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 Module;
  14 use Namespace::{self, TypeNS, ValueNS};
  15 use {NameBinding, NameBindingKind, PrivacyError, ToNameBinding};
  16 use ResolveResult;
  17 use ResolveResult::*;
  18 use Resolver;
  19 use UseLexicalScopeFlag::DontUseLexicalScope;
  20 use {names_to_string, module_to_string};
  21 use {resolve_error, ResolutionError};
  22
  23 use rustc::ty;
  24 use rustc::lint::builtin::PRIVATE_IN_PUBLIC;
  25 use rustc::hir::def::*;
  26
  27 use syntax::ast::{NodeId, Name};
  28 use syntax::util::lev_distance::find_best_match_for_name;
  29 use syntax_pos::{Span, DUMMY_SP};
  30
  31 use std::cell::{Cell, RefCell};
  32
  33 impl<'a> Resolver<'a> {
  34     pub fn resolve_imports(&mut self) {
  35         ImportResolver { resolver: self }.resolve_imports();
  36     }
  37 }
  38
  39 /// Contains data for specific types of import directives.
  40 #[derive(Clone, Debug)]
  41 pub enum ImportDirectiveSubclass {
  42     SingleImport {
  43         target: Name,
  44         source: Name,
  45         type_determined: Cell<bool>,
  46         value_determined: Cell<bool>,
  47     },
  48     GlobImport { is_prelude: bool },
  49 }
  50
  51 impl ImportDirectiveSubclass {
  52     pub fn single(target: Name, source: Name) -> Self {
  53         SingleImport {
  54             target: target,
  55             source: source,
  56             type_determined: Cell::new(false),
  57             value_determined: Cell::new(false),
  58         }
  59     }
  60 }
  61
  62 /// One import directive.
  63 #[derive(Debug,Clone)]
  64 pub struct ImportDirective<'a> {
  65     pub id: NodeId,
  66     module_path: Vec<Name>,
  67     target_module: Cell<Option<Module<'a>>>, // the resolution of `module_path`
  68     subclass: ImportDirectiveSubclass,
  69     span: Span,
  70     vis: ty::Visibility, // see note in ImportResolutionPerNamespace about how to use this
  71 }
  72
  73 impl<'a> ImportDirective<'a> {
  74     pub fn is_glob(&self) -> bool {
  75         match self.subclass { ImportDirectiveSubclass::GlobImport { .. } => true, _ => false }
  76     }
  77 }
  78
  79 #[derive(Clone, Default)]
  80 /// Records information about the resolution of a name in a namespace of a module.
  81 pub struct NameResolution<'a> {
  82     /// The single imports that define the name in the namespace.
  83     single_imports: SingleImports<'a>,
  84     /// The least shadowable known binding for this name, or None if there are no known bindings.
  85     pub binding: Option<&'a NameBinding<'a>>,
  86     duplicate_globs: Vec<&'a NameBinding<'a>>,
  87 }
  88
  89 #[derive(Clone, Debug)]
  90 enum SingleImports<'a> {
  91     /// No single imports can define the name in the namespace.
  92     None,
  93     /// Only the given single import can define the name in the namespace.
  94     MaybeOne(&'a ImportDirective<'a>),
  95     /// At least one single import will define the name in the namespace.
  96     AtLeastOne,
  97 }
  98
  99 impl<'a> Default for SingleImports<'a> {
 100     fn default() -> Self {
 101         SingleImports::None
 102     }
 103 }
 104
 105 impl<'a> SingleImports<'a> {
 106     fn add_directive(&mut self, directive: &'a ImportDirective<'a>) {
 107         match *self {
 108             SingleImports::None => *self = SingleImports::MaybeOne(directive),
 109             // If two single imports can define the name in the namespace, we can assume that at
 110             // least one of them will define it since otherwise both would have to define only one
 111             // namespace, leading to a duplicate error.
 112             SingleImports::MaybeOne(_) => *self = SingleImports::AtLeastOne,
 113             SingleImports::AtLeastOne => {}
 114         };
 115     }
 116
 117     fn directive_failed(&mut self) {
 118         match *self {
 119             SingleImports::None => unreachable!(),
 120             SingleImports::MaybeOne(_) => *self = SingleImports::None,
 121             SingleImports::AtLeastOne => {}
 122         }
 123     }
 124 }
 125
 126 impl<'a> NameResolution<'a> {
 127     // Returns the binding for the name if it is known or None if it not known.
 128     fn binding(&self) -> Option<&'a NameBinding<'a>> {
 129         self.binding.and_then(|binding| match self.single_imports {
 130             SingleImports::None => Some(binding),
 131             _ if !binding.is_glob_import() => Some(binding),
 132             _ => None, // The binding could be shadowed by a single import, so it is not known.
 133         })
 134     }
 135
 136     // Returns Some(the resolution of the name), or None if the resolution depends
 137     // on whether more globs can define the name.
 138     fn try_result(&self, ns: Namespace, allow_private_imports: bool)
 139                   -> Option<ResolveResult<&'a NameBinding<'a>>> {
 140         match self.binding {
 141             Some(binding) if !binding.is_glob_import() =>
 142                 return Some(Success(binding)),
 143             _ => {} // Items and single imports are not shadowable
 144         };
 145
 146         // Check if a single import can still define the name.
 147         match self.single_imports {
 148             SingleImports::None => {},
 149             SingleImports::AtLeastOne => return Some(Indeterminate),
 150             SingleImports::MaybeOne(directive) => {
 151                 // If (1) we don't allow private imports, (2) no public single import can define
 152                 // the name, and (3) no public glob has defined the name, the resolution depends
 153                 // on whether more globs can define the name.
 154                 if !allow_private_imports && directive.vis != ty::Visibility::Public &&
 155                    !self.binding.map(NameBinding::is_pseudo_public).unwrap_or(false) {
 156                     return None;
 157                 }
 158
 159                 let target_module = match directive.target_module.get() {
 160                     Some(target_module) => target_module,
 161                     None => return Some(Indeterminate),
 162                 };
 163                 let name = match directive.subclass {
 164                     SingleImport { source, .. } => source,
 165                     GlobImport { .. } => unreachable!(),
 166                 };
 167                 match target_module.resolve_name(name, ns, false) {
 168                     Failed(_) => {}
 169                     _ => return Some(Indeterminate),
 170                 }
 171             }
 172         }
 173
 174         self.binding.map(Success)
 175     }
 176 }
 177
 178 impl<'a> ::ModuleS<'a> {
 179     fn resolution(&self, name: Name, ns: Namespace) -> &'a RefCell<NameResolution<'a>> {
 180         *self.resolutions.borrow_mut().entry((name, ns))
 181              .or_insert_with(|| self.arenas.alloc_name_resolution())
 182     }
 183
 184     pub fn resolve_name(&self, name: Name, ns: Namespace, allow_private_imports: bool)
 185                         -> ResolveResult<&'a NameBinding<'a>> {
 186         let resolution = self.resolution(name, ns);
 187         let resolution = match resolution.borrow_state() {
 188             ::std::cell::BorrowState::Unused => resolution.borrow_mut(),
 189             _ => return Failed(None), // This happens when there is a cycle of imports
 190         };
 191
 192         if let Some(result) = resolution.try_result(ns, allow_private_imports) {
 193             // If the resolution doesn't depend on glob definability, check privacy and return.
 194             return result.and_then(|binding| {
 195                 let allowed = allow_private_imports || !binding.is_import() ||
 196                                                        binding.is_pseudo_public();
 197                 if allowed { Success(binding) } else { Failed(None) }
 198             });
 199         }
 200
 201         // Check if the globs are determined
 202         for directive in self.globs.borrow().iter() {
 203             if !allow_private_imports && directive.vis != ty::Visibility::Public { continue }
 204             match directive.target_module.get() {
 205                 None => return Indeterminate,
 206                 Some(target_module) => match target_module.resolve_name(name, ns, false) {
 207                     Indeterminate => return Indeterminate,
 208                     _ => {}
 209                 }
 210             }
 211         }
 212
 213         Failed(None)
 214     }
 215
 216     pub fn add_import_directive(&self,
 217                                 module_path: Vec<Name>,
 218                                 subclass: ImportDirectiveSubclass,
 219                                 span: Span,
 220                                 id: NodeId,
 221                                 vis: ty::Visibility) {
 222         let directive = self.arenas.alloc_import_directive(ImportDirective {
 223             module_path: module_path,
 224             target_module: Cell::new(None),
 225             subclass: subclass,
 226             span: span,
 227             id: id,
 228             vis: vis,
 229         });
 230
 231         self.unresolved_imports.borrow_mut().push(directive);
 232         match directive.subclass {
 233             SingleImport { target, .. } => {
 234                 for &ns in &[ValueNS, TypeNS] {
 235                     self.resolution(target, ns).borrow_mut().single_imports
 236                                                             .add_directive(directive);
 237                 }
 238             }
 239             // We don't add prelude imports to the globs since they only affect lexical scopes,
 240             // which are not relevant to import resolution.
 241             GlobImport { is_prelude: true } => {}
 242             GlobImport { .. } => self.globs.borrow_mut().push(directive),
 243         }
 244     }
 245 }
 246
 247 impl<'a> Resolver<'a> {
 248     // Given a binding and an import directive that resolves to it,
 249     // return the corresponding binding defined by the import directive.
 250     fn import(&mut self, binding: &'a NameBinding<'a>, directive: &'a ImportDirective<'a>)
 251               -> NameBinding<'a> {
 252         NameBinding {
 253             kind: NameBindingKind::Import {
 254                 binding: binding,
 255                 directive: directive,
 256             },
 257             span: directive.span,
 258             vis: directive.vis,
 259         }
 260     }
 261
 262     // Define the name or return the existing binding if there is a collision.
 263     pub fn try_define<T>(&mut self, module: Module<'a>, name: Name, ns: Namespace, binding: T)
 264                          -> Result<(), &'a NameBinding<'a>>
 265         where T: ToNameBinding<'a>
 266     {
 267         let binding = self.arenas.alloc_name_binding(binding.to_name_binding());
 268         self.update_resolution(module, name, ns, |_, resolution| {
 269             if let Some(old_binding) = resolution.binding {
 270                 if binding.is_glob_import() {
 271                     resolution.duplicate_globs.push(binding);
 272                 } else if old_binding.is_glob_import() {
 273                     resolution.duplicate_globs.push(old_binding);
 274                     resolution.binding = Some(binding);
 275                 } else {
 276                     return Err(old_binding);
 277                 }
 278             } else {
 279                 resolution.binding = Some(binding);
 280             }
 281
 282             Ok(())
 283         })
 284     }
 285
 286     // Use `f` to mutate the resolution of the name in the module.
 287     // If the resolution becomes a success, define it in the module's glob importers.
 288     fn update_resolution<T, F>(&mut self, module: Module<'a>, name: Name, ns: Namespace, f: F) -> T
 289         where F: FnOnce(&mut Resolver<'a>, &mut NameResolution<'a>) -> T
 290     {
 291         // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
 292         // during which the resolution might end up getting re-defined via a glob cycle.
 293         let (new_binding, t) = {
 294             let mut resolution = &mut *module.resolution(name, ns).borrow_mut();
 295             let was_known = resolution.binding().is_some();
 296
 297             let t = f(self, resolution);
 298
 299             if was_known { return t; }
 300             match resolution.binding() {
 301                 Some(binding) => (binding, t),
 302                 None => return t,
 303             }
 304         };
 305
 306         // Define `new_binding` in `module`s glob importers.
 307         if new_binding.is_importable() && new_binding.is_pseudo_public() {
 308             for &(importer, directive) in module.glob_importers.borrow_mut().iter() {
 309                 let imported_binding = self.import(new_binding, directive);
 310                 let _ = self.try_define(importer, name, ns, imported_binding);
 311             }
 312         }
 313
 314         t
 315     }
 316 }
 317
 318 struct ImportResolvingError<'a> {
 319     /// Module where the error happened
 320     source_module: Module<'a>,
 321     import_directive: &'a ImportDirective<'a>,
 322     span: Span,
 323     help: String,
 324 }
 325
 326 struct ImportResolver<'a, 'b: 'a> {
 327     resolver: &'a mut Resolver<'b>,
 328 }
 329
 330 impl<'a, 'b: 'a> ::std::ops::Deref for ImportResolver<'a, 'b> {
 331     type Target = Resolver<'b>;
 332     fn deref(&self) -> &Resolver<'b> {
 333         self.resolver
 334     }
 335 }
 336
 337 impl<'a, 'b: 'a> ::std::ops::DerefMut for ImportResolver<'a, 'b> {
 338     fn deref_mut(&mut self) -> &mut Resolver<'b> {
 339         self.resolver
 340     }
 341 }
 342
 343 impl<'a, 'b: 'a> ty::NodeIdTree for ImportResolver<'a, 'b> {
 344     fn is_descendant_of(&self, node: NodeId, ancestor: NodeId) -> bool {
 345         self.resolver.is_descendant_of(node, ancestor)
 346     }
 347 }
 348
 349 impl<'a, 'b:'a> ImportResolver<'a, 'b> {
 350     // Import resolution
 351     //
 352     // This is a fixed-point algorithm. We resolve imports until our efforts
 353     // are stymied by an unresolved import; then we bail out of the current
 354     // module and continue. We terminate successfully once no more imports
 355     // remain or unsuccessfully when no forward progress in resolving imports
 356     // is made.
 357
 358     /// Resolves all imports for the crate. This method performs the fixed-
 359     /// point iteration.
 360     fn resolve_imports(&mut self) {
 361         let mut i = 0;
 362         let mut prev_unresolved_imports = 0;
 363         let mut errors = Vec::new();
 364
 365         loop {
 366             debug!("(resolving imports) iteration {}, {} imports left", i, self.unresolved_imports);
 367
 368             // Attempt to resolve imports in all local modules.
 369             for module in self.arenas.local_modules().iter() {
 370                 self.current_module = module;
 371                 self.resolve_imports_in_current_module(&mut errors);
 372             }
 373
 374             if self.unresolved_imports == 0 {
 375                 debug!("(resolving imports) success");
 376                 for module in self.arenas.local_modules().iter() {
 377                     self.finalize_resolutions_in(module, false);
 378                 }
 379                 break;
 380             }
 381
 382             if self.unresolved_imports == prev_unresolved_imports {
 383                 // resolving failed
 384                 // Report unresolved imports only if no hard error was already reported
 385                 // to avoid generating multiple errors on the same import.
 386                 // Imports that are still indeterminate at this point are actually blocked
 387                 // by errored imports, so there is no point reporting them.
 388                 for module in self.arenas.local_modules().iter() {
 389                     self.finalize_resolutions_in(module, errors.len() == 0);
 390                 }
 391                 for e in errors {
 392                     self.import_resolving_error(e)
 393                 }
 394                 break;
 395             }
 396
 397             i += 1;
 398             prev_unresolved_imports = self.unresolved_imports;
 399         }
 400     }
 401
 402     // Define a "dummy" resolution containing a Def::Err as a placeholder for a
 403     // failed resolution
 404     fn import_dummy_binding(&mut self,
 405                             source_module: Module<'b>,
 406                             directive: &'b ImportDirective<'b>) {
 407         if let SingleImport { target, .. } = directive.subclass {
 408             let dummy_binding = self.arenas.alloc_name_binding(NameBinding {
 409                 kind: NameBindingKind::Def(Def::Err),
 410                 span: DUMMY_SP,
 411                 vis: ty::Visibility::Public,
 412             });
 413             let dummy_binding = self.import(dummy_binding, directive);
 414
 415             let _ = self.try_define(source_module, target, ValueNS, dummy_binding.clone());
 416             let _ = self.try_define(source_module, target, TypeNS, dummy_binding);
 417         }
 418     }
 419
 420     /// Resolves an `ImportResolvingError` into the correct enum discriminant
 421     /// and passes that on to `resolve_error`.
 422     fn import_resolving_error(&mut self, e: ImportResolvingError<'b>) {
 423         // If the error is a single failed import then create a "fake" import
 424         // resolution for it so that later resolve stages won't complain.
 425         self.import_dummy_binding(e.source_module, e.import_directive);
 426         let path = import_path_to_string(&e.import_directive.module_path,
 427                                          &e.import_directive.subclass);
 428         resolve_error(self.resolver,
 429                       e.span,
 430                       ResolutionError::UnresolvedImport(Some((&path, &e.help))));
 431     }
 432
 433     /// Attempts to resolve imports for the given module only.
 434     fn resolve_imports_in_current_module(&mut self, errors: &mut Vec<ImportResolvingError<'b>>) {
 435         let mut imports = Vec::new();
 436         let mut unresolved_imports = self.current_module.unresolved_imports.borrow_mut();
 437         ::std::mem::swap(&mut imports, &mut unresolved_imports);
 438
 439         for import_directive in imports {
 440             match self.resolve_import(&import_directive) {
 441                 Failed(err) => {
 442                     let (span, help) = match err {
 443                         Some((span, msg)) => (span, format!(". {}", msg)),
 444                         None => (import_directive.span, String::new()),
 445                     };
 446                     errors.push(ImportResolvingError {
 447                         source_module: self.current_module,
 448                         import_directive: import_directive,
 449                         span: span,
 450                         help: help,
 451                     });
 452                 }
 453                 Indeterminate => unresolved_imports.push(import_directive),
 454                 Success(()) => {
 455                     // Decrement the count of unresolved imports.
 456                     assert!(self.unresolved_imports >= 1);
 457                     self.unresolved_imports -= 1;
 458                 }
 459             }
 460         }
 461     }
 462
 463     /// Attempts to resolve the given import. The return value indicates
 464     /// failure if we're certain the name does not exist, indeterminate if we
 465     /// don't know whether the name exists at the moment due to other
 466     /// currently-unresolved imports, or success if we know the name exists.
 467     /// If successful, the resolved bindings are written into the module.
 468     fn resolve_import(&mut self, directive: &'b ImportDirective<'b>) -> ResolveResult<()> {
 469         debug!("(resolving import for module) resolving import `{}::...` in `{}`",
 470                names_to_string(&directive.module_path),
 471                module_to_string(self.current_module));
 472
 473         let target_module = match directive.target_module.get() {
 474             Some(module) => module,
 475             _ => match self.resolve_module_path(&directive.module_path,
 476                                                 DontUseLexicalScope,
 477                                                 directive.span) {
 478                 Success(module) => module,
 479                 Indeterminate => return Indeterminate,
 480                 Failed(err) => return Failed(err),
 481             },
 482         };
 483
 484         directive.target_module.set(Some(target_module));
 485         let (source, target, value_determined, type_determined) = match directive.subclass {
 486             SingleImport { source, target, ref value_determined, ref type_determined } =>
 487                 (source, target, value_determined, type_determined),
 488             GlobImport { .. } => return self.resolve_glob_import(target_module, directive),
 489         };
 490
 491         // We need to resolve both namespaces for this to succeed.
 492         let value_result = self.resolve_name_in_module(target_module, source, ValueNS, false, true);
 493         let type_result = self.resolve_name_in_module(target_module, source, TypeNS, false, true);
 494
 495         let module = self.current_module;
 496         let mut privacy_error = true;
 497         for &(ns, result, determined) in &[(ValueNS, &value_result, value_determined),
 498                                            (TypeNS, &type_result, type_determined)] {
 499             match *result {
 500                 Failed(..) if !determined.get() => {
 501                     determined.set(true);
 502                     self.update_resolution(module, target, ns, |_, resolution| {
 503                         resolution.single_imports.directive_failed()
 504                     });
 505                 }
 506                 Success(binding) if !binding.is_importable() => {
 507                     let msg = format!("`{}` is not directly importable", target);
 508                     struct_span_err!(self.session, directive.span, E0253, "{}", &msg)
 509                         .span_label(directive.span, &format!("cannot be imported directly"))
 510                         .emit();
 511                     // Do not import this illegal binding. Import a dummy binding and pretend
 512                     // everything is fine
 513                     self.import_dummy_binding(module, directive);
 514                     return Success(());
 515                 }
 516                 Success(binding) if !self.is_accessible(binding.vis) => {}
 517                 Success(binding) if !determined.get() => {
 518                     determined.set(true);
 519                     let imported_binding = self.import(binding, directive);
 520                     let conflict = self.try_define(module, target, ns, imported_binding);
 521                     if let Err(old_binding) = conflict {
 522                         let binding = &self.import(binding, directive);
 523                         self.report_conflict(module, target, ns, binding, old_binding);
 524                     }
 525                     privacy_error = false;
 526                 }
 527                 Success(_) => privacy_error = false,
 528                 _ => {}
 529             }
 530         }
 531
 532         match (&value_result, &type_result) {
 533             (&Indeterminate, _) | (_, &Indeterminate) => return Indeterminate,
 534             (&Failed(_), &Failed(_)) => {
 535                 let resolutions = target_module.resolutions.borrow();
 536                 let names = resolutions.iter().filter_map(|(&(ref name, _), resolution)| {
 537                     if *name == source { return None; } // Never suggest the same name
 538                     match *resolution.borrow() {
 539                         NameResolution { binding: Some(_), .. } => Some(name),
 540                         NameResolution { single_imports: SingleImports::None, .. } => None,
 541                         _ => Some(name),
 542                     }
 543                 });
 544                 let lev_suggestion = match find_best_match_for_name(names, &source.as_str(), None) {
 545                     Some(name) => format!(". Did you mean to use `{}`?", name),
 546                     None => "".to_owned(),
 547                 };
 548                 let module_str = module_to_string(target_module);
 549                 let msg = if &module_str == "???" {
 550                     format!("There is no `{}` in the crate root{}", source, lev_suggestion)
 551                 } else {
 552                     format!("There is no `{}` in `{}`{}", source, module_str, lev_suggestion)
 553                 };
 554                 return Failed(Some((directive.span, msg)));
 555             }
 556             _ => (),
 557         }
 558
 559         if privacy_error {
 560             for &(ns, result) in &[(ValueNS, &value_result), (TypeNS, &type_result)] {
 561                 let binding = match *result { Success(binding) => binding, _ => continue };
 562                 self.privacy_errors.push(PrivacyError(directive.span, source, binding));
 563                 let imported_binding = self.import(binding, directive);
 564                 let _ = self.try_define(module, target, ns, imported_binding);
 565             }
 566         }
 567
 568         match (&value_result, &type_result) {
 569             (&Success(binding), _) if !binding.pseudo_vis().is_at_least(directive.vis, self) &&
 570                                       self.is_accessible(binding.vis) => {
 571                 let msg = format!("`{}` is private, and cannot be reexported", source);
 572                 let note_msg = format!("consider marking `{}` as `pub` in the imported module",
 573                                         source);
 574                 struct_span_err!(self.session, directive.span, E0364, "{}", &msg)
 575                     .span_note(directive.span, &note_msg)
 576                     .emit();
 577             }
 578
 579             (_, &Success(binding)) if !binding.pseudo_vis().is_at_least(directive.vis, self) &&
 580                                       self.is_accessible(binding.vis) => {
 581                 if binding.is_extern_crate() {
 582                     let msg = format!("extern crate `{}` is private, and cannot be reexported \
 583                                        (error E0364), consider declaring with `pub`",
 584                                        source);
 585                     self.session.add_lint(PRIVATE_IN_PUBLIC, directive.id, directive.span, msg);
 586                 } else {
 587                     let msg = format!("`{}` is private, and cannot be reexported", source);
 588                     let note_msg =
 589                         format!("consider declaring type or module `{}` with `pub`", source);
 590                     struct_span_err!(self.session, directive.span, E0365, "{}", &msg)
 591                         .span_note(directive.span, &note_msg)
 592                         .emit();
 593                 }
 594             }
 595
 596             _ => {}
 597         }
 598
 599         // Record what this import resolves to for later uses in documentation,
 600         // this may resolve to either a value or a type, but for documentation
 601         // purposes it's good enough to just favor one over the other.
 602         let def = match type_result.success().and_then(NameBinding::def) {
 603             Some(def) => def,
 604             None => value_result.success().and_then(NameBinding::def).unwrap(),
 605         };
 606         let path_resolution = PathResolution::new(def);
 607         self.def_map.insert(directive.id, path_resolution);
 608
 609         debug!("(resolving single import) successfully resolved import");
 610         return Success(());
 611     }
 612
 613     // Resolves a glob import. Note that this function cannot fail; it either
 614     // succeeds or bails out (as importing * from an empty module or a module
 615     // that exports nothing is valid). target_module is the module we are
 616     // actually importing, i.e., `foo` in `use foo::*`.
 617     fn resolve_glob_import(&mut self, target_module: Module<'b>, directive: &'b ImportDirective<'b>)
 618                            -> ResolveResult<()> {
 619         if let Some(Def::Trait(_)) = target_module.def {
 620             self.session.span_err(directive.span, "items in traits are not importable.");
 621         }
 622
 623         let module = self.current_module;
 624         if module.def_id() == target_module.def_id() {
 625             // This means we are trying to glob import a module into itself, and it is a no-go
 626             let msg = "Cannot glob-import a module into itself.".into();
 627             return Failed(Some((directive.span, msg)));
 628         }
 629         self.populate_module_if_necessary(target_module);
 630
 631         if let GlobImport { is_prelude: true } = directive.subclass {
 632             self.prelude = Some(target_module);
 633             return Success(());
 634         }
 635
 636         // Add to target_module's glob_importers
 637         target_module.glob_importers.borrow_mut().push((module, directive));
 638
 639         // Ensure that `resolutions` isn't borrowed during `try_define`,
 640         // since it might get updated via a glob cycle.
 641         let bindings = target_module.resolutions.borrow().iter().filter_map(|(name, resolution)| {
 642             resolution.borrow().binding().map(|binding| (*name, binding))
 643         }).collect::<Vec<_>>();
 644         for ((name, ns), binding) in bindings {
 645             if binding.is_importable() && binding.is_pseudo_public() {
 646                 let imported_binding = self.import(binding, directive);
 647                 let _ = self.try_define(module, name, ns, imported_binding);
 648             }
 649         }
 650
 651         // Record the destination of this import
 652         if let Some(did) = target_module.def_id() {
 653             let resolution = PathResolution::new(Def::Mod(did));
 654             self.def_map.insert(directive.id, resolution);
 655         }
 656
 657         debug!("(resolving glob import) successfully resolved import");
 658         return Success(());
 659     }
 660
 661     // Miscellaneous post-processing, including recording reexports, reporting conflicts,
 662     // reporting the PRIVATE_IN_PUBLIC lint, and reporting unresolved imports.
 663     fn finalize_resolutions_in(&mut self, module: Module<'b>, report_unresolved_imports: bool) {
 664         // Since import resolution is finished, globs will not define any more names.
 665         *module.globs.borrow_mut() = Vec::new();
 666
 667         let mut reexports = Vec::new();
 668         for (&(name, ns), resolution) in module.resolutions.borrow().iter() {
 669             let resolution = resolution.borrow();
 670             let binding = match resolution.binding {
 671                 Some(binding) => binding,
 672                 None => continue,
 673             };
 674
 675             // Report conflicts
 676             for duplicate_glob in resolution.duplicate_globs.iter() {
 677                 // FIXME #31337: We currently allow items to shadow glob-imported re-exports.
 678                 if !binding.is_import() {
 679                     if let NameBindingKind::Import { binding, .. } = duplicate_glob.kind {
 680                         if binding.is_import() { continue }
 681                     }
 682                 }
 683
 684                 self.report_conflict(module, name, ns, duplicate_glob, binding);
 685             }
 686
 687             if binding.vis == ty::Visibility::Public &&
 688                (binding.is_import() || binding.is_extern_crate()) {
 689                 if let Some(def) = binding.def() {
 690                     reexports.push(Export { name: name, def_id: def.def_id() });
 691                 }
 692             }
 693
 694             if let NameBindingKind::Import { binding: orig_binding, directive, .. } = binding.kind {
 695                 if ns == TypeNS && orig_binding.is_variant() &&
 696                    !orig_binding.vis.is_at_least(binding.vis, self) {
 697                     let msg = format!("variant `{}` is private, and cannot be reexported \
 698                                        (error E0364), consider declaring its enum as `pub`",
 699                                       name);
 700                     self.session.add_lint(PRIVATE_IN_PUBLIC, directive.id, binding.span, msg);
 701                 }
 702             }
 703         }
 704
 705         if reexports.len() > 0 {
 706             if let Some(def_id) = module.def_id() {
 707                 let node_id = self.definitions.as_local_node_id(def_id).unwrap();
 708                 self.export_map.insert(node_id, reexports);
 709             }
 710         }
 711
 712         if report_unresolved_imports {
 713             for import in module.unresolved_imports.borrow().iter() {
 714                 resolve_error(self.resolver, import.span, ResolutionError::UnresolvedImport(None));
 715                 break;
 716             }
 717         }
 718     }
 719 }
 720
 721 fn import_path_to_string(names: &[Name], subclass: &ImportDirectiveSubclass) -> String {
 722     if names.is_empty() {
 723         import_directive_subclass_to_string(subclass)
 724     } else {
 725         (format!("{}::{}",
 726                  names_to_string(names),
 727                  import_directive_subclass_to_string(subclass)))
 728             .to_string()
 729     }
 730 }
 731
 732 fn import_directive_subclass_to_string(subclass: &ImportDirectiveSubclass) -> String {
 733     match *subclass {
 734         SingleImport { source, .. } => source.to_string(),
 735         GlobImport { .. } => "*".to_string(),
 736     }
 737 }