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};
  28 use tracing::debug;
  29
  30 use crate::imports::{Import, ImportKind, ImportResolver};
  31 use crate::late::{PatternSource, Rib};
  32 use crate::path_names_to_string;
  33 use crate::{AmbiguityError, AmbiguityErrorMisc, AmbiguityKind, BindingError, Finalize};
  34 use crate::{HasGenericParams, MacroRulesScope, Module, ModuleKind, ModuleOrUniformRoot};
  35 use crate::{LexicalScopeBinding, NameBinding, NameBindingKind, PrivacyError, VisResolutionError};
  36 use crate::{ParentScope, PathResult, ResolutionError, Resolver, Scope, ScopeSet};
  37 use crate::{Segment, UseError};
  38
  39 #[cfg(test)]
  40 mod tests;
  41
  42 type Res = def::Res<ast::NodeId>;
  43
  44 /// A vector of spans and replacements, a message and applicability.
  45 pub(crate) type Suggestion = (Vec<(Span, String)>, String, Applicability);
  46
  47 /// Potential candidate for an undeclared or out-of-scope label - contains the ident of a
  48 /// similarly named label and whether or not it is reachable.
  49 pub(crate) type LabelSuggestion = (Ident, bool);
  50
  51 pub(crate) enum SuggestionTarget {
  52     /// The target has a similar name as the name used by the programmer (probably a typo)
  53     SimilarlyNamed,
  54     /// The target is the only valid item that can be used in the corresponding context
  55     SingleItem,
  56 }
  57
  58 pub(crate) struct TypoSuggestion {
  59     pub candidate: Symbol,
  60     pub res: Res,
  61     pub target: SuggestionTarget,
  62 }
  63
  64 impl TypoSuggestion {
  65     pub(crate) fn typo_from_res(candidate: Symbol, res: Res) -> TypoSuggestion {
  66         Self { candidate, res, target: SuggestionTarget::SimilarlyNamed }
  67     }
  68     pub(crate) fn single_item_from_res(candidate: Symbol, res: Res) -> TypoSuggestion {
  69         Self { candidate, res, target: SuggestionTarget::SingleItem }
  70     }
  71 }
  72
  73 /// A free importable items suggested in case of resolution failure.
  74 pub(crate) struct ImportSuggestion {
  75     pub did: Option<DefId>,
  76     pub descr: &'static str,
  77     pub path: Path,
  78     pub accessible: bool,
  79     /// An extra note that should be issued if this item is suggested
  80     pub note: Option<String>,
  81 }
  82
  83 /// Adjust the impl span so that just the `impl` keyword is taken by removing
  84 /// everything after `<` (`"impl<T> Iterator for A<T> {}" -> "impl"`) and
  85 /// everything after the first whitespace (`"impl Iterator for A" -> "impl"`).
  86 ///
  87 /// *Attention*: the method used is very fragile since it essentially duplicates the work of the
  88 /// parser. If you need to use this function or something similar, please consider updating the
  89 /// `source_map` functions and this function to something more robust.
  90 fn reduce_impl_span_to_impl_keyword(sm: &SourceMap, impl_span: Span) -> Span {
  91     let impl_span = sm.span_until_char(impl_span, '<');
  92     sm.span_until_whitespace(impl_span)
  93 }
  94
  95 impl<'a> Resolver<'a> {
  96     pub(crate) fn report_errors(&mut self, krate: &Crate) {
  97         self.report_with_use_injections(krate);
  98
  99         for &(span_use, span_def) in &self.macro_expanded_macro_export_errors {
 100             let msg = "macro-expanded `macro_export` macros from the current crate \
 101                        cannot be referred to by absolute paths";
 102             self.lint_buffer.buffer_lint_with_diagnostic(
 103                 MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
 104                 CRATE_NODE_ID,
 105                 span_use,
 106                 msg,
 107                 BuiltinLintDiagnostics::MacroExpandedMacroExportsAccessedByAbsolutePaths(span_def),
 108             );
 109         }
 110
 111         for ambiguity_error in &self.ambiguity_errors {
 112             self.report_ambiguity_error(ambiguity_error);
 113         }
 114
 115         let mut reported_spans = FxHashSet::default();
 116         for error in &self.privacy_errors {
 117             if reported_spans.insert(error.dedup_span) {
 118                 self.report_privacy_error(error);
 119             }
 120         }
 121     }
 122
 123     fn report_with_use_injections(&mut self, krate: &Crate) {
 124         for UseError { mut err, candidates, def_id, instead, suggestion, path } in
 125             self.use_injections.drain(..)
 126         {
 127             let (span, found_use) = if let Some(def_id) = def_id.as_local() {
 128                 UsePlacementFinder::check(krate, self.def_id_to_node_id[def_id])
 129             } else {
 130                 (None, FoundUse::No)
 131             };
 132             if !candidates.is_empty() {
 133                 show_candidates(
 134                     &self.session,
 135                     &self.source_span,
 136                     &mut err,
 137                     span,
 138                     &candidates,
 139                     if instead { Instead::Yes } else { Instead::No },
 140                     found_use,
 141                     IsPattern::No,
 142                     path,
 143                 );
 144             } else if let Some((span, msg, sugg, appl)) = suggestion {
 145                 err.span_suggestion(span, msg, sugg, appl);
 146             }
 147             err.emit();
 148         }
 149     }
 150
 151     pub(crate) fn report_conflict<'b>(
 152         &mut self,
 153         parent: Module<'_>,
 154         ident: Ident,
 155         ns: Namespace,
 156         new_binding: &NameBinding<'b>,
 157         old_binding: &NameBinding<'b>,
 158     ) {
 159         // Error on the second of two conflicting names
 160         if old_binding.span.lo() > new_binding.span.lo() {
 161             return self.report_conflict(parent, ident, ns, old_binding, new_binding);
 162         }
 163
 164         let container = match parent.kind {
 165             ModuleKind::Def(kind, _, _) => kind.descr(parent.def_id()),
 166             ModuleKind::Block => "block",
 167         };
 168
 169         let old_noun = match old_binding.is_import() {
 170             true => "import",
 171             false => "definition",
 172         };
 173
 174         let new_participle = match new_binding.is_import() {
 175             true => "imported",
 176             false => "defined",
 177         };
 178
 179         let (name, span) =
 180             (ident.name, self.session.source_map().guess_head_span(new_binding.span));
 181
 182         if let Some(s) = self.name_already_seen.get(&name) {
 183             if s == &span {
 184                 return;
 185             }
 186         }
 187
 188         let old_kind = match (ns, old_binding.module()) {
 189             (ValueNS, _) => "value",
 190             (MacroNS, _) => "macro",
 191             (TypeNS, _) if old_binding.is_extern_crate() => "extern crate",
 192             (TypeNS, Some(module)) if module.is_normal() => "module",
 193             (TypeNS, Some(module)) if module.is_trait() => "trait",
 194             (TypeNS, _) => "type",
 195         };
 196
 197         let msg = format!("the name `{}` is defined multiple times", name);
 198
 199         let mut err = match (old_binding.is_extern_crate(), new_binding.is_extern_crate()) {
 200             (true, true) => struct_span_err!(self.session, span, E0259, "{}", msg),
 201             (true, _) | (_, true) => match new_binding.is_import() && old_binding.is_import() {
 202                 true => struct_span_err!(self.session, span, E0254, "{}", msg),
 203                 false => struct_span_err!(self.session, span, E0260, "{}", msg),
 204             },
 205             _ => match (old_binding.is_import(), new_binding.is_import()) {
 206                 (false, false) => struct_span_err!(self.session, span, E0428, "{}", msg),
 207                 (true, true) => struct_span_err!(self.session, span, E0252, "{}", msg),
 208                 _ => struct_span_err!(self.session, span, E0255, "{}", msg),
 209             },
 210         };
 211
 212         err.note(&format!(
 213             "`{}` must be defined only once in the {} namespace of this {}",
 214             name,
 215             ns.descr(),
 216             container
 217         ));
 218
 219         err.span_label(span, format!("`{}` re{} here", name, new_participle));
 220         err.span_label(
 221             self.session.source_map().guess_head_span(old_binding.span),
 222             format!("previous {} of the {} `{}` here", old_noun, old_kind, name),
 223         );
 224
 225         // See https://github.com/rust-lang/rust/issues/32354
 226         use NameBindingKind::Import;
 227         let import = match (&new_binding.kind, &old_binding.kind) {
 228             // If there are two imports where one or both have attributes then prefer removing the
 229             // import without attributes.
 230             (Import { import: new, .. }, Import { import: old, .. })
 231                 if {
 232                     !new_binding.span.is_dummy()
 233                         && !old_binding.span.is_dummy()
 234                         && (new.has_attributes || old.has_attributes)
 235                 } =>
 236             {
 237                 if old.has_attributes {
 238                     Some((new, new_binding.span, true))
 239                 } else {
 240                     Some((old, old_binding.span, true))
 241                 }
 242             }
 243             // Otherwise prioritize the new binding.
 244             (Import { import, .. }, other) if !new_binding.span.is_dummy() => {
 245                 Some((import, new_binding.span, other.is_import()))
 246             }
 247             (other, Import { import, .. }) if !old_binding.span.is_dummy() => {
 248                 Some((import, old_binding.span, other.is_import()))
 249             }
 250             _ => None,
 251         };
 252
 253         // Check if the target of the use for both bindings is the same.
 254         let duplicate = new_binding.res().opt_def_id() == old_binding.res().opt_def_id();
 255         let has_dummy_span = new_binding.span.is_dummy() || old_binding.span.is_dummy();
 256         let from_item =
 257             self.extern_prelude.get(&ident).map_or(true, |entry| entry.introduced_by_item);
 258         // Only suggest removing an import if both bindings are to the same def, if both spans
 259         // aren't dummy spans. Further, if both bindings are imports, then the ident must have
 260         // been introduced by an item.
 261         let should_remove_import = duplicate
 262             && !has_dummy_span
 263             && ((new_binding.is_extern_crate() || old_binding.is_extern_crate()) || from_item);
 264
 265         match import {
 266             Some((import, span, true)) if should_remove_import && import.is_nested() => {
 267                 self.add_suggestion_for_duplicate_nested_use(&mut err, import, span)
 268             }
 269             Some((import, _, true)) if should_remove_import && !import.is_glob() => {
 270                 // Simple case - remove the entire import. Due to the above match arm, this can
 271                 // only be a single use so just remove it entirely.
 272                 err.tool_only_span_suggestion(
 273                     import.use_span_with_attributes,
 274                     "remove unnecessary import",
 275                     "",
 276                     Applicability::MaybeIncorrect,
 277                 );
 278             }
 279             Some((import, span, _)) => {
 280                 self.add_suggestion_for_rename_of_use(&mut err, name, import, span)
 281             }
 282             _ => {}
 283         }
 284
 285         err.emit();
 286         self.name_already_seen.insert(name, span);
 287     }
 288
 289     /// This function adds a suggestion to change the binding name of a new import that conflicts
 290     /// with an existing import.
 291     ///
 292     /// ```text,ignore (diagnostic)
 293     /// help: you can use `as` to change the binding name of the import
 294     ///    |
 295     /// LL | use foo::bar as other_bar;
 296     ///    |     ^^^^^^^^^^^^^^^^^^^^^
 297     /// ```
 298     fn add_suggestion_for_rename_of_use(
 299         &self,
 300         err: &mut Diagnostic,
 301         name: Symbol,
 302         import: &Import<'_>,
 303         binding_span: Span,
 304     ) {
 305         let suggested_name = if name.as_str().chars().next().unwrap().is_uppercase() {
 306             format!("Other{}", name)
 307         } else {
 308             format!("other_{}", name)
 309         };
 310
 311         let mut suggestion = None;
 312         match import.kind {
 313             ImportKind::Single { type_ns_only: true, .. } => {
 314                 suggestion = Some(format!("self as {}", suggested_name))
 315             }
 316             ImportKind::Single { source, .. } => {
 317                 if let Some(pos) =
 318                     source.span.hi().0.checked_sub(binding_span.lo().0).map(|pos| pos as usize)
 319                 {
 320                     if let Ok(snippet) = self.session.source_map().span_to_snippet(binding_span) {
 321                         if pos <= snippet.len() {
 322                             suggestion = Some(format!(
 323                                 "{} as {}{}",
 324                                 &snippet[..pos],
 325                                 suggested_name,
 326                                 if snippet.ends_with(';') { ";" } else { "" }
 327                             ))
 328                         }
 329                     }
 330                 }
 331             }
 332             ImportKind::ExternCrate { source, target } => {
 333                 suggestion = Some(format!(
 334                     "extern crate {} as {};",
 335                     source.unwrap_or(target.name),
 336                     suggested_name,
 337                 ))
 338             }
 339             _ => unreachable!(),
 340         }
 341
 342         let rename_msg = "you can use `as` to change the binding name of the import";
 343         if let Some(suggestion) = suggestion {
 344             err.span_suggestion(
 345                 binding_span,
 346                 rename_msg,
 347                 suggestion,
 348                 Applicability::MaybeIncorrect,
 349             );
 350         } else {
 351             err.span_label(binding_span, rename_msg);
 352         }
 353     }
 354
 355     /// This function adds a suggestion to remove an unnecessary binding from an import that is
 356     /// nested. In the following example, this function will be invoked to remove the `a` binding
 357     /// in the second use statement:
 358     ///
 359     /// ```ignore (diagnostic)
 360     /// use issue_52891::a;
 361     /// use issue_52891::{d, a, e};
 362     /// ```
 363     ///
 364     /// The following suggestion will be added:
 365     ///
 366     /// ```ignore (diagnostic)
 367     /// use issue_52891::{d, a, e};
 368     ///                      ^-- help: remove unnecessary import
 369     /// ```
 370     ///
 371     /// If the nested use contains only one import then the suggestion will remove the entire
 372     /// line.
 373     ///
 374     /// It is expected that the provided import is nested - this isn't checked by the
 375     /// function. If this invariant is not upheld, this function's behaviour will be unexpected
 376     /// as characters expected by span manipulations won't be present.
 377     fn add_suggestion_for_duplicate_nested_use(
 378         &self,
 379         err: &mut Diagnostic,
 380         import: &Import<'_>,
 381         binding_span: Span,
 382     ) {
 383         assert!(import.is_nested());
 384         let message = "remove unnecessary import";
 385
 386         // Two examples will be used to illustrate the span manipulations we're doing:
 387         //
 388         // - Given `use issue_52891::{d, a, e};` where `a` is a duplicate then `binding_span` is
 389         //   `a` and `import.use_span` is `issue_52891::{d, a, e};`.
 390         // - Given `use issue_52891::{d, e, a};` where `a` is a duplicate then `binding_span` is
 391         //   `a` and `import.use_span` is `issue_52891::{d, e, a};`.
 392
 393         let (found_closing_brace, span) =
 394             find_span_of_binding_until_next_binding(self.session, binding_span, import.use_span);
 395
 396         // If there was a closing brace then identify the span to remove any trailing commas from
 397         // previous imports.
 398         if found_closing_brace {
 399             if let Some(span) = extend_span_to_previous_binding(self.session, span) {
 400                 err.tool_only_span_suggestion(span, message, "", Applicability::MaybeIncorrect);
 401             } else {
 402                 // Remove the entire line if we cannot extend the span back, this indicates an
 403                 // `issue_52891::{self}` case.
 404                 err.span_suggestion(
 405                     import.use_span_with_attributes,
 406                     message,
 407                     "",
 408                     Applicability::MaybeIncorrect,
 409                 );
 410             }
 411
 412             return;
 413         }
 414
 415         err.span_suggestion(span, message, "", Applicability::MachineApplicable);
 416     }
 417
 418     pub(crate) fn lint_if_path_starts_with_module(
 419         &mut self,
 420         finalize: Option<Finalize>,
 421         path: &[Segment],
 422         second_binding: Option<&NameBinding<'_>>,
 423     ) {
 424         let Some(Finalize { node_id, root_span, .. }) = finalize else {
 425             return;
 426         };
 427
 428         let first_name = match path.get(0) {
 429             // In the 2018 edition this lint is a hard error, so nothing to do
 430             Some(seg) if seg.ident.span.rust_2015() && self.session.rust_2015() => seg.ident.name,
 431             _ => return,
 432         };
 433
 434         // We're only interested in `use` paths which should start with
 435         // `{{root}}` currently.
 436         if first_name != kw::PathRoot {
 437             return;
 438         }
 439
 440         match path.get(1) {
 441             // If this import looks like `crate::...` it's already good
 442             Some(Segment { ident, .. }) if ident.name == kw::Crate => return,
 443             // Otherwise go below to see if it's an extern crate
 444             Some(_) => {}
 445             // If the path has length one (and it's `PathRoot` most likely)
 446             // then we don't know whether we're gonna be importing a crate or an
 447             // item in our crate. Defer this lint to elsewhere
 448             None => return,
 449         }
 450
 451         // If the first element of our path was actually resolved to an
 452         // `ExternCrate` (also used for `crate::...`) then no need to issue a
 453         // warning, this looks all good!
 454         if let Some(binding) = second_binding {
 455             if let NameBindingKind::Import { import, .. } = binding.kind {
 456                 // Careful: we still want to rewrite paths from renamed extern crates.
 457                 if let ImportKind::ExternCrate { source: None, .. } = import.kind {
 458                     return;
 459                 }
 460             }
 461         }
 462
 463         let diag = BuiltinLintDiagnostics::AbsPathWithModule(root_span);
 464         self.lint_buffer.buffer_lint_with_diagnostic(
 465             ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
 466             node_id,
 467             root_span,
 468             "absolute paths must start with `self`, `super`, \
 469              `crate`, or an external crate name in the 2018 edition",
 470             diag,
 471         );
 472     }
 473
 474     pub(crate) fn add_module_candidates(
 475         &mut self,
 476         module: Module<'a>,
 477         names: &mut Vec<TypoSuggestion>,
 478         filter_fn: &impl Fn(Res) -> bool,
 479     ) {
 480         for (key, resolution) in self.resolutions(module).borrow().iter() {
 481             if let Some(binding) = resolution.borrow().binding {
 482                 let res = binding.res();
 483                 if filter_fn(res) {
 484                     names.push(TypoSuggestion::typo_from_res(key.ident.name, res));
 485                 }
 486             }
 487         }
 488     }
 489
 490     /// Combines an error with provided span and emits it.
 491     ///
 492     /// This takes the error provided, combines it with the span and any additional spans inside the
 493     /// error and emits it.
 494     pub(crate) fn report_error(&mut self, span: Span, resolution_error: ResolutionError<'a>) {
 495         self.into_struct_error(span, resolution_error).emit();
 496     }
 497
 498     pub(crate) fn into_struct_error(
 499         &mut self,
 500         span: Span,
 501         resolution_error: ResolutionError<'a>,
 502     ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
 503         match resolution_error {
 504             ResolutionError::GenericParamsFromOuterFunction(outer_res, has_generic_params) => {
 505                 let mut err = struct_span_err!(
 506                     self.session,
 507                     span,
 508                     E0401,
 509                     "can't use generic parameters from outer function",
 510                 );
 511                 err.span_label(span, "use of generic parameter from outer function");
 512
 513                 let sm = self.session.source_map();
 514                 match outer_res {
 515                     Res::SelfTy { trait_: maybe_trait_defid, alias_to: maybe_impl_defid } => {
 516                         if let Some(impl_span) =
 517                             maybe_impl_defid.and_then(|(def_id, _)| self.opt_span(def_id))
 518                         {
 519                             err.span_label(
 520                                 reduce_impl_span_to_impl_keyword(sm, impl_span),
 521                                 "`Self` type implicitly declared here, by this `impl`",
 522                             );
 523                         }
 524                         match (maybe_trait_defid, maybe_impl_defid) {
 525                             (Some(_), None) => {
 526                                 err.span_label(span, "can't use `Self` here");
 527                             }
 528                             (_, Some(_)) => {
 529                                 err.span_label(span, "use a type here instead");
 530                             }
 531                             (None, None) => bug!("`impl` without trait nor type?"),
 532                         }
 533                         return err;
 534                     }
 535                     Res::Def(DefKind::TyParam, def_id) => {
 536                         if let Some(span) = self.opt_span(def_id) {
 537                             err.span_label(span, "type parameter from outer function");
 538                         }
 539                     }
 540                     Res::Def(DefKind::ConstParam, def_id) => {
 541                         if let Some(span) = self.opt_span(def_id) {
 542                             err.span_label(span, "const parameter from outer function");
 543                         }
 544                     }
 545                     _ => {
 546                         bug!(
 547                             "GenericParamsFromOuterFunction should only be used with Res::SelfTy, \
 548                             DefKind::TyParam or DefKind::ConstParam"
 549                         );
 550                     }
 551                 }
 552
 553                 if has_generic_params == HasGenericParams::Yes {
 554                     // Try to retrieve the span of the function signature and generate a new
 555                     // message with a local type or const parameter.
 556                     let sugg_msg = "try using a local generic parameter instead";
 557                     if let Some((sugg_span, snippet)) = sm.generate_local_type_param_snippet(span) {
 558                         // Suggest the modification to the user
 559                         err.span_suggestion(
 560                             sugg_span,
 561                             sugg_msg,
 562                             snippet,
 563                             Applicability::MachineApplicable,
 564                         );
 565                     } else if let Some(sp) = sm.generate_fn_name_span(span) {
 566                         err.span_label(
 567                             sp,
 568                             "try adding a local generic parameter in this method instead",
 569                         );
 570                     } else {
 571                         err.help("try using a local generic parameter instead");
 572                     }
 573                 }
 574
 575                 err
 576             }
 577             ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => {
 578                 let mut err = struct_span_err!(
 579                     self.session,
 580                     span,
 581                     E0403,
 582                     "the name `{}` is already used for a generic \
 583                      parameter in this item's generic parameters",
 584                     name,
 585                 );
 586                 err.span_label(span, "already used");
 587                 err.span_label(first_use_span, format!("first use of `{}`", name));
 588                 err
 589             }
 590             ResolutionError::MethodNotMemberOfTrait(method, trait_, candidate) => {
 591                 let mut err = struct_span_err!(
 592                     self.session,
 593                     span,
 594                     E0407,
 595                     "method `{}` is not a member of trait `{}`",
 596                     method,
 597                     trait_
 598                 );
 599                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 600                 if let Some(candidate) = candidate {
 601                     err.span_suggestion(
 602                         method.span,
 603                         "there is an associated function with a similar name",
 604                         candidate.to_ident_string(),
 605                         Applicability::MaybeIncorrect,
 606                     );
 607                 }
 608                 err
 609             }
 610             ResolutionError::TypeNotMemberOfTrait(type_, trait_, candidate) => {
 611                 let mut err = struct_span_err!(
 612                     self.session,
 613                     span,
 614                     E0437,
 615                     "type `{}` is not a member of trait `{}`",
 616                     type_,
 617                     trait_
 618                 );
 619                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 620                 if let Some(candidate) = candidate {
 621                     err.span_suggestion(
 622                         type_.span,
 623                         "there is an associated type with a similar name",
 624                         candidate.to_ident_string(),
 625                         Applicability::MaybeIncorrect,
 626                     );
 627                 }
 628                 err
 629             }
 630             ResolutionError::ConstNotMemberOfTrait(const_, trait_, candidate) => {
 631                 let mut err = struct_span_err!(
 632                     self.session,
 633                     span,
 634                     E0438,
 635                     "const `{}` is not a member of trait `{}`",
 636                     const_,
 637                     trait_
 638                 );
 639                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 640                 if let Some(candidate) = candidate {
 641                     err.span_suggestion(
 642                         const_.span,
 643                         "there is an associated constant with a similar name",
 644                         candidate.to_ident_string(),
 645                         Applicability::MaybeIncorrect,
 646                     );
 647                 }
 648                 err
 649             }
 650             ResolutionError::VariableNotBoundInPattern(binding_error, parent_scope) => {
 651                 let BindingError { name, target, origin, could_be_path } = binding_error;
 652
 653                 let target_sp = target.iter().copied().collect::<Vec<_>>();
 654                 let origin_sp = origin.iter().copied().collect::<Vec<_>>();
 655
 656                 let msp = MultiSpan::from_spans(target_sp.clone());
 657                 let mut err = struct_span_err!(
 658                     self.session,
 659                     msp,
 660                     E0408,
 661                     "variable `{}` is not bound in all patterns",
 662                     name,
 663                 );
 664                 for sp in target_sp {
 665                     err.span_label(sp, format!("pattern doesn't bind `{}`", name));
 666                 }
 667                 for sp in origin_sp {
 668                     err.span_label(sp, "variable not in all patterns");
 669                 }
 670                 if could_be_path {
 671                     let import_suggestions = self.lookup_import_candidates(
 672                         Ident::with_dummy_span(name),
 673                         Namespace::ValueNS,
 674                         &parent_scope,
 675                         &|res: Res| match res {
 676                             Res::Def(
 677                                 DefKind::Ctor(CtorOf::Variant, CtorKind::Const)
 678                                 | DefKind::Ctor(CtorOf::Struct, CtorKind::Const)
 679                                 | DefKind::Const
 680                                 | DefKind::AssocConst,
 681                                 _,
 682                             ) => true,
 683                             _ => false,
 684                         },
 685                     );
 686
 687                     if import_suggestions.is_empty() {
 688                         let help_msg = format!(
 689                             "if you meant to match on a variant or a `const` item, consider \
 690                              making the path in the pattern qualified: `path::to::ModOrType::{}`",
 691                             name,
 692                         );
 693                         err.span_help(span, &help_msg);
 694                     }
 695                     show_candidates(
 696                         &self.session,
 697                         &self.source_span,
 698                         &mut err,
 699                         Some(span),
 700                         &import_suggestions,
 701                         Instead::No,
 702                         FoundUse::Yes,
 703                         IsPattern::Yes,
 704                         vec![],
 705                     );
 706                 }
 707                 err
 708             }
 709             ResolutionError::VariableBoundWithDifferentMode(variable_name, first_binding_span) => {
 710                 let mut err = struct_span_err!(
 711                     self.session,
 712                     span,
 713                     E0409,
 714                     "variable `{}` is bound inconsistently across alternatives separated by `|`",
 715                     variable_name
 716                 );
 717                 err.span_label(span, "bound in different ways");
 718                 err.span_label(first_binding_span, "first binding");
 719                 err
 720             }
 721             ResolutionError::IdentifierBoundMoreThanOnceInParameterList(identifier) => {
 722                 let mut err = struct_span_err!(
 723                     self.session,
 724                     span,
 725                     E0415,
 726                     "identifier `{}` is bound more than once in this parameter list",
 727                     identifier
 728                 );
 729                 err.span_label(span, "used as parameter more than once");
 730                 err
 731             }
 732             ResolutionError::IdentifierBoundMoreThanOnceInSamePattern(identifier) => {
 733                 let mut err = struct_span_err!(
 734                     self.session,
 735                     span,
 736                     E0416,
 737                     "identifier `{}` is bound more than once in the same pattern",
 738                     identifier
 739                 );
 740                 err.span_label(span, "used in a pattern more than once");
 741                 err
 742             }
 743             ResolutionError::UndeclaredLabel { name, suggestion } => {
 744                 let mut err = struct_span_err!(
 745                     self.session,
 746                     span,
 747                     E0426,
 748                     "use of undeclared label `{}`",
 749                     name
 750                 );
 751
 752                 err.span_label(span, format!("undeclared label `{}`", name));
 753
 754                 match suggestion {
 755                     // A reachable label with a similar name exists.
 756                     Some((ident, true)) => {
 757                         err.span_label(ident.span, "a label with a similar name is reachable");
 758                         err.span_suggestion(
 759                             span,
 760                             "try using similarly named label",
 761                             ident.name,
 762                             Applicability::MaybeIncorrect,
 763                         );
 764                     }
 765                     // An unreachable label with a similar name exists.
 766                     Some((ident, false)) => {
 767                         err.span_label(
 768                             ident.span,
 769                             "a label with a similar name exists but is unreachable",
 770                         );
 771                     }
 772                     // No similarly-named labels exist.
 773                     None => (),
 774                 }
 775
 776                 err
 777             }
 778             ResolutionError::SelfImportsOnlyAllowedWithin { root, span_with_rename } => {
 779                 let mut err = struct_span_err!(
 780                     self.session,
 781                     span,
 782                     E0429,
 783                     "{}",
 784                     "`self` imports are only allowed within a { } list"
 785                 );
 786
 787                 // None of the suggestions below would help with a case like `use self`.
 788                 if !root {
 789                     // use foo::bar::self        -> foo::bar
 790                     // use foo::bar::self as abc -> foo::bar as abc
 791                     err.span_suggestion(
 792                         span,
 793                         "consider importing the module directly",
 794                         "",
 795                         Applicability::MachineApplicable,
 796                     );
 797
 798                     // use foo::bar::self        -> foo::bar::{self}
 799                     // use foo::bar::self as abc -> foo::bar::{self as abc}
 800                     let braces = vec![
 801                         (span_with_rename.shrink_to_lo(), "{".to_string()),
 802                         (span_with_rename.shrink_to_hi(), "}".to_string()),
 803                     ];
 804                     err.multipart_suggestion(
 805                         "alternatively, use the multi-path `use` syntax to import `self`",
 806                         braces,
 807                         Applicability::MachineApplicable,
 808                     );
 809                 }
 810                 err
 811             }
 812             ResolutionError::SelfImportCanOnlyAppearOnceInTheList => {
 813                 let mut err = struct_span_err!(
 814                     self.session,
 815                     span,
 816                     E0430,
 817                     "`self` import can only appear once in an import list"
 818                 );
 819                 err.span_label(span, "can only appear once in an import list");
 820                 err
 821             }
 822             ResolutionError::SelfImportOnlyInImportListWithNonEmptyPrefix => {
 823                 let mut err = struct_span_err!(
 824                     self.session,
 825                     span,
 826                     E0431,
 827                     "`self` import can only appear in an import list with \
 828                                                 a non-empty prefix"
 829                 );
 830                 err.span_label(span, "can only appear in an import list with a non-empty prefix");
 831                 err
 832             }
 833             ResolutionError::FailedToResolve { label, suggestion } => {
 834                 let mut err =
 835                     struct_span_err!(self.session, span, E0433, "failed to resolve: {}", &label);
 836                 err.span_label(span, label);
 837
 838                 if let Some((suggestions, msg, applicability)) = suggestion {
 839                     if suggestions.is_empty() {
 840                         err.help(&msg);
 841                         return err;
 842                     }
 843                     err.multipart_suggestion(&msg, suggestions, applicability);
 844                 }
 845
 846                 err
 847             }
 848             ResolutionError::CannotCaptureDynamicEnvironmentInFnItem => {
 849                 let mut err = struct_span_err!(
 850                     self.session,
 851                     span,
 852                     E0434,
 853                     "{}",
 854                     "can't capture dynamic environment in a fn item"
 855                 );
 856                 err.help("use the `|| { ... }` closure form instead");
 857                 err
 858             }
 859             ResolutionError::AttemptToUseNonConstantValueInConstant(ident, sugg, current) => {
 860                 let mut err = struct_span_err!(
 861                     self.session,
 862                     span,
 863                     E0435,
 864                     "attempt to use a non-constant value in a constant"
 865                 );
 866                 // let foo =...
 867                 //     ^^^ given this Span
 868                 // ------- get this Span to have an applicable suggestion
 869
 870                 // edit:
 871                 // only do this if the const and usage of the non-constant value are on the same line
 872                 // the further the two are apart, the higher the chance of the suggestion being wrong
 873
 874                 let sp = self
 875                     .session
 876                     .source_map()
 877                     .span_extend_to_prev_str(ident.span, current, true, false);
 878
 879                 match sp {
 880                     Some(sp) if !self.session.source_map().is_multiline(sp) => {
 881                         let sp = sp.with_lo(BytePos(sp.lo().0 - (current.len() as u32)));
 882                         err.span_suggestion(
 883                             sp,
 884                             &format!("consider using `{}` instead of `{}`", sugg, current),
 885                             format!("{} {}", sugg, ident),
 886                             Applicability::MaybeIncorrect,
 887                         );
 888                         err.span_label(span, "non-constant value");
 889                     }
 890                     _ => {
 891                         err.span_label(ident.span, &format!("this would need to be a `{}`", sugg));
 892                     }
 893                 }
 894
 895                 err
 896             }
 897             ResolutionError::BindingShadowsSomethingUnacceptable {
 898                 shadowing_binding,
 899                 name,
 900                 participle,
 901                 article,
 902                 shadowed_binding,
 903                 shadowed_binding_span,
 904             } => {
 905                 let shadowed_binding_descr = shadowed_binding.descr();
 906                 let mut err = struct_span_err!(
 907                     self.session,
 908                     span,
 909                     E0530,
 910                     "{}s cannot shadow {}s",
 911                     shadowing_binding.descr(),
 912                     shadowed_binding_descr,
 913                 );
 914                 err.span_label(
 915                     span,
 916                     format!("cannot be named the same as {} {}", article, shadowed_binding_descr),
 917                 );
 918                 match (shadowing_binding, shadowed_binding) {
 919                     (
 920                         PatternSource::Match,
 921                         Res::Def(DefKind::Ctor(CtorOf::Variant | CtorOf::Struct, CtorKind::Fn), _),
 922                     ) => {
 923                         err.span_suggestion(
 924                             span,
 925                             "try specify the pattern arguments",
 926                             format!("{}(..)", name),
 927                             Applicability::Unspecified,
 928                         );
 929                     }
 930                     _ => (),
 931                 }
 932                 let msg =
 933                     format!("the {} `{}` is {} here", shadowed_binding_descr, name, participle);
 934                 err.span_label(shadowed_binding_span, msg);
 935                 err
 936             }
 937             ResolutionError::ForwardDeclaredGenericParam => {
 938                 let mut err = struct_span_err!(
 939                     self.session,
 940                     span,
 941                     E0128,
 942                     "generic parameters with a default cannot use \
 943                                                 forward declared identifiers"
 944                 );
 945                 err.span_label(span, "defaulted generic parameters cannot be forward declared");
 946                 err
 947             }
 948             ResolutionError::ParamInTyOfConstParam(name) => {
 949                 let mut err = struct_span_err!(
 950                     self.session,
 951                     span,
 952                     E0770,
 953                     "the type of const parameters must not depend on other generic parameters"
 954                 );
 955                 err.span_label(
 956                     span,
 957                     format!("the type must not depend on the parameter `{}`", name),
 958                 );
 959                 err
 960             }
 961             ResolutionError::ParamInNonTrivialAnonConst { name, is_type } => {
 962                 let mut err = self.session.struct_span_err(
 963                     span,
 964                     "generic parameters may not be used in const operations",
 965                 );
 966                 err.span_label(span, &format!("cannot perform const operation using `{}`", name));
 967
 968                 if is_type {
 969                     err.note("type parameters may not be used in const expressions");
 970                 } else {
 971                     err.help(&format!(
 972                         "const parameters may only be used as standalone arguments, i.e. `{}`",
 973                         name
 974                     ));
 975                 }
 976
 977                 if self.session.is_nightly_build() {
 978                     err.help(
 979                         "use `#![feature(generic_const_exprs)]` to allow generic const expressions",
 980                     );
 981                 }
 982
 983                 err
 984             }
 985             ResolutionError::SelfInGenericParamDefault => {
 986                 let mut err = struct_span_err!(
 987                     self.session,
 988                     span,
 989                     E0735,
 990                     "generic parameters cannot use `Self` in their defaults"
 991                 );
 992                 err.span_label(span, "`Self` in generic parameter default");
 993                 err
 994             }
 995             ResolutionError::UnreachableLabel { name, definition_span, suggestion } => {
 996                 let mut err = struct_span_err!(
 997                     self.session,
 998                     span,
 999                     E0767,
1000                     "use of unreachable label `{}`",
1001                     name,
1002                 );
1003
1004                 err.span_label(definition_span, "unreachable label defined here");
1005                 err.span_label(span, format!("unreachable label `{}`", name));
1006                 err.note(
1007                     "labels are unreachable through functions, closures, async blocks and modules",
1008                 );
1009
1010                 match suggestion {
1011                     // A reachable label with a similar name exists.
1012                     Some((ident, true)) => {
1013                         err.span_label(ident.span, "a label with a similar name is reachable");
1014                         err.span_suggestion(
1015                             span,
1016                             "try using similarly named label",
1017                             ident.name,
1018                             Applicability::MaybeIncorrect,
1019                         );
1020                     }
1021                     // An unreachable label with a similar name exists.
1022                     Some((ident, false)) => {
1023                         err.span_label(
1024                             ident.span,
1025                             "a label with a similar name exists but is also unreachable",
1026                         );
1027                     }
1028                     // No similarly-named labels exist.
1029                     None => (),
1030                 }
1031
1032                 err
1033             }
1034             ResolutionError::TraitImplMismatch {
1035                 name,
1036                 kind,
1037                 code,
1038                 trait_item_span,
1039                 trait_path,
1040             } => {
1041                 let mut err = self.session.struct_span_err_with_code(
1042                     span,
1043                     &format!(
1044                         "item `{}` is an associated {}, which doesn't match its trait `{}`",
1045                         name, kind, trait_path,
1046                     ),
1047                     code,
1048                 );
1049                 err.span_label(span, "does not match trait");
1050                 err.span_label(trait_item_span, "item in trait");
1051                 err
1052             }
1053             ResolutionError::InvalidAsmSym => {
1054                 let mut err = self.session.struct_span_err(span, "invalid `sym` operand");
1055                 err.span_label(span, "is a local variable");
1056                 err.help("`sym` operands must refer to either a function or a static");
1057                 err
1058             }
1059         }
1060     }
1061
1062     pub(crate) fn report_vis_error(
1063         &mut self,
1064         vis_resolution_error: VisResolutionError<'_>,
1065     ) -> ErrorGuaranteed {
1066         match vis_resolution_error {
1067             VisResolutionError::Relative2018(span, path) => {
1068                 let mut err = self.session.struct_span_err(
1069                     span,
1070                     "relative paths are not supported in visibilities in 2018 edition or later",
1071                 );
1072                 err.span_suggestion(
1073                     path.span,
1074                     "try",
1075                     format!("crate::{}", pprust::path_to_string(&path)),
1076                     Applicability::MaybeIncorrect,
1077                 );
1078                 err
1079             }
1080             VisResolutionError::AncestorOnly(span) => struct_span_err!(
1081                 self.session,
1082                 span,
1083                 E0742,
1084                 "visibilities can only be restricted to ancestor modules"
1085             ),
1086             VisResolutionError::FailedToResolve(span, label, suggestion) => {
1087                 self.into_struct_error(span, ResolutionError::FailedToResolve { label, suggestion })
1088             }
1089             VisResolutionError::ExpectedFound(span, path_str, res) => {
1090                 let mut err = struct_span_err!(
1091                     self.session,
1092                     span,
1093                     E0577,
1094                     "expected module, found {} `{}`",
1095                     res.descr(),
1096                     path_str
1097                 );
1098                 err.span_label(span, "not a module");
1099                 err
1100             }
1101             VisResolutionError::Indeterminate(span) => struct_span_err!(
1102                 self.session,
1103                 span,
1104                 E0578,
1105                 "cannot determine resolution for the visibility"
1106             ),
1107             VisResolutionError::ModuleOnly(span) => {
1108                 self.session.struct_span_err(span, "visibility must resolve to a module")
1109             }
1110         }
1111         .emit()
1112     }
1113
1114     /// Lookup typo candidate in scope for a macro or import.
1115     fn early_lookup_typo_candidate(
1116         &mut self,
1117         scope_set: ScopeSet<'a>,
1118         parent_scope: &ParentScope<'a>,
1119         ident: Ident,
1120         filter_fn: &impl Fn(Res) -> bool,
1121     ) -> Option<TypoSuggestion> {
1122         let mut suggestions = Vec::new();
1123         let ctxt = ident.span.ctxt();
1124         self.visit_scopes(scope_set, parent_scope, ctxt, |this, scope, use_prelude, _| {
1125             match scope {
1126                 Scope::DeriveHelpers(expn_id) => {
1127                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
1128                     if filter_fn(res) {
1129                         suggestions.extend(
1130                             this.helper_attrs
1131                                 .get(&expn_id)
1132                                 .into_iter()
1133                                 .flatten()
1134                                 .map(|ident| TypoSuggestion::typo_from_res(ident.name, res)),
1135                         );
1136                     }
1137                 }
1138                 Scope::DeriveHelpersCompat => {
1139                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat);
1140                     if filter_fn(res) {
1141                         for derive in parent_scope.derives {
1142                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
1143                             if let Ok((Some(ext), _)) = this.resolve_macro_path(
1144                                 derive,
1145                                 Some(MacroKind::Derive),
1146                                 parent_scope,
1147                                 false,
1148                                 false,
1149                             ) {
1150                                 suggestions.extend(
1151                                     ext.helper_attrs
1152                                         .iter()
1153                                         .map(|name| TypoSuggestion::typo_from_res(*name, res)),
1154                                 );
1155                             }
1156                         }
1157                     }
1158                 }
1159                 Scope::MacroRules(macro_rules_scope) => {
1160                     if let MacroRulesScope::Binding(macro_rules_binding) = macro_rules_scope.get() {
1161                         let res = macro_rules_binding.binding.res();
1162                         if filter_fn(res) {
1163                             suggestions.push(TypoSuggestion::typo_from_res(
1164                                 macro_rules_binding.ident.name,
1165                                 res,
1166                             ))
1167                         }
1168                     }
1169                 }
1170                 Scope::CrateRoot => {
1171                     let root_ident = Ident::new(kw::PathRoot, ident.span);
1172                     let root_module = this.resolve_crate_root(root_ident);
1173                     this.add_module_candidates(root_module, &mut suggestions, filter_fn);
1174                 }
1175                 Scope::Module(module, _) => {
1176                     this.add_module_candidates(module, &mut suggestions, filter_fn);
1177                 }
1178                 Scope::RegisteredAttrs => {
1179                     let res = Res::NonMacroAttr(NonMacroAttrKind::Registered);
1180                     if filter_fn(res) {
1181                         suggestions.extend(
1182                             this.registered_attrs
1183                                 .iter()
1184                                 .map(|ident| TypoSuggestion::typo_from_res(ident.name, res)),
1185                         );
1186                     }
1187                 }
1188                 Scope::MacroUsePrelude => {
1189                     suggestions.extend(this.macro_use_prelude.iter().filter_map(
1190                         |(name, binding)| {
1191                             let res = binding.res();
1192                             filter_fn(res).then_some(TypoSuggestion::typo_from_res(*name, res))
1193                         },
1194                     ));
1195                 }
1196                 Scope::BuiltinAttrs => {
1197                     let res = Res::NonMacroAttr(NonMacroAttrKind::Builtin(kw::Empty));
1198                     if filter_fn(res) {
1199                         suggestions.extend(
1200                             BUILTIN_ATTRIBUTES
1201                                 .iter()
1202                                 .map(|attr| TypoSuggestion::typo_from_res(attr.name, res)),
1203                         );
1204                     }
1205                 }
1206                 Scope::ExternPrelude => {
1207                     suggestions.extend(this.extern_prelude.iter().filter_map(|(ident, _)| {
1208                         let res = Res::Def(DefKind::Mod, CRATE_DEF_ID.to_def_id());
1209                         filter_fn(res).then_some(TypoSuggestion::typo_from_res(ident.name, res))
1210                     }));
1211                 }
1212                 Scope::ToolPrelude => {
1213                     let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
1214                     suggestions.extend(
1215                         this.registered_tools
1216                             .iter()
1217                             .map(|ident| TypoSuggestion::typo_from_res(ident.name, res)),
1218                     );
1219                 }
1220                 Scope::StdLibPrelude => {
1221                     if let Some(prelude) = this.prelude {
1222                         let mut tmp_suggestions = Vec::new();
1223                         this.add_module_candidates(prelude, &mut tmp_suggestions, filter_fn);
1224                         suggestions.extend(
1225                             tmp_suggestions
1226                                 .into_iter()
1227                                 .filter(|s| use_prelude || this.is_builtin_macro(s.res)),
1228                         );
1229                     }
1230                 }
1231                 Scope::BuiltinTypes => {
1232                     suggestions.extend(PrimTy::ALL.iter().filter_map(|prim_ty| {
1233                         let res = Res::PrimTy(*prim_ty);
1234                         filter_fn(res).then_some(TypoSuggestion::typo_from_res(prim_ty.name(), res))
1235                     }))
1236                 }
1237             }
1238
1239             None::<()>
1240         });
1241
1242         // Make sure error reporting is deterministic.
1243         suggestions.sort_by(|a, b| a.candidate.as_str().partial_cmp(b.candidate.as_str()).unwrap());
1244
1245         match find_best_match_for_name(
1246             &suggestions.iter().map(|suggestion| suggestion.candidate).collect::<Vec<Symbol>>(),
1247             ident.name,
1248             None,
1249         ) {
1250             Some(found) if found != ident.name => {
1251                 suggestions.into_iter().find(|suggestion| suggestion.candidate == found)
1252             }
1253             _ => None,
1254         }
1255     }
1256
1257     fn lookup_import_candidates_from_module<FilterFn>(
1258         &mut self,
1259         lookup_ident: Ident,
1260         namespace: Namespace,
1261         parent_scope: &ParentScope<'a>,
1262         start_module: Module<'a>,
1263         crate_name: Ident,
1264         filter_fn: FilterFn,
1265     ) -> Vec<ImportSuggestion>
1266     where
1267         FilterFn: Fn(Res) -> bool,
1268     {
1269         let mut candidates = Vec::new();
1270         let mut seen_modules = FxHashSet::default();
1271         let mut worklist = vec![(start_module, Vec::<ast::PathSegment>::new(), true)];
1272         let mut worklist_via_import = vec![];
1273
1274         while let Some((in_module, path_segments, accessible)) = match worklist.pop() {
1275             None => worklist_via_import.pop(),
1276             Some(x) => Some(x),
1277         } {
1278             let in_module_is_extern = !in_module.def_id().is_local();
1279             // We have to visit module children in deterministic order to avoid
1280             // instabilities in reported imports (#43552).
1281             in_module.for_each_child(self, |this, ident, ns, name_binding| {
1282                 // avoid non-importable candidates
1283                 if !name_binding.is_importable() {
1284                     return;
1285                 }
1286
1287                 let child_accessible =
1288                     accessible && this.is_accessible_from(name_binding.vis, parent_scope.module);
1289
1290                 // do not venture inside inaccessible items of other crates
1291                 if in_module_is_extern && !child_accessible {
1292                     return;
1293                 }
1294
1295                 let via_import = name_binding.is_import() && !name_binding.is_extern_crate();
1296
1297                 // There is an assumption elsewhere that paths of variants are in the enum's
1298                 // declaration and not imported. With this assumption, the variant component is
1299                 // chopped and the rest of the path is assumed to be the enum's own path. For
1300                 // errors where a variant is used as the type instead of the enum, this causes
1301                 // funny looking invalid suggestions, i.e `foo` instead of `foo::MyEnum`.
1302                 if via_import && name_binding.is_possibly_imported_variant() {
1303                     return;
1304                 }
1305
1306                 // #90113: Do not count an inaccessible reexported item as a candidate.
1307                 if let NameBindingKind::Import { binding, .. } = name_binding.kind {
1308                     if this.is_accessible_from(binding.vis, parent_scope.module)
1309                         && !this.is_accessible_from(name_binding.vis, parent_scope.module)
1310                     {
1311                         return;
1312                     }
1313                 }
1314
1315                 // collect results based on the filter function
1316                 // avoid suggesting anything from the same module in which we are resolving
1317                 // avoid suggesting anything with a hygienic name
1318                 if ident.name == lookup_ident.name
1319                     && ns == namespace
1320                     && !ptr::eq(in_module, parent_scope.module)
1321                     && !ident.span.normalize_to_macros_2_0().from_expansion()
1322                 {
1323                     let res = name_binding.res();
1324                     if filter_fn(res) {
1325                         // create the path
1326                         let mut segms = path_segments.clone();
1327                         if lookup_ident.span.rust_2018() {
1328                             // crate-local absolute paths start with `crate::` in edition 2018
1329                             // FIXME: may also be stabilized for Rust 2015 (Issues #45477, #44660)
1330                             segms.insert(0, ast::PathSegment::from_ident(crate_name));
1331                         }
1332
1333                         segms.push(ast::PathSegment::from_ident(ident));
1334                         let path = Path { span: name_binding.span, segments: segms, tokens: None };
1335                         let did = match res {
1336                             Res::Def(DefKind::Ctor(..), did) => this.opt_parent(did),
1337                             _ => res.opt_def_id(),
1338                         };
1339
1340                         if child_accessible {
1341                             // Remove invisible match if exists
1342                             if let Some(idx) = candidates
1343                                 .iter()
1344                                 .position(|v: &ImportSuggestion| v.did == did && !v.accessible)
1345                             {
1346                                 candidates.remove(idx);
1347                             }
1348                         }
1349
1350                         if candidates.iter().all(|v: &ImportSuggestion| v.did != did) {
1351                             // See if we're recommending TryFrom, TryInto, or FromIterator and add
1352                             // a note about editions
1353                             let note = if let Some(did) = did {
1354                                 let requires_note = !did.is_local()
1355                                     && this.cstore().item_attrs_untracked(did, this.session).any(
1356                                         |attr| {
1357                                             if attr.has_name(sym::rustc_diagnostic_item) {
1358                                                 [sym::TryInto, sym::TryFrom, sym::FromIterator]
1359                                                     .map(|x| Some(x))
1360                                                     .contains(&attr.value_str())
1361                                             } else {
1362                                                 false
1363                                             }
1364                                         },
1365                                     );
1366
1367                                 requires_note.then(|| {
1368                                     format!(
1369                                         "'{}' is included in the prelude starting in Edition 2021",
1370                                         path_names_to_string(&path)
1371                                     )
1372                                 })
1373                             } else {
1374                                 None
1375                             };
1376
1377                             candidates.push(ImportSuggestion {
1378                                 did,
1379                                 descr: res.descr(),
1380                                 path,
1381                                 accessible: child_accessible,
1382                                 note,
1383                             });
1384                         }
1385                     }
1386                 }
1387
1388                 // collect submodules to explore
1389                 if let Some(module) = name_binding.module() {
1390                     // form the path
1391                     let mut path_segments = path_segments.clone();
1392                     path_segments.push(ast::PathSegment::from_ident(ident));
1393
1394                     let is_extern_crate_that_also_appears_in_prelude =
1395                         name_binding.is_extern_crate() && lookup_ident.span.rust_2018();
1396
1397                     if !is_extern_crate_that_also_appears_in_prelude {
1398                         // add the module to the lookup
1399                         if seen_modules.insert(module.def_id()) {
1400                             if via_import { &mut worklist_via_import } else { &mut worklist }
1401                                 .push((module, path_segments, child_accessible));
1402                         }
1403                     }
1404                 }
1405             })
1406         }
1407
1408         // If only some candidates are accessible, take just them
1409         if !candidates.iter().all(|v: &ImportSuggestion| !v.accessible) {
1410             candidates = candidates.into_iter().filter(|x| x.accessible).collect();
1411         }
1412
1413         candidates
1414     }
1415
1416     /// When name resolution fails, this method can be used to look up candidate
1417     /// entities with the expected name. It allows filtering them using the
1418     /// supplied predicate (which should be used to only accept the types of
1419     /// definitions expected, e.g., traits). The lookup spans across all crates.
1420     ///
1421     /// N.B., the method does not look into imports, but this is not a problem,
1422     /// since we report the definitions (thus, the de-aliased imports).
1423     pub(crate) fn lookup_import_candidates<FilterFn>(
1424         &mut self,
1425         lookup_ident: Ident,
1426         namespace: Namespace,
1427         parent_scope: &ParentScope<'a>,
1428         filter_fn: FilterFn,
1429     ) -> Vec<ImportSuggestion>
1430     where
1431         FilterFn: Fn(Res) -> bool,
1432     {
1433         let mut suggestions = self.lookup_import_candidates_from_module(
1434             lookup_ident,
1435             namespace,
1436             parent_scope,
1437             self.graph_root,
1438             Ident::with_dummy_span(kw::Crate),
1439             &filter_fn,
1440         );
1441
1442         if lookup_ident.span.rust_2018() {
1443             let extern_prelude_names = self.extern_prelude.clone();
1444             for (ident, _) in extern_prelude_names.into_iter() {
1445                 if ident.span.from_expansion() {
1446                     // Idents are adjusted to the root context before being
1447                     // resolved in the extern prelude, so reporting this to the
1448                     // user is no help. This skips the injected
1449                     // `extern crate std` in the 2018 edition, which would
1450                     // otherwise cause duplicate suggestions.
1451                     continue;
1452                 }
1453                 if let Some(crate_id) = self.crate_loader.maybe_process_path_extern(ident.name) {
1454                     let crate_root = self.expect_module(crate_id.as_def_id());
1455                     suggestions.extend(self.lookup_import_candidates_from_module(
1456                         lookup_ident,
1457                         namespace,
1458                         parent_scope,
1459                         crate_root,
1460                         ident,
1461                         &filter_fn,
1462                     ));
1463                 }
1464             }
1465         }
1466
1467         suggestions
1468     }
1469
1470     pub(crate) fn unresolved_macro_suggestions(
1471         &mut self,
1472         err: &mut Diagnostic,
1473         macro_kind: MacroKind,
1474         parent_scope: &ParentScope<'a>,
1475         ident: Ident,
1476     ) {
1477         let is_expected = &|res: Res| res.macro_kind() == Some(macro_kind);
1478         let suggestion = self.early_lookup_typo_candidate(
1479             ScopeSet::Macro(macro_kind),
1480             parent_scope,
1481             ident,
1482             is_expected,
1483         );
1484         self.add_typo_suggestion(err, suggestion, ident.span);
1485
1486         let import_suggestions =
1487             self.lookup_import_candidates(ident, Namespace::MacroNS, parent_scope, is_expected);
1488         show_candidates(
1489             &self.session,
1490             &self.source_span,
1491             err,
1492             None,
1493             &import_suggestions,
1494             Instead::No,
1495             FoundUse::Yes,
1496             IsPattern::No,
1497             vec![],
1498         );
1499
1500         if macro_kind == MacroKind::Derive && (ident.name == sym::Send || ident.name == sym::Sync) {
1501             let msg = format!("unsafe traits like `{}` should be implemented explicitly", ident);
1502             err.span_note(ident.span, &msg);
1503             return;
1504         }
1505         if self.macro_names.contains(&ident.normalize_to_macros_2_0()) {
1506             err.help("have you added the `#[macro_use]` on the module/import?");
1507             return;
1508         }
1509         if ident.name == kw::Default
1510             && let ModuleKind::Def(DefKind::Enum, def_id, _) = parent_scope.module.kind
1511             && let Some(span) = self.opt_span(def_id)
1512         {
1513             let source_map = self.session.source_map();
1514             let head_span = source_map.guess_head_span(span);
1515             if let Ok(head) = source_map.span_to_snippet(head_span) {
1516                 err.span_suggestion(head_span, "consider adding a derive", format!("#[derive(Default)]\n{head}"), Applicability::MaybeIncorrect);
1517             } else {
1518                 err.span_help(
1519                     head_span,
1520                     "consider adding `#[derive(Default)]` to this enum",
1521                 );
1522             }
1523         }
1524         for ns in [Namespace::MacroNS, Namespace::TypeNS, Namespace::ValueNS] {
1525             if let Ok(binding) = self.early_resolve_ident_in_lexical_scope(
1526                 ident,
1527                 ScopeSet::All(ns, false),
1528                 &parent_scope,
1529                 None,
1530                 false,
1531                 None,
1532             ) {
1533                 let desc = match binding.res() {
1534                     Res::Def(DefKind::Macro(MacroKind::Bang), _) => {
1535                         "a function-like macro".to_string()
1536                     }
1537                     Res::Def(DefKind::Macro(MacroKind::Attr), _) | Res::NonMacroAttr(..) => {
1538                         format!("an attribute: `#[{}]`", ident)
1539                     }
1540                     Res::Def(DefKind::Macro(MacroKind::Derive), _) => {
1541                         format!("a derive macro: `#[derive({})]`", ident)
1542                     }
1543                     Res::ToolMod => {
1544                         // Don't confuse the user with tool modules.
1545                         continue;
1546                     }
1547                     Res::Def(DefKind::Trait, _) if macro_kind == MacroKind::Derive => {
1548                         "only a trait, without a derive macro".to_string()
1549                     }
1550                     res => format!(
1551                         "{} {}, not {} {}",
1552                         res.article(),
1553                         res.descr(),
1554                         macro_kind.article(),
1555                         macro_kind.descr_expected(),
1556                     ),
1557                 };
1558                 if let crate::NameBindingKind::Import { import, .. } = binding.kind {
1559                     if !import.span.is_dummy() {
1560                         err.span_note(
1561                             import.span,
1562                             &format!("`{}` is imported here, but it is {}", ident, desc),
1563                         );
1564                         // Silence the 'unused import' warning we might get,
1565                         // since this diagnostic already covers that import.
1566                         self.record_use(ident, binding, false);
1567                         return;
1568                     }
1569                 }
1570                 err.note(&format!("`{}` is in scope, but it is {}", ident, desc));
1571                 return;
1572             }
1573         }
1574     }
1575
1576     pub(crate) fn add_typo_suggestion(
1577         &self,
1578         err: &mut Diagnostic,
1579         suggestion: Option<TypoSuggestion>,
1580         span: Span,
1581     ) -> bool {
1582         let suggestion = match suggestion {
1583             None => return false,
1584             // We shouldn't suggest underscore.
1585             Some(suggestion) if suggestion.candidate == kw::Underscore => return false,
1586             Some(suggestion) => suggestion,
1587         };
1588         let def_span = suggestion.res.opt_def_id().and_then(|def_id| match def_id.krate {
1589             LOCAL_CRATE => self.opt_span(def_id),
1590             _ => Some(self.cstore().get_span_untracked(def_id, self.session)),
1591         });
1592         if let Some(def_span) = def_span {
1593             if span.overlaps(def_span) {
1594                 // Don't suggest typo suggestion for itself like in the following:
1595                 // error[E0423]: expected function, tuple struct or tuple variant, found struct `X`
1596                 //   --> $DIR/issue-64792-bad-unicode-ctor.rs:3:14
1597                 //    |
1598                 // LL | struct X {}
1599                 //    | ----------- `X` defined here
1600                 // LL |
1601                 // LL | const Y: X = X("ö");
1602                 //    | -------------^^^^^^- similarly named constant `Y` defined here
1603                 //    |
1604                 // help: use struct literal syntax instead
1605                 //    |
1606                 // LL | const Y: X = X {};
1607                 //    |              ^^^^
1608                 // help: a constant with a similar name exists
1609                 //    |
1610                 // LL | const Y: X = Y("ö");
1611                 //    |              ^
1612                 return false;
1613             }
1614             let prefix = match suggestion.target {
1615                 SuggestionTarget::SimilarlyNamed => "similarly named ",
1616                 SuggestionTarget::SingleItem => "",
1617             };
1618
1619             err.span_label(
1620                 self.session.source_map().guess_head_span(def_span),
1621                 &format!(
1622                     "{}{} `{}` defined here",
1623                     prefix,
1624                     suggestion.res.descr(),
1625                     suggestion.candidate,
1626                 ),
1627             );
1628         }
1629         let msg = match suggestion.target {
1630             SuggestionTarget::SimilarlyNamed => format!(
1631                 "{} {} with a similar name exists",
1632                 suggestion.res.article(),
1633                 suggestion.res.descr()
1634             ),
1635             SuggestionTarget::SingleItem => {
1636                 format!("maybe you meant this {}", suggestion.res.descr())
1637             }
1638         };
1639         err.span_suggestion(span, &msg, suggestion.candidate, Applicability::MaybeIncorrect);
1640         true
1641     }
1642
1643     fn binding_description(&self, b: &NameBinding<'_>, ident: Ident, from_prelude: bool) -> String {
1644         let res = b.res();
1645         if b.span.is_dummy() || !self.session.source_map().is_span_accessible(b.span) {
1646             // These already contain the "built-in" prefix or look bad with it.
1647             let add_built_in =
1648                 !matches!(b.res(), Res::NonMacroAttr(..) | Res::PrimTy(..) | Res::ToolMod);
1649             let (built_in, from) = if from_prelude {
1650                 ("", " from prelude")
1651             } else if b.is_extern_crate()
1652                 && !b.is_import()
1653                 && self.session.opts.externs.get(ident.as_str()).is_some()
1654             {
1655                 ("", " passed with `--extern`")
1656             } else if add_built_in {
1657                 (" built-in", "")
1658             } else {
1659                 ("", "")
1660             };
1661
1662             let a = if built_in.is_empty() { res.article() } else { "a" };
1663             format!("{a}{built_in} {thing}{from}", thing = res.descr())
1664         } else {
1665             let introduced = if b.is_import() { "imported" } else { "defined" };
1666             format!("the {thing} {introduced} here", thing = res.descr())
1667         }
1668     }
1669
1670     fn report_ambiguity_error(&self, ambiguity_error: &AmbiguityError<'_>) {
1671         let AmbiguityError { kind, ident, b1, b2, misc1, misc2 } = *ambiguity_error;
1672         let (b1, b2, misc1, misc2, swapped) = if b2.span.is_dummy() && !b1.span.is_dummy() {
1673             // We have to print the span-less alternative first, otherwise formatting looks bad.
1674             (b2, b1, misc2, misc1, true)
1675         } else {
1676             (b1, b2, misc1, misc2, false)
1677         };
1678
1679         let mut err = struct_span_err!(self.session, ident.span, E0659, "`{ident}` is ambiguous");
1680         err.span_label(ident.span, "ambiguous name");
1681         err.note(&format!("ambiguous because of {}", kind.descr()));
1682
1683         let mut could_refer_to = |b: &NameBinding<'_>, misc: AmbiguityErrorMisc, also: &str| {
1684             let what = self.binding_description(b, ident, misc == AmbiguityErrorMisc::FromPrelude);
1685             let note_msg = format!("`{ident}` could{also} refer to {what}");
1686
1687             let thing = b.res().descr();
1688             let mut help_msgs = Vec::new();
1689             if b.is_glob_import()
1690                 && (kind == AmbiguityKind::GlobVsGlob
1691                     || kind == AmbiguityKind::GlobVsExpanded
1692                     || kind == AmbiguityKind::GlobVsOuter && swapped != also.is_empty())
1693             {
1694                 help_msgs.push(format!(
1695                     "consider adding an explicit import of `{ident}` to disambiguate"
1696                 ))
1697             }
1698             if b.is_extern_crate() && ident.span.rust_2018() {
1699                 help_msgs.push(format!("use `::{ident}` to refer to this {thing} unambiguously"))
1700             }
1701             if misc == AmbiguityErrorMisc::SuggestCrate {
1702                 help_msgs
1703                     .push(format!("use `crate::{ident}` to refer to this {thing} unambiguously"))
1704             } else if misc == AmbiguityErrorMisc::SuggestSelf {
1705                 help_msgs
1706                     .push(format!("use `self::{ident}` to refer to this {thing} unambiguously"))
1707             }
1708
1709             err.span_note(b.span, &note_msg);
1710             for (i, help_msg) in help_msgs.iter().enumerate() {
1711                 let or = if i == 0 { "" } else { "or " };
1712                 err.help(&format!("{}{}", or, help_msg));
1713             }
1714         };
1715
1716         could_refer_to(b1, misc1, "");
1717         could_refer_to(b2, misc2, " also");
1718         err.emit();
1719     }
1720
1721     /// If the binding refers to a tuple struct constructor with fields,
1722     /// returns the span of its fields.
1723     fn ctor_fields_span(&self, binding: &NameBinding<'_>) -> Option<Span> {
1724         if let NameBindingKind::Res(
1725             Res::Def(DefKind::Ctor(CtorOf::Struct, CtorKind::Fn), ctor_def_id),
1726             _,
1727         ) = binding.kind
1728         {
1729             let def_id = self.parent(ctor_def_id);
1730             let fields = self.field_names.get(&def_id)?;
1731             return fields.iter().map(|name| name.span).reduce(Span::to); // None for `struct Foo()`
1732         }
1733         None
1734     }
1735
1736     fn report_privacy_error(&self, privacy_error: &PrivacyError<'_>) {
1737         let PrivacyError { ident, binding, .. } = *privacy_error;
1738
1739         let res = binding.res();
1740         let ctor_fields_span = self.ctor_fields_span(binding);
1741         let plain_descr = res.descr().to_string();
1742         let nonimport_descr =
1743             if ctor_fields_span.is_some() { plain_descr + " constructor" } else { plain_descr };
1744         let import_descr = nonimport_descr.clone() + " import";
1745         let get_descr =
1746             |b: &NameBinding<'_>| if b.is_import() { &import_descr } else { &nonimport_descr };
1747
1748         // Print the primary message.
1749         let descr = get_descr(binding);
1750         let mut err =
1751             struct_span_err!(self.session, ident.span, E0603, "{} `{}` is private", descr, ident);
1752         err.span_label(ident.span, &format!("private {}", descr));
1753         if let Some(span) = ctor_fields_span {
1754             err.span_label(span, "a constructor is private if any of the fields is private");
1755         }
1756
1757         // Print the whole import chain to make it easier to see what happens.
1758         let first_binding = binding;
1759         let mut next_binding = Some(binding);
1760         let mut next_ident = ident;
1761         while let Some(binding) = next_binding {
1762             let name = next_ident;
1763             next_binding = match binding.kind {
1764                 _ if res == Res::Err => None,
1765                 NameBindingKind::Import { binding, import, .. } => match import.kind {
1766                     _ if binding.span.is_dummy() => None,
1767                     ImportKind::Single { source, .. } => {
1768                         next_ident = source;
1769                         Some(binding)
1770                     }
1771                     ImportKind::Glob { .. } | ImportKind::MacroUse => Some(binding),
1772                     ImportKind::ExternCrate { .. } => None,
1773                 },
1774                 _ => None,
1775             };
1776
1777             let first = ptr::eq(binding, first_binding);
1778             let msg = format!(
1779                 "{and_refers_to}the {item} `{name}`{which} is defined here{dots}",
1780                 and_refers_to = if first { "" } else { "...and refers to " },
1781                 item = get_descr(binding),
1782                 which = if first { "" } else { " which" },
1783                 dots = if next_binding.is_some() { "..." } else { "" },
1784             );
1785             let def_span = self.session.source_map().guess_head_span(binding.span);
1786             let mut note_span = MultiSpan::from_span(def_span);
1787             if !first && binding.vis.is_public() {
1788                 note_span.push_span_label(def_span, "consider importing it directly");
1789             }
1790             err.span_note(note_span, &msg);
1791         }
1792
1793         err.emit();
1794     }
1795
1796     pub(crate) fn find_similarly_named_module_or_crate(
1797         &mut self,
1798         ident: Symbol,
1799         current_module: &Module<'a>,
1800     ) -> Option<Symbol> {
1801         let mut candidates = self
1802             .extern_prelude
1803             .iter()
1804             .map(|(ident, _)| ident.name)
1805             .chain(
1806                 self.module_map
1807                     .iter()
1808                     .filter(|(_, module)| {
1809                         current_module.is_ancestor_of(module) && !ptr::eq(current_module, *module)
1810                     })
1811                     .flat_map(|(_, module)| module.kind.name()),
1812             )
1813             .filter(|c| !c.to_string().is_empty())
1814             .collect::<Vec<_>>();
1815         candidates.sort();
1816         candidates.dedup();
1817         match find_best_match_for_name(&candidates, ident, None) {
1818             Some(sugg) if sugg == ident => None,
1819             sugg => sugg,
1820         }
1821     }
1822
1823     pub(crate) fn report_path_resolution_error(
1824         &mut self,
1825         path: &[Segment],
1826         opt_ns: Option<Namespace>, // `None` indicates a module path in import
1827         parent_scope: &ParentScope<'a>,
1828         ribs: Option<&PerNS<Vec<Rib<'a>>>>,
1829         ignore_binding: Option<&'a NameBinding<'a>>,
1830         module: Option<ModuleOrUniformRoot<'a>>,
1831         i: usize,
1832         ident: Ident,
1833     ) -> (String, Option<Suggestion>) {
1834         let is_last = i == path.len() - 1;
1835         let ns = if is_last { opt_ns.unwrap_or(TypeNS) } else { TypeNS };
1836         let module_res = match module {
1837             Some(ModuleOrUniformRoot::Module(module)) => module.res(),
1838             _ => None,
1839         };
1840         if module_res == self.graph_root.res() {
1841             let is_mod = |res| matches!(res, Res::Def(DefKind::Mod, _));
1842             let mut candidates = self.lookup_import_candidates(ident, TypeNS, parent_scope, is_mod);
1843             candidates
1844                 .sort_by_cached_key(|c| (c.path.segments.len(), pprust::path_to_string(&c.path)));
1845             if let Some(candidate) = candidates.get(0) {
1846                 (
1847                     String::from("unresolved import"),
1848                     Some((
1849                         vec![(ident.span, pprust::path_to_string(&candidate.path))],
1850                         String::from("a similar path exists"),
1851                         Applicability::MaybeIncorrect,
1852                     )),
1853                 )
1854             } else if self.session.edition() == Edition::Edition2015 {
1855                 (
1856                     format!("maybe a missing crate `{ident}`?"),
1857                     Some((
1858                         vec![],
1859                         format!(
1860                             "consider adding `extern crate {ident}` to use the `{ident}` crate"
1861                         ),
1862                         Applicability::MaybeIncorrect,
1863                     )),
1864                 )
1865             } else {
1866                 (format!("could not find `{ident}` in the crate root"), None)
1867             }
1868         } else if i > 0 {
1869             let parent = path[i - 1].ident.name;
1870             let parent = match parent {
1871                 // ::foo is mounted at the crate root for 2015, and is the extern
1872                 // prelude for 2018+
1873                 kw::PathRoot if self.session.edition() > Edition::Edition2015 => {
1874                     "the list of imported crates".to_owned()
1875                 }
1876                 kw::PathRoot | kw::Crate => "the crate root".to_owned(),
1877                 _ => format!("`{parent}`"),
1878             };
1879
1880             let mut msg = format!("could not find `{}` in {}", ident, parent);
1881             if ns == TypeNS || ns == ValueNS {
1882                 let ns_to_try = if ns == TypeNS { ValueNS } else { TypeNS };
1883                 let binding = if let Some(module) = module {
1884                     self.resolve_ident_in_module(
1885                         module,
1886                         ident,
1887                         ns_to_try,
1888                         parent_scope,
1889                         None,
1890                         ignore_binding,
1891                     ).ok()
1892                 } else if let Some(ribs) = ribs
1893                     && let Some(TypeNS | ValueNS) = opt_ns
1894                 {
1895                     match self.resolve_ident_in_lexical_scope(
1896                         ident,
1897                         ns_to_try,
1898                         parent_scope,
1899                         None,
1900                         &ribs[ns_to_try],
1901                         ignore_binding,
1902                     ) {
1903                         // we found a locally-imported or available item/module
1904                         Some(LexicalScopeBinding::Item(binding)) => Some(binding),
1905                         _ => None,
1906                     }
1907                 } else {
1908                     let scopes = ScopeSet::All(ns_to_try, opt_ns.is_none());
1909                     self.early_resolve_ident_in_lexical_scope(
1910                         ident,
1911                         scopes,
1912                         parent_scope,
1913                         None,
1914                         false,
1915                         ignore_binding,
1916                     ).ok()
1917                 };
1918                 if let Some(binding) = binding {
1919                     let mut found = |what| {
1920                         msg = format!(
1921                             "expected {}, found {} `{}` in {}",
1922                             ns.descr(),
1923                             what,
1924                             ident,
1925                             parent
1926                         )
1927                     };
1928                     if binding.module().is_some() {
1929                         found("module")
1930                     } else {
1931                         match binding.res() {
1932                             Res::Def(kind, id) => found(kind.descr(id)),
1933                             _ => found(ns_to_try.descr()),
1934                         }
1935                     }
1936                 };
1937             }
1938             (msg, None)
1939         } else if ident.name == kw::SelfUpper {
1940             ("`Self` is only available in impls, traits, and type definitions".to_string(), None)
1941         } else if ident.name.as_str().chars().next().map_or(false, |c| c.is_ascii_uppercase()) {
1942             // Check whether the name refers to an item in the value namespace.
1943             let binding = if let Some(ribs) = ribs {
1944                 self.resolve_ident_in_lexical_scope(
1945                     ident,
1946                     ValueNS,
1947                     parent_scope,
1948                     None,
1949                     &ribs[ValueNS],
1950                     ignore_binding,
1951                 )
1952             } else {
1953                 None
1954             };
1955             let match_span = match binding {
1956                 // Name matches a local variable. For example:
1957                 // ```
1958                 // fn f() {
1959                 //     let Foo: &str = "";
1960                 //     println!("{}", Foo::Bar); // Name refers to local
1961                 //                               // variable `Foo`.
1962                 // }
1963                 // ```
1964                 Some(LexicalScopeBinding::Res(Res::Local(id))) => {
1965                     Some(*self.pat_span_map.get(&id).unwrap())
1966                 }
1967                 // Name matches item from a local name binding
1968                 // created by `use` declaration. For example:
1969                 // ```
1970                 // pub Foo: &str = "";
1971                 //
1972                 // mod submod {
1973                 //     use super::Foo;
1974                 //     println!("{}", Foo::Bar); // Name refers to local
1975                 //                               // binding `Foo`.
1976                 // }
1977                 // ```
1978                 Some(LexicalScopeBinding::Item(name_binding)) => Some(name_binding.span),
1979                 _ => None,
1980             };
1981             let suggestion = if let Some(span) = match_span {
1982                 Some((
1983                     vec![(span, String::from(""))],
1984                     format!("`{}` is defined here, but is not a type", ident),
1985                     Applicability::MaybeIncorrect,
1986                 ))
1987             } else {
1988                 None
1989             };
1990
1991             (format!("use of undeclared type `{}`", ident), suggestion)
1992         } else {
1993             let suggestion = if ident.name == sym::alloc {
1994                 Some((
1995                     vec![],
1996                     String::from("add `extern crate alloc` to use the `alloc` crate"),
1997                     Applicability::MaybeIncorrect,
1998                 ))
1999             } else {
2000                 self.find_similarly_named_module_or_crate(ident.name, &parent_scope.module).map(
2001                     |sugg| {
2002                         (
2003                             vec![(ident.span, sugg.to_string())],
2004                             String::from("there is a crate or module with a similar name"),
2005                             Applicability::MaybeIncorrect,
2006                         )
2007                     },
2008                 )
2009             };
2010             (format!("use of undeclared crate or module `{}`", ident), suggestion)
2011         }
2012     }
2013 }
2014
2015 impl<'a, 'b> ImportResolver<'a, 'b> {
2016     /// Adds suggestions for a path that cannot be resolved.
2017     pub(crate) fn make_path_suggestion(
2018         &mut self,
2019         span: Span,
2020         mut path: Vec<Segment>,
2021         parent_scope: &ParentScope<'b>,
2022     ) -> Option<(Vec<Segment>, Option<String>)> {
2023         debug!("make_path_suggestion: span={:?} path={:?}", span, path);
2024
2025         match (path.get(0), path.get(1)) {
2026             // `{{root}}::ident::...` on both editions.
2027             // On 2015 `{{root}}` is usually added implicitly.
2028             (Some(fst), Some(snd))
2029                 if fst.ident.name == kw::PathRoot && !snd.ident.is_path_segment_keyword() => {}
2030             // `ident::...` on 2018.
2031             (Some(fst), _)
2032                 if fst.ident.span.rust_2018() && !fst.ident.is_path_segment_keyword() =>
2033             {
2034                 // Insert a placeholder that's later replaced by `self`/`super`/etc.
2035                 path.insert(0, Segment::from_ident(Ident::empty()));
2036             }
2037             _ => return None,
2038         }
2039
2040         self.make_missing_self_suggestion(path.clone(), parent_scope)
2041             .or_else(|| self.make_missing_crate_suggestion(path.clone(), parent_scope))
2042             .or_else(|| self.make_missing_super_suggestion(path.clone(), parent_scope))
2043             .or_else(|| self.make_external_crate_suggestion(path, parent_scope))
2044     }
2045
2046     /// Suggest a missing `self::` if that resolves to an correct module.
2047     ///
2048     /// ```text
2049     ///    |
2050     /// LL | use foo::Bar;
2051     ///    |     ^^^ did you mean `self::foo`?
2052     /// ```
2053     fn make_missing_self_suggestion(
2054         &mut self,
2055         mut path: Vec<Segment>,
2056         parent_scope: &ParentScope<'b>,
2057     ) -> Option<(Vec<Segment>, Option<String>)> {
2058         // Replace first ident with `self` and check if that is valid.
2059         path[0].ident.name = kw::SelfLower;
2060         let result = self.r.maybe_resolve_path(&path, None, parent_scope);
2061         debug!("make_missing_self_suggestion: path={:?} result={:?}", path, result);
2062         if let PathResult::Module(..) = result { Some((path, None)) } else { None }
2063     }
2064
2065     /// Suggests a missing `crate::` if that resolves to an correct module.
2066     ///
2067     /// ```text
2068     ///    |
2069     /// LL | use foo::Bar;
2070     ///    |     ^^^ did you mean `crate::foo`?
2071     /// ```
2072     fn make_missing_crate_suggestion(
2073         &mut self,
2074         mut path: Vec<Segment>,
2075         parent_scope: &ParentScope<'b>,
2076     ) -> Option<(Vec<Segment>, Option<String>)> {
2077         // Replace first ident with `crate` and check if that is valid.
2078         path[0].ident.name = kw::Crate;
2079         let result = self.r.maybe_resolve_path(&path, None, parent_scope);
2080         debug!("make_missing_crate_suggestion:  path={:?} result={:?}", path, result);
2081         if let PathResult::Module(..) = result {
2082             Some((
2083                 path,
2084                 Some(
2085                     "`use` statements changed in Rust 2018; read more at \
2086                      <https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-\
2087                      clarity.html>"
2088                         .to_string(),
2089                 ),
2090             ))
2091         } else {
2092             None
2093         }
2094     }
2095
2096     /// Suggests a missing `super::` if that resolves to an correct module.
2097     ///
2098     /// ```text
2099     ///    |
2100     /// LL | use foo::Bar;
2101     ///    |     ^^^ did you mean `super::foo`?
2102     /// ```
2103     fn make_missing_super_suggestion(
2104         &mut self,
2105         mut path: Vec<Segment>,
2106         parent_scope: &ParentScope<'b>,
2107     ) -> Option<(Vec<Segment>, Option<String>)> {
2108         // Replace first ident with `crate` and check if that is valid.
2109         path[0].ident.name = kw::Super;
2110         let result = self.r.maybe_resolve_path(&path, None, parent_scope);
2111         debug!("make_missing_super_suggestion:  path={:?} result={:?}", path, result);
2112         if let PathResult::Module(..) = result { Some((path, None)) } else { None }
2113     }
2114
2115     /// Suggests a missing external crate name if that resolves to an correct module.
2116     ///
2117     /// ```text
2118     ///    |
2119     /// LL | use foobar::Baz;
2120     ///    |     ^^^^^^ did you mean `baz::foobar`?
2121     /// ```
2122     ///
2123     /// Used when importing a submodule of an external crate but missing that crate's
2124     /// name as the first part of path.
2125     fn make_external_crate_suggestion(
2126         &mut self,
2127         mut path: Vec<Segment>,
2128         parent_scope: &ParentScope<'b>,
2129     ) -> Option<(Vec<Segment>, Option<String>)> {
2130         if path[1].ident.span.rust_2015() {
2131             return None;
2132         }
2133
2134         // Sort extern crate names in *reverse* order to get
2135         // 1) some consistent ordering for emitted diagnostics, and
2136         // 2) `std` suggestions before `core` suggestions.
2137         let mut extern_crate_names =
2138             self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
2139         extern_crate_names.sort_by(|a, b| b.as_str().partial_cmp(a.as_str()).unwrap());
2140
2141         for name in extern_crate_names.into_iter() {
2142             // Replace first ident with a crate name and check if that is valid.
2143             path[0].ident.name = name;
2144             let result = self.r.maybe_resolve_path(&path, None, parent_scope);
2145             debug!(
2146                 "make_external_crate_suggestion: name={:?} path={:?} result={:?}",
2147                 name, path, result
2148             );
2149             if let PathResult::Module(..) = result {
2150                 return Some((path, None));
2151             }
2152         }
2153
2154         None
2155     }
2156
2157     /// Suggests importing a macro from the root of the crate rather than a module within
2158     /// the crate.
2159     ///
2160     /// ```text
2161     /// help: a macro with this name exists at the root of the crate
2162     ///    |
2163     /// LL | use issue_59764::makro;
2164     ///    |     ^^^^^^^^^^^^^^^^^^
2165     ///    |
2166     ///    = note: this could be because a macro annotated with `#[macro_export]` will be exported
2167     ///            at the root of the crate instead of the module where it is defined
2168     /// ```
2169     pub(crate) fn check_for_module_export_macro(
2170         &mut self,
2171         import: &'b Import<'b>,
2172         module: ModuleOrUniformRoot<'b>,
2173         ident: Ident,
2174     ) -> Option<(Option<Suggestion>, Option<String>)> {
2175         let ModuleOrUniformRoot::Module(mut crate_module) = module else {
2176             return None;
2177         };
2178
2179         while let Some(parent) = crate_module.parent {
2180             crate_module = parent;
2181         }
2182
2183         if ModuleOrUniformRoot::same_def(ModuleOrUniformRoot::Module(crate_module), module) {
2184             // Don't make a suggestion if the import was already from the root of the
2185             // crate.
2186             return None;
2187         }
2188
2189         let resolutions = self.r.resolutions(crate_module).borrow();
2190         let resolution = resolutions.get(&self.r.new_key(ident, MacroNS))?;
2191         let binding = resolution.borrow().binding()?;
2192         if let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() {
2193             let module_name = crate_module.kind.name().unwrap();
2194             let import_snippet = match import.kind {
2195                 ImportKind::Single { source, target, .. } if source != target => {
2196                     format!("{} as {}", source, target)
2197                 }
2198                 _ => format!("{}", ident),
2199             };
2200
2201             let mut corrections: Vec<(Span, String)> = Vec::new();
2202             if !import.is_nested() {
2203                 // Assume this is the easy case of `use issue_59764::foo::makro;` and just remove
2204                 // intermediate segments.
2205                 corrections.push((import.span, format!("{}::{}", module_name, import_snippet)));
2206             } else {
2207                 // Find the binding span (and any trailing commas and spaces).
2208                 //   ie. `use a::b::{c, d, e};`
2209                 //                      ^^^
2210                 let (found_closing_brace, binding_span) = find_span_of_binding_until_next_binding(
2211                     self.r.session,
2212                     import.span,
2213                     import.use_span,
2214                 );
2215                 debug!(
2216                     "check_for_module_export_macro: found_closing_brace={:?} binding_span={:?}",
2217                     found_closing_brace, binding_span
2218                 );
2219
2220                 let mut removal_span = binding_span;
2221                 if found_closing_brace {
2222                     // If the binding span ended with a closing brace, as in the below example:
2223                     //   ie. `use a::b::{c, d};`
2224                     //                      ^
2225                     // Then expand the span of characters to remove to include the previous
2226                     // binding's trailing comma.
2227                     //   ie. `use a::b::{c, d};`
2228                     //                    ^^^
2229                     if let Some(previous_span) =
2230                         extend_span_to_previous_binding(self.r.session, binding_span)
2231                     {
2232                         debug!("check_for_module_export_macro: previous_span={:?}", previous_span);
2233                         removal_span = removal_span.with_lo(previous_span.lo());
2234                     }
2235                 }
2236                 debug!("check_for_module_export_macro: removal_span={:?}", removal_span);
2237
2238                 // Remove the `removal_span`.
2239                 corrections.push((removal_span, "".to_string()));
2240
2241                 // Find the span after the crate name and if it has nested imports immediately
2242                 // after the crate name already.
2243                 //   ie. `use a::b::{c, d};`
2244                 //               ^^^^^^^^^
2245                 //   or  `use a::{b, c, d}};`
2246                 //               ^^^^^^^^^^^
2247                 let (has_nested, after_crate_name) = find_span_immediately_after_crate_name(
2248                     self.r.session,
2249                     module_name,
2250                     import.use_span,
2251                 );
2252                 debug!(
2253                     "check_for_module_export_macro: has_nested={:?} after_crate_name={:?}",
2254                     has_nested, after_crate_name
2255                 );
2256
2257                 let source_map = self.r.session.source_map();
2258
2259                 // Add the import to the start, with a `{` if required.
2260                 let start_point = source_map.start_point(after_crate_name);
2261                 if let Ok(start_snippet) = source_map.span_to_snippet(start_point) {
2262                     corrections.push((
2263                         start_point,
2264                         if has_nested {
2265                             // In this case, `start_snippet` must equal '{'.
2266                             format!("{}{}, ", start_snippet, import_snippet)
2267                         } else {
2268                             // In this case, add a `{`, then the moved import, then whatever
2269                             // was there before.
2270                             format!("{{{}, {}", import_snippet, start_snippet)
2271                         },
2272                     ));
2273                 }
2274
2275                 // Add a `};` to the end if nested, matching the `{` added at the start.
2276                 if !has_nested {
2277                     corrections.push((source_map.end_point(after_crate_name), "};".to_string()));
2278                 }
2279             }
2280
2281             let suggestion = Some((
2282                 corrections,
2283                 String::from("a macro with this name exists at the root of the crate"),
2284                 Applicability::MaybeIncorrect,
2285             ));
2286             Some((suggestion, Some("this could be because a macro annotated with `#[macro_export]` will be exported \
2287             at the root of the crate instead of the module where it is defined"
2288                .to_string())))
2289         } else {
2290             None
2291         }
2292     }
2293 }
2294
2295 /// Given a `binding_span` of a binding within a use statement:
2296 ///
2297 /// ```ignore (illustrative)
2298 /// use foo::{a, b, c};
2299 /// //           ^
2300 /// ```
2301 ///
2302 /// then return the span until the next binding or the end of the statement:
2303 ///
2304 /// ```ignore (illustrative)
2305 /// use foo::{a, b, c};
2306 /// //           ^^^
2307 /// ```
2308 fn find_span_of_binding_until_next_binding(
2309     sess: &Session,
2310     binding_span: Span,
2311     use_span: Span,
2312 ) -> (bool, Span) {
2313     let source_map = sess.source_map();
2314
2315     // Find the span of everything after the binding.
2316     //   ie. `a, e};` or `a};`
2317     let binding_until_end = binding_span.with_hi(use_span.hi());
2318
2319     // Find everything after the binding but not including the binding.
2320     //   ie. `, e};` or `};`
2321     let after_binding_until_end = binding_until_end.with_lo(binding_span.hi());
2322
2323     // Keep characters in the span until we encounter something that isn't a comma or
2324     // whitespace.
2325     //   ie. `, ` or ``.
2326     //
2327     // Also note whether a closing brace character was encountered. If there
2328     // was, then later go backwards to remove any trailing commas that are left.
2329     let mut found_closing_brace = false;
2330     let after_binding_until_next_binding =
2331         source_map.span_take_while(after_binding_until_end, |&ch| {
2332             if ch == '}' {
2333                 found_closing_brace = true;
2334             }
2335             ch == ' ' || ch == ','
2336         });
2337
2338     // Combine the two spans.
2339     //   ie. `a, ` or `a`.
2340     //
2341     // Removing these would leave `issue_52891::{d, e};` or `issue_52891::{d, e, };`
2342     let span = binding_span.with_hi(after_binding_until_next_binding.hi());
2343
2344     (found_closing_brace, span)
2345 }
2346
2347 /// Given a `binding_span`, return the span through to the comma or opening brace of the previous
2348 /// binding.
2349 ///
2350 /// ```ignore (illustrative)
2351 /// use foo::a::{a, b, c};
2352 /// //            ^^--- binding span
2353 /// //            |
2354 /// //            returned span
2355 ///
2356 /// use foo::{a, b, c};
2357 /// //        --- binding span
2358 /// ```
2359 fn extend_span_to_previous_binding(sess: &Session, binding_span: Span) -> Option<Span> {
2360     let source_map = sess.source_map();
2361
2362     // `prev_source` will contain all of the source that came before the span.
2363     // Then split based on a command and take the first (ie. closest to our span)
2364     // snippet. In the example, this is a space.
2365     let prev_source = source_map.span_to_prev_source(binding_span).ok()?;
2366
2367     let prev_comma = prev_source.rsplit(',').collect::<Vec<_>>();
2368     let prev_starting_brace = prev_source.rsplit('{').collect::<Vec<_>>();
2369     if prev_comma.len() <= 1 || prev_starting_brace.len() <= 1 {
2370         return None;
2371     }
2372
2373     let prev_comma = prev_comma.first().unwrap();
2374     let prev_starting_brace = prev_starting_brace.first().unwrap();
2375
2376     // If the amount of source code before the comma is greater than
2377     // the amount of source code before the starting brace then we've only
2378     // got one item in the nested item (eg. `issue_52891::{self}`).
2379     if prev_comma.len() > prev_starting_brace.len() {
2380         return None;
2381     }
2382
2383     Some(binding_span.with_lo(BytePos(
2384         // Take away the number of bytes for the characters we've found and an
2385         // extra for the comma.
2386         binding_span.lo().0 - (prev_comma.as_bytes().len() as u32) - 1,
2387     )))
2388 }
2389
2390 /// Given a `use_span` of a binding within a use statement, returns the highlighted span and if
2391 /// it is a nested use tree.
2392 ///
2393 /// ```ignore (illustrative)
2394 /// use foo::a::{b, c};
2395 /// //       ^^^^^^^^^^ -- false
2396 ///
2397 /// use foo::{a, b, c};
2398 /// //       ^^^^^^^^^^ -- true
2399 ///
2400 /// use foo::{a, b::{c, d}};
2401 /// //       ^^^^^^^^^^^^^^^ -- true
2402 /// ```
2403 fn find_span_immediately_after_crate_name(
2404     sess: &Session,
2405     module_name: Symbol,
2406     use_span: Span,
2407 ) -> (bool, Span) {
2408     debug!(
2409         "find_span_immediately_after_crate_name: module_name={:?} use_span={:?}",
2410         module_name, use_span
2411     );
2412     let source_map = sess.source_map();
2413
2414     // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
2415     let mut num_colons = 0;
2416     // Find second colon.. `use issue_59764:`
2417     let until_second_colon = source_map.span_take_while(use_span, |c| {
2418         if *c == ':' {
2419             num_colons += 1;
2420         }
2421         !matches!(c, ':' if num_colons == 2)
2422     });
2423     // Find everything after the second colon.. `foo::{baz, makro};`
2424     let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
2425
2426     let mut found_a_non_whitespace_character = false;
2427     // Find the first non-whitespace character in `from_second_colon`.. `f`
2428     let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
2429         if found_a_non_whitespace_character {
2430             return false;
2431         }
2432         if !c.is_whitespace() {
2433             found_a_non_whitespace_character = true;
2434         }
2435         true
2436     });
2437
2438     // Find the first `{` in from_second_colon.. `foo::{`
2439     let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
2440
2441     (next_left_bracket == after_second_colon, from_second_colon)
2442 }
2443
2444 /// A suggestion has already been emitted, change the wording slightly to clarify that both are
2445 /// independent options.
2446 enum Instead {
2447     Yes,
2448     No,
2449 }
2450
2451 /// Whether an existing place with an `use` item was found.
2452 enum FoundUse {
2453     Yes,
2454     No,
2455 }
2456
2457 /// Whether a binding is part of a pattern or an expression. Used for diagnostics.
2458 enum IsPattern {
2459     /// The binding is part of a pattern
2460     Yes,
2461     /// The binding is part of an expression
2462     No,
2463 }
2464
2465 /// When an entity with a given name is not available in scope, we search for
2466 /// entities with that name in all crates. This method allows outputting the
2467 /// results of this search in a programmer-friendly way
2468 fn show_candidates(
2469     session: &Session,
2470     source_span: &IndexVec<LocalDefId, Span>,
2471     err: &mut Diagnostic,
2472     // This is `None` if all placement locations are inside expansions
2473     use_placement_span: Option<Span>,
2474     candidates: &[ImportSuggestion],
2475     instead: Instead,
2476     found_use: FoundUse,
2477     is_pattern: IsPattern,
2478     path: Vec<Segment>,
2479 ) {
2480     if candidates.is_empty() {
2481         return;
2482     }
2483
2484     let mut accessible_path_strings: Vec<(String, &str, Option<DefId>, &Option<String>)> =
2485         Vec::new();
2486     let mut inaccessible_path_strings: Vec<(String, &str, Option<DefId>, &Option<String>)> =
2487         Vec::new();
2488
2489     candidates.iter().for_each(|c| {
2490         (if c.accessible { &mut accessible_path_strings } else { &mut inaccessible_path_strings })
2491             .push((path_names_to_string(&c.path), c.descr, c.did, &c.note))
2492     });
2493
2494     // we want consistent results across executions, but candidates are produced
2495     // by iterating through a hash map, so make sure they are ordered:
2496     for path_strings in [&mut accessible_path_strings, &mut inaccessible_path_strings] {
2497         path_strings.sort_by(|a, b| a.0.cmp(&b.0));
2498         let core_path_strings =
2499             path_strings.drain_filter(|p| p.0.starts_with("core::")).collect::<Vec<_>>();
2500         path_strings.extend(core_path_strings);
2501         path_strings.dedup_by(|a, b| a.0 == b.0);
2502     }
2503
2504     if !accessible_path_strings.is_empty() {
2505         let (determiner, kind, name) = if accessible_path_strings.len() == 1 {
2506             ("this", accessible_path_strings[0].1, format!(" `{}`", accessible_path_strings[0].0))
2507         } else {
2508             ("one of these", "items", String::new())
2509         };
2510
2511         let instead = if let Instead::Yes = instead { " instead" } else { "" };
2512         let mut msg = if let IsPattern::Yes = is_pattern {
2513             format!(
2514                 "if you meant to match on {}{}{}, use the full path in the pattern",
2515                 kind, instead, name
2516             )
2517         } else {
2518             format!("consider importing {} {}{}", determiner, kind, instead)
2519         };
2520
2521         for note in accessible_path_strings.iter().flat_map(|cand| cand.3.as_ref()) {
2522             err.note(note);
2523         }
2524
2525         if let (IsPattern::Yes, Some(span)) = (is_pattern, use_placement_span) {
2526             err.span_suggestions(
2527                 span,
2528                 &msg,
2529                 accessible_path_strings.into_iter().map(|a| a.0),
2530                 Applicability::MaybeIncorrect,
2531             );
2532         } else if let Some(span) = use_placement_span {
2533             for candidate in &mut accessible_path_strings {
2534                 // produce an additional newline to separate the new use statement
2535                 // from the directly following item.
2536                 let additional_newline = if let FoundUse::Yes = found_use { "" } else { "\n" };
2537                 candidate.0 = format!("use {};\n{}", &candidate.0, additional_newline);
2538             }
2539
2540             err.span_suggestions(
2541                 span,
2542                 &msg,
2543                 accessible_path_strings.into_iter().map(|a| a.0),
2544                 Applicability::MaybeIncorrect,
2545             );
2546             if let [first, .., last] = &path[..] {
2547                 let sp = first.ident.span.until(last.ident.span);
2548                 if sp.can_be_used_for_suggestions() {
2549                     err.span_suggestion_verbose(
2550                         sp,
2551                         &format!("if you import `{}`, refer to it directly", last.ident),
2552                         "",
2553                         Applicability::Unspecified,
2554                     );
2555                 }
2556             }
2557         } else {
2558             msg.push(':');
2559
2560             for candidate in accessible_path_strings {
2561                 msg.push('\n');
2562                 msg.push_str(&candidate.0);
2563             }
2564
2565             err.note(&msg);
2566         }
2567     } else {
2568         assert!(!inaccessible_path_strings.is_empty());
2569
2570         let prefix =
2571             if let IsPattern::Yes = is_pattern { "you might have meant to match on " } else { "" };
2572         if inaccessible_path_strings.len() == 1 {
2573             let (name, descr, def_id, note) = &inaccessible_path_strings[0];
2574             let msg = format!(
2575                 "{}{} `{}`{} exists but is inaccessible",
2576                 prefix,
2577                 descr,
2578                 name,
2579                 if let IsPattern::Yes = is_pattern { ", which" } else { "" }
2580             );
2581
2582             if let Some(local_def_id) = def_id.and_then(|did| did.as_local()) {
2583                 let span = source_span[local_def_id];
2584                 let span = session.source_map().guess_head_span(span);
2585                 let mut multi_span = MultiSpan::from_span(span);
2586                 multi_span.push_span_label(span, "not accessible");
2587                 err.span_note(multi_span, &msg);
2588             } else {
2589                 err.note(&msg);
2590             }
2591             if let Some(note) = (*note).as_deref() {
2592                 err.note(note);
2593             }
2594         } else {
2595             let (_, descr_first, _, _) = &inaccessible_path_strings[0];
2596             let descr = if inaccessible_path_strings
2597                 .iter()
2598                 .skip(1)
2599                 .all(|(_, descr, _, _)| descr == descr_first)
2600             {
2601                 descr_first
2602             } else {
2603                 "item"
2604             };
2605             let plural_descr =
2606                 if descr.ends_with('s') { format!("{}es", descr) } else { format!("{}s", descr) };
2607
2608             let mut msg = format!("{}these {} exist but are inaccessible", prefix, plural_descr);
2609             let mut has_colon = false;
2610
2611             let mut spans = Vec::new();
2612             for (name, _, def_id, _) in &inaccessible_path_strings {
2613                 if let Some(local_def_id) = def_id.and_then(|did| did.as_local()) {
2614                     let span = source_span[local_def_id];
2615                     let span = session.source_map().guess_head_span(span);
2616                     spans.push((name, span));
2617                 } else {
2618                     if !has_colon {
2619                         msg.push(':');
2620                         has_colon = true;
2621                     }
2622                     msg.push('\n');
2623                     msg.push_str(name);
2624                 }
2625             }
2626
2627             let mut multi_span = MultiSpan::from_spans(spans.iter().map(|(_, sp)| *sp).collect());
2628             for (name, span) in spans {
2629                 multi_span.push_span_label(span, format!("`{}`: not accessible", name));
2630             }
2631
2632             for note in inaccessible_path_strings.iter().flat_map(|cand| cand.3.as_ref()) {
2633                 err.note(note);
2634             }
2635
2636             err.span_note(multi_span, &msg);
2637         }
2638     }
2639 }
2640
2641 #[derive(Debug)]
2642 struct UsePlacementFinder {
2643     target_module: NodeId,
2644     first_legal_span: Option<Span>,
2645     first_use_span: Option<Span>,
2646 }
2647
2648 impl UsePlacementFinder {
2649     fn check(krate: &Crate, target_module: NodeId) -> (Option<Span>, FoundUse) {
2650         let mut finder =
2651             UsePlacementFinder { target_module, first_legal_span: None, first_use_span: None };
2652         finder.visit_crate(krate);
2653         if let Some(use_span) = finder.first_use_span {
2654             (Some(use_span), FoundUse::Yes)
2655         } else {
2656             (finder.first_legal_span, FoundUse::No)
2657         }
2658     }
2659 }
2660
2661 impl<'tcx> visit::Visitor<'tcx> for UsePlacementFinder {
2662     fn visit_crate(&mut self, c: &Crate) {
2663         if self.target_module == CRATE_NODE_ID {
2664             let inject = c.spans.inject_use_span;
2665             if is_span_suitable_for_use_injection(inject) {
2666                 self.first_legal_span = Some(inject);
2667             }
2668             self.first_use_span = search_for_any_use_in_items(&c.items);
2669             return;
2670         } else {
2671             visit::walk_crate(self, c);
2672         }
2673     }
2674
2675     fn visit_item(&mut self, item: &'tcx ast::Item) {
2676         if self.target_module == item.id {
2677             if let ItemKind::Mod(_, ModKind::Loaded(items, _inline, mod_spans)) = &item.kind {
2678                 let inject = mod_spans.inject_use_span;
2679                 if is_span_suitable_for_use_injection(inject) {
2680                     self.first_legal_span = Some(inject);
2681                 }
2682                 self.first_use_span = search_for_any_use_in_items(items);
2683                 return;
2684             }
2685         } else {
2686             visit::walk_item(self, item);
2687         }
2688     }
2689 }
2690
2691 fn search_for_any_use_in_items(items: &[P<ast::Item>]) -> Option<Span> {
2692     for item in items {
2693         if let ItemKind::Use(..) = item.kind {
2694             if is_span_suitable_for_use_injection(item.span) {
2695                 return Some(item.span.shrink_to_lo());
2696             }
2697         }
2698     }
2699     return None;
2700 }
2701
2702 fn is_span_suitable_for_use_injection(s: Span) -> bool {
2703     // don't suggest placing a use before the prelude
2704     // import or other generated ones
2705     !s.from_expansion()
2706 }
2707
2708 /// Convert the given number into the corresponding ordinal
2709 pub(crate) fn ordinalize(v: usize) -> String {
2710     let suffix = match ((11..=13).contains(&(v % 100)), v % 10) {
2711         (false, 1) => "st",
2712         (false, 2) => "nd",
2713         (false, 3) => "rd",
2714         _ => "th",
2715     };
2716     format!("{v}{suffix}")
2717 }