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