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