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