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 type Res = def::Res<ast::NodeId>;
  29
  30 /// A vector of spans and replacements, a message and applicability.
  31 crate type Suggestion = (Vec<(Span, String)>, String, Applicability);
  32
  33 crate struct TypoSuggestion {
  34     pub candidate: Symbol,
  35     pub res: Res,
  36 }
  37
  38 impl TypoSuggestion {
  39     crate fn from_res(candidate: Symbol, res: Res) -> TypoSuggestion {
  40         TypoSuggestion { candidate, res }
  41     }
  42 }
  43
  44 /// A free importable items suggested in case of resolution failure.
  45 crate struct ImportSuggestion {
  46     pub did: Option<DefId>,
  47     pub path: Path,
  48 }
  49
  50 /// Adjust the impl span so that just the `impl` keyword is taken by removing
  51 /// everything after `<` (`"impl<T> Iterator for A<T> {}" -> "impl"`) and
  52 /// everything after the first whitespace (`"impl Iterator for A" -> "impl"`).
  53 ///
  54 /// *Attention*: the method used is very fragile since it essentially duplicates the work of the
  55 /// parser. If you need to use this function or something similar, please consider updating the
  56 /// `source_map` functions and this function to something more robust.
  57 fn reduce_impl_span_to_impl_keyword(cm: &SourceMap, impl_span: Span) -> Span {
  58     let impl_span = cm.span_until_char(impl_span, '<');
  59     let impl_span = cm.span_until_whitespace(impl_span);
  60     impl_span
  61 }
  62
  63 impl<'a> Resolver<'a> {
  64     crate fn add_module_candidates(
  65         &mut self,
  66         module: Module<'a>,
  67         names: &mut Vec<TypoSuggestion>,
  68         filter_fn: &impl Fn(Res) -> bool,
  69     ) {
  70         for (key, resolution) in self.resolutions(module).borrow().iter() {
  71             if let Some(binding) = resolution.borrow().binding {
  72                 let res = binding.res();
  73                 if filter_fn(res) {
  74                     names.push(TypoSuggestion::from_res(key.ident.name, res));
  75                 }
  76             }
  77         }
  78     }
  79
  80     /// Combines an error with provided span and emits it.
  81     ///
  82     /// This takes the error provided, combines it with the span and any additional spans inside the
  83     /// error and emits it.
  84     crate fn report_error(&self, span: Span, resolution_error: ResolutionError<'_>) {
  85         self.into_struct_error(span, resolution_error).emit();
  86     }
  87
  88     crate fn into_struct_error(
  89         &self,
  90         span: Span,
  91         resolution_error: ResolutionError<'_>,
  92     ) -> DiagnosticBuilder<'_> {
  93         match resolution_error {
  94             ResolutionError::GenericParamsFromOuterFunction(outer_res, has_generic_params) => {
  95                 let mut err = struct_span_err!(
  96                     self.session,
  97                     span,
  98                     E0401,
  99                     "can't use generic parameters from outer function",
 100                 );
 101                 err.span_label(span, format!("use of generic parameter from outer function"));
 102
 103                 let cm = self.session.source_map();
 104                 match outer_res {
 105                     Res::SelfTy(maybe_trait_defid, maybe_impl_defid) => {
 106                         if let Some(impl_span) =
 107                             maybe_impl_defid.and_then(|def_id| self.definitions.opt_span(def_id))
 108                         {
 109                             err.span_label(
 110                                 reduce_impl_span_to_impl_keyword(cm, impl_span),
 111                                 "`Self` type implicitly declared here, by this `impl`",
 112                             );
 113                         }
 114                         match (maybe_trait_defid, maybe_impl_defid) {
 115                             (Some(_), None) => {
 116                                 err.span_label(span, "can't use `Self` here");
 117                             }
 118                             (_, Some(_)) => {
 119                                 err.span_label(span, "use a type here instead");
 120                             }
 121                             (None, None) => bug!("`impl` without trait nor type?"),
 122                         }
 123                         return err;
 124                     }
 125                     Res::Def(DefKind::TyParam, def_id) => {
 126                         if let Some(span) = self.definitions.opt_span(def_id) {
 127                             err.span_label(span, "type parameter from outer function");
 128                         }
 129                     }
 130                     Res::Def(DefKind::ConstParam, def_id) => {
 131                         if let Some(span) = self.definitions.opt_span(def_id) {
 132                             err.span_label(span, "const parameter from outer function");
 133                         }
 134                     }
 135                     _ => {
 136                         bug!(
 137                             "GenericParamsFromOuterFunction should only be used with Res::SelfTy, \
 138                             DefKind::TyParam"
 139                         );
 140                     }
 141                 }
 142
 143                 if has_generic_params == HasGenericParams::Yes {
 144                     // Try to retrieve the span of the function signature and generate a new
 145                     // message with a local type or const parameter.
 146                     let sugg_msg = &format!("try using a local generic parameter instead");
 147                     if let Some((sugg_span, snippet)) = cm.generate_local_type_param_snippet(span) {
 148                         // Suggest the modification to the user
 149                         err.span_suggestion(
 150                             sugg_span,
 151                             sugg_msg,
 152                             snippet,
 153                             Applicability::MachineApplicable,
 154                         );
 155                     } else if let Some(sp) = cm.generate_fn_name_span(span) {
 156                         err.span_label(
 157                             sp,
 158                             format!("try adding a local generic parameter in this method instead"),
 159                         );
 160                     } else {
 161                         err.help(&format!("try using a local generic parameter instead"));
 162                     }
 163                 }
 164
 165                 err
 166             }
 167             ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => {
 168                 let mut err = struct_span_err!(
 169                     self.session,
 170                     span,
 171                     E0403,
 172                     "the name `{}` is already used for a generic \
 173                      parameter in this item's generic parameters",
 174                     name,
 175                 );
 176                 err.span_label(span, "already used");
 177                 err.span_label(first_use_span, format!("first use of `{}`", name));
 178                 err
 179             }
 180             ResolutionError::MethodNotMemberOfTrait(method, trait_) => {
 181                 let mut err = struct_span_err!(
 182                     self.session,
 183                     span,
 184                     E0407,
 185                     "method `{}` is not a member of trait `{}`",
 186                     method,
 187                     trait_
 188                 );
 189                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 190                 err
 191             }
 192             ResolutionError::TypeNotMemberOfTrait(type_, trait_) => {
 193                 let mut err = struct_span_err!(
 194                     self.session,
 195                     span,
 196                     E0437,
 197                     "type `{}` is not a member of trait `{}`",
 198                     type_,
 199                     trait_
 200                 );
 201                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 202                 err
 203             }
 204             ResolutionError::ConstNotMemberOfTrait(const_, trait_) => {
 205                 let mut err = struct_span_err!(
 206                     self.session,
 207                     span,
 208                     E0438,
 209                     "const `{}` is not a member of trait `{}`",
 210                     const_,
 211                     trait_
 212                 );
 213                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 214                 err
 215             }
 216             ResolutionError::VariableNotBoundInPattern(binding_error) => {
 217                 let BindingError { name, target, origin, could_be_path } = binding_error;
 218
 219                 let target_sp = target.iter().copied().collect::<Vec<_>>();
 220                 let origin_sp = origin.iter().copied().collect::<Vec<_>>();
 221
 222                 let msp = MultiSpan::from_spans(target_sp.clone());
 223                 let mut err = struct_span_err!(
 224                     self.session,
 225                     msp,
 226                     E0408,
 227                     "variable `{}` is not bound in all patterns",
 228                     name,
 229                 );
 230                 for sp in target_sp {
 231                     err.span_label(sp, format!("pattern doesn't bind `{}`", name));
 232                 }
 233                 for sp in origin_sp {
 234                     err.span_label(sp, "variable not in all patterns");
 235                 }
 236                 if *could_be_path {
 237                     let help_msg = format!(
 238                         "if you meant to match on a variant or a `const` item, consider \
 239                          making the path in the pattern qualified: `?::{}`",
 240                         name,
 241                     );
 242                     err.span_help(span, &help_msg);
 243                 }
 244                 err
 245             }
 246             ResolutionError::VariableBoundWithDifferentMode(variable_name, first_binding_span) => {
 247                 let mut err = struct_span_err!(
 248                     self.session,
 249                     span,
 250                     E0409,
 251                     "variable `{}` is bound in inconsistent \
 252                                 ways within the same match arm",
 253                     variable_name
 254                 );
 255                 err.span_label(span, "bound in different ways");
 256                 err.span_label(first_binding_span, "first binding");
 257                 err
 258             }
 259             ResolutionError::IdentifierBoundMoreThanOnceInParameterList(identifier) => {
 260                 let mut err = struct_span_err!(
 261                     self.session,
 262                     span,
 263                     E0415,
 264                     "identifier `{}` is bound more than once in this parameter list",
 265                     identifier
 266                 );
 267                 err.span_label(span, "used as parameter more than once");
 268                 err
 269             }
 270             ResolutionError::IdentifierBoundMoreThanOnceInSamePattern(identifier) => {
 271                 let mut err = struct_span_err!(
 272                     self.session,
 273                     span,
 274                     E0416,
 275                     "identifier `{}` is bound more than once in the same pattern",
 276                     identifier
 277                 );
 278                 err.span_label(span, "used in a pattern more than once");
 279                 err
 280             }
 281             ResolutionError::UndeclaredLabel(name, lev_candidate) => {
 282                 let mut err = struct_span_err!(
 283                     self.session,
 284                     span,
 285                     E0426,
 286                     "use of undeclared label `{}`",
 287                     name
 288                 );
 289                 if let Some(lev_candidate) = lev_candidate {
 290                     err.span_suggestion(
 291                         span,
 292                         "a label with a similar name exists in this scope",
 293                         lev_candidate.to_string(),
 294                         Applicability::MaybeIncorrect,
 295                     );
 296                 } else {
 297                     err.span_label(span, format!("undeclared label `{}`", name));
 298                 }
 299                 err
 300             }
 301             ResolutionError::SelfImportsOnlyAllowedWithin => struct_span_err!(
 302                 self.session,
 303                 span,
 304                 E0429,
 305                 "{}",
 306                 "`self` imports are only allowed within a { } list"
 307             ),
 308             ResolutionError::SelfImportCanOnlyAppearOnceInTheList => {
 309                 let mut err = struct_span_err!(
 310                     self.session,
 311                     span,
 312                     E0430,
 313                     "`self` import can only appear once in an import list"
 314                 );
 315                 err.span_label(span, "can only appear once in an import list");
 316                 err
 317             }
 318             ResolutionError::SelfImportOnlyInImportListWithNonEmptyPrefix => {
 319                 let mut err = struct_span_err!(
 320                     self.session,
 321                     span,
 322                     E0431,
 323                     "`self` import can only appear in an import list with \
 324                                                 a non-empty prefix"
 325                 );
 326                 err.span_label(span, "can only appear in an import list with a non-empty prefix");
 327                 err
 328             }
 329             ResolutionError::FailedToResolve { label, suggestion } => {
 330                 let mut err =
 331                     struct_span_err!(self.session, span, E0433, "failed to resolve: {}", &label);
 332                 err.span_label(span, label);
 333
 334                 if let Some((suggestions, msg, applicability)) = suggestion {
 335                     err.multipart_suggestion(&msg, suggestions, applicability);
 336                 }
 337
 338                 err
 339             }
 340             ResolutionError::CannotCaptureDynamicEnvironmentInFnItem => {
 341                 let mut err = struct_span_err!(
 342                     self.session,
 343                     span,
 344                     E0434,
 345                     "{}",
 346                     "can't capture dynamic environment in a fn item"
 347                 );
 348                 err.help("use the `|| { ... }` closure form instead");
 349                 err
 350             }
 351             ResolutionError::AttemptToUseNonConstantValueInConstant => {
 352                 let mut err = struct_span_err!(
 353                     self.session,
 354                     span,
 355                     E0435,
 356                     "attempt to use a non-constant value in a constant"
 357                 );
 358                 err.span_label(span, "non-constant value");
 359                 err
 360             }
 361             ResolutionError::BindingShadowsSomethingUnacceptable(what_binding, name, binding) => {
 362                 let res = binding.res();
 363                 let shadows_what = res.descr();
 364                 let mut err = struct_span_err!(
 365                     self.session,
 366                     span,
 367                     E0530,
 368                     "{}s cannot shadow {}s",
 369                     what_binding,
 370                     shadows_what
 371                 );
 372                 err.span_label(
 373                     span,
 374                     format!("cannot be named the same as {} {}", res.article(), shadows_what),
 375                 );
 376                 let participle = if binding.is_import() { "imported" } else { "defined" };
 377                 let msg = format!("the {} `{}` is {} here", shadows_what, name, participle);
 378                 err.span_label(binding.span, msg);
 379                 err
 380             }
 381             ResolutionError::ForwardDeclaredTyParam => {
 382                 let mut err = struct_span_err!(
 383                     self.session,
 384                     span,
 385                     E0128,
 386                     "type parameters with a default cannot use \
 387                                                 forward declared identifiers"
 388                 );
 389                 err.span_label(
 390                     span,
 391                     "defaulted type parameters cannot be forward declared".to_string(),
 392                 );
 393                 err
 394             }
 395             ResolutionError::SelfInTyParamDefault => {
 396                 let mut err = struct_span_err!(
 397                     self.session,
 398                     span,
 399                     E0735,
 400                     "type parameters cannot use `Self` in their defaults"
 401                 );
 402                 err.span_label(span, "`Self` in type parameter default".to_string());
 403                 err
 404             }
 405         }
 406     }
 407
 408     crate fn report_vis_error(&self, vis_resolution_error: VisResolutionError<'_>) {
 409         match vis_resolution_error {
 410             VisResolutionError::Relative2018(span, path) => {
 411                 let mut err = self.session.struct_span_err(
 412                     span,
 413                     "relative paths are not supported in visibilities on 2018 edition",
 414                 );
 415                 err.span_suggestion(
 416                     path.span,
 417                     "try",
 418                     format!("crate::{}", pprust::path_to_string(&path)),
 419                     Applicability::MaybeIncorrect,
 420                 );
 421                 err
 422             }
 423             VisResolutionError::AncestorOnly(span) => struct_span_err!(
 424                 self.session,
 425                 span,
 426                 E0742,
 427                 "visibilities can only be restricted to ancestor modules"
 428             ),
 429             VisResolutionError::FailedToResolve(span, label, suggestion) => {
 430                 self.into_struct_error(span, ResolutionError::FailedToResolve { label, suggestion })
 431             }
 432             VisResolutionError::ExpectedFound(span, path_str, res) => {
 433                 let mut err = struct_span_err!(
 434                     self.session,
 435                     span,
 436                     E0577,
 437                     "expected module, found {} `{}`",
 438                     res.descr(),
 439                     path_str
 440                 );
 441                 err.span_label(span, "not a module");
 442                 err
 443             }
 444             VisResolutionError::Indeterminate(span) => struct_span_err!(
 445                 self.session,
 446                 span,
 447                 E0578,
 448                 "cannot determine resolution for the visibility"
 449             ),
 450             VisResolutionError::ModuleOnly(span) => {
 451                 self.session.struct_span_err(span, "visibility must resolve to a module")
 452             }
 453         }
 454         .emit()
 455     }
 456
 457     /// Lookup typo candidate in scope for a macro or import.
 458     fn early_lookup_typo_candidate(
 459         &mut self,
 460         scope_set: ScopeSet,
 461         parent_scope: &ParentScope<'a>,
 462         ident: Ident,
 463         filter_fn: &impl Fn(Res) -> bool,
 464     ) -> Option<TypoSuggestion> {
 465         let mut suggestions = Vec::new();
 466         self.visit_scopes(scope_set, parent_scope, ident, |this, scope, use_prelude, _| {
 467             match scope {
 468                 Scope::DeriveHelpers(expn_id) => {
 469                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 470                     if filter_fn(res) {
 471                         suggestions.extend(
 472                             this.helper_attrs
 473                                 .get(&expn_id)
 474                                 .into_iter()
 475                                 .flatten()
 476                                 .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 477                         );
 478                     }
 479                 }
 480                 Scope::DeriveHelpersCompat => {
 481                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 482                     if filter_fn(res) {
 483                         for derive in parent_scope.derives {
 484                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
 485                             if let Ok((Some(ext), _)) = this.resolve_macro_path(
 486                                 derive,
 487                                 Some(MacroKind::Derive),
 488                                 parent_scope,
 489                                 false,
 490                                 false,
 491                             ) {
 492                                 suggestions.extend(
 493                                     ext.helper_attrs
 494                                         .iter()
 495                                         .map(|name| TypoSuggestion::from_res(*name, res)),
 496                                 );
 497                             }
 498                         }
 499                     }
 500                 }
 501                 Scope::MacroRules(legacy_scope) => {
 502                     if let LegacyScope::Binding(legacy_binding) = legacy_scope {
 503                         let res = legacy_binding.binding.res();
 504                         if filter_fn(res) {
 505                             suggestions
 506                                 .push(TypoSuggestion::from_res(legacy_binding.ident.name, res))
 507                         }
 508                     }
 509                 }
 510                 Scope::CrateRoot => {
 511                     let root_ident = Ident::new(kw::PathRoot, ident.span);
 512                     let root_module = this.resolve_crate_root(root_ident);
 513                     this.add_module_candidates(root_module, &mut suggestions, filter_fn);
 514                 }
 515                 Scope::Module(module) => {
 516                     this.add_module_candidates(module, &mut suggestions, filter_fn);
 517                 }
 518                 Scope::RegisteredAttrs => {
 519                     let res = Res::NonMacroAttr(NonMacroAttrKind::Registered);
 520                     if filter_fn(res) {
 521                         suggestions.extend(
 522                             this.registered_attrs
 523                                 .iter()
 524                                 .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 525                         );
 526                     }
 527                 }
 528                 Scope::MacroUsePrelude => {
 529                     suggestions.extend(this.macro_use_prelude.iter().filter_map(
 530                         |(name, binding)| {
 531                             let res = binding.res();
 532                             filter_fn(res).then_some(TypoSuggestion::from_res(*name, res))
 533                         },
 534                     ));
 535                 }
 536                 Scope::BuiltinAttrs => {
 537                     let res = Res::NonMacroAttr(NonMacroAttrKind::Builtin);
 538                     if filter_fn(res) {
 539                         suggestions.extend(
 540                             BUILTIN_ATTRIBUTES
 541                                 .iter()
 542                                 .map(|(name, ..)| TypoSuggestion::from_res(*name, res)),
 543                         );
 544                     }
 545                 }
 546                 Scope::ExternPrelude => {
 547                     suggestions.extend(this.extern_prelude.iter().filter_map(|(ident, _)| {
 548                         let res = Res::Def(DefKind::Mod, DefId::local(CRATE_DEF_INDEX));
 549                         filter_fn(res).then_some(TypoSuggestion::from_res(ident.name, res))
 550                     }));
 551                 }
 552                 Scope::ToolPrelude => {
 553                     let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
 554                     suggestions.extend(
 555                         this.registered_tools
 556                             .iter()
 557                             .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 558                     );
 559                 }
 560                 Scope::StdLibPrelude => {
 561                     if let Some(prelude) = this.prelude {
 562                         let mut tmp_suggestions = Vec::new();
 563                         this.add_module_candidates(prelude, &mut tmp_suggestions, filter_fn);
 564                         suggestions.extend(
 565                             tmp_suggestions
 566                                 .into_iter()
 567                                 .filter(|s| use_prelude || this.is_builtin_macro(s.res)),
 568                         );
 569                     }
 570                 }
 571                 Scope::BuiltinTypes => {
 572                     let primitive_types = &this.primitive_type_table.primitive_types;
 573                     suggestions.extend(primitive_types.iter().flat_map(|(name, prim_ty)| {
 574                         let res = Res::PrimTy(*prim_ty);
 575                         filter_fn(res).then_some(TypoSuggestion::from_res(*name, res))
 576                     }))
 577                 }
 578             }
 579
 580             None::<()>
 581         });
 582
 583         // Make sure error reporting is deterministic.
 584         suggestions.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
 585
 586         match find_best_match_for_name(
 587             suggestions.iter().map(|suggestion| &suggestion.candidate),
 588             &ident.as_str(),
 589             None,
 590         ) {
 591             Some(found) if found != ident.name => {
 592                 suggestions.into_iter().find(|suggestion| suggestion.candidate == found)
 593             }
 594             _ => None,
 595         }
 596     }
 597
 598     fn lookup_import_candidates_from_module<FilterFn>(
 599         &mut self,
 600         lookup_ident: Ident,
 601         namespace: Namespace,
 602         start_module: Module<'a>,
 603         crate_name: Ident,
 604         filter_fn: FilterFn,
 605     ) -> Vec<ImportSuggestion>
 606     where
 607         FilterFn: Fn(Res) -> bool,
 608     {
 609         let mut candidates = Vec::new();
 610         let mut seen_modules = FxHashSet::default();
 611         let not_local_module = crate_name.name != kw::Crate;
 612         let mut worklist = vec![(start_module, Vec::<ast::PathSegment>::new(), not_local_module)];
 613
 614         while let Some((in_module, path_segments, in_module_is_extern)) = worklist.pop() {
 615             // We have to visit module children in deterministic order to avoid
 616             // instabilities in reported imports (#43552).
 617             in_module.for_each_child(self, |this, ident, ns, name_binding| {
 618                 // avoid imports entirely
 619                 if name_binding.is_import() && !name_binding.is_extern_crate() {
 620                     return;
 621                 }
 622                 // avoid non-importable candidates as well
 623                 if !name_binding.is_importable() {
 624                     return;
 625                 }
 626
 627                 // collect results based on the filter function
 628                 if ident.name == lookup_ident.name && ns == namespace {
 629                     let res = name_binding.res();
 630                     if filter_fn(res) {
 631                         // create the path
 632                         let mut segms = path_segments.clone();
 633                         if lookup_ident.span.rust_2018() {
 634                             // crate-local absolute paths start with `crate::` in edition 2018
 635                             // FIXME: may also be stabilized for Rust 2015 (Issues #45477, #44660)
 636                             segms.insert(0, ast::PathSegment::from_ident(crate_name));
 637                         }
 638
 639                         segms.push(ast::PathSegment::from_ident(ident));
 640                         let path = Path { span: name_binding.span, segments: segms };
 641                         // the entity is accessible in the following cases:
 642                         // 1. if it's defined in the same crate, it's always
 643                         // accessible (since private entities can be made public)
 644                         // 2. if it's defined in another crate, it's accessible
 645                         // only if both the module is public and the entity is
 646                         // declared as public (due to pruning, we don't explore
 647                         // outside crate private modules => no need to check this)
 648                         if !in_module_is_extern || name_binding.vis == ty::Visibility::Public {
 649                             let did = match res {
 650                                 Res::Def(DefKind::Ctor(..), did) => this.parent(did),
 651                                 _ => res.opt_def_id(),
 652                             };
 653                             candidates.push(ImportSuggestion { did, path });
 654                         }
 655                     }
 656                 }
 657
 658                 // collect submodules to explore
 659                 if let Some(module) = name_binding.module() {
 660                     // form the path
 661                     let mut path_segments = path_segments.clone();
 662                     path_segments.push(ast::PathSegment::from_ident(ident));
 663
 664                     let is_extern_crate_that_also_appears_in_prelude =
 665                         name_binding.is_extern_crate() && lookup_ident.span.rust_2018();
 666
 667                     let is_visible_to_user =
 668                         !in_module_is_extern || name_binding.vis == ty::Visibility::Public;
 669
 670                     if !is_extern_crate_that_also_appears_in_prelude && is_visible_to_user {
 671                         // add the module to the lookup
 672                         let is_extern = in_module_is_extern || name_binding.is_extern_crate();
 673                         if seen_modules.insert(module.def_id().unwrap()) {
 674                             worklist.push((module, path_segments, is_extern));
 675                         }
 676                     }
 677                 }
 678             })
 679         }
 680
 681         candidates
 682     }
 683
 684     /// When name resolution fails, this method can be used to look up candidate
 685     /// entities with the expected name. It allows filtering them using the
 686     /// supplied predicate (which should be used to only accept the types of
 687     /// definitions expected, e.g., traits). The lookup spans across all crates.
 688     ///
 689     /// N.B., the method does not look into imports, but this is not a problem,
 690     /// since we report the definitions (thus, the de-aliased imports).
 691     crate fn lookup_import_candidates<FilterFn>(
 692         &mut self,
 693         lookup_ident: Ident,
 694         namespace: Namespace,
 695         filter_fn: FilterFn,
 696     ) -> Vec<ImportSuggestion>
 697     where
 698         FilterFn: Fn(Res) -> bool,
 699     {
 700         let mut suggestions = self.lookup_import_candidates_from_module(
 701             lookup_ident,
 702             namespace,
 703             self.graph_root,
 704             Ident::with_dummy_span(kw::Crate),
 705             &filter_fn,
 706         );
 707
 708         if lookup_ident.span.rust_2018() {
 709             let extern_prelude_names = self.extern_prelude.clone();
 710             for (ident, _) in extern_prelude_names.into_iter() {
 711                 if ident.span.from_expansion() {
 712                     // Idents are adjusted to the root context before being
 713                     // resolved in the extern prelude, so reporting this to the
 714                     // user is no help. This skips the injected
 715                     // `extern crate std` in the 2018 edition, which would
 716                     // otherwise cause duplicate suggestions.
 717                     continue;
 718                 }
 719                 if let Some(crate_id) =
 720                     self.crate_loader.maybe_process_path_extern(ident.name, ident.span)
 721                 {
 722                     let crate_root =
 723                         self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
 724                     suggestions.extend(self.lookup_import_candidates_from_module(
 725                         lookup_ident,
 726                         namespace,
 727                         crate_root,
 728                         ident,
 729                         &filter_fn,
 730                     ));
 731                 }
 732             }
 733         }
 734
 735         suggestions
 736     }
 737
 738     crate fn unresolved_macro_suggestions(
 739         &mut self,
 740         err: &mut DiagnosticBuilder<'a>,
 741         macro_kind: MacroKind,
 742         parent_scope: &ParentScope<'a>,
 743         ident: Ident,
 744     ) {
 745         let is_expected = &|res: Res| res.macro_kind() == Some(macro_kind);
 746         let suggestion = self.early_lookup_typo_candidate(
 747             ScopeSet::Macro(macro_kind),
 748             parent_scope,
 749             ident,
 750             is_expected,
 751         );
 752         self.add_typo_suggestion(err, suggestion, ident.span);
 753
 754         if macro_kind == MacroKind::Derive && (ident.as_str() == "Send" || ident.as_str() == "Sync")
 755         {
 756             let msg = format!("unsafe traits like `{}` should be implemented explicitly", ident);
 757             err.span_note(ident.span, &msg);
 758         }
 759         if self.macro_names.contains(&ident.modern()) {
 760             err.help("have you added the `#[macro_use]` on the module/import?");
 761         }
 762     }
 763
 764     crate fn add_typo_suggestion(
 765         &self,
 766         err: &mut DiagnosticBuilder<'_>,
 767         suggestion: Option<TypoSuggestion>,
 768         span: Span,
 769     ) -> bool {
 770         if let Some(suggestion) = suggestion {
 771             let msg = format!(
 772                 "{} {} with a similar name exists",
 773                 suggestion.res.article(),
 774                 suggestion.res.descr()
 775             );
 776             err.span_suggestion(
 777                 span,
 778                 &msg,
 779                 suggestion.candidate.to_string(),
 780                 Applicability::MaybeIncorrect,
 781             );
 782             let def_span = suggestion.res.opt_def_id().and_then(|def_id| match def_id.krate {
 783                 LOCAL_CRATE => self.definitions.opt_span(def_id),
 784                 _ => Some(
 785                     self.session
 786                         .source_map()
 787                         .def_span(self.cstore().get_span_untracked(def_id, self.session)),
 788                 ),
 789             });
 790             if let Some(span) = def_span {
 791                 err.span_label(
 792                     span,
 793                     &format!(
 794                         "similarly named {} `{}` defined here",
 795                         suggestion.res.descr(),
 796                         suggestion.candidate.as_str(),
 797                     ),
 798                 );
 799             }
 800             return true;
 801         }
 802         false
 803     }
 804
 805     fn binding_description(&self, b: &NameBinding<'_>, ident: Ident, from_prelude: bool) -> String {
 806         let res = b.res();
 807         if b.span.is_dummy() {
 808             let add_built_in = match b.res() {
 809                 // These already contain the "built-in" prefix or look bad with it.
 810                 Res::NonMacroAttr(..) | Res::PrimTy(..) | Res::ToolMod => false,
 811                 _ => true,
 812             };
 813             let (built_in, from) = if from_prelude {
 814                 ("", " from prelude")
 815             } else if b.is_extern_crate()
 816                 && !b.is_import()
 817                 && self.session.opts.externs.get(&ident.as_str()).is_some()
 818             {
 819                 ("", " passed with `--extern`")
 820             } else if add_built_in {
 821                 (" built-in", "")
 822             } else {
 823                 ("", "")
 824             };
 825
 826             let article = if built_in.is_empty() { res.article() } else { "a" };
 827             format!(
 828                 "{a}{built_in} {thing}{from}",
 829                 a = article,
 830                 thing = res.descr(),
 831                 built_in = built_in,
 832                 from = from
 833             )
 834         } else {
 835             let introduced = if b.is_import() { "imported" } else { "defined" };
 836             format!("the {thing} {introduced} here", thing = res.descr(), introduced = introduced)
 837         }
 838     }
 839
 840     crate fn report_ambiguity_error(&self, ambiguity_error: &AmbiguityError<'_>) {
 841         let AmbiguityError { kind, ident, b1, b2, misc1, misc2 } = *ambiguity_error;
 842         let (b1, b2, misc1, misc2, swapped) = if b2.span.is_dummy() && !b1.span.is_dummy() {
 843             // We have to print the span-less alternative first, otherwise formatting looks bad.
 844             (b2, b1, misc2, misc1, true)
 845         } else {
 846             (b1, b2, misc1, misc2, false)
 847         };
 848
 849         let mut err = struct_span_err!(
 850             self.session,
 851             ident.span,
 852             E0659,
 853             "`{ident}` is ambiguous ({why})",
 854             ident = ident,
 855             why = kind.descr()
 856         );
 857         err.span_label(ident.span, "ambiguous name");
 858
 859         let mut could_refer_to = |b: &NameBinding<'_>, misc: AmbiguityErrorMisc, also: &str| {
 860             let what = self.binding_description(b, ident, misc == AmbiguityErrorMisc::FromPrelude);
 861             let note_msg = format!(
 862                 "`{ident}` could{also} refer to {what}",
 863                 ident = ident,
 864                 also = also,
 865                 what = what
 866             );
 867
 868             let thing = b.res().descr();
 869             let mut help_msgs = Vec::new();
 870             if b.is_glob_import()
 871                 && (kind == AmbiguityKind::GlobVsGlob
 872                     || kind == AmbiguityKind::GlobVsExpanded
 873                     || kind == AmbiguityKind::GlobVsOuter && swapped != also.is_empty())
 874             {
 875                 help_msgs.push(format!(
 876                     "consider adding an explicit import of \
 877                      `{ident}` to disambiguate",
 878                     ident = ident
 879                 ))
 880             }
 881             if b.is_extern_crate() && ident.span.rust_2018() {
 882                 help_msgs.push(format!(
 883                     "use `::{ident}` to refer to this {thing} unambiguously",
 884                     ident = ident,
 885                     thing = thing,
 886                 ))
 887             }
 888             if misc == AmbiguityErrorMisc::SuggestCrate {
 889                 help_msgs.push(format!(
 890                     "use `crate::{ident}` to refer to this {thing} unambiguously",
 891                     ident = ident,
 892                     thing = thing,
 893                 ))
 894             } else if misc == AmbiguityErrorMisc::SuggestSelf {
 895                 help_msgs.push(format!(
 896                     "use `self::{ident}` to refer to this {thing} unambiguously",
 897                     ident = ident,
 898                     thing = thing,
 899                 ))
 900             }
 901
 902             err.span_note(b.span, &note_msg);
 903             for (i, help_msg) in help_msgs.iter().enumerate() {
 904                 let or = if i == 0 { "" } else { "or " };
 905                 err.help(&format!("{}{}", or, help_msg));
 906             }
 907         };
 908
 909         could_refer_to(b1, misc1, "");
 910         could_refer_to(b2, misc2, " also");
 911         err.emit();
 912     }
 913
 914     crate fn report_privacy_error(&self, privacy_error: &PrivacyError<'_>) {
 915         let PrivacyError { ident, binding, .. } = *privacy_error;
 916         let session = &self.session;
 917         let mk_struct_span_error = |is_constructor| {
 918             let mut descr = binding.res().descr().to_string();
 919             if is_constructor {
 920                 descr += " constructor";
 921             }
 922             if binding.is_import() {
 923                 descr += " import";
 924             }
 925
 926             let mut err =
 927                 struct_span_err!(session, ident.span, E0603, "{} `{}` is private", descr, ident);
 928
 929             err.span_label(ident.span, &format!("this {} is private", descr));
 930             err.span_note(
 931                 session.source_map().def_span(binding.span),
 932                 &format!("the {} `{}` is defined here", descr, ident),
 933             );
 934
 935             err
 936         };
 937
 938         let mut err = if let NameBindingKind::Res(
 939             Res::Def(DefKind::Ctor(CtorOf::Struct, CtorKind::Fn), ctor_def_id),
 940             _,
 941         ) = binding.kind
 942         {
 943             let def_id = (&*self).parent(ctor_def_id).expect("no parent for a constructor");
 944             if let Some(fields) = self.field_names.get(&def_id) {
 945                 let mut err = mk_struct_span_error(true);
 946                 let first_field = fields.first().expect("empty field list in the map");
 947                 err.span_label(
 948                     fields.iter().fold(first_field.span, |acc, field| acc.to(field.span)),
 949                     "a constructor is private if any of the fields is private",
 950                 );
 951                 err
 952             } else {
 953                 mk_struct_span_error(false)
 954             }
 955         } else {
 956             mk_struct_span_error(false)
 957         };
 958
 959         err.emit();
 960     }
 961 }
 962
 963 impl<'a, 'b> ImportResolver<'a, 'b> {
 964     /// Adds suggestions for a path that cannot be resolved.
 965     pub(crate) fn make_path_suggestion(
 966         &mut self,
 967         span: Span,
 968         mut path: Vec<Segment>,
 969         parent_scope: &ParentScope<'b>,
 970     ) -> Option<(Vec<Segment>, Vec<String>)> {
 971         debug!("make_path_suggestion: span={:?} path={:?}", span, path);
 972
 973         match (path.get(0), path.get(1)) {
 974             // `{{root}}::ident::...` on both editions.
 975             // On 2015 `{{root}}` is usually added implicitly.
 976             (Some(fst), Some(snd))
 977                 if fst.ident.name == kw::PathRoot && !snd.ident.is_path_segment_keyword() => {}
 978             // `ident::...` on 2018.
 979             (Some(fst), _)
 980                 if fst.ident.span.rust_2018() && !fst.ident.is_path_segment_keyword() =>
 981             {
 982                 // Insert a placeholder that's later replaced by `self`/`super`/etc.
 983                 path.insert(0, Segment::from_ident(Ident::invalid()));
 984             }
 985             _ => return None,
 986         }
 987
 988         self.make_missing_self_suggestion(span, path.clone(), parent_scope)
 989             .or_else(|| self.make_missing_crate_suggestion(span, path.clone(), parent_scope))
 990             .or_else(|| self.make_missing_super_suggestion(span, path.clone(), parent_scope))
 991             .or_else(|| self.make_external_crate_suggestion(span, path, parent_scope))
 992     }
 993
 994     /// Suggest a missing `self::` if that resolves to an correct module.
 995     ///
 996     /// ```
 997     ///    |
 998     /// LL | use foo::Bar;
 999     ///    |     ^^^ did you mean `self::foo`?
1000     /// ```
1001     fn make_missing_self_suggestion(
1002         &mut self,
1003         span: Span,
1004         mut path: Vec<Segment>,
1005         parent_scope: &ParentScope<'b>,
1006     ) -> Option<(Vec<Segment>, Vec<String>)> {
1007         // Replace first ident with `self` and check if that is valid.
1008         path[0].ident.name = kw::SelfLower;
1009         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1010         debug!("make_missing_self_suggestion: path={:?} result={:?}", path, result);
1011         if let PathResult::Module(..) = result { Some((path, Vec::new())) } else { None }
1012     }
1013
1014     /// Suggests a missing `crate::` if that resolves to an correct module.
1015     ///
1016     /// ```
1017     ///    |
1018     /// LL | use foo::Bar;
1019     ///    |     ^^^ did you mean `crate::foo`?
1020     /// ```
1021     fn make_missing_crate_suggestion(
1022         &mut self,
1023         span: Span,
1024         mut path: Vec<Segment>,
1025         parent_scope: &ParentScope<'b>,
1026     ) -> Option<(Vec<Segment>, Vec<String>)> {
1027         // Replace first ident with `crate` and check if that is valid.
1028         path[0].ident.name = kw::Crate;
1029         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1030         debug!("make_missing_crate_suggestion:  path={:?} result={:?}", path, result);
1031         if let PathResult::Module(..) = result {
1032             Some((
1033                 path,
1034                 vec![
1035                     "`use` statements changed in Rust 2018; read more at \
1036                      <https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-\
1037                      clarity.html>"
1038                         .to_string(),
1039                 ],
1040             ))
1041         } else {
1042             None
1043         }
1044     }
1045
1046     /// Suggests a missing `super::` if that resolves to an correct module.
1047     ///
1048     /// ```
1049     ///    |
1050     /// LL | use foo::Bar;
1051     ///    |     ^^^ did you mean `super::foo`?
1052     /// ```
1053     fn make_missing_super_suggestion(
1054         &mut self,
1055         span: Span,
1056         mut path: Vec<Segment>,
1057         parent_scope: &ParentScope<'b>,
1058     ) -> Option<(Vec<Segment>, Vec<String>)> {
1059         // Replace first ident with `crate` and check if that is valid.
1060         path[0].ident.name = kw::Super;
1061         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1062         debug!("make_missing_super_suggestion:  path={:?} result={:?}", path, result);
1063         if let PathResult::Module(..) = result { Some((path, Vec::new())) } else { None }
1064     }
1065
1066     /// Suggests a missing external crate name if that resolves to an correct module.
1067     ///
1068     /// ```
1069     ///    |
1070     /// LL | use foobar::Baz;
1071     ///    |     ^^^^^^ did you mean `baz::foobar`?
1072     /// ```
1073     ///
1074     /// Used when importing a submodule of an external crate but missing that crate's
1075     /// name as the first part of path.
1076     fn make_external_crate_suggestion(
1077         &mut self,
1078         span: Span,
1079         mut path: Vec<Segment>,
1080         parent_scope: &ParentScope<'b>,
1081     ) -> Option<(Vec<Segment>, Vec<String>)> {
1082         if path[1].ident.span.rust_2015() {
1083             return None;
1084         }
1085
1086         // Sort extern crate names in reverse order to get
1087         // 1) some consistent ordering for emitted dignostics, and
1088         // 2) `std` suggestions before `core` suggestions.
1089         let mut extern_crate_names =
1090             self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
1091         extern_crate_names.sort_by_key(|name| Reverse(name.as_str()));
1092
1093         for name in extern_crate_names.into_iter() {
1094             // Replace first ident with a crate name and check if that is valid.
1095             path[0].ident.name = name;
1096             let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1097             debug!(
1098                 "make_external_crate_suggestion: name={:?} path={:?} result={:?}",
1099                 name, path, result
1100             );
1101             if let PathResult::Module(..) = result {
1102                 return Some((path, Vec::new()));
1103             }
1104         }
1105
1106         None
1107     }
1108
1109     /// Suggests importing a macro from the root of the crate rather than a module within
1110     /// the crate.
1111     ///
1112     /// ```
1113     /// help: a macro with this name exists at the root of the crate
1114     ///    |
1115     /// LL | use issue_59764::makro;
1116     ///    |     ^^^^^^^^^^^^^^^^^^
1117     ///    |
1118     ///    = note: this could be because a macro annotated with `#[macro_export]` will be exported
1119     ///            at the root of the crate instead of the module where it is defined
1120     /// ```
1121     pub(crate) fn check_for_module_export_macro(
1122         &mut self,
1123         directive: &'b ImportDirective<'b>,
1124         module: ModuleOrUniformRoot<'b>,
1125         ident: Ident,
1126     ) -> Option<(Option<Suggestion>, Vec<String>)> {
1127         let mut crate_module = if let ModuleOrUniformRoot::Module(module) = module {
1128             module
1129         } else {
1130             return None;
1131         };
1132
1133         while let Some(parent) = crate_module.parent {
1134             crate_module = parent;
1135         }
1136
1137         if ModuleOrUniformRoot::same_def(ModuleOrUniformRoot::Module(crate_module), module) {
1138             // Don't make a suggestion if the import was already from the root of the
1139             // crate.
1140             return None;
1141         }
1142
1143         let resolutions = self.r.resolutions(crate_module).borrow();
1144         let resolution = resolutions.get(&self.r.new_key(ident, MacroNS))?;
1145         let binding = resolution.borrow().binding()?;
1146         if let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() {
1147             let module_name = crate_module.kind.name().unwrap();
1148             let import = match directive.subclass {
1149                 ImportDirectiveSubclass::SingleImport { source, target, .. }
1150                     if source != target =>
1151                 {
1152                     format!("{} as {}", source, target)
1153                 }
1154                 _ => format!("{}", ident),
1155             };
1156
1157             let mut corrections: Vec<(Span, String)> = Vec::new();
1158             if !directive.is_nested() {
1159                 // Assume this is the easy case of `use issue_59764::foo::makro;` and just remove
1160                 // intermediate segments.
1161                 corrections.push((directive.span, format!("{}::{}", module_name, import)));
1162             } else {
1163                 // Find the binding span (and any trailing commas and spaces).
1164                 //   ie. `use a::b::{c, d, e};`
1165                 //                      ^^^
1166                 let (found_closing_brace, binding_span) = find_span_of_binding_until_next_binding(
1167                     self.r.session,
1168                     directive.span,
1169                     directive.use_span,
1170                 );
1171                 debug!(
1172                     "check_for_module_export_macro: found_closing_brace={:?} binding_span={:?}",
1173                     found_closing_brace, binding_span
1174                 );
1175
1176                 let mut removal_span = binding_span;
1177                 if found_closing_brace {
1178                     // If the binding span ended with a closing brace, as in the below example:
1179                     //   ie. `use a::b::{c, d};`
1180                     //                      ^
1181                     // Then expand the span of characters to remove to include the previous
1182                     // binding's trailing comma.
1183                     //   ie. `use a::b::{c, d};`
1184                     //                    ^^^
1185                     if let Some(previous_span) =
1186                         extend_span_to_previous_binding(self.r.session, binding_span)
1187                     {
1188                         debug!("check_for_module_export_macro: previous_span={:?}", previous_span);
1189                         removal_span = removal_span.with_lo(previous_span.lo());
1190                     }
1191                 }
1192                 debug!("check_for_module_export_macro: removal_span={:?}", removal_span);
1193
1194                 // Remove the `removal_span`.
1195                 corrections.push((removal_span, "".to_string()));
1196
1197                 // Find the span after the crate name and if it has nested imports immediatately
1198                 // after the crate name already.
1199                 //   ie. `use a::b::{c, d};`
1200                 //               ^^^^^^^^^
1201                 //   or  `use a::{b, c, d}};`
1202                 //               ^^^^^^^^^^^
1203                 let (has_nested, after_crate_name) = find_span_immediately_after_crate_name(
1204                     self.r.session,
1205                     module_name,
1206                     directive.use_span,
1207                 );
1208                 debug!(
1209                     "check_for_module_export_macro: has_nested={:?} after_crate_name={:?}",
1210                     has_nested, after_crate_name
1211                 );
1212
1213                 let source_map = self.r.session.source_map();
1214
1215                 // Add the import to the start, with a `{` if required.
1216                 let start_point = source_map.start_point(after_crate_name);
1217                 if let Ok(start_snippet) = source_map.span_to_snippet(start_point) {
1218                     corrections.push((
1219                         start_point,
1220                         if has_nested {
1221                             // In this case, `start_snippet` must equal '{'.
1222                             format!("{}{}, ", start_snippet, import)
1223                         } else {
1224                             // In this case, add a `{`, then the moved import, then whatever
1225                             // was there before.
1226                             format!("{{{}, {}", import, start_snippet)
1227                         },
1228                     ));
1229                 }
1230
1231                 // Add a `};` to the end if nested, matching the `{` added at the start.
1232                 if !has_nested {
1233                     corrections.push((source_map.end_point(after_crate_name), "};".to_string()));
1234                 }
1235             }
1236
1237             let suggestion = Some((
1238                 corrections,
1239                 String::from("a macro with this name exists at the root of the crate"),
1240                 Applicability::MaybeIncorrect,
1241             ));
1242             let note = vec![
1243                 "this could be because a macro annotated with `#[macro_export]` will be exported \
1244                  at the root of the crate instead of the module where it is defined"
1245                     .to_string(),
1246             ];
1247             Some((suggestion, note))
1248         } else {
1249             None
1250         }
1251     }
1252 }
1253
1254 /// Given a `binding_span` of a binding within a use statement:
1255 ///
1256 /// ```
1257 /// use foo::{a, b, c};
1258 ///              ^
1259 /// ```
1260 ///
1261 /// then return the span until the next binding or the end of the statement:
1262 ///
1263 /// ```
1264 /// use foo::{a, b, c};
1265 ///              ^^^
1266 /// ```
1267 pub(crate) fn find_span_of_binding_until_next_binding(
1268     sess: &Session,
1269     binding_span: Span,
1270     use_span: Span,
1271 ) -> (bool, Span) {
1272     let source_map = sess.source_map();
1273
1274     // Find the span of everything after the binding.
1275     //   ie. `a, e};` or `a};`
1276     let binding_until_end = binding_span.with_hi(use_span.hi());
1277
1278     // Find everything after the binding but not including the binding.
1279     //   ie. `, e};` or `};`
1280     let after_binding_until_end = binding_until_end.with_lo(binding_span.hi());
1281
1282     // Keep characters in the span until we encounter something that isn't a comma or
1283     // whitespace.
1284     //   ie. `, ` or ``.
1285     //
1286     // Also note whether a closing brace character was encountered. If there
1287     // was, then later go backwards to remove any trailing commas that are left.
1288     let mut found_closing_brace = false;
1289     let after_binding_until_next_binding =
1290         source_map.span_take_while(after_binding_until_end, |&ch| {
1291             if ch == '}' {
1292                 found_closing_brace = true;
1293             }
1294             ch == ' ' || ch == ','
1295         });
1296
1297     // Combine the two spans.
1298     //   ie. `a, ` or `a`.
1299     //
1300     // Removing these would leave `issue_52891::{d, e};` or `issue_52891::{d, e, };`
1301     let span = binding_span.with_hi(after_binding_until_next_binding.hi());
1302
1303     (found_closing_brace, span)
1304 }
1305
1306 /// Given a `binding_span`, return the span through to the comma or opening brace of the previous
1307 /// binding.
1308 ///
1309 /// ```
1310 /// use foo::a::{a, b, c};
1311 ///               ^^--- binding span
1312 ///               |
1313 ///               returned span
1314 ///
1315 /// use foo::{a, b, c};
1316 ///           --- binding span
1317 /// ```
1318 pub(crate) fn extend_span_to_previous_binding(sess: &Session, binding_span: Span) -> Option<Span> {
1319     let source_map = sess.source_map();
1320
1321     // `prev_source` will contain all of the source that came before the span.
1322     // Then split based on a command and take the first (ie. closest to our span)
1323     // snippet. In the example, this is a space.
1324     let prev_source = source_map.span_to_prev_source(binding_span).ok()?;
1325
1326     let prev_comma = prev_source.rsplit(',').collect::<Vec<_>>();
1327     let prev_starting_brace = prev_source.rsplit('{').collect::<Vec<_>>();
1328     if prev_comma.len() <= 1 || prev_starting_brace.len() <= 1 {
1329         return None;
1330     }
1331
1332     let prev_comma = prev_comma.first().unwrap();
1333     let prev_starting_brace = prev_starting_brace.first().unwrap();
1334
1335     // If the amount of source code before the comma is greater than
1336     // the amount of source code before the starting brace then we've only
1337     // got one item in the nested item (eg. `issue_52891::{self}`).
1338     if prev_comma.len() > prev_starting_brace.len() {
1339         return None;
1340     }
1341
1342     Some(binding_span.with_lo(BytePos(
1343         // Take away the number of bytes for the characters we've found and an
1344         // extra for the comma.
1345         binding_span.lo().0 - (prev_comma.as_bytes().len() as u32) - 1,
1346     )))
1347 }
1348
1349 /// Given a `use_span` of a binding within a use statement, returns the highlighted span and if
1350 /// it is a nested use tree.
1351 ///
1352 /// ```
1353 /// use foo::a::{b, c};
1354 ///          ^^^^^^^^^^ // false
1355 ///
1356 /// use foo::{a, b, c};
1357 ///          ^^^^^^^^^^ // true
1358 ///
1359 /// use foo::{a, b::{c, d}};
1360 ///          ^^^^^^^^^^^^^^^ // true
1361 /// ```
1362 fn find_span_immediately_after_crate_name(
1363     sess: &Session,
1364     module_name: Symbol,
1365     use_span: Span,
1366 ) -> (bool, Span) {
1367     debug!(
1368         "find_span_immediately_after_crate_name: module_name={:?} use_span={:?}",
1369         module_name, use_span
1370     );
1371     let source_map = sess.source_map();
1372
1373     // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
1374     let mut num_colons = 0;
1375     // Find second colon.. `use issue_59764:`
1376     let until_second_colon = source_map.span_take_while(use_span, |c| {
1377         if *c == ':' {
1378             num_colons += 1;
1379         }
1380         match c {
1381             ':' if num_colons == 2 => false,
1382             _ => true,
1383         }
1384     });
1385     // Find everything after the second colon.. `foo::{baz, makro};`
1386     let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
1387
1388     let mut found_a_non_whitespace_character = false;
1389     // Find the first non-whitespace character in `from_second_colon`.. `f`
1390     let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
1391         if found_a_non_whitespace_character {
1392             return false;
1393         }
1394         if !c.is_whitespace() {
1395             found_a_non_whitespace_character = true;
1396         }
1397         true
1398     });
1399
1400     // Find the first `{` in from_second_colon.. `foo::{`
1401     let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
1402
1403     (next_left_bracket == after_second_colon, from_second_colon)
1404 }
1405
1406 /// When an entity with a given name is not available in scope, we search for
1407 /// entities with that name in all crates. This method allows outputting the
1408 /// results of this search in a programmer-friendly way
1409 crate fn show_candidates(
1410     err: &mut DiagnosticBuilder<'_>,
1411     // This is `None` if all placement locations are inside expansions
1412     span: Option<Span>,
1413     candidates: &[ImportSuggestion],
1414     better: bool,
1415     found_use: bool,
1416 ) {
1417     // we want consistent results across executions, but candidates are produced
1418     // by iterating through a hash map, so make sure they are ordered:
1419     let mut path_strings: Vec<_> =
1420         candidates.into_iter().map(|c| path_names_to_string(&c.path)).collect();
1421     path_strings.sort();
1422
1423     let better = if better { "better " } else { "" };
1424     let msg_diff = match path_strings.len() {
1425         1 => " is found in another module, you can import it",
1426         _ => "s are found in other modules, you can import them",
1427     };
1428     let msg = format!("possible {}candidate{} into scope", better, msg_diff);
1429
1430     if let Some(span) = span {
1431         for candidate in &mut path_strings {
1432             // produce an additional newline to separate the new use statement
1433             // from the directly following item.
1434             let additional_newline = if found_use { "" } else { "\n" };
1435             *candidate = format!("use {};\n{}", candidate, additional_newline);
1436         }
1437
1438         err.span_suggestions(span, &msg, path_strings.into_iter(), Applicability::Unspecified);
1439     } else {
1440         let mut msg = msg;
1441         msg.push(':');
1442         for candidate in path_strings {
1443             msg.push('\n');
1444             msg.push_str(&candidate);
1445         }
1446     }
1447 }