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::{
   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     candidate: 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                     let path = import_path_to_string(
 479                         &import.module_path.iter().map(|seg| seg.ident).collect::<Vec<_>>(),
 480                         &import.kind,
 481                         err.span,
 482                     );
 483                     errors.push((path, err));
 484                     prev_root_id = import.root_id;
 485                 }
 486             } else if is_indeterminate {
 487                 let path = import_path_to_string(
 488                     &import.module_path.iter().map(|seg| seg.ident).collect::<Vec<_>>(),
 489                     &import.kind,
 490                     import.span,
 491                 );
 492                 let err = UnresolvedImportError {
 493                     span: import.span,
 494                     label: None,
 495                     note: None,
 496                     suggestion: None,
 497                     candidate: None,
 498                 };
 499                 if path.contains("::") {
 500                     errors.push((path, err))
 501                 }
 502             }
 503         }
 504
 505         if !errors.is_empty() {
 506             self.throw_unresolved_import_error(errors);
 507         }
 508     }
 509
 510     fn throw_unresolved_import_error(&self, errors: Vec<(String, UnresolvedImportError)>) {
 511         if errors.is_empty() {
 512             return;
 513         }
 514
 515         /// Upper limit on the number of `span_label` messages.
 516         const MAX_LABEL_COUNT: usize = 10;
 517
 518         let span = MultiSpan::from_spans(errors.iter().map(|(_, err)| err.span).collect());
 519         let paths = errors.iter().map(|(path, _)| format!("`{}`", path)).collect::<Vec<_>>();
 520         let msg = format!("unresolved import{} {}", pluralize!(paths.len()), paths.join(", "),);
 521
 522         let mut diag = struct_span_err!(self.r.session, span, E0432, "{}", &msg);
 523
 524         if let Some((_, UnresolvedImportError { note: Some(note), .. })) = errors.iter().last() {
 525             diag.note(note);
 526         }
 527
 528         for (_, err) in errors.into_iter().take(MAX_LABEL_COUNT) {
 529             if let Some(label) = err.label {
 530                 diag.span_label(err.span, label);
 531             }
 532
 533             if let Some((suggestions, msg, applicability)) = err.suggestion {
 534                 if suggestions.is_empty() {
 535                     diag.help(&msg);
 536                     continue;
 537                 }
 538                 diag.multipart_suggestion(&msg, suggestions, applicability);
 539             }
 540
 541             if let Some(candidate) = &err.candidate {
 542                 import_candidates(
 543                     self.r.session,
 544                     &self.r.untracked.source_span,
 545                     &mut diag,
 546                     Some(err.span),
 547                     &candidate,
 548                 )
 549             }
 550         }
 551
 552         diag.emit();
 553     }
 554
 555     /// Attempts to resolve the given import, returning true if its resolution is determined.
 556     /// If successful, the resolved bindings are written into the module.
 557     fn resolve_import(&mut self, import: &'b Import<'b>) -> bool {
 558         debug!(
 559             "(resolving import for module) resolving import `{}::...` in `{}`",
 560             Segment::names_to_string(&import.module_path),
 561             module_to_string(import.parent_scope.module).unwrap_or_else(|| "???".to_string()),
 562         );
 563
 564         let module = if let Some(module) = import.imported_module.get() {
 565             module
 566         } else {
 567             // For better failure detection, pretend that the import will
 568             // not define any names while resolving its module path.
 569             let orig_vis = import.vis.take();
 570             let path_res =
 571                 self.r.maybe_resolve_path(&import.module_path, None, &import.parent_scope);
 572             import.vis.set(orig_vis);
 573
 574             match path_res {
 575                 PathResult::Module(module) => module,
 576                 PathResult::Indeterminate => return false,
 577                 PathResult::NonModule(..) | PathResult::Failed { .. } => return true,
 578             }
 579         };
 580
 581         import.imported_module.set(Some(module));
 582         let (source, target, source_bindings, target_bindings, type_ns_only) = match import.kind {
 583             ImportKind::Single {
 584                 source,
 585                 target,
 586                 ref source_bindings,
 587                 ref target_bindings,
 588                 type_ns_only,
 589                 ..
 590             } => (source, target, source_bindings, target_bindings, type_ns_only),
 591             ImportKind::Glob { .. } => {
 592                 self.resolve_glob_import(import);
 593                 return true;
 594             }
 595             _ => unreachable!(),
 596         };
 597
 598         let mut indeterminate = false;
 599         self.r.per_ns(|this, ns| {
 600             if !type_ns_only || ns == TypeNS {
 601                 if let Err(Undetermined) = source_bindings[ns].get() {
 602                     // For better failure detection, pretend that the import will
 603                     // not define any names while resolving its module path.
 604                     let orig_vis = import.vis.take();
 605                     let binding = this.resolve_ident_in_module(
 606                         module,
 607                         source,
 608                         ns,
 609                         &import.parent_scope,
 610                         None,
 611                         None,
 612                     );
 613                     import.vis.set(orig_vis);
 614                     source_bindings[ns].set(binding);
 615                 } else {
 616                     return;
 617                 };
 618
 619                 let parent = import.parent_scope.module;
 620                 match source_bindings[ns].get() {
 621                     Err(Undetermined) => indeterminate = true,
 622                     // Don't update the resolution, because it was never added.
 623                     Err(Determined) if target.name == kw::Underscore => {}
 624                     Ok(binding) if binding.is_importable() => {
 625                         let imported_binding = this.import(binding, import);
 626                         target_bindings[ns].set(Some(imported_binding));
 627                         this.define(parent, target, ns, imported_binding);
 628                     }
 629                     source_binding @ (Ok(..) | Err(Determined)) => {
 630                         if source_binding.is_ok() {
 631                             let msg = format!("`{}` is not directly importable", target);
 632                             struct_span_err!(this.session, import.span, E0253, "{}", &msg)
 633                                 .span_label(import.span, "cannot be imported directly")
 634                                 .emit();
 635                         }
 636                         let key = this.new_key(target, ns);
 637                         this.update_resolution(parent, key, |_, resolution| {
 638                             resolution.single_imports.remove(&Interned::new_unchecked(import));
 639                         });
 640                     }
 641                 }
 642             }
 643         });
 644
 645         !indeterminate
 646     }
 647
 648     /// Performs final import resolution, consistency checks and error reporting.
 649     ///
 650     /// Optionally returns an unresolved import error. This error is buffered and used to
 651     /// consolidate multiple unresolved import errors into a single diagnostic.
 652     fn finalize_import(&mut self, import: &'b Import<'b>) -> Option<UnresolvedImportError> {
 653         let orig_vis = import.vis.take();
 654         let ignore_binding = match &import.kind {
 655             ImportKind::Single { target_bindings, .. } => target_bindings[TypeNS].get(),
 656             _ => None,
 657         };
 658         let prev_ambiguity_errors_len = self.r.ambiguity_errors.len();
 659         let finalize = Finalize::with_root_span(import.root_id, import.span, import.root_span);
 660         let path_res = self.r.resolve_path(
 661             &import.module_path,
 662             None,
 663             &import.parent_scope,
 664             Some(finalize),
 665             ignore_binding,
 666         );
 667
 668         let no_ambiguity = self.r.ambiguity_errors.len() == prev_ambiguity_errors_len;
 669         import.vis.set(orig_vis);
 670         let module = match path_res {
 671             PathResult::Module(module) => {
 672                 // Consistency checks, analogous to `finalize_macro_resolutions`.
 673                 if let Some(initial_module) = import.imported_module.get() {
 674                     if !ModuleOrUniformRoot::same_def(module, initial_module) && no_ambiguity {
 675                         span_bug!(import.span, "inconsistent resolution for an import");
 676                     }
 677                 } else if self.r.privacy_errors.is_empty() {
 678                     let msg = "cannot determine resolution for the import";
 679                     let msg_note = "import resolution is stuck, try simplifying other imports";
 680                     self.r.session.struct_span_err(import.span, msg).note(msg_note).emit();
 681                 }
 682
 683                 module
 684             }
 685             PathResult::Failed { is_error_from_last_segment: false, span, label, suggestion } => {
 686                 if no_ambiguity {
 687                     assert!(import.imported_module.get().is_none());
 688                     self.r
 689                         .report_error(span, ResolutionError::FailedToResolve { label, suggestion });
 690                 }
 691                 return None;
 692             }
 693             PathResult::Failed { is_error_from_last_segment: true, span, label, suggestion } => {
 694                 if no_ambiguity {
 695                     assert!(import.imported_module.get().is_none());
 696                     let err = match self.make_path_suggestion(
 697                         span,
 698                         import.module_path.clone(),
 699                         &import.parent_scope,
 700                     ) {
 701                         Some((suggestion, note)) => UnresolvedImportError {
 702                             span,
 703                             label: None,
 704                             note,
 705                             suggestion: Some((
 706                                 vec![(span, Segment::names_to_string(&suggestion))],
 707                                 String::from("a similar path exists"),
 708                                 Applicability::MaybeIncorrect,
 709                             )),
 710                             candidate: None,
 711                         },
 712                         None => UnresolvedImportError {
 713                             span,
 714                             label: Some(label),
 715                             note: None,
 716                             suggestion,
 717                             candidate: None,
 718                         },
 719                     };
 720                     return Some(err);
 721                 }
 722                 return None;
 723             }
 724             PathResult::NonModule(_) => {
 725                 if no_ambiguity {
 726                     assert!(import.imported_module.get().is_none());
 727                 }
 728                 // The error was already reported earlier.
 729                 return None;
 730             }
 731             PathResult::Indeterminate => unreachable!(),
 732         };
 733
 734         let (ident, target, source_bindings, target_bindings, type_ns_only, import_id) =
 735             match import.kind {
 736                 ImportKind::Single {
 737                     source,
 738                     target,
 739                     ref source_bindings,
 740                     ref target_bindings,
 741                     type_ns_only,
 742                     id,
 743                     ..
 744                 } => (source, target, source_bindings, target_bindings, type_ns_only, id),
 745                 ImportKind::Glob { is_prelude, ref max_vis, id } => {
 746                     if import.module_path.len() <= 1 {
 747                         // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
 748                         // 2 segments, so the `resolve_path` above won't trigger it.
 749                         let mut full_path = import.module_path.clone();
 750                         full_path.push(Segment::from_ident(Ident::empty()));
 751                         self.r.lint_if_path_starts_with_module(Some(finalize), &full_path, None);
 752                     }
 753
 754                     if let ModuleOrUniformRoot::Module(module) = module {
 755                         if ptr::eq(module, import.parent_scope.module) {
 756                             // Importing a module into itself is not allowed.
 757                             return Some(UnresolvedImportError {
 758                                 span: import.span,
 759                                 label: Some(String::from(
 760                                     "cannot glob-import a module into itself",
 761                                 )),
 762                                 note: None,
 763                                 suggestion: None,
 764                                 candidate: None,
 765                             });
 766                         }
 767                     }
 768                     if !is_prelude
 769                     && let Some(max_vis) = max_vis.get()
 770                     && !max_vis.is_at_least(import.expect_vis(), &*self.r)
 771                 {
 772                     let msg = "glob import doesn't reexport anything because no candidate is public enough";
 773                     self.r.lint_buffer.buffer_lint(UNUSED_IMPORTS, id, import.span, msg);
 774                 }
 775                     return None;
 776                 }
 777                 _ => unreachable!(),
 778             };
 779
 780         let mut all_ns_err = true;
 781         self.r.per_ns(|this, ns| {
 782             if !type_ns_only || ns == TypeNS {
 783                 let orig_vis = import.vis.take();
 784                 let binding = this.resolve_ident_in_module(
 785                     module,
 786                     ident,
 787                     ns,
 788                     &import.parent_scope,
 789                     Some(Finalize { report_private: false, ..finalize }),
 790                     target_bindings[ns].get(),
 791                 );
 792                 import.vis.set(orig_vis);
 793
 794                 match binding {
 795                     Ok(binding) => {
 796                         // Consistency checks, analogous to `finalize_macro_resolutions`.
 797                         let initial_binding = source_bindings[ns].get().map(|initial_binding| {
 798                             all_ns_err = false;
 799                             if let Some(target_binding) = target_bindings[ns].get() {
 800                                 if target.name == kw::Underscore
 801                                     && initial_binding.is_extern_crate()
 802                                     && !initial_binding.is_import()
 803                                 {
 804                                     this.record_use(
 805                                         ident,
 806                                         target_binding,
 807                                         import.module_path.is_empty(),
 808                                     );
 809                                 }
 810                             }
 811                             initial_binding
 812                         });
 813                         let res = binding.res();
 814                         if let Ok(initial_binding) = initial_binding {
 815                             let initial_res = initial_binding.res();
 816                             if res != initial_res && this.ambiguity_errors.is_empty() {
 817                                 this.ambiguity_errors.push(AmbiguityError {
 818                                     kind: AmbiguityKind::Import,
 819                                     ident,
 820                                     b1: initial_binding,
 821                                     b2: binding,
 822                                     misc1: AmbiguityErrorMisc::None,
 823                                     misc2: AmbiguityErrorMisc::None,
 824                                 });
 825                             }
 826                         } else if res != Res::Err
 827                             && this.ambiguity_errors.is_empty()
 828                             && this.privacy_errors.is_empty()
 829                         {
 830                             let msg = "cannot determine resolution for the import";
 831                             let msg_note =
 832                                 "import resolution is stuck, try simplifying other imports";
 833                             this.session.struct_span_err(import.span, msg).note(msg_note).emit();
 834                         }
 835                     }
 836                     Err(..) => {
 837                         // FIXME: This assert may fire if public glob is later shadowed by a private
 838                         // single import (see test `issue-55884-2.rs`). In theory single imports should
 839                         // always block globs, even if they are not yet resolved, so that this kind of
 840                         // self-inconsistent resolution never happens.
 841                         // Re-enable the assert when the issue is fixed.
 842                         // assert!(result[ns].get().is_err());
 843                     }
 844                 }
 845             }
 846         });
 847
 848         if all_ns_err {
 849             let mut all_ns_failed = true;
 850             self.r.per_ns(|this, ns| {
 851                 if !type_ns_only || ns == TypeNS {
 852                     let binding = this.resolve_ident_in_module(
 853                         module,
 854                         ident,
 855                         ns,
 856                         &import.parent_scope,
 857                         Some(finalize),
 858                         None,
 859                     );
 860                     if binding.is_ok() {
 861                         all_ns_failed = false;
 862                     }
 863                 }
 864             });
 865
 866             return if all_ns_failed {
 867                 let resolutions = match module {
 868                     ModuleOrUniformRoot::Module(module) => {
 869                         Some(self.r.resolutions(module).borrow())
 870                     }
 871                     _ => None,
 872                 };
 873                 let resolutions = resolutions.as_ref().into_iter().flat_map(|r| r.iter());
 874                 let names = resolutions
 875                     .filter_map(|(BindingKey { ident: i, .. }, resolution)| {
 876                         if *i == ident {
 877                             return None;
 878                         } // Never suggest the same name
 879                         match *resolution.borrow() {
 880                             NameResolution { binding: Some(name_binding), .. } => {
 881                                 match name_binding.kind {
 882                                     NameBindingKind::Import { binding, .. } => {
 883                                         match binding.kind {
 884                                             // Never suggest the name that has binding error
 885                                             // i.e., the name that cannot be previously resolved
 886                                             NameBindingKind::Res(Res::Err) => None,
 887                                             _ => Some(i.name),
 888                                         }
 889                                     }
 890                                     _ => Some(i.name),
 891                                 }
 892                             }
 893                             NameResolution { ref single_imports, .. }
 894                                 if single_imports.is_empty() =>
 895                             {
 896                                 None
 897                             }
 898                             _ => Some(i.name),
 899                         }
 900                     })
 901                     .collect::<Vec<Symbol>>();
 902
 903                 let lev_suggestion =
 904                     find_best_match_for_name(&names, ident.name, None).map(|suggestion| {
 905                         (
 906                             vec![(ident.span, suggestion.to_string())],
 907                             String::from("a similar name exists in the module"),
 908                             Applicability::MaybeIncorrect,
 909                         )
 910                     });
 911
 912                 let (suggestion, note) =
 913                     match self.check_for_module_export_macro(import, module, ident) {
 914                         Some((suggestion, note)) => (suggestion.or(lev_suggestion), note),
 915                         _ => (lev_suggestion, None),
 916                     };
 917
 918                 let label = match module {
 919                     ModuleOrUniformRoot::Module(module) => {
 920                         let module_str = module_to_string(module);
 921                         if let Some(module_str) = module_str {
 922                             format!("no `{}` in `{}`", ident, module_str)
 923                         } else {
 924                             format!("no `{}` in the root", ident)
 925                         }
 926                     }
 927                     _ => {
 928                         if !ident.is_path_segment_keyword() {
 929                             format!("no external crate `{}`", ident)
 930                         } else {
 931                             // HACK(eddyb) this shows up for `self` & `super`, which
 932                             // should work instead - for now keep the same error message.
 933                             format!("no `{}` in the root", ident)
 934                         }
 935                     }
 936                 };
 937
 938                 let parent_suggestion =
 939                     self.r.lookup_import_candidates(ident, TypeNS, &import.parent_scope, |_| true);
 940
 941                 Some(UnresolvedImportError {
 942                     span: import.span,
 943                     label: Some(label),
 944                     note,
 945                     suggestion,
 946                     candidate: if !parent_suggestion.is_empty() {
 947                         Some(parent_suggestion)
 948                     } else {
 949                         None
 950                     },
 951                 })
 952             } else {
 953                 // `resolve_ident_in_module` reported a privacy error.
 954                 None
 955             };
 956         }
 957
 958         let mut reexport_error = None;
 959         let mut any_successful_reexport = false;
 960         let mut crate_private_reexport = false;
 961         self.r.per_ns(|this, ns| {
 962             if let Ok(binding) = source_bindings[ns].get() {
 963                 if !binding.vis.is_at_least(import.expect_vis(), &*this) {
 964                     reexport_error = Some((ns, binding));
 965                     if let ty::Visibility::Restricted(binding_def_id) = binding.vis {
 966                         if binding_def_id.is_top_level_module() {
 967                             crate_private_reexport = true;
 968                         }
 969                     }
 970                 } else {
 971                     any_successful_reexport = true;
 972                 }
 973             }
 974         });
 975
 976         // All namespaces must be re-exported with extra visibility for an error to occur.
 977         if !any_successful_reexport {
 978             let (ns, binding) = reexport_error.unwrap();
 979             if pub_use_of_private_extern_crate_hack(import, binding) {
 980                 let msg = format!(
 981                     "extern crate `{}` is private, and cannot be \
 982                                    re-exported (error E0365), consider declaring with \
 983                                    `pub`",
 984                     ident
 985                 );
 986                 self.r.lint_buffer.buffer_lint(
 987                     PUB_USE_OF_PRIVATE_EXTERN_CRATE,
 988                     import_id,
 989                     import.span,
 990                     &msg,
 991                 );
 992             } else {
 993                 let error_msg = if crate_private_reexport {
 994                     format!(
 995                         "`{}` is only public within the crate, and cannot be re-exported outside",
 996                         ident
 997                     )
 998                 } else {
 999                     format!("`{}` is private, and cannot be re-exported", ident)
1000                 };
1001
1002                 if ns == TypeNS {
1003                     let label_msg = if crate_private_reexport {
1004                         format!("re-export of crate public `{}`", ident)
1005                     } else {
1006                         format!("re-export of private `{}`", ident)
1007                     };
1008
1009                     struct_span_err!(self.r.session, import.span, E0365, "{}", error_msg)
1010                         .span_label(import.span, label_msg)
1011                         .note(&format!("consider declaring type or module `{}` with `pub`", ident))
1012                         .emit();
1013                 } else {
1014                     let mut err =
1015                         struct_span_err!(self.r.session, import.span, E0364, "{error_msg}");
1016                     match binding.kind {
1017                         NameBindingKind::Res(Res::Def(DefKind::Macro(_), def_id))
1018                             // exclude decl_macro
1019                             if self.r.get_macro_by_def_id(def_id).macro_rules =>
1020                         {
1021                             err.span_help(
1022                                 binding.span,
1023                                 "consider adding a `#[macro_export]` to the macro in the imported module",
1024                             );
1025                         }
1026                         _ => {
1027                             err.span_note(
1028                                 import.span,
1029                                 &format!(
1030                                     "consider marking `{ident}` as `pub` in the imported module"
1031                                 ),
1032                             );
1033                         }
1034                     }
1035                     err.emit();
1036                 }
1037             }
1038         }
1039
1040         if import.module_path.len() <= 1 {
1041             // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
1042             // 2 segments, so the `resolve_path` above won't trigger it.
1043             let mut full_path = import.module_path.clone();
1044             full_path.push(Segment::from_ident(ident));
1045             self.r.per_ns(|this, ns| {
1046                 if let Ok(binding) = source_bindings[ns].get() {
1047                     this.lint_if_path_starts_with_module(Some(finalize), &full_path, Some(binding));
1048                 }
1049             });
1050         }
1051
1052         // Record what this import resolves to for later uses in documentation,
1053         // this may resolve to either a value or a type, but for documentation
1054         // purposes it's good enough to just favor one over the other.
1055         self.r.per_ns(|this, ns| {
1056             if let Ok(binding) = source_bindings[ns].get() {
1057                 this.import_res_map.entry(import_id).or_default()[ns] = Some(binding.res());
1058             }
1059         });
1060
1061         self.check_for_redundant_imports(ident, import, source_bindings, target_bindings, target);
1062
1063         debug!("(resolving single import) successfully resolved import");
1064         None
1065     }
1066
1067     fn check_for_redundant_imports(
1068         &mut self,
1069         ident: Ident,
1070         import: &'b Import<'b>,
1071         source_bindings: &PerNS<Cell<Result<&'b NameBinding<'b>, Determinacy>>>,
1072         target_bindings: &PerNS<Cell<Option<&'b NameBinding<'b>>>>,
1073         target: Ident,
1074     ) {
1075         // This function is only called for single imports.
1076         let ImportKind::Single { id, .. } = import.kind else { unreachable!() };
1077
1078         // Skip if the import was produced by a macro.
1079         if import.parent_scope.expansion != LocalExpnId::ROOT {
1080             return;
1081         }
1082
1083         // Skip if we are inside a named module (in contrast to an anonymous
1084         // module defined by a block).
1085         if let ModuleKind::Def(..) = import.parent_scope.module.kind {
1086             return;
1087         }
1088
1089         let mut is_redundant = PerNS { value_ns: None, type_ns: None, macro_ns: None };
1090
1091         let mut redundant_span = PerNS { value_ns: None, type_ns: None, macro_ns: None };
1092
1093         self.r.per_ns(|this, ns| {
1094             if let Ok(binding) = source_bindings[ns].get() {
1095                 if binding.res() == Res::Err {
1096                     return;
1097                 }
1098
1099                 match this.early_resolve_ident_in_lexical_scope(
1100                     target,
1101                     ScopeSet::All(ns, false),
1102                     &import.parent_scope,
1103                     None,
1104                     false,
1105                     target_bindings[ns].get(),
1106                 ) {
1107                     Ok(other_binding) => {
1108                         is_redundant[ns] = Some(
1109                             binding.res() == other_binding.res() && !other_binding.is_ambiguity(),
1110                         );
1111                         redundant_span[ns] = Some((other_binding.span, other_binding.is_import()));
1112                     }
1113                     Err(_) => is_redundant[ns] = Some(false),
1114                 }
1115             }
1116         });
1117
1118         if !is_redundant.is_empty() && is_redundant.present_items().all(|is_redundant| is_redundant)
1119         {
1120             let mut redundant_spans: Vec<_> = redundant_span.present_items().collect();
1121             redundant_spans.sort();
1122             redundant_spans.dedup();
1123             self.r.lint_buffer.buffer_lint_with_diagnostic(
1124                 UNUSED_IMPORTS,
1125                 id,
1126                 import.span,
1127                 &format!("the item `{}` is imported redundantly", ident),
1128                 BuiltinLintDiagnostics::RedundantImport(redundant_spans, ident),
1129             );
1130         }
1131     }
1132
1133     fn resolve_glob_import(&mut self, import: &'b Import<'b>) {
1134         // This function is only called for glob imports.
1135         let ImportKind::Glob { id, is_prelude, .. } = import.kind else { unreachable!() };
1136
1137         let ModuleOrUniformRoot::Module(module) = import.imported_module.get().unwrap() else {
1138             self.r.session.span_err(import.span, "cannot glob-import all possible crates");
1139             return;
1140         };
1141
1142         if module.is_trait() {
1143             self.r.session.span_err(import.span, "items in traits are not importable");
1144             return;
1145         } else if ptr::eq(module, import.parent_scope.module) {
1146             return;
1147         } else if is_prelude {
1148             self.r.prelude = Some(module);
1149             return;
1150         }
1151
1152         // Add to module's glob_importers
1153         module.glob_importers.borrow_mut().push(import);
1154
1155         // Ensure that `resolutions` isn't borrowed during `try_define`,
1156         // since it might get updated via a glob cycle.
1157         let bindings = self
1158             .r
1159             .resolutions(module)
1160             .borrow()
1161             .iter()
1162             .filter_map(|(key, resolution)| {
1163                 resolution.borrow().binding().map(|binding| (*key, binding))
1164             })
1165             .collect::<Vec<_>>();
1166         for (mut key, binding) in bindings {
1167             let scope = match key.ident.span.reverse_glob_adjust(module.expansion, import.span) {
1168                 Some(Some(def)) => self.r.expn_def_scope(def),
1169                 Some(None) => import.parent_scope.module,
1170                 None => continue,
1171             };
1172             if self.r.is_accessible_from(binding.vis, scope) {
1173                 let imported_binding = self.r.import(binding, import);
1174                 let _ = self.r.try_define(import.parent_scope.module, key, imported_binding);
1175             }
1176         }
1177
1178         // Record the destination of this import
1179         self.r.record_partial_res(id, PartialRes::new(module.res().unwrap()));
1180     }
1181
1182     // Miscellaneous post-processing, including recording re-exports,
1183     // reporting conflicts, and reporting unresolved imports.
1184     fn finalize_resolutions_in(&mut self, module: Module<'b>) {
1185         // Since import resolution is finished, globs will not define any more names.
1186         *module.globs.borrow_mut() = Vec::new();
1187
1188         if let Some(def_id) = module.opt_def_id() {
1189             let mut reexports = Vec::new();
1190
1191             module.for_each_child(self.r, |this, ident, _, binding| {
1192                 if let Some(res) = this.is_reexport(binding) {
1193                     reexports.push(ModChild {
1194                         ident,
1195                         res,
1196                         vis: binding.vis,
1197                         span: binding.span,
1198                         macro_rules: false,
1199                     });
1200                 }
1201             });
1202
1203             if !reexports.is_empty() {
1204                 // Call to `expect_local` should be fine because current
1205                 // code is only called for local modules.
1206                 self.r.reexport_map.insert(def_id.expect_local(), reexports);
1207             }
1208         }
1209     }
1210 }
1211
1212 fn import_path_to_string(names: &[Ident], import_kind: &ImportKind<'_>, span: Span) -> String {
1213     let pos = names.iter().position(|p| span == p.span && p.name != kw::PathRoot);
1214     let global = !names.is_empty() && names[0].name == kw::PathRoot;
1215     if let Some(pos) = pos {
1216         let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
1217         names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>())
1218     } else {
1219         let names = if global { &names[1..] } else { names };
1220         if names.is_empty() {
1221             import_kind_to_string(import_kind)
1222         } else {
1223             format!(
1224                 "{}::{}",
1225                 names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>()),
1226                 import_kind_to_string(import_kind),
1227             )
1228         }
1229     }
1230 }
1231
1232 fn import_kind_to_string(import_kind: &ImportKind<'_>) -> String {
1233     match import_kind {
1234         ImportKind::Single { source, .. } => source.to_string(),
1235         ImportKind::Glob { .. } => "*".to_string(),
1236         ImportKind::ExternCrate { .. } => "<extern crate>".to_string(),
1237         ImportKind::MacroUse => "#[macro_use]".to_string(),
1238         ImportKind::MacroExport => "#[macro_export]".to_string(),
1239     }
1240 }