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::{Import, ImportKind, ImportResolver};
  22 use crate::path_names_to_string;
  23 use crate::{AmbiguityError, AmbiguityErrorMisc, AmbiguityKind};
  24 use crate::{
  25     BindingError, CrateLint, HasGenericParams, MacroRulesScope, Module, ModuleOrUniformRoot,
  26 };
  27 use crate::{NameBinding, NameBindingKind, PrivacyError, VisResolutionError};
  28 use crate::{ParentScope, PathResult, ResolutionError, Resolver, Scope, ScopeSet, Segment};
  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(sm: &SourceMap, impl_span: Span) -> Span {
  60     let impl_span = sm.span_until_char(impl_span, '<');
  61     let impl_span = sm.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, "use of generic parameter from outer function".to_string());
 104
 105                 let sm = 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(sm, 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 = "try using a local generic parameter instead";
 149                     if let Some((sugg_span, snippet)) = sm.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) = sm.generate_fn_name_span(span) {
 158                         err.span_label(
 159                             sp,
 160                             "try adding a local generic parameter in this method instead"
 161                                 .to_string(),
 162                         );
 163                     } else {
 164                         err.help("try using a local generic parameter instead");
 165                     }
 166                 }
 167
 168                 err
 169             }
 170             ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => {
 171                 let mut err = struct_span_err!(
 172                     self.session,
 173                     span,
 174                     E0403,
 175                     "the name `{}` is already used for a generic \
 176                      parameter in this item's generic parameters",
 177                     name,
 178                 );
 179                 err.span_label(span, "already used");
 180                 err.span_label(first_use_span, format!("first use of `{}`", name));
 181                 err
 182             }
 183             ResolutionError::MethodNotMemberOfTrait(method, trait_) => {
 184                 let mut err = struct_span_err!(
 185                     self.session,
 186                     span,
 187                     E0407,
 188                     "method `{}` is not a member of trait `{}`",
 189                     method,
 190                     trait_
 191                 );
 192                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 193                 err
 194             }
 195             ResolutionError::TypeNotMemberOfTrait(type_, trait_) => {
 196                 let mut err = struct_span_err!(
 197                     self.session,
 198                     span,
 199                     E0437,
 200                     "type `{}` is not a member of trait `{}`",
 201                     type_,
 202                     trait_
 203                 );
 204                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 205                 err
 206             }
 207             ResolutionError::ConstNotMemberOfTrait(const_, trait_) => {
 208                 let mut err = struct_span_err!(
 209                     self.session,
 210                     span,
 211                     E0438,
 212                     "const `{}` is not a member of trait `{}`",
 213                     const_,
 214                     trait_
 215                 );
 216                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 217                 err
 218             }
 219             ResolutionError::VariableNotBoundInPattern(binding_error) => {
 220                 let BindingError { name, target, origin, could_be_path } = binding_error;
 221
 222                 let target_sp = target.iter().copied().collect::<Vec<_>>();
 223                 let origin_sp = origin.iter().copied().collect::<Vec<_>>();
 224
 225                 let msp = MultiSpan::from_spans(target_sp.clone());
 226                 let mut err = struct_span_err!(
 227                     self.session,
 228                     msp,
 229                     E0408,
 230                     "variable `{}` is not bound in all patterns",
 231                     name,
 232                 );
 233                 for sp in target_sp {
 234                     err.span_label(sp, format!("pattern doesn't bind `{}`", name));
 235                 }
 236                 for sp in origin_sp {
 237                     err.span_label(sp, "variable not in all patterns");
 238                 }
 239                 if *could_be_path {
 240                     let help_msg = format!(
 241                         "if you meant to match on a variant or a `const` item, consider \
 242                          making the path in the pattern qualified: `?::{}`",
 243                         name,
 244                     );
 245                     err.span_help(span, &help_msg);
 246                 }
 247                 err
 248             }
 249             ResolutionError::VariableBoundWithDifferentMode(variable_name, first_binding_span) => {
 250                 let mut err = struct_span_err!(
 251                     self.session,
 252                     span,
 253                     E0409,
 254                     "variable `{}` is bound inconsistently across alternatives separated by `|`",
 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(macro_rules_scope) => {
 504                     if let MacroRulesScope::Binding(macro_rules_binding) = macro_rules_scope {
 505                         let res = macro_rules_binding.binding.res();
 506                         if filter_fn(res) {
 507                             suggestions
 508                                 .push(TypoSuggestion::from_res(macro_rules_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.normalize_to_macros_2_0()) {
 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             // We shouldn't suggest underscore.
 774             if suggestion.candidate == kw::Underscore {
 775                 return false;
 776             }
 777
 778             let msg = format!(
 779                 "{} {} with a similar name exists",
 780                 suggestion.res.article(),
 781                 suggestion.res.descr()
 782             );
 783             err.span_suggestion(
 784                 span,
 785                 &msg,
 786                 suggestion.candidate.to_string(),
 787                 Applicability::MaybeIncorrect,
 788             );
 789             let def_span = suggestion.res.opt_def_id().and_then(|def_id| match def_id.krate {
 790                 LOCAL_CRATE => self.definitions.opt_span(def_id),
 791                 _ => Some(
 792                     self.session
 793                         .source_map()
 794                         .def_span(self.cstore().get_span_untracked(def_id, self.session)),
 795                 ),
 796             });
 797             if let Some(span) = def_span {
 798                 err.span_label(
 799                     span,
 800                     &format!(
 801                         "similarly named {} `{}` defined here",
 802                         suggestion.res.descr(),
 803                         suggestion.candidate.as_str(),
 804                     ),
 805                 );
 806             }
 807             return true;
 808         }
 809         false
 810     }
 811
 812     fn binding_description(&self, b: &NameBinding<'_>, ident: Ident, from_prelude: bool) -> String {
 813         let res = b.res();
 814         if b.span.is_dummy() {
 815             let add_built_in = match b.res() {
 816                 // These already contain the "built-in" prefix or look bad with it.
 817                 Res::NonMacroAttr(..) | Res::PrimTy(..) | Res::ToolMod => false,
 818                 _ => true,
 819             };
 820             let (built_in, from) = if from_prelude {
 821                 ("", " from prelude")
 822             } else if b.is_extern_crate()
 823                 && !b.is_import()
 824                 && self.session.opts.externs.get(&ident.as_str()).is_some()
 825             {
 826                 ("", " passed with `--extern`")
 827             } else if add_built_in {
 828                 (" built-in", "")
 829             } else {
 830                 ("", "")
 831             };
 832
 833             let article = if built_in.is_empty() { res.article() } else { "a" };
 834             format!(
 835                 "{a}{built_in} {thing}{from}",
 836                 a = article,
 837                 thing = res.descr(),
 838                 built_in = built_in,
 839                 from = from
 840             )
 841         } else {
 842             let introduced = if b.is_import() { "imported" } else { "defined" };
 843             format!("the {thing} {introduced} here", thing = res.descr(), introduced = introduced)
 844         }
 845     }
 846
 847     crate fn report_ambiguity_error(&self, ambiguity_error: &AmbiguityError<'_>) {
 848         let AmbiguityError { kind, ident, b1, b2, misc1, misc2 } = *ambiguity_error;
 849         let (b1, b2, misc1, misc2, swapped) = if b2.span.is_dummy() && !b1.span.is_dummy() {
 850             // We have to print the span-less alternative first, otherwise formatting looks bad.
 851             (b2, b1, misc2, misc1, true)
 852         } else {
 853             (b1, b2, misc1, misc2, false)
 854         };
 855
 856         let mut err = struct_span_err!(
 857             self.session,
 858             ident.span,
 859             E0659,
 860             "`{ident}` is ambiguous ({why})",
 861             ident = ident,
 862             why = kind.descr()
 863         );
 864         err.span_label(ident.span, "ambiguous name");
 865
 866         let mut could_refer_to = |b: &NameBinding<'_>, misc: AmbiguityErrorMisc, also: &str| {
 867             let what = self.binding_description(b, ident, misc == AmbiguityErrorMisc::FromPrelude);
 868             let note_msg = format!(
 869                 "`{ident}` could{also} refer to {what}",
 870                 ident = ident,
 871                 also = also,
 872                 what = what
 873             );
 874
 875             let thing = b.res().descr();
 876             let mut help_msgs = Vec::new();
 877             if b.is_glob_import()
 878                 && (kind == AmbiguityKind::GlobVsGlob
 879                     || kind == AmbiguityKind::GlobVsExpanded
 880                     || kind == AmbiguityKind::GlobVsOuter && swapped != also.is_empty())
 881             {
 882                 help_msgs.push(format!(
 883                     "consider adding an explicit import of \
 884                      `{ident}` to disambiguate",
 885                     ident = ident
 886                 ))
 887             }
 888             if b.is_extern_crate() && ident.span.rust_2018() {
 889                 help_msgs.push(format!(
 890                     "use `::{ident}` to refer to this {thing} unambiguously",
 891                     ident = ident,
 892                     thing = thing,
 893                 ))
 894             }
 895             if misc == AmbiguityErrorMisc::SuggestCrate {
 896                 help_msgs.push(format!(
 897                     "use `crate::{ident}` to refer to this {thing} unambiguously",
 898                     ident = ident,
 899                     thing = thing,
 900                 ))
 901             } else if misc == AmbiguityErrorMisc::SuggestSelf {
 902                 help_msgs.push(format!(
 903                     "use `self::{ident}` to refer to this {thing} unambiguously",
 904                     ident = ident,
 905                     thing = thing,
 906                 ))
 907             }
 908
 909             err.span_note(b.span, &note_msg);
 910             for (i, help_msg) in help_msgs.iter().enumerate() {
 911                 let or = if i == 0 { "" } else { "or " };
 912                 err.help(&format!("{}{}", or, help_msg));
 913             }
 914         };
 915
 916         could_refer_to(b1, misc1, "");
 917         could_refer_to(b2, misc2, " also");
 918         err.emit();
 919     }
 920
 921     crate fn report_privacy_error(&self, privacy_error: &PrivacyError<'_>) {
 922         let PrivacyError { ident, binding, .. } = *privacy_error;
 923         let session = &self.session;
 924         let mk_struct_span_error = |is_constructor| {
 925             let mut descr = binding.res().descr().to_string();
 926             if is_constructor {
 927                 descr += " constructor";
 928             }
 929             if binding.is_import() {
 930                 descr += " import";
 931             }
 932
 933             let mut err =
 934                 struct_span_err!(session, ident.span, E0603, "{} `{}` is private", descr, ident);
 935
 936             err.span_label(ident.span, &format!("this {} is private", descr));
 937             err.span_note(
 938                 session.source_map().def_span(binding.span),
 939                 &format!("the {} `{}` is defined here", descr, ident),
 940             );
 941
 942             err
 943         };
 944
 945         let mut err = if let NameBindingKind::Res(
 946             Res::Def(DefKind::Ctor(CtorOf::Struct, CtorKind::Fn), ctor_def_id),
 947             _,
 948         ) = binding.kind
 949         {
 950             let def_id = (&*self).parent(ctor_def_id).expect("no parent for a constructor");
 951             if let Some(fields) = self.field_names.get(&def_id) {
 952                 let mut err = mk_struct_span_error(true);
 953                 let first_field = fields.first().expect("empty field list in the map");
 954                 err.span_label(
 955                     fields.iter().fold(first_field.span, |acc, field| acc.to(field.span)),
 956                     "a constructor is private if any of the fields is private",
 957                 );
 958                 err
 959             } else {
 960                 mk_struct_span_error(false)
 961             }
 962         } else {
 963             mk_struct_span_error(false)
 964         };
 965
 966         err.emit();
 967     }
 968 }
 969
 970 impl<'a, 'b> ImportResolver<'a, 'b> {
 971     /// Adds suggestions for a path that cannot be resolved.
 972     pub(crate) fn make_path_suggestion(
 973         &mut self,
 974         span: Span,
 975         mut path: Vec<Segment>,
 976         parent_scope: &ParentScope<'b>,
 977     ) -> Option<(Vec<Segment>, Vec<String>)> {
 978         debug!("make_path_suggestion: span={:?} path={:?}", span, path);
 979
 980         match (path.get(0), path.get(1)) {
 981             // `{{root}}::ident::...` on both editions.
 982             // On 2015 `{{root}}` is usually added implicitly.
 983             (Some(fst), Some(snd))
 984                 if fst.ident.name == kw::PathRoot && !snd.ident.is_path_segment_keyword() => {}
 985             // `ident::...` on 2018.
 986             (Some(fst), _)
 987                 if fst.ident.span.rust_2018() && !fst.ident.is_path_segment_keyword() =>
 988             {
 989                 // Insert a placeholder that's later replaced by `self`/`super`/etc.
 990                 path.insert(0, Segment::from_ident(Ident::invalid()));
 991             }
 992             _ => return None,
 993         }
 994
 995         self.make_missing_self_suggestion(span, path.clone(), parent_scope)
 996             .or_else(|| self.make_missing_crate_suggestion(span, path.clone(), parent_scope))
 997             .or_else(|| self.make_missing_super_suggestion(span, path.clone(), parent_scope))
 998             .or_else(|| self.make_external_crate_suggestion(span, path, parent_scope))
 999     }
1000
1001     /// Suggest a missing `self::` if that resolves to an correct module.
1002     ///
1003     /// ```
1004     ///    |
1005     /// LL | use foo::Bar;
1006     ///    |     ^^^ did you mean `self::foo`?
1007     /// ```
1008     fn make_missing_self_suggestion(
1009         &mut self,
1010         span: Span,
1011         mut path: Vec<Segment>,
1012         parent_scope: &ParentScope<'b>,
1013     ) -> Option<(Vec<Segment>, Vec<String>)> {
1014         // Replace first ident with `self` and check if that is valid.
1015         path[0].ident.name = kw::SelfLower;
1016         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1017         debug!("make_missing_self_suggestion: path={:?} result={:?}", path, result);
1018         if let PathResult::Module(..) = result { Some((path, Vec::new())) } else { None }
1019     }
1020
1021     /// Suggests a missing `crate::` if that resolves to an correct module.
1022     ///
1023     /// ```
1024     ///    |
1025     /// LL | use foo::Bar;
1026     ///    |     ^^^ did you mean `crate::foo`?
1027     /// ```
1028     fn make_missing_crate_suggestion(
1029         &mut self,
1030         span: Span,
1031         mut path: Vec<Segment>,
1032         parent_scope: &ParentScope<'b>,
1033     ) -> Option<(Vec<Segment>, Vec<String>)> {
1034         // Replace first ident with `crate` and check if that is valid.
1035         path[0].ident.name = kw::Crate;
1036         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1037         debug!("make_missing_crate_suggestion:  path={:?} result={:?}", path, result);
1038         if let PathResult::Module(..) = result {
1039             Some((
1040                 path,
1041                 vec![
1042                     "`use` statements changed in Rust 2018; read more at \
1043                      <https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-\
1044                      clarity.html>"
1045                         .to_string(),
1046                 ],
1047             ))
1048         } else {
1049             None
1050         }
1051     }
1052
1053     /// Suggests a missing `super::` if that resolves to an correct module.
1054     ///
1055     /// ```
1056     ///    |
1057     /// LL | use foo::Bar;
1058     ///    |     ^^^ did you mean `super::foo`?
1059     /// ```
1060     fn make_missing_super_suggestion(
1061         &mut self,
1062         span: Span,
1063         mut path: Vec<Segment>,
1064         parent_scope: &ParentScope<'b>,
1065     ) -> Option<(Vec<Segment>, Vec<String>)> {
1066         // Replace first ident with `crate` and check if that is valid.
1067         path[0].ident.name = kw::Super;
1068         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1069         debug!("make_missing_super_suggestion:  path={:?} result={:?}", path, result);
1070         if let PathResult::Module(..) = result { Some((path, Vec::new())) } else { None }
1071     }
1072
1073     /// Suggests a missing external crate name if that resolves to an correct module.
1074     ///
1075     /// ```
1076     ///    |
1077     /// LL | use foobar::Baz;
1078     ///    |     ^^^^^^ did you mean `baz::foobar`?
1079     /// ```
1080     ///
1081     /// Used when importing a submodule of an external crate but missing that crate's
1082     /// name as the first part of path.
1083     fn make_external_crate_suggestion(
1084         &mut self,
1085         span: Span,
1086         mut path: Vec<Segment>,
1087         parent_scope: &ParentScope<'b>,
1088     ) -> Option<(Vec<Segment>, Vec<String>)> {
1089         if path[1].ident.span.rust_2015() {
1090             return None;
1091         }
1092
1093         // Sort extern crate names in reverse order to get
1094         // 1) some consistent ordering for emitted diagnostics, and
1095         // 2) `std` suggestions before `core` suggestions.
1096         let mut extern_crate_names =
1097             self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
1098         extern_crate_names.sort_by_key(|name| Reverse(name.as_str()));
1099
1100         for name in extern_crate_names.into_iter() {
1101             // Replace first ident with a crate name and check if that is valid.
1102             path[0].ident.name = name;
1103             let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1104             debug!(
1105                 "make_external_crate_suggestion: name={:?} path={:?} result={:?}",
1106                 name, path, result
1107             );
1108             if let PathResult::Module(..) = result {
1109                 return Some((path, Vec::new()));
1110             }
1111         }
1112
1113         None
1114     }
1115
1116     /// Suggests importing a macro from the root of the crate rather than a module within
1117     /// the crate.
1118     ///
1119     /// ```
1120     /// help: a macro with this name exists at the root of the crate
1121     ///    |
1122     /// LL | use issue_59764::makro;
1123     ///    |     ^^^^^^^^^^^^^^^^^^
1124     ///    |
1125     ///    = note: this could be because a macro annotated with `#[macro_export]` will be exported
1126     ///            at the root of the crate instead of the module where it is defined
1127     /// ```
1128     pub(crate) fn check_for_module_export_macro(
1129         &mut self,
1130         import: &'b Import<'b>,
1131         module: ModuleOrUniformRoot<'b>,
1132         ident: Ident,
1133     ) -> Option<(Option<Suggestion>, Vec<String>)> {
1134         let mut crate_module = if let ModuleOrUniformRoot::Module(module) = module {
1135             module
1136         } else {
1137             return None;
1138         };
1139
1140         while let Some(parent) = crate_module.parent {
1141             crate_module = parent;
1142         }
1143
1144         if ModuleOrUniformRoot::same_def(ModuleOrUniformRoot::Module(crate_module), module) {
1145             // Don't make a suggestion if the import was already from the root of the
1146             // crate.
1147             return None;
1148         }
1149
1150         let resolutions = self.r.resolutions(crate_module).borrow();
1151         let resolution = resolutions.get(&self.r.new_key(ident, MacroNS))?;
1152         let binding = resolution.borrow().binding()?;
1153         if let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() {
1154             let module_name = crate_module.kind.name().unwrap();
1155             let import_snippet = match import.kind {
1156                 ImportKind::Single { source, target, .. } if source != target => {
1157                     format!("{} as {}", source, target)
1158                 }
1159                 _ => format!("{}", ident),
1160             };
1161
1162             let mut corrections: Vec<(Span, String)> = Vec::new();
1163             if !import.is_nested() {
1164                 // Assume this is the easy case of `use issue_59764::foo::makro;` and just remove
1165                 // intermediate segments.
1166                 corrections.push((import.span, format!("{}::{}", module_name, import_snippet)));
1167             } else {
1168                 // Find the binding span (and any trailing commas and spaces).
1169                 //   ie. `use a::b::{c, d, e};`
1170                 //                      ^^^
1171                 let (found_closing_brace, binding_span) = find_span_of_binding_until_next_binding(
1172                     self.r.session,
1173                     import.span,
1174                     import.use_span,
1175                 );
1176                 debug!(
1177                     "check_for_module_export_macro: found_closing_brace={:?} binding_span={:?}",
1178                     found_closing_brace, binding_span
1179                 );
1180
1181                 let mut removal_span = binding_span;
1182                 if found_closing_brace {
1183                     // If the binding span ended with a closing brace, as in the below example:
1184                     //   ie. `use a::b::{c, d};`
1185                     //                      ^
1186                     // Then expand the span of characters to remove to include the previous
1187                     // binding's trailing comma.
1188                     //   ie. `use a::b::{c, d};`
1189                     //                    ^^^
1190                     if let Some(previous_span) =
1191                         extend_span_to_previous_binding(self.r.session, binding_span)
1192                     {
1193                         debug!("check_for_module_export_macro: previous_span={:?}", previous_span);
1194                         removal_span = removal_span.with_lo(previous_span.lo());
1195                     }
1196                 }
1197                 debug!("check_for_module_export_macro: removal_span={:?}", removal_span);
1198
1199                 // Remove the `removal_span`.
1200                 corrections.push((removal_span, "".to_string()));
1201
1202                 // Find the span after the crate name and if it has nested imports immediatately
1203                 // after the crate name already.
1204                 //   ie. `use a::b::{c, d};`
1205                 //               ^^^^^^^^^
1206                 //   or  `use a::{b, c, d}};`
1207                 //               ^^^^^^^^^^^
1208                 let (has_nested, after_crate_name) = find_span_immediately_after_crate_name(
1209                     self.r.session,
1210                     module_name,
1211                     import.use_span,
1212                 );
1213                 debug!(
1214                     "check_for_module_export_macro: has_nested={:?} after_crate_name={:?}",
1215                     has_nested, after_crate_name
1216                 );
1217
1218                 let source_map = self.r.session.source_map();
1219
1220                 // Add the import to the start, with a `{` if required.
1221                 let start_point = source_map.start_point(after_crate_name);
1222                 if let Ok(start_snippet) = source_map.span_to_snippet(start_point) {
1223                     corrections.push((
1224                         start_point,
1225                         if has_nested {
1226                             // In this case, `start_snippet` must equal '{'.
1227                             format!("{}{}, ", start_snippet, import_snippet)
1228                         } else {
1229                             // In this case, add a `{`, then the moved import, then whatever
1230                             // was there before.
1231                             format!("{{{}, {}", import_snippet, start_snippet)
1232                         },
1233                     ));
1234                 }
1235
1236                 // Add a `};` to the end if nested, matching the `{` added at the start.
1237                 if !has_nested {
1238                     corrections.push((source_map.end_point(after_crate_name), "};".to_string()));
1239                 }
1240             }
1241
1242             let suggestion = Some((
1243                 corrections,
1244                 String::from("a macro with this name exists at the root of the crate"),
1245                 Applicability::MaybeIncorrect,
1246             ));
1247             let note = vec![
1248                 "this could be because a macro annotated with `#[macro_export]` will be exported \
1249                  at the root of the crate instead of the module where it is defined"
1250                     .to_string(),
1251             ];
1252             Some((suggestion, note))
1253         } else {
1254             None
1255         }
1256     }
1257 }
1258
1259 /// Given a `binding_span` of a binding within a use statement:
1260 ///
1261 /// ```
1262 /// use foo::{a, b, c};
1263 ///              ^
1264 /// ```
1265 ///
1266 /// then return the span until the next binding or the end of the statement:
1267 ///
1268 /// ```
1269 /// use foo::{a, b, c};
1270 ///              ^^^
1271 /// ```
1272 pub(crate) fn find_span_of_binding_until_next_binding(
1273     sess: &Session,
1274     binding_span: Span,
1275     use_span: Span,
1276 ) -> (bool, Span) {
1277     let source_map = sess.source_map();
1278
1279     // Find the span of everything after the binding.
1280     //   ie. `a, e};` or `a};`
1281     let binding_until_end = binding_span.with_hi(use_span.hi());
1282
1283     // Find everything after the binding but not including the binding.
1284     //   ie. `, e};` or `};`
1285     let after_binding_until_end = binding_until_end.with_lo(binding_span.hi());
1286
1287     // Keep characters in the span until we encounter something that isn't a comma or
1288     // whitespace.
1289     //   ie. `, ` or ``.
1290     //
1291     // Also note whether a closing brace character was encountered. If there
1292     // was, then later go backwards to remove any trailing commas that are left.
1293     let mut found_closing_brace = false;
1294     let after_binding_until_next_binding =
1295         source_map.span_take_while(after_binding_until_end, |&ch| {
1296             if ch == '}' {
1297                 found_closing_brace = true;
1298             }
1299             ch == ' ' || ch == ','
1300         });
1301
1302     // Combine the two spans.
1303     //   ie. `a, ` or `a`.
1304     //
1305     // Removing these would leave `issue_52891::{d, e};` or `issue_52891::{d, e, };`
1306     let span = binding_span.with_hi(after_binding_until_next_binding.hi());
1307
1308     (found_closing_brace, span)
1309 }
1310
1311 /// Given a `binding_span`, return the span through to the comma or opening brace of the previous
1312 /// binding.
1313 ///
1314 /// ```
1315 /// use foo::a::{a, b, c};
1316 ///               ^^--- binding span
1317 ///               |
1318 ///               returned span
1319 ///
1320 /// use foo::{a, b, c};
1321 ///           --- binding span
1322 /// ```
1323 pub(crate) fn extend_span_to_previous_binding(sess: &Session, binding_span: Span) -> Option<Span> {
1324     let source_map = sess.source_map();
1325
1326     // `prev_source` will contain all of the source that came before the span.
1327     // Then split based on a command and take the first (ie. closest to our span)
1328     // snippet. In the example, this is a space.
1329     let prev_source = source_map.span_to_prev_source(binding_span).ok()?;
1330
1331     let prev_comma = prev_source.rsplit(',').collect::<Vec<_>>();
1332     let prev_starting_brace = prev_source.rsplit('{').collect::<Vec<_>>();
1333     if prev_comma.len() <= 1 || prev_starting_brace.len() <= 1 {
1334         return None;
1335     }
1336
1337     let prev_comma = prev_comma.first().unwrap();
1338     let prev_starting_brace = prev_starting_brace.first().unwrap();
1339
1340     // If the amount of source code before the comma is greater than
1341     // the amount of source code before the starting brace then we've only
1342     // got one item in the nested item (eg. `issue_52891::{self}`).
1343     if prev_comma.len() > prev_starting_brace.len() {
1344         return None;
1345     }
1346
1347     Some(binding_span.with_lo(BytePos(
1348         // Take away the number of bytes for the characters we've found and an
1349         // extra for the comma.
1350         binding_span.lo().0 - (prev_comma.as_bytes().len() as u32) - 1,
1351     )))
1352 }
1353
1354 /// Given a `use_span` of a binding within a use statement, returns the highlighted span and if
1355 /// it is a nested use tree.
1356 ///
1357 /// ```
1358 /// use foo::a::{b, c};
1359 ///          ^^^^^^^^^^ // false
1360 ///
1361 /// use foo::{a, b, c};
1362 ///          ^^^^^^^^^^ // true
1363 ///
1364 /// use foo::{a, b::{c, d}};
1365 ///          ^^^^^^^^^^^^^^^ // true
1366 /// ```
1367 fn find_span_immediately_after_crate_name(
1368     sess: &Session,
1369     module_name: Symbol,
1370     use_span: Span,
1371 ) -> (bool, Span) {
1372     debug!(
1373         "find_span_immediately_after_crate_name: module_name={:?} use_span={:?}",
1374         module_name, use_span
1375     );
1376     let source_map = sess.source_map();
1377
1378     // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
1379     let mut num_colons = 0;
1380     // Find second colon.. `use issue_59764:`
1381     let until_second_colon = source_map.span_take_while(use_span, |c| {
1382         if *c == ':' {
1383             num_colons += 1;
1384         }
1385         match c {
1386             ':' if num_colons == 2 => false,
1387             _ => true,
1388         }
1389     });
1390     // Find everything after the second colon.. `foo::{baz, makro};`
1391     let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
1392
1393     let mut found_a_non_whitespace_character = false;
1394     // Find the first non-whitespace character in `from_second_colon`.. `f`
1395     let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
1396         if found_a_non_whitespace_character {
1397             return false;
1398         }
1399         if !c.is_whitespace() {
1400             found_a_non_whitespace_character = true;
1401         }
1402         true
1403     });
1404
1405     // Find the first `{` in from_second_colon.. `foo::{`
1406     let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
1407
1408     (next_left_bracket == after_second_colon, from_second_colon)
1409 }
1410
1411 /// When an entity with a given name is not available in scope, we search for
1412 /// entities with that name in all crates. This method allows outputting the
1413 /// results of this search in a programmer-friendly way
1414 crate fn show_candidates(
1415     err: &mut DiagnosticBuilder<'_>,
1416     // This is `None` if all placement locations are inside expansions
1417     span: Option<Span>,
1418     candidates: &[ImportSuggestion],
1419     better: bool,
1420     found_use: bool,
1421 ) {
1422     if candidates.is_empty() {
1423         return;
1424     }
1425     // we want consistent results across executions, but candidates are produced
1426     // by iterating through a hash map, so make sure they are ordered:
1427     let mut path_strings: Vec<_> =
1428         candidates.iter().map(|c| path_names_to_string(&c.path)).collect();
1429     path_strings.sort();
1430     path_strings.dedup();
1431
1432     let better = if better { "better " } else { "" };
1433     let msg_diff = match path_strings.len() {
1434         1 => " is found in another module, you can import it",
1435         _ => "s are found in other modules, you can import them",
1436     };
1437     let msg = format!("possible {}candidate{} into scope", better, msg_diff);
1438
1439     if let Some(span) = span {
1440         for candidate in &mut path_strings {
1441             // produce an additional newline to separate the new use statement
1442             // from the directly following item.
1443             let additional_newline = if found_use { "" } else { "\n" };
1444             *candidate = format!("use {};\n{}", candidate, additional_newline);
1445         }
1446
1447         err.span_suggestions(span, &msg, path_strings.into_iter(), Applicability::Unspecified);
1448     } else {
1449         let mut msg = msg;
1450         msg.push(':');
1451         for candidate in path_strings {
1452             msg.push('\n');
1453             msg.push_str(&candidate);
1454         }
1455         err.note(&msg);
1456     }
1457 }