compiler/rustc_resolve/src/diagnostics.rs

   1 use std::ptr;
   2
   3 use rustc_ast::ptr::P;
   4 use rustc_ast::visit::{self, Visitor};
   5 use rustc_ast::{self as ast, Crate, ItemKind, ModKind, NodeId, Path, CRATE_NODE_ID};
   6 use rustc_ast_pretty::pprust;
   7 use rustc_data_structures::fx::FxHashSet;
   8 use rustc_errors::struct_span_err;
   9 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, MultiSpan};
  10 use rustc_feature::BUILTIN_ATTRIBUTES;
  11 use rustc_hir::def::Namespace::{self, *};
  12 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind, NonMacroAttrKind, PerNS};
  13 use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID, LOCAL_CRATE};
  14 use rustc_hir::PrimTy;
  15 use rustc_index::vec::IndexVec;
  16 use rustc_middle::bug;
  17 use rustc_middle::ty::DefIdTree;
  18 use rustc_session::lint::builtin::ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE;
  19 use rustc_session::lint::builtin::MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS;
  20 use rustc_session::lint::BuiltinLintDiagnostics;
  21 use rustc_session::Session;
  22 use rustc_span::edition::Edition;
  23 use rustc_span::hygiene::MacroKind;
  24 use rustc_span::lev_distance::find_best_match_for_name;
  25 use rustc_span::source_map::SourceMap;
  26 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  27 use rustc_span::{BytePos, Span, SyntaxContext};
  28 use thin_vec::ThinVec;
  29
  30 use crate::errors as errs;
  31 use crate::imports::{Import, ImportKind, ImportResolver};
  32 use crate::late::{PatternSource, Rib};
  33 use crate::path_names_to_string;
  34 use crate::{AmbiguityError, AmbiguityErrorMisc, AmbiguityKind, BindingError, Finalize};
  35 use crate::{HasGenericParams, MacroRulesScope, Module, ModuleKind, ModuleOrUniformRoot};
  36 use crate::{LexicalScopeBinding, NameBinding, NameBindingKind, PrivacyError, VisResolutionError};
  37 use crate::{ParentScope, PathResult, ResolutionError, Resolver, Scope, ScopeSet};
  38 use crate::{Segment, UseError};
  39
  40 #[cfg(test)]
  41 mod tests;
  42
  43 type Res = def::Res<ast::NodeId>;
  44
  45 /// A vector of spans and replacements, a message and applicability.
  46 pub(crate) type Suggestion = (Vec<(Span, String)>, String, Applicability);
  47
  48 /// Potential candidate for an undeclared or out-of-scope label - contains the ident of a
  49 /// similarly named label and whether or not it is reachable.
  50 pub(crate) type LabelSuggestion = (Ident, bool);
  51
  52 #[derive(Debug)]
  53 pub(crate) enum SuggestionTarget {
  54     /// The target has a similar name as the name used by the programmer (probably a typo)
  55     SimilarlyNamed,
  56     /// The target is the only valid item that can be used in the corresponding context
  57     SingleItem,
  58 }
  59
  60 #[derive(Debug)]
  61 pub(crate) struct TypoSuggestion {
  62     pub candidate: Symbol,
  63     /// The source location where the name is defined; None if the name is not defined
  64     /// in source e.g. primitives
  65     pub span: Option<Span>,
  66     pub res: Res,
  67     pub target: SuggestionTarget,
  68 }
  69
  70 impl TypoSuggestion {
  71     pub(crate) fn typo_from_ident(ident: Ident, res: Res) -> TypoSuggestion {
  72         Self {
  73             candidate: ident.name,
  74             span: Some(ident.span),
  75             res,
  76             target: SuggestionTarget::SimilarlyNamed,
  77         }
  78     }
  79     pub(crate) fn typo_from_name(candidate: Symbol, res: Res) -> TypoSuggestion {
  80         Self { candidate, span: None, res, target: SuggestionTarget::SimilarlyNamed }
  81     }
  82     pub(crate) fn single_item_from_ident(ident: Ident, res: Res) -> TypoSuggestion {
  83         Self {
  84             candidate: ident.name,
  85             span: Some(ident.span),
  86             res,
  87             target: SuggestionTarget::SingleItem,
  88         }
  89     }
  90 }
  91
  92 /// A free importable items suggested in case of resolution failure.
  93 #[derive(Debug, Clone)]
  94 pub(crate) struct ImportSuggestion {
  95     pub did: Option<DefId>,
  96     pub descr: &'static str,
  97     pub path: Path,
  98     pub accessible: bool,
  99     /// An extra note that should be issued if this item is suggested
 100     pub note: Option<String>,
 101 }
 102
 103 /// Adjust the impl span so that just the `impl` keyword is taken by removing
 104 /// everything after `<` (`"impl<T> Iterator for A<T> {}" -> "impl"`) and
 105 /// everything after the first whitespace (`"impl Iterator for A" -> "impl"`).
 106 ///
 107 /// *Attention*: the method used is very fragile since it essentially duplicates the work of the
 108 /// parser. If you need to use this function or something similar, please consider updating the
 109 /// `source_map` functions and this function to something more robust.
 110 fn reduce_impl_span_to_impl_keyword(sm: &SourceMap, impl_span: Span) -> Span {
 111     let impl_span = sm.span_until_char(impl_span, '<');
 112     sm.span_until_whitespace(impl_span)
 113 }
 114
 115 impl<'a> Resolver<'a> {
 116     pub(crate) fn report_errors(&mut self, krate: &Crate) {
 117         self.report_with_use_injections(krate);
 118
 119         for &(span_use, span_def) in &self.macro_expanded_macro_export_errors {
 120             let msg = "macro-expanded `macro_export` macros from the current crate \
 121                        cannot be referred to by absolute paths";
 122             self.lint_buffer.buffer_lint_with_diagnostic(
 123                 MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
 124                 CRATE_NODE_ID,
 125                 span_use,
 126                 msg,
 127                 BuiltinLintDiagnostics::MacroExpandedMacroExportsAccessedByAbsolutePaths(span_def),
 128             );
 129         }
 130
 131         for ambiguity_error in &self.ambiguity_errors {
 132             self.report_ambiguity_error(ambiguity_error);
 133         }
 134
 135         let mut reported_spans = FxHashSet::default();
 136         for error in &self.privacy_errors {
 137             if reported_spans.insert(error.dedup_span) {
 138                 self.report_privacy_error(error);
 139             }
 140         }
 141     }
 142
 143     fn report_with_use_injections(&mut self, krate: &Crate) {
 144         for UseError { mut err, candidates, def_id, instead, suggestion, path, is_call } in
 145             self.use_injections.drain(..)
 146         {
 147             let (span, found_use) = if let Some(def_id) = def_id.as_local() {
 148                 UsePlacementFinder::check(krate, self.def_id_to_node_id[def_id])
 149             } else {
 150                 (None, FoundUse::No)
 151             };
 152
 153             if !candidates.is_empty() {
 154                 show_candidates(
 155                     &self.session,
 156                     &self.source_span,
 157                     &mut err,
 158                     span,
 159                     &candidates,
 160                     if instead { Instead::Yes } else { Instead::No },
 161                     found_use,
 162                     DiagnosticMode::Normal,
 163                     path,
 164                 );
 165                 err.emit();
 166             } else if let Some((span, msg, sugg, appl)) = suggestion {
 167                 err.span_suggestion(span, msg, sugg, appl);
 168                 err.emit();
 169             } else if let [segment] = path.as_slice() && is_call {
 170                 err.stash(segment.ident.span, rustc_errors::StashKey::CallIntoMethod);
 171             } else {
 172                 err.emit();
 173             }
 174         }
 175     }
 176
 177     pub(crate) fn report_conflict<'b>(
 178         &mut self,
 179         parent: Module<'_>,
 180         ident: Ident,
 181         ns: Namespace,
 182         new_binding: &NameBinding<'b>,
 183         old_binding: &NameBinding<'b>,
 184     ) {
 185         // Error on the second of two conflicting names
 186         if old_binding.span.lo() > new_binding.span.lo() {
 187             return self.report_conflict(parent, ident, ns, old_binding, new_binding);
 188         }
 189
 190         let container = match parent.kind {
 191             ModuleKind::Def(kind, _, _) => kind.descr(parent.def_id()),
 192             ModuleKind::Block => "block",
 193         };
 194
 195         let old_noun = match old_binding.is_import_user_facing() {
 196             true => "import",
 197             false => "definition",
 198         };
 199
 200         let new_participle = match new_binding.is_import_user_facing() {
 201             true => "imported",
 202             false => "defined",
 203         };
 204
 205         let (name, span) =
 206             (ident.name, self.session.source_map().guess_head_span(new_binding.span));
 207
 208         if let Some(s) = self.name_already_seen.get(&name) {
 209             if s == &span {
 210                 return;
 211             }
 212         }
 213
 214         let old_kind = match (ns, old_binding.module()) {
 215             (ValueNS, _) => "value",
 216             (MacroNS, _) => "macro",
 217             (TypeNS, _) if old_binding.is_extern_crate() => "extern crate",
 218             (TypeNS, Some(module)) if module.is_normal() => "module",
 219             (TypeNS, Some(module)) if module.is_trait() => "trait",
 220             (TypeNS, _) => "type",
 221         };
 222
 223         let msg = format!("the name `{}` is defined multiple times", name);
 224
 225         let mut err = match (old_binding.is_extern_crate(), new_binding.is_extern_crate()) {
 226             (true, true) => struct_span_err!(self.session, span, E0259, "{}", msg),
 227             (true, _) | (_, true) => match new_binding.is_import() && old_binding.is_import() {
 228                 true => struct_span_err!(self.session, span, E0254, "{}", msg),
 229                 false => struct_span_err!(self.session, span, E0260, "{}", msg),
 230             },
 231             _ => match (old_binding.is_import_user_facing(), new_binding.is_import_user_facing()) {
 232                 (false, false) => struct_span_err!(self.session, span, E0428, "{}", msg),
 233                 (true, true) => struct_span_err!(self.session, span, E0252, "{}", msg),
 234                 _ => struct_span_err!(self.session, span, E0255, "{}", msg),
 235             },
 236         };
 237
 238         err.note(&format!(
 239             "`{}` must be defined only once in the {} namespace of this {}",
 240             name,
 241             ns.descr(),
 242             container
 243         ));
 244
 245         err.span_label(span, format!("`{}` re{} here", name, new_participle));
 246         if !old_binding.span.is_dummy() && old_binding.span != span {
 247             err.span_label(
 248                 self.session.source_map().guess_head_span(old_binding.span),
 249                 format!("previous {} of the {} `{}` here", old_noun, old_kind, name),
 250             );
 251         }
 252
 253         // See https://github.com/rust-lang/rust/issues/32354
 254         use NameBindingKind::Import;
 255         let can_suggest = |binding: &NameBinding<'_>, import: &self::Import<'_>| {
 256             !binding.span.is_dummy()
 257                 && !matches!(import.kind, ImportKind::MacroUse | ImportKind::MacroExport)
 258         };
 259         let import = match (&new_binding.kind, &old_binding.kind) {
 260             // If there are two imports where one or both have attributes then prefer removing the
 261             // import without attributes.
 262             (Import { import: new, .. }, Import { import: old, .. })
 263                 if {
 264                     (new.has_attributes || old.has_attributes)
 265                         && can_suggest(old_binding, old)
 266                         && can_suggest(new_binding, new)
 267                 } =>
 268             {
 269                 if old.has_attributes {
 270                     Some((new, new_binding.span, true))
 271                 } else {
 272                     Some((old, old_binding.span, true))
 273                 }
 274             }
 275             // Otherwise prioritize the new binding.
 276             (Import { import, .. }, other) if can_suggest(new_binding, import) => {
 277                 Some((import, new_binding.span, other.is_import()))
 278             }
 279             (other, Import { import, .. }) if can_suggest(old_binding, import) => {
 280                 Some((import, old_binding.span, other.is_import()))
 281             }
 282             _ => None,
 283         };
 284
 285         // Check if the target of the use for both bindings is the same.
 286         let duplicate = new_binding.res().opt_def_id() == old_binding.res().opt_def_id();
 287         let has_dummy_span = new_binding.span.is_dummy() || old_binding.span.is_dummy();
 288         let from_item =
 289             self.extern_prelude.get(&ident).map_or(true, |entry| entry.introduced_by_item);
 290         // Only suggest removing an import if both bindings are to the same def, if both spans
 291         // aren't dummy spans. Further, if both bindings are imports, then the ident must have
 292         // been introduced by an item.
 293         let should_remove_import = duplicate
 294             && !has_dummy_span
 295             && ((new_binding.is_extern_crate() || old_binding.is_extern_crate()) || from_item);
 296
 297         match import {
 298             Some((import, span, true)) if should_remove_import && import.is_nested() => {
 299                 self.add_suggestion_for_duplicate_nested_use(&mut err, import, span)
 300             }
 301             Some((import, _, true)) if should_remove_import && !import.is_glob() => {
 302                 // Simple case - remove the entire import. Due to the above match arm, this can
 303                 // only be a single use so just remove it entirely.
 304                 err.tool_only_span_suggestion(
 305                     import.use_span_with_attributes,
 306                     "remove unnecessary import",
 307                     "",
 308                     Applicability::MaybeIncorrect,
 309                 );
 310             }
 311             Some((import, span, _)) => {
 312                 self.add_suggestion_for_rename_of_use(&mut err, name, import, span)
 313             }
 314             _ => {}
 315         }
 316
 317         err.emit();
 318         self.name_already_seen.insert(name, span);
 319     }
 320
 321     /// This function adds a suggestion to change the binding name of a new import that conflicts
 322     /// with an existing import.
 323     ///
 324     /// ```text,ignore (diagnostic)
 325     /// help: you can use `as` to change the binding name of the import
 326     ///    |
 327     /// LL | use foo::bar as other_bar;
 328     ///    |     ^^^^^^^^^^^^^^^^^^^^^
 329     /// ```
 330     fn add_suggestion_for_rename_of_use(
 331         &self,
 332         err: &mut Diagnostic,
 333         name: Symbol,
 334         import: &Import<'_>,
 335         binding_span: Span,
 336     ) {
 337         let suggested_name = if name.as_str().chars().next().unwrap().is_uppercase() {
 338             format!("Other{}", name)
 339         } else {
 340             format!("other_{}", name)
 341         };
 342
 343         let mut suggestion = None;
 344         match import.kind {
 345             ImportKind::Single { type_ns_only: true, .. } => {
 346                 suggestion = Some(format!("self as {}", suggested_name))
 347             }
 348             ImportKind::Single { source, .. } => {
 349                 if let Some(pos) =
 350                     source.span.hi().0.checked_sub(binding_span.lo().0).map(|pos| pos as usize)
 351                 {
 352                     if let Ok(snippet) = self.session.source_map().span_to_snippet(binding_span) {
 353                         if pos <= snippet.len() {
 354                             suggestion = Some(format!(
 355                                 "{} as {}{}",
 356                                 &snippet[..pos],
 357                                 suggested_name,
 358                                 if snippet.ends_with(';') { ";" } else { "" }
 359                             ))
 360                         }
 361                     }
 362                 }
 363             }
 364             ImportKind::ExternCrate { source, target, .. } => {
 365                 suggestion = Some(format!(
 366                     "extern crate {} as {};",
 367                     source.unwrap_or(target.name),
 368                     suggested_name,
 369                 ))
 370             }
 371             _ => unreachable!(),
 372         }
 373
 374         let rename_msg = "you can use `as` to change the binding name of the import";
 375         if let Some(suggestion) = suggestion {
 376             err.span_suggestion(
 377                 binding_span,
 378                 rename_msg,
 379                 suggestion,
 380                 Applicability::MaybeIncorrect,
 381             );
 382         } else {
 383             err.span_label(binding_span, rename_msg);
 384         }
 385     }
 386
 387     /// This function adds a suggestion to remove an unnecessary binding from an import that is
 388     /// nested. In the following example, this function will be invoked to remove the `a` binding
 389     /// in the second use statement:
 390     ///
 391     /// ```ignore (diagnostic)
 392     /// use issue_52891::a;
 393     /// use issue_52891::{d, a, e};
 394     /// ```
 395     ///
 396     /// The following suggestion will be added:
 397     ///
 398     /// ```ignore (diagnostic)
 399     /// use issue_52891::{d, a, e};
 400     ///                      ^-- help: remove unnecessary import
 401     /// ```
 402     ///
 403     /// If the nested use contains only one import then the suggestion will remove the entire
 404     /// line.
 405     ///
 406     /// It is expected that the provided import is nested - this isn't checked by the
 407     /// function. If this invariant is not upheld, this function's behaviour will be unexpected
 408     /// as characters expected by span manipulations won't be present.
 409     fn add_suggestion_for_duplicate_nested_use(
 410         &self,
 411         err: &mut Diagnostic,
 412         import: &Import<'_>,
 413         binding_span: Span,
 414     ) {
 415         assert!(import.is_nested());
 416         let message = "remove unnecessary import";
 417
 418         // Two examples will be used to illustrate the span manipulations we're doing:
 419         //
 420         // - Given `use issue_52891::{d, a, e};` where `a` is a duplicate then `binding_span` is
 421         //   `a` and `import.use_span` is `issue_52891::{d, a, e};`.
 422         // - Given `use issue_52891::{d, e, a};` where `a` is a duplicate then `binding_span` is
 423         //   `a` and `import.use_span` is `issue_52891::{d, e, a};`.
 424
 425         let (found_closing_brace, span) =
 426             find_span_of_binding_until_next_binding(self.session, binding_span, import.use_span);
 427
 428         // If there was a closing brace then identify the span to remove any trailing commas from
 429         // previous imports.
 430         if found_closing_brace {
 431             if let Some(span) = extend_span_to_previous_binding(self.session, span) {
 432                 err.tool_only_span_suggestion(span, message, "", Applicability::MaybeIncorrect);
 433             } else {
 434                 // Remove the entire line if we cannot extend the span back, this indicates an
 435                 // `issue_52891::{self}` case.
 436                 err.span_suggestion(
 437                     import.use_span_with_attributes,
 438                     message,
 439                     "",
 440                     Applicability::MaybeIncorrect,
 441                 );
 442             }
 443
 444             return;
 445         }
 446
 447         err.span_suggestion(span, message, "", Applicability::MachineApplicable);
 448     }
 449
 450     pub(crate) fn lint_if_path_starts_with_module(
 451         &mut self,
 452         finalize: Option<Finalize>,
 453         path: &[Segment],
 454         second_binding: Option<&NameBinding<'_>>,
 455     ) {
 456         let Some(Finalize { node_id, root_span, .. }) = finalize else {
 457             return;
 458         };
 459
 460         let first_name = match path.get(0) {
 461             // In the 2018 edition this lint is a hard error, so nothing to do
 462             Some(seg) if seg.ident.span.rust_2015() && self.session.rust_2015() => seg.ident.name,
 463             _ => return,
 464         };
 465
 466         // We're only interested in `use` paths which should start with
 467         // `{{root}}` currently.
 468         if first_name != kw::PathRoot {
 469             return;
 470         }
 471
 472         match path.get(1) {
 473             // If this import looks like `crate::...` it's already good
 474             Some(Segment { ident, .. }) if ident.name == kw::Crate => return,
 475             // Otherwise go below to see if it's an extern crate
 476             Some(_) => {}
 477             // If the path has length one (and it's `PathRoot` most likely)
 478             // then we don't know whether we're gonna be importing a crate or an
 479             // item in our crate. Defer this lint to elsewhere
 480             None => return,
 481         }
 482
 483         // If the first element of our path was actually resolved to an
 484         // `ExternCrate` (also used for `crate::...`) then no need to issue a
 485         // warning, this looks all good!
 486         if let Some(binding) = second_binding {
 487             if let NameBindingKind::Import { import, .. } = binding.kind {
 488                 // Careful: we still want to rewrite paths from renamed extern crates.
 489                 if let ImportKind::ExternCrate { source: None, .. } = import.kind {
 490                     return;
 491                 }
 492             }
 493         }
 494
 495         let diag = BuiltinLintDiagnostics::AbsPathWithModule(root_span);
 496         self.lint_buffer.buffer_lint_with_diagnostic(
 497             ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
 498             node_id,
 499             root_span,
 500             "absolute paths must start with `self`, `super`, \
 501              `crate`, or an external crate name in the 2018 edition",
 502             diag,
 503         );
 504     }
 505
 506     pub(crate) fn add_module_candidates(
 507         &mut self,
 508         module: Module<'a>,
 509         names: &mut Vec<TypoSuggestion>,
 510         filter_fn: &impl Fn(Res) -> bool,
 511         ctxt: Option<SyntaxContext>,
 512     ) {
 513         for (key, resolution) in self.resolutions(module).borrow().iter() {
 514             if let Some(binding) = resolution.borrow().binding {
 515                 let res = binding.res();
 516                 if filter_fn(res) && ctxt.map_or(true, |ctxt| ctxt == key.ident.span.ctxt()) {
 517                     names.push(TypoSuggestion::typo_from_ident(key.ident, res));
 518                 }
 519             }
 520         }
 521     }
 522
 523     /// Combines an error with provided span and emits it.
 524     ///
 525     /// This takes the error provided, combines it with the span and any additional spans inside the
 526     /// error and emits it.
 527     pub(crate) fn report_error(&mut self, span: Span, resolution_error: ResolutionError<'a>) {
 528         self.into_struct_error(span, resolution_error).emit();
 529     }
 530
 531     pub(crate) fn into_struct_error(
 532         &mut self,
 533         span: Span,
 534         resolution_error: ResolutionError<'a>,
 535     ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
 536         match resolution_error {
 537             ResolutionError::GenericParamsFromOuterFunction(outer_res, has_generic_params) => {
 538                 let mut err = struct_span_err!(
 539                     self.session,
 540                     span,
 541                     E0401,
 542                     "can't use generic parameters from outer function",
 543                 );
 544                 err.span_label(span, "use of generic parameter from outer function");
 545
 546                 let sm = self.session.source_map();
 547                 let def_id = match outer_res {
 548                     Res::SelfTyParam { .. } => {
 549                         err.span_label(span, "can't use `Self` here");
 550                         return err;
 551                     }
 552                     Res::SelfTyAlias { alias_to: def_id, .. } => {
 553                         if let Some(impl_span) = self.opt_span(def_id) {
 554                             err.span_label(
 555                                 reduce_impl_span_to_impl_keyword(sm, impl_span),
 556                                 "`Self` type implicitly declared here, by this `impl`",
 557                             );
 558                         }
 559                         err.span_label(span, "use a type here instead");
 560                         return err;
 561                     }
 562                     Res::Def(DefKind::TyParam, def_id) => {
 563                         if let Some(span) = self.opt_span(def_id) {
 564                             err.span_label(span, "type parameter from outer function");
 565                         }
 566                         def_id
 567                     }
 568                     Res::Def(DefKind::ConstParam, def_id) => {
 569                         if let Some(span) = self.opt_span(def_id) {
 570                             err.span_label(span, "const parameter from outer function");
 571                         }
 572                         def_id
 573                     }
 574                     _ => {
 575                         bug!(
 576                             "GenericParamsFromOuterFunction should only be used with \
 577                             Res::SelfTyParam, Res::SelfTyAlias, DefKind::TyParam or \
 578                             DefKind::ConstParam"
 579                         );
 580                     }
 581                 };
 582
 583                 if let HasGenericParams::Yes(span) = has_generic_params {
 584                     // Try to retrieve the span of the function signature and generate a new
 585                     // message with a local type or const parameter.
 586                     let sugg_msg = "try using a local generic parameter instead";
 587                     let name = self.opt_name(def_id).unwrap_or(sym::T);
 588                     let (span, snippet) = if span.is_empty() {
 589                         let snippet = format!("<{}>", name);
 590                         (span, snippet)
 591                     } else {
 592                         let span = sm.span_through_char(span, '<').shrink_to_hi();
 593                         let snippet = format!("{}, ", name);
 594                         (span, snippet)
 595                     };
 596                     // Suggest the modification to the user
 597                     err.span_suggestion(span, sugg_msg, snippet, Applicability::MaybeIncorrect);
 598                 }
 599
 600                 err
 601             }
 602             ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => self
 603                 .session
 604                 .create_err(errs::NameAlreadyUsedInParameterList { span, first_use_span, name }),
 605             ResolutionError::MethodNotMemberOfTrait(method, trait_, candidate) => {
 606                 self.session.create_err(errs::MethodNotMemberOfTrait {
 607                     span,
 608                     method,
 609                     trait_,
 610                     sub: candidate.map(|c| errs::AssociatedFnWithSimilarNameExists {
 611                         span: method.span,
 612                         candidate: c,
 613                     }),
 614                 })
 615             }
 616             ResolutionError::TypeNotMemberOfTrait(type_, trait_, candidate) => {
 617                 self.session.create_err(errs::TypeNotMemberOfTrait {
 618                     span,
 619                     type_,
 620                     trait_,
 621                     sub: candidate.map(|c| errs::AssociatedTypeWithSimilarNameExists {
 622                         span: type_.span,
 623                         candidate: c,
 624                     }),
 625                 })
 626             }
 627             ResolutionError::ConstNotMemberOfTrait(const_, trait_, candidate) => {
 628                 self.session.create_err(errs::ConstNotMemberOfTrait {
 629                     span,
 630                     const_,
 631                     trait_,
 632                     sub: candidate.map(|c| errs::AssociatedConstWithSimilarNameExists {
 633                         span: const_.span,
 634                         candidate: c,
 635                     }),
 636                 })
 637             }
 638             ResolutionError::VariableNotBoundInPattern(binding_error, parent_scope) => {
 639                 let BindingError { name, target, origin, could_be_path } = binding_error;
 640
 641                 let target_sp = target.iter().copied().collect::<Vec<_>>();
 642                 let origin_sp = origin.iter().copied().collect::<Vec<_>>();
 643
 644                 let msp = MultiSpan::from_spans(target_sp.clone());
 645                 let mut err = struct_span_err!(
 646                     self.session,
 647                     msp,
 648                     E0408,
 649                     "variable `{}` is not bound in all patterns",
 650                     name,
 651                 );
 652                 for sp in target_sp {
 653                     err.span_label(sp, format!("pattern doesn't bind `{}`", name));
 654                 }
 655                 for sp in origin_sp {
 656                     err.span_label(sp, "variable not in all patterns");
 657                 }
 658                 if could_be_path {
 659                     let import_suggestions = self.lookup_import_candidates(
 660                         Ident::with_dummy_span(name),
 661                         Namespace::ValueNS,
 662                         &parent_scope,
 663                         &|res: Res| match res {
 664                             Res::Def(
 665                                 DefKind::Ctor(CtorOf::Variant, CtorKind::Const)
 666                                 | DefKind::Ctor(CtorOf::Struct, CtorKind::Const)
 667                                 | DefKind::Const
 668                                 | DefKind::AssocConst,
 669                                 _,
 670                             ) => true,
 671                             _ => false,
 672                         },
 673                     );
 674
 675                     if import_suggestions.is_empty() {
 676                         let help_msg = format!(
 677                             "if you meant to match on a variant or a `const` item, consider \
 678                              making the path in the pattern qualified: `path::to::ModOrType::{}`",
 679                             name,
 680                         );
 681                         err.span_help(span, &help_msg);
 682                     }
 683                     show_candidates(
 684                         &self.session,
 685                         &self.source_span,
 686                         &mut err,
 687                         Some(span),
 688                         &import_suggestions,
 689                         Instead::No,
 690                         FoundUse::Yes,
 691                         DiagnosticMode::Pattern,
 692                         vec![],
 693                     );
 694                 }
 695                 err
 696             }
 697             ResolutionError::VariableBoundWithDifferentMode(variable_name, first_binding_span) => {
 698                 self.session.create_err(errs::VariableBoundWithDifferentMode {
 699                     span,
 700                     first_binding_span,
 701                     variable_name,
 702                 })
 703             }
 704             ResolutionError::IdentifierBoundMoreThanOnceInParameterList(identifier) => self
 705                 .session
 706                 .create_err(errs::IdentifierBoundMoreThanOnceInParameterList { span, identifier }),
 707             ResolutionError::IdentifierBoundMoreThanOnceInSamePattern(identifier) => self
 708                 .session
 709                 .create_err(errs::IdentifierBoundMoreThanOnceInSamePattern { span, identifier }),
 710             ResolutionError::UndeclaredLabel { name, suggestion } => {
 711                 let ((sub_reachable, sub_reachable_suggestion), sub_unreachable) = match suggestion
 712                 {
 713                     // A reachable label with a similar name exists.
 714                     Some((ident, true)) => (
 715                         (
 716                             Some(errs::LabelWithSimilarNameReachable(ident.span)),
 717                             Some(errs::TryUsingSimilarlyNamedLabel {
 718                                 span,
 719                                 ident_name: ident.name,
 720                             }),
 721                         ),
 722                         None,
 723                     ),
 724                     // An unreachable label with a similar name exists.
 725                     Some((ident, false)) => (
 726                         (None, None),
 727                         Some(errs::UnreachableLabelWithSimilarNameExists {
 728                             ident_span: ident.span,
 729                         }),
 730                     ),
 731                     // No similarly-named labels exist.
 732                     None => ((None, None), None),
 733                 };
 734                 self.session.create_err(errs::UndeclaredLabel {
 735                     span,
 736                     name,
 737                     sub_reachable,
 738                     sub_reachable_suggestion,
 739                     sub_unreachable,
 740                 })
 741             }
 742             ResolutionError::SelfImportsOnlyAllowedWithin { root, span_with_rename } => {
 743                 // None of the suggestions below would help with a case like `use self`.
 744                 let (suggestion, mpart_suggestion) = if root {
 745                     (None, None)
 746                 } else {
 747                     // use foo::bar::self        -> foo::bar
 748                     // use foo::bar::self as abc -> foo::bar as abc
 749                     let suggestion = errs::SelfImportsOnlyAllowedWithinSuggestion { span };
 750
 751                     // use foo::bar::self        -> foo::bar::{self}
 752                     // use foo::bar::self as abc -> foo::bar::{self as abc}
 753                     let mpart_suggestion = errs::SelfImportsOnlyAllowedWithinMultipartSuggestion {
 754                         multipart_start: span_with_rename.shrink_to_lo(),
 755                         multipart_end: span_with_rename.shrink_to_hi(),
 756                     };
 757                     (Some(suggestion), Some(mpart_suggestion))
 758                 };
 759                 self.session.create_err(errs::SelfImportsOnlyAllowedWithin {
 760                     span,
 761                     suggestion,
 762                     mpart_suggestion,
 763                 })
 764             }
 765             ResolutionError::SelfImportCanOnlyAppearOnceInTheList => {
 766                 self.session.create_err(errs::SelfImportCanOnlyAppearOnceInTheList { span })
 767             }
 768             ResolutionError::SelfImportOnlyInImportListWithNonEmptyPrefix => {
 769                 self.session.create_err(errs::SelfImportOnlyInImportListWithNonEmptyPrefix { span })
 770             }
 771             ResolutionError::FailedToResolve { label, suggestion } => {
 772                 let mut err =
 773                     struct_span_err!(self.session, span, E0433, "failed to resolve: {}", &label);
 774                 err.span_label(span, label);
 775
 776                 if let Some((suggestions, msg, applicability)) = suggestion {
 777                     if suggestions.is_empty() {
 778                         err.help(&msg);
 779                         return err;
 780                     }
 781                     err.multipart_suggestion(&msg, suggestions, applicability);
 782                 }
 783
 784                 err
 785             }
 786             ResolutionError::CannotCaptureDynamicEnvironmentInFnItem => {
 787                 self.session.create_err(errs::CannotCaptureDynamicEnvironmentInFnItem { span })
 788             }
 789             ResolutionError::AttemptToUseNonConstantValueInConstant(ident, suggestion, current) => {
 790                 // let foo =...
 791                 //     ^^^ given this Span
 792                 // ------- get this Span to have an applicable suggestion
 793
 794                 // edit:
 795                 // only do this if the const and usage of the non-constant value are on the same line
 796                 // the further the two are apart, the higher the chance of the suggestion being wrong
 797
 798                 let sp = self
 799                     .session
 800                     .source_map()
 801                     .span_extend_to_prev_str(ident.span, current, true, false);
 802
 803                 let ((with, with_label), without) = match sp {
 804                     Some(sp) if !self.session.source_map().is_multiline(sp) => {
 805                         let sp = sp.with_lo(BytePos(sp.lo().0 - (current.len() as u32)));
 806                         (
 807                         (Some(errs::AttemptToUseNonConstantValueInConstantWithSuggestion {
 808                                 span: sp,
 809                                 ident,
 810                                 suggestion,
 811                                 current,
 812                             }), Some(errs::AttemptToUseNonConstantValueInConstantLabelWithSuggestion {span})),
 813                             None,
 814                         )
 815                     }
 816                     _ => (
 817                         (None, None),
 818                         Some(errs::AttemptToUseNonConstantValueInConstantWithoutSuggestion {
 819                             ident_span: ident.span,
 820                             suggestion,
 821                         }),
 822                     ),
 823                 };
 824
 825                 self.session.create_err(errs::AttemptToUseNonConstantValueInConstant {
 826                     span,
 827                     with,
 828                     with_label,
 829                     without,
 830                 })
 831             }
 832             ResolutionError::BindingShadowsSomethingUnacceptable {
 833                 shadowing_binding,
 834                 name,
 835                 participle,
 836                 article,
 837                 shadowed_binding,
 838                 shadowed_binding_span,
 839             } => self.session.create_err(errs::BindingShadowsSomethingUnacceptable {
 840                 span,
 841                 shadowing_binding,
 842                 shadowed_binding,
 843                 article,
 844                 sub_suggestion: match (shadowing_binding, shadowed_binding) {
 845                     (
 846                         PatternSource::Match,
 847                         Res::Def(DefKind::Ctor(CtorOf::Variant | CtorOf::Struct, CtorKind::Fn), _),
 848                     ) => Some(errs::BindingShadowsSomethingUnacceptableSuggestion { span, name }),
 849                     _ => None,
 850                 },
 851                 shadowed_binding_span,
 852                 participle,
 853                 name,
 854             }),
 855             ResolutionError::ForwardDeclaredGenericParam => {
 856                 self.session.create_err(errs::ForwardDeclaredGenericParam { span })
 857             }
 858             ResolutionError::ParamInTyOfConstParam(name) => {
 859                 self.session.create_err(errs::ParamInTyOfConstParam { span, name })
 860             }
 861             ResolutionError::ParamInNonTrivialAnonConst { name, is_type } => {
 862                 self.session.create_err(errs::ParamInNonTrivialAnonConst {
 863                     span,
 864                     name,
 865                     sub_is_type: if is_type {
 866                         errs::ParamInNonTrivialAnonConstIsType::AType
 867                     } else {
 868                         errs::ParamInNonTrivialAnonConstIsType::NotAType { name }
 869                     },
 870                     help: self
 871                         .session
 872                         .is_nightly_build()
 873                         .then_some(errs::ParamInNonTrivialAnonConstHelp),
 874                 })
 875             }
 876             ResolutionError::SelfInGenericParamDefault => {
 877                 self.session.create_err(errs::SelfInGenericParamDefault { span })
 878             }
 879             ResolutionError::UnreachableLabel { name, definition_span, suggestion } => {
 880                 let ((sub_suggestion_label, sub_suggestion), sub_unreachable_label) =
 881                     match suggestion {
 882                         // A reachable label with a similar name exists.
 883                         Some((ident, true)) => (
 884                             (
 885                                 Some(errs::UnreachableLabelSubLabel { ident_span: ident.span }),
 886                                 Some(errs::UnreachableLabelSubSuggestion {
 887                                     span,
 888                                     // intentionally taking 'ident.name' instead of 'ident' itself, as this
 889                                     // could be used in suggestion context
 890                                     ident_name: ident.name,
 891                                 }),
 892                             ),
 893                             None,
 894                         ),
 895                         // An unreachable label with a similar name exists.
 896                         Some((ident, false)) => (
 897                             (None, None),
 898                             Some(errs::UnreachableLabelSubLabelUnreachable {
 899                                 ident_span: ident.span,
 900                             }),
 901                         ),
 902                         // No similarly-named labels exist.
 903                         None => ((None, None), None),
 904                     };
 905                 self.session.create_err(errs::UnreachableLabel {
 906                     span,
 907                     name,
 908                     definition_span,
 909                     sub_suggestion,
 910                     sub_suggestion_label,
 911                     sub_unreachable_label,
 912                 })
 913             }
 914             ResolutionError::TraitImplMismatch {
 915                 name,
 916                 kind,
 917                 code,
 918                 trait_item_span,
 919                 trait_path,
 920             } => {
 921                 let mut err = self.session.struct_span_err_with_code(
 922                     span,
 923                     &format!(
 924                         "item `{}` is an associated {}, which doesn't match its trait `{}`",
 925                         name, kind, trait_path,
 926                     ),
 927                     code,
 928                 );
 929                 err.span_label(span, "does not match trait");
 930                 err.span_label(trait_item_span, "item in trait");
 931                 err
 932             }
 933             ResolutionError::TraitImplDuplicate { name, trait_item_span, old_span } => self
 934                 .session
 935                 .create_err(errs::TraitImplDuplicate { span, name, trait_item_span, old_span }),
 936             ResolutionError::InvalidAsmSym => self.session.create_err(errs::InvalidAsmSym { span }),
 937         }
 938     }
 939
 940     pub(crate) fn report_vis_error(
 941         &mut self,
 942         vis_resolution_error: VisResolutionError<'_>,
 943     ) -> ErrorGuaranteed {
 944         match vis_resolution_error {
 945             VisResolutionError::Relative2018(span, path) => {
 946                 self.session.create_err(errs::Relative2018 {
 947                     span,
 948                     path_span: path.span,
 949                     // intentionally converting to String, as the text would also be used as
 950                     // in suggestion context
 951                     path_str: pprust::path_to_string(&path),
 952                 })
 953             }
 954             VisResolutionError::AncestorOnly(span) => {
 955                 self.session.create_err(errs::AncestorOnly(span))
 956             }
 957             VisResolutionError::FailedToResolve(span, label, suggestion) => {
 958                 self.into_struct_error(span, ResolutionError::FailedToResolve { label, suggestion })
 959             }
 960             VisResolutionError::ExpectedFound(span, path_str, res) => {
 961                 self.session.create_err(errs::ExpectedFound { span, res, path_str })
 962             }
 963             VisResolutionError::Indeterminate(span) => {
 964                 self.session.create_err(errs::Indeterminate(span))
 965             }
 966             VisResolutionError::ModuleOnly(span) => self.session.create_err(errs::ModuleOnly(span)),
 967         }
 968         .emit()
 969     }
 970
 971     /// Lookup typo candidate in scope for a macro or import.
 972     fn early_lookup_typo_candidate(
 973         &mut self,
 974         scope_set: ScopeSet<'a>,
 975         parent_scope: &ParentScope<'a>,
 976         ident: Ident,
 977         filter_fn: &impl Fn(Res) -> bool,
 978     ) -> Option<TypoSuggestion> {
 979         let mut suggestions = Vec::new();
 980         let ctxt = ident.span.ctxt();
 981         self.visit_scopes(scope_set, parent_scope, ctxt, |this, scope, use_prelude, _| {
 982             match scope {
 983                 Scope::DeriveHelpers(expn_id) => {
 984                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 985                     if filter_fn(res) {
 986                         suggestions.extend(
 987                             this.helper_attrs
 988                                 .get(&expn_id)
 989                                 .into_iter()
 990                                 .flatten()
 991                                 .map(|ident| TypoSuggestion::typo_from_ident(*ident, res)),
 992                         );
 993                     }
 994                 }
 995                 Scope::DeriveHelpersCompat => {
 996                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat);
 997                     if filter_fn(res) {
 998                         for derive in parent_scope.derives {
 999                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
1000                             if let Ok((Some(ext), _)) = this.resolve_macro_path(
1001                                 derive,
1002                                 Some(MacroKind::Derive),
1003                                 parent_scope,
1004                                 false,
1005                                 false,
1006                             ) {
1007                                 suggestions.extend(
1008                                     ext.helper_attrs
1009                                         .iter()
1010                                         .map(|name| TypoSuggestion::typo_from_name(*name, res)),
1011                                 );
1012                             }
1013                         }
1014                     }
1015                 }
1016                 Scope::MacroRules(macro_rules_scope) => {
1017                     if let MacroRulesScope::Binding(macro_rules_binding) = macro_rules_scope.get() {
1018                         let res = macro_rules_binding.binding.res();
1019                         if filter_fn(res) {
1020                             suggestions.push(TypoSuggestion::typo_from_ident(
1021                                 macro_rules_binding.ident,
1022                                 res,
1023                             ))
1024                         }
1025                     }
1026                 }
1027                 Scope::CrateRoot => {
1028                     let root_ident = Ident::new(kw::PathRoot, ident.span);
1029                     let root_module = this.resolve_crate_root(root_ident);
1030                     this.add_module_candidates(root_module, &mut suggestions, filter_fn, None);
1031                 }
1032                 Scope::Module(module) => {
1033                     this.add_module_candidates(module, &mut suggestions, filter_fn, None);
1034                 }
1035                 Scope::MacroUsePrelude => {
1036                     suggestions.extend(this.macro_use_prelude.iter().filter_map(
1037                         |(name, binding)| {
1038                             let res = binding.res();
1039                             filter_fn(res).then_some(TypoSuggestion::typo_from_name(*name, res))
1040                         },
1041                     ));
1042                 }
1043                 Scope::BuiltinAttrs => {
1044                     let res = Res::NonMacroAttr(NonMacroAttrKind::Builtin(kw::Empty));
1045                     if filter_fn(res) {
1046                         suggestions.extend(
1047                             BUILTIN_ATTRIBUTES
1048                                 .iter()
1049                                 .map(|attr| TypoSuggestion::typo_from_name(attr.name, res)),
1050                         );
1051                     }
1052                 }
1053                 Scope::ExternPrelude => {
1054                     suggestions.extend(this.extern_prelude.iter().filter_map(|(ident, _)| {
1055                         let res = Res::Def(DefKind::Mod, CRATE_DEF_ID.to_def_id());
1056                         filter_fn(res).then_some(TypoSuggestion::typo_from_ident(*ident, res))
1057                     }));
1058                 }
1059                 Scope::ToolPrelude => {
1060                     let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
1061                     suggestions.extend(
1062                         this.registered_tools
1063                             .iter()
1064                             .map(|ident| TypoSuggestion::typo_from_ident(*ident, res)),
1065                     );
1066                 }
1067                 Scope::StdLibPrelude => {
1068                     if let Some(prelude) = this.prelude {
1069                         let mut tmp_suggestions = Vec::new();
1070                         this.add_module_candidates(prelude, &mut tmp_suggestions, filter_fn, None);
1071                         suggestions.extend(
1072                             tmp_suggestions
1073                                 .into_iter()
1074                                 .filter(|s| use_prelude || this.is_builtin_macro(s.res)),
1075                         );
1076                     }
1077                 }
1078                 Scope::BuiltinTypes => {
1079                     suggestions.extend(PrimTy::ALL.iter().filter_map(|prim_ty| {
1080                         let res = Res::PrimTy(*prim_ty);
1081                         filter_fn(res)
1082                             .then_some(TypoSuggestion::typo_from_name(prim_ty.name(), res))
1083                     }))
1084                 }
1085             }
1086
1087             None::<()>
1088         });
1089
1090         // Make sure error reporting is deterministic.
1091         suggestions.sort_by(|a, b| a.candidate.as_str().partial_cmp(b.candidate.as_str()).unwrap());
1092
1093         match find_best_match_for_name(
1094             &suggestions.iter().map(|suggestion| suggestion.candidate).collect::<Vec<Symbol>>(),
1095             ident.name,
1096             None,
1097         ) {
1098             Some(found) if found != ident.name => {
1099                 suggestions.into_iter().find(|suggestion| suggestion.candidate == found)
1100             }
1101             _ => None,
1102         }
1103     }
1104
1105     fn lookup_import_candidates_from_module<FilterFn>(
1106         &mut self,
1107         lookup_ident: Ident,
1108         namespace: Namespace,
1109         parent_scope: &ParentScope<'a>,
1110         start_module: Module<'a>,
1111         crate_name: Ident,
1112         filter_fn: FilterFn,
1113     ) -> Vec<ImportSuggestion>
1114     where
1115         FilterFn: Fn(Res) -> bool,
1116     {
1117         let mut candidates = Vec::new();
1118         let mut seen_modules = FxHashSet::default();
1119         let mut worklist = vec![(start_module, ThinVec::<ast::PathSegment>::new(), true)];
1120         let mut worklist_via_import = vec![];
1121
1122         while let Some((in_module, path_segments, accessible)) = match worklist.pop() {
1123             None => worklist_via_import.pop(),
1124             Some(x) => Some(x),
1125         } {
1126             let in_module_is_extern = !in_module.def_id().is_local();
1127             // We have to visit module children in deterministic order to avoid
1128             // instabilities in reported imports (#43552).
1129             in_module.for_each_child(self, |this, ident, ns, name_binding| {
1130                 // avoid non-importable candidates
1131                 if !name_binding.is_importable() {
1132                     return;
1133                 }
1134
1135                 let child_accessible =
1136                     accessible && this.is_accessible_from(name_binding.vis, parent_scope.module);
1137
1138                 // do not venture inside inaccessible items of other crates
1139                 if in_module_is_extern && !child_accessible {
1140                     return;
1141                 }
1142
1143                 let via_import = name_binding.is_import() && !name_binding.is_extern_crate();
1144
1145                 // There is an assumption elsewhere that paths of variants are in the enum's
1146                 // declaration and not imported. With this assumption, the variant component is
1147                 // chopped and the rest of the path is assumed to be the enum's own path. For
1148                 // errors where a variant is used as the type instead of the enum, this causes
1149                 // funny looking invalid suggestions, i.e `foo` instead of `foo::MyEnum`.
1150                 if via_import && name_binding.is_possibly_imported_variant() {
1151                     return;
1152                 }
1153
1154                 // #90113: Do not count an inaccessible reexported item as a candidate.
1155                 if let NameBindingKind::Import { binding, .. } = name_binding.kind {
1156                     if this.is_accessible_from(binding.vis, parent_scope.module)
1157                         && !this.is_accessible_from(name_binding.vis, parent_scope.module)
1158                     {
1159                         return;
1160                     }
1161                 }
1162
1163                 // collect results based on the filter function
1164                 // avoid suggesting anything from the same module in which we are resolving
1165                 // avoid suggesting anything with a hygienic name
1166                 if ident.name == lookup_ident.name
1167                     && ns == namespace
1168                     && !ptr::eq(in_module, parent_scope.module)
1169                     && !ident.span.normalize_to_macros_2_0().from_expansion()
1170                 {
1171                     let res = name_binding.res();
1172                     if filter_fn(res) {
1173                         // create the path
1174                         let mut segms = path_segments.clone();
1175                         if lookup_ident.span.rust_2018() {
1176                             // crate-local absolute paths start with `crate::` in edition 2018
1177                             // FIXME: may also be stabilized for Rust 2015 (Issues #45477, #44660)
1178                             segms.insert(0, ast::PathSegment::from_ident(crate_name));
1179                         }
1180
1181                         segms.push(ast::PathSegment::from_ident(ident));
1182                         let path = Path { span: name_binding.span, segments: segms, tokens: None };
1183                         let did = match res {
1184                             Res::Def(DefKind::Ctor(..), did) => this.opt_parent(did),
1185                             _ => res.opt_def_id(),
1186                         };
1187
1188                         if child_accessible {
1189                             // Remove invisible match if exists
1190                             if let Some(idx) = candidates
1191                                 .iter()
1192                                 .position(|v: &ImportSuggestion| v.did == did && !v.accessible)
1193                             {
1194                                 candidates.remove(idx);
1195                             }
1196                         }
1197
1198                         if candidates.iter().all(|v: &ImportSuggestion| v.did != did) {
1199                             // See if we're recommending TryFrom, TryInto, or FromIterator and add
1200                             // a note about editions
1201                             let note = if let Some(did) = did {
1202                                 let requires_note = !did.is_local()
1203                                     && this.cstore().item_attrs_untracked(did, this.session).any(
1204                                         |attr| {
1205                                             if attr.has_name(sym::rustc_diagnostic_item) {
1206                                                 [sym::TryInto, sym::TryFrom, sym::FromIterator]
1207                                                     .map(|x| Some(x))
1208                                                     .contains(&attr.value_str())
1209                                             } else {
1210                                                 false
1211                                             }
1212                                         },
1213                                     );
1214
1215                                 requires_note.then(|| {
1216                                     format!(
1217                                         "'{}' is included in the prelude starting in Edition 2021",
1218                                         path_names_to_string(&path)
1219                                     )
1220                                 })
1221                             } else {
1222                                 None
1223                             };
1224
1225                             candidates.push(ImportSuggestion {
1226                                 did,
1227                                 descr: res.descr(),
1228                                 path,
1229                                 accessible: child_accessible,
1230                                 note,
1231                             });
1232                         }
1233                     }
1234                 }
1235
1236                 // collect submodules to explore
1237                 if let Some(module) = name_binding.module() {
1238                     // form the path
1239                     let mut path_segments = path_segments.clone();
1240                     path_segments.push(ast::PathSegment::from_ident(ident));
1241
1242                     let is_extern_crate_that_also_appears_in_prelude =
1243                         name_binding.is_extern_crate() && lookup_ident.span.rust_2018();
1244
1245                     if !is_extern_crate_that_also_appears_in_prelude {
1246                         // add the module to the lookup
1247                         if seen_modules.insert(module.def_id()) {
1248                             if via_import { &mut worklist_via_import } else { &mut worklist }
1249                                 .push((module, path_segments, child_accessible));
1250                         }
1251                     }
1252                 }
1253             })
1254         }
1255
1256         // If only some candidates are accessible, take just them
1257         if !candidates.iter().all(|v: &ImportSuggestion| !v.accessible) {
1258             candidates.retain(|x| x.accessible)
1259         }
1260
1261         candidates
1262     }
1263
1264     /// When name resolution fails, this method can be used to look up candidate
1265     /// entities with the expected name. It allows filtering them using the
1266     /// supplied predicate (which should be used to only accept the types of
1267     /// definitions expected, e.g., traits). The lookup spans across all crates.
1268     ///
1269     /// N.B., the method does not look into imports, but this is not a problem,
1270     /// since we report the definitions (thus, the de-aliased imports).
1271     pub(crate) fn lookup_import_candidates<FilterFn>(
1272         &mut self,
1273         lookup_ident: Ident,
1274         namespace: Namespace,
1275         parent_scope: &ParentScope<'a>,
1276         filter_fn: FilterFn,
1277     ) -> Vec<ImportSuggestion>
1278     where
1279         FilterFn: Fn(Res) -> bool,
1280     {
1281         let mut suggestions = self.lookup_import_candidates_from_module(
1282             lookup_ident,
1283             namespace,
1284             parent_scope,
1285             self.graph_root,
1286             Ident::with_dummy_span(kw::Crate),
1287             &filter_fn,
1288         );
1289
1290         if lookup_ident.span.rust_2018() {
1291             let extern_prelude_names = self.extern_prelude.clone();
1292             for (ident, _) in extern_prelude_names.into_iter() {
1293                 if ident.span.from_expansion() {
1294                     // Idents are adjusted to the root context before being
1295                     // resolved in the extern prelude, so reporting this to the
1296                     // user is no help. This skips the injected
1297                     // `extern crate std` in the 2018 edition, which would
1298                     // otherwise cause duplicate suggestions.
1299                     continue;
1300                 }
1301                 if let Some(crate_id) = self.crate_loader.maybe_process_path_extern(ident.name) {
1302                     let crate_root = self.expect_module(crate_id.as_def_id());
1303                     suggestions.extend(self.lookup_import_candidates_from_module(
1304                         lookup_ident,
1305                         namespace,
1306                         parent_scope,
1307                         crate_root,
1308                         ident,
1309                         &filter_fn,
1310                     ));
1311                 }
1312             }
1313         }
1314
1315         suggestions
1316     }
1317
1318     pub(crate) fn unresolved_macro_suggestions(
1319         &mut self,
1320         err: &mut Diagnostic,
1321         macro_kind: MacroKind,
1322         parent_scope: &ParentScope<'a>,
1323         ident: Ident,
1324     ) {
1325         let is_expected = &|res: Res| res.macro_kind() == Some(macro_kind);
1326         let suggestion = self.early_lookup_typo_candidate(
1327             ScopeSet::Macro(macro_kind),
1328             parent_scope,
1329             ident,
1330             is_expected,
1331         );
1332         self.add_typo_suggestion(err, suggestion, ident.span);
1333
1334         let import_suggestions =
1335             self.lookup_import_candidates(ident, Namespace::MacroNS, parent_scope, is_expected);
1336         show_candidates(
1337             &self.session,
1338             &self.source_span,
1339             err,
1340             None,
1341             &import_suggestions,
1342             Instead::No,
1343             FoundUse::Yes,
1344             DiagnosticMode::Normal,
1345             vec![],
1346         );
1347
1348         if macro_kind == MacroKind::Derive && (ident.name == sym::Send || ident.name == sym::Sync) {
1349             let msg = format!("unsafe traits like `{}` should be implemented explicitly", ident);
1350             err.span_note(ident.span, &msg);
1351             return;
1352         }
1353         if self.macro_names.contains(&ident.normalize_to_macros_2_0()) {
1354             err.help("have you added the `#[macro_use]` on the module/import?");
1355             return;
1356         }
1357         if ident.name == kw::Default
1358             && let ModuleKind::Def(DefKind::Enum, def_id, _) = parent_scope.module.kind
1359             && let Some(span) = self.opt_span(def_id)
1360         {
1361             let source_map = self.session.source_map();
1362             let head_span = source_map.guess_head_span(span);
1363             if let Ok(head) = source_map.span_to_snippet(head_span) {
1364                 err.span_suggestion(head_span, "consider adding a derive", format!("#[derive(Default)]\n{head}"), Applicability::MaybeIncorrect);
1365             } else {
1366                 err.span_help(
1367                     head_span,
1368                     "consider adding `#[derive(Default)]` to this enum",
1369                 );
1370             }
1371         }
1372         for ns in [Namespace::MacroNS, Namespace::TypeNS, Namespace::ValueNS] {
1373             if let Ok(binding) = self.early_resolve_ident_in_lexical_scope(
1374                 ident,
1375                 ScopeSet::All(ns, false),
1376                 &parent_scope,
1377                 None,
1378                 false,
1379                 None,
1380             ) {
1381                 let desc = match binding.res() {
1382                     Res::Def(DefKind::Macro(MacroKind::Bang), _) => {
1383                         "a function-like macro".to_string()
1384                     }
1385                     Res::Def(DefKind::Macro(MacroKind::Attr), _) | Res::NonMacroAttr(..) => {
1386                         format!("an attribute: `#[{}]`", ident)
1387                     }
1388                     Res::Def(DefKind::Macro(MacroKind::Derive), _) => {
1389                         format!("a derive macro: `#[derive({})]`", ident)
1390                     }
1391                     Res::ToolMod => {
1392                         // Don't confuse the user with tool modules.
1393                         continue;
1394                     }
1395                     Res::Def(DefKind::Trait, _) if macro_kind == MacroKind::Derive => {
1396                         "only a trait, without a derive macro".to_string()
1397                     }
1398                     res => format!(
1399                         "{} {}, not {} {}",
1400                         res.article(),
1401                         res.descr(),
1402                         macro_kind.article(),
1403                         macro_kind.descr_expected(),
1404                     ),
1405                 };
1406                 if let crate::NameBindingKind::Import { import, .. } = binding.kind {
1407                     if !import.span.is_dummy() {
1408                         err.span_note(
1409                             import.span,
1410                             &format!("`{}` is imported here, but it is {}", ident, desc),
1411                         );
1412                         // Silence the 'unused import' warning we might get,
1413                         // since this diagnostic already covers that import.
1414                         self.record_use(ident, binding, false);
1415                         return;
1416                     }
1417                 }
1418                 err.note(&format!("`{}` is in scope, but it is {}", ident, desc));
1419                 return;
1420             }
1421         }
1422     }
1423
1424     pub(crate) fn add_typo_suggestion(
1425         &self,
1426         err: &mut Diagnostic,
1427         suggestion: Option<TypoSuggestion>,
1428         span: Span,
1429     ) -> bool {
1430         let suggestion = match suggestion {
1431             None => return false,
1432             // We shouldn't suggest underscore.
1433             Some(suggestion) if suggestion.candidate == kw::Underscore => return false,
1434             Some(suggestion) => suggestion,
1435         };
1436         let def_span = suggestion.res.opt_def_id().and_then(|def_id| match def_id.krate {
1437             LOCAL_CRATE => self.opt_span(def_id),
1438             _ => Some(self.cstore().get_span_untracked(def_id, self.session)),
1439         });
1440         if let Some(def_span) = def_span {
1441             if span.overlaps(def_span) {
1442                 // Don't suggest typo suggestion for itself like in the following:
1443                 // error[E0423]: expected function, tuple struct or tuple variant, found struct `X`
1444                 //   --> $DIR/issue-64792-bad-unicode-ctor.rs:3:14
1445                 //    |
1446                 // LL | struct X {}
1447                 //    | ----------- `X` defined here
1448                 // LL |
1449                 // LL | const Y: X = X("ö");
1450                 //    | -------------^^^^^^- similarly named constant `Y` defined here
1451                 //    |
1452                 // help: use struct literal syntax instead
1453                 //    |
1454                 // LL | const Y: X = X {};
1455                 //    |              ^^^^
1456                 // help: a constant with a similar name exists
1457                 //    |
1458                 // LL | const Y: X = Y("ö");
1459                 //    |              ^
1460                 return false;
1461             }
1462             let prefix = match suggestion.target {
1463                 SuggestionTarget::SimilarlyNamed => "similarly named ",
1464                 SuggestionTarget::SingleItem => "",
1465             };
1466
1467             err.span_label(
1468                 self.session.source_map().guess_head_span(def_span),
1469                 &format!(
1470                     "{}{} `{}` defined here",
1471                     prefix,
1472                     suggestion.res.descr(),
1473                     suggestion.candidate,
1474                 ),
1475             );
1476         }
1477         let msg = match suggestion.target {
1478             SuggestionTarget::SimilarlyNamed => format!(
1479                 "{} {} with a similar name exists",
1480                 suggestion.res.article(),
1481                 suggestion.res.descr()
1482             ),
1483             SuggestionTarget::SingleItem => {
1484                 format!("maybe you meant this {}", suggestion.res.descr())
1485             }
1486         };
1487         err.span_suggestion(span, &msg, suggestion.candidate, Applicability::MaybeIncorrect);
1488         true
1489     }
1490
1491     fn binding_description(&self, b: &NameBinding<'_>, ident: Ident, from_prelude: bool) -> String {
1492         let res = b.res();
1493         if b.span.is_dummy() || !self.session.source_map().is_span_accessible(b.span) {
1494             // These already contain the "built-in" prefix or look bad with it.
1495             let add_built_in =
1496                 !matches!(b.res(), Res::NonMacroAttr(..) | Res::PrimTy(..) | Res::ToolMod);
1497             let (built_in, from) = if from_prelude {
1498                 ("", " from prelude")
1499             } else if b.is_extern_crate()
1500                 && !b.is_import()
1501                 && self.session.opts.externs.get(ident.as_str()).is_some()
1502             {
1503                 ("", " passed with `--extern`")
1504             } else if add_built_in {
1505                 (" built-in", "")
1506             } else {
1507                 ("", "")
1508             };
1509
1510             let a = if built_in.is_empty() { res.article() } else { "a" };
1511             format!("{a}{built_in} {thing}{from}", thing = res.descr())
1512         } else {
1513             let introduced = if b.is_import_user_facing() { "imported" } else { "defined" };
1514             format!("the {thing} {introduced} here", thing = res.descr())
1515         }
1516     }
1517
1518     fn report_ambiguity_error(&self, ambiguity_error: &AmbiguityError<'_>) {
1519         let AmbiguityError { kind, ident, b1, b2, misc1, misc2 } = *ambiguity_error;
1520         let (b1, b2, misc1, misc2, swapped) = if b2.span.is_dummy() && !b1.span.is_dummy() {
1521             // We have to print the span-less alternative first, otherwise formatting looks bad.
1522             (b2, b1, misc2, misc1, true)
1523         } else {
1524             (b1, b2, misc1, misc2, false)
1525         };
1526
1527         let mut err = struct_span_err!(self.session, ident.span, E0659, "`{ident}` is ambiguous");
1528         err.span_label(ident.span, "ambiguous name");
1529         err.note(&format!("ambiguous because of {}", kind.descr()));
1530
1531         let mut could_refer_to = |b: &NameBinding<'_>, misc: AmbiguityErrorMisc, also: &str| {
1532             let what = self.binding_description(b, ident, misc == AmbiguityErrorMisc::FromPrelude);
1533             let note_msg = format!("`{ident}` could{also} refer to {what}");
1534
1535             let thing = b.res().descr();
1536             let mut help_msgs = Vec::new();
1537             if b.is_glob_import()
1538                 && (kind == AmbiguityKind::GlobVsGlob
1539                     || kind == AmbiguityKind::GlobVsExpanded
1540                     || kind == AmbiguityKind::GlobVsOuter && swapped != also.is_empty())
1541             {
1542                 help_msgs.push(format!(
1543                     "consider adding an explicit import of `{ident}` to disambiguate"
1544                 ))
1545             }
1546             if b.is_extern_crate() && ident.span.rust_2018() {
1547                 help_msgs.push(format!("use `::{ident}` to refer to this {thing} unambiguously"))
1548             }
1549             if misc == AmbiguityErrorMisc::SuggestCrate {
1550                 help_msgs
1551                     .push(format!("use `crate::{ident}` to refer to this {thing} unambiguously"))
1552             } else if misc == AmbiguityErrorMisc::SuggestSelf {
1553                 help_msgs
1554                     .push(format!("use `self::{ident}` to refer to this {thing} unambiguously"))
1555             }
1556
1557             err.span_note(b.span, &note_msg);
1558             for (i, help_msg) in help_msgs.iter().enumerate() {
1559                 let or = if i == 0 { "" } else { "or " };
1560                 err.help(&format!("{}{}", or, help_msg));
1561             }
1562         };
1563
1564         could_refer_to(b1, misc1, "");
1565         could_refer_to(b2, misc2, " also");
1566         err.emit();
1567     }
1568
1569     /// If the binding refers to a tuple struct constructor with fields,
1570     /// returns the span of its fields.
1571     fn ctor_fields_span(&self, binding: &NameBinding<'_>) -> Option<Span> {
1572         if let NameBindingKind::Res(Res::Def(
1573             DefKind::Ctor(CtorOf::Struct, CtorKind::Fn),
1574             ctor_def_id,
1575         )) = binding.kind
1576         {
1577             let def_id = self.parent(ctor_def_id);
1578             let fields = self.field_names.get(&def_id)?;
1579             return fields.iter().map(|name| name.span).reduce(Span::to); // None for `struct Foo()`
1580         }
1581         None
1582     }
1583
1584     fn report_privacy_error(&self, privacy_error: &PrivacyError<'_>) {
1585         let PrivacyError { ident, binding, .. } = *privacy_error;
1586
1587         let res = binding.res();
1588         let ctor_fields_span = self.ctor_fields_span(binding);
1589         let plain_descr = res.descr().to_string();
1590         let nonimport_descr =
1591             if ctor_fields_span.is_some() { plain_descr + " constructor" } else { plain_descr };
1592         let import_descr = nonimport_descr.clone() + " import";
1593         let get_descr =
1594             |b: &NameBinding<'_>| if b.is_import() { &import_descr } else { &nonimport_descr };
1595
1596         // Print the primary message.
1597         let descr = get_descr(binding);
1598         let mut err =
1599             struct_span_err!(self.session, ident.span, E0603, "{} `{}` is private", descr, ident);
1600         err.span_label(ident.span, &format!("private {}", descr));
1601         if let Some(span) = ctor_fields_span {
1602             err.span_label(span, "a constructor is private if any of the fields is private");
1603         }
1604
1605         // Print the whole import chain to make it easier to see what happens.
1606         let first_binding = binding;
1607         let mut next_binding = Some(binding);
1608         let mut next_ident = ident;
1609         while let Some(binding) = next_binding {
1610             let name = next_ident;
1611             next_binding = match binding.kind {
1612                 _ if res == Res::Err => None,
1613                 NameBindingKind::Import { binding, import, .. } => match import.kind {
1614                     _ if binding.span.is_dummy() => None,
1615                     ImportKind::Single { source, .. } => {
1616                         next_ident = source;
1617                         Some(binding)
1618                     }
1619                     ImportKind::Glob { .. } | ImportKind::MacroUse | ImportKind::MacroExport => {
1620                         Some(binding)
1621                     }
1622                     ImportKind::ExternCrate { .. } => None,
1623                 },
1624                 _ => None,
1625             };
1626
1627             let first = ptr::eq(binding, first_binding);
1628             let msg = format!(
1629                 "{and_refers_to}the {item} `{name}`{which} is defined here{dots}",
1630                 and_refers_to = if first { "" } else { "...and refers to " },
1631                 item = get_descr(binding),
1632                 which = if first { "" } else { " which" },
1633                 dots = if next_binding.is_some() { "..." } else { "" },
1634             );
1635             let def_span = self.session.source_map().guess_head_span(binding.span);
1636             let mut note_span = MultiSpan::from_span(def_span);
1637             if !first && binding.vis.is_public() {
1638                 note_span.push_span_label(def_span, "consider importing it directly");
1639             }
1640             err.span_note(note_span, &msg);
1641         }
1642
1643         err.emit();
1644     }
1645
1646     pub(crate) fn find_similarly_named_module_or_crate(
1647         &mut self,
1648         ident: Symbol,
1649         current_module: &Module<'a>,
1650     ) -> Option<Symbol> {
1651         let mut candidates = self
1652             .extern_prelude
1653             .iter()
1654             .map(|(ident, _)| ident.name)
1655             .chain(
1656                 self.module_map
1657                     .iter()
1658                     .filter(|(_, module)| {
1659                         current_module.is_ancestor_of(module) && !ptr::eq(current_module, *module)
1660                     })
1661                     .flat_map(|(_, module)| module.kind.name()),
1662             )
1663             .filter(|c| !c.to_string().is_empty())
1664             .collect::<Vec<_>>();
1665         candidates.sort();
1666         candidates.dedup();
1667         match find_best_match_for_name(&candidates, ident, None) {
1668             Some(sugg) if sugg == ident => None,
1669             sugg => sugg,
1670         }
1671     }
1672
1673     pub(crate) fn report_path_resolution_error(
1674         &mut self,
1675         path: &[Segment],
1676         opt_ns: Option<Namespace>, // `None` indicates a module path in import
1677         parent_scope: &ParentScope<'a>,
1678         ribs: Option<&PerNS<Vec<Rib<'a>>>>,
1679         ignore_binding: Option<&'a NameBinding<'a>>,
1680         module: Option<ModuleOrUniformRoot<'a>>,
1681         i: usize,
1682         ident: Ident,
1683     ) -> (String, Option<Suggestion>) {
1684         let is_last = i == path.len() - 1;
1685         let ns = if is_last { opt_ns.unwrap_or(TypeNS) } else { TypeNS };
1686         let module_res = match module {
1687             Some(ModuleOrUniformRoot::Module(module)) => module.res(),
1688             _ => None,
1689         };
1690         if module_res == self.graph_root.res() {
1691             let is_mod = |res| matches!(res, Res::Def(DefKind::Mod, _));
1692             let mut candidates = self.lookup_import_candidates(ident, TypeNS, parent_scope, is_mod);
1693             candidates
1694                 .sort_by_cached_key(|c| (c.path.segments.len(), pprust::path_to_string(&c.path)));
1695             if let Some(candidate) = candidates.get(0) {
1696                 (
1697                     String::from("unresolved import"),
1698                     Some((
1699                         vec![(ident.span, pprust::path_to_string(&candidate.path))],
1700                         String::from("a similar path exists"),
1701                         Applicability::MaybeIncorrect,
1702                     )),
1703                 )
1704             } else if self.session.edition() == Edition::Edition2015 {
1705                 (
1706                     format!("maybe a missing crate `{ident}`?"),
1707                     Some((
1708                         vec![],
1709                         format!(
1710                             "consider adding `extern crate {ident}` to use the `{ident}` crate"
1711                         ),
1712                         Applicability::MaybeIncorrect,
1713                     )),
1714                 )
1715             } else {
1716                 (format!("could not find `{ident}` in the crate root"), None)
1717             }
1718         } else if i > 0 {
1719             let parent = path[i - 1].ident.name;
1720             let parent = match parent {
1721                 // ::foo is mounted at the crate root for 2015, and is the extern
1722                 // prelude for 2018+
1723                 kw::PathRoot if self.session.edition() > Edition::Edition2015 => {
1724                     "the list of imported crates".to_owned()
1725                 }
1726                 kw::PathRoot | kw::Crate => "the crate root".to_owned(),
1727                 _ => format!("`{parent}`"),
1728             };
1729
1730             let mut msg = format!("could not find `{}` in {}", ident, parent);
1731             if ns == TypeNS || ns == ValueNS {
1732                 let ns_to_try = if ns == TypeNS { ValueNS } else { TypeNS };
1733                 let binding = if let Some(module) = module {
1734                     self.resolve_ident_in_module(
1735                         module,
1736                         ident,
1737                         ns_to_try,
1738                         parent_scope,
1739                         None,
1740                         ignore_binding,
1741                     ).ok()
1742                 } else if let Some(ribs) = ribs
1743                     && let Some(TypeNS | ValueNS) = opt_ns
1744                 {
1745                     match self.resolve_ident_in_lexical_scope(
1746                         ident,
1747                         ns_to_try,
1748                         parent_scope,
1749                         None,
1750                         &ribs[ns_to_try],
1751                         ignore_binding,
1752                     ) {
1753                         // we found a locally-imported or available item/module
1754                         Some(LexicalScopeBinding::Item(binding)) => Some(binding),
1755                         _ => None,
1756                     }
1757                 } else {
1758                     let scopes = ScopeSet::All(ns_to_try, opt_ns.is_none());
1759                     self.early_resolve_ident_in_lexical_scope(
1760                         ident,
1761                         scopes,
1762                         parent_scope,
1763                         None,
1764                         false,
1765                         ignore_binding,
1766                     ).ok()
1767                 };
1768                 if let Some(binding) = binding {
1769                     let mut found = |what| {
1770                         msg = format!(
1771                             "expected {}, found {} `{}` in {}",
1772                             ns.descr(),
1773                             what,
1774                             ident,
1775                             parent
1776                         )
1777                     };
1778                     if binding.module().is_some() {
1779                         found("module")
1780                     } else {
1781                         match binding.res() {
1782                             Res::Def(kind, id) => found(kind.descr(id)),
1783                             _ => found(ns_to_try.descr()),
1784                         }
1785                     }
1786                 };
1787             }
1788             (msg, None)
1789         } else if ident.name == kw::SelfUpper {
1790             ("`Self` is only available in impls, traits, and type definitions".to_string(), None)
1791         } else if ident.name.as_str().chars().next().map_or(false, |c| c.is_ascii_uppercase()) {
1792             // Check whether the name refers to an item in the value namespace.
1793             let binding = if let Some(ribs) = ribs {
1794                 self.resolve_ident_in_lexical_scope(
1795                     ident,
1796                     ValueNS,
1797                     parent_scope,
1798                     None,
1799                     &ribs[ValueNS],
1800                     ignore_binding,
1801                 )
1802             } else {
1803                 None
1804             };
1805             let match_span = match binding {
1806                 // Name matches a local variable. For example:
1807                 // ```
1808                 // fn f() {
1809                 //     let Foo: &str = "";
1810                 //     println!("{}", Foo::Bar); // Name refers to local
1811                 //                               // variable `Foo`.
1812                 // }
1813                 // ```
1814                 Some(LexicalScopeBinding::Res(Res::Local(id))) => {
1815                     Some(*self.pat_span_map.get(&id).unwrap())
1816                 }
1817                 // Name matches item from a local name binding
1818                 // created by `use` declaration. For example:
1819                 // ```
1820                 // pub Foo: &str = "";
1821                 //
1822                 // mod submod {
1823                 //     use super::Foo;
1824                 //     println!("{}", Foo::Bar); // Name refers to local
1825                 //                               // binding `Foo`.
1826                 // }
1827                 // ```
1828                 Some(LexicalScopeBinding::Item(name_binding)) => Some(name_binding.span),
1829                 _ => None,
1830             };
1831             let suggestion = if let Some(span) = match_span {
1832                 Some((
1833                     vec![(span, String::from(""))],
1834                     format!("`{}` is defined here, but is not a type", ident),
1835                     Applicability::MaybeIncorrect,
1836                 ))
1837             } else {
1838                 None
1839             };
1840
1841             (format!("use of undeclared type `{}`", ident), suggestion)
1842         } else {
1843             let mut suggestion = None;
1844             if ident.name == sym::alloc {
1845                 suggestion = Some((
1846                     vec![],
1847                     String::from("add `extern crate alloc` to use the `alloc` crate"),
1848                     Applicability::MaybeIncorrect,
1849                 ))
1850             }
1851
1852             suggestion = suggestion.or_else(|| {
1853                 self.find_similarly_named_module_or_crate(ident.name, &parent_scope.module).map(
1854                     |sugg| {
1855                         (
1856                             vec![(ident.span, sugg.to_string())],
1857                             String::from("there is a crate or module with a similar name"),
1858                             Applicability::MaybeIncorrect,
1859                         )
1860                     },
1861                 )
1862             });
1863             (format!("use of undeclared crate or module `{}`", ident), suggestion)
1864         }
1865     }
1866 }
1867
1868 impl<'a, 'b> ImportResolver<'a, 'b> {
1869     /// Adds suggestions for a path that cannot be resolved.
1870     pub(crate) fn make_path_suggestion(
1871         &mut self,
1872         span: Span,
1873         mut path: Vec<Segment>,
1874         parent_scope: &ParentScope<'b>,
1875     ) -> Option<(Vec<Segment>, Option<String>)> {
1876         debug!("make_path_suggestion: span={:?} path={:?}", span, path);
1877
1878         match (path.get(0), path.get(1)) {
1879             // `{{root}}::ident::...` on both editions.
1880             // On 2015 `{{root}}` is usually added implicitly.
1881             (Some(fst), Some(snd))
1882                 if fst.ident.name == kw::PathRoot && !snd.ident.is_path_segment_keyword() => {}
1883             // `ident::...` on 2018.
1884             (Some(fst), _)
1885                 if fst.ident.span.rust_2018() && !fst.ident.is_path_segment_keyword() =>
1886             {
1887                 // Insert a placeholder that's later replaced by `self`/`super`/etc.
1888                 path.insert(0, Segment::from_ident(Ident::empty()));
1889             }
1890             _ => return None,
1891         }
1892
1893         self.make_missing_self_suggestion(path.clone(), parent_scope)
1894             .or_else(|| self.make_missing_crate_suggestion(path.clone(), parent_scope))
1895             .or_else(|| self.make_missing_super_suggestion(path.clone(), parent_scope))
1896             .or_else(|| self.make_external_crate_suggestion(path, parent_scope))
1897     }
1898
1899     /// Suggest a missing `self::` if that resolves to an correct module.
1900     ///
1901     /// ```text
1902     ///    |
1903     /// LL | use foo::Bar;
1904     ///    |     ^^^ did you mean `self::foo`?
1905     /// ```
1906     fn make_missing_self_suggestion(
1907         &mut self,
1908         mut path: Vec<Segment>,
1909         parent_scope: &ParentScope<'b>,
1910     ) -> Option<(Vec<Segment>, Option<String>)> {
1911         // Replace first ident with `self` and check if that is valid.
1912         path[0].ident.name = kw::SelfLower;
1913         let result = self.r.maybe_resolve_path(&path, None, parent_scope);
1914         debug!("make_missing_self_suggestion: path={:?} result={:?}", path, result);
1915         if let PathResult::Module(..) = result { Some((path, None)) } else { None }
1916     }
1917
1918     /// Suggests a missing `crate::` if that resolves to an correct module.
1919     ///
1920     /// ```text
1921     ///    |
1922     /// LL | use foo::Bar;
1923     ///    |     ^^^ did you mean `crate::foo`?
1924     /// ```
1925     fn make_missing_crate_suggestion(
1926         &mut self,
1927         mut path: Vec<Segment>,
1928         parent_scope: &ParentScope<'b>,
1929     ) -> Option<(Vec<Segment>, Option<String>)> {
1930         // Replace first ident with `crate` and check if that is valid.
1931         path[0].ident.name = kw::Crate;
1932         let result = self.r.maybe_resolve_path(&path, None, parent_scope);
1933         debug!("make_missing_crate_suggestion:  path={:?} result={:?}", path, result);
1934         if let PathResult::Module(..) = result {
1935             Some((
1936                 path,
1937                 Some(
1938                     "`use` statements changed in Rust 2018; read more at \
1939                      <https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-\
1940                      clarity.html>"
1941                         .to_string(),
1942                 ),
1943             ))
1944         } else {
1945             None
1946         }
1947     }
1948
1949     /// Suggests a missing `super::` if that resolves to an correct module.
1950     ///
1951     /// ```text
1952     ///    |
1953     /// LL | use foo::Bar;
1954     ///    |     ^^^ did you mean `super::foo`?
1955     /// ```
1956     fn make_missing_super_suggestion(
1957         &mut self,
1958         mut path: Vec<Segment>,
1959         parent_scope: &ParentScope<'b>,
1960     ) -> Option<(Vec<Segment>, Option<String>)> {
1961         // Replace first ident with `crate` and check if that is valid.
1962         path[0].ident.name = kw::Super;
1963         let result = self.r.maybe_resolve_path(&path, None, parent_scope);
1964         debug!("make_missing_super_suggestion:  path={:?} result={:?}", path, result);
1965         if let PathResult::Module(..) = result { Some((path, None)) } else { None }
1966     }
1967
1968     /// Suggests a missing external crate name if that resolves to an correct module.
1969     ///
1970     /// ```text
1971     ///    |
1972     /// LL | use foobar::Baz;
1973     ///    |     ^^^^^^ did you mean `baz::foobar`?
1974     /// ```
1975     ///
1976     /// Used when importing a submodule of an external crate but missing that crate's
1977     /// name as the first part of path.
1978     fn make_external_crate_suggestion(
1979         &mut self,
1980         mut path: Vec<Segment>,
1981         parent_scope: &ParentScope<'b>,
1982     ) -> Option<(Vec<Segment>, Option<String>)> {
1983         if path[1].ident.span.rust_2015() {
1984             return None;
1985         }
1986
1987         // Sort extern crate names in *reverse* order to get
1988         // 1) some consistent ordering for emitted diagnostics, and
1989         // 2) `std` suggestions before `core` suggestions.
1990         let mut extern_crate_names =
1991             self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
1992         extern_crate_names.sort_by(|a, b| b.as_str().partial_cmp(a.as_str()).unwrap());
1993
1994         for name in extern_crate_names.into_iter() {
1995             // Replace first ident with a crate name and check if that is valid.
1996             path[0].ident.name = name;
1997             let result = self.r.maybe_resolve_path(&path, None, parent_scope);
1998             debug!(
1999                 "make_external_crate_suggestion: name={:?} path={:?} result={:?}",
2000                 name, path, result
2001             );
2002             if let PathResult::Module(..) = result {
2003                 return Some((path, None));
2004             }
2005         }
2006
2007         None
2008     }
2009
2010     /// Suggests importing a macro from the root of the crate rather than a module within
2011     /// the crate.
2012     ///
2013     /// ```text
2014     /// help: a macro with this name exists at the root of the crate
2015     ///    |
2016     /// LL | use issue_59764::makro;
2017     ///    |     ^^^^^^^^^^^^^^^^^^
2018     ///    |
2019     ///    = note: this could be because a macro annotated with `#[macro_export]` will be exported
2020     ///            at the root of the crate instead of the module where it is defined
2021     /// ```
2022     pub(crate) fn check_for_module_export_macro(
2023         &mut self,
2024         import: &'b Import<'b>,
2025         module: ModuleOrUniformRoot<'b>,
2026         ident: Ident,
2027     ) -> Option<(Option<Suggestion>, Option<String>)> {
2028         let ModuleOrUniformRoot::Module(mut crate_module) = module else {
2029             return None;
2030         };
2031
2032         while let Some(parent) = crate_module.parent {
2033             crate_module = parent;
2034         }
2035
2036         if ModuleOrUniformRoot::same_def(ModuleOrUniformRoot::Module(crate_module), module) {
2037             // Don't make a suggestion if the import was already from the root of the
2038             // crate.
2039             return None;
2040         }
2041
2042         let resolutions = self.r.resolutions(crate_module).borrow();
2043         let resolution = resolutions.get(&self.r.new_key(ident, MacroNS))?;
2044         let binding = resolution.borrow().binding()?;
2045         if let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() {
2046             let module_name = crate_module.kind.name().unwrap();
2047             let import_snippet = match import.kind {
2048                 ImportKind::Single { source, target, .. } if source != target => {
2049                     format!("{} as {}", source, target)
2050                 }
2051                 _ => format!("{}", ident),
2052             };
2053
2054             let mut corrections: Vec<(Span, String)> = Vec::new();
2055             if !import.is_nested() {
2056                 // Assume this is the easy case of `use issue_59764::foo::makro;` and just remove
2057                 // intermediate segments.
2058                 corrections.push((import.span, format!("{}::{}", module_name, import_snippet)));
2059             } else {
2060                 // Find the binding span (and any trailing commas and spaces).
2061                 //   ie. `use a::b::{c, d, e};`
2062                 //                      ^^^
2063                 let (found_closing_brace, binding_span) = find_span_of_binding_until_next_binding(
2064                     self.r.session,
2065                     import.span,
2066                     import.use_span,
2067                 );
2068                 debug!(
2069                     "check_for_module_export_macro: found_closing_brace={:?} binding_span={:?}",
2070                     found_closing_brace, binding_span
2071                 );
2072
2073                 let mut removal_span = binding_span;
2074                 if found_closing_brace {
2075                     // If the binding span ended with a closing brace, as in the below example:
2076                     //   ie. `use a::b::{c, d};`
2077                     //                      ^
2078                     // Then expand the span of characters to remove to include the previous
2079                     // binding's trailing comma.
2080                     //   ie. `use a::b::{c, d};`
2081                     //                    ^^^
2082                     if let Some(previous_span) =
2083                         extend_span_to_previous_binding(self.r.session, binding_span)
2084                     {
2085                         debug!("check_for_module_export_macro: previous_span={:?}", previous_span);
2086                         removal_span = removal_span.with_lo(previous_span.lo());
2087                     }
2088                 }
2089                 debug!("check_for_module_export_macro: removal_span={:?}", removal_span);
2090
2091                 // Remove the `removal_span`.
2092                 corrections.push((removal_span, "".to_string()));
2093
2094                 // Find the span after the crate name and if it has nested imports immediately
2095                 // after the crate name already.
2096                 //   ie. `use a::b::{c, d};`
2097                 //               ^^^^^^^^^
2098                 //   or  `use a::{b, c, d}};`
2099                 //               ^^^^^^^^^^^
2100                 let (has_nested, after_crate_name) = find_span_immediately_after_crate_name(
2101                     self.r.session,
2102                     module_name,
2103                     import.use_span,
2104                 );
2105                 debug!(
2106                     "check_for_module_export_macro: has_nested={:?} after_crate_name={:?}",
2107                     has_nested, after_crate_name
2108                 );
2109
2110                 let source_map = self.r.session.source_map();
2111
2112                 // Add the import to the start, with a `{` if required.
2113                 let start_point = source_map.start_point(after_crate_name);
2114                 if let Ok(start_snippet) = source_map.span_to_snippet(start_point) {
2115                     corrections.push((
2116                         start_point,
2117                         if has_nested {
2118                             // In this case, `start_snippet` must equal '{'.
2119                             format!("{}{}, ", start_snippet, import_snippet)
2120                         } else {
2121                             // In this case, add a `{`, then the moved import, then whatever
2122                             // was there before.
2123                             format!("{{{}, {}", import_snippet, start_snippet)
2124                         },
2125                     ));
2126                 }
2127
2128                 // Add a `};` to the end if nested, matching the `{` added at the start.
2129                 if !has_nested {
2130                     corrections.push((source_map.end_point(after_crate_name), "};".to_string()));
2131                 }
2132             }
2133
2134             let suggestion = Some((
2135                 corrections,
2136                 String::from("a macro with this name exists at the root of the crate"),
2137                 Applicability::MaybeIncorrect,
2138             ));
2139             Some((suggestion, Some("this could be because a macro annotated with `#[macro_export]` will be exported \
2140             at the root of the crate instead of the module where it is defined"
2141                .to_string())))
2142         } else {
2143             None
2144         }
2145     }
2146 }
2147
2148 /// Given a `binding_span` of a binding within a use statement:
2149 ///
2150 /// ```ignore (illustrative)
2151 /// use foo::{a, b, c};
2152 /// //           ^
2153 /// ```
2154 ///
2155 /// then return the span until the next binding or the end of the statement:
2156 ///
2157 /// ```ignore (illustrative)
2158 /// use foo::{a, b, c};
2159 /// //           ^^^
2160 /// ```
2161 fn find_span_of_binding_until_next_binding(
2162     sess: &Session,
2163     binding_span: Span,
2164     use_span: Span,
2165 ) -> (bool, Span) {
2166     let source_map = sess.source_map();
2167
2168     // Find the span of everything after the binding.
2169     //   ie. `a, e};` or `a};`
2170     let binding_until_end = binding_span.with_hi(use_span.hi());
2171
2172     // Find everything after the binding but not including the binding.
2173     //   ie. `, e};` or `};`
2174     let after_binding_until_end = binding_until_end.with_lo(binding_span.hi());
2175
2176     // Keep characters in the span until we encounter something that isn't a comma or
2177     // whitespace.
2178     //   ie. `, ` or ``.
2179     //
2180     // Also note whether a closing brace character was encountered. If there
2181     // was, then later go backwards to remove any trailing commas that are left.
2182     let mut found_closing_brace = false;
2183     let after_binding_until_next_binding =
2184         source_map.span_take_while(after_binding_until_end, |&ch| {
2185             if ch == '}' {
2186                 found_closing_brace = true;
2187             }
2188             ch == ' ' || ch == ','
2189         });
2190
2191     // Combine the two spans.
2192     //   ie. `a, ` or `a`.
2193     //
2194     // Removing these would leave `issue_52891::{d, e};` or `issue_52891::{d, e, };`
2195     let span = binding_span.with_hi(after_binding_until_next_binding.hi());
2196
2197     (found_closing_brace, span)
2198 }
2199
2200 /// Given a `binding_span`, return the span through to the comma or opening brace of the previous
2201 /// binding.
2202 ///
2203 /// ```ignore (illustrative)
2204 /// use foo::a::{a, b, c};
2205 /// //            ^^--- binding span
2206 /// //            |
2207 /// //            returned span
2208 ///
2209 /// use foo::{a, b, c};
2210 /// //        --- binding span
2211 /// ```
2212 fn extend_span_to_previous_binding(sess: &Session, binding_span: Span) -> Option<Span> {
2213     let source_map = sess.source_map();
2214
2215     // `prev_source` will contain all of the source that came before the span.
2216     // Then split based on a command and take the first (ie. closest to our span)
2217     // snippet. In the example, this is a space.
2218     let prev_source = source_map.span_to_prev_source(binding_span).ok()?;
2219
2220     let prev_comma = prev_source.rsplit(',').collect::<Vec<_>>();
2221     let prev_starting_brace = prev_source.rsplit('{').collect::<Vec<_>>();
2222     if prev_comma.len() <= 1 || prev_starting_brace.len() <= 1 {
2223         return None;
2224     }
2225
2226     let prev_comma = prev_comma.first().unwrap();
2227     let prev_starting_brace = prev_starting_brace.first().unwrap();
2228
2229     // If the amount of source code before the comma is greater than
2230     // the amount of source code before the starting brace then we've only
2231     // got one item in the nested item (eg. `issue_52891::{self}`).
2232     if prev_comma.len() > prev_starting_brace.len() {
2233         return None;
2234     }
2235
2236     Some(binding_span.with_lo(BytePos(
2237         // Take away the number of bytes for the characters we've found and an
2238         // extra for the comma.
2239         binding_span.lo().0 - (prev_comma.as_bytes().len() as u32) - 1,
2240     )))
2241 }
2242
2243 /// Given a `use_span` of a binding within a use statement, returns the highlighted span and if
2244 /// it is a nested use tree.
2245 ///
2246 /// ```ignore (illustrative)
2247 /// use foo::a::{b, c};
2248 /// //       ^^^^^^^^^^ -- false
2249 ///
2250 /// use foo::{a, b, c};
2251 /// //       ^^^^^^^^^^ -- true
2252 ///
2253 /// use foo::{a, b::{c, d}};
2254 /// //       ^^^^^^^^^^^^^^^ -- true
2255 /// ```
2256 fn find_span_immediately_after_crate_name(
2257     sess: &Session,
2258     module_name: Symbol,
2259     use_span: Span,
2260 ) -> (bool, Span) {
2261     debug!(
2262         "find_span_immediately_after_crate_name: module_name={:?} use_span={:?}",
2263         module_name, use_span
2264     );
2265     let source_map = sess.source_map();
2266
2267     // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
2268     let mut num_colons = 0;
2269     // Find second colon.. `use issue_59764:`
2270     let until_second_colon = source_map.span_take_while(use_span, |c| {
2271         if *c == ':' {
2272             num_colons += 1;
2273         }
2274         !matches!(c, ':' if num_colons == 2)
2275     });
2276     // Find everything after the second colon.. `foo::{baz, makro};`
2277     let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
2278
2279     let mut found_a_non_whitespace_character = false;
2280     // Find the first non-whitespace character in `from_second_colon`.. `f`
2281     let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
2282         if found_a_non_whitespace_character {
2283             return false;
2284         }
2285         if !c.is_whitespace() {
2286             found_a_non_whitespace_character = true;
2287         }
2288         true
2289     });
2290
2291     // Find the first `{` in from_second_colon.. `foo::{`
2292     let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
2293
2294     (next_left_bracket == after_second_colon, from_second_colon)
2295 }
2296
2297 /// A suggestion has already been emitted, change the wording slightly to clarify that both are
2298 /// independent options.
2299 enum Instead {
2300     Yes,
2301     No,
2302 }
2303
2304 /// Whether an existing place with an `use` item was found.
2305 enum FoundUse {
2306     Yes,
2307     No,
2308 }
2309
2310 /// Whether a binding is part of a pattern or a use statement. Used for diagnostics.
2311 enum DiagnosticMode {
2312     Normal,
2313     /// The binding is part of a pattern
2314     Pattern,
2315     /// The binding is part of a use statement
2316     Import,
2317 }
2318
2319 pub(crate) fn import_candidates(
2320     session: &Session,
2321     source_span: &IndexVec<LocalDefId, Span>,
2322     err: &mut Diagnostic,
2323     // This is `None` if all placement locations are inside expansions
2324     use_placement_span: Option<Span>,
2325     candidates: &[ImportSuggestion],
2326 ) {
2327     show_candidates(
2328         session,
2329         source_span,
2330         err,
2331         use_placement_span,
2332         candidates,
2333         Instead::Yes,
2334         FoundUse::Yes,
2335         DiagnosticMode::Import,
2336         vec![],
2337     );
2338 }
2339
2340 /// When an entity with a given name is not available in scope, we search for
2341 /// entities with that name in all crates. This method allows outputting the
2342 /// results of this search in a programmer-friendly way
2343 fn show_candidates(
2344     session: &Session,
2345     source_span: &IndexVec<LocalDefId, Span>,
2346     err: &mut Diagnostic,
2347     // This is `None` if all placement locations are inside expansions
2348     use_placement_span: Option<Span>,
2349     candidates: &[ImportSuggestion],
2350     instead: Instead,
2351     found_use: FoundUse,
2352     mode: DiagnosticMode,
2353     path: Vec<Segment>,
2354 ) {
2355     if candidates.is_empty() {
2356         return;
2357     }
2358
2359     let mut accessible_path_strings: Vec<(String, &str, Option<DefId>, &Option<String>)> =
2360         Vec::new();
2361     let mut inaccessible_path_strings: Vec<(String, &str, Option<DefId>, &Option<String>)> =
2362         Vec::new();
2363
2364     candidates.iter().for_each(|c| {
2365         (if c.accessible { &mut accessible_path_strings } else { &mut inaccessible_path_strings })
2366             .push((path_names_to_string(&c.path), c.descr, c.did, &c.note))
2367     });
2368
2369     // we want consistent results across executions, but candidates are produced
2370     // by iterating through a hash map, so make sure they are ordered:
2371     for path_strings in [&mut accessible_path_strings, &mut inaccessible_path_strings] {
2372         path_strings.sort_by(|a, b| a.0.cmp(&b.0));
2373         let core_path_strings =
2374             path_strings.drain_filter(|p| p.0.starts_with("core::")).collect::<Vec<_>>();
2375         path_strings.extend(core_path_strings);
2376         path_strings.dedup_by(|a, b| a.0 == b.0);
2377     }
2378
2379     if !accessible_path_strings.is_empty() {
2380         let (determiner, kind, name) = if accessible_path_strings.len() == 1 {
2381             ("this", accessible_path_strings[0].1, format!(" `{}`", accessible_path_strings[0].0))
2382         } else {
2383             ("one of these", "items", String::new())
2384         };
2385
2386         let instead = if let Instead::Yes = instead { " instead" } else { "" };
2387         let mut msg = if let DiagnosticMode::Pattern = mode {
2388             format!(
2389                 "if you meant to match on {}{}{}, use the full path in the pattern",
2390                 kind, instead, name
2391             )
2392         } else {
2393             format!("consider importing {} {}{}", determiner, kind, instead)
2394         };
2395
2396         for note in accessible_path_strings.iter().flat_map(|cand| cand.3.as_ref()) {
2397             err.note(note);
2398         }
2399
2400         if let Some(span) = use_placement_span {
2401             let add_use = match mode {
2402                 DiagnosticMode::Pattern => {
2403                     err.span_suggestions(
2404                         span,
2405                         &msg,
2406                         accessible_path_strings.into_iter().map(|a| a.0),
2407                         Applicability::MaybeIncorrect,
2408                     );
2409                     return;
2410                 }
2411                 DiagnosticMode::Import => "",
2412                 DiagnosticMode::Normal => "use ",
2413             };
2414             for candidate in &mut accessible_path_strings {
2415                 // produce an additional newline to separate the new use statement
2416                 // from the directly following item.
2417                 let additional_newline = if let FoundUse::Yes = found_use { "" } else { "\n" };
2418                 candidate.0 = format!("{}{};\n{}", add_use, &candidate.0, additional_newline);
2419             }
2420
2421             err.span_suggestions(
2422                 span,
2423                 &msg,
2424                 accessible_path_strings.into_iter().map(|a| a.0),
2425                 Applicability::MaybeIncorrect,
2426             );
2427             if let [first, .., last] = &path[..] {
2428                 let sp = first.ident.span.until(last.ident.span);
2429                 if sp.can_be_used_for_suggestions() {
2430                     err.span_suggestion_verbose(
2431                         sp,
2432                         &format!("if you import `{}`, refer to it directly", last.ident),
2433                         "",
2434                         Applicability::Unspecified,
2435                     );
2436                 }
2437             }
2438         } else {
2439             msg.push(':');
2440
2441             for candidate in accessible_path_strings {
2442                 msg.push('\n');
2443                 msg.push_str(&candidate.0);
2444             }
2445
2446             err.note(&msg);
2447         }
2448     } else if !matches!(mode, DiagnosticMode::Import) {
2449         assert!(!inaccessible_path_strings.is_empty());
2450
2451         let prefix = if let DiagnosticMode::Pattern = mode {
2452             "you might have meant to match on "
2453         } else {
2454             ""
2455         };
2456         if inaccessible_path_strings.len() == 1 {
2457             let (name, descr, def_id, note) = &inaccessible_path_strings[0];
2458             let msg = format!(
2459                 "{}{} `{}`{} exists but is inaccessible",
2460                 prefix,
2461                 descr,
2462                 name,
2463                 if let DiagnosticMode::Pattern = mode { ", which" } else { "" }
2464             );
2465
2466             if let Some(local_def_id) = def_id.and_then(|did| did.as_local()) {
2467                 let span = source_span[local_def_id];
2468                 let span = session.source_map().guess_head_span(span);
2469                 let mut multi_span = MultiSpan::from_span(span);
2470                 multi_span.push_span_label(span, "not accessible");
2471                 err.span_note(multi_span, &msg);
2472             } else {
2473                 err.note(&msg);
2474             }
2475             if let Some(note) = (*note).as_deref() {
2476                 err.note(note);
2477             }
2478         } else {
2479             let (_, descr_first, _, _) = &inaccessible_path_strings[0];
2480             let descr = if inaccessible_path_strings
2481                 .iter()
2482                 .skip(1)
2483                 .all(|(_, descr, _, _)| descr == descr_first)
2484             {
2485                 descr_first
2486             } else {
2487                 "item"
2488             };
2489             let plural_descr =
2490                 if descr.ends_with('s') { format!("{}es", descr) } else { format!("{}s", descr) };
2491
2492             let mut msg = format!("{}these {} exist but are inaccessible", prefix, plural_descr);
2493             let mut has_colon = false;
2494
2495             let mut spans = Vec::new();
2496             for (name, _, def_id, _) in &inaccessible_path_strings {
2497                 if let Some(local_def_id) = def_id.and_then(|did| did.as_local()) {
2498                     let span = source_span[local_def_id];
2499                     let span = session.source_map().guess_head_span(span);
2500                     spans.push((name, span));
2501                 } else {
2502                     if !has_colon {
2503                         msg.push(':');
2504                         has_colon = true;
2505                     }
2506                     msg.push('\n');
2507                     msg.push_str(name);
2508                 }
2509             }
2510
2511             let mut multi_span = MultiSpan::from_spans(spans.iter().map(|(_, sp)| *sp).collect());
2512             for (name, span) in spans {
2513                 multi_span.push_span_label(span, format!("`{}`: not accessible", name));
2514             }
2515
2516             for note in inaccessible_path_strings.iter().flat_map(|cand| cand.3.as_ref()) {
2517                 err.note(note);
2518             }
2519
2520             err.span_note(multi_span, &msg);
2521         }
2522     }
2523 }
2524
2525 #[derive(Debug)]
2526 struct UsePlacementFinder {
2527     target_module: NodeId,
2528     first_legal_span: Option<Span>,
2529     first_use_span: Option<Span>,
2530 }
2531
2532 impl UsePlacementFinder {
2533     fn check(krate: &Crate, target_module: NodeId) -> (Option<Span>, FoundUse) {
2534         let mut finder =
2535             UsePlacementFinder { target_module, first_legal_span: None, first_use_span: None };
2536         finder.visit_crate(krate);
2537         if let Some(use_span) = finder.first_use_span {
2538             (Some(use_span), FoundUse::Yes)
2539         } else {
2540             (finder.first_legal_span, FoundUse::No)
2541         }
2542     }
2543 }
2544
2545 impl<'tcx> visit::Visitor<'tcx> for UsePlacementFinder {
2546     fn visit_crate(&mut self, c: &Crate) {
2547         if self.target_module == CRATE_NODE_ID {
2548             let inject = c.spans.inject_use_span;
2549             if is_span_suitable_for_use_injection(inject) {
2550                 self.first_legal_span = Some(inject);
2551             }
2552             self.first_use_span = search_for_any_use_in_items(&c.items);
2553             return;
2554         } else {
2555             visit::walk_crate(self, c);
2556         }
2557     }
2558
2559     fn visit_item(&mut self, item: &'tcx ast::Item) {
2560         if self.target_module == item.id {
2561             if let ItemKind::Mod(_, ModKind::Loaded(items, _inline, mod_spans)) = &item.kind {
2562                 let inject = mod_spans.inject_use_span;
2563                 if is_span_suitable_for_use_injection(inject) {
2564                     self.first_legal_span = Some(inject);
2565                 }
2566                 self.first_use_span = search_for_any_use_in_items(items);
2567                 return;
2568             }
2569         } else {
2570             visit::walk_item(self, item);
2571         }
2572     }
2573 }
2574
2575 fn search_for_any_use_in_items(items: &[P<ast::Item>]) -> Option<Span> {
2576     for item in items {
2577         if let ItemKind::Use(..) = item.kind {
2578             if is_span_suitable_for_use_injection(item.span) {
2579                 return Some(item.span.shrink_to_lo());
2580             }
2581         }
2582     }
2583     return None;
2584 }
2585
2586 fn is_span_suitable_for_use_injection(s: Span) -> bool {
2587     // don't suggest placing a use before the prelude
2588     // import or other generated ones
2589     !s.from_expansion()
2590 }
2591
2592 /// Convert the given number into the corresponding ordinal
2593 pub(crate) fn ordinalize(v: usize) -> String {
2594     let suffix = match ((11..=13).contains(&(v % 100)), v % 10) {
2595         (false, 1) => "st",
2596         (false, 2) => "nd",
2597         (false, 3) => "rd",
2598         _ => "th",
2599     };
2600     format!("{v}{suffix}")
2601 }