bad.
 846             (b2, b1, misc2, misc1, true)
 847         } else {
 848             (b1, b2, misc1, misc2, false)
 849         };
 850
 851         let mut err = struct_span_err!(
 852             self.session,
 853             ident.span,
 854             E0659,
 855             "`{ident}` is ambiguous ({why})",
 856             ident = ident,
 857             why = kind.descr()
 858         );
 859         err.span_label(ident.span, "ambiguous name");
 860
 861         let mut could_refer_to = |b: &NameBinding<'_>, misc: AmbiguityErrorMisc, also: &str| {
 862             let what = self.binding_description(b, ident, misc == AmbiguityErrorMisc::FromPrelude);
 863             let note_msg = format!(
 864                 "`{ident}` could{also} refer to {what}",
 865                 ident = ident,
 866                 also = also,
 867                 what = what
 868             );
 869
 870             let thing = b.res().descr();
 871             let mut help_msgs = Vec::new();
 872             if b.is_glob_import()
 873                 && (kind == AmbiguityKind::GlobVsGlob
 874                     || kind == AmbiguityKind::GlobVsExpanded
 875                     || kind == AmbiguityKind::GlobVsOuter && swapped != also.is_empty())
 876             {
 877                 help_msgs.push(format!(
 878                     "consider adding an explicit import of \
 879                      `{ident}` to disambiguate",
 880                     ident = ident
 881                 ))
 882             }
 883             if b.is_extern_crate() && ident.span.rust_2018() {
 884                 help_msgs.push(format!(
 885                     "use `::{ident}` to refer to this {thing} unambiguously",
 886                     ident = ident,
 887                     thing = thing,
 888                 ))
 889             }
 890             if misc == AmbiguityErrorMisc::SuggestCrate {
 891                 help_msgs.push(format!(
 892                     "use `crate::{ident}` to refer to this {thing} unambiguously",
 893                     ident = ident,
 894                     thing = thing,
 895                 ))
 896             } else if misc == AmbiguityErrorMisc::SuggestSelf {
 897                 help_msgs.push(format!(
 898                     "use `self::{ident}` to refer to this {thing} unambiguously",
 899                     ident = ident,
 900                     thing = thing,
 901                 ))
 902             }
 903
 904             err.span_note(b.span, &note_msg);
 905             for (i, help_msg) in help_msgs.iter().enumerate() {
 906                 let or = if i == 0 { "" } else { "or " };
 907                 err.help(&format!("{}{}", or, help_msg));
 908             }
 909         };
 910
 911         could_refer_to(b1, misc1, "");
 912         could_refer_to(b2, misc2, " also");
 913         err.emit();
 914     }
 915
 916     crate fn report_privacy_error(&self, privacy_error: &PrivacyError<'_>) {
 917         let PrivacyError { ident, binding, .. } = *privacy_error;
 918         let session = &self.session;
 919         let mk_struct_span_error = |is_constructor| {
 920             let mut descr = binding.res().descr().to_string();
 921             if is_constructor {
 922                 descr += " constructor";
 923             }
 924
 925             let mut err =
 926                 struct_span_err!(session, ident.span, E0603, "{} `{}` is private", descr, ident);
 927
 928             err.span_label(ident.span, &format!("this {} is private", descr));
 929             err.span_note(
 930                 session.source_map().def_span(binding.span),
 931                 &format!("the {} `{}` is defined here", descr, ident),
 932             );
 933
 934             err
 935         };
 936
 937         let mut err = if let NameBindingKind::Res(
 938             Res::Def(DefKind::Ctor(CtorOf::Struct, CtorKind::Fn), ctor_def_id),
 939             _,
 940         ) = binding.kind
 941         {
 942             let def_id = (&*self).parent(ctor_def_id).expect("no parent for a constructor");
 943             if let Some(fields) = self.field_names.get(&def_id) {
 944                 let mut err = mk_struct_span_error(true);
 945                 let first_field = fields.first().expect("empty field list in the map");
 946                 err.span_label(
 947                     fields.iter().fold(first_field.span, |acc, field| acc.to(field.span)),
 948                     "a constructor is private if any of the fields is private",
 949                 );
 950                 err
 951             } else {
 952                 mk_struct_span_error(false)
 953             }
 954         } else {
 955             mk_struct_span_error(false)
 956         };
 957
 958         err.emit();
 959     }
 960 }
 961
 962 impl<'a, 'b> ImportResolver<'a, 'b> {
 963     /// Adds suggestions for a path that cannot be resolved.
 964     pub(crate) fn make_path_suggestion(
 965         &mut self,
 966         span: Span,
 967         mut path: Vec<Segment>,
 968         parent_scope: &ParentScope<'b>,
 969     ) -> Option<(Vec<Segment>, Vec<String>)> {
 970         debug!("make_path_suggestion: span={:?} path={:?}", span, path);
 971
 972         match (path.get(0), path.get(1)) {
 973             // `{{root}}::ident::...` on both editions.
 974             // On 2015 `{{root}}` is usually added implicitly.
 975             (Some(fst), Some(snd))
 976                 if fst.ident.name == kw::PathRoot && !snd.ident.is_path_segment_keyword() => {}
 977             // `ident::...` on 2018.
 978             (Some(fst), _)
 979                 if fst.ident.span.rust_2018() && !fst.ident.is_path_segment_keyword() =>
 980             {
 981                 // Insert a placeholder that's later replaced by `self`/`super`/etc.
 982                 path.insert(0, Segment::from_ident(Ident::invalid()));
 983             }
 984             _ => return None,
 985         }
 986
 987         self.make_missing_self_suggestion(span, path.clone(), parent_scope)
 988             .or_else(|| self.make_missing_crate_suggestion(span, path.clone(), parent_scope))
 989             .or_else(|| self.make_missing_super_suggestion(span, path.clone(), parent_scope))
 990             .or_else(|| self.make_external_crate_suggestion(span, path, parent_scope))
 991     }
 992
 993     /// Suggest a missing `self::` if that resolves to an correct module.
 994     ///
 995     /// ```
 996     ///    |
 997     /// LL | use foo::Bar;
 998     ///    |     ^^^ did you mean `self::foo`?
 999     /// ```
1000     fn make_missing_self_suggestion(
1001         &mut self,
1002         span: Span,
1003         mut path: Vec<Segment>,
1004         parent_scope: &ParentScope<'b>,
1005     ) -> Option<(Vec<Segment>, Vec<String>)> {
1006         // Replace first ident with `self` and check if that is valid.
1007         path[0].ident.name = kw::SelfLower;
1008         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1009         debug!("make_missing_self_suggestion: path={:?} result={:?}", path, result);
1010         if let PathResult::Module(..) = result { Some((path, Vec::new())) } else { None }
1011     }
1012
1013     /// Suggests a missing `crate::` if that resolves to an correct module.
1014     ///
1015     /// ```
1016     ///    |
1017     /// LL | use foo::Bar;
1018     ///    |     ^^^ did you mean `crate::foo`?
1019     /// ```
1020     fn make_missing_crate_suggestion(
1021         &mut self,
1022         span: Span,
1023         mut path: Vec<Segment>,
1024         parent_scope: &ParentScope<'b>,
1025     ) -> Option<(Vec<Segment>, Vec<String>)> {
1026         // Replace first ident with `crate` and check if that is valid.
1027         path[0].ident.name = kw::Crate;
1028         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1029         debug!("make_missing_crate_suggestion:  path={:?} result={:?}", path, result);
1030         if let PathResult::Module(..) = result {
1031             Some((
1032                 path,
1033                 vec![
1034                     "`use` statements changed in Rust 2018; read more at \
1035                      <https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-\
1036                      clarity.html>"
1037                         .to_string(),
1038                 ],
1039             ))
1040         } else {
1041             None
1042         }
1043     }
1044
1045     /// Suggests a missing `super::` if that resolves to an correct module.
1046     ///
1047     /// ```
1048     ///    |
1049     /// LL | use foo::Bar;
1050     ///    |     ^^^ did you mean `super::foo`?
1051     /// ```
1052     fn make_missing_super_suggestion(
1053         &mut self,
1054         span: Span,
1055         mut path: Vec<Segment>,
1056         parent_scope: &ParentScope<'b>,
1057     ) -> Option<(Vec<Segment>, Vec<String>)> {
1058         // Replace first ident with `crate` and check if that is valid.
1059         path[0].ident.name = kw::Super;
1060         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1061         debug!("make_missing_super_suggestion:  path={:?} result={:?}", path, result);
1062         if let PathResult::Module(..) = result { Some((path, Vec::new())) } else { None }
1063     }
1064
1065     /// Suggests a missing external crate name if that resolves to an correct module.
1066     ///
1067     /// ```
1068     ///    |
1069     /// LL | use foobar::Baz;
1070     ///    |     ^^^^^^ did you mean `baz::foobar`?
1071     /// ```
1072     ///
1073     /// Used when importing a submodule of an external crate but missing that crate's
1074     /// name as the first part of path.
1075     fn make_external_crate_suggestion(
1076         &mut self,
1077         span: Span,
1078         mut path: Vec<Segment>,
1079         parent_scope: &ParentScope<'b>,
1080     ) -> Option<(Vec<Segment>, Vec<String>)> {
1081         if path[1].ident.span.rust_2015() {
1082             return None;
1083         }
1084
1085         // Sort extern crate names in reverse order to get
1086         // 1) some consistent ordering for emitted dignostics, and
1087         // 2) `std` suggestions before `core` suggestions.
1088         let mut extern_crate_names =
1089             self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
1090         extern_crate_names.sort_by_key(|name| Reverse(name.as_str()));
1091
1092         for name in extern_crate_names.into_iter() {
1093             // Replace first ident with a crate name and check if that is valid.
1094             path[0].ident.name = name;
1095             let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1096             debug!(
1097                 "make_external_crate_suggestion: name={:?} path={:?} result={:?}",
1098                 name, path, result
1099             );
1100             if let PathResult::Module(..) = result {
1101                 return Some((path, Vec::new()));
1102             }
1103         }
1104
1105         None
1106     }
1107
1108     /// Suggests importing a macro from the root of the crate rather than a module within
1109     /// the crate.
1110     ///
1111     /// ```
1112     /// help: a macro with this name exists at the root of the crate
1113     ///    |
1114     /// LL | use issue_59764::makro;
1115     ///    |     ^^^^^^^^^^^^^^^^^^
1116     ///    |
1117     ///    = note: this could be because a macro annotated with `#[macro_export]` will be exported
1118     ///            at the root of the crate instead of the module where it is defined
1119     /// ```
1120     pub(crate) fn check_for_module_export_macro(
1121         &mut self,
1122         directive: &'b ImportDirective<'b>,
1123         module: ModuleOrUniformRoot<'b>,
1124         ident: Ident,
1125     ) -> Option<(Option<Suggestion>, Vec<String>)> {
1126         let mut crate_module = if let ModuleOrUniformRoot::Module(module) = module {
1127             module
1128         } else {
1129             return None;
1130         };
1131
1132         while let Some(parent) = crate_module.parent {
1133             crate_module = parent;
1134         }
1135
1136         if ModuleOrUniformRoot::same_def(ModuleOrUniformRoot::Module(crate_module), module) {
1137             // Don't make a suggestion if the import was already from the root of the
1138             // crate.
1139             return None;
1140         }
1141
1142         let resolutions = self.r.resolutions(crate_module).borrow();
1143         let resolution = resolutions.get(&self.r.new_key(ident, MacroNS))?;
1144         let binding = resolution.borrow().binding()?;
1145         if let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() {
1146             let module_name = crate_module.kind.name().unwrap();
1147             let import = match directive.subclass {
1148                 ImportDirectiveSubclass::SingleImport { source, target, .. }
1149                     if source != target =>
1150                 {
1151                     format!("{} as {}", source, target)
1152                 }
1153                 _ => format!("{}", ident),
1154             };
1155
1156             let mut corrections: Vec<(Span, String)> = Vec::new();
1157             if !directive.is_nested() {
1158                 // Assume this is the easy case of `use issue_59764::foo::makro;` and just remove
1159                 // intermediate segments.
1160                 corrections.push((directive.span, format!("{}::{}", module_name, import)));
1161             } else {
1162                 // Find the binding span (and any trailing commas and spaces).
1163                 //   ie. `use a::b::{c, d, e};`
1164                 //                      ^^^
1165                 let (found_closing_brace, binding_span) = find_span_of_binding_until_next_binding(
1166                     self.r.session,
1167                     directive.span,
1168                     directive.use_span,
1169                 );
1170                 debug!(
1171                     "check_for_module_export_macro: found_closing_brace={:?} binding_span={:?}",
1172                     found_closing_brace, binding_span
1173                 );
1174
1175                 let mut removal_span = binding_span;
1176                 if found_closing_brace {
1177                     // If the binding span ended with a closing brace, as in the below example:
1178                     //   ie. `use a::b::{c, d};`
1179                     //                      ^
1180                     // Then expand the span of characters to remove to include the previous
1181                     // binding's trailing comma.
1182                     //   ie. `use a::b::{c, d};`
1183                     //                    ^^^
1184                     if let Some(previous_span) =
1185                         extend_span_to_previous_binding(self.r.session, binding_span)
1186                     {
1187                         debug!("check_for_module_export_macro: previous_span={:?}", previous_span);
1188                         removal_span = removal_span.with_lo(previous_span.lo());
1189                     }
1190                 }
1191                 debug!("check_for_module_export_macro: removal_span={:?}", removal_span);
1192
1193                 // Remove the `removal_span`.
1194                 corrections.push((removal_span, "".to_string()));
1195
1196                 // Find the span after the crate name and if it has nested imports immediatately
1197                 // after the crate name already.
1198                 //   ie. `use a::b::{c, d};`
1199                 //               ^^^^^^^^^
1200                 //   or  `use a::{b, c, d}};`
1201                 //               ^^^^^^^^^^^
1202                 let (has_nested, after_crate_name) = find_span_immediately_after_crate_name(
1203                     self.r.session,
1204                     module_name,
1205                     directive.use_span,
1206                 );
1207                 debug!(
1208                     "check_for_module_export_macro: has_nested={:?} after_crate_name={:?}",
1209                     has_nested, after_crate_name
1210                 );
1211
1212                 let source_map = self.r.session.source_map();
1213
1214                 // Add the import to the start, with a `{` if required.
1215                 let start_point = source_map.start_point(after_crate_name);
1216                 if let Ok(start_snippet) = source_map.span_to_snippet(start_point) {
1217                     corrections.push((
1218                         start_point,
1219                         if has_nested {
1220                             // In this case, `start_snippet` must equal '{'.
1221                             format!("{}{}, ", start_snippet, import)
1222                         } else {
1223                             // In this case, add a `{`, then the moved import, then whatever
1224                             // was there before.
1225                             format!("{{{}, {}", import, start_snippet)
1226                         },
1227                     ));
1228                 }
1229
1230                 // Add a `};` to the end if nested, matching the `{` added at the start.
1231                 if !has_nested {
1232                     corrections.push((source_map.end_point(after_crate_name), "};".to_string()));
1233                 }
1234             }
1235
1236             let suggestion = Some((
1237                 corrections,
1238                 String::from("a macro with this name exists at the root of the crate"),
1239                 Applicability::MaybeIncorrect,
1240             ));
1241             let note = vec![
1242                 "this could be because a macro annotated with `#[macro_export]` will be exported \
1243                  at the root of the crate instead of the module where it is defined"
1244                     .to_string(),
1245             ];
1246             Some((suggestion, note))
1247         } else {
1248             None
1249         }
1250     }
1251 }
1252
1253 /// Given a `binding_span` of a binding within a use statement:
1254 ///
1255 /// ```
1256 /// use foo::{a, b, c};
1257 ///              ^
1258 /// ```
1259 ///
1260 /// then return the span until the next binding or the end of the statement:
1261 ///
1262 /// ```
1263 /// use foo::{a, b, c};
1264 ///              ^^^
1265 /// ```
1266 pub(crate) fn find_span_of_binding_until_next_binding(
1267     sess: &Session,
1268     binding_span: Span,
1269     use_span: Span,
1270 ) -> (bool, Span) {
1271     let source_map = sess.source_map();
1272
1273     // Find the span of everything after the binding.
1274     //   ie. `a, e};` or `a};`
1275     let binding_until_end = binding_span.with_hi(use_span.hi());
1276
1277     // Find everything after the binding but not including the binding.
1278     //   ie. `, e};` or `};`
1279     let after_binding_until_end = binding_until_end.with_lo(binding_span.hi());
1280
1281     // Keep characters in the span until we encounter something that isn't a comma or
1282     // whitespace.
1283     //   ie. `, ` or ``.
1284     //
1285     // Also note whether a closing brace character was encountered. If there
1286     // was, then later go backwards to remove any trailing commas that are left.
1287     let mut found_closing_brace = false;
1288     let after_binding_until_next_binding =
1289         source_map.span_take_while(after_binding_until_end, |&ch| {
1290             if ch == '}' {
1291                 found_closing_brace = true;
1292             }
1293             ch == ' ' || ch == ','
1294         });
1295
1296     // Combine the two spans.
1297     //   ie. `a, ` or `a`.
1298     //
1299     // Removing these would leave `issue_52891::{d, e};` or `issue_52891::{d, e, };`
1300     let span = binding_span.with_hi(after_binding_until_next_binding.hi());
1301
1302     (found_closing_brace, span)
1303 }
1304
1305 /// Given a `binding_span`, return the span through to the comma or opening brace of the previous
1306 /// binding.
1307 ///
1308 /// ```
1309 /// use foo::a::{a, b, c};
1310 ///               ^^--- binding span
1311 ///               |
1312 ///               returned span
1313 ///
1314 /// use foo::{a, b, c};
1315 ///           --- binding span
1316 /// ```
1317 pub(crate) fn extend_span_to_previous_binding(sess: &Session, binding_span: Span) -> Option<Span> {
1318     let source_map = sess.source_map();
1319
1320     // `prev_source` will contain all of the source that came before the span.
1321     // Then split based on a command and take the first (ie. closest to our span)
1322     // snippet. In the example, this is a space.
1323     let prev_source = source_map.span_to_prev_source(binding_span).ok()?;
1324
1325     let prev_comma = prev_source.rsplit(',').collect::<Vec<_>>();
1326     let prev_starting_brace = prev_source.rsplit('{').collect::<Vec<_>>();
1327     if prev_comma.len() <= 1 || prev_starting_brace.len() <= 1 {
1328         return None;
1329     }
1330
1331     let prev_comma = prev_comma.first().unwrap();
1332     let prev_starting_brace = prev_starting_brace.first().unwrap();
1333
1334     // If the amount of source code before the comma is greater than
1335     // the amount of source code before the starting brace then we've only
1336     // got one item in the nested item (eg. `issue_52891::{self}`).
1337     if prev_comma.len() > prev_starting_brace.len() {
1338         return None;
1339     }
1340
1341     Some(binding_span.with_lo(BytePos(
1342         // Take away the number of bytes for the characters we've found and an
1343         // extra for the comma.
1344         binding_span.lo().0 - (prev_comma.as_bytes().len() as u32) - 1,
1345     )))
1346 }
1347
1348 /// Given a `use_span` of a binding within a use statement, returns the highlighted span and if
1349 /// it is a nested use tree.
1350 ///
1351 /// ```
1352 /// use foo::a::{b, c};
1353 ///          ^^^^^^^^^^ // false
1354 ///
1355 /// use foo::{a, b, c};
1356 ///          ^^^^^^^^^^ // true
1357 ///
1358 /// use foo::{a, b::{c, d}};
1359 ///          ^^^^^^^^^^^^^^^ // true
1360 /// ```
1361 fn find_span_immediately_after_crate_name(
1362     sess: &Session,
1363     module_name: Symbol,
1364     use_span: Span,
1365 ) -> (bool, Span) {
1366     debug!(
1367         "find_span_immediately_after_crate_name: module_name={:?} use_span={:?}",
1368         module_name, use_span
1369     );
1370     let source_map = sess.source_map();
1371
1372     // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
1373     let mut num_colons = 0;
1374     // Find second colon.. `use issue_59764:`
1375     let until_second_colon = source_map.span_take_while(use_span, |c| {
1376         if *c == ':' {
1377             num_colons += 1;
1378         }
1379         match c {
1380             ':' if num_colons == 2 => false,
1381             _ => true,
1382         }
1383     });
1384     // Find everything after the second colon.. `foo::{baz, makro};`
1385     let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
1386
1387     let mut found_a_non_whitespace_character = false;
1388     // Find the first non-whitespace character in `from_second_colon`.. `f`
1389     let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
1390         if found_a_non_whitespace_character {
1391             return false;
1392         }
1393         if !c.is_whitespace() {
1394             found_a_non_whitespace_character = true;
1395         }
1396         true
1397     });
1398
1399     // Find the first `{` in from_second_colon.. `foo::{`
1400     let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
1401
1402     (next_left_bracket == after_second_colon, from_second_colon)
1403 }
1404
1405 /// When an entity with a given name is not available in scope, we search for
1406 /// entities with that name in all crates. This method allows outputting the
1407 /// results of this search in a programmer-friendly way
1408 crate fn show_candidates(
1409     err: &mut DiagnosticBuilder<'_>,
1410     // This is `None` if all placement locations are inside expansions
1411     span: Option<Span>,
1412     candidates: &[ImportSuggestion],
1413     better: bool,
1414     found_use: bool,
1415 ) {
1416     // we want consistent results across executions, but candidates are produced
1417     // by iterating through a hash map, so make sure they are ordered:
1418     let mut path_strings: Vec<_> =
1419         candidates.into_iter().map(|c| path_names_to_string(&c.path)).collect();
1420     path_strings.sort();
1421
1422     let better = if better { "better " } else { "" };
1423     let msg_diff = match path_strings.len() {
1424         1 => " is found in another module, you can import it",
1425         _ => "s are found in other modules, you can import them",
1426     };
1427     let msg = format!("possible {}candidate{} into scope", better, msg_diff);
1428
1429     if let Some(span) = span {
1430         for candidate in &mut path_strings {
1431             // produce an additional newline to separate the new use statement
1432             // from the directly following item.
1433             let additional_newline = if found_use { "" } else { "\n" };
1434             *candidate = format!("use {};\n{}", candidate, additional_newline);
1435         }
1436
1437         err.span_suggestions(span, &msg, path_strings.into_iter(), Applicability::Unspecified);
1438     } else {
1439         let mut msg = msg;
1440         msg.push(':');
1441         for candidate in path_strings {
1442             msg.push('\n');
1443             msg.push_str(&candidate);
1444         }
1445     }
1446 }