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, Suggestion};
   4 use crate::Determinacy::{self, *};
   5 use crate::Namespace::*;
   6 use crate::{module_to_string, names_to_string, ImportSuggestion};
   7 use crate::{AmbiguityKind, BindingKey, ModuleKind, ResolutionError, Resolver, Segment};
   8 use crate::{Finalize, Module, ModuleOrUniformRoot, ParentScope, PerNS, ScopeSet};
   9 use crate::{NameBinding, NameBindingKind, PathResult};
  10
  11 use rustc_ast::NodeId;
  12 use rustc_data_structures::fx::FxHashSet;
  13 use rustc_data_structures::intern::Interned;
  14 use rustc_errors::{pluralize, struct_span_err, Applicability, MultiSpan};
  15 use rustc_hir::def::{self, DefKind, PartialRes};
  16 use rustc_middle::metadata::ModChild;
  17 use rustc_middle::span_bug;
  18 use rustc_middle::ty;
  19 use rustc_session::lint::builtin::{PUB_USE_OF_PRIVATE_EXTERN_CRATE, UNUSED_IMPORTS};
  20 use rustc_session::lint::BuiltinLintDiagnostics;
  21 use rustc_span::hygiene::LocalExpnId;
  22 use rustc_span::lev_distance::find_best_match_for_name;
  23 use rustc_span::symbol::{kw, Ident, Symbol};
  24 use rustc_span::Span;
  25
  26 use std::cell::Cell;
  27 use std::{mem, ptr};
  28
  29 type Res = def::Res<NodeId>;
  30
  31 /// Contains data for specific kinds of imports.
  32 #[derive(Clone)]
  33 pub enum ImportKind<'a> {
  34     Single {
  35         /// `source` in `use prefix::source as target`.
  36         source: Ident,
  37         /// `target` in `use prefix::source as target`.
  38         target: Ident,
  39         /// Bindings to which `source` refers to.
  40         source_bindings: PerNS<Cell<Result<&'a NameBinding<'a>, Determinacy>>>,
  41         /// Bindings introduced by `target`.
  42         target_bindings: PerNS<Cell<Option<&'a NameBinding<'a>>>>,
  43         /// `true` for `...::{self [as target]}` imports, `false` otherwise.
  44         type_ns_only: bool,
  45         /// Did this import result from a nested import? ie. `use foo::{bar, baz};`
  46         nested: bool,
  47         /// The ID of the `UseTree` that imported this `Import`.
  48         ///
  49         /// In the case where the `Import` was expanded from a "nested" use tree,
  50         /// this id is the ID of the leaf tree. For example:
  51         ///
  52         /// ```ignore (pacify the merciless tidy)
  53         /// use foo::bar::{a, b}
  54         /// ```
  55         ///
  56         /// If this is the import for `foo::bar::a`, we would have the ID of the `UseTree`
  57         /// for `a` in this field.
  58         id: NodeId,
  59         /// Additional `NodeId`s allocated to a `ast::UseTree` for automatically generated `use` statement
  60         /// (eg. implicit struct constructors)
  61         additional_ids: (NodeId, NodeId),
  62     },
  63     Glob {
  64         is_prelude: bool,
  65         // The visibility of the greatest re-export.
  66         // n.b. `max_vis` is only used in `finalize_import` to check for re-export errors.
  67         max_vis: Cell<Option<ty::Visibility>>,
  68         id: NodeId,
  69     },
  70     ExternCrate {
  71         source: Option<Symbol>,
  72         target: Ident,
  73         id: NodeId,
  74     },
  75     MacroUse,
  76     MacroExport,
  77 }
  78
  79 /// Manually implement `Debug` for `ImportKind` because the `source/target_bindings`
  80 /// contain `Cell`s which can introduce infinite loops while printing.
  81 impl<'a> std::fmt::Debug for ImportKind<'a> {
  82     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
  83         use ImportKind::*;
  84         match self {
  85             Single {
  86                 ref source,
  87                 ref target,
  88                 ref type_ns_only,
  89                 ref nested,
  90                 ref id,
  91                 ref additional_ids,
  92                 // Ignore the following to avoid an infinite loop while printing.
  93                 source_bindings: _,
  94                 target_bindings: _,
  95             } => f
  96                 .debug_struct("Single")
  97                 .field("source", source)
  98                 .field("target", target)
  99                 .field("type_ns_only", type_ns_only)
 100                 .field("nested", nested)
 101                 .field("id", id)
 102                 .field("additional_ids", additional_ids)
 103                 .finish_non_exhaustive(),
 104             Glob { ref is_prelude, ref max_vis, ref id } => f
 105                 .debug_struct("Glob")
 106                 .field("is_prelude", is_prelude)
 107                 .field("max_vis", max_vis)
 108                 .field("id", id)
 109                 .finish(),
 110             ExternCrate { ref source, ref target, ref id } => f
 111                 .debug_struct("ExternCrate")
 112                 .field("source", source)
 113                 .field("target", target)
 114                 .field("id", id)
 115                 .finish(),
 116             MacroUse => f.debug_struct("MacroUse").finish(),
 117             MacroExport => f.debug_struct("MacroExport").finish(),
 118         }
 119     }
 120 }
 121
 122 /// One import.
 123 #[derive(Debug, Clone)]
 124 pub(crate) struct Import<'a> {
 125     pub kind: ImportKind<'a>,
 126
 127     /// Node ID of the "root" use item -- this is always the same as `ImportKind`'s `id`
 128     /// (if it exists) except in the case of "nested" use trees, in which case
 129     /// it will be the ID of the root use tree. e.g., in the example
 130     /// ```ignore (incomplete code)
 131     /// use foo::bar::{a, b}
 132     /// ```
 133     /// this would be the ID of the `use foo::bar` `UseTree` node.
 134     /// In case of imports without their own node ID it's the closest node that can be used,
 135     /// for example, for reporting lints.
 136     pub root_id: NodeId,
 137
 138     /// Span of the entire use statement.
 139     pub use_span: Span,
 140
 141     /// Span of the entire use statement with attributes.
 142     pub use_span_with_attributes: Span,
 143
 144     /// Did the use statement have any attributes?
 145     pub has_attributes: bool,
 146
 147     /// Span of this use tree.
 148     pub span: Span,
 149
 150     /// Span of the *root* use tree (see `root_id`).
 151     pub root_span: Span,
 152
 153     pub parent_scope: ParentScope<'a>,
 154     pub module_path: Vec<Segment>,
 155     /// The resolution of `module_path`.
 156     pub imported_module: Cell<Option<ModuleOrUniformRoot<'a>>>,
 157     pub vis: Cell<Option<ty::Visibility>>,
 158     pub used: Cell<bool>,
 159 }
 160
 161 impl<'a> Import<'a> {
 162     pub fn is_glob(&self) -> bool {
 163         matches!(self.kind, ImportKind::Glob { .. })
 164     }
 165
 166     pub fn is_nested(&self) -> bool {
 167         match self.kind {
 168             ImportKind::Single { nested, .. } => nested,
 169             _ => false,
 170         }
 171     }
 172
 173     pub(crate) fn expect_vis(&self) -> ty::Visibility {
 174         self.vis.get().expect("encountered cleared import visibility")
 175     }
 176
 177     pub(crate) fn id(&self) -> Option<NodeId> {
 178         match self.kind {
 179             ImportKind::Single { id, .. }
 180             | ImportKind::Glob { id, .. }
 181             | ImportKind::ExternCrate { id, .. } => Some(id),
 182             ImportKind::MacroUse | ImportKind::MacroExport => None,
 183         }
 184     }
 185 }
 186
 187 /// Records information about the resolution of a name in a namespace of a module.
 188 #[derive(Clone, Default, Debug)]
 189 pub(crate) struct NameResolution<'a> {
 190     /// Single imports that may define the name in the namespace.
 191     /// Imports are arena-allocated, so it's ok to use pointers as keys.
 192     pub single_imports: FxHashSet<Interned<'a, Import<'a>>>,
 193     /// The least shadowable known binding for this name, or None if there are no known bindings.
 194     pub binding: Option<&'a NameBinding<'a>>,
 195     pub shadowed_glob: Option<&'a NameBinding<'a>>,
 196 }
 197
 198 impl<'a> NameResolution<'a> {
 199     // Returns the binding for the name if it is known or None if it not known.
 200     pub(crate) fn binding(&self) -> Option<&'a NameBinding<'a>> {
 201         self.binding.and_then(|binding| {
 202             if !binding.is_glob_import() || self.single_imports.is_empty() {
 203                 Some(binding)
 204             } else {
 205                 None
 206             }
 207         })
 208     }
 209
 210     pub(crate) fn add_single_import(&mut self, import: &'a Import<'a>) {
 211         self.single_imports.insert(Interned::new_unchecked(import));
 212     }
 213 }
 214
 215 // Reexports of the form `pub use foo as bar;` where `foo` is `extern crate foo;`
 216 // are permitted for backward-compatibility under a deprecation lint.
 217 fn pub_use_of_private_extern_crate_hack(import: &Import<'_>, binding: &NameBinding<'_>) -> bool {
 218     match (&import.kind, &binding.kind) {
 219         (
 220             ImportKind::Single { .. },
 221             NameBindingKind::Import {
 222                 import: Import { kind: ImportKind::ExternCrate { .. }, .. },
 223                 ..
 224             },
 225         ) => import.expect_vis().is_public(),
 226         _ => false,
 227     }
 228 }
 229
 230 impl<'a> Resolver<'a> {
 231     // Given a binding and an import that resolves to it,
 232     // return the corresponding binding defined by the import.
 233     pub(crate) fn import(
 234         &self,
 235         binding: &'a NameBinding<'a>,
 236         import: &'a Import<'a>,
 237     ) -> &'a NameBinding<'a> {
 238         let import_vis = import.expect_vis().to_def_id();
 239         let vis = if binding.vis.is_at_least(import_vis, self)
 240             || pub_use_of_private_extern_crate_hack(import, binding)
 241         {
 242             import_vis
 243         } else {
 244             binding.vis
 245         };
 246
 247         if let ImportKind::Glob { ref max_vis, .. } = import.kind {
 248             if vis == import_vis
 249                 || max_vis.get().map_or(true, |max_vis| vis.is_at_least(max_vis, self))
 250             {
 251                 max_vis.set(Some(vis.expect_local()))
 252             }
 253         }
 254
 255         self.arenas.alloc_name_binding(NameBinding {
 256             kind: NameBindingKind::Import { binding, import, used: Cell::new(false) },
 257             ambiguity: None,
 258             span: import.span,
 259             vis,
 260             expansion: import.parent_scope.expansion,
 261         })
 262     }
 263
 264     // Define the name or return the existing binding if there is a collision.
 265     pub(crate) fn try_define(
 266         &mut self,
 267         module: Module<'a>,
 268         key: BindingKey,
 269         binding: &'a NameBinding<'a>,
 270     ) -> Result<(), &'a NameBinding<'a>> {
 271         let res = binding.res();
 272         self.check_reserved_macro_name(key.ident, res);
 273         self.set_binding_parent_module(binding, module);
 274         self.update_resolution(module, key, |this, resolution| {
 275             if let Some(old_binding) = resolution.binding {
 276                 if res == Res::Err && old_binding.res() != Res::Err {
 277                     // Do not override real bindings with `Res::Err`s from error recovery.
 278                     return Ok(());
 279                 }
 280                 match (old_binding.is_glob_import(), binding.is_glob_import()) {
 281                     (true, true) => {
 282                         if res != old_binding.res() {
 283                             resolution.binding = Some(this.ambiguity(
 284                                 AmbiguityKind::GlobVsGlob,
 285                                 old_binding,
 286                                 binding,
 287                             ));
 288                         } else if !old_binding.vis.is_at_least(binding.vis, &*this) {
 289                             // We are glob-importing the same item but with greater visibility.
 290                             resolution.binding = Some(binding);
 291                         }
 292                     }
 293                     (old_glob @ true, false) | (old_glob @ false, true) => {
 294                         let (glob_binding, nonglob_binding) =
 295                             if old_glob { (old_binding, binding) } else { (binding, old_binding) };
 296                         if glob_binding.res() != nonglob_binding.res()
 297                             && key.ns == MacroNS
 298                             && nonglob_binding.expansion != LocalExpnId::ROOT
 299                         {
 300                             resolution.binding = Some(this.ambiguity(
 301                                 AmbiguityKind::GlobVsExpanded,
 302                                 nonglob_binding,
 303                                 glob_binding,
 304                             ));
 305                         } else {
 306                             resolution.binding = Some(nonglob_binding);
 307                         }
 308                         resolution.shadowed_glob = Some(glob_binding);
 309                     }
 310                     (false, false) => {
 311                         return Err(old_binding);
 312                     }
 313                 }
 314             } else {
 315                 resolution.binding = Some(binding);
 316             }
 317
 318             Ok(())
 319         })
 320     }
 321
 322     fn ambiguity(
 323         &self,
 324         kind: AmbiguityKind,
 325         primary_binding: &'a NameBinding<'a>,
 326         secondary_binding: &'a NameBinding<'a>,
 327     ) -> &'a NameBinding<'a> {
 328         self.arenas.alloc_name_binding(NameBinding {
 329             ambiguity: Some((secondary_binding, kind)),
 330             ..primary_binding.clone()
 331         })
 332     }
 333
 334     // Use `f` to mutate the resolution of the name in the module.
 335     // If the resolution becomes a success, define it in the module's glob importers.
 336     fn update_resolution<T, F>(&mut self, module: Module<'a>, key: BindingKey, f: F) -> T
 337     where
 338         F: FnOnce(&mut Resolver<'a>, &mut NameResolution<'a>) -> T,
 339     {
 340         // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
 341         // during which the resolution might end up getting re-defined via a glob cycle.
 342         let (binding, t) = {
 343             let resolution = &mut *self.resolution(module, key).borrow_mut();
 344             let old_binding = resolution.binding();
 345
 346             let t = f(self, resolution);
 347
 348             match resolution.binding() {
 349                 _ if old_binding.is_some() => return t,
 350                 None => return t,
 351                 Some(binding) => match old_binding {
 352                     Some(old_binding) if ptr::eq(old_binding, binding) => return t,
 353                     _ => (binding, t),
 354                 },
 355             }
 356         };
 357
 358         // Define `binding` in `module`s glob importers.
 359         for import in module.glob_importers.borrow_mut().iter() {
 360             let mut ident = key.ident;
 361             let scope = match ident.span.reverse_glob_adjust(module.expansion, import.span) {
 362                 Some(Some(def)) => self.expn_def_scope(def),
 363                 Some(None) => import.parent_scope.module,
 364                 None => continue,
 365             };
 366             if self.is_accessible_from(binding.vis, scope) {
 367                 let imported_binding = self.import(binding, import);
 368                 let key = BindingKey { ident, ..key };
 369                 let _ = self.try_define(import.parent_scope.module, key, imported_binding);
 370             }
 371         }
 372
 373         t
 374     }
 375
 376     // Define a dummy resolution containing a `Res::Err` as a placeholder for a failed resolution,
 377     // also mark such failed imports as used to avoid duplicate diagnostics.
 378     fn import_dummy_binding(&mut self, import: &'a Import<'a>) {
 379         if let ImportKind::Single { target, ref target_bindings, .. } = import.kind {
 380             if target_bindings.iter().any(|binding| binding.get().is_some()) {
 381                 return; // Has resolution, do not create the dummy binding
 382             }
 383             let dummy_binding = self.dummy_binding;
 384             let dummy_binding = self.import(dummy_binding, import);
 385             self.per_ns(|this, ns| {
 386                 let key = this.new_key(target, ns);
 387                 let _ = this.try_define(import.parent_scope.module, key, dummy_binding);
 388             });
 389             self.record_use(target, dummy_binding, false);
 390         } else if import.imported_module.get().is_none() {
 391             import.used.set(true);
 392             if let Some(id) = import.id() {
 393                 self.used_imports.insert(id);
 394             }
 395         }
 396     }
 397 }
 398
 399 /// An error that may be transformed into a diagnostic later. Used to combine multiple unresolved
 400 /// import errors within the same use tree into a single diagnostic.
 401 #[derive(Debug, Clone)]
 402 struct UnresolvedImportError {
 403     span: Span,
 404     label: Option<String>,
 405     note: Option<String>,
 406     suggestion: Option<Suggestion>,
 407     candidate: Option<Vec<ImportSuggestion>>,
 408 }
 409
 410 pub struct ImportResolver<'a, 'b> {
 411     pub r: &'a mut Resolver<'b>,
 412 }
 413
 414 impl<'a, 'b> ImportResolver<'a, 'b> {
 415     // Import resolution
 416     //
 417     // This is a fixed-point algorithm. We resolve imports until our efforts
 418     // are stymied by an unresolved import; then we bail out of the current
 419     // module and continue. We terminate successfully once no more imports
 420     // remain or unsuccessfully when no forward progress in resolving imports
 421     // is made.
 422
 423     /// Resolves all imports for the crate. This method performs the fixed-
 424     /// point iteration.
 425     pub fn resolve_imports(&mut self) {
 426         let mut prev_num_indeterminates = self.r.indeterminate_imports.len() + 1;
 427         while self.r.indeterminate_imports.len() < prev_num_indeterminates {
 428             prev_num_indeterminates = self.r.indeterminate_imports.len();
 429             for import in mem::take(&mut self.r.indeterminate_imports) {
 430                 match self.resolve_import(&import) {
 431                     true => self.r.determined_imports.push(import),
 432                     false => self.r.indeterminate_imports.push(import),
 433                 }
 434             }
 435         }
 436     }
 437
 438     pub fn finalize_imports(&mut self) {
 439         for module in self.r.arenas.local_modules().iter() {
 440             self.finalize_resolutions_in(module);
 441         }
 442
 443         let mut seen_spans = FxHashSet::default();
 444         let mut errors = vec![];
 445         let mut prev_root_id: NodeId = NodeId::from_u32(0);
 446         let determined_imports = mem::take(&mut self.r.determined_imports);
 447         let indeterminate_imports = mem::take(&mut self.r.indeterminate_imports);
 448
 449         for (is_indeterminate, import) in determined_imports
 450             .into_iter()
 451             .map(|i| (false, i))
 452             .chain(indeterminate_imports.into_iter().map(|i| (true, i)))
 453         {
 454             let unresolved_import_error = self.finalize_import(import);
 455
 456             // If this import is unresolved then create a dummy import
 457             // resolution for it so that later resolve stages won't complain.
 458             self.r.import_dummy_binding(import);
 459
 460             if let Some(err) = unresolved_import_error {
 461                 if let ImportKind::Single { source, ref source_bindings, .. } = import.kind {
 462                     if source.name == kw::SelfLower {
 463                         // Silence `unresolved import` error if E0429 is already emitted
 464                         if let Err(Determined) = source_bindings.value_ns.get() {
 465                             continue;
 466                         }
 467                     }
 468                 }
 469
 470                 if prev_root_id.as_u32() != 0
 471                     && prev_root_id.as_u32() != import.root_id.as_u32()
 472                     && !errors.is_empty()
 473                 {
 474                     // In the case of a new import line, throw a diagnostic message
 475                     // for the previous line.
 476                     self.throw_unresolved_import_error(errors);
 477                     errors = vec![];
 478                 }
 479                 if seen_spans.insert(err.span) {
 480                     let path = import_path_to_string(
 481                         &import.module_path.iter().map(|seg| seg.ident).collect::<Vec<_>>(),
 482                         &import.kind,
 483                         err.span,
 484                     );
 485                     errors.push((path, err));
 486                     prev_root_id = import.root_id;
 487                 }
 488             } else if is_indeterminate {
 489                 let path = import_path_to_string(
 490                     &import.module_path.iter().map(|seg| seg.ident).collect::<Vec<_>>(),
 491                     &import.kind,
 492                     import.span,
 493                 );
 494                 let err = UnresolvedImportError {
 495                     span: import.span,
 496                     label: None,
 497                     note: None,
 498                     suggestion: None,
 499                     candidate: None,
 500                 };
 501                 if path.contains("::") {
 502                     errors.push((path, err))
 503                 }
 504             }
 505         }
 506
 507         if !errors.is_empty() {
 508             self.throw_unresolved_import_error(errors);
 509         }
 510     }
 511
 512     fn throw_unresolved_import_error(&self, errors: Vec<(String, UnresolvedImportError)>) {
 513         if errors.is_empty() {
 514             return;
 515         }
 516
 517         /// Upper limit on the number of `span_label` messages.
 518         const MAX_LABEL_COUNT: usize = 10;
 519
 520         let span = MultiSpan::from_spans(errors.iter().map(|(_, err)| err.span).collect());
 521         let paths = errors.iter().map(|(path, _)| format!("`{}`", path)).collect::<Vec<_>>();
 522         let msg = format!("unresolved import{} {}", pluralize!(paths.len()), paths.join(", "),);
 523
 524         let mut diag = struct_span_err!(self.r.session, span, E0432, "{}", &msg);
 525
 526         if let Some((_, UnresolvedImportError { note: Some(note), .. })) = errors.iter().last() {
 527             diag.note(note);
 528         }
 529
 530         for (_, err) in errors.into_iter().take(MAX_LABEL_COUNT) {
 531             if let Some(label) = err.label {
 532                 diag.span_label(err.span, label);
 533             }
 534
 535             if let Some((suggestions, msg, applicability)) = err.suggestion {
 536                 if suggestions.is_empty() {
 537                     diag.help(&msg);
 538                     continue;
 539                 }
 540                 diag.multipart_suggestion(&msg, suggestions, applicability);
 541             }
 542
 543             if let Some(candidate) = &err.candidate {
 544                 import_candidates(
 545                     self.r.session,
 546                     &self.r.source_span,
 547                     &mut diag,
 548                     Some(err.span),
 549                     &candidate,
 550                 )
 551             }
 552         }
 553
 554         diag.emit();
 555     }
 556
 557     /// Attempts to resolve the given import, returning true if its resolution is determined.
 558     /// If successful, the resolved bindings are written into the module.
 559     fn resolve_import(&mut self, import: &'b Import<'b>) -> bool {
 560         debug!(
 561             "(resolving import for module) resolving import `{}::...` in `{}`",
 562             Segment::names_to_string(&import.module_path),
 563             module_to_string(import.parent_scope.module).unwrap_or_else(|| "???".to_string()),
 564         );
 565
 566         let module = if let Some(module) = import.imported_module.get() {
 567             module
 568         } else {
 569             // For better failure detection, pretend that the import will
 570             // not define any names while resolving its module path.
 571             let orig_vis = import.vis.take();
 572             let path_res =
 573                 self.r.maybe_resolve_path(&import.module_path, None, &import.parent_scope);
 574             import.vis.set(orig_vis);
 575
 576             match path_res {
 577                 PathResult::Module(module) => module,
 578                 PathResult::Indeterminate => return false,
 579                 PathResult::NonModule(..) | PathResult::Failed { .. } => return true,
 580             }
 581         };
 582
 583         import.imported_module.set(Some(module));
 584         let (source, target, source_bindings, target_bindings, type_ns_only) = match import.kind {
 585             ImportKind::Single {
 586                 source,
 587                 target,
 588                 ref source_bindings,
 589                 ref target_bindings,
 590                 type_ns_only,
 591                 ..
 592             } => (source, target, source_bindings, target_bindings, type_ns_only),
 593             ImportKind::Glob { .. } => {
 594                 self.resolve_glob_import(import);
 595                 return true;
 596             }
 597             _ => unreachable!(),
 598         };
 599
 600         let mut indeterminate = false;
 601         self.r.per_ns(|this, ns| {
 602             if !type_ns_only || ns == TypeNS {
 603                 if let Err(Undetermined) = source_bindings[ns].get() {
 604                     // For better failure detection, pretend that the import will
 605                     // not define any names while resolving its module path.
 606                     let orig_vis = import.vis.take();
 607                     let binding = this.resolve_ident_in_module(
 608                         module,
 609                         source,
 610                         ns,
 611                         &import.parent_scope,
 612                         None,
 613                         None,
 614                     );
 615                     import.vis.set(orig_vis);
 616                     source_bindings[ns].set(binding);
 617                 } else {
 618                     return;
 619                 };
 620
 621                 let parent = import.parent_scope.module;
 622                 match source_bindings[ns].get() {
 623                     Err(Undetermined) => indeterminate = true,
 624                     // Don't update the resolution, because it was never added.
 625                     Err(Determined) if target.name == kw::Underscore => {}
 626                     Ok(binding) if binding.is_importable() => {
 627                         let imported_binding = this.import(binding, import);
 628                         target_bindings[ns].set(Some(imported_binding));
 629                         this.define(parent, target, ns, imported_binding);
 630                     }
 631                     source_binding @ (Ok(..) | Err(Determined)) => {
 632                         if source_binding.is_ok() {
 633                             let msg = format!("`{}` is not directly importable", target);
 634                             struct_span_err!(this.session, import.span, E0253, "{}", &msg)
 635                                 .span_label(import.span, "cannot be imported directly")
 636                                 .emit();
 637                         }
 638                         let key = this.new_key(target, ns);
 639                         this.update_resolution(parent, key, |_, resolution| {
 640                             resolution.single_imports.remove(&Interned::new_unchecked(import));
 641                         });
 642                     }
 643                 }
 644             }
 645         });
 646
 647         !indeterminate
 648     }
 649
 650     /// Performs final import resolution, consistency checks and error reporting.
 651     ///
 652     /// Optionally returns an unresolved import error. This error is buffered and used to
 653     /// consolidate multiple unresolved import errors into a single diagnostic.
 654     fn finalize_import(&mut self, import: &'b Import<'b>) -> Option<UnresolvedImportError> {
 655         let orig_vis = import.vis.take();
 656         let ignore_binding = match &import.kind {
 657             ImportKind::Single { target_bindings, .. } => target_bindings[TypeNS].get(),
 658             _ => None,
 659         };
 660         let prev_ambiguity_errors_len = self.r.ambiguity_errors.len();
 661         let finalize = Finalize::with_root_span(import.root_id, import.span, import.root_span);
 662         let path_res = self.r.resolve_path(
 663             &import.module_path,
 664             None,
 665             &import.parent_scope,
 666             Some(finalize),
 667             ignore_binding,
 668         );
 669
 670         let no_ambiguity = self.r.ambiguity_errors.len() == prev_ambiguity_errors_len;
 671         import.vis.set(orig_vis);
 672         let module = match path_res {
 673             PathResult::Module(module) => {
 674                 // Consistency checks, analogous to `finalize_macro_resolutions`.
 675                 if let Some(initial_module) = import.imported_module.get() {
 676                     if !ModuleOrUniformRoot::same_def(module, initial_module) && no_ambiguity {
 677                         span_bug!(import.span, "inconsistent resolution for an import");
 678                     }
 679                 } else if self.r.privacy_errors.is_empty() {
 680                     let msg = "cannot determine resolution for the import";
 681                     let msg_note = "import resolution is stuck, try simplifying other imports";
 682                     self.r.session.struct_span_err(import.span, msg).note(msg_note).emit();
 683                 }
 684
 685                 module
 686             }
 687             PathResult::Failed { is_error_from_last_segment: false, span, label, suggestion } => {
 688                 if no_ambiguity {
 689                     assert!(import.imported_module.get().is_none());
 690                     self.r
 691                         .report_error(span, ResolutionError::FailedToResolve { label, suggestion });
 692                 }
 693                 return None;
 694             }
 695             PathResult::Failed { is_error_from_last_segment: true, span, label, suggestion } => {
 696                 if no_ambiguity {
 697                     assert!(import.imported_module.get().is_none());
 698                     let err = match self.make_path_suggestion(
 699                         span,
 700                         import.module_path.clone(),
 701                         &import.parent_scope,
 702                     ) {
 703                         Some((suggestion, note)) => UnresolvedImportError {
 704                             span,
 705                             label: None,
 706                             note,
 707                             suggestion: Some((
 708                                 vec![(span, Segment::names_to_string(&suggestion))],
 709                                 String::from("a similar path exists"),
 710                                 Applicability::MaybeIncorrect,
 711                             )),
 712                             candidate: None,
 713                         },
 714                         None => UnresolvedImportError {
 715                             span,
 716                             label: Some(label),
 717                             note: None,
 718                             suggestion,
 719                             candidate: None,
 720                         },
 721                     };
 722                     return Some(err);
 723                 }
 724                 return None;
 725             }
 726             PathResult::NonModule(_) => {
 727                 if no_ambiguity {
 728                     assert!(import.imported_module.get().is_none());
 729                 }
 730                 // The error was already reported earlier.
 731                 return None;
 732             }
 733             PathResult::Indeterminate => unreachable!(),
 734         };
 735
 736         let (ident, target, source_bindings, target_bindings, type_ns_only, import_id) =
 737             match import.kind {
 738                 ImportKind::Single {
 739                     source,
 740                     target,
 741                     ref source_bindings,
 742                     ref target_bindings,
 743                     type_ns_only,
 744                     id,
 745                     ..
 746                 } => (source, target, source_bindings, target_bindings, type_ns_only, id),
 747                 ImportKind::Glob { is_prelude, ref max_vis, id } => {
 748                     if import.module_path.len() <= 1 {
 749                         // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
 750                         // 2 segments, so the `resolve_path` above won't trigger it.
 751                         let mut full_path = import.module_path.clone();
 752                         full_path.push(Segment::from_ident(Ident::empty()));
 753                         self.r.lint_if_path_starts_with_module(Some(finalize), &full_path, None);
 754                     }
 755
 756                     if let ModuleOrUniformRoot::Module(module) = module {
 757                         if ptr::eq(module, import.parent_scope.module) {
 758                             // Importing a module into itself is not allowed.
 759                             return Some(UnresolvedImportError {
 760                                 span: import.span,
 761                                 label: Some(String::from(
 762                                     "cannot glob-import a module into itself",
 763                                 )),
 764                                 note: None,
 765                                 suggestion: None,
 766                                 candidate: None,
 767                             });
 768                         }
 769                     }
 770                     if !is_prelude
 771                     && let Some(max_vis) = max_vis.get()
 772                     && !max_vis.is_at_least(import.expect_vis(), &*self.r)
 773                 {
 774                     let msg = "glob import doesn't reexport anything because no candidate is public enough";
 775                     self.r.lint_buffer.buffer_lint(UNUSED_IMPORTS, id, import.span, msg);
 776                 }
 777                     return None;
 778                 }
 779                 _ => unreachable!(),
 780             };
 781
 782         let mut all_ns_err = true;
 783         self.r.per_ns(|this, ns| {
 784             if !type_ns_only || ns == TypeNS {
 785                 let orig_vis = import.vis.take();
 786                 let binding = this.resolve_ident_in_module(
 787                     module,
 788                     ident,
 789                     ns,
 790                     &import.parent_scope,
 791                     Some(Finalize { report_private: false, ..finalize }),
 792                     target_bindings[ns].get(),
 793                 );
 794                 import.vis.set(orig_vis);
 795
 796                 match binding {
 797                     Ok(binding) => {
 798                         // Consistency checks, analogous to `finalize_macro_resolutions`.
 799                         let initial_res = source_bindings[ns].get().map(|initial_binding| {
 800                             all_ns_err = false;
 801                             if let Some(target_binding) = target_bindings[ns].get() {
 802                                 if target.name == kw::Underscore
 803                                     && initial_binding.is_extern_crate()
 804                                     && !initial_binding.is_import()
 805                                 {
 806                                     this.record_use(
 807                                         ident,
 808                                         target_binding,
 809                                         import.module_path.is_empty(),
 810                                     );
 811                                 }
 812                             }
 813                             initial_binding.res()
 814                         });
 815                         let res = binding.res();
 816                         if let Ok(initial_res) = initial_res {
 817                             if res != initial_res && this.ambiguity_errors.is_empty() {
 818                                 span_bug!(import.span, "inconsistent resolution for an import");
 819                             }
 820                         } else if res != Res::Err
 821                             && this.ambiguity_errors.is_empty()
 822                             && this.privacy_errors.is_empty()
 823                         {
 824                             let msg = "cannot determine resolution for the import";
 825                             let msg_note =
 826                                 "import resolution is stuck, try simplifying other imports";
 827                             this.session.struct_span_err(import.span, msg).note(msg_note).emit();
 828                         }
 829                     }
 830                     Err(..) => {
 831                         // FIXME: This assert may fire if public glob is later shadowed by a private
 832                         // single import (see test `issue-55884-2.rs`). In theory single imports should
 833                         // always block globs, even if they are not yet resolved, so that this kind of
 834                         // self-inconsistent resolution never happens.
 835                         // Re-enable the assert when the issue is fixed.
 836                         // assert!(result[ns].get().is_err());
 837                     }
 838                 }
 839             }
 840         });
 841
 842         if all_ns_err {
 843             let mut all_ns_failed = true;
 844             self.r.per_ns(|this, ns| {
 845                 if !type_ns_only || ns == TypeNS {
 846                     let binding = this.resolve_ident_in_module(
 847                         module,
 848                         ident,
 849                         ns,
 850                         &import.parent_scope,
 851                         Some(finalize),
 852                         None,
 853                     );
 854                     if binding.is_ok() {
 855                         all_ns_failed = false;
 856                     }
 857                 }
 858             });
 859
 860             return if all_ns_failed {
 861                 let resolutions = match module {
 862                     ModuleOrUniformRoot::Module(module) => {
 863                         Some(self.r.resolutions(module).borrow())
 864                     }
 865                     _ => None,
 866                 };
 867                 let resolutions = resolutions.as_ref().into_iter().flat_map(|r| r.iter());
 868                 let names = resolutions
 869                     .filter_map(|(BindingKey { ident: i, .. }, resolution)| {
 870                         if *i == ident {
 871                             return None;
 872                         } // Never suggest the same name
 873                         match *resolution.borrow() {
 874                             NameResolution { binding: Some(name_binding), .. } => {
 875                                 match name_binding.kind {
 876                                     NameBindingKind::Import { binding, .. } => {
 877                                         match binding.kind {
 878                                             // Never suggest the name that has binding error
 879                                             // i.e., the name that cannot be previously resolved
 880                                             NameBindingKind::Res(Res::Err) => None,
 881                                             _ => Some(i.name),
 882                                         }
 883                                     }
 884                                     _ => Some(i.name),
 885                                 }
 886                             }
 887                             NameResolution { ref single_imports, .. }
 888                                 if single_imports.is_empty() =>
 889                             {
 890                                 None
 891                             }
 892                             _ => Some(i.name),
 893                         }
 894                     })
 895                     .collect::<Vec<Symbol>>();
 896
 897                 let lev_suggestion =
 898                     find_best_match_for_name(&names, ident.name, None).map(|suggestion| {
 899                         (
 900                             vec![(ident.span, suggestion.to_string())],
 901                             String::from("a similar name exists in the module"),
 902                             Applicability::MaybeIncorrect,
 903                         )
 904                     });
 905
 906                 let (suggestion, note) =
 907                     match self.check_for_module_export_macro(import, module, ident) {
 908                         Some((suggestion, note)) => (suggestion.or(lev_suggestion), note),
 909                         _ => (lev_suggestion, None),
 910                     };
 911
 912                 let label = match module {
 913                     ModuleOrUniformRoot::Module(module) => {
 914                         let module_str = module_to_string(module);
 915                         if let Some(module_str) = module_str {
 916                             format!("no `{}` in `{}`", ident, module_str)
 917                         } else {
 918                             format!("no `{}` in the root", ident)
 919                         }
 920                     }
 921                     _ => {
 922                         if !ident.is_path_segment_keyword() {
 923                             format!("no external crate `{}`", ident)
 924                         } else {
 925                             // HACK(eddyb) this shows up for `self` & `super`, which
 926                             // should work instead - for now keep the same error message.
 927                             format!("no `{}` in the root", ident)
 928                         }
 929                     }
 930                 };
 931
 932                 let parent_suggestion =
 933                     self.r.lookup_import_candidates(ident, TypeNS, &import.parent_scope, |_| true);
 934
 935                 Some(UnresolvedImportError {
 936                     span: import.span,
 937                     label: Some(label),
 938                     note,
 939                     suggestion,
 940                     candidate: if !parent_suggestion.is_empty() {
 941                         Some(parent_suggestion)
 942                     } else {
 943                         None
 944                     },
 945                 })
 946             } else {
 947                 // `resolve_ident_in_module` reported a privacy error.
 948                 None
 949             };
 950         }
 951
 952         let mut reexport_error = None;
 953         let mut any_successful_reexport = false;
 954         let mut crate_private_reexport = false;
 955         self.r.per_ns(|this, ns| {
 956             if let Ok(binding) = source_bindings[ns].get() {
 957                 if !binding.vis.is_at_least(import.expect_vis(), &*this) {
 958                     reexport_error = Some((ns, binding));
 959                     if let ty::Visibility::Restricted(binding_def_id) = binding.vis {
 960                         if binding_def_id.is_top_level_module() {
 961                             crate_private_reexport = true;
 962                         }
 963                     }
 964                 } else {
 965                     any_successful_reexport = true;
 966                 }
 967             }
 968         });
 969
 970         // All namespaces must be re-exported with extra visibility for an error to occur.
 971         if !any_successful_reexport {
 972             let (ns, binding) = reexport_error.unwrap();
 973             if pub_use_of_private_extern_crate_hack(import, binding) {
 974                 let msg = format!(
 975                     "extern crate `{}` is private, and cannot be \
 976                                    re-exported (error E0365), consider declaring with \
 977                                    `pub`",
 978                     ident
 979                 );
 980                 self.r.lint_buffer.buffer_lint(
 981                     PUB_USE_OF_PRIVATE_EXTERN_CRATE,
 982                     import_id,
 983                     import.span,
 984                     &msg,
 985                 );
 986             } else {
 987                 let error_msg = if crate_private_reexport {
 988                     format!(
 989                         "`{}` is only public within the crate, and cannot be re-exported outside",
 990                         ident
 991                     )
 992                 } else {
 993                     format!("`{}` is private, and cannot be re-exported", ident)
 994                 };
 995
 996                 if ns == TypeNS {
 997                     let label_msg = if crate_private_reexport {
 998                         format!("re-export of crate public `{}`", ident)
 999                     } else {
1000                         format!("re-export of private `{}`", ident)
1001                     };
1002
1003                     struct_span_err!(self.r.session, import.span, E0365, "{}", error_msg)
1004                         .span_label(import.span, label_msg)
1005                         .note(&format!("consider declaring type or module `{}` with `pub`", ident))
1006                         .emit();
1007                 } else {
1008                     let mut err =
1009                         struct_span_err!(self.r.session, import.span, E0364, "{error_msg}");
1010                     match binding.kind {
1011                         NameBindingKind::Res(Res::Def(DefKind::Macro(_), def_id))
1012                             // exclude decl_macro
1013                             if self.r.get_macro_by_def_id(def_id).macro_rules =>
1014                         {
1015                             err.span_help(
1016                                 binding.span,
1017                                 "consider adding a `#[macro_export]` to the macro in the imported module",
1018                             );
1019                         }
1020                         _ => {
1021                             err.span_note(
1022                                 import.span,
1023                                 &format!(
1024                                     "consider marking `{ident}` as `pub` in the imported module"
1025                                 ),
1026                             );
1027                         }
1028                     }
1029                     err.emit();
1030                 }
1031             }
1032         }
1033
1034         if import.module_path.len() <= 1 {
1035             // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
1036             // 2 segments, so the `resolve_path` above won't trigger it.
1037             let mut full_path = import.module_path.clone();
1038             full_path.push(Segment::from_ident(ident));
1039             self.r.per_ns(|this, ns| {
1040                 if let Ok(binding) = source_bindings[ns].get() {
1041                     this.lint_if_path_starts_with_module(Some(finalize), &full_path, Some(binding));
1042                 }
1043             });
1044         }
1045
1046         // Record what this import resolves to for later uses in documentation,
1047         // this may resolve to either a value or a type, but for documentation
1048         // purposes it's good enough to just favor one over the other.
1049         self.r.per_ns(|this, ns| {
1050             if let Ok(binding) = source_bindings[ns].get() {
1051                 this.import_res_map.entry(import_id).or_default()[ns] = Some(binding.res());
1052             }
1053         });
1054
1055         self.check_for_redundant_imports(ident, import, source_bindings, target_bindings, target);
1056
1057         debug!("(resolving single import) successfully resolved import");
1058         None
1059     }
1060
1061     fn check_for_redundant_imports(
1062         &mut self,
1063         ident: Ident,
1064         import: &'b Import<'b>,
1065         source_bindings: &PerNS<Cell<Result<&'b NameBinding<'b>, Determinacy>>>,
1066         target_bindings: &PerNS<Cell<Option<&'b NameBinding<'b>>>>,
1067         target: Ident,
1068     ) {
1069         // This function is only called for single imports.
1070         let ImportKind::Single { id, .. } = import.kind else { unreachable!() };
1071
1072         // Skip if the import was produced by a macro.
1073         if import.parent_scope.expansion != LocalExpnId::ROOT {
1074             return;
1075         }
1076
1077         // Skip if we are inside a named module (in contrast to an anonymous
1078         // module defined by a block).
1079         if let ModuleKind::Def(..) = import.parent_scope.module.kind {
1080             return;
1081         }
1082
1083         let mut is_redundant = PerNS { value_ns: None, type_ns: None, macro_ns: None };
1084
1085         let mut redundant_span = PerNS { value_ns: None, type_ns: None, macro_ns: None };
1086
1087         self.r.per_ns(|this, ns| {
1088             if let Ok(binding) = source_bindings[ns].get() {
1089                 if binding.res() == Res::Err {
1090                     return;
1091                 }
1092
1093                 match this.early_resolve_ident_in_lexical_scope(
1094                     target,
1095                     ScopeSet::All(ns, false),
1096                     &import.parent_scope,
1097                     None,
1098                     false,
1099                     target_bindings[ns].get(),
1100                 ) {
1101                     Ok(other_binding) => {
1102                         is_redundant[ns] = Some(
1103                             binding.res() == other_binding.res() && !other_binding.is_ambiguity(),
1104                         );
1105                         redundant_span[ns] = Some((other_binding.span, other_binding.is_import()));
1106                     }
1107                     Err(_) => is_redundant[ns] = Some(false),
1108                 }
1109             }
1110         });
1111
1112         if !is_redundant.is_empty() && is_redundant.present_items().all(|is_redundant| is_redundant)
1113         {
1114             let mut redundant_spans: Vec<_> = redundant_span.present_items().collect();
1115             redundant_spans.sort();
1116             redundant_spans.dedup();
1117             self.r.lint_buffer.buffer_lint_with_diagnostic(
1118                 UNUSED_IMPORTS,
1119                 id,
1120                 import.span,
1121                 &format!("the item `{}` is imported redundantly", ident),
1122                 BuiltinLintDiagnostics::RedundantImport(redundant_spans, ident),
1123             );
1124         }
1125     }
1126
1127     fn resolve_glob_import(&mut self, import: &'b Import<'b>) {
1128         // This function is only called for glob imports.
1129         let ImportKind::Glob { id, is_prelude, .. } = import.kind else { unreachable!() };
1130
1131         let ModuleOrUniformRoot::Module(module) = import.imported_module.get().unwrap() else {
1132             self.r.session.span_err(import.span, "cannot glob-import all possible crates");
1133             return;
1134         };
1135
1136         if module.is_trait() {
1137             self.r.session.span_err(import.span, "items in traits are not importable");
1138             return;
1139         } else if ptr::eq(module, import.parent_scope.module) {
1140             return;
1141         } else if is_prelude {
1142             self.r.prelude = Some(module);
1143             return;
1144         }
1145
1146         // Add to module's glob_importers
1147         module.glob_importers.borrow_mut().push(import);
1148
1149         // Ensure that `resolutions` isn't borrowed during `try_define`,
1150         // since it might get updated via a glob cycle.
1151         let bindings = self
1152             .r
1153             .resolutions(module)
1154             .borrow()
1155             .iter()
1156             .filter_map(|(key, resolution)| {
1157                 resolution.borrow().binding().map(|binding| (*key, binding))
1158             })
1159             .collect::<Vec<_>>();
1160         for (mut key, binding) in bindings {
1161             let scope = match key.ident.span.reverse_glob_adjust(module.expansion, import.span) {
1162                 Some(Some(def)) => self.r.expn_def_scope(def),
1163                 Some(None) => import.parent_scope.module,
1164                 None => continue,
1165             };
1166             if self.r.is_accessible_from(binding.vis, scope) {
1167                 let imported_binding = self.r.import(binding, import);
1168                 let _ = self.r.try_define(import.parent_scope.module, key, imported_binding);
1169             }
1170         }
1171
1172         // Record the destination of this import
1173         self.r.record_partial_res(id, PartialRes::new(module.res().unwrap()));
1174     }
1175
1176     // Miscellaneous post-processing, including recording re-exports,
1177     // reporting conflicts, and reporting unresolved imports.
1178     fn finalize_resolutions_in(&mut self, module: Module<'b>) {
1179         // Since import resolution is finished, globs will not define any more names.
1180         *module.globs.borrow_mut() = Vec::new();
1181
1182         if let Some(def_id) = module.opt_def_id() {
1183             let mut reexports = Vec::new();
1184
1185             module.for_each_child(self.r, |this, ident, _, binding| {
1186                 if let Some(res) = this.is_reexport(binding) {
1187                     reexports.push(ModChild {
1188                         ident,
1189                         res,
1190                         vis: binding.vis,
1191                         span: binding.span,
1192                         macro_rules: false,
1193                     });
1194                 }
1195             });
1196
1197             if !reexports.is_empty() {
1198                 // Call to `expect_local` should be fine because current
1199                 // code is only called for local modules.
1200                 self.r.reexport_map.insert(def_id.expect_local(), reexports);
1201             }
1202         }
1203     }
1204 }
1205
1206 fn import_path_to_string(names: &[Ident], import_kind: &ImportKind<'_>, span: Span) -> String {
1207     let pos = names.iter().position(|p| span == p.span && p.name != kw::PathRoot);
1208     let global = !names.is_empty() && names[0].name == kw::PathRoot;
1209     if let Some(pos) = pos {
1210         let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
1211         names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>())
1212     } else {
1213         let names = if global { &names[1..] } else { names };
1214         if names.is_empty() {
1215             import_kind_to_string(import_kind)
1216         } else {
1217             format!(
1218                 "{}::{}",
1219                 names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>()),
1220                 import_kind_to_string(import_kind),
1221             )
1222         }
1223     }
1224 }
1225
1226 fn import_kind_to_string(import_kind: &ImportKind<'_>) -> String {
1227     match import_kind {
1228         ImportKind::Single { source, .. } => source.to_string(),
1229         ImportKind::Glob { .. } => "*".to_string(),
1230         ImportKind::ExternCrate { .. } => "<extern crate>".to_string(),
1231         ImportKind::MacroUse => "#[macro_use]".to_string(),
1232         ImportKind::MacroExport => "#[macro_export]".to_string(),
1233     }
1234 }