src/librustc_resolve/diagnostics.rs

   1 use std::cmp::Reverse;
   2 use std::ptr;
   3
   4 use rustc_ast::ast::{self, Path};
   5 use rustc_ast::util::lev_distance::find_best_match_for_name;
   6 use rustc_ast_pretty::pprust;
   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_middle::bug;
  14 use rustc_middle::ty::{self, DefIdTree};
  15 use rustc_session::Session;
  16 use rustc_span::hygiene::MacroKind;
  17 use rustc_span::source_map::SourceMap;
  18 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  19 use rustc_span::{BytePos, MultiSpan, Span};
  20 use tracing::debug;
  21
  22 use crate::imports::{Import, ImportKind, ImportResolver};
  23 use crate::path_names_to_string;
  24 use crate::{AmbiguityError, AmbiguityErrorMisc, AmbiguityKind};
  25 use crate::{
  26     BindingError, CrateLint, HasGenericParams, MacroRulesScope, Module, ModuleOrUniformRoot,
  27 };
  28 use crate::{NameBinding, NameBindingKind, PrivacyError, VisResolutionError};
  29 use crate::{ParentScope, PathResult, ResolutionError, Resolver, Scope, ScopeSet, Segment};
  30
  31 type Res = def::Res<ast::NodeId>;
  32
  33 /// A vector of spans and replacements, a message and applicability.
  34 crate type Suggestion = (Vec<(Span, String)>, String, Applicability);
  35
  36 /// Potential candidate for an undeclared or out-of-scope label - contains the ident of a
  37 /// similarly named label and whether or not it is reachable.
  38 crate type LabelSuggestion = (Ident, bool);
  39
  40 crate struct TypoSuggestion {
  41     pub candidate: Symbol,
  42     pub res: Res,
  43 }
  44
  45 impl TypoSuggestion {
  46     crate fn from_res(candidate: Symbol, res: Res) -> TypoSuggestion {
  47         TypoSuggestion { candidate, res }
  48     }
  49 }
  50
  51 /// A free importable items suggested in case of resolution failure.
  52 crate struct ImportSuggestion {
  53     pub did: Option<DefId>,
  54     pub descr: &'static str,
  55     pub path: Path,
  56     pub accessible: bool,
  57 }
  58
  59 /// Adjust the impl span so that just the `impl` keyword is taken by removing
  60 /// everything after `<` (`"impl<T> Iterator for A<T> {}" -> "impl"`) and
  61 /// everything after the first whitespace (`"impl Iterator for A" -> "impl"`).
  62 ///
  63 /// *Attention*: the method used is very fragile since it essentially duplicates the work of the
  64 /// parser. If you need to use this function or something similar, please consider updating the
  65 /// `source_map` functions and this function to something more robust.
  66 fn reduce_impl_span_to_impl_keyword(sm: &SourceMap, impl_span: Span) -> Span {
  67     let impl_span = sm.span_until_char(impl_span, '<');
  68     sm.span_until_whitespace(impl_span)
  69 }
  70
  71 impl<'a> Resolver<'a> {
  72     crate fn add_module_candidates(
  73         &mut self,
  74         module: Module<'a>,
  75         names: &mut Vec<TypoSuggestion>,
  76         filter_fn: &impl Fn(Res) -> bool,
  77     ) {
  78         for (key, resolution) in self.resolutions(module).borrow().iter() {
  79             if let Some(binding) = resolution.borrow().binding {
  80                 let res = binding.res();
  81                 if filter_fn(res) {
  82                     names.push(TypoSuggestion::from_res(key.ident.name, res));
  83                 }
  84             }
  85         }
  86     }
  87
  88     /// Combines an error with provided span and emits it.
  89     ///
  90     /// This takes the error provided, combines it with the span and any additional spans inside the
  91     /// error and emits it.
  92     crate fn report_error(&self, span: Span, resolution_error: ResolutionError<'_>) {
  93         self.into_struct_error(span, resolution_error).emit();
  94     }
  95
  96     crate fn into_struct_error(
  97         &self,
  98         span: Span,
  99         resolution_error: ResolutionError<'_>,
 100     ) -> DiagnosticBuilder<'_> {
 101         match resolution_error {
 102             ResolutionError::GenericParamsFromOuterFunction(outer_res, has_generic_params) => {
 103                 let mut err = struct_span_err!(
 104                     self.session,
 105                     span,
 106                     E0401,
 107                     "can't use generic parameters from outer function",
 108                 );
 109                 err.span_label(span, "use of generic parameter from outer function".to_string());
 110
 111                 let sm = self.session.source_map();
 112                 match outer_res {
 113                     Res::SelfTy(maybe_trait_defid, maybe_impl_defid) => {
 114                         if let Some(impl_span) =
 115                             maybe_impl_defid.and_then(|def_id| self.opt_span(def_id))
 116                         {
 117                             err.span_label(
 118                                 reduce_impl_span_to_impl_keyword(sm, impl_span),
 119                                 "`Self` type implicitly declared here, by this `impl`",
 120                             );
 121                         }
 122                         match (maybe_trait_defid, maybe_impl_defid) {
 123                             (Some(_), None) => {
 124                                 err.span_label(span, "can't use `Self` here");
 125                             }
 126                             (_, Some(_)) => {
 127                                 err.span_label(span, "use a type here instead");
 128                             }
 129                             (None, None) => bug!("`impl` without trait nor type?"),
 130                         }
 131                         return err;
 132                     }
 133                     Res::Def(DefKind::TyParam, def_id) => {
 134                         if let Some(span) = self.opt_span(def_id) {
 135                             err.span_label(span, "type parameter from outer function");
 136                         }
 137                     }
 138                     Res::Def(DefKind::ConstParam, def_id) => {
 139                         if let Some(span) = self.opt_span(def_id) {
 140                             err.span_label(span, "const parameter from outer function");
 141                         }
 142                     }
 143                     _ => {
 144                         bug!(
 145                             "GenericParamsFromOuterFunction should only be used with Res::SelfTy, \
 146                             DefKind::TyParam"
 147                         );
 148                     }
 149                 }
 150
 151                 if has_generic_params == HasGenericParams::Yes {
 152                     // Try to retrieve the span of the function signature and generate a new
 153                     // message with a local type or const parameter.
 154                     let sugg_msg = "try using a local generic parameter instead";
 155                     if let Some((sugg_span, snippet)) = sm.generate_local_type_param_snippet(span) {
 156                         // Suggest the modification to the user
 157                         err.span_suggestion(
 158                             sugg_span,
 159                             sugg_msg,
 160                             snippet,
 161                             Applicability::MachineApplicable,
 162                         );
 163                     } else if let Some(sp) = sm.generate_fn_name_span(span) {
 164                         err.span_label(
 165                             sp,
 166                             "try adding a local generic parameter in this method instead"
 167                                 .to_string(),
 168                         );
 169                     } else {
 170                         err.help("try using a local generic parameter instead");
 171                     }
 172                 }
 173
 174                 err
 175             }
 176             ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => {
 177                 let mut err = struct_span_err!(
 178                     self.session,
 179                     span,
 180                     E0403,
 181                     "the name `{}` is already used for a generic \
 182                      parameter in this item's generic parameters",
 183                     name,
 184                 );
 185                 err.span_label(span, "already used");
 186                 err.span_label(first_use_span, format!("first use of `{}`", name));
 187                 err
 188             }
 189             ResolutionError::MethodNotMemberOfTrait(method, trait_) => {
 190                 let mut err = struct_span_err!(
 191                     self.session,
 192                     span,
 193                     E0407,
 194                     "method `{}` is not a member of trait `{}`",
 195                     method,
 196                     trait_
 197                 );
 198                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 199                 err
 200             }
 201             ResolutionError::TypeNotMemberOfTrait(type_, trait_) => {
 202                 let mut err = struct_span_err!(
 203                     self.session,
 204                     span,
 205                     E0437,
 206                     "type `{}` is not a member of trait `{}`",
 207                     type_,
 208                     trait_
 209                 );
 210                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 211                 err
 212             }
 213             ResolutionError::ConstNotMemberOfTrait(const_, trait_) => {
 214                 let mut err = struct_span_err!(
 215                     self.session,
 216                     span,
 217                     E0438,
 218                     "const `{}` is not a member of trait `{}`",
 219                     const_,
 220                     trait_
 221                 );
 222                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 223                 err
 224             }
 225             ResolutionError::VariableNotBoundInPattern(binding_error) => {
 226                 let BindingError { name, target, origin, could_be_path } = binding_error;
 227
 228                 let target_sp = target.iter().copied().collect::<Vec<_>>();
 229                 let origin_sp = origin.iter().copied().collect::<Vec<_>>();
 230
 231                 let msp = MultiSpan::from_spans(target_sp.clone());
 232                 let mut err = struct_span_err!(
 233                     self.session,
 234                     msp,
 235                     E0408,
 236                     "variable `{}` is not bound in all patterns",
 237                     name,
 238                 );
 239                 for sp in target_sp {
 240                     err.span_label(sp, format!("pattern doesn't bind `{}`", name));
 241                 }
 242                 for sp in origin_sp {
 243                     err.span_label(sp, "variable not in all patterns");
 244                 }
 245                 if *could_be_path {
 246                     let help_msg = format!(
 247                         "if you meant to match on a variant or a `const` item, consider \
 248                          making the path in the pattern qualified: `?::{}`",
 249                         name,
 250                     );
 251                     err.span_help(span, &help_msg);
 252                 }
 253                 err
 254             }
 255             ResolutionError::VariableBoundWithDifferentMode(variable_name, first_binding_span) => {
 256                 let mut err = struct_span_err!(
 257                     self.session,
 258                     span,
 259                     E0409,
 260                     "variable `{}` is bound inconsistently across alternatives separated by `|`",
 261                     variable_name
 262                 );
 263                 err.span_label(span, "bound in different ways");
 264                 err.span_label(first_binding_span, "first binding");
 265                 err
 266             }
 267             ResolutionError::IdentifierBoundMoreThanOnceInParameterList(identifier) => {
 268                 let mut err = struct_span_err!(
 269                     self.session,
 270                     span,
 271                     E0415,
 272                     "identifier `{}` is bound more than once in this parameter list",
 273                     identifier
 274                 );
 275                 err.span_label(span, "used as parameter more than once");
 276                 err
 277             }
 278             ResolutionError::IdentifierBoundMoreThanOnceInSamePattern(identifier) => {
 279                 let mut err = struct_span_err!(
 280                     self.session,
 281                     span,
 282                     E0416,
 283                     "identifier `{}` is bound more than once in the same pattern",
 284                     identifier
 285                 );
 286                 err.span_label(span, "used in a pattern more than once");
 287                 err
 288             }
 289             ResolutionError::UndeclaredLabel { name, suggestion } => {
 290                 let mut err = struct_span_err!(
 291                     self.session,
 292                     span,
 293                     E0426,
 294                     "use of undeclared label `{}`",
 295                     name
 296                 );
 297
 298                 err.span_label(span, format!("undeclared label `{}`", name));
 299
 300                 match suggestion {
 301                     // A reachable label with a similar name exists.
 302                     Some((ident, true)) => {
 303                         err.span_label(ident.span, "a label with a similar name is reachable");
 304                         err.span_suggestion(
 305                             span,
 306                             "try using similarly named label",
 307                             ident.name.to_string(),
 308                             Applicability::MaybeIncorrect,
 309                         );
 310                     }
 311                     // An unreachable label with a similar name exists.
 312                     Some((ident, false)) => {
 313                         err.span_label(
 314                             ident.span,
 315                             "a label with a similar name exists but is unreachable",
 316                         );
 317                     }
 318                     // No similarly-named labels exist.
 319                     None => (),
 320                 }
 321
 322                 err
 323             }
 324             ResolutionError::SelfImportsOnlyAllowedWithin { root, span_with_rename } => {
 325                 let mut err = struct_span_err!(
 326                     self.session,
 327                     span,
 328                     E0429,
 329                     "{}",
 330                     "`self` imports are only allowed within a { } list"
 331                 );
 332
 333                 // None of the suggestions below would help with a case like `use self`.
 334                 if !root {
 335                     // use foo::bar::self        -> foo::bar
 336                     // use foo::bar::self as abc -> foo::bar as abc
 337                     err.span_suggestion(
 338                         span,
 339                         "consider importing the module directly",
 340                         "".to_string(),
 341                         Applicability::MachineApplicable,
 342                     );
 343
 344                     // use foo::bar::self        -> foo::bar::{self}
 345                     // use foo::bar::self as abc -> foo::bar::{self as abc}
 346                     let braces = vec![
 347                         (span_with_rename.shrink_to_lo(), "{".to_string()),
 348                         (span_with_rename.shrink_to_hi(), "}".to_string()),
 349                     ];
 350                     err.multipart_suggestion(
 351                         "alternatively, use the multi-path `use` syntax to import `self`",
 352                         braces,
 353                         Applicability::MachineApplicable,
 354                     );
 355                 }
 356                 err
 357             }
 358             ResolutionError::SelfImportCanOnlyAppearOnceInTheList => {
 359                 let mut err = struct_span_err!(
 360                     self.session,
 361                     span,
 362                     E0430,
 363                     "`self` import can only appear once in an import list"
 364                 );
 365                 err.span_label(span, "can only appear once in an import list");
 366                 err
 367             }
 368             ResolutionError::SelfImportOnlyInImportListWithNonEmptyPrefix => {
 369                 let mut err = struct_span_err!(
 370                     self.session,
 371                     span,
 372                     E0431,
 373                     "`self` import can only appear in an import list with \
 374                                                 a non-empty prefix"
 375                 );
 376                 err.span_label(span, "can only appear in an import list with a non-empty prefix");
 377                 err
 378             }
 379             ResolutionError::FailedToResolve { label, suggestion } => {
 380                 let mut err =
 381                     struct_span_err!(self.session, span, E0433, "failed to resolve: {}", &label);
 382                 err.span_label(span, label);
 383
 384                 if let Some((suggestions, msg, applicability)) = suggestion {
 385                     err.multipart_suggestion(&msg, suggestions, applicability);
 386                 }
 387
 388                 err
 389             }
 390             ResolutionError::CannotCaptureDynamicEnvironmentInFnItem => {
 391                 let mut err = struct_span_err!(
 392                     self.session,
 393                     span,
 394                     E0434,
 395                     "{}",
 396                     "can't capture dynamic environment in a fn item"
 397                 );
 398                 err.help("use the `|| { ... }` closure form instead");
 399                 err
 400             }
 401             ResolutionError::AttemptToUseNonConstantValueInConstant => {
 402                 let mut err = struct_span_err!(
 403                     self.session,
 404                     span,
 405                     E0435,
 406                     "attempt to use a non-constant value in a constant"
 407                 );
 408                 err.span_label(span, "non-constant value");
 409                 err
 410             }
 411             ResolutionError::BindingShadowsSomethingUnacceptable(what_binding, name, binding) => {
 412                 let res = binding.res();
 413                 let shadows_what = res.descr();
 414                 let mut err = struct_span_err!(
 415                     self.session,
 416                     span,
 417                     E0530,
 418                     "{}s cannot shadow {}s",
 419                     what_binding,
 420                     shadows_what
 421                 );
 422                 err.span_label(
 423                     span,
 424                     format!("cannot be named the same as {} {}", res.article(), shadows_what),
 425                 );
 426                 let participle = if binding.is_import() { "imported" } else { "defined" };
 427                 let msg = format!("the {} `{}` is {} here", shadows_what, name, participle);
 428                 err.span_label(binding.span, msg);
 429                 err
 430             }
 431             ResolutionError::ForwardDeclaredTyParam => {
 432                 let mut err = struct_span_err!(
 433                     self.session,
 434                     span,
 435                     E0128,
 436                     "type parameters with a default cannot use \
 437                                                 forward declared identifiers"
 438                 );
 439                 err.span_label(
 440                     span,
 441                     "defaulted type parameters cannot be forward declared".to_string(),
 442                 );
 443                 err
 444             }
 445             ResolutionError::ParamInTyOfConstParam(name) => {
 446                 let mut err = struct_span_err!(
 447                     self.session,
 448                     span,
 449                     E0770,
 450                     "the type of const parameters must not depend on other generic parameters"
 451                 );
 452                 err.span_label(
 453                     span,
 454                     format!("the type must not depend on the parameter `{}`", name),
 455                 );
 456                 err
 457             }
 458             ResolutionError::ParamInAnonConstInTyDefault(name) => {
 459                 let mut err = self.session.struct_span_err(
 460                     span,
 461                     "constant values inside of type parameter defaults must not depend on generic parameters",
 462                 );
 463                 err.span_label(
 464                     span,
 465                     format!("the anonymous constant must not depend on the parameter `{}`", name),
 466                 );
 467                 err
 468             }
 469             ResolutionError::ParamInNonTrivialAnonConst(name) => {
 470                 let mut err = self.session.struct_span_err(
 471                     span,
 472                     "generic parameters must not be used inside of non trivial constant values",
 473                 );
 474                 err.span_label(
 475                     span,
 476                     &format!(
 477                         "non-trivial anonymous constants must not depend on the parameter `{}`",
 478                         name
 479                     ),
 480                 );
 481                 err.help(
 482                     &format!("it is currently only allowed to use either `{0}` or `{{ {0} }}` as generic constants", name)
 483                 );
 484                 err
 485             }
 486             ResolutionError::SelfInTyParamDefault => {
 487                 let mut err = struct_span_err!(
 488                     self.session,
 489                     span,
 490                     E0735,
 491                     "type parameters cannot use `Self` in their defaults"
 492                 );
 493                 err.span_label(span, "`Self` in type parameter default".to_string());
 494                 err
 495             }
 496             ResolutionError::UnreachableLabel { name, definition_span, suggestion } => {
 497                 let mut err = struct_span_err!(
 498                     self.session,
 499                     span,
 500                     E0767,
 501                     "use of unreachable label `{}`",
 502                     name,
 503                 );
 504
 505                 err.span_label(definition_span, "unreachable label defined here");
 506                 err.span_label(span, format!("unreachable label `{}`", name));
 507                 err.note(
 508                     "labels are unreachable through functions, closures, async blocks and modules",
 509                 );
 510
 511                 match suggestion {
 512                     // A reachable label with a similar name exists.
 513                     Some((ident, true)) => {
 514                         err.span_label(ident.span, "a label with a similar name is reachable");
 515                         err.span_suggestion(
 516                             span,
 517                             "try using similarly named label",
 518                             ident.name.to_string(),
 519                             Applicability::MaybeIncorrect,
 520                         );
 521                     }
 522                     // An unreachable label with a similar name exists.
 523                     Some((ident, false)) => {
 524                         err.span_label(
 525                             ident.span,
 526                             "a label with a similar name exists but is also unreachable",
 527                         );
 528                     }
 529                     // No similarly-named labels exist.
 530                     None => (),
 531                 }
 532
 533                 err
 534             }
 535         }
 536     }
 537
 538     crate fn report_vis_error(&self, vis_resolution_error: VisResolutionError<'_>) {
 539         match vis_resolution_error {
 540             VisResolutionError::Relative2018(span, path) => {
 541                 let mut err = self.session.struct_span_err(
 542                     span,
 543                     "relative paths are not supported in visibilities on 2018 edition",
 544                 );
 545                 err.span_suggestion(
 546                     path.span,
 547                     "try",
 548                     format!("crate::{}", pprust::path_to_string(&path)),
 549                     Applicability::MaybeIncorrect,
 550                 );
 551                 err
 552             }
 553             VisResolutionError::AncestorOnly(span) => struct_span_err!(
 554                 self.session,
 555                 span,
 556                 E0742,
 557                 "visibilities can only be restricted to ancestor modules"
 558             ),
 559             VisResolutionError::FailedToResolve(span, label, suggestion) => {
 560                 self.into_struct_error(span, ResolutionError::FailedToResolve { label, suggestion })
 561             }
 562             VisResolutionError::ExpectedFound(span, path_str, res) => {
 563                 let mut err = struct_span_err!(
 564                     self.session,
 565                     span,
 566                     E0577,
 567                     "expected module, found {} `{}`",
 568                     res.descr(),
 569                     path_str
 570                 );
 571                 err.span_label(span, "not a module");
 572                 err
 573             }
 574             VisResolutionError::Indeterminate(span) => struct_span_err!(
 575                 self.session,
 576                 span,
 577                 E0578,
 578                 "cannot determine resolution for the visibility"
 579             ),
 580             VisResolutionError::ModuleOnly(span) => {
 581                 self.session.struct_span_err(span, "visibility must resolve to a module")
 582             }
 583         }
 584         .emit()
 585     }
 586
 587     /// Lookup typo candidate in scope for a macro or import.
 588     fn early_lookup_typo_candidate(
 589         &mut self,
 590         scope_set: ScopeSet,
 591         parent_scope: &ParentScope<'a>,
 592         ident: Ident,
 593         filter_fn: &impl Fn(Res) -> bool,
 594     ) -> Option<TypoSuggestion> {
 595         let mut suggestions = Vec::new();
 596         self.visit_scopes(scope_set, parent_scope, ident, |this, scope, use_prelude, _| {
 597             match scope {
 598                 Scope::DeriveHelpers(expn_id) => {
 599                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 600                     if filter_fn(res) {
 601                         suggestions.extend(
 602                             this.helper_attrs
 603                                 .get(&expn_id)
 604                                 .into_iter()
 605                                 .flatten()
 606                                 .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 607                         );
 608                     }
 609                 }
 610                 Scope::DeriveHelpersCompat => {
 611                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 612                     if filter_fn(res) {
 613                         for derive in parent_scope.derives {
 614                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
 615                             if let Ok((Some(ext), _)) = this.resolve_macro_path(
 616                                 derive,
 617                                 Some(MacroKind::Derive),
 618                                 parent_scope,
 619                                 false,
 620                                 false,
 621                             ) {
 622                                 suggestions.extend(
 623                                     ext.helper_attrs
 624                                         .iter()
 625                                         .map(|name| TypoSuggestion::from_res(*name, res)),
 626                                 );
 627                             }
 628                         }
 629                     }
 630                 }
 631                 Scope::MacroRules(macro_rules_scope) => {
 632                     if let MacroRulesScope::Binding(macro_rules_binding) = macro_rules_scope {
 633                         let res = macro_rules_binding.binding.res();
 634                         if filter_fn(res) {
 635                             suggestions
 636                                 .push(TypoSuggestion::from_res(macro_rules_binding.ident.name, res))
 637                         }
 638                     }
 639                 }
 640                 Scope::CrateRoot => {
 641                     let root_ident = Ident::new(kw::PathRoot, ident.span);
 642                     let root_module = this.resolve_crate_root(root_ident);
 643                     this.add_module_candidates(root_module, &mut suggestions, filter_fn);
 644                 }
 645                 Scope::Module(module) => {
 646                     this.add_module_candidates(module, &mut suggestions, filter_fn);
 647                 }
 648                 Scope::RegisteredAttrs => {
 649                     let res = Res::NonMacroAttr(NonMacroAttrKind::Registered);
 650                     if filter_fn(res) {
 651                         suggestions.extend(
 652                             this.registered_attrs
 653                                 .iter()
 654                                 .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 655                         );
 656                     }
 657                 }
 658                 Scope::MacroUsePrelude => {
 659                     suggestions.extend(this.macro_use_prelude.iter().filter_map(
 660                         |(name, binding)| {
 661                             let res = binding.res();
 662                             filter_fn(res).then_some(TypoSuggestion::from_res(*name, res))
 663                         },
 664                     ));
 665                 }
 666                 Scope::BuiltinAttrs => {
 667                     let res = Res::NonMacroAttr(NonMacroAttrKind::Builtin);
 668                     if filter_fn(res) {
 669                         suggestions.extend(
 670                             BUILTIN_ATTRIBUTES
 671                                 .iter()
 672                                 .map(|(name, ..)| TypoSuggestion::from_res(*name, res)),
 673                         );
 674                     }
 675                 }
 676                 Scope::ExternPrelude => {
 677                     suggestions.extend(this.extern_prelude.iter().filter_map(|(ident, _)| {
 678                         let res = Res::Def(DefKind::Mod, DefId::local(CRATE_DEF_INDEX));
 679                         filter_fn(res).then_some(TypoSuggestion::from_res(ident.name, res))
 680                     }));
 681                 }
 682                 Scope::ToolPrelude => {
 683                     let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
 684                     suggestions.extend(
 685                         this.registered_tools
 686                             .iter()
 687                             .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 688                     );
 689                 }
 690                 Scope::StdLibPrelude => {
 691                     if let Some(prelude) = this.prelude {
 692                         let mut tmp_suggestions = Vec::new();
 693                         this.add_module_candidates(prelude, &mut tmp_suggestions, filter_fn);
 694                         suggestions.extend(
 695                             tmp_suggestions
 696                                 .into_iter()
 697                                 .filter(|s| use_prelude || this.is_builtin_macro(s.res)),
 698                         );
 699                     }
 700                 }
 701                 Scope::BuiltinTypes => {
 702                     let primitive_types = &this.primitive_type_table.primitive_types;
 703                     suggestions.extend(primitive_types.iter().flat_map(|(name, prim_ty)| {
 704                         let res = Res::PrimTy(*prim_ty);
 705                         filter_fn(res).then_some(TypoSuggestion::from_res(*name, res))
 706                     }))
 707                 }
 708             }
 709
 710             None::<()>
 711         });
 712
 713         // Make sure error reporting is deterministic.
 714         suggestions.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
 715
 716         match find_best_match_for_name(
 717             suggestions.iter().map(|suggestion| &suggestion.candidate),
 718             ident.name,
 719             None,
 720         ) {
 721             Some(found) if found != ident.name => {
 722                 suggestions.into_iter().find(|suggestion| suggestion.candidate == found)
 723             }
 724             _ => None,
 725         }
 726     }
 727
 728     fn lookup_import_candidates_from_module<FilterFn>(
 729         &mut self,
 730         lookup_ident: Ident,
 731         namespace: Namespace,
 732         parent_scope: &ParentScope<'a>,
 733         start_module: Module<'a>,
 734         crate_name: Ident,
 735         filter_fn: FilterFn,
 736     ) -> Vec<ImportSuggestion>
 737     where
 738         FilterFn: Fn(Res) -> bool,
 739     {
 740         let mut candidates = Vec::new();
 741         let mut seen_modules = FxHashSet::default();
 742         let not_local_module = crate_name.name != kw::Crate;
 743         let mut worklist =
 744             vec![(start_module, Vec::<ast::PathSegment>::new(), true, not_local_module)];
 745         let mut worklist_via_import = vec![];
 746
 747         while let Some((in_module, path_segments, accessible, in_module_is_extern)) =
 748             match worklist.pop() {
 749                 None => worklist_via_import.pop(),
 750                 Some(x) => Some(x),
 751             }
 752         {
 753             // We have to visit module children in deterministic order to avoid
 754             // instabilities in reported imports (#43552).
 755             in_module.for_each_child(self, |this, ident, ns, name_binding| {
 756                 // avoid non-importable candidates
 757                 if !name_binding.is_importable() {
 758                     return;
 759                 }
 760
 761                 let child_accessible =
 762                     accessible && this.is_accessible_from(name_binding.vis, parent_scope.module);
 763
 764                 // do not venture inside inaccessible items of other crates
 765                 if in_module_is_extern && !child_accessible {
 766                     return;
 767                 }
 768
 769                 let via_import = name_binding.is_import() && !name_binding.is_extern_crate();
 770
 771                 // There is an assumption elsewhere that paths of variants are in the enum's
 772                 // declaration and not imported. With this assumption, the variant component is
 773                 // chopped and the rest of the path is assumed to be the enum's own path. For
 774                 // errors where a variant is used as the type instead of the enum, this causes
 775                 // funny looking invalid suggestions, i.e `foo` instead of `foo::MyEnum`.
 776                 if via_import && name_binding.is_possibly_imported_variant() {
 777                     return;
 778                 }
 779
 780                 // collect results based on the filter function
 781                 // avoid suggesting anything from the same module in which we are resolving
 782                 if ident.name == lookup_ident.name
 783                     && ns == namespace
 784                     && !ptr::eq(in_module, parent_scope.module)
 785                 {
 786                     let res = name_binding.res();
 787                     if filter_fn(res) {
 788                         // create the path
 789                         let mut segms = path_segments.clone();
 790                         if lookup_ident.span.rust_2018() {
 791                             // crate-local absolute paths start with `crate::` in edition 2018
 792                             // FIXME: may also be stabilized for Rust 2015 (Issues #45477, #44660)
 793                             segms.insert(0, ast::PathSegment::from_ident(crate_name));
 794                         }
 795
 796                         segms.push(ast::PathSegment::from_ident(ident));
 797                         let path = Path { span: name_binding.span, segments: segms };
 798                         let did = match res {
 799                             Res::Def(DefKind::Ctor(..), did) => this.parent(did),
 800                             _ => res.opt_def_id(),
 801                         };
 802
 803                         if child_accessible {
 804                             // Remove invisible match if exists
 805                             if let Some(idx) = candidates
 806                                 .iter()
 807                                 .position(|v: &ImportSuggestion| v.did == did && !v.accessible)
 808                             {
 809                                 candidates.remove(idx);
 810                             }
 811                         }
 812
 813                         if candidates.iter().all(|v: &ImportSuggestion| v.did != did) {
 814                             candidates.push(ImportSuggestion {
 815                                 did,
 816                                 descr: res.descr(),
 817                                 path,
 818                                 accessible: child_accessible,
 819                             });
 820                         }
 821                     }
 822                 }
 823
 824                 // collect submodules to explore
 825                 if let Some(module) = name_binding.module() {
 826                     // form the path
 827                     let mut path_segments = path_segments.clone();
 828                     path_segments.push(ast::PathSegment::from_ident(ident));
 829
 830                     let is_extern_crate_that_also_appears_in_prelude =
 831                         name_binding.is_extern_crate() && lookup_ident.span.rust_2018();
 832
 833                     if !is_extern_crate_that_also_appears_in_prelude {
 834                         let is_extern = in_module_is_extern || name_binding.is_extern_crate();
 835                         // add the module to the lookup
 836                         if seen_modules.insert(module.def_id().unwrap()) {
 837                             if via_import { &mut worklist_via_import } else { &mut worklist }
 838                                 .push((module, path_segments, child_accessible, is_extern));
 839                         }
 840                     }
 841                 }
 842             })
 843         }
 844
 845         // If only some candidates are accessible, take just them
 846         if !candidates.iter().all(|v: &ImportSuggestion| !v.accessible) {
 847             candidates = candidates.into_iter().filter(|x| x.accessible).collect();
 848         }
 849
 850         candidates
 851     }
 852
 853     /// When name resolution fails, this method can be used to look up candidate
 854     /// entities with the expected name. It allows filtering them using the
 855     /// supplied predicate (which should be used to only accept the types of
 856     /// definitions expected, e.g., traits). The lookup spans across all crates.
 857     ///
 858     /// N.B., the method does not look into imports, but this is not a problem,
 859     /// since we report the definitions (thus, the de-aliased imports).
 860     crate fn lookup_import_candidates<FilterFn>(
 861         &mut self,
 862         lookup_ident: Ident,
 863         namespace: Namespace,
 864         parent_scope: &ParentScope<'a>,
 865         filter_fn: FilterFn,
 866     ) -> Vec<ImportSuggestion>
 867     where
 868         FilterFn: Fn(Res) -> bool,
 869     {
 870         let mut suggestions = self.lookup_import_candidates_from_module(
 871             lookup_ident,
 872             namespace,
 873             parent_scope,
 874             self.graph_root,
 875             Ident::with_dummy_span(kw::Crate),
 876             &filter_fn,
 877         );
 878
 879         if lookup_ident.span.rust_2018() {
 880             let extern_prelude_names = self.extern_prelude.clone();
 881             for (ident, _) in extern_prelude_names.into_iter() {
 882                 if ident.span.from_expansion() {
 883                     // Idents are adjusted to the root context before being
 884                     // resolved in the extern prelude, so reporting this to the
 885                     // user is no help. This skips the injected
 886                     // `extern crate std` in the 2018 edition, which would
 887                     // otherwise cause duplicate suggestions.
 888                     continue;
 889                 }
 890                 if let Some(crate_id) = self.crate_loader.maybe_process_path_extern(ident.name) {
 891                     let crate_root =
 892                         self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
 893                     suggestions.extend(self.lookup_import_candidates_from_module(
 894                         lookup_ident,
 895                         namespace,
 896                         parent_scope,
 897                         crate_root,
 898                         ident,
 899                         &filter_fn,
 900                     ));
 901                 }
 902             }
 903         }
 904
 905         suggestions
 906     }
 907
 908     crate fn unresolved_macro_suggestions(
 909         &mut self,
 910         err: &mut DiagnosticBuilder<'a>,
 911         macro_kind: MacroKind,
 912         parent_scope: &ParentScope<'a>,
 913         ident: Ident,
 914     ) {
 915         let is_expected = &|res: Res| res.macro_kind() == Some(macro_kind);
 916         let suggestion = self.early_lookup_typo_candidate(
 917             ScopeSet::Macro(macro_kind),
 918             parent_scope,
 919             ident,
 920             is_expected,
 921         );
 922         self.add_typo_suggestion(err, suggestion, ident.span);
 923
 924         if macro_kind == MacroKind::Derive && (ident.name == sym::Send || ident.name == sym::Sync) {
 925             let msg = format!("unsafe traits like `{}` should be implemented explicitly", ident);
 926             err.span_note(ident.span, &msg);
 927         }
 928         if self.macro_names.contains(&ident.normalize_to_macros_2_0()) {
 929             err.help("have you added the `#[macro_use]` on the module/import?");
 930         }
 931     }
 932
 933     crate fn add_typo_suggestion(
 934         &self,
 935         err: &mut DiagnosticBuilder<'_>,
 936         suggestion: Option<TypoSuggestion>,
 937         span: Span,
 938     ) -> bool {
 939         let suggestion = match suggestion {
 940             None => return false,
 941             // We shouldn't suggest underscore.
 942             Some(suggestion) if suggestion.candidate == kw::Underscore => return false,
 943             Some(suggestion) => suggestion,
 944         };
 945         let def_span = suggestion.res.opt_def_id().and_then(|def_id| match def_id.krate {
 946             LOCAL_CRATE => self.opt_span(def_id),
 947             _ => Some(
 948                 self.session
 949                     .source_map()
 950                     .guess_head_span(self.cstore().get_span_untracked(def_id, self.session)),
 951             ),
 952         });
 953         if let Some(def_span) = def_span {
 954             if span.overlaps(def_span) {
 955                 // Don't suggest typo suggestion for itself like in the followoing:
 956                 // error[E0423]: expected function, tuple struct or tuple variant, found struct `X`
 957                 //   --> $DIR/issue-64792-bad-unicode-ctor.rs:3:14
 958                 //    |
 959                 // LL | struct X {}
 960                 //    | ----------- `X` defined here
 961                 // LL |
 962                 // LL | const Y: X = X("ö");
 963                 //    | -------------^^^^^^- similarly named constant `Y` defined here
 964                 //    |
 965                 // help: use struct literal syntax instead
 966                 //    |
 967                 // LL | const Y: X = X {};
 968                 //    |              ^^^^
 969                 // help: a constant with a similar name exists
 970                 //    |
 971                 // LL | const Y: X = Y("ö");
 972                 //    |              ^
 973                 return false;
 974             }
 975             err.span_label(
 976                 self.session.source_map().guess_head_span(def_span),
 977                 &format!(
 978                     "similarly named {} `{}` defined here",
 979                     suggestion.res.descr(),
 980                     suggestion.candidate.as_str(),
 981                 ),
 982             );
 983         }
 984         let msg = format!(
 985             "{} {} with a similar name exists",
 986             suggestion.res.article(),
 987             suggestion.res.descr()
 988         );
 989         err.span_suggestion(
 990             span,
 991             &msg,
 992             suggestion.candidate.to_string(),
 993             Applicability::MaybeIncorrect,
 994         );
 995         true
 996     }
 997
 998     fn binding_description(&self, b: &NameBinding<'_>, ident: Ident, from_prelude: bool) -> String {
 999         let res = b.res();
1000         if b.span.is_dummy() {
1001             let add_built_in = match b.res() {
1002                 // These already contain the "built-in" prefix or look bad with it.
1003                 Res::NonMacroAttr(..) | Res::PrimTy(..) | Res::ToolMod => false,
1004                 _ => true,
1005             };
1006             let (built_in, from) = if from_prelude {
1007                 ("", " from prelude")
1008             } else if b.is_extern_crate()
1009                 && !b.is_import()
1010                 && self.session.opts.externs.get(&ident.as_str()).is_some()
1011             {
1012                 ("", " passed with `--extern`")
1013             } else if add_built_in {
1014                 (" built-in", "")
1015             } else {
1016                 ("", "")
1017             };
1018
1019             let article = if built_in.is_empty() { res.article() } else { "a" };
1020             format!(
1021                 "{a}{built_in} {thing}{from}",
1022                 a = article,
1023                 thing = res.descr(),
1024                 built_in = built_in,
1025                 from = from
1026             )
1027         } else {
1028             let introduced = if b.is_import() { "imported" } else { "defined" };
1029             format!("the {thing} {introduced} here", thing = res.descr(), introduced = introduced)
1030         }
1031     }
1032
1033     crate fn report_ambiguity_error(&self, ambiguity_error: &AmbiguityError<'_>) {
1034         let AmbiguityError { kind, ident, b1, b2, misc1, misc2 } = *ambiguity_error;
1035         let (b1, b2, misc1, misc2, swapped) = if b2.span.is_dummy() && !b1.span.is_dummy() {
1036             // We have to print the span-less alternative first, otherwise formatting looks bad.
1037             (b2, b1, misc2, misc1, true)
1038         } else {
1039             (b1, b2, misc1, misc2, false)
1040         };
1041
1042         let mut err = struct_span_err!(
1043             self.session,
1044             ident.span,
1045             E0659,
1046             "`{ident}` is ambiguous ({why})",
1047             ident = ident,
1048             why = kind.descr()
1049         );
1050         err.span_label(ident.span, "ambiguous name");
1051
1052         let mut could_refer_to = |b: &NameBinding<'_>, misc: AmbiguityErrorMisc, also: &str| {
1053             let what = self.binding_description(b, ident, misc == AmbiguityErrorMisc::FromPrelude);
1054             let note_msg = format!(
1055                 "`{ident}` could{also} refer to {what}",
1056                 ident = ident,
1057                 also = also,
1058                 what = what
1059             );
1060
1061             let thing = b.res().descr();
1062             let mut help_msgs = Vec::new();
1063             if b.is_glob_import()
1064                 && (kind == AmbiguityKind::GlobVsGlob
1065                     || kind == AmbiguityKind::GlobVsExpanded
1066                     || kind == AmbiguityKind::GlobVsOuter && swapped != also.is_empty())
1067             {
1068                 help_msgs.push(format!(
1069                     "consider adding an explicit import of \
1070                      `{ident}` to disambiguate",
1071                     ident = ident
1072                 ))
1073             }
1074             if b.is_extern_crate() && ident.span.rust_2018() {
1075                 help_msgs.push(format!(
1076                     "use `::{ident}` to refer to this {thing} unambiguously",
1077                     ident = ident,
1078                     thing = thing,
1079                 ))
1080             }
1081             if misc == AmbiguityErrorMisc::SuggestCrate {
1082                 help_msgs.push(format!(
1083                     "use `crate::{ident}` to refer to this {thing} unambiguously",
1084                     ident = ident,
1085                     thing = thing,
1086                 ))
1087             } else if misc == AmbiguityErrorMisc::SuggestSelf {
1088                 help_msgs.push(format!(
1089                     "use `self::{ident}` to refer to this {thing} unambiguously",
1090                     ident = ident,
1091                     thing = thing,
1092                 ))
1093             }
1094
1095             err.span_note(b.span, &note_msg);
1096             for (i, help_msg) in help_msgs.iter().enumerate() {
1097                 let or = if i == 0 { "" } else { "or " };
1098                 err.help(&format!("{}{}", or, help_msg));
1099             }
1100         };
1101
1102         could_refer_to(b1, misc1, "");
1103         could_refer_to(b2, misc2, " also");
1104         err.emit();
1105     }
1106
1107     /// If the binding refers to a tuple struct constructor with fields,
1108     /// returns the span of its fields.
1109     fn ctor_fields_span(&self, binding: &NameBinding<'_>) -> Option<Span> {
1110         if let NameBindingKind::Res(
1111             Res::Def(DefKind::Ctor(CtorOf::Struct, CtorKind::Fn), ctor_def_id),
1112             _,
1113         ) = binding.kind
1114         {
1115             let def_id = (&*self).parent(ctor_def_id).expect("no parent for a constructor");
1116             let fields = self.field_names.get(&def_id)?;
1117             let first_field = fields.first()?; // Handle `struct Foo()`
1118             return Some(fields.iter().fold(first_field.span, |acc, field| acc.to(field.span)));
1119         }
1120         None
1121     }
1122
1123     crate fn report_privacy_error(&self, privacy_error: &PrivacyError<'_>) {
1124         let PrivacyError { ident, binding, .. } = *privacy_error;
1125
1126         let res = binding.res();
1127         let ctor_fields_span = self.ctor_fields_span(binding);
1128         let plain_descr = res.descr().to_string();
1129         let nonimport_descr =
1130             if ctor_fields_span.is_some() { plain_descr + " constructor" } else { plain_descr };
1131         let import_descr = nonimport_descr.clone() + " import";
1132         let get_descr =
1133             |b: &NameBinding<'_>| if b.is_import() { &import_descr } else { &nonimport_descr };
1134
1135         // Print the primary message.
1136         let descr = get_descr(binding);
1137         let mut err =
1138             struct_span_err!(self.session, ident.span, E0603, "{} `{}` is private", descr, ident);
1139         err.span_label(ident.span, &format!("private {}", descr));
1140         if let Some(span) = ctor_fields_span {
1141             err.span_label(span, "a constructor is private if any of the fields is private");
1142         }
1143
1144         // Print the whole import chain to make it easier to see what happens.
1145         let first_binding = binding;
1146         let mut next_binding = Some(binding);
1147         let mut next_ident = ident;
1148         while let Some(binding) = next_binding {
1149             let name = next_ident;
1150             next_binding = match binding.kind {
1151                 _ if res == Res::Err => None,
1152                 NameBindingKind::Import { binding, import, .. } => match import.kind {
1153                     _ if binding.span.is_dummy() => None,
1154                     ImportKind::Single { source, .. } => {
1155                         next_ident = source;
1156                         Some(binding)
1157                     }
1158                     ImportKind::Glob { .. } | ImportKind::MacroUse => Some(binding),
1159                     ImportKind::ExternCrate { .. } => None,
1160                 },
1161                 _ => None,
1162             };
1163
1164             let first = ptr::eq(binding, first_binding);
1165             let descr = get_descr(binding);
1166             let msg = format!(
1167                 "{and_refers_to}the {item} `{name}`{which} is defined here{dots}",
1168                 and_refers_to = if first { "" } else { "...and refers to " },
1169                 item = descr,
1170                 name = name,
1171                 which = if first { "" } else { " which" },
1172                 dots = if next_binding.is_some() { "..." } else { "" },
1173             );
1174             let def_span = self.session.source_map().guess_head_span(binding.span);
1175             let mut note_span = MultiSpan::from_span(def_span);
1176             if !first && binding.vis == ty::Visibility::Public {
1177                 note_span.push_span_label(def_span, "consider importing it directly".into());
1178             }
1179             err.span_note(note_span, &msg);
1180         }
1181
1182         err.emit();
1183     }
1184 }
1185
1186 impl<'a, 'b> ImportResolver<'a, 'b> {
1187     /// Adds suggestions for a path that cannot be resolved.
1188     pub(crate) fn make_path_suggestion(
1189         &mut self,
1190         span: Span,
1191         mut path: Vec<Segment>,
1192         parent_scope: &ParentScope<'b>,
1193     ) -> Option<(Vec<Segment>, Vec<String>)> {
1194         debug!("make_path_suggestion: span={:?} path={:?}", span, path);
1195
1196         match (path.get(0), path.get(1)) {
1197             // `{{root}}::ident::...` on both editions.
1198             // On 2015 `{{root}}` is usually added implicitly.
1199             (Some(fst), Some(snd))
1200                 if fst.ident.name == kw::PathRoot && !snd.ident.is_path_segment_keyword() => {}
1201             // `ident::...` on 2018.
1202             (Some(fst), _)
1203                 if fst.ident.span.rust_2018() && !fst.ident.is_path_segment_keyword() =>
1204             {
1205                 // Insert a placeholder that's later replaced by `self`/`super`/etc.
1206                 path.insert(0, Segment::from_ident(Ident::invalid()));
1207             }
1208             _ => return None,
1209         }
1210
1211         self.make_missing_self_suggestion(span, path.clone(), parent_scope)
1212             .or_else(|| self.make_missing_crate_suggestion(span, path.clone(), parent_scope))
1213             .or_else(|| self.make_missing_super_suggestion(span, path.clone(), parent_scope))
1214             .or_else(|| self.make_external_crate_suggestion(span, path, parent_scope))
1215     }
1216
1217     /// Suggest a missing `self::` if that resolves to an correct module.
1218     ///
1219     /// ```text
1220     ///    |
1221     /// LL | use foo::Bar;
1222     ///    |     ^^^ did you mean `self::foo`?
1223     /// ```
1224     fn make_missing_self_suggestion(
1225         &mut self,
1226         span: Span,
1227         mut path: Vec<Segment>,
1228         parent_scope: &ParentScope<'b>,
1229     ) -> Option<(Vec<Segment>, Vec<String>)> {
1230         // Replace first ident with `self` and check if that is valid.
1231         path[0].ident.name = kw::SelfLower;
1232         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1233         debug!("make_missing_self_suggestion: path={:?} result={:?}", path, result);
1234         if let PathResult::Module(..) = result { Some((path, Vec::new())) } else { None }
1235     }
1236
1237     /// Suggests a missing `crate::` if that resolves to an correct module.
1238     ///
1239     /// ```text
1240     ///    |
1241     /// LL | use foo::Bar;
1242     ///    |     ^^^ did you mean `crate::foo`?
1243     /// ```
1244     fn make_missing_crate_suggestion(
1245         &mut self,
1246         span: Span,
1247         mut path: Vec<Segment>,
1248         parent_scope: &ParentScope<'b>,
1249     ) -> Option<(Vec<Segment>, Vec<String>)> {
1250         // Replace first ident with `crate` and check if that is valid.
1251         path[0].ident.name = kw::Crate;
1252         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1253         debug!("make_missing_crate_suggestion:  path={:?} result={:?}", path, result);
1254         if let PathResult::Module(..) = result {
1255             Some((
1256                 path,
1257                 vec![
1258                     "`use` statements changed in Rust 2018; read more at \
1259                      <https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-\
1260                      clarity.html>"
1261                         .to_string(),
1262                 ],
1263             ))
1264         } else {
1265             None
1266         }
1267     }
1268
1269     /// Suggests a missing `super::` if that resolves to an correct module.
1270     ///
1271     /// ```text
1272     ///    |
1273     /// LL | use foo::Bar;
1274     ///    |     ^^^ did you mean `super::foo`?
1275     /// ```
1276     fn make_missing_super_suggestion(
1277         &mut self,
1278         span: Span,
1279         mut path: Vec<Segment>,
1280         parent_scope: &ParentScope<'b>,
1281     ) -> Option<(Vec<Segment>, Vec<String>)> {
1282         // Replace first ident with `crate` and check if that is valid.
1283         path[0].ident.name = kw::Super;
1284         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1285         debug!("make_missing_super_suggestion:  path={:?} result={:?}", path, result);
1286         if let PathResult::Module(..) = result { Some((path, Vec::new())) } else { None }
1287     }
1288
1289     /// Suggests a missing external crate name if that resolves to an correct module.
1290     ///
1291     /// ```text
1292     ///    |
1293     /// LL | use foobar::Baz;
1294     ///    |     ^^^^^^ did you mean `baz::foobar`?
1295     /// ```
1296     ///
1297     /// Used when importing a submodule of an external crate but missing that crate's
1298     /// name as the first part of path.
1299     fn make_external_crate_suggestion(
1300         &mut self,
1301         span: Span,
1302         mut path: Vec<Segment>,
1303         parent_scope: &ParentScope<'b>,
1304     ) -> Option<(Vec<Segment>, Vec<String>)> {
1305         if path[1].ident.span.rust_2015() {
1306             return None;
1307         }
1308
1309         // Sort extern crate names in reverse order to get
1310         // 1) some consistent ordering for emitted diagnostics, and
1311         // 2) `std` suggestions before `core` suggestions.
1312         let mut extern_crate_names =
1313             self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
1314         extern_crate_names.sort_by_key(|name| Reverse(name.as_str()));
1315
1316         for name in extern_crate_names.into_iter() {
1317             // Replace first ident with a crate name and check if that is valid.
1318             path[0].ident.name = name;
1319             let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1320             debug!(
1321                 "make_external_crate_suggestion: name={:?} path={:?} result={:?}",
1322                 name, path, result
1323             );
1324             if let PathResult::Module(..) = result {
1325                 return Some((path, Vec::new()));
1326             }
1327         }
1328
1329         None
1330     }
1331
1332     /// Suggests importing a macro from the root of the crate rather than a module within
1333     /// the crate.
1334     ///
1335     /// ```text
1336     /// help: a macro with this name exists at the root of the crate
1337     ///    |
1338     /// LL | use issue_59764::makro;
1339     ///    |     ^^^^^^^^^^^^^^^^^^
1340     ///    |
1341     ///    = note: this could be because a macro annotated with `#[macro_export]` will be exported
1342     ///            at the root of the crate instead of the module where it is defined
1343     /// ```
1344     pub(crate) fn check_for_module_export_macro(
1345         &mut self,
1346         import: &'b Import<'b>,
1347         module: ModuleOrUniformRoot<'b>,
1348         ident: Ident,
1349     ) -> Option<(Option<Suggestion>, Vec<String>)> {
1350         let mut crate_module = if let ModuleOrUniformRoot::Module(module) = module {
1351             module
1352         } else {
1353             return None;
1354         };
1355
1356         while let Some(parent) = crate_module.parent {
1357             crate_module = parent;
1358         }
1359
1360         if ModuleOrUniformRoot::same_def(ModuleOrUniformRoot::Module(crate_module), module) {
1361             // Don't make a suggestion if the import was already from the root of the
1362             // crate.
1363             return None;
1364         }
1365
1366         let resolutions = self.r.resolutions(crate_module).borrow();
1367         let resolution = resolutions.get(&self.r.new_key(ident, MacroNS))?;
1368         let binding = resolution.borrow().binding()?;
1369         if let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() {
1370             let module_name = crate_module.kind.name().unwrap();
1371             let import_snippet = match import.kind {
1372                 ImportKind::Single { source, target, .. } if source != target => {
1373                     format!("{} as {}", source, target)
1374                 }
1375                 _ => format!("{}", ident),
1376             };
1377
1378             let mut corrections: Vec<(Span, String)> = Vec::new();
1379             if !import.is_nested() {
1380                 // Assume this is the easy case of `use issue_59764::foo::makro;` and just remove
1381                 // intermediate segments.
1382                 corrections.push((import.span, format!("{}::{}", module_name, import_snippet)));
1383             } else {
1384                 // Find the binding span (and any trailing commas and spaces).
1385                 //   ie. `use a::b::{c, d, e};`
1386                 //                      ^^^
1387                 let (found_closing_brace, binding_span) = find_span_of_binding_until_next_binding(
1388                     self.r.session,
1389                     import.span,
1390                     import.use_span,
1391                 );
1392                 debug!(
1393                     "check_for_module_export_macro: found_closing_brace={:?} binding_span={:?}",
1394                     found_closing_brace, binding_span
1395                 );
1396
1397                 let mut removal_span = binding_span;
1398                 if found_closing_brace {
1399                     // If the binding span ended with a closing brace, as in the below example:
1400                     //   ie. `use a::b::{c, d};`
1401                     //                      ^
1402                     // Then expand the span of characters to remove to include the previous
1403                     // binding's trailing comma.
1404                     //   ie. `use a::b::{c, d};`
1405                     //                    ^^^
1406                     if let Some(previous_span) =
1407                         extend_span_to_previous_binding(self.r.session, binding_span)
1408                     {
1409                         debug!("check_for_module_export_macro: previous_span={:?}", previous_span);
1410                         removal_span = removal_span.with_lo(previous_span.lo());
1411                     }
1412                 }
1413                 debug!("check_for_module_export_macro: removal_span={:?}", removal_span);
1414
1415                 // Remove the `removal_span`.
1416                 corrections.push((removal_span, "".to_string()));
1417
1418                 // Find the span after the crate name and if it has nested imports immediatately
1419                 // after the crate name already.
1420                 //   ie. `use a::b::{c, d};`
1421                 //               ^^^^^^^^^
1422                 //   or  `use a::{b, c, d}};`
1423                 //               ^^^^^^^^^^^
1424                 let (has_nested, after_crate_name) = find_span_immediately_after_crate_name(
1425                     self.r.session,
1426                     module_name,
1427                     import.use_span,
1428                 );
1429                 debug!(
1430                     "check_for_module_export_macro: has_nested={:?} after_crate_name={:?}",
1431                     has_nested, after_crate_name
1432                 );
1433
1434                 let source_map = self.r.session.source_map();
1435
1436                 // Add the import to the start, with a `{` if required.
1437                 let start_point = source_map.start_point(after_crate_name);
1438                 if let Ok(start_snippet) = source_map.span_to_snippet(start_point) {
1439                     corrections.push((
1440                         start_point,
1441                         if has_nested {
1442                             // In this case, `start_snippet` must equal '{'.
1443                             format!("{}{}, ", start_snippet, import_snippet)
1444                         } else {
1445                             // In this case, add a `{`, then the moved import, then whatever
1446                             // was there before.
1447                             format!("{{{}, {}", import_snippet, start_snippet)
1448                         },
1449                     ));
1450                 }
1451
1452                 // Add a `};` to the end if nested, matching the `{` added at the start.
1453                 if !has_nested {
1454                     corrections.push((source_map.end_point(after_crate_name), "};".to_string()));
1455                 }
1456             }
1457
1458             let suggestion = Some((
1459                 corrections,
1460                 String::from("a macro with this name exists at the root of the crate"),
1461                 Applicability::MaybeIncorrect,
1462             ));
1463             let note = vec![
1464                 "this could be because a macro annotated with `#[macro_export]` will be exported \
1465                  at the root of the crate instead of the module where it is defined"
1466                     .to_string(),
1467             ];
1468             Some((suggestion, note))
1469         } else {
1470             None
1471         }
1472     }
1473 }
1474
1475 /// Given a `binding_span` of a binding within a use statement:
1476 ///
1477 /// ```
1478 /// use foo::{a, b, c};
1479 ///              ^
1480 /// ```
1481 ///
1482 /// then return the span until the next binding or the end of the statement:
1483 ///
1484 /// ```
1485 /// use foo::{a, b, c};
1486 ///              ^^^
1487 /// ```
1488 pub(crate) fn find_span_of_binding_until_next_binding(
1489     sess: &Session,
1490     binding_span: Span,
1491     use_span: Span,
1492 ) -> (bool, Span) {
1493     let source_map = sess.source_map();
1494
1495     // Find the span of everything after the binding.
1496     //   ie. `a, e};` or `a};`
1497     let binding_until_end = binding_span.with_hi(use_span.hi());
1498
1499     // Find everything after the binding but not including the binding.
1500     //   ie. `, e};` or `};`
1501     let after_binding_until_end = binding_until_end.with_lo(binding_span.hi());
1502
1503     // Keep characters in the span until we encounter something that isn't a comma or
1504     // whitespace.
1505     //   ie. `, ` or ``.
1506     //
1507     // Also note whether a closing brace character was encountered. If there
1508     // was, then later go backwards to remove any trailing commas that are left.
1509     let mut found_closing_brace = false;
1510     let after_binding_until_next_binding =
1511         source_map.span_take_while(after_binding_until_end, |&ch| {
1512             if ch == '}' {
1513                 found_closing_brace = true;
1514             }
1515             ch == ' ' || ch == ','
1516         });
1517
1518     // Combine the two spans.
1519     //   ie. `a, ` or `a`.
1520     //
1521     // Removing these would leave `issue_52891::{d, e};` or `issue_52891::{d, e, };`
1522     let span = binding_span.with_hi(after_binding_until_next_binding.hi());
1523
1524     (found_closing_brace, span)
1525 }
1526
1527 /// Given a `binding_span`, return the span through to the comma or opening brace of the previous
1528 /// binding.
1529 ///
1530 /// ```
1531 /// use foo::a::{a, b, c};
1532 ///               ^^--- binding span
1533 ///               |
1534 ///               returned span
1535 ///
1536 /// use foo::{a, b, c};
1537 ///           --- binding span
1538 /// ```
1539 pub(crate) fn extend_span_to_previous_binding(sess: &Session, binding_span: Span) -> Option<Span> {
1540     let source_map = sess.source_map();
1541
1542     // `prev_source` will contain all of the source that came before the span.
1543     // Then split based on a command and take the first (ie. closest to our span)
1544     // snippet. In the example, this is a space.
1545     let prev_source = source_map.span_to_prev_source(binding_span).ok()?;
1546
1547     let prev_comma = prev_source.rsplit(',').collect::<Vec<_>>();
1548     let prev_starting_brace = prev_source.rsplit('{').collect::<Vec<_>>();
1549     if prev_comma.len() <= 1 || prev_starting_brace.len() <= 1 {
1550         return None;
1551     }
1552
1553     let prev_comma = prev_comma.first().unwrap();
1554     let prev_starting_brace = prev_starting_brace.first().unwrap();
1555
1556     // If the amount of source code before the comma is greater than
1557     // the amount of source code before the starting brace then we've only
1558     // got one item in the nested item (eg. `issue_52891::{self}`).
1559     if prev_comma.len() > prev_starting_brace.len() {
1560         return None;
1561     }
1562
1563     Some(binding_span.with_lo(BytePos(
1564         // Take away the number of bytes for the characters we've found and an
1565         // extra for the comma.
1566         binding_span.lo().0 - (prev_comma.as_bytes().len() as u32) - 1,
1567     )))
1568 }
1569
1570 /// Given a `use_span` of a binding within a use statement, returns the highlighted span and if
1571 /// it is a nested use tree.
1572 ///
1573 /// ```
1574 /// use foo::a::{b, c};
1575 ///          ^^^^^^^^^^ // false
1576 ///
1577 /// use foo::{a, b, c};
1578 ///          ^^^^^^^^^^ // true
1579 ///
1580 /// use foo::{a, b::{c, d}};
1581 ///          ^^^^^^^^^^^^^^^ // true
1582 /// ```
1583 fn find_span_immediately_after_crate_name(
1584     sess: &Session,
1585     module_name: Symbol,
1586     use_span: Span,
1587 ) -> (bool, Span) {
1588     debug!(
1589         "find_span_immediately_after_crate_name: module_name={:?} use_span={:?}",
1590         module_name, use_span
1591     );
1592     let source_map = sess.source_map();
1593
1594     // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
1595     let mut num_colons = 0;
1596     // Find second colon.. `use issue_59764:`
1597     let until_second_colon = source_map.span_take_while(use_span, |c| {
1598         if *c == ':' {
1599             num_colons += 1;
1600         }
1601         match c {
1602             ':' if num_colons == 2 => false,
1603             _ => true,
1604         }
1605     });
1606     // Find everything after the second colon.. `foo::{baz, makro};`
1607     let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
1608
1609     let mut found_a_non_whitespace_character = false;
1610     // Find the first non-whitespace character in `from_second_colon`.. `f`
1611     let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
1612         if found_a_non_whitespace_character {
1613             return false;
1614         }
1615         if !c.is_whitespace() {
1616             found_a_non_whitespace_character = true;
1617         }
1618         true
1619     });
1620
1621     // Find the first `{` in from_second_colon.. `foo::{`
1622     let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
1623
1624     (next_left_bracket == after_second_colon, from_second_colon)
1625 }
1626
1627 /// When an entity with a given name is not available in scope, we search for
1628 /// entities with that name in all crates. This method allows outputting the
1629 /// results of this search in a programmer-friendly way
1630 crate fn show_candidates(
1631     err: &mut DiagnosticBuilder<'_>,
1632     // This is `None` if all placement locations are inside expansions
1633     use_placement_span: Option<Span>,
1634     candidates: &[ImportSuggestion],
1635     instead: bool,
1636     found_use: bool,
1637 ) {
1638     if candidates.is_empty() {
1639         return;
1640     }
1641
1642     // we want consistent results across executions, but candidates are produced
1643     // by iterating through a hash map, so make sure they are ordered:
1644     let mut path_strings: Vec<_> =
1645         candidates.iter().map(|c| path_names_to_string(&c.path)).collect();
1646
1647     path_strings.sort();
1648     path_strings.dedup();
1649
1650     let (determiner, kind) = if candidates.len() == 1 {
1651         ("this", candidates[0].descr)
1652     } else {
1653         ("one of these", "items")
1654     };
1655
1656     let instead = if instead { " instead" } else { "" };
1657     let mut msg = format!("consider importing {} {}{}", determiner, kind, instead);
1658
1659     if let Some(span) = use_placement_span {
1660         for candidate in &mut path_strings {
1661             // produce an additional newline to separate the new use statement
1662             // from the directly following item.
1663             let additional_newline = if found_use { "" } else { "\n" };
1664             *candidate = format!("use {};\n{}", candidate, additional_newline);
1665         }
1666
1667         err.span_suggestions(span, &msg, path_strings.into_iter(), Applicability::Unspecified);
1668     } else {
1669         msg.push(':');
1670
1671         for candidate in path_strings {
1672             msg.push('\n');
1673             msg.push_str(&candidate);
1674         }
1675
1676         err.note(&msg);
1677     }
1678 }