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::PRIVATE_IN_PUBLIC;
  22 use rustc::hir::def_id::DefId;
  23 use rustc::hir::def::*;
  24 use rustc::util::nodemap::FxHashMap;
  25
  26 use syntax::ast::{Ident, 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,
  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<Ident>,
  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         let ident = ident.unhygienize();
 138         *module.resolutions.borrow_mut().entry((ident, ns))
 139                .or_insert_with(|| self.arenas.alloc_name_resolution())
 140     }
 141
 142     /// Attempts to resolve `ident` in namespaces `ns` of `module`.
 143     /// Invariant: if `record_used` is `Some`, import resolution must be complete.
 144     pub fn resolve_ident_in_module(&mut self,
 145                                    module: Module<'a>,
 146                                    ident: Ident,
 147                                    ns: Namespace,
 148                                    restricted_shadowing: bool,
 149                                    record_used: bool,
 150                                    path_span: Span)
 151                                    -> Result<&'a NameBinding<'a>, Determinacy> {
 152         self.populate_module_if_necessary(module);
 153
 154         let resolution = self.resolution(module, ident, ns)
 155             .try_borrow_mut()
 156             .map_err(|_| Determined)?; // This happens when there is a cycle of imports
 157
 158         if record_used {
 159             if let Some(binding) = resolution.binding {
 160                 if let Some(shadowed_glob) = resolution.shadows_glob {
 161                     let name = ident.name;
 162                     // Forbid expanded shadowing to avoid time travel.
 163                     if restricted_shadowing &&
 164                        binding.expansion != Mark::root() &&
 165                        ns != MacroNS && // In MacroNS, `try_define` always forbids this shadowing
 166                        binding.def() != shadowed_glob.def() {
 167                         self.ambiguity_errors.push(AmbiguityError {
 168                             span: path_span,
 169                             name: name,
 170                             lexical: false,
 171                             b1: binding,
 172                             b2: shadowed_glob,
 173                             legacy: false,
 174                         });
 175                     }
 176                 }
 177                 if self.record_use(ident, ns, binding, path_span) {
 178                     return Ok(self.dummy_binding);
 179                 }
 180                 if !self.is_accessible(binding.vis) {
 181                     self.privacy_errors.push(PrivacyError(path_span, ident.name, binding));
 182                 }
 183             }
 184
 185             return resolution.binding.ok_or(Determined);
 186         }
 187
 188         let check_usable = |this: &mut Self, binding: &'a NameBinding<'a>| {
 189             // `extern crate` are always usable for backwards compatability, see issue #37020.
 190             let usable = this.is_accessible(binding.vis) || binding.is_extern_crate();
 191             if usable { Ok(binding) } else { Err(Determined) }
 192         };
 193
 194         // Items and single imports are not shadowable.
 195         if let Some(binding) = resolution.binding {
 196             if !binding.is_glob_import() {
 197                 return check_usable(self, binding);
 198             }
 199         }
 200
 201         // Check if a single import can still define the name.
 202         match resolution.single_imports {
 203             SingleImports::AtLeastOne => return Err(Undetermined),
 204             SingleImports::MaybeOne(directive) if self.is_accessible(directive.vis.get()) => {
 205                 let module = match directive.imported_module.get() {
 206                     Some(module) => module,
 207                     None => return Err(Undetermined),
 208                 };
 209                 let ident = match directive.subclass {
 210                     SingleImport { source, .. } => source,
 211                     _ => unreachable!(),
 212                 };
 213                 match self.resolve_ident_in_module(module, ident, ns, false, false, path_span) {
 214                     Err(Determined) => {}
 215                     _ => return Err(Undetermined),
 216                 }
 217             }
 218             SingleImports::MaybeOne(_) | SingleImports::None => {},
 219         }
 220
 221         let no_unresolved_invocations =
 222             restricted_shadowing || module.unresolved_invocations.borrow().is_empty();
 223         match resolution.binding {
 224             // In `MacroNS`, expanded bindings do not shadow (enforced in `try_define`).
 225             Some(binding) if no_unresolved_invocations || ns == MacroNS =>
 226                 return check_usable(self, binding),
 227             None if no_unresolved_invocations => {}
 228             _ => return Err(Undetermined),
 229         }
 230
 231         // Check if the globs are determined
 232         if restricted_shadowing && module.def().is_some() {
 233             return Err(Determined);
 234         }
 235         for directive in module.globs.borrow().iter() {
 236             if self.is_accessible(directive.vis.get()) {
 237                 if let Some(module) = directive.imported_module.get() {
 238                     let result = self.resolve_ident_in_module(module,
 239                                                               ident,
 240                                                               ns,
 241                                                               false,
 242                                                               false,
 243                                                               path_span);
 244                     if let Err(Undetermined) = result {
 245                         return Err(Undetermined);
 246                     }
 247                 } else {
 248                     return Err(Undetermined);
 249                 }
 250             }
 251         }
 252
 253         Err(Determined)
 254     }
 255
 256     // Add an import directive to the current module.
 257     pub fn add_import_directive(&mut self,
 258                                 module_path: Vec<Ident>,
 259                                 subclass: ImportDirectiveSubclass<'a>,
 260                                 span: Span,
 261                                 id: NodeId,
 262                                 vis: ty::Visibility,
 263                                 expansion: Mark) {
 264         let current_module = self.current_module;
 265         let directive = self.arenas.alloc_import_directive(ImportDirective {
 266             parent: current_module,
 267             module_path: module_path,
 268             imported_module: Cell::new(None),
 269             subclass: subclass,
 270             span: span,
 271             id: id,
 272             vis: Cell::new(vis),
 273             expansion: expansion,
 274             used: Cell::new(false),
 275         });
 276
 277         self.indeterminate_imports.push(directive);
 278         match directive.subclass {
 279             SingleImport { target, .. } => {
 280                 self.per_ns(|this, ns| {
 281                     let mut resolution = this.resolution(current_module, target, ns).borrow_mut();
 282                     resolution.single_imports.add_directive(directive);
 283                 });
 284             }
 285             // We don't add prelude imports to the globs since they only affect lexical scopes,
 286             // which are not relevant to import resolution.
 287             GlobImport { is_prelude: true, .. } => {}
 288             GlobImport { .. } => self.current_module.globs.borrow_mut().push(directive),
 289             _ => unreachable!(),
 290         }
 291     }
 292
 293     // Given a binding and an import directive that resolves to it,
 294     // return the corresponding binding defined by the import directive.
 295     pub fn import(&self, binding: &'a NameBinding<'a>, directive: &'a ImportDirective<'a>)
 296                   -> &'a NameBinding<'a> {
 297         let vis = if binding.pseudo_vis().is_at_least(directive.vis.get(), self) ||
 298                      !directive.is_glob() && binding.is_extern_crate() { // c.f. `PRIVATE_IN_PUBLIC`
 299             directive.vis.get()
 300         } else {
 301             binding.pseudo_vis()
 302         };
 303
 304         if let GlobImport { ref max_vis, .. } = directive.subclass {
 305             if vis == directive.vis.get() || vis.is_at_least(max_vis.get(), self) {
 306                 max_vis.set(vis)
 307             }
 308         }
 309
 310         self.arenas.alloc_name_binding(NameBinding {
 311             kind: NameBindingKind::Import {
 312                 binding: binding,
 313                 directive: directive,
 314                 used: Cell::new(false),
 315                 legacy_self_import: false,
 316             },
 317             span: directive.span,
 318             vis: vis,
 319             expansion: directive.expansion,
 320         })
 321     }
 322
 323     // Define the name or return the existing binding if there is a collision.
 324     pub fn try_define(&mut self,
 325                       module: Module<'a>,
 326                       ident: Ident,
 327                       ns: Namespace,
 328                       binding: &'a NameBinding<'a>)
 329                       -> Result<(), &'a NameBinding<'a>> {
 330         self.update_resolution(module, ident, ns, |this, resolution| {
 331             if let Some(old_binding) = resolution.binding {
 332                 if binding.is_glob_import() {
 333                     if !old_binding.is_glob_import() &&
 334                        !(ns == MacroNS && old_binding.expansion != Mark::root()) {
 335                         resolution.shadows_glob = Some(binding);
 336                     } else if binding.def() != old_binding.def() {
 337                         resolution.binding = Some(this.ambiguity(old_binding, binding));
 338                     } else if !old_binding.vis.is_at_least(binding.vis, &*this) {
 339                         // We are glob-importing the same item but with greater visibility.
 340                         resolution.binding = Some(binding);
 341                     }
 342                 } else if old_binding.is_glob_import() {
 343                     if ns == MacroNS && binding.expansion != Mark::root() &&
 344                        binding.def() != old_binding.def() {
 345                         resolution.binding = Some(this.ambiguity(binding, old_binding));
 346                     } else {
 347                         resolution.binding = Some(binding);
 348                         resolution.shadows_glob = Some(old_binding);
 349                     }
 350                 } else {
 351                     return Err(old_binding);
 352                 }
 353             } else {
 354                 resolution.binding = Some(binding);
 355             }
 356
 357             Ok(())
 358         })
 359     }
 360
 361     pub fn ambiguity(&self, b1: &'a NameBinding<'a>, b2: &'a NameBinding<'a>)
 362                      -> &'a NameBinding<'a> {
 363         self.arenas.alloc_name_binding(NameBinding {
 364             kind: NameBindingKind::Ambiguity { b1: b1, b2: b2, legacy: false },
 365             vis: if b1.vis.is_at_least(b2.vis, self) { b1.vis } else { b2.vis },
 366             span: b1.span,
 367             expansion: Mark::root(),
 368         })
 369     }
 370
 371     // Use `f` to mutate the resolution of the name in the module.
 372     // If the resolution becomes a success, define it in the module's glob importers.
 373     fn update_resolution<T, F>(&mut self, module: Module<'a>, ident: Ident, ns: Namespace, f: F)
 374                                -> T
 375         where F: FnOnce(&mut Resolver<'a>, &mut NameResolution<'a>) -> T
 376     {
 377         // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
 378         // during which the resolution might end up getting re-defined via a glob cycle.
 379         let (binding, t) = {
 380             let mut resolution = &mut *self.resolution(module, ident, ns).borrow_mut();
 381             let old_binding = resolution.binding();
 382
 383             let t = f(self, resolution);
 384
 385             match resolution.binding() {
 386                 _ if old_binding.is_some() => return t,
 387                 None => return t,
 388                 Some(binding) => match old_binding {
 389                     Some(old_binding) if old_binding as *const _ == binding as *const _ => return t,
 390                     _ => (binding, t),
 391                 }
 392             }
 393         };
 394
 395         // Define `binding` in `module`s glob importers.
 396         for directive in module.glob_importers.borrow_mut().iter() {
 397             if self.is_accessible_from(binding.vis, directive.parent) {
 398                 let imported_binding = self.import(binding, directive);
 399                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
 400             }
 401         }
 402
 403         t
 404     }
 405
 406     // Define a "dummy" resolution containing a Def::Err as a placeholder for a
 407     // failed resolution
 408     fn import_dummy_binding(&mut self, directive: &'a ImportDirective<'a>) {
 409         if let SingleImport { target, .. } = directive.subclass {
 410             let dummy_binding = self.dummy_binding;
 411             let dummy_binding = self.import(dummy_binding, directive);
 412             self.per_ns(|this, ns| {
 413                 let _ = this.try_define(directive.parent, target, ns, dummy_binding);
 414             });
 415         }
 416     }
 417 }
 418
 419 pub struct ImportResolver<'a, 'b: 'a> {
 420     pub resolver: &'a mut Resolver<'b>,
 421 }
 422
 423 impl<'a, 'b: 'a> ::std::ops::Deref for ImportResolver<'a, 'b> {
 424     type Target = Resolver<'b>;
 425     fn deref(&self) -> &Resolver<'b> {
 426         self.resolver
 427     }
 428 }
 429
 430 impl<'a, 'b: 'a> ::std::ops::DerefMut for ImportResolver<'a, 'b> {
 431     fn deref_mut(&mut self) -> &mut Resolver<'b> {
 432         self.resolver
 433     }
 434 }
 435
 436 impl<'a, 'b: 'a> ty::DefIdTree for &'a ImportResolver<'a, 'b> {
 437     fn parent(self, id: DefId) -> Option<DefId> {
 438         self.resolver.parent(id)
 439     }
 440 }
 441
 442 impl<'a, 'b:'a> ImportResolver<'a, 'b> {
 443     // Import resolution
 444     //
 445     // This is a fixed-point algorithm. We resolve imports until our efforts
 446     // are stymied by an unresolved import; then we bail out of the current
 447     // module and continue. We terminate successfully once no more imports
 448     // remain or unsuccessfully when no forward progress in resolving imports
 449     // is made.
 450
 451     /// Resolves all imports for the crate. This method performs the fixed-
 452     /// point iteration.
 453     pub fn resolve_imports(&mut self) {
 454         let mut prev_num_indeterminates = self.indeterminate_imports.len() + 1;
 455         while self.indeterminate_imports.len() < prev_num_indeterminates {
 456             prev_num_indeterminates = self.indeterminate_imports.len();
 457             for import in mem::replace(&mut self.indeterminate_imports, Vec::new()) {
 458                 match self.resolve_import(&import) {
 459                     true => self.determined_imports.push(import),
 460                     false => self.indeterminate_imports.push(import),
 461                 }
 462             }
 463         }
 464     }
 465
 466     pub fn finalize_imports(&mut self) {
 467         for module in self.arenas.local_modules().iter() {
 468             self.finalize_resolutions_in(module);
 469         }
 470
 471         let mut errors = false;
 472         for i in 0 .. self.determined_imports.len() {
 473             let import = self.determined_imports[i];
 474             if let Some(err) = self.finalize_import(import) {
 475                 errors = true;
 476
 477                 // If the error is a single failed import then create a "fake" import
 478                 // resolution for it so that later resolve stages won't complain.
 479                 self.import_dummy_binding(import);
 480                 let path = import_path_to_string(&import.module_path, &import.subclass);
 481                 let error = ResolutionError::UnresolvedImport(Some((&path, &err)));
 482                 resolve_error(self.resolver, import.span, error);
 483             }
 484         }
 485
 486         // Report unresolved imports only if no hard error was already reported
 487         // to avoid generating multiple errors on the same import.
 488         if !errors {
 489             if let Some(import) = self.indeterminate_imports.iter().next() {
 490                 let error = ResolutionError::UnresolvedImport(None);
 491                 resolve_error(self.resolver, import.span, error);
 492             }
 493         }
 494     }
 495
 496     /// Attempts to resolve the given import, returning true if its resolution is determined.
 497     /// If successful, the resolved bindings are written into the module.
 498     fn resolve_import(&mut self, directive: &'b ImportDirective<'b>) -> bool {
 499         debug!("(resolving import for module) resolving import `{}::...` in `{}`",
 500                names_to_string(&directive.module_path),
 501                module_to_string(self.current_module));
 502
 503         self.current_module = directive.parent;
 504
 505         let module = if let Some(module) = directive.imported_module.get() {
 506             module
 507         } else {
 508             let vis = directive.vis.get();
 509             // For better failure detection, pretend that the import will not define any names
 510             // while resolving its module path.
 511             directive.vis.set(ty::Visibility::Invisible);
 512             let result = self.resolve_path(&directive.module_path, None, false, directive.span);
 513             directive.vis.set(vis);
 514
 515             match result {
 516                 PathResult::Module(module) => module,
 517                 PathResult::Indeterminate => return false,
 518                 _ => return true,
 519             }
 520         };
 521
 522         directive.imported_module.set(Some(module));
 523         let (source, target, result, type_ns_only) = match directive.subclass {
 524             SingleImport { source, target, ref result, type_ns_only } =>
 525                 (source, target, result, type_ns_only),
 526             GlobImport { .. } => {
 527                 self.resolve_glob_import(directive);
 528                 return true;
 529             }
 530             _ => unreachable!(),
 531         };
 532
 533         let mut indeterminate = false;
 534         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 535             if let Err(Undetermined) = result[ns].get() {
 536                 result[ns].set(this.resolve_ident_in_module(module,
 537                                                             source,
 538                                                             ns,
 539                                                             false,
 540                                                             false,
 541                                                             directive.span));
 542             } else {
 543                 return
 544             };
 545
 546             let parent = directive.parent;
 547             match result[ns].get() {
 548                 Err(Undetermined) => indeterminate = true,
 549                 Err(Determined) => {
 550                     this.update_resolution(parent, target, ns, |_, resolution| {
 551                         resolution.single_imports.directive_failed()
 552                     });
 553                 }
 554                 Ok(binding) if !binding.is_importable() => {
 555                     let msg = format!("`{}` is not directly importable", target);
 556                     struct_span_err!(this.session, directive.span, E0253, "{}", &msg)
 557                         .span_label(directive.span, "cannot be imported directly")
 558                         .emit();
 559                     // Do not import this illegal binding. Import a dummy binding and pretend
 560                     // everything is fine
 561                     this.import_dummy_binding(directive);
 562                 }
 563                 Ok(binding) => {
 564                     let imported_binding = this.import(binding, directive);
 565                     let conflict = this.try_define(parent, target, ns, imported_binding);
 566                     if let Err(old_binding) = conflict {
 567                         this.report_conflict(parent, target, ns, imported_binding, old_binding);
 568                     }
 569                 }
 570             }
 571         });
 572
 573         !indeterminate
 574     }
 575
 576     // If appropriate, returns an error to report.
 577     fn finalize_import(&mut self, directive: &'b ImportDirective<'b>) -> Option<String> {
 578         self.current_module = directive.parent;
 579
 580         let ImportDirective { ref module_path, span, .. } = *directive;
 581         let module_result = self.resolve_path(&module_path, None, true, span);
 582         let module = match module_result {
 583             PathResult::Module(module) => module,
 584             PathResult::Failed(msg, _) => {
 585                 let (mut self_path, mut self_result) = (module_path.clone(), None);
 586                 if !self_path.is_empty() && !token::Ident(self_path[0]).is_path_segment_keyword() {
 587                     self_path[0].name = keywords::SelfValue.name();
 588                     self_result = Some(self.resolve_path(&self_path, None, false, span));
 589                 }
 590                 return if let Some(PathResult::Module(..)) = self_result {
 591                     Some(format!("Did you mean `{}`?", names_to_string(&self_path)))
 592                 } else {
 593                     Some(msg)
 594                 };
 595             },
 596             _ => return None,
 597         };
 598
 599         let (ident, result, type_ns_only) = match directive.subclass {
 600             SingleImport { source, ref result, type_ns_only, .. } => (source, result, type_ns_only),
 601             GlobImport { .. } if module.def_id() == directive.parent.def_id() => {
 602                 // Importing a module into itself is not allowed.
 603                 return Some("Cannot glob-import a module into itself.".to_string());
 604             }
 605             GlobImport { is_prelude, ref max_vis } => {
 606                 if !is_prelude &&
 607                    max_vis.get() != ty::Visibility::Invisible && // Allow empty globs.
 608                    !max_vis.get().is_at_least(directive.vis.get(), &*self) {
 609                     let msg = "A non-empty glob must import something with the glob's visibility";
 610                     self.session.span_err(directive.span, msg);
 611                 }
 612                 return None;
 613             }
 614             _ => unreachable!(),
 615         };
 616
 617         let mut all_ns_err = true;
 618         let mut legacy_self_import = None;
 619         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 620             if let Ok(binding) = result[ns].get() {
 621                 all_ns_err = false;
 622                 if this.record_use(ident, ns, binding, directive.span) {
 623                     this.resolution(module, ident, ns).borrow_mut().binding =
 624                         Some(this.dummy_binding);
 625                 }
 626             }
 627         } else if let Ok(binding) = this.resolve_ident_in_module(module,
 628                                                                  ident,
 629                                                                  ns,
 630                                                                  false,
 631                                                                  false,
 632                                                                  directive.span) {
 633             legacy_self_import = Some(directive);
 634             let binding = this.arenas.alloc_name_binding(NameBinding {
 635                 kind: NameBindingKind::Import {
 636                     binding: binding,
 637                     directive: directive,
 638                     used: Cell::new(false),
 639                     legacy_self_import: true,
 640                 },
 641                 ..*binding
 642             });
 643             let _ = this.try_define(directive.parent, ident, ns, binding);
 644         });
 645
 646         if all_ns_err {
 647             if let Some(directive) = legacy_self_import {
 648                 self.warn_legacy_self_import(directive);
 649                 return None;
 650             }
 651             let mut all_ns_failed = true;
 652             self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 653                 match this.resolve_ident_in_module(module, ident, ns, false, true, span) {
 654                     Ok(_) => all_ns_failed = false,
 655                     _ => {}
 656                 }
 657             });
 658
 659             return if all_ns_failed {
 660                 let resolutions = module.resolutions.borrow();
 661                 let names = resolutions.iter().filter_map(|(&(ref i, _), resolution)| {
 662                     if *i == ident { return None; } // Never suggest the same name
 663                     match *resolution.borrow() {
 664                         NameResolution { binding: Some(name_binding), .. } => {
 665                             match name_binding.kind {
 666                                 NameBindingKind::Import { binding, .. } => {
 667                                     match binding.kind {
 668                                         // Never suggest the name that has binding error
 669                                         // i.e. the name that cannot be previously resolved
 670                                         NameBindingKind::Def(Def::Err) => return None,
 671                                         _ => Some(&i.name),
 672                                     }
 673                                 },
 674                                 _ => Some(&i.name),
 675                             }
 676                         },
 677                         NameResolution { single_imports: SingleImports::None, .. } => None,
 678                         _ => Some(&i.name),
 679                     }
 680                 });
 681                 let lev_suggestion =
 682                     match find_best_match_for_name(names, &ident.name.as_str(), None) {
 683                         Some(name) => format!(". Did you mean to use `{}`?", name),
 684                         None => "".to_owned(),
 685                     };
 686                 let module_str = module_to_string(module);
 687                 let msg = if &module_str == "???" {
 688                     format!("no `{}` in the root{}", ident, lev_suggestion)
 689                 } else {
 690                     format!("no `{}` in `{}`{}", ident, module_str, lev_suggestion)
 691                 };
 692                 Some(msg)
 693             } else {
 694                 // `resolve_ident_in_module` reported a privacy error.
 695                 self.import_dummy_binding(directive);
 696                 None
 697             }
 698         }
 699
 700         let mut reexport_error = None;
 701         let mut any_successful_reexport = false;
 702         self.per_ns(|this, ns| {
 703             if let Ok(binding) = result[ns].get() {
 704                 let vis = directive.vis.get();
 705                 if !binding.pseudo_vis().is_at_least(vis, &*this) {
 706                     reexport_error = Some((ns, binding));
 707                 } else {
 708                     any_successful_reexport = true;
 709                 }
 710             }
 711         });
 712
 713         // All namespaces must be re-exported with extra visibility for an error to occur.
 714         if !any_successful_reexport {
 715             let (ns, binding) = reexport_error.unwrap();
 716             if ns == TypeNS && binding.is_extern_crate() {
 717                 let msg = format!("extern crate `{}` is private, and cannot be reexported \
 718                                    (error E0364), consider declaring with `pub`",
 719                                    ident);
 720                 self.session.add_lint(PRIVATE_IN_PUBLIC, directive.id, directive.span, msg);
 721             } else if ns == TypeNS {
 722                 struct_span_err!(self.session, directive.span, E0365,
 723                                  "`{}` is private, and cannot be reexported", ident)
 724                     .span_label(directive.span, format!("reexport of private `{}`", ident))
 725                     .note(&format!("consider declaring type or module `{}` with `pub`", ident))
 726                     .emit();
 727             } else {
 728                 let msg = format!("`{}` is private, and cannot be reexported", ident);
 729                 let note_msg =
 730                     format!("consider marking `{}` as `pub` in the imported module", ident);
 731                 struct_span_err!(self.session, directive.span, E0364, "{}", &msg)
 732                     .span_note(directive.span, &note_msg)
 733                     .emit();
 734             }
 735         }
 736
 737         // Record what this import resolves to for later uses in documentation,
 738         // this may resolve to either a value or a type, but for documentation
 739         // purposes it's good enough to just favor one over the other.
 740         self.per_ns(|this, ns| if let Some(binding) = result[ns].get().ok() {
 741             this.def_map.entry(directive.id).or_insert(PathResolution::new(binding.def()));
 742         });
 743
 744         debug!("(resolving single import) successfully resolved import");
 745         None
 746     }
 747
 748     fn resolve_glob_import(&mut self, directive: &'b ImportDirective<'b>) {
 749         let module = directive.imported_module.get().unwrap();
 750         self.populate_module_if_necessary(module);
 751
 752         if let Some(Def::Trait(_)) = module.def() {
 753             self.session.span_err(directive.span, "items in traits are not importable.");
 754             return;
 755         } else if module.def_id() == directive.parent.def_id()  {
 756             return;
 757         } else if let GlobImport { is_prelude: true, .. } = directive.subclass {
 758             self.prelude = Some(module);
 759             return;
 760         }
 761
 762         // Add to module's glob_importers
 763         module.glob_importers.borrow_mut().push(directive);
 764
 765         // Ensure that `resolutions` isn't borrowed during `try_define`,
 766         // since it might get updated via a glob cycle.
 767         let bindings = module.resolutions.borrow().iter().filter_map(|(&ident, resolution)| {
 768             resolution.borrow().binding().map(|binding| (ident, binding))
 769         }).collect::<Vec<_>>();
 770         for ((ident, ns), binding) in bindings {
 771             if binding.pseudo_vis() == ty::Visibility::Public || self.is_accessible(binding.vis) {
 772                 let imported_binding = self.import(binding, directive);
 773                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
 774             }
 775         }
 776
 777         // Record the destination of this import
 778         self.record_def(directive.id, PathResolution::new(module.def().unwrap()));
 779     }
 780
 781     // Miscellaneous post-processing, including recording reexports, reporting conflicts,
 782     // reporting the PRIVATE_IN_PUBLIC lint, and reporting unresolved imports.
 783     fn finalize_resolutions_in(&mut self, module: Module<'b>) {
 784         // Since import resolution is finished, globs will not define any more names.
 785         *module.globs.borrow_mut() = Vec::new();
 786
 787         let mut reexports = Vec::new();
 788         let mut exported_macro_names = FxHashMap();
 789         if module as *const _ == self.graph_root as *const _ {
 790             let macro_exports = mem::replace(&mut self.macro_exports, Vec::new());
 791             for export in macro_exports.into_iter().rev() {
 792                 if exported_macro_names.insert(export.name, export.span).is_none() {
 793                     reexports.push(export);
 794                 }
 795             }
 796         }
 797
 798         for (&(ident, ns), resolution) in module.resolutions.borrow().iter() {
 799             let resolution = &mut *resolution.borrow_mut();
 800             let binding = match resolution.binding {
 801                 Some(binding) => binding,
 802                 None => continue,
 803             };
 804
 805             if binding.vis == ty::Visibility::Public &&
 806                (binding.is_import() || binding.is_macro_def()) {
 807                 let def = binding.def();
 808                 if def != Def::Err {
 809                     if !def.def_id().is_local() {
 810                         self.session.cstore.export_macros(def.def_id().krate);
 811                     }
 812                     if let Def::Macro(..) = def {
 813                         if let Some(&span) = exported_macro_names.get(&ident.name) {
 814                             let msg =
 815                                 format!("a macro named `{}` has already been exported", ident);
 816                             self.session.struct_span_err(span, &msg)
 817                                 .span_label(span, format!("`{}` already exported", ident))
 818                                 .span_note(binding.span, "previous macro export here")
 819                                 .emit();
 820                         }
 821                     }
 822                     reexports.push(Export { name: ident.name, def: def, span: binding.span });
 823                 }
 824             }
 825
 826             match binding.kind {
 827                 NameBindingKind::Import { binding: orig_binding, directive, .. } => {
 828                     if ns == TypeNS && orig_binding.is_variant() &&
 829                        !orig_binding.vis.is_at_least(binding.vis, &*self) {
 830                         let msg = format!("variant `{}` is private, and cannot be reexported \
 831                                            (error E0364), consider declaring its enum as `pub`",
 832                                           ident);
 833                         self.session.add_lint(PRIVATE_IN_PUBLIC, directive.id, binding.span, msg);
 834                     }
 835                 }
 836                 NameBindingKind::Ambiguity { b1, b2, .. }
 837                         if b1.is_glob_import() && b2.is_glob_import() => {
 838                     let (orig_b1, orig_b2) = match (&b1.kind, &b2.kind) {
 839                         (&NameBindingKind::Import { binding: b1, .. },
 840                          &NameBindingKind::Import { binding: b2, .. }) => (b1, b2),
 841                         _ => continue,
 842                     };
 843                     let (b1, b2) = match (orig_b1.vis, orig_b2.vis) {
 844                         (ty::Visibility::Public, ty::Visibility::Public) => continue,
 845                         (ty::Visibility::Public, _) => (b1, b2),
 846                         (_, ty::Visibility::Public) => (b2, b1),
 847                         _ => continue,
 848                     };
 849                     resolution.binding = Some(self.arenas.alloc_name_binding(NameBinding {
 850                         kind: NameBindingKind::Ambiguity { b1: b1, b2: b2, legacy: true }, ..*b1
 851                     }));
 852                 }
 853                 _ => {}
 854             }
 855         }
 856
 857         if reexports.len() > 0 {
 858             if let Some(def_id) = module.def_id() {
 859                 let node_id = self.definitions.as_local_node_id(def_id).unwrap();
 860                 self.export_map.insert(node_id, reexports);
 861             }
 862         }
 863     }
 864 }
 865
 866 fn import_path_to_string(names: &[Ident], subclass: &ImportDirectiveSubclass) -> String {
 867     let global = !names.is_empty() && names[0].name == keywords::CrateRoot.name();
 868     let names = if global { &names[1..] } else { names };
 869     if names.is_empty() {
 870         import_directive_subclass_to_string(subclass)
 871     } else {
 872         (format!("{}::{}",
 873                  names_to_string(names),
 874                  import_directive_subclass_to_string(subclass)))
 875             .to_string()
 876     }
 877 }
 878
 879 fn import_directive_subclass_to_string(subclass: &ImportDirectiveSubclass) -> String {
 880     match *subclass {
 881         SingleImport { source, .. } => source.to_string(),
 882         GlobImport { .. } => "*".to_string(),
 883         ExternCrate => "<extern crate>".to_string(),
 884         MacroUse => "#[macro_use]".to_string(),
 885     }
 886 }