compiler/rustc_resolve/src/imports.rs

   1 //! A bunch of methods and structures more or less related to resolving imports.
   2
   3 use crate::diagnostics::{import_candidates, DiagnosticMode, Suggestion};
   4 use crate::errors::{
   5     CannotBeReexportedCratePublic, CannotBeReexportedCratePublicNS, CannotBeReexportedPrivate,
   6     CannotBeReexportedPrivateNS, CannotDetermineImportResolution, CannotGlobImportAllCrates,
   7     ConsiderAddingMacroExport, ConsiderMarkingAsPub, IsNotDirectlyImportable,
   8     ItemsInTraitsAreNotImportable,
   9 };
  10 use crate::Determinacy::{self, *};
  11 use crate::{fluent_generated as fluent, Namespace::*};
  12 use crate::{module_to_string, names_to_string, ImportSuggestion};
  13 use crate::{AmbiguityKind, BindingKey, ModuleKind, ResolutionError, Resolver, Segment};
  14 use crate::{Finalize, Module, ModuleOrUniformRoot, ParentScope, PerNS, ScopeSet};
  15 use crate::{NameBinding, NameBindingData, NameBindingKind, PathResult};
  16
  17 use rustc_ast::NodeId;
  18 use rustc_data_structures::fx::FxHashSet;
  19 use rustc_data_structures::intern::Interned;
  20 use rustc_errors::{pluralize, struct_span_err, Applicability, MultiSpan};
  21 use rustc_hir::def::{self, DefKind, PartialRes};
  22 use rustc_middle::metadata::ModChild;
  23 use rustc_middle::metadata::Reexport;
  24 use rustc_middle::span_bug;
  25 use rustc_middle::ty;
  26 use rustc_session::lint::builtin::{
  27     AMBIGUOUS_GLOB_REEXPORTS, HIDDEN_GLOB_REEXPORTS, PUB_USE_OF_PRIVATE_EXTERN_CRATE,
  28     UNUSED_IMPORTS,
  29 };
  30 use rustc_session::lint::BuiltinLintDiagnostics;
  31 use rustc_span::edit_distance::find_best_match_for_name;
  32 use rustc_span::hygiene::LocalExpnId;
  33 use rustc_span::symbol::{kw, Ident, Symbol};
  34 use rustc_span::Span;
  35 use smallvec::SmallVec;
  36
  37 use std::cell::Cell;
  38 use std::mem;
  39
  40 type Res = def::Res<NodeId>;
  41
  42 /// Contains data for specific kinds of imports.
  43 #[derive(Clone)]
  44 pub(crate) enum ImportKind<'a> {
  45     Single {
  46         /// `source` in `use prefix::source as target`.
  47         source: Ident,
  48         /// `target` in `use prefix::source as target`.
  49         target: Ident,
  50         /// Bindings to which `source` refers to.
  51         source_bindings: PerNS<Cell<Result<NameBinding<'a>, Determinacy>>>,
  52         /// Bindings introduced by `target`.
  53         target_bindings: PerNS<Cell<Option<NameBinding<'a>>>>,
  54         /// `true` for `...::{self [as target]}` imports, `false` otherwise.
  55         type_ns_only: bool,
  56         /// Did this import result from a nested import? ie. `use foo::{bar, baz};`
  57         nested: bool,
  58         /// The ID of the `UseTree` that imported this `Import`.
  59         ///
  60         /// In the case where the `Import` was expanded from a "nested" use tree,
  61         /// this id is the ID of the leaf tree. For example:
  62         ///
  63         /// ```ignore (pacify the merciless tidy)
  64         /// use foo::bar::{a, b}
  65         /// ```
  66         ///
  67         /// If this is the import for `foo::bar::a`, we would have the ID of the `UseTree`
  68         /// for `a` in this field.
  69         id: NodeId,
  70     },
  71     Glob {
  72         is_prelude: bool,
  73         // The visibility of the greatest re-export.
  74         // n.b. `max_vis` is only used in `finalize_import` to check for re-export errors.
  75         max_vis: Cell<Option<ty::Visibility>>,
  76         id: NodeId,
  77     },
  78     ExternCrate {
  79         source: Option<Symbol>,
  80         target: Ident,
  81         id: NodeId,
  82     },
  83     MacroUse,
  84     MacroExport,
  85 }
  86
  87 /// Manually implement `Debug` for `ImportKind` because the `source/target_bindings`
  88 /// contain `Cell`s which can introduce infinite loops while printing.
  89 impl<'a> std::fmt::Debug for ImportKind<'a> {
  90     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
  91         use ImportKind::*;
  92         match self {
  93             Single {
  94                 ref source,
  95                 ref target,
  96                 ref source_bindings,
  97                 ref target_bindings,
  98                 ref type_ns_only,
  99                 ref nested,
 100                 ref id,
 101             } => f
 102                 .debug_struct("Single")
 103                 .field("source", source)
 104                 .field("target", target)
 105                 // Ignore the nested bindings to avoid an infinite loop while printing.
 106                 .field(
 107                     "source_bindings",
 108                     &source_bindings.clone().map(|b| b.into_inner().map(|_| format_args!(".."))),
 109                 )
 110                 .field(
 111                     "target_bindings",
 112                     &target_bindings.clone().map(|b| b.into_inner().map(|_| format_args!(".."))),
 113                 )
 114                 .field("type_ns_only", type_ns_only)
 115                 .field("nested", nested)
 116                 .field("id", id)
 117                 .finish(),
 118             Glob { ref is_prelude, ref max_vis, ref id } => f
 119                 .debug_struct("Glob")
 120                 .field("is_prelude", is_prelude)
 121                 .field("max_vis", max_vis)
 122                 .field("id", id)
 123                 .finish(),
 124             ExternCrate { ref source, ref target, ref id } => f
 125                 .debug_struct("ExternCrate")
 126                 .field("source", source)
 127                 .field("target", target)
 128                 .field("id", id)
 129                 .finish(),
 130             MacroUse => f.debug_struct("MacroUse").finish(),
 131             MacroExport => f.debug_struct("MacroExport").finish(),
 132         }
 133     }
 134 }
 135
 136 /// One import.
 137 #[derive(Debug, Clone)]
 138 pub(crate) struct ImportData<'a> {
 139     pub kind: ImportKind<'a>,
 140
 141     /// Node ID of the "root" use item -- this is always the same as `ImportKind`'s `id`
 142     /// (if it exists) except in the case of "nested" use trees, in which case
 143     /// it will be the ID of the root use tree. e.g., in the example
 144     /// ```ignore (incomplete code)
 145     /// use foo::bar::{a, b}
 146     /// ```
 147     /// this would be the ID of the `use foo::bar` `UseTree` node.
 148     /// In case of imports without their own node ID it's the closest node that can be used,
 149     /// for example, for reporting lints.
 150     pub root_id: NodeId,
 151
 152     /// Span of the entire use statement.
 153     pub use_span: Span,
 154
 155     /// Span of the entire use statement with attributes.
 156     pub use_span_with_attributes: Span,
 157
 158     /// Did the use statement have any attributes?
 159     pub has_attributes: bool,
 160
 161     /// Span of this use tree.
 162     pub span: Span,
 163
 164     /// Span of the *root* use tree (see `root_id`).
 165     pub root_span: Span,
 166
 167     pub parent_scope: ParentScope<'a>,
 168     pub module_path: Vec<Segment>,
 169     /// The resolution of `module_path`.
 170     pub imported_module: Cell<Option<ModuleOrUniformRoot<'a>>>,
 171     pub vis: Cell<Option<ty::Visibility>>,
 172     pub used: Cell<bool>,
 173 }
 174
 175 /// All imports are unique and allocated on a same arena,
 176 /// so we can use referential equality to compare them.
 177 pub(crate) type Import<'a> = Interned<'a, ImportData<'a>>;
 178
 179 impl<'a> ImportData<'a> {
 180     pub(crate) fn is_glob(&self) -> bool {
 181         matches!(self.kind, ImportKind::Glob { .. })
 182     }
 183
 184     pub(crate) fn is_nested(&self) -> bool {
 185         match self.kind {
 186             ImportKind::Single { nested, .. } => nested,
 187             _ => false,
 188         }
 189     }
 190
 191     pub(crate) fn expect_vis(&self) -> ty::Visibility {
 192         self.vis.get().expect("encountered cleared import visibility")
 193     }
 194
 195     pub(crate) fn id(&self) -> Option<NodeId> {
 196         match self.kind {
 197             ImportKind::Single { id, .. }
 198             | ImportKind::Glob { id, .. }
 199             | ImportKind::ExternCrate { id, .. } => Some(id),
 200             ImportKind::MacroUse | ImportKind::MacroExport => None,
 201         }
 202     }
 203
 204     fn simplify(&self, r: &Resolver<'_, '_>) -> Reexport {
 205         let to_def_id = |id| r.local_def_id(id).to_def_id();
 206         match self.kind {
 207             ImportKind::Single { id, .. } => Reexport::Single(to_def_id(id)),
 208             ImportKind::Glob { id, .. } => Reexport::Glob(to_def_id(id)),
 209             ImportKind::ExternCrate { id, .. } => Reexport::ExternCrate(to_def_id(id)),
 210             ImportKind::MacroUse => Reexport::MacroUse,
 211             ImportKind::MacroExport => Reexport::MacroExport,
 212         }
 213     }
 214 }
 215
 216 /// Records information about the resolution of a name in a namespace of a module.
 217 #[derive(Clone, Default, Debug)]
 218 pub(crate) struct NameResolution<'a> {
 219     /// Single imports that may define the name in the namespace.
 220     /// Imports are arena-allocated, so it's ok to use pointers as keys.
 221     pub single_imports: FxHashSet<Import<'a>>,
 222     /// The least shadowable known binding for this name, or None if there are no known bindings.
 223     pub binding: Option<NameBinding<'a>>,
 224     pub shadowed_glob: Option<NameBinding<'a>>,
 225 }
 226
 227 impl<'a> NameResolution<'a> {
 228     /// Returns the binding for the name if it is known or None if it not known.
 229     pub(crate) fn binding(&self) -> Option<NameBinding<'a>> {
 230         self.binding.and_then(|binding| {
 231             if !binding.is_glob_import() || self.single_imports.is_empty() {
 232                 Some(binding)
 233             } else {
 234                 None
 235             }
 236         })
 237     }
 238 }
 239
 240 /// An error that may be transformed into a diagnostic later. Used to combine multiple unresolved
 241 /// import errors within the same use tree into a single diagnostic.
 242 #[derive(Debug, Clone)]
 243 struct UnresolvedImportError {
 244     span: Span,
 245     label: Option<String>,
 246     note: Option<String>,
 247     suggestion: Option<Suggestion>,
 248     candidates: Option<Vec<ImportSuggestion>>,
 249 }
 250
 251 // Reexports of the form `pub use foo as bar;` where `foo` is `extern crate foo;`
 252 // are permitted for backward-compatibility under a deprecation lint.
 253 fn pub_use_of_private_extern_crate_hack(import: Import<'_>, binding: NameBinding<'_>) -> bool {
 254     match (&import.kind, &binding.kind) {
 255         (ImportKind::Single { .. }, NameBindingKind::Import { import: binding_import, .. }) => {
 256             matches!(binding_import.kind, ImportKind::ExternCrate { .. })
 257                 && import.expect_vis().is_public()
 258         }
 259         _ => false,
 260     }
 261 }
 262
 263 impl<'a, 'tcx> Resolver<'a, 'tcx> {
 264     /// Given a binding and an import that resolves to it,
 265     /// return the corresponding binding defined by the import.
 266     pub(crate) fn import(&self, binding: NameBinding<'a>, import: Import<'a>) -> NameBinding<'a> {
 267         let import_vis = import.expect_vis().to_def_id();
 268         let vis = if binding.vis.is_at_least(import_vis, self.tcx)
 269             || pub_use_of_private_extern_crate_hack(import, binding)
 270         {
 271             import_vis
 272         } else {
 273             binding.vis
 274         };
 275
 276         if let ImportKind::Glob { ref max_vis, .. } = import.kind {
 277             if vis == import_vis
 278                 || max_vis.get().map_or(true, |max_vis| vis.is_at_least(max_vis, self.tcx))
 279             {
 280                 max_vis.set(Some(vis.expect_local()))
 281             }
 282         }
 283
 284         self.arenas.alloc_name_binding(NameBindingData {
 285             kind: NameBindingKind::Import { binding, import, used: Cell::new(false) },
 286             ambiguity: None,
 287             warn_ambiguity: false,
 288             span: import.span,
 289             vis,
 290             expansion: import.parent_scope.expansion,
 291         })
 292     }
 293
 294     /// Define the name or return the existing binding if there is a collision.
 295     /// `update` indicates if the definition is a redefinition of an existing binding.
 296     pub(crate) fn try_define(
 297         &mut self,
 298         module: Module<'a>,
 299         key: BindingKey,
 300         binding: NameBinding<'a>,
 301         warn_ambiguity: bool,
 302     ) -> Result<(), NameBinding<'a>> {
 303         let res = binding.res();
 304         self.check_reserved_macro_name(key.ident, res);
 305         self.set_binding_parent_module(binding, module);
 306         self.update_resolution(module, key, warn_ambiguity, |this, resolution| {
 307             if let Some(old_binding) = resolution.binding {
 308                 if res == Res::Err && old_binding.res() != Res::Err {
 309                     // Do not override real bindings with `Res::Err`s from error recovery.
 310                     return Ok(());
 311                 }
 312                 match (old_binding.is_glob_import(), binding.is_glob_import()) {
 313                     (true, true) => {
 314                         // FIXME: remove `!binding.is_ambiguity()` after delete the warning ambiguity.
 315                         if !binding.is_ambiguity()
 316                             && let NameBindingKind::Import { import: old_import, .. } =
 317                                 old_binding.kind
 318                             && let NameBindingKind::Import { import, .. } = binding.kind
 319                             && old_import == import
 320                         {
 321                             // We should replace the `old_binding` with `binding` regardless
 322                             // of whether they has same resolution or not when they are
 323                             // imported from the same glob-import statement.
 324                             resolution.binding = Some(binding);
 325                         } else if res != old_binding.res() {
 326                             let binding = if warn_ambiguity {
 327                                 this.warn_ambiguity(AmbiguityKind::GlobVsGlob, old_binding, binding)
 328                             } else {
 329                                 this.ambiguity(AmbiguityKind::GlobVsGlob, old_binding, binding)
 330                             };
 331                             resolution.binding = Some(binding);
 332                         } else if !old_binding.vis.is_at_least(binding.vis, this.tcx) {
 333                             // We are glob-importing the same item but with greater visibility.
 334                             resolution.binding = Some(binding);
 335                         } else if binding.is_ambiguity() {
 336                             resolution.binding =
 337                                 Some(self.arenas.alloc_name_binding(NameBindingData {
 338                                     warn_ambiguity: true,
 339                                     ..(*binding).clone()
 340                                 }));
 341                         }
 342                     }
 343                     (old_glob @ true, false) | (old_glob @ false, true) => {
 344                         let (glob_binding, nonglob_binding) =
 345                             if old_glob { (old_binding, binding) } else { (binding, old_binding) };
 346                         if glob_binding.res() != nonglob_binding.res()
 347                             && key.ns == MacroNS
 348                             && nonglob_binding.expansion != LocalExpnId::ROOT
 349                         {
 350                             resolution.binding = Some(this.ambiguity(
 351                                 AmbiguityKind::GlobVsExpanded,
 352                                 nonglob_binding,
 353                                 glob_binding,
 354                             ));
 355                         } else {
 356                             resolution.binding = Some(nonglob_binding);
 357                         }
 358
 359                         if let Some(old_binding) = resolution.shadowed_glob {
 360                             assert!(old_binding.is_glob_import());
 361                             if glob_binding.res() != old_binding.res() {
 362                                 resolution.shadowed_glob = Some(this.ambiguity(
 363                                     AmbiguityKind::GlobVsGlob,
 364                                     old_binding,
 365                                     glob_binding,
 366                                 ));
 367                             } else if !old_binding.vis.is_at_least(binding.vis, this.tcx) {
 368                                 resolution.shadowed_glob = Some(glob_binding);
 369                             }
 370                         } else {
 371                             resolution.shadowed_glob = Some(glob_binding);
 372                         }
 373                     }
 374                     (false, false) => {
 375                         return Err(old_binding);
 376                     }
 377                 }
 378             } else {
 379                 resolution.binding = Some(binding);
 380             }
 381
 382             Ok(())
 383         })
 384     }
 385
 386     fn ambiguity(
 387         &self,
 388         kind: AmbiguityKind,
 389         primary_binding: NameBinding<'a>,
 390         secondary_binding: NameBinding<'a>,
 391     ) -> NameBinding<'a> {
 392         self.arenas.alloc_name_binding(NameBindingData {
 393             ambiguity: Some((secondary_binding, kind)),
 394             ..(*primary_binding).clone()
 395         })
 396     }
 397
 398     fn warn_ambiguity(
 399         &self,
 400         kind: AmbiguityKind,
 401         primary_binding: NameBinding<'a>,
 402         secondary_binding: NameBinding<'a>,
 403     ) -> NameBinding<'a> {
 404         self.arenas.alloc_name_binding(NameBindingData {
 405             ambiguity: Some((secondary_binding, kind)),
 406             warn_ambiguity: true,
 407             ..(*primary_binding).clone()
 408         })
 409     }
 410
 411     // Use `f` to mutate the resolution of the name in the module.
 412     // If the resolution becomes a success, define it in the module's glob importers.
 413     fn update_resolution<T, F>(
 414         &mut self,
 415         module: Module<'a>,
 416         key: BindingKey,
 417         warn_ambiguity: bool,
 418         f: F,
 419     ) -> T
 420     where
 421         F: FnOnce(&mut Resolver<'a, 'tcx>, &mut NameResolution<'a>) -> T,
 422     {
 423         // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
 424         // during which the resolution might end up getting re-defined via a glob cycle.
 425         let (binding, t, warn_ambiguity) = {
 426             let resolution = &mut *self.resolution(module, key).borrow_mut();
 427             let old_binding = resolution.binding();
 428
 429             let t = f(self, resolution);
 430
 431             if let Some(binding) = resolution.binding()
 432                 && old_binding != Some(binding)
 433             {
 434                 (binding, t, warn_ambiguity || old_binding.is_some())
 435             } else {
 436                 return t;
 437             }
 438         };
 439
 440         let Ok(glob_importers) = module.glob_importers.try_borrow_mut() else {
 441             return t;
 442         };
 443
 444         // Define or update `binding` in `module`s glob importers.
 445         for import in glob_importers.iter() {
 446             let mut ident = key.ident;
 447             let scope = match ident.span.reverse_glob_adjust(module.expansion, import.span) {
 448                 Some(Some(def)) => self.expn_def_scope(def),
 449                 Some(None) => import.parent_scope.module,
 450                 None => continue,
 451             };
 452             if self.is_accessible_from(binding.vis, scope) {
 453                 let imported_binding = self.import(binding, *import);
 454                 let key = BindingKey { ident, ..key };
 455                 let _ = self.try_define(
 456                     import.parent_scope.module,
 457                     key,
 458                     imported_binding,
 459                     warn_ambiguity,
 460                 );
 461             }
 462         }
 463
 464         t
 465     }
 466
 467     // Define a dummy resolution containing a `Res::Err` as a placeholder for a failed
 468     // or indeterminate resolution, also mark such failed imports as used to avoid duplicate diagnostics.
 469     fn import_dummy_binding(&mut self, import: Import<'a>, is_indeterminate: bool) {
 470         if let ImportKind::Single { target, ref target_bindings, .. } = import.kind {
 471             if !(is_indeterminate || target_bindings.iter().all(|binding| binding.get().is_none()))
 472             {
 473                 return; // Has resolution, do not create the dummy binding
 474             }
 475             let dummy_binding = self.dummy_binding;
 476             let dummy_binding = self.import(dummy_binding, import);
 477             self.per_ns(|this, ns| {
 478                 let key = BindingKey::new(target, ns);
 479                 let _ = this.try_define(import.parent_scope.module, key, dummy_binding, false);
 480             });
 481             self.record_use(target, dummy_binding, false);
 482         } else if import.imported_module.get().is_none() {
 483             import.used.set(true);
 484             if let Some(id) = import.id() {
 485                 self.used_imports.insert(id);
 486             }
 487         }
 488     }
 489
 490     // Import resolution
 491     //
 492     // This is a fixed-point algorithm. We resolve imports until our efforts
 493     // are stymied by an unresolved import; then we bail out of the current
 494     // module and continue. We terminate successfully once no more imports
 495     // remain or unsuccessfully when no forward progress in resolving imports
 496     // is made.
 497
 498     /// Resolves all imports for the crate. This method performs the fixed-
 499     /// point iteration.
 500     pub(crate) fn resolve_imports(&mut self) {
 501         let mut prev_indeterminate_count = usize::MAX;
 502         let mut indeterminate_count = self.indeterminate_imports.len() * 3;
 503         while indeterminate_count < prev_indeterminate_count {
 504             prev_indeterminate_count = indeterminate_count;
 505             indeterminate_count = 0;
 506             for import in mem::take(&mut self.indeterminate_imports) {
 507                 let import_indeterminate_count = self.resolve_import(import);
 508                 indeterminate_count += import_indeterminate_count;
 509                 match import_indeterminate_count {
 510                     0 => self.determined_imports.push(import),
 511                     _ => self.indeterminate_imports.push(import),
 512                 }
 513             }
 514         }
 515     }
 516
 517     pub(crate) fn finalize_imports(&mut self) {
 518         for module in self.arenas.local_modules().iter() {
 519             self.finalize_resolutions_in(*module);
 520         }
 521
 522         let mut seen_spans = FxHashSet::default();
 523         let mut errors = vec![];
 524         let mut prev_root_id: NodeId = NodeId::from_u32(0);
 525         let determined_imports = mem::take(&mut self.determined_imports);
 526         let indeterminate_imports = mem::take(&mut self.indeterminate_imports);
 527
 528         for (is_indeterminate, import) in determined_imports
 529             .iter()
 530             .map(|i| (false, i))
 531             .chain(indeterminate_imports.iter().map(|i| (true, i)))
 532         {
 533             let unresolved_import_error = self.finalize_import(*import);
 534
 535             // If this import is unresolved then create a dummy import
 536             // resolution for it so that later resolve stages won't complain.
 537             self.import_dummy_binding(*import, is_indeterminate);
 538
 539             if let Some(err) = unresolved_import_error {
 540                 if let ImportKind::Single { source, ref source_bindings, .. } = import.kind {
 541                     if source.name == kw::SelfLower {
 542                         // Silence `unresolved import` error if E0429 is already emitted
 543                         if let Err(Determined) = source_bindings.value_ns.get() {
 544                             continue;
 545                         }
 546                     }
 547                 }
 548
 549                 if prev_root_id.as_u32() != 0
 550                     && prev_root_id.as_u32() != import.root_id.as_u32()
 551                     && !errors.is_empty()
 552                 {
 553                     // In the case of a new import line, throw a diagnostic message
 554                     // for the previous line.
 555                     self.throw_unresolved_import_error(errors);
 556                     errors = vec![];
 557                 }
 558                 if seen_spans.insert(err.span) {
 559                     errors.push((*import, err));
 560                     prev_root_id = import.root_id;
 561                 }
 562             }
 563         }
 564
 565         if !errors.is_empty() {
 566             self.throw_unresolved_import_error(errors);
 567             return;
 568         }
 569
 570         for import in &indeterminate_imports {
 571             let path = import_path_to_string(
 572                 &import.module_path.iter().map(|seg| seg.ident).collect::<Vec<_>>(),
 573                 &import.kind,
 574                 import.span,
 575             );
 576             let err = UnresolvedImportError {
 577                 span: import.span,
 578                 label: None,
 579                 note: None,
 580                 suggestion: None,
 581                 candidates: None,
 582             };
 583             // FIXME: there should be a better way of doing this than
 584             // formatting this as a string then checking for `::`
 585             if path.contains("::") {
 586                 errors.push((*import, err))
 587             }
 588         }
 589
 590         if !errors.is_empty() {
 591             self.throw_unresolved_import_error(errors);
 592         }
 593     }
 594
 595     pub(crate) fn check_hidden_glob_reexports(
 596         &mut self,
 597         exported_ambiguities: FxHashSet<NameBinding<'a>>,
 598     ) {
 599         for module in self.arenas.local_modules().iter() {
 600             for (key, resolution) in self.resolutions(*module).borrow().iter() {
 601                 let resolution = resolution.borrow();
 602
 603                 if let Some(binding) = resolution.binding {
 604                     if let NameBindingKind::Import { import, .. } = binding.kind
 605                         && let Some((amb_binding, _)) = binding.ambiguity
 606                         && binding.res() != Res::Err
 607                         && exported_ambiguities.contains(&binding)
 608                     {
 609                         self.lint_buffer.buffer_lint_with_diagnostic(
 610                             AMBIGUOUS_GLOB_REEXPORTS,
 611                             import.root_id,
 612                             import.root_span,
 613                             "ambiguous glob re-exports",
 614                             BuiltinLintDiagnostics::AmbiguousGlobReexports {
 615                                 name: key.ident.to_string(),
 616                                 namespace: key.ns.descr().to_string(),
 617                                 first_reexport_span: import.root_span,
 618                                 duplicate_reexport_span: amb_binding.span,
 619                             },
 620                         );
 621                     }
 622
 623                     if let Some(glob_binding) = resolution.shadowed_glob {
 624                         let binding_id = match binding.kind {
 625                             NameBindingKind::Res(res) => {
 626                                 Some(self.def_id_to_node_id[res.def_id().expect_local()])
 627                             }
 628                             NameBindingKind::Module(module) => {
 629                                 Some(self.def_id_to_node_id[module.def_id().expect_local()])
 630                             }
 631                             NameBindingKind::Import { import, .. } => import.id(),
 632                         };
 633
 634                         if binding.res() != Res::Err
 635                             && glob_binding.res() != Res::Err
 636                             && let NameBindingKind::Import { import: glob_import, .. } =
 637                                 glob_binding.kind
 638                             && let Some(binding_id) = binding_id
 639                             && let Some(glob_import_id) = glob_import.id()
 640                             && let glob_import_def_id = self.local_def_id(glob_import_id)
 641                             && self.effective_visibilities.is_exported(glob_import_def_id)
 642                             && glob_binding.vis.is_public()
 643                             && !binding.vis.is_public()
 644                         {
 645                             self.lint_buffer.buffer_lint_with_diagnostic(
 646                                 HIDDEN_GLOB_REEXPORTS,
 647                                 binding_id,
 648                                 binding.span,
 649                                 "private item shadows public glob re-export",
 650                                 BuiltinLintDiagnostics::HiddenGlobReexports {
 651                                     name: key.ident.name.to_string(),
 652                                     namespace: key.ns.descr().to_owned(),
 653                                     glob_reexport_span: glob_binding.span,
 654                                     private_item_span: binding.span,
 655                                 },
 656                             );
 657                         }
 658                     }
 659                 }
 660             }
 661         }
 662     }
 663
 664     fn throw_unresolved_import_error(&mut self, errors: Vec<(Import<'_>, UnresolvedImportError)>) {
 665         if errors.is_empty() {
 666             return;
 667         }
 668
 669         /// Upper limit on the number of `span_label` messages.
 670         const MAX_LABEL_COUNT: usize = 10;
 671
 672         let span = MultiSpan::from_spans(errors.iter().map(|(_, err)| err.span).collect());
 673         let paths = errors
 674             .iter()
 675             .map(|(import, err)| {
 676                 let path = import_path_to_string(
 677                     &import.module_path.iter().map(|seg| seg.ident).collect::<Vec<_>>(),
 678                     &import.kind,
 679                     err.span,
 680                 );
 681                 format!("`{path}`")
 682             })
 683             .collect::<Vec<_>>();
 684         let msg = format!("unresolved import{} {}", pluralize!(paths.len()), paths.join(", "),);
 685
 686         let mut diag = struct_span_err!(self.tcx.sess, span, E0432, "{}", &msg);
 687
 688         if let Some((_, UnresolvedImportError { note: Some(note), .. })) = errors.iter().last() {
 689             diag.note(note.clone());
 690         }
 691
 692         for (import, err) in errors.into_iter().take(MAX_LABEL_COUNT) {
 693             if let Some(label) = err.label {
 694                 diag.span_label(err.span, label);
 695             }
 696
 697             if let Some((suggestions, msg, applicability)) = err.suggestion {
 698                 if suggestions.is_empty() {
 699                     diag.help(msg);
 700                     continue;
 701                 }
 702                 diag.multipart_suggestion(msg, suggestions, applicability);
 703             }
 704
 705             if let Some(candidates) = &err.candidates {
 706                 match &import.kind {
 707                     ImportKind::Single { nested: false, source, target, .. } => import_candidates(
 708                         self.tcx,
 709                         &mut diag,
 710                         Some(err.span),
 711                         &candidates,
 712                         DiagnosticMode::Import,
 713                         (source != target)
 714                             .then(|| format!(" as {target}"))
 715                             .as_deref()
 716                             .unwrap_or(""),
 717                     ),
 718                     ImportKind::Single { nested: true, source, target, .. } => {
 719                         import_candidates(
 720                             self.tcx,
 721                             &mut diag,
 722                             None,
 723                             &candidates,
 724                             DiagnosticMode::Normal,
 725                             (source != target)
 726                                 .then(|| format!(" as {target}"))
 727                                 .as_deref()
 728                                 .unwrap_or(""),
 729                         );
 730                     }
 731                     _ => {}
 732                 }
 733             }
 734
 735             match &import.kind {
 736                 ImportKind::Single { source, .. } => {
 737                     if let Some(ModuleOrUniformRoot::Module(module)) = import.imported_module.get()
 738                         && let Some(module) = module.opt_def_id()
 739                     {
 740                         self.find_cfg_stripped(&mut diag, &source.name, module)
 741                     }
 742                 }
 743                 _ => {}
 744             }
 745         }
 746
 747         diag.emit();
 748     }
 749
 750     /// Attempts to resolve the given import, returning:
 751     /// - `0` means its resolution is determined.
 752     /// - Other values mean that indeterminate exists under certain namespaces.
 753     ///
 754     /// Meanwhile, if resolve successful, the resolved bindings are written
 755     /// into the module.
 756     fn resolve_import(&mut self, import: Import<'a>) -> usize {
 757         debug!(
 758             "(resolving import for module) resolving import `{}::...` in `{}`",
 759             Segment::names_to_string(&import.module_path),
 760             module_to_string(import.parent_scope.module).unwrap_or_else(|| "???".to_string()),
 761         );
 762         let module = if let Some(module) = import.imported_module.get() {
 763             module
 764         } else {
 765             // For better failure detection, pretend that the import will
 766             // not define any names while resolving its module path.
 767             let orig_vis = import.vis.take();
 768             let path_res = self.maybe_resolve_path(&import.module_path, None, &import.parent_scope);
 769             import.vis.set(orig_vis);
 770
 771             match path_res {
 772                 PathResult::Module(module) => module,
 773                 PathResult::Indeterminate => return 3,
 774                 PathResult::NonModule(..) | PathResult::Failed { .. } => return 0,
 775             }
 776         };
 777
 778         import.imported_module.set(Some(module));
 779         let (source, target, source_bindings, target_bindings, type_ns_only) = match import.kind {
 780             ImportKind::Single {
 781                 source,
 782                 target,
 783                 ref source_bindings,
 784                 ref target_bindings,
 785                 type_ns_only,
 786                 ..
 787             } => (source, target, source_bindings, target_bindings, type_ns_only),
 788             ImportKind::Glob { .. } => {
 789                 self.resolve_glob_import(import);
 790                 return 0;
 791             }
 792             _ => unreachable!(),
 793         };
 794
 795         let mut indeterminate_count = 0;
 796         self.per_ns(|this, ns| {
 797             if !type_ns_only || ns == TypeNS {
 798                 if let Err(Undetermined) = source_bindings[ns].get() {
 799                     // For better failure detection, pretend that the import will
 800                     // not define any names while resolving its module path.
 801                     let orig_vis = import.vis.take();
 802                     let binding = this.maybe_resolve_ident_in_module(
 803                         module,
 804                         source,
 805                         ns,
 806                         &import.parent_scope,
 807                     );
 808                     import.vis.set(orig_vis);
 809                     source_bindings[ns].set(binding);
 810                 } else {
 811                     return;
 812                 };
 813
 814                 let parent = import.parent_scope.module;
 815                 match source_bindings[ns].get() {
 816                     Err(Undetermined) => indeterminate_count += 1,
 817                     // Don't update the resolution, because it was never added.
 818                     Err(Determined) if target.name == kw::Underscore => {}
 819                     Ok(binding) if binding.is_importable() => {
 820                         let imported_binding = this.import(binding, import);
 821                         target_bindings[ns].set(Some(imported_binding));
 822                         this.define(parent, target, ns, imported_binding);
 823                     }
 824                     source_binding @ (Ok(..) | Err(Determined)) => {
 825                         if source_binding.is_ok() {
 826                             this.tcx
 827                                 .sess
 828                                 .create_err(IsNotDirectlyImportable { span: import.span, target })
 829                                 .emit();
 830                         }
 831                         let key = BindingKey::new(target, ns);
 832                         this.update_resolution(parent, key, false, |_, resolution| {
 833                             resolution.single_imports.remove(&import);
 834                         });
 835                     }
 836                 }
 837             }
 838         });
 839
 840         indeterminate_count
 841     }
 842
 843     /// Performs final import resolution, consistency checks and error reporting.
 844     ///
 845     /// Optionally returns an unresolved import error. This error is buffered and used to
 846     /// consolidate multiple unresolved import errors into a single diagnostic.
 847     fn finalize_import(&mut self, import: Import<'a>) -> Option<UnresolvedImportError> {
 848         let orig_vis = import.vis.take();
 849         let ignore_binding = match &import.kind {
 850             ImportKind::Single { target_bindings, .. } => target_bindings[TypeNS].get(),
 851             _ => None,
 852         };
 853         let prev_ambiguity_errors_len = self.ambiguity_errors.len();
 854         let finalize = Finalize::with_root_span(import.root_id, import.span, import.root_span);
 855
 856         // We'll provide more context to the privacy errors later, up to `len`.
 857         let privacy_errors_len = self.privacy_errors.len();
 858
 859         let path_res = self.resolve_path(
 860             &import.module_path,
 861             None,
 862             &import.parent_scope,
 863             Some(finalize),
 864             ignore_binding,
 865         );
 866
 867         let no_ambiguity = self.ambiguity_errors.len() == prev_ambiguity_errors_len;
 868         import.vis.set(orig_vis);
 869         let module = match path_res {
 870             PathResult::Module(module) => {
 871                 // Consistency checks, analogous to `finalize_macro_resolutions`.
 872                 if let Some(initial_module) = import.imported_module.get() {
 873                     if module != initial_module && no_ambiguity {
 874                         span_bug!(import.span, "inconsistent resolution for an import");
 875                     }
 876                 } else if self.privacy_errors.is_empty() {
 877                     self.tcx
 878                         .sess
 879                         .create_err(CannotDetermineImportResolution { span: import.span })
 880                         .emit();
 881                 }
 882
 883                 module
 884             }
 885             PathResult::Failed {
 886                 is_error_from_last_segment: false,
 887                 span,
 888                 label,
 889                 suggestion,
 890                 module,
 891             } => {
 892                 if no_ambiguity {
 893                     assert!(import.imported_module.get().is_none());
 894                     self.report_error(
 895                         span,
 896                         ResolutionError::FailedToResolve {
 897                             last_segment: None,
 898                             label,
 899                             suggestion,
 900                             module,
 901                         },
 902                     );
 903                 }
 904                 return None;
 905             }
 906             PathResult::Failed {
 907                 is_error_from_last_segment: true,
 908                 span,
 909                 label,
 910                 suggestion,
 911                 ..
 912             } => {
 913                 if no_ambiguity {
 914                     assert!(import.imported_module.get().is_none());
 915                     let err = match self.make_path_suggestion(
 916                         span,
 917                         import.module_path.clone(),
 918                         &import.parent_scope,
 919                     ) {
 920                         Some((suggestion, note)) => UnresolvedImportError {
 921                             span,
 922                             label: None,
 923                             note,
 924                             suggestion: Some((
 925                                 vec![(span, Segment::names_to_string(&suggestion))],
 926                                 String::from("a similar path exists"),
 927                                 Applicability::MaybeIncorrect,
 928                             )),
 929                             candidates: None,
 930                         },
 931                         None => UnresolvedImportError {
 932                             span,
 933                             label: Some(label),
 934                             note: None,
 935                             suggestion,
 936                             candidates: None,
 937                         },
 938                     };
 939                     return Some(err);
 940                 }
 941                 return None;
 942             }
 943             PathResult::NonModule(partial_res) => {
 944                 if no_ambiguity && partial_res.full_res() != Some(Res::Err) {
 945                     // Check if there are no ambiguities and the result is not dummy.
 946                     assert!(import.imported_module.get().is_none());
 947                 }
 948                 // The error was already reported earlier.
 949                 return None;
 950             }
 951             PathResult::Indeterminate => unreachable!(),
 952         };
 953
 954         let (ident, target, source_bindings, target_bindings, type_ns_only, import_id) =
 955             match import.kind {
 956                 ImportKind::Single {
 957                     source,
 958                     target,
 959                     ref source_bindings,
 960                     ref target_bindings,
 961                     type_ns_only,
 962                     id,
 963                     ..
 964                 } => (source, target, source_bindings, target_bindings, type_ns_only, id),
 965                 ImportKind::Glob { is_prelude, ref max_vis, id } => {
 966                     if import.module_path.len() <= 1 {
 967                         // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
 968                         // 2 segments, so the `resolve_path` above won't trigger it.
 969                         let mut full_path = import.module_path.clone();
 970                         full_path.push(Segment::from_ident(Ident::empty()));
 971                         self.lint_if_path_starts_with_module(Some(finalize), &full_path, None);
 972                     }
 973
 974                     if let ModuleOrUniformRoot::Module(module) = module {
 975                         if module == import.parent_scope.module {
 976                             // Importing a module into itself is not allowed.
 977                             return Some(UnresolvedImportError {
 978                                 span: import.span,
 979                                 label: Some(String::from(
 980                                     "cannot glob-import a module into itself",
 981                                 )),
 982                                 note: None,
 983                                 suggestion: None,
 984                                 candidates: None,
 985                             });
 986                         }
 987                     }
 988                     if !is_prelude
 989                         && let Some(max_vis) = max_vis.get()
 990                         && !max_vis.is_at_least(import.expect_vis(), self.tcx)
 991                     {
 992                         self.lint_buffer.buffer_lint(
 993                             UNUSED_IMPORTS,
 994                             id,
 995                             import.span,
 996                             fluent::resolve_glob_import_doesnt_reexport,
 997                         );
 998                     }
 999                     return None;
1000                 }
1001                 _ => unreachable!(),
1002             };
1003
1004         if self.privacy_errors.len() != privacy_errors_len {
1005             // Get the Res for the last element, so that we can point to alternative ways of
1006             // importing it if available.
1007             let mut path = import.module_path.clone();
1008             path.push(Segment::from_ident(ident));
1009             if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
1010                 self.resolve_path(&path, None, &import.parent_scope, Some(finalize), ignore_binding)
1011             {
1012                 let res = module.res().map(|r| (r, ident));
1013                 for error in &mut self.privacy_errors[privacy_errors_len..] {
1014                     error.outermost_res = res;
1015                 }
1016             }
1017         }
1018
1019         let mut all_ns_err = true;
1020         self.per_ns(|this, ns| {
1021             if !type_ns_only || ns == TypeNS {
1022                 let orig_vis = import.vis.take();
1023                 let binding = this.resolve_ident_in_module(
1024                     module,
1025                     ident,
1026                     ns,
1027                     &import.parent_scope,
1028                     Some(Finalize { report_private: false, ..finalize }),
1029                     target_bindings[ns].get(),
1030                 );
1031                 import.vis.set(orig_vis);
1032
1033                 match binding {
1034                     Ok(binding) => {
1035                         // Consistency checks, analogous to `finalize_macro_resolutions`.
1036                         let initial_res = source_bindings[ns].get().map(|initial_binding| {
1037                             all_ns_err = false;
1038                             if let Some(target_binding) = target_bindings[ns].get() {
1039                                 if target.name == kw::Underscore
1040                                     && initial_binding.is_extern_crate()
1041                                     && !initial_binding.is_import()
1042                                 {
1043                                     this.record_use(
1044                                         ident,
1045                                         target_binding,
1046                                         import.module_path.is_empty(),
1047                                     );
1048                                 }
1049                             }
1050                             initial_binding.res()
1051                         });
1052                         let res = binding.res();
1053                         let has_ambiguity_error = this
1054                             .ambiguity_errors
1055                             .iter()
1056                             .filter(|error| !error.warning)
1057                             .next()
1058                             .is_some();
1059                         if res == Res::Err || has_ambiguity_error {
1060                             this.tcx
1061                                 .sess
1062                                 .delay_span_bug(import.span, "some error happened for an import");
1063                             return;
1064                         }
1065                         if let Ok(initial_res) = initial_res {
1066                             if res != initial_res {
1067                                 span_bug!(import.span, "inconsistent resolution for an import");
1068                             }
1069                         } else if this.privacy_errors.is_empty() {
1070                             this.tcx
1071                                 .sess
1072                                 .create_err(CannotDetermineImportResolution { span: import.span })
1073                                 .emit();
1074                         }
1075                     }
1076                     Err(..) => {
1077                         // FIXME: This assert may fire if public glob is later shadowed by a private
1078                         // single import (see test `issue-55884-2.rs`). In theory single imports should
1079                         // always block globs, even if they are not yet resolved, so that this kind of
1080                         // self-inconsistent resolution never happens.
1081                         // Re-enable the assert when the issue is fixed.
1082                         // assert!(result[ns].get().is_err());
1083                     }
1084                 }
1085             }
1086         });
1087
1088         if all_ns_err {
1089             let mut all_ns_failed = true;
1090             self.per_ns(|this, ns| {
1091                 if !type_ns_only || ns == TypeNS {
1092                     let binding = this.resolve_ident_in_module(
1093                         module,
1094                         ident,
1095                         ns,
1096                         &import.parent_scope,
1097                         Some(finalize),
1098                         None,
1099                     );
1100                     if binding.is_ok() {
1101                         all_ns_failed = false;
1102                     }
1103                 }
1104             });
1105
1106             return if all_ns_failed {
1107                 let resolutions = match module {
1108                     ModuleOrUniformRoot::Module(module) => Some(self.resolutions(module).borrow()),
1109                     _ => None,
1110                 };
1111                 let resolutions = resolutions.as_ref().into_iter().flat_map(|r| r.iter());
1112                 let names = resolutions
1113                     .filter_map(|(BindingKey { ident: i, .. }, resolution)| {
1114                         if i.name == ident.name {
1115                             return None;
1116                         } // Never suggest the same name
1117                         match *resolution.borrow() {
1118                             NameResolution { binding: Some(name_binding), .. } => {
1119                                 match name_binding.kind {
1120                                     NameBindingKind::Import { binding, .. } => {
1121                                         match binding.kind {
1122                                             // Never suggest the name that has binding error
1123                                             // i.e., the name that cannot be previously resolved
1124                                             NameBindingKind::Res(Res::Err) => None,
1125                                             _ => Some(i.name),
1126                                         }
1127                                     }
1128                                     _ => Some(i.name),
1129                                 }
1130                             }
1131                             NameResolution { ref single_imports, .. }
1132                                 if single_imports.is_empty() =>
1133                             {
1134                                 None
1135                             }
1136                             _ => Some(i.name),
1137                         }
1138                     })
1139                     .collect::<Vec<Symbol>>();
1140
1141                 let lev_suggestion =
1142                     find_best_match_for_name(&names, ident.name, None).map(|suggestion| {
1143                         (
1144                             vec![(ident.span, suggestion.to_string())],
1145                             String::from("a similar name exists in the module"),
1146                             Applicability::MaybeIncorrect,
1147                         )
1148                     });
1149
1150                 let (suggestion, note) =
1151                     match self.check_for_module_export_macro(import, module, ident) {
1152                         Some((suggestion, note)) => (suggestion.or(lev_suggestion), note),
1153                         _ => (lev_suggestion, None),
1154                     };
1155
1156                 let label = match module {
1157                     ModuleOrUniformRoot::Module(module) => {
1158                         let module_str = module_to_string(module);
1159                         if let Some(module_str) = module_str {
1160                             format!("no `{ident}` in `{module_str}`")
1161                         } else {
1162                             format!("no `{ident}` in the root")
1163                         }
1164                     }
1165                     _ => {
1166                         if !ident.is_path_segment_keyword() {
1167                             format!("no external crate `{ident}`")
1168                         } else {
1169                             // HACK(eddyb) this shows up for `self` & `super`, which
1170                             // should work instead - for now keep the same error message.
1171                             format!("no `{ident}` in the root")
1172                         }
1173                     }
1174                 };
1175
1176                 let parent_suggestion =
1177                     self.lookup_import_candidates(ident, TypeNS, &import.parent_scope, |_| true);
1178
1179                 Some(UnresolvedImportError {
1180                     span: import.span,
1181                     label: Some(label),
1182                     note,
1183                     suggestion,
1184                     candidates: if !parent_suggestion.is_empty() {
1185                         Some(parent_suggestion)
1186                     } else {
1187                         None
1188                     },
1189                 })
1190             } else {
1191                 // `resolve_ident_in_module` reported a privacy error.
1192                 None
1193             };
1194         }
1195
1196         let mut reexport_error = None;
1197         let mut any_successful_reexport = false;
1198         let mut crate_private_reexport = false;
1199         self.per_ns(|this, ns| {
1200             if let Ok(binding) = source_bindings[ns].get() {
1201                 if !binding.vis.is_at_least(import.expect_vis(), this.tcx) {
1202                     reexport_error = Some((ns, binding));
1203                     if let ty::Visibility::Restricted(binding_def_id) = binding.vis {
1204                         if binding_def_id.is_top_level_module() {
1205                             crate_private_reexport = true;
1206                         }
1207                     }
1208                 } else {
1209                     any_successful_reexport = true;
1210                 }
1211             }
1212         });
1213
1214         // All namespaces must be re-exported with extra visibility for an error to occur.
1215         if !any_successful_reexport {
1216             let (ns, binding) = reexport_error.unwrap();
1217             if pub_use_of_private_extern_crate_hack(import, binding) {
1218                 let msg = format!(
1219                     "extern crate `{ident}` is private, and cannot be \
1220                                    re-exported (error E0365), consider declaring with \
1221                                    `pub`"
1222                 );
1223                 self.lint_buffer.buffer_lint(
1224                     PUB_USE_OF_PRIVATE_EXTERN_CRATE,
1225                     import_id,
1226                     import.span,
1227                     msg,
1228                 );
1229             } else {
1230                 if ns == TypeNS {
1231                     let mut err = if crate_private_reexport {
1232                         self.tcx.sess.create_err(CannotBeReexportedCratePublicNS {
1233                             span: import.span,
1234                             ident,
1235                         })
1236                     } else {
1237                         self.tcx
1238                             .sess
1239                             .create_err(CannotBeReexportedPrivateNS { span: import.span, ident })
1240                     };
1241                     err.emit();
1242                 } else {
1243                     let mut err = if crate_private_reexport {
1244                         self.tcx
1245                             .sess
1246                             .create_err(CannotBeReexportedCratePublic { span: import.span, ident })
1247                     } else {
1248                         self.tcx
1249                             .sess
1250                             .create_err(CannotBeReexportedPrivate { span: import.span, ident })
1251                     };
1252
1253                     match binding.kind {
1254                         NameBindingKind::Res(Res::Def(DefKind::Macro(_), def_id))
1255                             // exclude decl_macro
1256                             if self.get_macro_by_def_id(def_id).macro_rules =>
1257                         {
1258                             err.subdiagnostic(ConsiderAddingMacroExport {
1259                                 span: binding.span,
1260                             });
1261                         }
1262                         _ => {
1263                             err.subdiagnostic(ConsiderMarkingAsPub {
1264                                 span: import.span,
1265                                 ident,
1266                             });
1267                         }
1268                     }
1269                     err.emit();
1270                 }
1271             }
1272         }
1273
1274         if import.module_path.len() <= 1 {
1275             // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
1276             // 2 segments, so the `resolve_path` above won't trigger it.
1277             let mut full_path = import.module_path.clone();
1278             full_path.push(Segment::from_ident(ident));
1279             self.per_ns(|this, ns| {
1280                 if let Ok(binding) = source_bindings[ns].get() {
1281                     this.lint_if_path_starts_with_module(Some(finalize), &full_path, Some(binding));
1282                 }
1283             });
1284         }
1285
1286         // Record what this import resolves to for later uses in documentation,
1287         // this may resolve to either a value or a type, but for documentation
1288         // purposes it's good enough to just favor one over the other.
1289         self.per_ns(|this, ns| {
1290             if let Ok(binding) = source_bindings[ns].get() {
1291                 this.import_res_map.entry(import_id).or_default()[ns] = Some(binding.res());
1292             }
1293         });
1294
1295         self.check_for_redundant_imports(ident, import, source_bindings, target_bindings, target);
1296
1297         debug!("(resolving single import) successfully resolved import");
1298         None
1299     }
1300
1301     fn check_for_redundant_imports(
1302         &mut self,
1303         ident: Ident,
1304         import: Import<'a>,
1305         source_bindings: &PerNS<Cell<Result<NameBinding<'a>, Determinacy>>>,
1306         target_bindings: &PerNS<Cell<Option<NameBinding<'a>>>>,
1307         target: Ident,
1308     ) {
1309         // This function is only called for single imports.
1310         let ImportKind::Single { id, .. } = import.kind else { unreachable!() };
1311
1312         // Skip if the import was produced by a macro.
1313         if import.parent_scope.expansion != LocalExpnId::ROOT {
1314             return;
1315         }
1316
1317         // Skip if we are inside a named module (in contrast to an anonymous
1318         // module defined by a block).
1319         if let ModuleKind::Def(..) = import.parent_scope.module.kind {
1320             return;
1321         }
1322
1323         let mut is_redundant = PerNS { value_ns: None, type_ns: None, macro_ns: None };
1324
1325         let mut redundant_span = PerNS { value_ns: None, type_ns: None, macro_ns: None };
1326
1327         self.per_ns(|this, ns| {
1328             if let Ok(binding) = source_bindings[ns].get() {
1329                 if binding.res() == Res::Err {
1330                     return;
1331                 }
1332
1333                 match this.early_resolve_ident_in_lexical_scope(
1334                     target,
1335                     ScopeSet::All(ns),
1336                     &import.parent_scope,
1337                     None,
1338                     false,
1339                     target_bindings[ns].get(),
1340                 ) {
1341                     Ok(other_binding) => {
1342                         is_redundant[ns] = Some(
1343                             binding.res() == other_binding.res() && !other_binding.is_ambiguity(),
1344                         );
1345                         redundant_span[ns] = Some((other_binding.span, other_binding.is_import()));
1346                     }
1347                     Err(_) => is_redundant[ns] = Some(false),
1348                 }
1349             }
1350         });
1351
1352         if !is_redundant.is_empty() && is_redundant.present_items().all(|is_redundant| is_redundant)
1353         {
1354             let mut redundant_spans: Vec<_> = redundant_span.present_items().collect();
1355             redundant_spans.sort();
1356             redundant_spans.dedup();
1357             self.lint_buffer.buffer_lint_with_diagnostic(
1358                 UNUSED_IMPORTS,
1359                 id,
1360                 import.span,
1361                 format!("the item `{ident}` is imported redundantly"),
1362                 BuiltinLintDiagnostics::RedundantImport(redundant_spans, ident),
1363             );
1364         }
1365     }
1366
1367     fn resolve_glob_import(&mut self, import: Import<'a>) {
1368         // This function is only called for glob imports.
1369         let ImportKind::Glob { id, is_prelude, .. } = import.kind else { unreachable!() };
1370
1371         let ModuleOrUniformRoot::Module(module) = import.imported_module.get().unwrap() else {
1372             self.tcx.sess.create_err(CannotGlobImportAllCrates { span: import.span }).emit();
1373             return;
1374         };
1375
1376         if module.is_trait() {
1377             self.tcx.sess.create_err(ItemsInTraitsAreNotImportable { span: import.span }).emit();
1378             return;
1379         } else if module == import.parent_scope.module {
1380             return;
1381         } else if is_prelude {
1382             self.prelude = Some(module);
1383             return;
1384         }
1385
1386         // Add to module's glob_importers
1387         module.glob_importers.borrow_mut().push(import);
1388
1389         // Ensure that `resolutions` isn't borrowed during `try_define`,
1390         // since it might get updated via a glob cycle.
1391         let bindings = self
1392             .resolutions(module)
1393             .borrow()
1394             .iter()
1395             .filter_map(|(key, resolution)| {
1396                 resolution.borrow().binding().map(|binding| (*key, binding))
1397             })
1398             .collect::<Vec<_>>();
1399         for (mut key, binding) in bindings {
1400             let scope = match key.ident.span.reverse_glob_adjust(module.expansion, import.span) {
1401                 Some(Some(def)) => self.expn_def_scope(def),
1402                 Some(None) => import.parent_scope.module,
1403                 None => continue,
1404             };
1405             if self.is_accessible_from(binding.vis, scope) {
1406                 let imported_binding = self.import(binding, import);
1407                 let warn_ambiguity = self
1408                     .resolution(import.parent_scope.module, key)
1409                     .borrow()
1410                     .binding()
1411                     .is_some_and(|binding| binding.is_warn_ambiguity());
1412                 let _ = self.try_define(
1413                     import.parent_scope.module,
1414                     key,
1415                     imported_binding,
1416                     warn_ambiguity,
1417                 );
1418             }
1419         }
1420
1421         // Record the destination of this import
1422         self.record_partial_res(id, PartialRes::new(module.res().unwrap()));
1423     }
1424
1425     // Miscellaneous post-processing, including recording re-exports,
1426     // reporting conflicts, and reporting unresolved imports.
1427     fn finalize_resolutions_in(&mut self, module: Module<'a>) {
1428         // Since import resolution is finished, globs will not define any more names.
1429         *module.globs.borrow_mut() = Vec::new();
1430
1431         if let Some(def_id) = module.opt_def_id() {
1432             let mut children = Vec::new();
1433
1434             module.for_each_child(self, |this, ident, _, binding| {
1435                 let res = binding.res().expect_non_local();
1436                 let error_ambiguity = binding.is_ambiguity() && !binding.warn_ambiguity;
1437                 if res != def::Res::Err && !error_ambiguity {
1438                     let mut reexport_chain = SmallVec::new();
1439                     let mut next_binding = binding;
1440                     while let NameBindingKind::Import { binding, import, .. } = next_binding.kind {
1441                         reexport_chain.push(import.simplify(this));
1442                         next_binding = binding;
1443                     }
1444
1445                     children.push(ModChild { ident, res, vis: binding.vis, reexport_chain });
1446                 }
1447             });
1448
1449             if !children.is_empty() {
1450                 // Should be fine because this code is only called for local modules.
1451                 self.module_children.insert(def_id.expect_local(), children);
1452             }
1453         }
1454     }
1455 }
1456
1457 fn import_path_to_string(names: &[Ident], import_kind: &ImportKind<'_>, span: Span) -> String {
1458     let pos = names.iter().position(|p| span == p.span && p.name != kw::PathRoot);
1459     let global = !names.is_empty() && names[0].name == kw::PathRoot;
1460     if let Some(pos) = pos {
1461         let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
1462         names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>())
1463     } else {
1464         let names = if global { &names[1..] } else { names };
1465         if names.is_empty() {
1466             import_kind_to_string(import_kind)
1467         } else {
1468             format!(
1469                 "{}::{}",
1470                 names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>()),
1471                 import_kind_to_string(import_kind),
1472             )
1473         }
1474     }
1475 }
1476
1477 fn import_kind_to_string(import_kind: &ImportKind<'_>) -> String {
1478     match import_kind {
1479         ImportKind::Single { source, .. } => source.to_string(),
1480         ImportKind::Glob { .. } => "*".to_string(),
1481         ImportKind::ExternCrate { .. } => "<extern crate>".to_string(),
1482         ImportKind::MacroUse => "#[macro_use]".to_string(),
1483         ImportKind::MacroExport => "#[macro_export]".to_string(),
1484     }
1485 }