src/librustc_resolve/resolve_imports.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use self::ImportDirectiveSubclass::*;
  12
  13 use {AmbiguityError, CrateLint, Module, ModuleOrUniformRoot, PerNS};
  14 use Namespace::{self, TypeNS, MacroNS, ValueNS};
  15 use {NameBinding, NameBindingKind, ToNameBinding, PathResult, PrivacyError};
  16 use Resolver;
  17 use {names_to_string, module_to_string};
  18 use {resolve_error, ResolutionError};
  19
  20 use rustc_data_structures::ptr_key::PtrKey;
  21 use rustc::ty;
  22 use rustc::lint::builtin::BuiltinLintDiagnostics;
  23 use rustc::lint::builtin::{DUPLICATE_MACRO_EXPORTS, PUB_USE_OF_PRIVATE_EXTERN_CRATE};
  24 use rustc::hir::def_id::{CRATE_DEF_INDEX, DefId};
  25 use rustc::hir::def::*;
  26 use rustc::session::DiagnosticMessageId;
  27 use rustc::util::nodemap::{FxHashMap, FxHashSet};
  28
  29 use syntax::ast::{Ident, Name, NodeId, CRATE_NODE_ID};
  30 use syntax::ext::base::Determinacy::{self, Determined, Undetermined};
  31 use syntax::ext::hygiene::Mark;
  32 use syntax::symbol::keywords;
  33 use syntax::util::lev_distance::find_best_match_for_name;
  34 use syntax_pos::Span;
  35
  36 use std::cell::{Cell, RefCell};
  37 use std::{mem, ptr};
  38
  39 /// Contains data for specific types of import directives.
  40 #[derive(Clone, Debug)]
  41 pub enum ImportDirectiveSubclass<'a> {
  42     SingleImport {
  43         target: Ident,
  44         source: Ident,
  45         result: PerNS<Cell<Result<&'a NameBinding<'a>, Determinacy>>>,
  46         type_ns_only: bool,
  47     },
  48     GlobImport {
  49         is_prelude: bool,
  50         max_vis: Cell<ty::Visibility>, // The visibility of the greatest re-export.
  51         // n.b. `max_vis` is only used in `finalize_import` to check for re-export errors.
  52     },
  53     ExternCrate(Option<Name>),
  54     MacroUse,
  55 }
  56
  57 /// One import directive.
  58 #[derive(Debug,Clone)]
  59 pub struct ImportDirective<'a> {
  60     /// The id of the `extern crate`, `UseTree` etc that imported this `ImportDirective`.
  61     ///
  62     /// In the case where the `ImportDirective` was expanded from a "nested" use tree,
  63     /// this id is the id of the leaf tree. For example:
  64     ///
  65     /// ```ignore (pacify the mercilous tidy)
  66     /// use foo::bar::{a, b}
  67     /// ```
  68     ///
  69     /// If this is the import directive for `foo::bar::a`, we would have the id of the `UseTree`
  70     /// for `a` in this field.
  71     pub id: NodeId,
  72
  73     /// The `id` of the "root" use-kind -- this is always the same as
  74     /// `id` except in the case of "nested" use trees, in which case
  75     /// it will be the `id` of the root use tree. e.g., in the example
  76     /// from `id`, this would be the id of the `use foo::bar`
  77     /// `UseTree` node.
  78     pub root_id: NodeId,
  79
  80     /// Span of this use tree.
  81     pub span: Span,
  82
  83     /// Span of the *root* use tree (see `root_id`).
  84     pub root_span: Span,
  85
  86     pub parent: Module<'a>,
  87     pub module_path: Vec<Ident>,
  88     /// The resolution of `module_path`.
  89     pub imported_module: Cell<Option<ModuleOrUniformRoot<'a>>>,
  90     pub subclass: ImportDirectiveSubclass<'a>,
  91     pub vis: Cell<ty::Visibility>,
  92     pub expansion: Mark,
  93     pub used: Cell<bool>,
  94
  95     /// Whether this import is a "canary" for the `uniform_paths` feature,
  96     /// i.e. `use x::...;` results in an `use self::x as _;` canary.
  97     /// This flag affects diagnostics: an error is reported if and only if
  98     /// the import resolves successfully and an external crate with the same
  99     /// name (`x` above) also exists; any resolution failures are ignored.
 100     pub is_uniform_paths_canary: bool,
 101 }
 102
 103 impl<'a> ImportDirective<'a> {
 104     pub fn is_glob(&self) -> bool {
 105         match self.subclass { ImportDirectiveSubclass::GlobImport { .. } => true, _ => false }
 106     }
 107
 108     crate fn crate_lint(&self) -> CrateLint {
 109         CrateLint::UsePath { root_id: self.root_id, root_span: self.root_span }
 110     }
 111 }
 112
 113 #[derive(Clone, Default, Debug)]
 114 /// Records information about the resolution of a name in a namespace of a module.
 115 pub struct NameResolution<'a> {
 116     /// Single imports that may define the name in the namespace.
 117     /// Import directives are arena-allocated, so it's ok to use pointers as keys.
 118     single_imports: FxHashSet<PtrKey<'a, ImportDirective<'a>>>,
 119     /// The least shadowable known binding for this name, or None if there are no known bindings.
 120     pub binding: Option<&'a NameBinding<'a>>,
 121     shadowed_glob: Option<&'a NameBinding<'a>>,
 122 }
 123
 124 impl<'a> NameResolution<'a> {
 125     // Returns the binding for the name if it is known or None if it not known.
 126     fn binding(&self) -> Option<&'a NameBinding<'a>> {
 127         self.binding.and_then(|binding| {
 128             if !binding.is_glob_import() ||
 129                self.single_imports.is_empty() { Some(binding) } else { None }
 130         })
 131     }
 132 }
 133
 134 impl<'a, 'crateloader> Resolver<'a, 'crateloader> {
 135     fn resolution(&self, module: Module<'a>, ident: Ident, ns: Namespace)
 136                   -> &'a RefCell<NameResolution<'a>> {
 137         *module.resolutions.borrow_mut().entry((ident.modern(), ns))
 138                .or_insert_with(|| self.arenas.alloc_name_resolution())
 139     }
 140
 141     /// Attempts to resolve `ident` in namespaces `ns` of `module`.
 142     /// Invariant: if `record_used` is `Some`, expansion and import resolution must be complete.
 143     pub fn resolve_ident_in_module_unadjusted(&mut self,
 144                                               module: ModuleOrUniformRoot<'a>,
 145                                               ident: Ident,
 146                                               ns: Namespace,
 147                                               restricted_shadowing: bool,
 148                                               record_used: bool,
 149                                               path_span: Span)
 150                                               -> Result<&'a NameBinding<'a>, Determinacy> {
 151         let module = match module {
 152             ModuleOrUniformRoot::Module(module) => module,
 153             ModuleOrUniformRoot::UniformRoot(root) => {
 154                 // HACK(eddyb): `resolve_path` uses `keywords::Invalid` to indicate
 155                 // paths of length 0, and currently these are relative `use` paths.
 156                 let can_be_relative = !ident.is_path_segment_keyword() &&
 157                     root == keywords::Invalid.name();
 158                 if can_be_relative {
 159                     // Relative paths should only get here if the feature-gate is on.
 160                     assert!(self.session.rust_2018() &&
 161                             self.session.features_untracked().uniform_paths);
 162
 163                     // Try first to resolve relatively.
 164                     let mut ctxt = ident.span.ctxt().modern();
 165                     let self_module = self.resolve_self(&mut ctxt, self.current_module);
 166
 167                     let binding = self.resolve_ident_in_module_unadjusted(
 168                         ModuleOrUniformRoot::Module(self_module),
 169                         ident,
 170                         ns,
 171                         restricted_shadowing,
 172                         record_used,
 173                         path_span,
 174                     );
 175
 176                     // FIXME(eddyb) This may give false negatives, specifically
 177                     // if a crate with the same name is found in `extern_prelude`,
 178                     // preventing the check below this one from returning `binding`
 179                     // in all cases.
 180                     //
 181                     // That is, if there's no crate with the same name, `binding`
 182                     // is always returned, which is the result of doing the exact
 183                     // same lookup of `ident`, in the `self` module.
 184                     // But when a crate does exist, it will get chosen even when
 185                     // macro expansion could result in a success from the lookup
 186                     // in the `self` module, later on.
 187                     //
 188                     // NB. This is currently alleviated by the "ambiguity canaries"
 189                     // (see `is_uniform_paths_canary`) that get introduced for the
 190                     // maybe-relative imports handled here: if the false negative
 191                     // case were to arise, it would *also* cause an ambiguity error.
 192                     if binding.is_ok() {
 193                         return binding;
 194                     }
 195
 196                     // Fall back to resolving to an external crate.
 197                     if !(ns == TypeNS && self.extern_prelude.contains(&ident.name)) {
 198                         // ... unless the crate name is not in the `extern_prelude`.
 199                         return binding;
 200                     }
 201                 }
 202
 203                 let crate_root = if
 204                     ns == TypeNS &&
 205                     root != keywords::Extern.name() &&
 206                     (
 207                         ident.name == keywords::Crate.name() ||
 208                         ident.name == keywords::DollarCrate.name()
 209                     )
 210                 {
 211                     self.resolve_crate_root(ident)
 212                 } else if ns == TypeNS && !ident.is_path_segment_keyword() {
 213                     let crate_id =
 214                         self.crate_loader.process_path_extern(ident.name, ident.span);
 215                     self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX })
 216                 } else {
 217                     return Err(Determined);
 218                 };
 219                 self.populate_module_if_necessary(crate_root);
 220                 let binding = (crate_root, ty::Visibility::Public,
 221                                ident.span, Mark::root()).to_name_binding(self.arenas);
 222                 return Ok(binding);
 223             }
 224         };
 225
 226         self.populate_module_if_necessary(module);
 227
 228         let resolution = self.resolution(module, ident, ns)
 229             .try_borrow_mut()
 230             .map_err(|_| Determined)?; // This happens when there is a cycle of imports
 231
 232         if let Some(binding) = resolution.binding {
 233             if !restricted_shadowing && binding.expansion != Mark::root() {
 234                 if let NameBindingKind::Def(_, true) = binding.kind {
 235                     self.macro_expanded_macro_export_errors.insert((path_span, binding.span));
 236                 }
 237             }
 238         }
 239
 240         if record_used {
 241             if let Some(binding) = resolution.binding {
 242                 if let Some(shadowed_glob) = resolution.shadowed_glob {
 243                     let name = ident.name;
 244                     // Forbid expanded shadowing to avoid time travel.
 245                     if restricted_shadowing &&
 246                        binding.expansion != Mark::root() &&
 247                        ns != MacroNS && // In MacroNS, `try_define` always forbids this shadowing
 248                        binding.def() != shadowed_glob.def() {
 249                         self.ambiguity_errors.push(AmbiguityError {
 250                             span: path_span,
 251                             name,
 252                             lexical: false,
 253                             b1: binding,
 254                             b2: shadowed_glob,
 255                         });
 256                     }
 257                 }
 258                 if self.record_use(ident, ns, binding, path_span) {
 259                     return Ok(self.dummy_binding);
 260                 }
 261                 if !self.is_accessible(binding.vis) {
 262                     self.privacy_errors.push(PrivacyError(path_span, ident.name, binding));
 263                 }
 264             }
 265
 266             return resolution.binding.ok_or(Determined);
 267         }
 268
 269         let check_usable = |this: &mut Self, binding: &'a NameBinding<'a>| {
 270             // `extern crate` are always usable for backwards compatibility, see issue #37020.
 271             let usable = this.is_accessible(binding.vis) || binding.is_extern_crate();
 272             if usable { Ok(binding) } else { Err(Determined) }
 273         };
 274
 275         // Items and single imports are not shadowable, if we have one, then it's determined.
 276         if let Some(binding) = resolution.binding {
 277             if !binding.is_glob_import() {
 278                 return check_usable(self, binding);
 279             }
 280         }
 281
 282         // --- From now on we either have a glob resolution or no resolution. ---
 283
 284         // Check if one of single imports can still define the name,
 285         // if it can then our result is not determined and can be invalidated.
 286         for single_import in &resolution.single_imports {
 287             if !self.is_accessible(single_import.vis.get()) {
 288                 continue;
 289             }
 290             let module = unwrap_or!(single_import.imported_module.get(), return Err(Undetermined));
 291             let ident = match single_import.subclass {
 292                 SingleImport { source, .. } => source,
 293                 _ => unreachable!(),
 294             };
 295             match self.resolve_ident_in_module(module, ident, ns, false, path_span) {
 296                 Err(Determined) => continue,
 297                 Ok(_) | Err(Undetermined) => return Err(Undetermined),
 298             }
 299         }
 300
 301         // So we have a resolution that's from a glob import. This resolution is determined
 302         // if it cannot be shadowed by some new item/import expanded from a macro.
 303         // This happens either if there are no unexpanded macros, or expanded names cannot
 304         // shadow globs (that happens in macro namespace or with restricted shadowing).
 305         //
 306         // Additionally, any macro in any module can plant names in the root module if it creates
 307         // `macro_export` macros, so the root module effectively has unresolved invocations if any
 308         // module has unresolved invocations.
 309         // However, it causes resolution/expansion to stuck too often (#53144), so, to make
 310         // progress, we have to ignore those potential unresolved invocations from other modules
 311         // and prohibit access to macro-expanded `macro_export` macros instead (unless restricted
 312         // shadowing is enabled, see `macro_expanded_macro_export_errors`).
 313         let unexpanded_macros = !module.unresolved_invocations.borrow().is_empty();
 314         if let Some(binding) = resolution.binding {
 315             if !unexpanded_macros || ns == MacroNS || restricted_shadowing {
 316                 return check_usable(self, binding);
 317             } else {
 318                 return Err(Undetermined);
 319             }
 320         }
 321
 322         // --- From now on we have no resolution. ---
 323
 324         // Now we are in situation when new item/import can appear only from a glob or a macro
 325         // expansion. With restricted shadowing names from globs and macro expansions cannot
 326         // shadow names from outer scopes, so we can freely fallback from module search to search
 327         // in outer scopes. To continue search in outer scopes we have to lie a bit and return
 328         // `Determined` to `resolve_lexical_macro_path_segment` even if the correct answer
 329         // for in-module resolution could be `Undetermined`.
 330         if restricted_shadowing {
 331             return Err(Determined);
 332         }
 333
 334         // Check if one of unexpanded macros can still define the name,
 335         // if it can then our "no resolution" result is not determined and can be invalidated.
 336         if unexpanded_macros {
 337             return Err(Undetermined);
 338         }
 339
 340         // Check if one of glob imports can still define the name,
 341         // if it can then our "no resolution" result is not determined and can be invalidated.
 342         for glob_import in module.globs.borrow().iter() {
 343             if !self.is_accessible(glob_import.vis.get()) {
 344                 continue
 345             }
 346             let module = match glob_import.imported_module.get() {
 347                 Some(ModuleOrUniformRoot::Module(module)) => module,
 348                 Some(ModuleOrUniformRoot::UniformRoot(_)) => continue,
 349                 None => return Err(Undetermined),
 350             };
 351             let (orig_current_module, mut ident) = (self.current_module, ident.modern());
 352             match ident.span.glob_adjust(module.expansion, glob_import.span.ctxt().modern()) {
 353                 Some(Some(def)) => self.current_module = self.macro_def_scope(def),
 354                 Some(None) => {}
 355                 None => continue,
 356             };
 357             let result = self.resolve_ident_in_module_unadjusted(
 358                 ModuleOrUniformRoot::Module(module),
 359                 ident,
 360                 ns,
 361                 false,
 362                 false,
 363                 path_span,
 364             );
 365             self.current_module = orig_current_module;
 366             match result {
 367                 Err(Determined) => continue,
 368                 Ok(_) | Err(Undetermined) => return Err(Undetermined),
 369             }
 370         }
 371
 372         // No resolution and no one else can define the name - determinate error.
 373         Err(Determined)
 374     }
 375
 376     // Add an import directive to the current module.
 377     pub fn add_import_directive(&mut self,
 378                                 module_path: Vec<Ident>,
 379                                 subclass: ImportDirectiveSubclass<'a>,
 380                                 span: Span,
 381                                 id: NodeId,
 382                                 root_span: Span,
 383                                 root_id: NodeId,
 384                                 vis: ty::Visibility,
 385                                 expansion: Mark,
 386                                 is_uniform_paths_canary: bool) {
 387         let current_module = self.current_module;
 388         let directive = self.arenas.alloc_import_directive(ImportDirective {
 389             parent: current_module,
 390             module_path,
 391             imported_module: Cell::new(None),
 392             subclass,
 393             span,
 394             id,
 395             root_span,
 396             root_id,
 397             vis: Cell::new(vis),
 398             expansion,
 399             used: Cell::new(false),
 400             is_uniform_paths_canary,
 401         });
 402
 403         debug!("add_import_directive({:?})", directive);
 404
 405         self.indeterminate_imports.push(directive);
 406         match directive.subclass {
 407             SingleImport { target, type_ns_only, .. } => {
 408                 self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 409                     let mut resolution = this.resolution(current_module, target, ns).borrow_mut();
 410                     resolution.single_imports.insert(PtrKey(directive));
 411                 });
 412             }
 413             // We don't add prelude imports to the globs since they only affect lexical scopes,
 414             // which are not relevant to import resolution.
 415             GlobImport { is_prelude: true, .. } => {}
 416             GlobImport { .. } => self.current_module.globs.borrow_mut().push(directive),
 417             _ => unreachable!(),
 418         }
 419     }
 420
 421     // Given a binding and an import directive that resolves to it,
 422     // return the corresponding binding defined by the import directive.
 423     pub fn import(&self, binding: &'a NameBinding<'a>, directive: &'a ImportDirective<'a>)
 424                   -> &'a NameBinding<'a> {
 425         let vis = if binding.pseudo_vis().is_at_least(directive.vis.get(), self) ||
 426                      // c.f. `PUB_USE_OF_PRIVATE_EXTERN_CRATE`
 427                      !directive.is_glob() && binding.is_extern_crate() {
 428             directive.vis.get()
 429         } else {
 430             binding.pseudo_vis()
 431         };
 432
 433         if let GlobImport { ref max_vis, .. } = directive.subclass {
 434             if vis == directive.vis.get() || vis.is_at_least(max_vis.get(), self) {
 435                 max_vis.set(vis)
 436             }
 437         }
 438
 439         self.arenas.alloc_name_binding(NameBinding {
 440             kind: NameBindingKind::Import {
 441                 binding,
 442                 directive,
 443                 used: Cell::new(false),
 444             },
 445             span: directive.span,
 446             vis,
 447             expansion: directive.expansion,
 448         })
 449     }
 450
 451     // Define the name or return the existing binding if there is a collision.
 452     pub fn try_define(&mut self,
 453                       module: Module<'a>,
 454                       ident: Ident,
 455                       ns: Namespace,
 456                       binding: &'a NameBinding<'a>)
 457                       -> Result<(), &'a NameBinding<'a>> {
 458         self.update_resolution(module, ident, ns, |this, resolution| {
 459             if let Some(old_binding) = resolution.binding {
 460                 if binding.is_glob_import() {
 461                     if !old_binding.is_glob_import() &&
 462                        !(ns == MacroNS && old_binding.expansion != Mark::root()) {
 463                         resolution.shadowed_glob = Some(binding);
 464                     } else if binding.def() != old_binding.def() {
 465                         resolution.binding = Some(this.ambiguity(old_binding, binding));
 466                     } else if !old_binding.vis.is_at_least(binding.vis, &*this) {
 467                         // We are glob-importing the same item but with greater visibility.
 468                         resolution.binding = Some(binding);
 469                     }
 470                 } else if old_binding.is_glob_import() {
 471                     if ns == MacroNS && binding.expansion != Mark::root() &&
 472                        binding.def() != old_binding.def() {
 473                         resolution.binding = Some(this.ambiguity(binding, old_binding));
 474                     } else {
 475                         resolution.binding = Some(binding);
 476                         resolution.shadowed_glob = Some(old_binding);
 477                     }
 478                 } else if let (&NameBindingKind::Def(_, true), &NameBindingKind::Def(_, true)) =
 479                         (&old_binding.kind, &binding.kind) {
 480
 481                     this.session.buffer_lint_with_diagnostic(
 482                         DUPLICATE_MACRO_EXPORTS,
 483                         CRATE_NODE_ID,
 484                         binding.span,
 485                         &format!("a macro named `{}` has already been exported", ident),
 486                         BuiltinLintDiagnostics::DuplicatedMacroExports(
 487                             ident, old_binding.span, binding.span));
 488
 489                     resolution.binding = Some(binding);
 490                 } else {
 491                     return Err(old_binding);
 492                 }
 493             } else {
 494                 resolution.binding = Some(binding);
 495             }
 496
 497             Ok(())
 498         })
 499     }
 500
 501     pub fn ambiguity(&self, b1: &'a NameBinding<'a>, b2: &'a NameBinding<'a>)
 502                      -> &'a NameBinding<'a> {
 503         self.arenas.alloc_name_binding(NameBinding {
 504             kind: NameBindingKind::Ambiguity { b1, b2 },
 505             vis: if b1.vis.is_at_least(b2.vis, self) { b1.vis } else { b2.vis },
 506             span: b1.span,
 507             expansion: Mark::root(),
 508         })
 509     }
 510
 511     // Use `f` to mutate the resolution of the name in the module.
 512     // If the resolution becomes a success, define it in the module's glob importers.
 513     fn update_resolution<T, F>(&mut self, module: Module<'a>, ident: Ident, ns: Namespace, f: F)
 514                                -> T
 515         where F: FnOnce(&mut Resolver<'a, 'crateloader>, &mut NameResolution<'a>) -> T
 516     {
 517         // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
 518         // during which the resolution might end up getting re-defined via a glob cycle.
 519         let (binding, t) = {
 520             let resolution = &mut *self.resolution(module, ident, ns).borrow_mut();
 521             let old_binding = resolution.binding();
 522
 523             let t = f(self, resolution);
 524
 525             match resolution.binding() {
 526                 _ if old_binding.is_some() => return t,
 527                 None => return t,
 528                 Some(binding) => match old_binding {
 529                     Some(old_binding) if ptr::eq(old_binding, binding) => return t,
 530                     _ => (binding, t),
 531                 }
 532             }
 533         };
 534
 535         // Define `binding` in `module`s glob importers.
 536         for directive in module.glob_importers.borrow_mut().iter() {
 537             let mut ident = ident.modern();
 538             let scope = match ident.span.reverse_glob_adjust(module.expansion,
 539                                                              directive.span.ctxt().modern()) {
 540                 Some(Some(def)) => self.macro_def_scope(def),
 541                 Some(None) => directive.parent,
 542                 None => continue,
 543             };
 544             if self.is_accessible_from(binding.vis, scope) {
 545                 let imported_binding = self.import(binding, directive);
 546                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
 547             }
 548         }
 549
 550         t
 551     }
 552
 553     // Define a "dummy" resolution containing a Def::Err as a placeholder for a
 554     // failed resolution
 555     fn import_dummy_binding(&mut self, directive: &'a ImportDirective<'a>) {
 556         if let SingleImport { target, .. } = directive.subclass {
 557             let dummy_binding = self.dummy_binding;
 558             let dummy_binding = self.import(dummy_binding, directive);
 559             self.per_ns(|this, ns| {
 560                 let _ = this.try_define(directive.parent, target, ns, dummy_binding);
 561             });
 562         }
 563     }
 564 }
 565
 566 pub struct ImportResolver<'a, 'b: 'a, 'c: 'a + 'b> {
 567     pub resolver: &'a mut Resolver<'b, 'c>,
 568 }
 569
 570 impl<'a, 'b: 'a, 'c: 'a + 'b> ::std::ops::Deref for ImportResolver<'a, 'b, 'c> {
 571     type Target = Resolver<'b, 'c>;
 572     fn deref(&self) -> &Resolver<'b, 'c> {
 573         self.resolver
 574     }
 575 }
 576
 577 impl<'a, 'b: 'a, 'c: 'a + 'b> ::std::ops::DerefMut for ImportResolver<'a, 'b, 'c> {
 578     fn deref_mut(&mut self) -> &mut Resolver<'b, 'c> {
 579         self.resolver
 580     }
 581 }
 582
 583 impl<'a, 'b: 'a, 'c: 'a + 'b> ty::DefIdTree for &'a ImportResolver<'a, 'b, 'c> {
 584     fn parent(self, id: DefId) -> Option<DefId> {
 585         self.resolver.parent(id)
 586     }
 587 }
 588
 589 impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
 590     // Import resolution
 591     //
 592     // This is a fixed-point algorithm. We resolve imports until our efforts
 593     // are stymied by an unresolved import; then we bail out of the current
 594     // module and continue. We terminate successfully once no more imports
 595     // remain or unsuccessfully when no forward progress in resolving imports
 596     // is made.
 597
 598     /// Resolves all imports for the crate. This method performs the fixed-
 599     /// point iteration.
 600     pub fn resolve_imports(&mut self) {
 601         let mut prev_num_indeterminates = self.indeterminate_imports.len() + 1;
 602         while self.indeterminate_imports.len() < prev_num_indeterminates {
 603             prev_num_indeterminates = self.indeterminate_imports.len();
 604             for import in mem::replace(&mut self.indeterminate_imports, Vec::new()) {
 605                 match self.resolve_import(&import) {
 606                     true => self.determined_imports.push(import),
 607                     false => self.indeterminate_imports.push(import),
 608                 }
 609             }
 610         }
 611     }
 612
 613     pub fn finalize_imports(&mut self) {
 614         for module in self.arenas.local_modules().iter() {
 615             self.finalize_resolutions_in(module);
 616         }
 617
 618         let mut errors = false;
 619         let mut seen_spans = FxHashSet();
 620         for i in 0 .. self.determined_imports.len() {
 621             let import = self.determined_imports[i];
 622             let error = self.finalize_import(import);
 623
 624             // For a `#![feature(uniform_paths)]` `use self::x as _` canary,
 625             // failure is ignored, while success may cause an ambiguity error.
 626             if import.is_uniform_paths_canary {
 627                 let (name, result) = match import.subclass {
 628                     SingleImport { source, ref result, .. } => {
 629                         let type_ns = result[TypeNS].get().ok();
 630                         let value_ns = result[ValueNS].get().ok();
 631                         (source.name, type_ns.or(value_ns))
 632                     }
 633                     _ => bug!(),
 634                 };
 635
 636                 if error.is_some() {
 637                     continue;
 638                 }
 639
 640                 let is_explicit_self =
 641                     import.module_path.len() > 0 &&
 642                     import.module_path[0].name == keywords::SelfValue.name();
 643                 let extern_crate_exists = self.extern_prelude.contains(&name);
 644
 645                 // A successful `self::x` is ambiguous with an `x` external crate.
 646                 if is_explicit_self && !extern_crate_exists {
 647                     continue;
 648                 }
 649
 650                 errors = true;
 651
 652                 let msg = format!("import from `{}` is ambiguous", name);
 653                 let mut err = self.session.struct_span_err(import.span, &msg);
 654                 if extern_crate_exists {
 655                     err.span_label(import.span,
 656                         format!("could refer to external crate `::{}`", name));
 657                 }
 658                 if let Some(result) = result {
 659                     if is_explicit_self {
 660                         err.span_label(result.span,
 661                             format!("could also refer to `self::{}`", name));
 662                     } else {
 663                         err.span_label(result.span,
 664                             format!("shadowed by block-scoped `{}`", name));
 665                     }
 666                 }
 667                 err.help(&format!("write `::{0}` or `self::{0}` explicitly instead", name));
 668                 err.note("relative `use` paths enabled by `#![feature(uniform_paths)]`");
 669                 err.emit();
 670             } else if let Some((span, err)) = error {
 671                 errors = true;
 672
 673                 if let SingleImport { source, ref result, .. } = import.subclass {
 674                     if source.name == "self" {
 675                         // Silence `unresolved import` error if E0429 is already emitted
 676                         match result.value_ns.get() {
 677                             Err(Determined) => continue,
 678                             _ => {},
 679                         }
 680                     }
 681                 }
 682
 683                 // If the error is a single failed import then create a "fake" import
 684                 // resolution for it so that later resolve stages won't complain.
 685                 self.import_dummy_binding(import);
 686                 if !seen_spans.contains(&span) {
 687                     let path = import_path_to_string(&import.module_path[..],
 688                                                      &import.subclass,
 689                                                      span);
 690                     let error = ResolutionError::UnresolvedImport(Some((span, &path, &err)));
 691                     resolve_error(self.resolver, span, error);
 692                     seen_spans.insert(span);
 693                 }
 694             }
 695         }
 696
 697         // Report unresolved imports only if no hard error was already reported
 698         // to avoid generating multiple errors on the same import.
 699         if !errors {
 700             for import in &self.indeterminate_imports {
 701                 if import.is_uniform_paths_canary {
 702                     continue;
 703                 }
 704
 705                 let error = ResolutionError::UnresolvedImport(None);
 706                 resolve_error(self.resolver, import.span, error);
 707                 break;
 708             }
 709         }
 710     }
 711
 712     /// Attempts to resolve the given import, returning true if its resolution is determined.
 713     /// If successful, the resolved bindings are written into the module.
 714     fn resolve_import(&mut self, directive: &'b ImportDirective<'b>) -> bool {
 715         debug!("(resolving import for module) resolving import `{}::...` in `{}`",
 716                names_to_string(&directive.module_path[..]),
 717                module_to_string(self.current_module).unwrap_or("???".to_string()));
 718
 719         self.current_module = directive.parent;
 720
 721         let module = if let Some(module) = directive.imported_module.get() {
 722             module
 723         } else {
 724             let vis = directive.vis.get();
 725             // For better failure detection, pretend that the import will not define any names
 726             // while resolving its module path.
 727             directive.vis.set(ty::Visibility::Invisible);
 728             let result = self.resolve_path(
 729                 Some(if directive.is_uniform_paths_canary {
 730                     ModuleOrUniformRoot::Module(directive.parent)
 731                 } else {
 732                     ModuleOrUniformRoot::UniformRoot(keywords::Invalid.name())
 733                 }),
 734                 &directive.module_path[..],
 735                 None,
 736                 false,
 737                 directive.span,
 738                 directive.crate_lint(),
 739             );
 740             directive.vis.set(vis);
 741
 742             match result {
 743                 PathResult::Module(module) => module,
 744                 PathResult::Indeterminate => return false,
 745                 _ => return true,
 746             }
 747         };
 748
 749         directive.imported_module.set(Some(module));
 750         let (source, target, result, type_ns_only) = match directive.subclass {
 751             SingleImport { source, target, ref result, type_ns_only } =>
 752                 (source, target, result, type_ns_only),
 753             GlobImport { .. } => {
 754                 self.resolve_glob_import(directive);
 755                 return true;
 756             }
 757             _ => unreachable!(),
 758         };
 759
 760         let mut indeterminate = false;
 761         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 762             if let Err(Undetermined) = result[ns].get() {
 763                 result[ns].set(this.resolve_ident_in_module(module,
 764                                                             source,
 765                                                             ns,
 766                                                             false,
 767                                                             directive.span));
 768             } else {
 769                 return
 770             };
 771
 772             let parent = directive.parent;
 773             match result[ns].get() {
 774                 Err(Undetermined) => indeterminate = true,
 775                 Err(Determined) => {
 776                     this.update_resolution(parent, target, ns, |_, resolution| {
 777                         resolution.single_imports.remove(&PtrKey(directive));
 778                     });
 779                 }
 780                 Ok(binding) if !binding.is_importable() => {
 781                     let msg = format!("`{}` is not directly importable", target);
 782                     struct_span_err!(this.session, directive.span, E0253, "{}", &msg)
 783                         .span_label(directive.span, "cannot be imported directly")
 784                         .emit();
 785                     // Do not import this illegal binding. Import a dummy binding and pretend
 786                     // everything is fine
 787                     this.import_dummy_binding(directive);
 788                 }
 789                 Ok(binding) => {
 790                     let imported_binding = this.import(binding, directive);
 791                     let conflict = this.try_define(parent, target, ns, imported_binding);
 792                     if let Err(old_binding) = conflict {
 793                         this.report_conflict(parent, target, ns, imported_binding, old_binding);
 794                     }
 795                 }
 796             }
 797         });
 798
 799         !indeterminate
 800     }
 801
 802     // If appropriate, returns an error to report.
 803     fn finalize_import(&mut self, directive: &'b ImportDirective<'b>) -> Option<(Span, String)> {
 804         self.current_module = directive.parent;
 805         let ImportDirective { ref module_path, span, .. } = *directive;
 806
 807         let module_result = self.resolve_path(
 808             Some(if directive.is_uniform_paths_canary {
 809                 ModuleOrUniformRoot::Module(directive.parent)
 810             } else {
 811                 ModuleOrUniformRoot::UniformRoot(keywords::Invalid.name())
 812             }),
 813             &module_path,
 814             None,
 815             true,
 816             span,
 817             directive.crate_lint(),
 818         );
 819         let module = match module_result {
 820             PathResult::Module(module) => module,
 821             PathResult::Failed(span, msg, false) => {
 822                 resolve_error(self, span, ResolutionError::FailedToResolve(&msg));
 823                 return None;
 824             }
 825             PathResult::Failed(span, msg, true) => {
 826                 let (mut self_path, mut self_result) = (module_path.clone(), None);
 827                 let is_special = |ident: Ident| ident.is_path_segment_keyword() &&
 828                                                 ident.name != keywords::CrateRoot.name();
 829                 if !self_path.is_empty() && !is_special(self_path[0]) &&
 830                    !(self_path.len() > 1 && is_special(self_path[1])) {
 831                     self_path[0].name = keywords::SelfValue.name();
 832                     self_result = Some(self.resolve_path(None, &self_path, None, false,
 833                                                          span, CrateLint::No));
 834                 }
 835                 return if let Some(PathResult::Module(..)) = self_result {
 836                     Some((span, format!("Did you mean `{}`?", names_to_string(&self_path[..]))))
 837                 } else {
 838                     Some((span, msg))
 839                 };
 840             },
 841             _ => return None,
 842         };
 843
 844         let (ident, result, type_ns_only) = match directive.subclass {
 845             SingleImport { source, ref result, type_ns_only, .. } => (source, result, type_ns_only),
 846             GlobImport { is_prelude, ref max_vis } => {
 847                 if module_path.len() <= 1 {
 848                     // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
 849                     // 2 segments, so the `resolve_path` above won't trigger it.
 850                     let mut full_path = module_path.clone();
 851                     full_path.push(keywords::Invalid.ident());
 852                     self.lint_if_path_starts_with_module(
 853                         directive.crate_lint(),
 854                         &full_path,
 855                         directive.span,
 856                         None,
 857                     );
 858                 }
 859
 860                 if let ModuleOrUniformRoot::Module(module) = module {
 861                     if module.def_id() == directive.parent.def_id() {
 862                         // Importing a module into itself is not allowed.
 863                         return Some((directive.span,
 864                             "Cannot glob-import a module into itself.".to_string()));
 865                     }
 866                 }
 867                 if !is_prelude &&
 868                    max_vis.get() != ty::Visibility::Invisible && // Allow empty globs.
 869                    !max_vis.get().is_at_least(directive.vis.get(), &*self) {
 870                     let msg = "A non-empty glob must import something with the glob's visibility";
 871                     self.session.span_err(directive.span, msg);
 872                 }
 873                 return None;
 874             }
 875             _ => unreachable!(),
 876         };
 877
 878         let mut all_ns_err = true;
 879         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 880             if let Ok(binding) = result[ns].get() {
 881                 all_ns_err = false;
 882                 if this.record_use(ident, ns, binding, directive.span) {
 883                     if let ModuleOrUniformRoot::Module(module) = module {
 884                         this.resolution(module, ident, ns).borrow_mut().binding =
 885                             Some(this.dummy_binding);
 886                     }
 887                 }
 888             }
 889         });
 890
 891         if all_ns_err {
 892             let mut all_ns_failed = true;
 893             self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 894                 match this.resolve_ident_in_module(module, ident, ns, true, span) {
 895                     Ok(_) => all_ns_failed = false,
 896                     _ => {}
 897                 }
 898             });
 899
 900             return if all_ns_failed {
 901                 let resolutions = match module {
 902                     ModuleOrUniformRoot::Module(module) =>
 903                         Some(module.resolutions.borrow()),
 904                     ModuleOrUniformRoot::UniformRoot(_) => None,
 905                 };
 906                 let resolutions = resolutions.as_ref().into_iter().flat_map(|r| r.iter());
 907                 let names = resolutions.filter_map(|(&(ref i, _), resolution)| {
 908                     if *i == ident { return None; } // Never suggest the same name
 909                     match *resolution.borrow() {
 910                         NameResolution { binding: Some(name_binding), .. } => {
 911                             match name_binding.kind {
 912                                 NameBindingKind::Import { binding, .. } => {
 913                                     match binding.kind {
 914                                         // Never suggest the name that has binding error
 915                                         // i.e. the name that cannot be previously resolved
 916                                         NameBindingKind::Def(Def::Err, _) => return None,
 917                                         _ => Some(&i.name),
 918                                     }
 919                                 },
 920                                 _ => Some(&i.name),
 921                             }
 922                         },
 923                         NameResolution { ref single_imports, .. }
 924                             if single_imports.is_empty() => None,
 925                         _ => Some(&i.name),
 926                     }
 927                 });
 928                 let lev_suggestion =
 929                     match find_best_match_for_name(names, &ident.as_str(), None) {
 930                         Some(name) => format!(". Did you mean to use `{}`?", name),
 931                         None => "".to_owned(),
 932                     };
 933                 let msg = match module {
 934                     ModuleOrUniformRoot::Module(module) => {
 935                         let module_str = module_to_string(module);
 936                         if let Some(module_str) = module_str {
 937                             format!("no `{}` in `{}`{}", ident, module_str, lev_suggestion)
 938                         } else {
 939                             format!("no `{}` in the root{}", ident, lev_suggestion)
 940                         }
 941                     }
 942                     ModuleOrUniformRoot::UniformRoot(_) => {
 943                         if !ident.is_path_segment_keyword() {
 944                             format!("no `{}` external crate{}", ident, lev_suggestion)
 945                         } else {
 946                             // HACK(eddyb) this shows up for `self` & `super`, which
 947                             // should work instead - for now keep the same error message.
 948                             format!("no `{}` in the root{}", ident, lev_suggestion)
 949                         }
 950                     }
 951                 };
 952                 Some((span, msg))
 953             } else {
 954                 // `resolve_ident_in_module` reported a privacy error.
 955                 self.import_dummy_binding(directive);
 956                 None
 957             }
 958         }
 959
 960         let mut reexport_error = None;
 961         let mut any_successful_reexport = false;
 962         self.per_ns(|this, ns| {
 963             if let Ok(binding) = result[ns].get() {
 964                 let vis = directive.vis.get();
 965                 if !binding.pseudo_vis().is_at_least(vis, &*this) {
 966                     reexport_error = Some((ns, binding));
 967                 } else {
 968                     any_successful_reexport = true;
 969                 }
 970             }
 971         });
 972
 973         // All namespaces must be re-exported with extra visibility for an error to occur.
 974         if !any_successful_reexport {
 975             let (ns, binding) = reexport_error.unwrap();
 976             if ns == TypeNS && binding.is_extern_crate() {
 977                 let msg = format!("extern crate `{}` is private, and cannot be \
 978                                    re-exported (error E0365), consider declaring with \
 979                                    `pub`",
 980                                    ident);
 981                 self.session.buffer_lint(PUB_USE_OF_PRIVATE_EXTERN_CRATE,
 982                                          directive.id,
 983                                          directive.span,
 984                                          &msg);
 985             } else if ns == TypeNS {
 986                 struct_span_err!(self.session, directive.span, E0365,
 987                                  "`{}` is private, and cannot be re-exported", ident)
 988                     .span_label(directive.span, format!("re-export of private `{}`", ident))
 989                     .note(&format!("consider declaring type or module `{}` with `pub`", ident))
 990                     .emit();
 991             } else {
 992                 let msg = format!("`{}` is private, and cannot be re-exported", ident);
 993                 let note_msg =
 994                     format!("consider marking `{}` as `pub` in the imported module", ident);
 995                 struct_span_err!(self.session, directive.span, E0364, "{}", &msg)
 996                     .span_note(directive.span, &note_msg)
 997                     .emit();
 998             }
 999         }
1000
1001         if module_path.len() <= 1 {
1002             // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
1003             // 2 segments, so the `resolve_path` above won't trigger it.
1004             let mut full_path = module_path.clone();
1005             full_path.push(ident);
1006             self.per_ns(|this, ns| {
1007                 if let Ok(binding) = result[ns].get() {
1008                     this.lint_if_path_starts_with_module(
1009                         directive.crate_lint(),
1010                         &full_path,
1011                         directive.span,
1012                         Some(binding),
1013                     );
1014                 }
1015             });
1016         }
1017
1018         // Record what this import resolves to for later uses in documentation,
1019         // this may resolve to either a value or a type, but for documentation
1020         // purposes it's good enough to just favor one over the other.
1021         self.per_ns(|this, ns| if let Some(binding) = result[ns].get().ok() {
1022             let import = this.import_map.entry(directive.id).or_default();
1023             import[ns] = Some(PathResolution::new(binding.def()));
1024         });
1025
1026         debug!("(resolving single import) successfully resolved import");
1027         None
1028     }
1029
1030     fn resolve_glob_import(&mut self, directive: &'b ImportDirective<'b>) {
1031         let module = match directive.imported_module.get().unwrap() {
1032             ModuleOrUniformRoot::Module(module) => module,
1033             ModuleOrUniformRoot::UniformRoot(_) => {
1034                 self.session.span_err(directive.span,
1035                     "cannot glob-import all possible crates");
1036                 return;
1037             }
1038         };
1039
1040         self.populate_module_if_necessary(module);
1041
1042         if let Some(Def::Trait(_)) = module.def() {
1043             self.session.span_err(directive.span, "items in traits are not importable.");
1044             return;
1045         } else if module.def_id() == directive.parent.def_id()  {
1046             return;
1047         } else if let GlobImport { is_prelude: true, .. } = directive.subclass {
1048             self.prelude = Some(module);
1049             return;
1050         }
1051
1052         // Add to module's glob_importers
1053         module.glob_importers.borrow_mut().push(directive);
1054
1055         // Ensure that `resolutions` isn't borrowed during `try_define`,
1056         // since it might get updated via a glob cycle.
1057         let bindings = module.resolutions.borrow().iter().filter_map(|(&ident, resolution)| {
1058             resolution.borrow().binding().map(|binding| (ident, binding))
1059         }).collect::<Vec<_>>();
1060         for ((mut ident, ns), binding) in bindings {
1061             let scope = match ident.span.reverse_glob_adjust(module.expansion,
1062                                                              directive.span.ctxt().modern()) {
1063                 Some(Some(def)) => self.macro_def_scope(def),
1064                 Some(None) => self.current_module,
1065                 None => continue,
1066             };
1067             if self.is_accessible_from(binding.pseudo_vis(), scope) {
1068                 let imported_binding = self.import(binding, directive);
1069                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
1070             }
1071         }
1072
1073         // Record the destination of this import
1074         self.record_def(directive.id, PathResolution::new(module.def().unwrap()));
1075     }
1076
1077     // Miscellaneous post-processing, including recording re-exports,
1078     // reporting conflicts, and reporting unresolved imports.
1079     fn finalize_resolutions_in(&mut self, module: Module<'b>) {
1080         // Since import resolution is finished, globs will not define any more names.
1081         *module.globs.borrow_mut() = Vec::new();
1082
1083         let mut reexports = Vec::new();
1084         let mut exported_macro_names = FxHashMap();
1085         if ptr::eq(module, self.graph_root) {
1086             let macro_exports = mem::replace(&mut self.macro_exports, Vec::new());
1087             for export in macro_exports.into_iter().rev() {
1088                 if let Some(later_span) = exported_macro_names.insert(export.ident.modern(),
1089                                                                       export.span) {
1090                     self.session.buffer_lint_with_diagnostic(
1091                         DUPLICATE_MACRO_EXPORTS,
1092                         CRATE_NODE_ID,
1093                         later_span,
1094                         &format!("a macro named `{}` has already been exported", export.ident),
1095                         BuiltinLintDiagnostics::DuplicatedMacroExports(
1096                             export.ident, export.span, later_span));
1097                 } else {
1098                     reexports.push(export);
1099                 }
1100             }
1101         }
1102
1103         for (&(ident, ns), resolution) in module.resolutions.borrow().iter() {
1104             let resolution = &mut *resolution.borrow_mut();
1105             let binding = match resolution.binding {
1106                 Some(binding) => binding,
1107                 None => continue,
1108             };
1109
1110             if binding.is_import() || binding.is_macro_def() {
1111                 let def = binding.def();
1112                 if def != Def::Err {
1113                     if !def.def_id().is_local() {
1114                         self.cstore.export_macros_untracked(def.def_id().krate);
1115                     }
1116                     if let Def::Macro(..) = def {
1117                         if let Some(&span) = exported_macro_names.get(&ident.modern()) {
1118                             let msg =
1119                                 format!("a macro named `{}` has already been exported", ident);
1120                             self.session.struct_span_err(span, &msg)
1121                                 .span_label(span, format!("`{}` already exported", ident))
1122                                 .span_note(binding.span, "previous macro export here")
1123                                 .emit();
1124                         }
1125                     }
1126                     reexports.push(Export {
1127                         ident: ident.modern(),
1128                         def: def,
1129                         span: binding.span,
1130                         vis: binding.vis,
1131                     });
1132                 }
1133             }
1134
1135             match binding.kind {
1136                 NameBindingKind::Import { binding: orig_binding, directive, .. } => {
1137                     if ns == TypeNS && orig_binding.is_variant() &&
1138                         !orig_binding.vis.is_at_least(binding.vis, &*self) {
1139                             let msg = match directive.subclass {
1140                                 ImportDirectiveSubclass::SingleImport { .. } => {
1141                                     format!("variant `{}` is private and cannot be re-exported",
1142                                             ident)
1143                                 },
1144                                 ImportDirectiveSubclass::GlobImport { .. } => {
1145                                     let msg = "enum is private and its variants \
1146                                                cannot be re-exported".to_owned();
1147                                     let error_id = (DiagnosticMessageId::ErrorId(0), // no code?!
1148                                                     Some(binding.span),
1149                                                     msg.clone());
1150                                     let fresh = self.session.one_time_diagnostics
1151                                         .borrow_mut().insert(error_id);
1152                                     if !fresh {
1153                                         continue;
1154                                     }
1155                                     msg
1156                                 },
1157                                 ref s @ _ => bug!("unexpected import subclass {:?}", s)
1158                             };
1159                             let mut err = self.session.struct_span_err(binding.span, &msg);
1160
1161                             let imported_module = match directive.imported_module.get() {
1162                                 Some(ModuleOrUniformRoot::Module(module)) => module,
1163                                 _ => bug!("module should exist"),
1164                             };
1165                             let resolutions = imported_module.parent.expect("parent should exist")
1166                                 .resolutions.borrow();
1167                             let enum_path_segment_index = directive.module_path.len() - 1;
1168                             let enum_ident = directive.module_path[enum_path_segment_index];
1169
1170                             let enum_resolution = resolutions.get(&(enum_ident, TypeNS))
1171                                 .expect("resolution should exist");
1172                             let enum_span = enum_resolution.borrow()
1173                                 .binding.expect("binding should exist")
1174                                 .span;
1175                             let enum_def_span = self.session.codemap().def_span(enum_span);
1176                             let enum_def_snippet = self.session.codemap()
1177                                 .span_to_snippet(enum_def_span).expect("snippet should exist");
1178                             // potentially need to strip extant `crate`/`pub(path)` for suggestion
1179                             let after_vis_index = enum_def_snippet.find("enum")
1180                                 .expect("`enum` keyword should exist in snippet");
1181                             let suggestion = format!("pub {}",
1182                                                      &enum_def_snippet[after_vis_index..]);
1183
1184                             self.session
1185                                 .diag_span_suggestion_once(&mut err,
1186                                                            DiagnosticMessageId::ErrorId(0),
1187                                                            enum_def_span,
1188                                                            "consider making the enum public",
1189                                                            suggestion);
1190                             err.emit();
1191                     }
1192                 }
1193                 _ => {}
1194             }
1195         }
1196
1197         if reexports.len() > 0 {
1198             if let Some(def_id) = module.def_id() {
1199                 self.export_map.insert(def_id, reexports);
1200             }
1201         }
1202     }
1203 }
1204
1205 fn import_path_to_string(names: &[Ident],
1206                          subclass: &ImportDirectiveSubclass,
1207                          span: Span) -> String {
1208     let pos = names.iter()
1209         .position(|p| span == p.span && p.name != keywords::CrateRoot.name());
1210     let global = !names.is_empty() && names[0].name == keywords::CrateRoot.name();
1211     if let Some(pos) = pos {
1212         let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
1213         names_to_string(names)
1214     } else {
1215         let names = if global { &names[1..] } else { names };
1216         if names.is_empty() {
1217             import_directive_subclass_to_string(subclass)
1218         } else {
1219             format!("{}::{}",
1220                     names_to_string(names),
1221                     import_directive_subclass_to_string(subclass))
1222         }
1223     }
1224 }
1225
1226 fn import_directive_subclass_to_string(subclass: &ImportDirectiveSubclass) -> String {
1227     match *subclass {
1228         SingleImport { source, .. } => source.to_string(),
1229         GlobImport { .. } => "*".to_string(),
1230         ExternCrate(_) => "<extern crate>".to_string(),
1231         MacroUse => "#[macro_use]".to_string(),
1232     }
1233 }