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, Module, PerNS};
  14 use Namespace::{self, TypeNS, MacroNS};
  15 use {NameBinding, NameBindingKind, PathResult, PrivacyError};
  16 use Resolver;
  17 use {names_to_string, module_to_string};
  18 use {resolve_error, ResolutionError};
  19
  20 use rustc::ty;
  21 use rustc::lint::builtin::PUB_USE_OF_PRIVATE_EXTERN_CRATE;
  22 use rustc::hir::def_id::DefId;
  23 use rustc::hir::def::*;
  24 use rustc::util::nodemap::{FxHashMap, FxHashSet};
  25
  26 use syntax::ast::{Ident, Name, SpannedIdent, NodeId};
  27 use syntax::ext::base::Determinacy::{self, Determined, Undetermined};
  28 use syntax::ext::hygiene::Mark;
  29 use syntax::parse::token;
  30 use syntax::symbol::keywords;
  31 use syntax::util::lev_distance::find_best_match_for_name;
  32 use syntax_pos::Span;
  33
  34 use std::cell::{Cell, RefCell};
  35 use std::mem;
  36
  37 /// Contains data for specific types of import directives.
  38 #[derive(Clone, Debug)]
  39 pub enum ImportDirectiveSubclass<'a> {
  40     SingleImport {
  41         target: Ident,
  42         source: Ident,
  43         result: PerNS<Cell<Result<&'a NameBinding<'a>, Determinacy>>>,
  44         type_ns_only: bool,
  45     },
  46     GlobImport {
  47         is_prelude: bool,
  48         max_vis: Cell<ty::Visibility>, // The visibility of the greatest reexport.
  49         // n.b. `max_vis` is only used in `finalize_import` to check for reexport errors.
  50     },
  51     ExternCrate(Option<Name>),
  52     MacroUse,
  53 }
  54
  55 /// One import directive.
  56 #[derive(Debug,Clone)]
  57 pub struct ImportDirective<'a> {
  58     pub id: NodeId,
  59     pub parent: Module<'a>,
  60     pub module_path: Vec<SpannedIdent>,
  61     pub imported_module: Cell<Option<Module<'a>>>, // the resolution of `module_path`
  62     pub subclass: ImportDirectiveSubclass<'a>,
  63     pub span: Span,
  64     pub vis: Cell<ty::Visibility>,
  65     pub expansion: Mark,
  66     pub used: Cell<bool>,
  67 }
  68
  69 impl<'a> ImportDirective<'a> {
  70     pub fn is_glob(&self) -> bool {
  71         match self.subclass { ImportDirectiveSubclass::GlobImport { .. } => true, _ => false }
  72     }
  73 }
  74
  75 #[derive(Clone, Default)]
  76 /// Records information about the resolution of a name in a namespace of a module.
  77 pub struct NameResolution<'a> {
  78     /// The single imports that define the name in the namespace.
  79     single_imports: SingleImports<'a>,
  80     /// The least shadowable known binding for this name, or None if there are no known bindings.
  81     pub binding: Option<&'a NameBinding<'a>>,
  82     shadows_glob: Option<&'a NameBinding<'a>>,
  83 }
  84
  85 #[derive(Clone, Debug)]
  86 enum SingleImports<'a> {
  87     /// No single imports can define the name in the namespace.
  88     None,
  89     /// Only the given single import can define the name in the namespace.
  90     MaybeOne(&'a ImportDirective<'a>),
  91     /// At least one single import will define the name in the namespace.
  92     AtLeastOne,
  93 }
  94
  95 impl<'a> Default for SingleImports<'a> {
  96     /// Creates a `SingleImports<'a>` of None type.
  97     fn default() -> Self {
  98         SingleImports::None
  99     }
 100 }
 101
 102 impl<'a> SingleImports<'a> {
 103     fn add_directive(&mut self, directive: &'a ImportDirective<'a>) {
 104         match *self {
 105             SingleImports::None => *self = SingleImports::MaybeOne(directive),
 106             // If two single imports can define the name in the namespace, we can assume that at
 107             // least one of them will define it since otherwise both would have to define only one
 108             // namespace, leading to a duplicate error.
 109             SingleImports::MaybeOne(_) => *self = SingleImports::AtLeastOne,
 110             SingleImports::AtLeastOne => {}
 111         };
 112     }
 113
 114     fn directive_failed(&mut self) {
 115         match *self {
 116             SingleImports::None => unreachable!(),
 117             SingleImports::MaybeOne(_) => *self = SingleImports::None,
 118             SingleImports::AtLeastOne => {}
 119         }
 120     }
 121 }
 122
 123 impl<'a> NameResolution<'a> {
 124     // Returns the binding for the name if it is known or None if it not known.
 125     fn binding(&self) -> Option<&'a NameBinding<'a>> {
 126         self.binding.and_then(|binding| match self.single_imports {
 127             SingleImports::None => Some(binding),
 128             _ if !binding.is_glob_import() => Some(binding),
 129             _ => None, // The binding could be shadowed by a single import, so it is not known.
 130         })
 131     }
 132 }
 133
 134 impl<'a> Resolver<'a> {
 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`, import resolution must be complete.
 143     pub fn resolve_ident_in_module_unadjusted(&mut self,
 144                                               module: Module<'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         self.populate_module_if_necessary(module);
 152
 153         let resolution = self.resolution(module, ident, ns)
 154             .try_borrow_mut()
 155             .map_err(|_| Determined)?; // This happens when there is a cycle of imports
 156
 157         if record_used {
 158             if let Some(binding) = resolution.binding {
 159                 if let Some(shadowed_glob) = resolution.shadows_glob {
 160                     let name = ident.name;
 161                     // Forbid expanded shadowing to avoid time travel.
 162                     if restricted_shadowing &&
 163                        binding.expansion != Mark::root() &&
 164                        ns != MacroNS && // In MacroNS, `try_define` always forbids this shadowing
 165                        binding.def() != shadowed_glob.def() {
 166                         self.ambiguity_errors.push(AmbiguityError {
 167                             span: path_span,
 168                             name,
 169                             lexical: false,
 170                             b1: binding,
 171                             b2: shadowed_glob,
 172                             legacy: false,
 173                         });
 174                     }
 175                 }
 176                 if self.record_use(ident, ns, binding, path_span) {
 177                     return Ok(self.dummy_binding);
 178                 }
 179                 if !self.is_accessible(binding.vis) {
 180                     self.privacy_errors.push(PrivacyError(path_span, ident.name, binding));
 181                 }
 182             }
 183
 184             return resolution.binding.ok_or(Determined);
 185         }
 186
 187         let check_usable = |this: &mut Self, binding: &'a NameBinding<'a>| {
 188             // `extern crate` are always usable for backwards compatability, see issue #37020.
 189             let usable = this.is_accessible(binding.vis) || binding.is_extern_crate();
 190             if usable { Ok(binding) } else { Err(Determined) }
 191         };
 192
 193         // Items and single imports are not shadowable.
 194         if let Some(binding) = resolution.binding {
 195             if !binding.is_glob_import() {
 196                 return check_usable(self, binding);
 197             }
 198         }
 199
 200         // Check if a single import can still define the name.
 201         match resolution.single_imports {
 202             SingleImports::AtLeastOne => return Err(Undetermined),
 203             SingleImports::MaybeOne(directive) if self.is_accessible(directive.vis.get()) => {
 204                 let module = match directive.imported_module.get() {
 205                     Some(module) => module,
 206                     None => return Err(Undetermined),
 207                 };
 208                 let ident = match directive.subclass {
 209                     SingleImport { source, .. } => source,
 210                     _ => unreachable!(),
 211                 };
 212                 match self.resolve_ident_in_module(module, ident, ns, false, false, path_span) {
 213                     Err(Determined) => {}
 214                     _ => return Err(Undetermined),
 215                 }
 216             }
 217             SingleImports::MaybeOne(_) | SingleImports::None => {},
 218         }
 219
 220         let no_unresolved_invocations =
 221             restricted_shadowing || module.unresolved_invocations.borrow().is_empty();
 222         match resolution.binding {
 223             // In `MacroNS`, expanded bindings do not shadow (enforced in `try_define`).
 224             Some(binding) if no_unresolved_invocations || ns == MacroNS =>
 225                 return check_usable(self, binding),
 226             None if no_unresolved_invocations => {}
 227             _ => return Err(Undetermined),
 228         }
 229
 230         // Check if the globs are determined
 231         if restricted_shadowing && module.def().is_some() {
 232             return Err(Determined);
 233         }
 234         for directive in module.globs.borrow().iter() {
 235             if !self.is_accessible(directive.vis.get()) {
 236                 continue
 237             }
 238             let module = unwrap_or!(directive.imported_module.get(), return Err(Undetermined));
 239             let (orig_current_module, mut ident) = (self.current_module, ident.modern());
 240             match ident.ctxt.glob_adjust(module.expansion, directive.span.ctxt().modern()) {
 241                 Some(Some(def)) => self.current_module = self.macro_def_scope(def),
 242                 Some(None) => {}
 243                 None => continue,
 244             };
 245             let result = self.resolve_ident_in_module_unadjusted(
 246                 module, ident, ns, false, false, path_span,
 247             );
 248             self.current_module = orig_current_module;
 249             if let Err(Undetermined) = result {
 250                 return Err(Undetermined);
 251             }
 252         }
 253
 254         Err(Determined)
 255     }
 256
 257     // Add an import directive to the current module.
 258     pub fn add_import_directive(&mut self,
 259                                 module_path: Vec<SpannedIdent>,
 260                                 subclass: ImportDirectiveSubclass<'a>,
 261                                 span: Span,
 262                                 id: NodeId,
 263                                 vis: ty::Visibility,
 264                                 expansion: Mark) {
 265         let current_module = self.current_module;
 266         let directive = self.arenas.alloc_import_directive(ImportDirective {
 267             parent: current_module,
 268             module_path,
 269             imported_module: Cell::new(None),
 270             subclass,
 271             span,
 272             id,
 273             vis: Cell::new(vis),
 274             expansion,
 275             used: Cell::new(false),
 276         });
 277
 278         self.indeterminate_imports.push(directive);
 279         match directive.subclass {
 280             SingleImport { target, .. } => {
 281                 self.per_ns(|this, ns| {
 282                     let mut resolution = this.resolution(current_module, target, ns).borrow_mut();
 283                     resolution.single_imports.add_directive(directive);
 284                 });
 285             }
 286             // We don't add prelude imports to the globs since they only affect lexical scopes,
 287             // which are not relevant to import resolution.
 288             GlobImport { is_prelude: true, .. } => {}
 289             GlobImport { .. } => self.current_module.globs.borrow_mut().push(directive),
 290             _ => unreachable!(),
 291         }
 292     }
 293
 294     // Given a binding and an import directive that resolves to it,
 295     // return the corresponding binding defined by the import directive.
 296     pub fn import(&self, binding: &'a NameBinding<'a>, directive: &'a ImportDirective<'a>)
 297                   -> &'a NameBinding<'a> {
 298         let vis = if binding.pseudo_vis().is_at_least(directive.vis.get(), self) ||
 299                      // c.f. `PUB_USE_OF_PRIVATE_EXTERN_CRATE`
 300                      !directive.is_glob() && binding.is_extern_crate() {
 301             directive.vis.get()
 302         } else {
 303             binding.pseudo_vis()
 304         };
 305
 306         if let GlobImport { ref max_vis, .. } = directive.subclass {
 307             if vis == directive.vis.get() || vis.is_at_least(max_vis.get(), self) {
 308                 max_vis.set(vis)
 309             }
 310         }
 311
 312         self.arenas.alloc_name_binding(NameBinding {
 313             kind: NameBindingKind::Import {
 314                 binding,
 315                 directive,
 316                 used: Cell::new(false),
 317                 legacy_self_import: false,
 318             },
 319             span: directive.span,
 320             vis,
 321             expansion: directive.expansion,
 322         })
 323     }
 324
 325     // Define the name or return the existing binding if there is a collision.
 326     pub fn try_define(&mut self,
 327                       module: Module<'a>,
 328                       ident: Ident,
 329                       ns: Namespace,
 330                       binding: &'a NameBinding<'a>)
 331                       -> Result<(), &'a NameBinding<'a>> {
 332         self.update_resolution(module, ident, ns, |this, resolution| {
 333             if let Some(old_binding) = resolution.binding {
 334                 if binding.is_glob_import() {
 335                     if !old_binding.is_glob_import() &&
 336                        !(ns == MacroNS && old_binding.expansion != Mark::root()) {
 337                         resolution.shadows_glob = Some(binding);
 338                     } else if binding.def() != old_binding.def() {
 339                         resolution.binding = Some(this.ambiguity(old_binding, binding));
 340                     } else if !old_binding.vis.is_at_least(binding.vis, &*this) {
 341                         // We are glob-importing the same item but with greater visibility.
 342                         resolution.binding = Some(binding);
 343                     }
 344                 } else if old_binding.is_glob_import() {
 345                     if ns == MacroNS && binding.expansion != Mark::root() &&
 346                        binding.def() != old_binding.def() {
 347                         resolution.binding = Some(this.ambiguity(binding, old_binding));
 348                     } else {
 349                         resolution.binding = Some(binding);
 350                         resolution.shadows_glob = Some(old_binding);
 351                     }
 352                 } else {
 353                     return Err(old_binding);
 354                 }
 355             } else {
 356                 resolution.binding = Some(binding);
 357             }
 358
 359             Ok(())
 360         })
 361     }
 362
 363     pub fn ambiguity(&self, b1: &'a NameBinding<'a>, b2: &'a NameBinding<'a>)
 364                      -> &'a NameBinding<'a> {
 365         self.arenas.alloc_name_binding(NameBinding {
 366             kind: NameBindingKind::Ambiguity { b1: b1, b2: b2, legacy: false },
 367             vis: if b1.vis.is_at_least(b2.vis, self) { b1.vis } else { b2.vis },
 368             span: b1.span,
 369             expansion: Mark::root(),
 370         })
 371     }
 372
 373     // Use `f` to mutate the resolution of the name in the module.
 374     // If the resolution becomes a success, define it in the module's glob importers.
 375     fn update_resolution<T, F>(&mut self, module: Module<'a>, ident: Ident, ns: Namespace, f: F)
 376                                -> T
 377         where F: FnOnce(&mut Resolver<'a>, &mut NameResolution<'a>) -> T
 378     {
 379         // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
 380         // during which the resolution might end up getting re-defined via a glob cycle.
 381         let (binding, t) = {
 382             let resolution = &mut *self.resolution(module, ident, ns).borrow_mut();
 383             let old_binding = resolution.binding();
 384
 385             let t = f(self, resolution);
 386
 387             match resolution.binding() {
 388                 _ if old_binding.is_some() => return t,
 389                 None => return t,
 390                 Some(binding) => match old_binding {
 391                     Some(old_binding) if old_binding as *const _ == binding as *const _ => return t,
 392                     _ => (binding, t),
 393                 }
 394             }
 395         };
 396
 397         // Define `binding` in `module`s glob importers.
 398         for directive in module.glob_importers.borrow_mut().iter() {
 399             let mut ident = ident.modern();
 400             let scope = match ident.ctxt.reverse_glob_adjust(module.expansion,
 401                                                              directive.span.ctxt().modern()) {
 402                 Some(Some(def)) => self.macro_def_scope(def),
 403                 Some(None) => directive.parent,
 404                 None => continue,
 405             };
 406             if self.is_accessible_from(binding.vis, scope) {
 407                 let imported_binding = self.import(binding, directive);
 408                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
 409             }
 410         }
 411
 412         t
 413     }
 414
 415     // Define a "dummy" resolution containing a Def::Err as a placeholder for a
 416     // failed resolution
 417     fn import_dummy_binding(&mut self, directive: &'a ImportDirective<'a>) {
 418         if let SingleImport { target, .. } = directive.subclass {
 419             let dummy_binding = self.dummy_binding;
 420             let dummy_binding = self.import(dummy_binding, directive);
 421             self.per_ns(|this, ns| {
 422                 let _ = this.try_define(directive.parent, target, ns, dummy_binding);
 423             });
 424         }
 425     }
 426 }
 427
 428 pub struct ImportResolver<'a, 'b: 'a> {
 429     pub resolver: &'a mut Resolver<'b>,
 430 }
 431
 432 impl<'a, 'b: 'a> ::std::ops::Deref for ImportResolver<'a, 'b> {
 433     type Target = Resolver<'b>;
 434     fn deref(&self) -> &Resolver<'b> {
 435         self.resolver
 436     }
 437 }
 438
 439 impl<'a, 'b: 'a> ::std::ops::DerefMut for ImportResolver<'a, 'b> {
 440     fn deref_mut(&mut self) -> &mut Resolver<'b> {
 441         self.resolver
 442     }
 443 }
 444
 445 impl<'a, 'b: 'a> ty::DefIdTree for &'a ImportResolver<'a, 'b> {
 446     fn parent(self, id: DefId) -> Option<DefId> {
 447         self.resolver.parent(id)
 448     }
 449 }
 450
 451 impl<'a, 'b:'a> ImportResolver<'a, 'b> {
 452     // Import resolution
 453     //
 454     // This is a fixed-point algorithm. We resolve imports until our efforts
 455     // are stymied by an unresolved import; then we bail out of the current
 456     // module and continue. We terminate successfully once no more imports
 457     // remain or unsuccessfully when no forward progress in resolving imports
 458     // is made.
 459
 460     /// Resolves all imports for the crate. This method performs the fixed-
 461     /// point iteration.
 462     pub fn resolve_imports(&mut self) {
 463         let mut prev_num_indeterminates = self.indeterminate_imports.len() + 1;
 464         while self.indeterminate_imports.len() < prev_num_indeterminates {
 465             prev_num_indeterminates = self.indeterminate_imports.len();
 466             for import in mem::replace(&mut self.indeterminate_imports, Vec::new()) {
 467                 match self.resolve_import(&import) {
 468                     true => self.determined_imports.push(import),
 469                     false => self.indeterminate_imports.push(import),
 470                 }
 471             }
 472         }
 473     }
 474
 475     pub fn finalize_imports(&mut self) {
 476         for module in self.arenas.local_modules().iter() {
 477             self.finalize_resolutions_in(module);
 478         }
 479
 480         let mut errors = false;
 481         let mut seen_spans = FxHashSet();
 482         for i in 0 .. self.determined_imports.len() {
 483             let import = self.determined_imports[i];
 484             if let Some((span, err)) = self.finalize_import(import) {
 485                 errors = true;
 486
 487                 if let SingleImport { source, ref result, .. } = import.subclass {
 488                     if source.name == "self" {
 489                         // Silence `unresolved import` error if E0429 is already emitted
 490                         match result.value_ns.get() {
 491                             Err(Determined) => continue,
 492                             _ => {},
 493                         }
 494                     }
 495                 }
 496
 497                 // If the error is a single failed import then create a "fake" import
 498                 // resolution for it so that later resolve stages won't complain.
 499                 self.import_dummy_binding(import);
 500                 if !seen_spans.contains(&span) {
 501                     let path = import_path_to_string(&import.module_path[..],
 502                                                      &import.subclass,
 503                                                      span);
 504                     let error = ResolutionError::UnresolvedImport(Some((span, &path, &err)));
 505                     resolve_error(self.resolver, span, error);
 506                     seen_spans.insert(span);
 507                 }
 508             }
 509         }
 510
 511         // Report unresolved imports only if no hard error was already reported
 512         // to avoid generating multiple errors on the same import.
 513         if !errors {
 514             if let Some(import) = self.indeterminate_imports.iter().next() {
 515                 let error = ResolutionError::UnresolvedImport(None);
 516                 resolve_error(self.resolver, import.span, error);
 517             }
 518         }
 519     }
 520
 521     /// Attempts to resolve the given import, returning true if its resolution is determined.
 522     /// If successful, the resolved bindings are written into the module.
 523     fn resolve_import(&mut self, directive: &'b ImportDirective<'b>) -> bool {
 524         debug!("(resolving import for module) resolving import `{}::...` in `{}`",
 525                names_to_string(&directive.module_path[..]),
 526                module_to_string(self.current_module));
 527
 528         self.current_module = directive.parent;
 529
 530         let module = if let Some(module) = directive.imported_module.get() {
 531             module
 532         } else {
 533             let vis = directive.vis.get();
 534             // For better failure detection, pretend that the import will not define any names
 535             // while resolving its module path.
 536             directive.vis.set(ty::Visibility::Invisible);
 537             let result = self.resolve_path(&directive.module_path[..], None, false, directive.span);
 538             directive.vis.set(vis);
 539
 540             match result {
 541                 PathResult::Module(module) => module,
 542                 PathResult::Indeterminate => return false,
 543                 _ => return true,
 544             }
 545         };
 546
 547         directive.imported_module.set(Some(module));
 548         let (source, target, result, type_ns_only) = match directive.subclass {
 549             SingleImport { source, target, ref result, type_ns_only } =>
 550                 (source, target, result, type_ns_only),
 551             GlobImport { .. } => {
 552                 self.resolve_glob_import(directive);
 553                 return true;
 554             }
 555             _ => unreachable!(),
 556         };
 557
 558         let mut indeterminate = false;
 559         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 560             if let Err(Undetermined) = result[ns].get() {
 561                 result[ns].set(this.resolve_ident_in_module(module,
 562                                                             source,
 563                                                             ns,
 564                                                             false,
 565                                                             false,
 566                                                             directive.span));
 567             } else {
 568                 return
 569             };
 570
 571             let parent = directive.parent;
 572             match result[ns].get() {
 573                 Err(Undetermined) => indeterminate = true,
 574                 Err(Determined) => {
 575                     this.update_resolution(parent, target, ns, |_, resolution| {
 576                         resolution.single_imports.directive_failed()
 577                     });
 578                 }
 579                 Ok(binding) if !binding.is_importable() => {
 580                     let msg = format!("`{}` is not directly importable", target);
 581                     struct_span_err!(this.session, directive.span, E0253, "{}", &msg)
 582                         .span_label(directive.span, "cannot be imported directly")
 583                         .emit();
 584                     // Do not import this illegal binding. Import a dummy binding and pretend
 585                     // everything is fine
 586                     this.import_dummy_binding(directive);
 587                 }
 588                 Ok(binding) => {
 589                     let imported_binding = this.import(binding, directive);
 590                     let conflict = this.try_define(parent, target, ns, imported_binding);
 591                     if let Err(old_binding) = conflict {
 592                         this.report_conflict(parent, target, ns, imported_binding, old_binding);
 593                     }
 594                 }
 595             }
 596         });
 597
 598         !indeterminate
 599     }
 600
 601     // If appropriate, returns an error to report.
 602     fn finalize_import(&mut self, directive: &'b ImportDirective<'b>) -> Option<(Span, String)> {
 603         self.current_module = directive.parent;
 604
 605         let ImportDirective { ref module_path, span, .. } = *directive;
 606         let module_result = self.resolve_path(&module_path, None, true, span);
 607         let module = match module_result {
 608             PathResult::Module(module) => module,
 609             PathResult::Failed(span, msg, _) => {
 610                 let (mut self_path, mut self_result) = (module_path.clone(), None);
 611                 if !self_path.is_empty() &&
 612                     !token::Ident(self_path[0].node).is_path_segment_keyword()
 613                 {
 614                     self_path[0].node.name = keywords::SelfValue.name();
 615                     self_result = Some(self.resolve_path(&self_path, None, false, span));
 616                 }
 617                 return if let Some(PathResult::Module(..)) = self_result {
 618                     Some((span, format!("Did you mean `{}`?", names_to_string(&self_path[..]))))
 619                 } else {
 620                     Some((span, msg))
 621                 };
 622             },
 623             _ => return None,
 624         };
 625
 626         let (ident, result, type_ns_only) = match directive.subclass {
 627             SingleImport { source, ref result, type_ns_only, .. } => (source, result, type_ns_only),
 628             GlobImport { .. } if module.def_id() == directive.parent.def_id() => {
 629                 // Importing a module into itself is not allowed.
 630                 return Some((directive.span,
 631                              "Cannot glob-import a module into itself.".to_string()));
 632             }
 633             GlobImport { is_prelude, ref max_vis } => {
 634                 if !is_prelude &&
 635                    max_vis.get() != ty::Visibility::Invisible && // Allow empty globs.
 636                    !max_vis.get().is_at_least(directive.vis.get(), &*self) {
 637                     let msg = "A non-empty glob must import something with the glob's visibility";
 638                     self.session.span_err(directive.span, msg);
 639                 }
 640                 return None;
 641             }
 642             _ => unreachable!(),
 643         };
 644
 645         let mut all_ns_err = true;
 646         let mut legacy_self_import = None;
 647         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 648             if let Ok(binding) = result[ns].get() {
 649                 all_ns_err = false;
 650                 if this.record_use(ident, ns, binding, directive.span) {
 651                     this.resolution(module, ident, ns).borrow_mut().binding =
 652                         Some(this.dummy_binding);
 653                 }
 654             }
 655         } else if let Ok(binding) = this.resolve_ident_in_module(module,
 656                                                                  ident,
 657                                                                  ns,
 658                                                                  false,
 659                                                                  false,
 660                                                                  directive.span) {
 661             legacy_self_import = Some(directive);
 662             let binding = this.arenas.alloc_name_binding(NameBinding {
 663                 kind: NameBindingKind::Import {
 664                     binding,
 665                     directive,
 666                     used: Cell::new(false),
 667                     legacy_self_import: true,
 668                 },
 669                 ..*binding
 670             });
 671             let _ = this.try_define(directive.parent, ident, ns, binding);
 672         });
 673
 674         if all_ns_err {
 675             if let Some(directive) = legacy_self_import {
 676                 self.warn_legacy_self_import(directive);
 677                 return None;
 678             }
 679             let mut all_ns_failed = true;
 680             self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 681                 match this.resolve_ident_in_module(module, ident, ns, false, true, span) {
 682                     Ok(_) => all_ns_failed = false,
 683                     _ => {}
 684                 }
 685             });
 686
 687             return if all_ns_failed {
 688                 let resolutions = module.resolutions.borrow();
 689                 let names = resolutions.iter().filter_map(|(&(ref i, _), resolution)| {
 690                     if *i == ident { return None; } // Never suggest the same name
 691                     match *resolution.borrow() {
 692                         NameResolution { binding: Some(name_binding), .. } => {
 693                             match name_binding.kind {
 694                                 NameBindingKind::Import { binding, .. } => {
 695                                     match binding.kind {
 696                                         // Never suggest the name that has binding error
 697                                         // i.e. the name that cannot be previously resolved
 698                                         NameBindingKind::Def(Def::Err) => return None,
 699                                         _ => Some(&i.name),
 700                                     }
 701                                 },
 702                                 _ => Some(&i.name),
 703                             }
 704                         },
 705                         NameResolution { single_imports: SingleImports::None, .. } => None,
 706                         _ => Some(&i.name),
 707                     }
 708                 });
 709                 let lev_suggestion =
 710                     match find_best_match_for_name(names, &ident.name.as_str(), None) {
 711                         Some(name) => format!(". Did you mean to use `{}`?", name),
 712                         None => "".to_owned(),
 713                     };
 714                 let module_str = module_to_string(module);
 715                 let msg = if &module_str == "???" {
 716                     format!("no `{}` in the root{}", ident, lev_suggestion)
 717                 } else {
 718                     format!("no `{}` in `{}`{}", ident, module_str, lev_suggestion)
 719                 };
 720                 Some((span, msg))
 721             } else {
 722                 // `resolve_ident_in_module` reported a privacy error.
 723                 self.import_dummy_binding(directive);
 724                 None
 725             }
 726         }
 727
 728         let mut reexport_error = None;
 729         let mut any_successful_reexport = false;
 730         self.per_ns(|this, ns| {
 731             if let Ok(binding) = result[ns].get() {
 732                 let vis = directive.vis.get();
 733                 if !binding.pseudo_vis().is_at_least(vis, &*this) {
 734                     reexport_error = Some((ns, binding));
 735                 } else {
 736                     any_successful_reexport = true;
 737                 }
 738             }
 739         });
 740
 741         // All namespaces must be re-exported with extra visibility for an error to occur.
 742         if !any_successful_reexport {
 743             let (ns, binding) = reexport_error.unwrap();
 744             if ns == TypeNS && binding.is_extern_crate() {
 745                 let msg = format!("extern crate `{}` is private, and cannot be reexported \
 746                                    (error E0365), consider declaring with `pub`",
 747                                    ident);
 748                 self.session.buffer_lint(PUB_USE_OF_PRIVATE_EXTERN_CRATE,
 749                                          directive.id,
 750                                          directive.span,
 751                                          &msg);
 752             } else if ns == TypeNS {
 753                 struct_span_err!(self.session, directive.span, E0365,
 754                                  "`{}` is private, and cannot be reexported", ident)
 755                     .span_label(directive.span, format!("reexport of private `{}`", ident))
 756                     .note(&format!("consider declaring type or module `{}` with `pub`", ident))
 757                     .emit();
 758             } else {
 759                 let msg = format!("`{}` is private, and cannot be reexported", ident);
 760                 let note_msg =
 761                     format!("consider marking `{}` as `pub` in the imported module", ident);
 762                 struct_span_err!(self.session, directive.span, E0364, "{}", &msg)
 763                     .span_note(directive.span, &note_msg)
 764                     .emit();
 765             }
 766         }
 767
 768         // Record what this import resolves to for later uses in documentation,
 769         // this may resolve to either a value or a type, but for documentation
 770         // purposes it's good enough to just favor one over the other.
 771         self.per_ns(|this, ns| if let Some(binding) = result[ns].get().ok() {
 772             this.def_map.entry(directive.id).or_insert(PathResolution::new(binding.def()));
 773         });
 774
 775         debug!("(resolving single import) successfully resolved import");
 776         None
 777     }
 778
 779     fn resolve_glob_import(&mut self, directive: &'b ImportDirective<'b>) {
 780         let module = directive.imported_module.get().unwrap();
 781         self.populate_module_if_necessary(module);
 782
 783         if let Some(Def::Trait(_)) = module.def() {
 784             self.session.span_err(directive.span, "items in traits are not importable.");
 785             return;
 786         } else if module.def_id() == directive.parent.def_id()  {
 787             return;
 788         } else if let GlobImport { is_prelude: true, .. } = directive.subclass {
 789             self.prelude = Some(module);
 790             return;
 791         }
 792
 793         // Add to module's glob_importers
 794         module.glob_importers.borrow_mut().push(directive);
 795
 796         // Ensure that `resolutions` isn't borrowed during `try_define`,
 797         // since it might get updated via a glob cycle.
 798         let bindings = module.resolutions.borrow().iter().filter_map(|(&ident, resolution)| {
 799             resolution.borrow().binding().map(|binding| (ident, binding))
 800         }).collect::<Vec<_>>();
 801         for ((mut ident, ns), binding) in bindings {
 802             let scope = match ident.ctxt.reverse_glob_adjust(module.expansion,
 803                                                              directive.span.ctxt().modern()) {
 804                 Some(Some(def)) => self.macro_def_scope(def),
 805                 Some(None) => self.current_module,
 806                 None => continue,
 807             };
 808             if self.is_accessible_from(binding.pseudo_vis(), scope) {
 809                 let imported_binding = self.import(binding, directive);
 810                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
 811             }
 812         }
 813
 814         // Record the destination of this import
 815         self.record_def(directive.id, PathResolution::new(module.def().unwrap()));
 816     }
 817
 818     // Miscellaneous post-processing, including recording reexports,
 819     // reporting conflicts, and reporting unresolved imports.
 820     fn finalize_resolutions_in(&mut self, module: Module<'b>) {
 821         // Since import resolution is finished, globs will not define any more names.
 822         *module.globs.borrow_mut() = Vec::new();
 823
 824         let mut reexports = Vec::new();
 825         let mut exported_macro_names = FxHashMap();
 826         if module as *const _ == self.graph_root as *const _ {
 827             let macro_exports = mem::replace(&mut self.macro_exports, Vec::new());
 828             for export in macro_exports.into_iter().rev() {
 829                 if exported_macro_names.insert(export.ident.modern(), export.span).is_none() {
 830                     reexports.push(export);
 831                 }
 832             }
 833         }
 834
 835         for (&(ident, ns), resolution) in module.resolutions.borrow().iter() {
 836             let resolution = &mut *resolution.borrow_mut();
 837             let binding = match resolution.binding {
 838                 Some(binding) => binding,
 839                 None => continue,
 840             };
 841
 842             if binding.vis == ty::Visibility::Public &&
 843                (binding.is_import() || binding.is_macro_def()) {
 844                 let def = binding.def();
 845                 if def != Def::Err {
 846                     if !def.def_id().is_local() {
 847                         self.cstore.export_macros_untracked(def.def_id().krate);
 848                     }
 849                     if let Def::Macro(..) = def {
 850                         if let Some(&span) = exported_macro_names.get(&ident.modern()) {
 851                             let msg =
 852                                 format!("a macro named `{}` has already been exported", ident);
 853                             self.session.struct_span_err(span, &msg)
 854                                 .span_label(span, format!("`{}` already exported", ident))
 855                                 .span_note(binding.span, "previous macro export here")
 856                                 .emit();
 857                         }
 858                     }
 859                     reexports.push(Export { ident: ident.modern(), def: def, span: binding.span });
 860                 }
 861             }
 862
 863             match binding.kind {
 864                 NameBindingKind::Import { binding: orig_binding, .. } => {
 865                     if ns == TypeNS && orig_binding.is_variant() &&
 866                        !orig_binding.vis.is_at_least(binding.vis, &*self) {
 867                         let msg = format!("variant `{}` is private, and cannot be reexported, \
 868                                            consider declaring its enum as `pub`", ident);
 869                         self.session.span_err(binding.span, &msg);
 870                     }
 871                 }
 872                 NameBindingKind::Ambiguity { b1, b2, .. }
 873                         if b1.is_glob_import() && b2.is_glob_import() => {
 874                     let (orig_b1, orig_b2) = match (&b1.kind, &b2.kind) {
 875                         (&NameBindingKind::Import { binding: b1, .. },
 876                          &NameBindingKind::Import { binding: b2, .. }) => (b1, b2),
 877                         _ => continue,
 878                     };
 879                     let (b1, b2) = match (orig_b1.vis, orig_b2.vis) {
 880                         (ty::Visibility::Public, ty::Visibility::Public) => continue,
 881                         (ty::Visibility::Public, _) => (b1, b2),
 882                         (_, ty::Visibility::Public) => (b2, b1),
 883                         _ => continue,
 884                     };
 885                     resolution.binding = Some(self.arenas.alloc_name_binding(NameBinding {
 886                         kind: NameBindingKind::Ambiguity { b1: b1, b2: b2, legacy: true }, ..*b1
 887                     }));
 888                 }
 889                 _ => {}
 890             }
 891         }
 892
 893         if reexports.len() > 0 {
 894             if let Some(def_id) = module.def_id() {
 895                 self.export_map.insert(def_id, reexports);
 896             }
 897         }
 898     }
 899 }
 900
 901 fn import_path_to_string(names: &[SpannedIdent],
 902                          subclass: &ImportDirectiveSubclass,
 903                          span: Span) -> String {
 904     let pos = names.iter()
 905         .position(|p| span == p.span && p.node.name != keywords::CrateRoot.name());
 906     let global = !names.is_empty() && names[0].node.name == keywords::CrateRoot.name();
 907     if let Some(pos) = pos {
 908         let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
 909         names_to_string(names)
 910     } else {
 911         let names = if global { &names[1..] } else { names };
 912         if names.is_empty() {
 913             import_directive_subclass_to_string(subclass)
 914         } else {
 915             (format!("{}::{}",
 916                      names_to_string(names),
 917                      import_directive_subclass_to_string(subclass)))
 918         }
 919     }
 920 }
 921
 922 fn import_directive_subclass_to_string(subclass: &ImportDirectiveSubclass) -> String {
 923     match *subclass {
 924         SingleImport { source, .. } => source.to_string(),
 925         GlobImport { .. } => "*".to_string(),
 926         ExternCrate(_) => "<extern crate>".to_string(),
 927         MacroUse => "#[macro_use]".to_string(),
 928     }
 929 }