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::Determinacy::{self, *};
   5 use crate::Namespace::*;
   6 use crate::{module_to_string, names_to_string, ImportSuggestion};
   7 use crate::{
   8     AmbiguityError, AmbiguityErrorMisc, AmbiguityKind, BindingKey, ModuleKind, ResolutionError,
   9     Resolver, Segment,
  10 };
  11 use crate::{Finalize, Module, ModuleOrUniformRoot, ParentScope, PerNS, ScopeSet};
  12 use crate::{NameBinding, NameBindingKind, PathResult};
  13
  14 use rustc_ast::NodeId;
  15 use rustc_data_structures::fx::FxHashSet;
  16 use rustc_data_structures::intern::Interned;
  17 use rustc_errors::{pluralize, struct_span_err, Applicability, MultiSpan};
  18 use rustc_hir::def::{self, DefKind, PartialRes};
  19 use rustc_middle::metadata::ModChild;
  20 use rustc_middle::span_bug;
  21 use rustc_middle::ty;
  22 use rustc_session::lint::builtin::{PUB_USE_OF_PRIVATE_EXTERN_CRATE, UNUSED_IMPORTS};
  23 use rustc_session::lint::BuiltinLintDiagnostics;
  24 use rustc_span::hygiene::LocalExpnId;
  25 use rustc_span::lev_distance::find_best_match_for_name;
  26 use rustc_span::symbol::{kw, Ident, Symbol};
  27 use rustc_span::Span;
  28
  29 use std::cell::Cell;
  30 use std::{mem, ptr};
  31
  32 type Res = def::Res<NodeId>;
  33
  34 /// Contains data for specific kinds of imports.
  35 #[derive(Clone)]
  36 pub enum ImportKind<'a> {
  37     Single {
  38         /// `source` in `use prefix::source as target`.
  39         source: Ident,
  40         /// `target` in `use prefix::source as target`.
  41         target: Ident,
  42         /// Bindings to which `source` refers to.
  43         source_bindings: PerNS<Cell<Result<&'a NameBinding<'a>, Determinacy>>>,
  44         /// Bindings introduced by `target`.
  45         target_bindings: PerNS<Cell<Option<&'a NameBinding<'a>>>>,
  46         /// `true` for `...::{self [as target]}` imports, `false` otherwise.
  47         type_ns_only: bool,
  48         /// Did this import result from a nested import? ie. `use foo::{bar, baz};`
  49         nested: bool,
  50         /// The ID of the `UseTree` that imported this `Import`.
  51         ///
  52         /// In the case where the `Import` was expanded from a "nested" use tree,
  53         /// this id is the ID of the leaf tree. For example:
  54         ///
  55         /// ```ignore (pacify the merciless tidy)
  56         /// use foo::bar::{a, b}
  57         /// ```
  58         ///
  59         /// If this is the import for `foo::bar::a`, we would have the ID of the `UseTree`
  60         /// for `a` in this field.
  61         id: 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                 // Ignore the following to avoid an infinite loop while printing.
  92                 source_bindings: _,
  93                 target_bindings: _,
  94             } => f
  95                 .debug_struct("Single")
  96                 .field("source", source)
  97                 .field("target", target)
  98                 .field("type_ns_only", type_ns_only)
  99                 .field("nested", nested)
 100                 .field("id", id)
 101                 .finish_non_exhaustive(),
 102             Glob { ref is_prelude, ref max_vis, ref id } => f
 103                 .debug_struct("Glob")
 104                 .field("is_prelude", is_prelude)
 105                 .field("max_vis", max_vis)
 106                 .field("id", id)
 107                 .finish(),
 108             ExternCrate { ref source, ref target, ref id } => f
 109                 .debug_struct("ExternCrate")
 110                 .field("source", source)
 111                 .field("target", target)
 112                 .field("id", id)
 113                 .finish(),
 114             MacroUse => f.debug_struct("MacroUse").finish(),
 115             MacroExport => f.debug_struct("MacroExport").finish(),
 116         }
 117     }
 118 }
 119
 120 /// One import.
 121 #[derive(Debug, Clone)]
 122 pub(crate) struct Import<'a> {
 123     pub kind: ImportKind<'a>,
 124
 125     /// Node ID of the "root" use item -- this is always the same as `ImportKind`'s `id`
 126     /// (if it exists) except in the case of "nested" use trees, in which case
 127     /// it will be the ID of the root use tree. e.g., in the example
 128     /// ```ignore (incomplete code)
 129     /// use foo::bar::{a, b}
 130     /// ```
 131     /// this would be the ID of the `use foo::bar` `UseTree` node.
 132     /// In case of imports without their own node ID it's the closest node that can be used,
 133     /// for example, for reporting lints.
 134     pub root_id: NodeId,
 135
 136     /// Span of the entire use statement.
 137     pub use_span: Span,
 138
 139     /// Span of the entire use statement with attributes.
 140     pub use_span_with_attributes: Span,
 141
 142     /// Did the use statement have any attributes?
 143     pub has_attributes: bool,
 144
 145     /// Span of this use tree.
 146     pub span: Span,
 147
 148     /// Span of the *root* use tree (see `root_id`).
 149     pub root_span: Span,
 150
 151     pub parent_scope: ParentScope<'a>,
 152     pub module_path: Vec<Segment>,
 153     /// The resolution of `module_path`.
 154     pub imported_module: Cell<Option<ModuleOrUniformRoot<'a>>>,
 155     pub vis: Cell<Option<ty::Visibility>>,
 156     pub used: Cell<bool>,
 157 }
 158
 159 impl<'a> Import<'a> {
 160     pub fn is_glob(&self) -> bool {
 161         matches!(self.kind, ImportKind::Glob { .. })
 162     }
 163
 164     pub fn is_nested(&self) -> bool {
 165         match self.kind {
 166             ImportKind::Single { nested, .. } => nested,
 167             _ => false,
 168         }
 169     }
 170
 171     pub(crate) fn expect_vis(&self) -> ty::Visibility {
 172         self.vis.get().expect("encountered cleared import visibility")
 173     }
 174
 175     pub(crate) fn id(&self) -> Option<NodeId> {
 176         match self.kind {
 177             ImportKind::Single { id, .. }
 178             | ImportKind::Glob { id, .. }
 179             | ImportKind::ExternCrate { id, .. } => Some(id),
 180             ImportKind::MacroUse | ImportKind::MacroExport => None,
 181         }
 182     }
 183 }
 184
 185 /// Records information about the resolution of a name in a namespace of a module.
 186 #[derive(Clone, Default, Debug)]
 187 pub(crate) struct NameResolution<'a> {
 188     /// Single imports that may define the name in the namespace.
 189     /// Imports are arena-allocated, so it's ok to use pointers as keys.
 190     pub single_imports: FxHashSet<Interned<'a, Import<'a>>>,
 191     /// The least shadowable known binding for this name, or None if there are no known bindings.
 192     pub binding: Option<&'a NameBinding<'a>>,
 193     pub shadowed_glob: Option<&'a NameBinding<'a>>,
 194 }
 195
 196 impl<'a> NameResolution<'a> {
 197     /// Returns the binding for the name if it is known or None if it not known.
 198     pub(crate) fn binding(&self) -> Option<&'a NameBinding<'a>> {
 199         self.binding.and_then(|binding| {
 200             if !binding.is_glob_import() || self.single_imports.is_empty() {
 201                 Some(binding)
 202             } else {
 203                 None
 204             }
 205         })
 206     }
 207
 208     pub(crate) fn add_single_import(&mut self, import: &'a Import<'a>) {
 209         self.single_imports.insert(Interned::new_unchecked(import));
 210     }
 211 }
 212
 213 // Reexports of the form `pub use foo as bar;` where `foo` is `extern crate foo;`
 214 // are permitted for backward-compatibility under a deprecation lint.
 215 fn pub_use_of_private_extern_crate_hack(import: &Import<'_>, binding: &NameBinding<'_>) -> bool {
 216     match (&import.kind, &binding.kind) {
 217         (
 218             ImportKind::Single { .. },
 219             NameBindingKind::Import {
 220                 import: Import { kind: ImportKind::ExternCrate { .. }, .. },
 221                 ..
 222             },
 223         ) => import.expect_vis().is_public(),
 224         _ => false,
 225     }
 226 }
 227
 228 impl<'a> Resolver<'a> {
 229     /// Given a binding and an import that resolves to it,
 230     /// return the corresponding binding defined by the import.
 231     pub(crate) fn import(
 232         &self,
 233         binding: &'a NameBinding<'a>,
 234         import: &'a Import<'a>,
 235     ) -> &'a NameBinding<'a> {
 236         let import_vis = import.expect_vis().to_def_id();
 237         let vis = if binding.vis.is_at_least(import_vis, self)
 238             || pub_use_of_private_extern_crate_hack(import, binding)
 239         {
 240             import_vis
 241         } else {
 242             binding.vis
 243         };
 244
 245         if let ImportKind::Glob { ref max_vis, .. } = import.kind {
 246             if vis == import_vis
 247                 || max_vis.get().map_or(true, |max_vis| vis.is_at_least(max_vis, self))
 248             {
 249                 max_vis.set(Some(vis.expect_local()))
 250             }
 251         }
 252
 253         self.arenas.alloc_name_binding(NameBinding {
 254             kind: NameBindingKind::Import { binding, import, used: Cell::new(false) },
 255             ambiguity: None,
 256             span: import.span,
 257             vis,
 258             expansion: import.parent_scope.expansion,
 259         })
 260     }
 261
 262     /// Define the name or return the existing binding if there is a collision.
 263     pub(crate) fn try_define(
 264         &mut self,
 265         module: Module<'a>,
 266         key: BindingKey,
 267         binding: &'a NameBinding<'a>,
 268     ) -> Result<(), &'a NameBinding<'a>> {
 269         let res = binding.res();
 270         self.check_reserved_macro_name(key.ident, res);
 271         self.set_binding_parent_module(binding, module);
 272         self.update_resolution(module, key, |this, resolution| {
 273             if let Some(old_binding) = resolution.binding {
 274                 if res == Res::Err && old_binding.res() != Res::Err {
 275                     // Do not override real bindings with `Res::Err`s from error recovery.
 276                     return Ok(());
 277                 }
 278                 match (old_binding.is_glob_import(), binding.is_glob_import()) {
 279                     (true, true) => {
 280                         if res != old_binding.res() {
 281                             resolution.binding = Some(this.ambiguity(
 282                                 AmbiguityKind::GlobVsGlob,
 283                                 old_binding,
 284                                 binding,
 285                             ));
 286                         } else if !old_binding.vis.is_at_least(binding.vis, &*this) {
 287                             // We are glob-importing the same item but with greater visibility.
 288                             resolution.binding = Some(binding);
 289                         }
 290                     }
 291                     (old_glob @ true, false) | (old_glob @ false, true) => {
 292                         let (glob_binding, nonglob_binding) =
 293                             if old_glob { (old_binding, binding) } else { (binding, old_binding) };
 294                         if glob_binding.res() != nonglob_binding.res()
 295                             && key.ns == MacroNS
 296                             && nonglob_binding.expansion != LocalExpnId::ROOT
 297                         {
 298                             resolution.binding = Some(this.ambiguity(
 299                                 AmbiguityKind::GlobVsExpanded,
 300                                 nonglob_binding,
 301                                 glob_binding,
 302                             ));
 303                         } else {
 304                             resolution.binding = Some(nonglob_binding);
 305                         }
 306                         resolution.shadowed_glob = Some(glob_binding);
 307                     }
 308                     (false, false) => {
 309                         return Err(old_binding);
 310                     }
 311                 }
 312             } else {
 313                 resolution.binding = Some(binding);
 314             }
 315
 316             Ok(())
 317         })
 318     }
 319
 320     fn ambiguity(
 321         &self,
 322         kind: AmbiguityKind,
 323         primary_binding: &'a NameBinding<'a>,
 324         secondary_binding: &'a NameBinding<'a>,
 325     ) -> &'a NameBinding<'a> {
 326         self.arenas.alloc_name_binding(NameBinding {
 327             ambiguity: Some((secondary_binding, kind)),
 328             ..primary_binding.clone()
 329         })
 330     }
 331
 332     // Use `f` to mutate the resolution of the name in the module.
 333     // If the resolution becomes a success, define it in the module's glob importers.
 334     fn update_resolution<T, F>(&mut self, module: Module<'a>, key: BindingKey, f: F) -> T
 335     where
 336         F: FnOnce(&mut Resolver<'a>, &mut NameResolution<'a>) -> T,
 337     {
 338         // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
 339         // during which the resolution might end up getting re-defined via a glob cycle.
 340         let (binding, t) = {
 341             let resolution = &mut *self.resolution(module, key).borrow_mut();
 342             let old_binding = resolution.binding();
 343
 344             let t = f(self, resolution);
 345
 346             match resolution.binding() {
 347                 _ if old_binding.is_some() => return t,
 348                 None => return t,
 349                 Some(binding) => match old_binding {
 350                     Some(old_binding) if ptr::eq(old_binding, binding) => return t,
 351                     _ => (binding, t),
 352                 },
 353             }
 354         };
 355
 356         // Define `binding` in `module`s glob importers.
 357         for import in module.glob_importers.borrow_mut().iter() {
 358             let mut ident = key.ident;
 359             let scope = match ident.span.reverse_glob_adjust(module.expansion, import.span) {
 360                 Some(Some(def)) => self.expn_def_scope(def),
 361                 Some(None) => import.parent_scope.module,
 362                 None => continue,
 363             };
 364             if self.is_accessible_from(binding.vis, scope) {
 365                 let imported_binding = self.import(binding, import);
 366                 let key = BindingKey { ident, ..key };
 367                 let _ = self.try_define(import.parent_scope.module, key, imported_binding);
 368             }
 369         }
 370
 371         t
 372     }
 373
 374     // Define a dummy resolution containing a `Res::Err` as a placeholder for a failed resolution,
 375     // also mark such failed imports as used to avoid duplicate diagnostics.
 376     fn import_dummy_binding(&mut self, import: &'a Import<'a>) {
 377         if let ImportKind::Single { target, ref target_bindings, .. } = import.kind {
 378             if target_bindings.iter().any(|binding| binding.get().is_some()) {
 379                 return; // Has resolution, do not create the dummy binding
 380             }
 381             let dummy_binding = self.dummy_binding;
 382             let dummy_binding = self.import(dummy_binding, import);
 383             self.per_ns(|this, ns| {
 384                 let key = this.new_key(target, ns);
 385                 let _ = this.try_define(import.parent_scope.module, key, dummy_binding);
 386             });
 387             self.record_use(target, dummy_binding, false);
 388         } else if import.imported_module.get().is_none() {
 389             import.used.set(true);
 390             if let Some(id) = import.id() {
 391                 self.used_imports.insert(id);
 392             }
 393         }
 394     }
 395 }
 396
 397 /// An error that may be transformed into a diagnostic later. Used to combine multiple unresolved
 398 /// import errors within the same use tree into a single diagnostic.
 399 #[derive(Debug, Clone)]
 400 struct UnresolvedImportError {
 401     span: Span,
 402     label: Option<String>,
 403     note: Option<String>,
 404     suggestion: Option<Suggestion>,
 405     candidates: Option<Vec<ImportSuggestion>>,
 406 }
 407
 408 pub struct ImportResolver<'a, 'b> {
 409     pub r: &'a mut Resolver<'b>,
 410 }
 411
 412 impl<'a, 'b> ImportResolver<'a, 'b> {
 413     // Import resolution
 414     //
 415     // This is a fixed-point algorithm. We resolve imports until our efforts
 416     // are stymied by an unresolved import; then we bail out of the current
 417     // module and continue. We terminate successfully once no more imports
 418     // remain or unsuccessfully when no forward progress in resolving imports
 419     // is made.
 420
 421     /// Resolves all imports for the crate. This method performs the fixed-
 422     /// point iteration.
 423     pub fn resolve_imports(&mut self) {
 424         let mut prev_num_indeterminates = self.r.indeterminate_imports.len() + 1;
 425         while self.r.indeterminate_imports.len() < prev_num_indeterminates {
 426             prev_num_indeterminates = self.r.indeterminate_imports.len();
 427             for import in mem::take(&mut self.r.indeterminate_imports) {
 428                 match self.resolve_import(&import) {
 429                     true => self.r.determined_imports.push(import),
 430                     false => self.r.indeterminate_imports.push(import),
 431                 }
 432             }
 433         }
 434     }
 435
 436     pub fn finalize_imports(&mut self) {
 437         for module in self.r.arenas.local_modules().iter() {
 438             self.finalize_resolutions_in(module);
 439         }
 440
 441         let mut seen_spans = FxHashSet::default();
 442         let mut errors = vec![];
 443         let mut prev_root_id: NodeId = NodeId::from_u32(0);
 444         let determined_imports = mem::take(&mut self.r.determined_imports);
 445         let indeterminate_imports = mem::take(&mut self.r.indeterminate_imports);
 446
 447         for (is_indeterminate, import) in determined_imports
 448             .into_iter()
 449             .map(|i| (false, i))
 450             .chain(indeterminate_imports.into_iter().map(|i| (true, i)))
 451         {
 452             let unresolved_import_error = self.finalize_import(import);
 453
 454             // If this import is unresolved then create a dummy import
 455             // resolution for it so that later resolve stages won't complain.
 456             self.r.import_dummy_binding(import);
 457
 458             if let Some(err) = unresolved_import_error {
 459                 if let ImportKind::Single { source, ref source_bindings, .. } = import.kind {
 460                     if source.name == kw::SelfLower {
 461                         // Silence `unresolved import` error if E0429 is already emitted
 462                         if let Err(Determined) = source_bindings.value_ns.get() {
 463                             continue;
 464                         }
 465                     }
 466                 }
 467
 468                 if prev_root_id.as_u32() != 0
 469                     && prev_root_id.as_u32() != import.root_id.as_u32()
 470                     && !errors.is_empty()
 471                 {
 472                     // In the case of a new import line, throw a diagnostic message
 473                     // for the previous line.
 474                     self.throw_unresolved_import_error(errors);
 475                     errors = vec![];
 476                 }
 477                 if seen_spans.insert(err.span) {
 478                     errors.push((import, err));
 479                     prev_root_id = import.root_id;
 480                 }
 481             } else if is_indeterminate {
 482                 let path = import_path_to_string(
 483                     &import.module_path.iter().map(|seg| seg.ident).collect::<Vec<_>>(),
 484                     &import.kind,
 485                     import.span,
 486                 );
 487                 let err = UnresolvedImportError {
 488                     span: import.span,
 489                     label: None,
 490                     note: None,
 491                     suggestion: None,
 492                     candidates: None,
 493                 };
 494                 // FIXME: there should be a better way of doing this than
 495                 // formatting this as a string then checking for `::`
 496                 if path.contains("::") {
 497                     errors.push((import, err))
 498                 }
 499             }
 500         }
 501
 502         if !errors.is_empty() {
 503             self.throw_unresolved_import_error(errors);
 504         }
 505     }
 506
 507     fn throw_unresolved_import_error(&self, errors: Vec<(&Import<'_>, UnresolvedImportError)>) {
 508         if errors.is_empty() {
 509             return;
 510         }
 511
 512         /// Upper limit on the number of `span_label` messages.
 513         const MAX_LABEL_COUNT: usize = 10;
 514
 515         let span = MultiSpan::from_spans(errors.iter().map(|(_, err)| err.span).collect());
 516         let paths = errors
 517             .iter()
 518             .map(|(import, err)| {
 519                 let path = import_path_to_string(
 520                     &import.module_path.iter().map(|seg| seg.ident).collect::<Vec<_>>(),
 521                     &import.kind,
 522                     err.span,
 523                 );
 524                 format!("`{path}`")
 525             })
 526             .collect::<Vec<_>>();
 527         let msg = format!("unresolved import{} {}", pluralize!(paths.len()), paths.join(", "),);
 528
 529         let mut diag = struct_span_err!(self.r.session, span, E0432, "{}", &msg);
 530
 531         if let Some((_, UnresolvedImportError { note: Some(note), .. })) = errors.iter().last() {
 532             diag.note(note);
 533         }
 534
 535         for (import, err) in errors.into_iter().take(MAX_LABEL_COUNT) {
 536             if let Some(label) = err.label {
 537                 diag.span_label(err.span, label);
 538             }
 539
 540             if let Some((suggestions, msg, applicability)) = err.suggestion {
 541                 if suggestions.is_empty() {
 542                     diag.help(&msg);
 543                     continue;
 544                 }
 545                 diag.multipart_suggestion(&msg, suggestions, applicability);
 546             }
 547
 548             if let Some(candidates) = &err.candidates {
 549                 match &import.kind {
 550                     ImportKind::Single { nested: false, source, target, .. } => import_candidates(
 551                         self.r.session,
 552                         &self.r.untracked.source_span,
 553                         &mut diag,
 554                         Some(err.span),
 555                         &candidates,
 556                         DiagnosticMode::Import,
 557                         (source != target)
 558                             .then(|| format!(" as {target}"))
 559                             .as_deref()
 560                             .unwrap_or(""),
 561                     ),
 562                     ImportKind::Single { nested: true, source, target, .. } => {
 563                         import_candidates(
 564                             self.r.session,
 565                             &self.r.untracked.source_span,
 566                             &mut diag,
 567                             None,
 568                             &candidates,
 569                             DiagnosticMode::Normal,
 570                             (source != target)
 571                                 .then(|| format!(" as {target}"))
 572                                 .as_deref()
 573                                 .unwrap_or(""),
 574                         );
 575                     }
 576                     _ => {}
 577                 }
 578             }
 579         }
 580
 581         diag.emit();
 582     }
 583
 584     /// Attempts to resolve the given import, returning true if its resolution is determined.
 585     /// If successful, the resolved bindings are written into the module.
 586     fn resolve_import(&mut self, import: &'b Import<'b>) -> bool {
 587         debug!(
 588             "(resolving import for module) resolving import `{}::...` in `{}`",
 589             Segment::names_to_string(&import.module_path),
 590             module_to_string(import.parent_scope.module).unwrap_or_else(|| "???".to_string()),
 591         );
 592
 593         let module = if let Some(module) = import.imported_module.get() {
 594             module
 595         } else {
 596             // For better failure detection, pretend that the import will
 597             // not define any names while resolving its module path.
 598             let orig_vis = import.vis.take();
 599             let path_res =
 600                 self.r.maybe_resolve_path(&import.module_path, None, &import.parent_scope);
 601             import.vis.set(orig_vis);
 602
 603             match path_res {
 604                 PathResult::Module(module) => module,
 605                 PathResult::Indeterminate => return false,
 606                 PathResult::NonModule(..) | PathResult::Failed { .. } => return true,
 607             }
 608         };
 609
 610         import.imported_module.set(Some(module));
 611         let (source, target, source_bindings, target_bindings, type_ns_only) = match import.kind {
 612             ImportKind::Single {
 613                 source,
 614                 target,
 615                 ref source_bindings,
 616                 ref target_bindings,
 617                 type_ns_only,
 618                 ..
 619             } => (source, target, source_bindings, target_bindings, type_ns_only),
 620             ImportKind::Glob { .. } => {
 621                 self.resolve_glob_import(import);
 622                 return true;
 623             }
 624             _ => unreachable!(),
 625         };
 626
 627         let mut indeterminate = false;
 628         self.r.per_ns(|this, ns| {
 629             if !type_ns_only || ns == TypeNS {
 630                 if let Err(Undetermined) = source_bindings[ns].get() {
 631                     // For better failure detection, pretend that the import will
 632                     // not define any names while resolving its module path.
 633                     let orig_vis = import.vis.take();
 634                     let binding = this.resolve_ident_in_module(
 635                         module,
 636                         source,
 637                         ns,
 638                         &import.parent_scope,
 639                         None,
 640                         None,
 641                     );
 642                     import.vis.set(orig_vis);
 643                     source_bindings[ns].set(binding);
 644                 } else {
 645                     return;
 646                 };
 647
 648                 let parent = import.parent_scope.module;
 649                 match source_bindings[ns].get() {
 650                     Err(Undetermined) => indeterminate = true,
 651                     // Don't update the resolution, because it was never added.
 652                     Err(Determined) if target.name == kw::Underscore => {}
 653                     Ok(binding) if binding.is_importable() => {
 654                         let imported_binding = this.import(binding, import);
 655                         target_bindings[ns].set(Some(imported_binding));
 656                         this.define(parent, target, ns, imported_binding);
 657                     }
 658                     source_binding @ (Ok(..) | Err(Determined)) => {
 659                         if source_binding.is_ok() {
 660                             let msg = format!("`{}` is not directly importable", target);
 661                             struct_span_err!(this.session, import.span, E0253, "{}", &msg)
 662                                 .span_label(import.span, "cannot be imported directly")
 663                                 .emit();
 664                         }
 665                         let key = this.new_key(target, ns);
 666                         this.update_resolution(parent, key, |_, resolution| {
 667                             resolution.single_imports.remove(&Interned::new_unchecked(import));
 668                         });
 669                     }
 670                 }
 671             }
 672         });
 673
 674         !indeterminate
 675     }
 676
 677     /// Performs final import resolution, consistency checks and error reporting.
 678     ///
 679     /// Optionally returns an unresolved import error. This error is buffered and used to
 680     /// consolidate multiple unresolved import errors into a single diagnostic.
 681     fn finalize_import(&mut self, import: &'b Import<'b>) -> Option<UnresolvedImportError> {
 682         let orig_vis = import.vis.take();
 683         let ignore_binding = match &import.kind {
 684             ImportKind::Single { target_bindings, .. } => target_bindings[TypeNS].get(),
 685             _ => None,
 686         };
 687         let prev_ambiguity_errors_len = self.r.ambiguity_errors.len();
 688         let finalize = Finalize::with_root_span(import.root_id, import.span, import.root_span);
 689         let path_res = self.r.resolve_path(
 690             &import.module_path,
 691             None,
 692             &import.parent_scope,
 693             Some(finalize),
 694             ignore_binding,
 695         );
 696
 697         let no_ambiguity = self.r.ambiguity_errors.len() == prev_ambiguity_errors_len;
 698         import.vis.set(orig_vis);
 699         let module = match path_res {
 700             PathResult::Module(module) => {
 701                 // Consistency checks, analogous to `finalize_macro_resolutions`.
 702                 if let Some(initial_module) = import.imported_module.get() {
 703                     if !ModuleOrUniformRoot::same_def(module, initial_module) && no_ambiguity {
 704                         span_bug!(import.span, "inconsistent resolution for an import");
 705                     }
 706                 } else if self.r.privacy_errors.is_empty() {
 707                     let msg = "cannot determine resolution for the import";
 708                     let msg_note = "import resolution is stuck, try simplifying other imports";
 709                     self.r.session.struct_span_err(import.span, msg).note(msg_note).emit();
 710                 }
 711
 712                 module
 713             }
 714             PathResult::Failed { is_error_from_last_segment: false, span, label, suggestion } => {
 715                 if no_ambiguity {
 716                     assert!(import.imported_module.get().is_none());
 717                     self.r
 718                         .report_error(span, ResolutionError::FailedToResolve { label, suggestion });
 719                 }
 720                 return None;
 721             }
 722             PathResult::Failed { is_error_from_last_segment: true, span, label, suggestion } => {
 723                 if no_ambiguity {
 724                     assert!(import.imported_module.get().is_none());
 725                     let err = match self.make_path_suggestion(
 726                         span,
 727                         import.module_path.clone(),
 728                         &import.parent_scope,
 729                     ) {
 730                         Some((suggestion, note)) => UnresolvedImportError {
 731                             span,
 732                             label: None,
 733                             note,
 734                             suggestion: Some((
 735                                 vec![(span, Segment::names_to_string(&suggestion))],
 736                                 String::from("a similar path exists"),
 737                                 Applicability::MaybeIncorrect,
 738                             )),
 739                             candidates: None,
 740                         },
 741                         None => UnresolvedImportError {
 742                             span,
 743                             label: Some(label),
 744                             note: None,
 745                             suggestion,
 746                             candidates: None,
 747                         },
 748                     };
 749                     return Some(err);
 750                 }
 751                 return None;
 752             }
 753             PathResult::NonModule(_) => {
 754                 if no_ambiguity {
 755                     assert!(import.imported_module.get().is_none());
 756                 }
 757                 // The error was already reported earlier.
 758                 return None;
 759             }
 760             PathResult::Indeterminate => unreachable!(),
 761         };
 762
 763         let (ident, target, source_bindings, target_bindings, type_ns_only, import_id) =
 764             match import.kind {
 765                 ImportKind::Single {
 766                     source,
 767                     target,
 768                     ref source_bindings,
 769                     ref target_bindings,
 770                     type_ns_only,
 771                     id,
 772                     ..
 773                 } => (source, target, source_bindings, target_bindings, type_ns_only, id),
 774                 ImportKind::Glob { is_prelude, ref max_vis, id } => {
 775                     if import.module_path.len() <= 1 {
 776                         // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
 777                         // 2 segments, so the `resolve_path` above won't trigger it.
 778                         let mut full_path = import.module_path.clone();
 779                         full_path.push(Segment::from_ident(Ident::empty()));
 780                         self.r.lint_if_path_starts_with_module(Some(finalize), &full_path, None);
 781                     }
 782
 783                     if let ModuleOrUniformRoot::Module(module) = module {
 784                         if ptr::eq(module, import.parent_scope.module) {
 785                             // Importing a module into itself is not allowed.
 786                             return Some(UnresolvedImportError {
 787                                 span: import.span,
 788                                 label: Some(String::from(
 789                                     "cannot glob-import a module into itself",
 790                                 )),
 791                                 note: None,
 792                                 suggestion: None,
 793                                 candidates: None,
 794                             });
 795                         }
 796                     }
 797                     if !is_prelude
 798                     && let Some(max_vis) = max_vis.get()
 799                     && !max_vis.is_at_least(import.expect_vis(), &*self.r)
 800                 {
 801                     let msg = "glob import doesn't reexport anything because no candidate is public enough";
 802                     self.r.lint_buffer.buffer_lint(UNUSED_IMPORTS, id, import.span, msg);
 803                 }
 804                     return None;
 805                 }
 806                 _ => unreachable!(),
 807             };
 808
 809         let mut all_ns_err = true;
 810         self.r.per_ns(|this, ns| {
 811             if !type_ns_only || ns == TypeNS {
 812                 let orig_vis = import.vis.take();
 813                 let binding = this.resolve_ident_in_module(
 814                     module,
 815                     ident,
 816                     ns,
 817                     &import.parent_scope,
 818                     Some(Finalize { report_private: false, ..finalize }),
 819                     target_bindings[ns].get(),
 820                 );
 821                 import.vis.set(orig_vis);
 822
 823                 match binding {
 824                     Ok(binding) => {
 825                         // Consistency checks, analogous to `finalize_macro_resolutions`.
 826                         let initial_binding = source_bindings[ns].get().map(|initial_binding| {
 827                             all_ns_err = false;
 828                             if let Some(target_binding) = target_bindings[ns].get() {
 829                                 if target.name == kw::Underscore
 830                                     && initial_binding.is_extern_crate()
 831                                     && !initial_binding.is_import()
 832                                 {
 833                                     this.record_use(
 834                                         ident,
 835                                         target_binding,
 836                                         import.module_path.is_empty(),
 837                                     );
 838                                 }
 839                             }
 840                             initial_binding
 841                         });
 842                         let res = binding.res();
 843                         if let Ok(initial_binding) = initial_binding {
 844                             let initial_res = initial_binding.res();
 845                             if res != initial_res && this.ambiguity_errors.is_empty() {
 846                                 this.ambiguity_errors.push(AmbiguityError {
 847                                     kind: AmbiguityKind::Import,
 848                                     ident,
 849                                     b1: initial_binding,
 850                                     b2: binding,
 851                                     misc1: AmbiguityErrorMisc::None,
 852                                     misc2: AmbiguityErrorMisc::None,
 853                                 });
 854                             }
 855                         } else if res != Res::Err
 856                             && this.ambiguity_errors.is_empty()
 857                             && this.privacy_errors.is_empty()
 858                         {
 859                             let msg = "cannot determine resolution for the import";
 860                             let msg_note =
 861                                 "import resolution is stuck, try simplifying other imports";
 862                             this.session.struct_span_err(import.span, msg).note(msg_note).emit();
 863                         }
 864                     }
 865                     Err(..) => {
 866                         // FIXME: This assert may fire if public glob is later shadowed by a private
 867                         // single import (see test `issue-55884-2.rs`). In theory single imports should
 868                         // always block globs, even if they are not yet resolved, so that this kind of
 869                         // self-inconsistent resolution never happens.
 870                         // Re-enable the assert when the issue is fixed.
 871                         // assert!(result[ns].get().is_err());
 872                     }
 873                 }
 874             }
 875         });
 876
 877         if all_ns_err {
 878             let mut all_ns_failed = true;
 879             self.r.per_ns(|this, ns| {
 880                 if !type_ns_only || ns == TypeNS {
 881                     let binding = this.resolve_ident_in_module(
 882                         module,
 883                         ident,
 884                         ns,
 885                         &import.parent_scope,
 886                         Some(finalize),
 887                         None,
 888                     );
 889                     if binding.is_ok() {
 890                         all_ns_failed = false;
 891                     }
 892                 }
 893             });
 894
 895             return if all_ns_failed {
 896                 let resolutions = match module {
 897                     ModuleOrUniformRoot::Module(module) => {
 898                         Some(self.r.resolutions(module).borrow())
 899                     }
 900                     _ => None,
 901                 };
 902                 let resolutions = resolutions.as_ref().into_iter().flat_map(|r| r.iter());
 903                 let names = resolutions
 904                     .filter_map(|(BindingKey { ident: i, .. }, resolution)| {
 905                         if i.name == ident.name {
 906                             return None;
 907                         } // Never suggest the same name
 908                         match *resolution.borrow() {
 909                             NameResolution { binding: Some(name_binding), .. } => {
 910                                 match name_binding.kind {
 911                                     NameBindingKind::Import { binding, .. } => {
 912                                         match binding.kind {
 913                                             // Never suggest the name that has binding error
 914                                             // i.e., the name that cannot be previously resolved
 915                                             NameBindingKind::Res(Res::Err) => None,
 916                                             _ => Some(i.name),
 917                                         }
 918                                     }
 919                                     _ => Some(i.name),
 920                                 }
 921                             }
 922                             NameResolution { ref single_imports, .. }
 923                                 if single_imports.is_empty() =>
 924                             {
 925                                 None
 926                             }
 927                             _ => Some(i.name),
 928                         }
 929                     })
 930                     .collect::<Vec<Symbol>>();
 931
 932                 let lev_suggestion =
 933                     find_best_match_for_name(&names, ident.name, None).map(|suggestion| {
 934                         (
 935                             vec![(ident.span, suggestion.to_string())],
 936                             String::from("a similar name exists in the module"),
 937                             Applicability::MaybeIncorrect,
 938                         )
 939                     });
 940
 941                 let (suggestion, note) =
 942                     match self.check_for_module_export_macro(import, module, ident) {
 943                         Some((suggestion, note)) => (suggestion.or(lev_suggestion), note),
 944                         _ => (lev_suggestion, None),
 945                     };
 946
 947                 let label = match module {
 948                     ModuleOrUniformRoot::Module(module) => {
 949                         let module_str = module_to_string(module);
 950                         if let Some(module_str) = module_str {
 951                             format!("no `{}` in `{}`", ident, module_str)
 952                         } else {
 953                             format!("no `{}` in the root", ident)
 954                         }
 955                     }
 956                     _ => {
 957                         if !ident.is_path_segment_keyword() {
 958                             format!("no external crate `{}`", ident)
 959                         } else {
 960                             // HACK(eddyb) this shows up for `self` & `super`, which
 961                             // should work instead - for now keep the same error message.
 962                             format!("no `{}` in the root", ident)
 963                         }
 964                     }
 965                 };
 966
 967                 let parent_suggestion =
 968                     self.r.lookup_import_candidates(ident, TypeNS, &import.parent_scope, |_| true);
 969
 970                 Some(UnresolvedImportError {
 971                     span: import.span,
 972                     label: Some(label),
 973                     note,
 974                     suggestion,
 975                     candidates: if !parent_suggestion.is_empty() {
 976                         Some(parent_suggestion)
 977                     } else {
 978                         None
 979                     },
 980                 })
 981             } else {
 982                 // `resolve_ident_in_module` reported a privacy error.
 983                 None
 984             };
 985         }
 986
 987         let mut reexport_error = None;
 988         let mut any_successful_reexport = false;
 989         let mut crate_private_reexport = false;
 990         self.r.per_ns(|this, ns| {
 991             if let Ok(binding) = source_bindings[ns].get() {
 992                 if !binding.vis.is_at_least(import.expect_vis(), &*this) {
 993                     reexport_error = Some((ns, binding));
 994                     if let ty::Visibility::Restricted(binding_def_id) = binding.vis {
 995                         if binding_def_id.is_top_level_module() {
 996                             crate_private_reexport = true;
 997                         }
 998                     }
 999                 } else {
1000                     any_successful_reexport = true;
1001                 }
1002             }
1003         });
1004
1005         // All namespaces must be re-exported with extra visibility for an error to occur.
1006         if !any_successful_reexport {
1007             let (ns, binding) = reexport_error.unwrap();
1008             if pub_use_of_private_extern_crate_hack(import, binding) {
1009                 let msg = format!(
1010                     "extern crate `{}` is private, and cannot be \
1011                                    re-exported (error E0365), consider declaring with \
1012                                    `pub`",
1013                     ident
1014                 );
1015                 self.r.lint_buffer.buffer_lint(
1016                     PUB_USE_OF_PRIVATE_EXTERN_CRATE,
1017                     import_id,
1018                     import.span,
1019                     &msg,
1020                 );
1021             } else {
1022                 let error_msg = if crate_private_reexport {
1023                     format!(
1024                         "`{}` is only public within the crate, and cannot be re-exported outside",
1025                         ident
1026                     )
1027                 } else {
1028                     format!("`{}` is private, and cannot be re-exported", ident)
1029                 };
1030
1031                 if ns == TypeNS {
1032                     let label_msg = if crate_private_reexport {
1033                         format!("re-export of crate public `{}`", ident)
1034                     } else {
1035                         format!("re-export of private `{}`", ident)
1036                     };
1037
1038                     struct_span_err!(self.r.session, import.span, E0365, "{}", error_msg)
1039                         .span_label(import.span, label_msg)
1040                         .note(&format!("consider declaring type or module `{}` with `pub`", ident))
1041                         .emit();
1042                 } else {
1043                     let mut err =
1044                         struct_span_err!(self.r.session, import.span, E0364, "{error_msg}");
1045                     match binding.kind {
1046                         NameBindingKind::Res(Res::Def(DefKind::Macro(_), def_id))
1047                             // exclude decl_macro
1048                             if self.r.get_macro_by_def_id(def_id).macro_rules =>
1049                         {
1050                             err.span_help(
1051                                 binding.span,
1052                                 "consider adding a `#[macro_export]` to the macro in the imported module",
1053                             );
1054                         }
1055                         _ => {
1056                             err.span_note(
1057                                 import.span,
1058                                 &format!(
1059                                     "consider marking `{ident}` as `pub` in the imported module"
1060                                 ),
1061                             );
1062                         }
1063                     }
1064                     err.emit();
1065                 }
1066             }
1067         }
1068
1069         if import.module_path.len() <= 1 {
1070             // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
1071             // 2 segments, so the `resolve_path` above won't trigger it.
1072             let mut full_path = import.module_path.clone();
1073             full_path.push(Segment::from_ident(ident));
1074             self.r.per_ns(|this, ns| {
1075                 if let Ok(binding) = source_bindings[ns].get() {
1076                     this.lint_if_path_starts_with_module(Some(finalize), &full_path, Some(binding));
1077                 }
1078             });
1079         }
1080
1081         // Record what this import resolves to for later uses in documentation,
1082         // this may resolve to either a value or a type, but for documentation
1083         // purposes it's good enough to just favor one over the other.
1084         self.r.per_ns(|this, ns| {
1085             if let Ok(binding) = source_bindings[ns].get() {
1086                 this.import_res_map.entry(import_id).or_default()[ns] = Some(binding.res());
1087             }
1088         });
1089
1090         self.check_for_redundant_imports(ident, import, source_bindings, target_bindings, target);
1091
1092         debug!("(resolving single import) successfully resolved import");
1093         None
1094     }
1095
1096     fn check_for_redundant_imports(
1097         &mut self,
1098         ident: Ident,
1099         import: &'b Import<'b>,
1100         source_bindings: &PerNS<Cell<Result<&'b NameBinding<'b>, Determinacy>>>,
1101         target_bindings: &PerNS<Cell<Option<&'b NameBinding<'b>>>>,
1102         target: Ident,
1103     ) {
1104         // This function is only called for single imports.
1105         let ImportKind::Single { id, .. } = import.kind else { unreachable!() };
1106
1107         // Skip if the import was produced by a macro.
1108         if import.parent_scope.expansion != LocalExpnId::ROOT {
1109             return;
1110         }
1111
1112         // Skip if we are inside a named module (in contrast to an anonymous
1113         // module defined by a block).
1114         if let ModuleKind::Def(..) = import.parent_scope.module.kind {
1115             return;
1116         }
1117
1118         let mut is_redundant = PerNS { value_ns: None, type_ns: None, macro_ns: None };
1119
1120         let mut redundant_span = PerNS { value_ns: None, type_ns: None, macro_ns: None };
1121
1122         self.r.per_ns(|this, ns| {
1123             if let Ok(binding) = source_bindings[ns].get() {
1124                 if binding.res() == Res::Err {
1125                     return;
1126                 }
1127
1128                 match this.early_resolve_ident_in_lexical_scope(
1129                     target,
1130                     ScopeSet::All(ns, false),
1131                     &import.parent_scope,
1132                     None,
1133                     false,
1134                     target_bindings[ns].get(),
1135                 ) {
1136                     Ok(other_binding) => {
1137                         is_redundant[ns] = Some(
1138                             binding.res() == other_binding.res() && !other_binding.is_ambiguity(),
1139                         );
1140                         redundant_span[ns] = Some((other_binding.span, other_binding.is_import()));
1141                     }
1142                     Err(_) => is_redundant[ns] = Some(false),
1143                 }
1144             }
1145         });
1146
1147         if !is_redundant.is_empty() && is_redundant.present_items().all(|is_redundant| is_redundant)
1148         {
1149             let mut redundant_spans: Vec<_> = redundant_span.present_items().collect();
1150             redundant_spans.sort();
1151             redundant_spans.dedup();
1152             self.r.lint_buffer.buffer_lint_with_diagnostic(
1153                 UNUSED_IMPORTS,
1154                 id,
1155                 import.span,
1156                 &format!("the item `{}` is imported redundantly", ident),
1157                 BuiltinLintDiagnostics::RedundantImport(redundant_spans, ident),
1158             );
1159         }
1160     }
1161
1162     fn resolve_glob_import(&mut self, import: &'b Import<'b>) {
1163         // This function is only called for glob imports.
1164         let ImportKind::Glob { id, is_prelude, .. } = import.kind else { unreachable!() };
1165
1166         let ModuleOrUniformRoot::Module(module) = import.imported_module.get().unwrap() else {
1167             self.r.session.span_err(import.span, "cannot glob-import all possible crates");
1168             return;
1169         };
1170
1171         if module.is_trait() {
1172             self.r.session.span_err(import.span, "items in traits are not importable");
1173             return;
1174         } else if ptr::eq(module, import.parent_scope.module) {
1175             return;
1176         } else if is_prelude {
1177             self.r.prelude = Some(module);
1178             return;
1179         }
1180
1181         // Add to module's glob_importers
1182         module.glob_importers.borrow_mut().push(import);
1183
1184         // Ensure that `resolutions` isn't borrowed during `try_define`,
1185         // since it might get updated via a glob cycle.
1186         let bindings = self
1187             .r
1188             .resolutions(module)
1189             .borrow()
1190             .iter()
1191             .filter_map(|(key, resolution)| {
1192                 resolution.borrow().binding().map(|binding| (*key, binding))
1193             })
1194             .collect::<Vec<_>>();
1195         for (mut key, binding) in bindings {
1196             let scope = match key.ident.span.reverse_glob_adjust(module.expansion, import.span) {
1197                 Some(Some(def)) => self.r.expn_def_scope(def),
1198                 Some(None) => import.parent_scope.module,
1199                 None => continue,
1200             };
1201             if self.r.is_accessible_from(binding.vis, scope) {
1202                 let imported_binding = self.r.import(binding, import);
1203                 let _ = self.r.try_define(import.parent_scope.module, key, imported_binding);
1204             }
1205         }
1206
1207         // Record the destination of this import
1208         self.r.record_partial_res(id, PartialRes::new(module.res().unwrap()));
1209     }
1210
1211     // Miscellaneous post-processing, including recording re-exports,
1212     // reporting conflicts, and reporting unresolved imports.
1213     fn finalize_resolutions_in(&mut self, module: Module<'b>) {
1214         // Since import resolution is finished, globs will not define any more names.
1215         *module.globs.borrow_mut() = Vec::new();
1216
1217         if let Some(def_id) = module.opt_def_id() {
1218             let mut reexports = Vec::new();
1219
1220             module.for_each_child(self.r, |this, ident, _, binding| {
1221                 if let Some(res) = this.is_reexport(binding) {
1222                     reexports.push(ModChild {
1223                         ident,
1224                         res,
1225                         vis: binding.vis,
1226                         span: binding.span,
1227                         macro_rules: false,
1228                     });
1229                 }
1230             });
1231
1232             if !reexports.is_empty() {
1233                 // Call to `expect_local` should be fine because current
1234                 // code is only called for local modules.
1235                 self.r.reexport_map.insert(def_id.expect_local(), reexports);
1236             }
1237         }
1238     }
1239 }
1240
1241 fn import_path_to_string(names: &[Ident], import_kind: &ImportKind<'_>, span: Span) -> String {
1242     let pos = names.iter().position(|p| span == p.span && p.name != kw::PathRoot);
1243     let global = !names.is_empty() && names[0].name == kw::PathRoot;
1244     if let Some(pos) = pos {
1245         let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
1246         names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>())
1247     } else {
1248         let names = if global { &names[1..] } else { names };
1249         if names.is_empty() {
1250             import_kind_to_string(import_kind)
1251         } else {
1252             format!(
1253                 "{}::{}",
1254                 names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>()),
1255                 import_kind_to_string(import_kind),
1256             )
1257         }
1258     }
1259 }
1260
1261 fn import_kind_to_string(import_kind: &ImportKind<'_>) -> String {
1262     match import_kind {
1263         ImportKind::Single { source, .. } => source.to_string(),
1264         ImportKind::Glob { .. } => "*".to_string(),
1265         ImportKind::ExternCrate { .. } => "<extern crate>".to_string(),
1266         ImportKind::MacroUse => "#[macro_use]".to_string(),
1267         ImportKind::MacroExport => "#[macro_export]".to_string(),
1268     }
1269 }