src/librustc_resolve/resolve_imports.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use self::ImportDirectiveSubclass::*;
  12
  13 use {AmbiguityError, Module, PerNS};
  14 use Namespace::{self, TypeNS, MacroNS};
  15 use {NameBinding, NameBindingKind, PathResult, PrivacyError};
  16 use Resolver;
  17 use {names_to_string, module_to_string};
  18 use {resolve_error, ResolutionError};
  19
  20 use rustc::ty;
  21 use rustc::lint::builtin::PUB_USE_OF_PRIVATE_EXTERN_CRATE;
  22 use rustc::hir::def_id::DefId;
  23 use rustc::hir::def::*;
  24 use rustc::session::DiagnosticMessageId;
  25 use rustc::util::nodemap::{FxHashMap, FxHashSet};
  26
  27 use syntax::ast::{Ident, Name, SpannedIdent, NodeId};
  28 use syntax::ext::base::Determinacy::{self, Determined, Undetermined};
  29 use syntax::ext::hygiene::Mark;
  30 use syntax::parse::token;
  31 use syntax::symbol::keywords;
  32 use syntax::util::lev_distance::find_best_match_for_name;
  33 use syntax_pos::Span;
  34
  35 use std::cell::{Cell, RefCell};
  36 use std::mem;
  37
  38 /// Contains data for specific types of import directives.
  39 #[derive(Clone, Debug)]
  40 pub enum ImportDirectiveSubclass<'a> {
  41     SingleImport {
  42         target: Ident,
  43         source: Ident,
  44         result: PerNS<Cell<Result<&'a NameBinding<'a>, Determinacy>>>,
  45         type_ns_only: bool,
  46     },
  47     GlobImport {
  48         is_prelude: bool,
  49         max_vis: Cell<ty::Visibility>, // The visibility of the greatest reexport.
  50         // n.b. `max_vis` is only used in `finalize_import` to check for reexport errors.
  51     },
  52     ExternCrate(Option<Name>),
  53     MacroUse,
  54 }
  55
  56 /// One import directive.
  57 #[derive(Debug,Clone)]
  58 pub struct ImportDirective<'a> {
  59     pub id: NodeId,
  60     pub parent: Module<'a>,
  61     pub module_path: Vec<SpannedIdent>,
  62     pub imported_module: Cell<Option<Module<'a>>>, // the resolution of `module_path`
  63     pub subclass: ImportDirectiveSubclass<'a>,
  64     pub span: Span,
  65     pub vis: Cell<ty::Visibility>,
  66     pub expansion: Mark,
  67     pub used: Cell<bool>,
  68 }
  69
  70 impl<'a> ImportDirective<'a> {
  71     pub fn is_glob(&self) -> bool {
  72         match self.subclass { ImportDirectiveSubclass::GlobImport { .. } => true, _ => false }
  73     }
  74 }
  75
  76 #[derive(Clone, Default, Debug)]
  77 /// Records information about the resolution of a name in a namespace of a module.
  78 pub struct NameResolution<'a> {
  79     /// The single imports that define the name in the namespace.
  80     single_imports: SingleImports<'a>,
  81     /// The least shadowable known binding for this name, or None if there are no known bindings.
  82     pub binding: Option<&'a NameBinding<'a>>,
  83     shadows_glob: Option<&'a NameBinding<'a>>,
  84 }
  85
  86 #[derive(Clone, Debug)]
  87 enum SingleImports<'a> {
  88     /// No single imports can define the name in the namespace.
  89     None,
  90     /// Only the given single import can define the name in the namespace.
  91     MaybeOne(&'a ImportDirective<'a>),
  92     /// At least one single import will define the name in the namespace.
  93     AtLeastOne,
  94 }
  95
  96 impl<'a> Default for SingleImports<'a> {
  97     /// Creates a `SingleImports<'a>` of None type.
  98     fn default() -> Self {
  99         SingleImports::None
 100     }
 101 }
 102
 103 impl<'a> SingleImports<'a> {
 104     fn add_directive(&mut self, directive: &'a ImportDirective<'a>) {
 105         match *self {
 106             SingleImports::None => *self = SingleImports::MaybeOne(directive),
 107             // If two single imports can define the name in the namespace, we can assume that at
 108             // least one of them will define it since otherwise both would have to define only one
 109             // namespace, leading to a duplicate error.
 110             SingleImports::MaybeOne(_) => *self = SingleImports::AtLeastOne,
 111             SingleImports::AtLeastOne => {}
 112         };
 113     }
 114
 115     fn directive_failed(&mut self) {
 116         match *self {
 117             SingleImports::None => unreachable!(),
 118             SingleImports::MaybeOne(_) => *self = SingleImports::None,
 119             SingleImports::AtLeastOne => {}
 120         }
 121     }
 122 }
 123
 124 impl<'a> NameResolution<'a> {
 125     // Returns the binding for the name if it is known or None if it not known.
 126     fn binding(&self) -> Option<&'a NameBinding<'a>> {
 127         self.binding.and_then(|binding| match self.single_imports {
 128             SingleImports::None => Some(binding),
 129             _ if !binding.is_glob_import() => Some(binding),
 130             _ => None, // The binding could be shadowed by a single import, so it is not known.
 131         })
 132     }
 133 }
 134
 135 impl<'a> Resolver<'a> {
 136     fn resolution(&self, module: Module<'a>, ident: Ident, ns: Namespace)
 137                   -> &'a RefCell<NameResolution<'a>> {
 138         *module.resolutions.borrow_mut().entry((ident.modern(), 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_unadjusted(&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,
 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                 continue
 238             }
 239             let module = unwrap_or!(directive.imported_module.get(), return Err(Undetermined));
 240             let (orig_current_module, mut ident) = (self.current_module, ident.modern());
 241             match ident.ctxt.glob_adjust(module.expansion, directive.span.ctxt().modern()) {
 242                 Some(Some(def)) => self.current_module = self.macro_def_scope(def),
 243                 Some(None) => {}
 244                 None => continue,
 245             };
 246             let result = self.resolve_ident_in_module_unadjusted(
 247                 module, ident, ns, false, false, path_span,
 248             );
 249             self.current_module = orig_current_module;
 250             if let Err(Undetermined) = result {
 251                 return Err(Undetermined);
 252             }
 253         }
 254
 255         Err(Determined)
 256     }
 257
 258     // Add an import directive to the current module.
 259     pub fn add_import_directive(&mut self,
 260                                 module_path: Vec<SpannedIdent>,
 261                                 subclass: ImportDirectiveSubclass<'a>,
 262                                 span: Span,
 263                                 id: NodeId,
 264                                 vis: ty::Visibility,
 265                                 expansion: Mark) {
 266         let current_module = self.current_module;
 267         let directive = self.arenas.alloc_import_directive(ImportDirective {
 268             parent: current_module,
 269             module_path,
 270             imported_module: Cell::new(None),
 271             subclass,
 272             span,
 273             id,
 274             vis: Cell::new(vis),
 275             expansion,
 276             used: Cell::new(false),
 277         });
 278
 279         self.indeterminate_imports.push(directive);
 280         match directive.subclass {
 281             SingleImport { target, .. } => {
 282                 self.per_ns(|this, ns| {
 283                     let mut resolution = this.resolution(current_module, target, ns).borrow_mut();
 284                     resolution.single_imports.add_directive(directive);
 285                 });
 286             }
 287             // We don't add prelude imports to the globs since they only affect lexical scopes,
 288             // which are not relevant to import resolution.
 289             GlobImport { is_prelude: true, .. } => {}
 290             GlobImport { .. } => self.current_module.globs.borrow_mut().push(directive),
 291             _ => unreachable!(),
 292         }
 293     }
 294
 295     // Given a binding and an import directive that resolves to it,
 296     // return the corresponding binding defined by the import directive.
 297     pub fn import(&self, binding: &'a NameBinding<'a>, directive: &'a ImportDirective<'a>)
 298                   -> &'a NameBinding<'a> {
 299         let vis = if binding.pseudo_vis().is_at_least(directive.vis.get(), self) ||
 300                      // c.f. `PUB_USE_OF_PRIVATE_EXTERN_CRATE`
 301                      !directive.is_glob() && binding.is_extern_crate() {
 302             directive.vis.get()
 303         } else {
 304             binding.pseudo_vis()
 305         };
 306
 307         if let GlobImport { ref max_vis, .. } = directive.subclass {
 308             if vis == directive.vis.get() || vis.is_at_least(max_vis.get(), self) {
 309                 max_vis.set(vis)
 310             }
 311         }
 312
 313         self.arenas.alloc_name_binding(NameBinding {
 314             kind: NameBindingKind::Import {
 315                 binding,
 316                 directive,
 317                 used: Cell::new(false),
 318                 legacy_self_import: false,
 319             },
 320             span: directive.span,
 321             vis,
 322             expansion: directive.expansion,
 323         })
 324     }
 325
 326     // Define the name or return the existing binding if there is a collision.
 327     pub fn try_define(&mut self,
 328                       module: Module<'a>,
 329                       ident: Ident,
 330                       ns: Namespace,
 331                       binding: &'a NameBinding<'a>)
 332                       -> Result<(), &'a NameBinding<'a>> {
 333         self.update_resolution(module, ident, ns, |this, resolution| {
 334             if let Some(old_binding) = resolution.binding {
 335                 if binding.is_glob_import() {
 336                     if !old_binding.is_glob_import() &&
 337                        !(ns == MacroNS && old_binding.expansion != Mark::root()) {
 338                         resolution.shadows_glob = Some(binding);
 339                     } else if binding.def() != old_binding.def() {
 340                         resolution.binding = Some(this.ambiguity(old_binding, binding));
 341                     } else if !old_binding.vis.is_at_least(binding.vis, &*this) {
 342                         // We are glob-importing the same item but with greater visibility.
 343                         resolution.binding = Some(binding);
 344                     }
 345                 } else if old_binding.is_glob_import() {
 346                     if ns == MacroNS && binding.expansion != Mark::root() &&
 347                        binding.def() != old_binding.def() {
 348                         resolution.binding = Some(this.ambiguity(binding, old_binding));
 349                     } else {
 350                         resolution.binding = Some(binding);
 351                         resolution.shadows_glob = Some(old_binding);
 352                     }
 353                 } else {
 354                     return Err(old_binding);
 355                 }
 356             } else {
 357                 resolution.binding = Some(binding);
 358             }
 359
 360             Ok(())
 361         })
 362     }
 363
 364     pub fn ambiguity(&self, b1: &'a NameBinding<'a>, b2: &'a NameBinding<'a>)
 365                      -> &'a NameBinding<'a> {
 366         self.arenas.alloc_name_binding(NameBinding {
 367             kind: NameBindingKind::Ambiguity { b1: b1, b2: b2, legacy: false },
 368             vis: if b1.vis.is_at_least(b2.vis, self) { b1.vis } else { b2.vis },
 369             span: b1.span,
 370             expansion: Mark::root(),
 371         })
 372     }
 373
 374     // Use `f` to mutate the resolution of the name in the module.
 375     // If the resolution becomes a success, define it in the module's glob importers.
 376     fn update_resolution<T, F>(&mut self, module: Module<'a>, ident: Ident, ns: Namespace, f: F)
 377                                -> T
 378         where F: FnOnce(&mut Resolver<'a>, &mut NameResolution<'a>) -> T
 379     {
 380         // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
 381         // during which the resolution might end up getting re-defined via a glob cycle.
 382         let (binding, t) = {
 383             let resolution = &mut *self.resolution(module, ident, ns).borrow_mut();
 384             let old_binding = resolution.binding();
 385
 386             let t = f(self, resolution);
 387
 388             match resolution.binding() {
 389                 _ if old_binding.is_some() => return t,
 390                 None => return t,
 391                 Some(binding) => match old_binding {
 392                     Some(old_binding) if old_binding as *const _ == binding as *const _ => return t,
 393                     _ => (binding, t),
 394                 }
 395             }
 396         };
 397
 398         // Define `binding` in `module`s glob importers.
 399         for directive in module.glob_importers.borrow_mut().iter() {
 400             let mut ident = ident.modern();
 401             let scope = match ident.ctxt.reverse_glob_adjust(module.expansion,
 402                                                              directive.span.ctxt().modern()) {
 403                 Some(Some(def)) => self.macro_def_scope(def),
 404                 Some(None) => directive.parent,
 405                 None => continue,
 406             };
 407             if self.is_accessible_from(binding.vis, scope) {
 408                 let imported_binding = self.import(binding, directive);
 409                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
 410             }
 411         }
 412
 413         t
 414     }
 415
 416     // Define a "dummy" resolution containing a Def::Err as a placeholder for a
 417     // failed resolution
 418     fn import_dummy_binding(&mut self, directive: &'a ImportDirective<'a>) {
 419         if let SingleImport { target, .. } = directive.subclass {
 420             let dummy_binding = self.dummy_binding;
 421             let dummy_binding = self.import(dummy_binding, directive);
 422             self.per_ns(|this, ns| {
 423                 let _ = this.try_define(directive.parent, target, ns, dummy_binding);
 424             });
 425         }
 426     }
 427 }
 428
 429 pub struct ImportResolver<'a, 'b: 'a> {
 430     pub resolver: &'a mut Resolver<'b>,
 431 }
 432
 433 impl<'a, 'b: 'a> ::std::ops::Deref for ImportResolver<'a, 'b> {
 434     type Target = Resolver<'b>;
 435     fn deref(&self) -> &Resolver<'b> {
 436         self.resolver
 437     }
 438 }
 439
 440 impl<'a, 'b: 'a> ::std::ops::DerefMut for ImportResolver<'a, 'b> {
 441     fn deref_mut(&mut self) -> &mut Resolver<'b> {
 442         self.resolver
 443     }
 444 }
 445
 446 impl<'a, 'b: 'a> ty::DefIdTree for &'a ImportResolver<'a, 'b> {
 447     fn parent(self, id: DefId) -> Option<DefId> {
 448         self.resolver.parent(id)
 449     }
 450 }
 451
 452 impl<'a, 'b:'a> ImportResolver<'a, 'b> {
 453     // Import resolution
 454     //
 455     // This is a fixed-point algorithm. We resolve imports until our efforts
 456     // are stymied by an unresolved import; then we bail out of the current
 457     // module and continue. We terminate successfully once no more imports
 458     // remain or unsuccessfully when no forward progress in resolving imports
 459     // is made.
 460
 461     /// Resolves all imports for the crate. This method performs the fixed-
 462     /// point iteration.
 463     pub fn resolve_imports(&mut self) {
 464         let mut prev_num_indeterminates = self.indeterminate_imports.len() + 1;
 465         while self.indeterminate_imports.len() < prev_num_indeterminates {
 466             prev_num_indeterminates = self.indeterminate_imports.len();
 467             for import in mem::replace(&mut self.indeterminate_imports, Vec::new()) {
 468                 match self.resolve_import(&import) {
 469                     true => self.determined_imports.push(import),
 470                     false => self.indeterminate_imports.push(import),
 471                 }
 472             }
 473         }
 474     }
 475
 476     pub fn finalize_imports(&mut self) {
 477         for module in self.arenas.local_modules().iter() {
 478             self.finalize_resolutions_in(module);
 479         }
 480
 481         let mut errors = false;
 482         let mut seen_spans = FxHashSet();
 483         for i in 0 .. self.determined_imports.len() {
 484             let import = self.determined_imports[i];
 485             if let Some((span, err)) = self.finalize_import(import) {
 486                 errors = true;
 487
 488                 if let SingleImport { source, ref result, .. } = import.subclass {
 489                     if source.name == "self" {
 490                         // Silence `unresolved import` error if E0429 is already emitted
 491                         match result.value_ns.get() {
 492                             Err(Determined) => continue,
 493                             _ => {},
 494                         }
 495                     }
 496                 }
 497
 498                 // If the error is a single failed import then create a "fake" import
 499                 // resolution for it so that later resolve stages won't complain.
 500                 self.import_dummy_binding(import);
 501                 if !seen_spans.contains(&span) {
 502                     let path = import_path_to_string(&import.module_path[..],
 503                                                      &import.subclass,
 504                                                      span);
 505                     let error = ResolutionError::UnresolvedImport(Some((span, &path, &err)));
 506                     resolve_error(self.resolver, span, error);
 507                     seen_spans.insert(span);
 508                 }
 509             }
 510         }
 511
 512         // Report unresolved imports only if no hard error was already reported
 513         // to avoid generating multiple errors on the same import.
 514         if !errors {
 515             if let Some(import) = self.indeterminate_imports.iter().next() {
 516                 let error = ResolutionError::UnresolvedImport(None);
 517                 resolve_error(self.resolver, import.span, error);
 518             }
 519         }
 520     }
 521
 522     /// Attempts to resolve the given import, returning true if its resolution is determined.
 523     /// If successful, the resolved bindings are written into the module.
 524     fn resolve_import(&mut self, directive: &'b ImportDirective<'b>) -> bool {
 525         debug!("(resolving import for module) resolving import `{}::...` in `{}`",
 526                names_to_string(&directive.module_path[..]),
 527                module_to_string(self.current_module));
 528
 529         self.current_module = directive.parent;
 530
 531         let module = if let Some(module) = directive.imported_module.get() {
 532             module
 533         } else {
 534             let vis = directive.vis.get();
 535             // For better failure detection, pretend that the import will not define any names
 536             // while resolving its module path.
 537             directive.vis.set(ty::Visibility::Invisible);
 538             let result = self.resolve_path(&directive.module_path[..], None, false, directive.span);
 539             directive.vis.set(vis);
 540
 541             match result {
 542                 PathResult::Module(module) => module,
 543                 PathResult::Indeterminate => return false,
 544                 _ => return true,
 545             }
 546         };
 547
 548         directive.imported_module.set(Some(module));
 549         let (source, target, result, type_ns_only) = match directive.subclass {
 550             SingleImport { source, target, ref result, type_ns_only } =>
 551                 (source, target, result, type_ns_only),
 552             GlobImport { .. } => {
 553                 self.resolve_glob_import(directive);
 554                 return true;
 555             }
 556             _ => unreachable!(),
 557         };
 558
 559         let mut indeterminate = false;
 560         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 561             if let Err(Undetermined) = result[ns].get() {
 562                 result[ns].set(this.resolve_ident_in_module(module,
 563                                                             source,
 564                                                             ns,
 565                                                             false,
 566                                                             false,
 567                                                             directive.span));
 568             } else {
 569                 return
 570             };
 571
 572             let parent = directive.parent;
 573             match result[ns].get() {
 574                 Err(Undetermined) => indeterminate = true,
 575                 Err(Determined) => {
 576                     this.update_resolution(parent, target, ns, |_, resolution| {
 577                         resolution.single_imports.directive_failed()
 578                     });
 579                 }
 580                 Ok(binding) if !binding.is_importable() => {
 581                     let msg = format!("`{}` is not directly importable", target);
 582                     struct_span_err!(this.session, directive.span, E0253, "{}", &msg)
 583                         .span_label(directive.span, "cannot be imported directly")
 584                         .emit();
 585                     // Do not import this illegal binding. Import a dummy binding and pretend
 586                     // everything is fine
 587                     this.import_dummy_binding(directive);
 588                 }
 589                 Ok(binding) => {
 590                     let imported_binding = this.import(binding, directive);
 591                     let conflict = this.try_define(parent, target, ns, imported_binding);
 592                     if let Err(old_binding) = conflict {
 593                         this.report_conflict(parent, target, ns, imported_binding, old_binding);
 594                     }
 595                 }
 596             }
 597         });
 598
 599         !indeterminate
 600     }
 601
 602     // If appropriate, returns an error to report.
 603     fn finalize_import(&mut self, directive: &'b ImportDirective<'b>) -> Option<(Span, String)> {
 604         self.current_module = directive.parent;
 605
 606         let ImportDirective { ref module_path, span, .. } = *directive;
 607         let module_result = self.resolve_path(&module_path, None, true, span);
 608         let module = match module_result {
 609             PathResult::Module(module) => module,
 610             PathResult::Failed(span, msg, false) => {
 611                 resolve_error(self, span, ResolutionError::FailedToResolve(&msg));
 612                 return None;
 613             }
 614             PathResult::Failed(span, msg, true) => {
 615                 let (mut self_path, mut self_result) = (module_path.clone(), None);
 616                 if !self_path.is_empty() &&
 617                     !token::Ident(self_path[0].node).is_path_segment_keyword() &&
 618                     !(self_path.len() > 1 &&
 619                       token::Ident(self_path[1].node).is_path_segment_keyword())
 620                 {
 621                     self_path[0].node.name = keywords::SelfValue.name();
 622                     self_result = Some(self.resolve_path(&self_path, None, false, span));
 623                 }
 624                 return if let Some(PathResult::Module(..)) = self_result {
 625                     Some((span, format!("Did you mean `{}`?", names_to_string(&self_path[..]))))
 626                 } else {
 627                     Some((span, msg))
 628                 };
 629             },
 630             _ => return None,
 631         };
 632
 633         let (ident, result, type_ns_only) = match directive.subclass {
 634             SingleImport { source, ref result, type_ns_only, .. } => (source, result, type_ns_only),
 635             GlobImport { .. } if module.def_id() == directive.parent.def_id() => {
 636                 // Importing a module into itself is not allowed.
 637                 return Some((directive.span,
 638                              "Cannot glob-import a module into itself.".to_string()));
 639             }
 640             GlobImport { is_prelude, ref max_vis } => {
 641                 if !is_prelude &&
 642                    max_vis.get() != ty::Visibility::Invisible && // Allow empty globs.
 643                    !max_vis.get().is_at_least(directive.vis.get(), &*self) {
 644                     let msg = "A non-empty glob must import something with the glob's visibility";
 645                     self.session.span_err(directive.span, msg);
 646                 }
 647                 return None;
 648             }
 649             _ => unreachable!(),
 650         };
 651
 652         let mut all_ns_err = true;
 653         let mut legacy_self_import = None;
 654         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 655             if let Ok(binding) = result[ns].get() {
 656                 all_ns_err = false;
 657                 if this.record_use(ident, ns, binding, directive.span) {
 658                     this.resolution(module, ident, ns).borrow_mut().binding =
 659                         Some(this.dummy_binding);
 660                 }
 661             }
 662         } else if let Ok(binding) = this.resolve_ident_in_module(module,
 663                                                                  ident,
 664                                                                  ns,
 665                                                                  false,
 666                                                                  false,
 667                                                                  directive.span) {
 668             legacy_self_import = Some(directive);
 669             let binding = this.arenas.alloc_name_binding(NameBinding {
 670                 kind: NameBindingKind::Import {
 671                     binding,
 672                     directive,
 673                     used: Cell::new(false),
 674                     legacy_self_import: true,
 675                 },
 676                 ..*binding
 677             });
 678             let _ = this.try_define(directive.parent, ident, ns, binding);
 679         });
 680
 681         if all_ns_err {
 682             if let Some(directive) = legacy_self_import {
 683                 self.warn_legacy_self_import(directive);
 684                 return None;
 685             }
 686             let mut all_ns_failed = true;
 687             self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 688                 match this.resolve_ident_in_module(module, ident, ns, false, true, span) {
 689                     Ok(_) => all_ns_failed = false,
 690                     _ => {}
 691                 }
 692             });
 693
 694             return if all_ns_failed {
 695                 let resolutions = module.resolutions.borrow();
 696                 let names = resolutions.iter().filter_map(|(&(ref i, _), resolution)| {
 697                     if *i == ident { return None; } // Never suggest the same name
 698                     match *resolution.borrow() {
 699                         NameResolution { binding: Some(name_binding), .. } => {
 700                             match name_binding.kind {
 701                                 NameBindingKind::Import { binding, .. } => {
 702                                     match binding.kind {
 703                                         // Never suggest the name that has binding error
 704                                         // i.e. the name that cannot be previously resolved
 705                                         NameBindingKind::Def(Def::Err) => return None,
 706                                         _ => Some(&i.name),
 707                                     }
 708                                 },
 709                                 _ => Some(&i.name),
 710                             }
 711                         },
 712                         NameResolution { single_imports: SingleImports::None, .. } => None,
 713                         _ => Some(&i.name),
 714                     }
 715                 });
 716                 let lev_suggestion =
 717                     match find_best_match_for_name(names, &ident.name.as_str(), None) {
 718                         Some(name) => format!(". Did you mean to use `{}`?", name),
 719                         None => "".to_owned(),
 720                     };
 721                 let module_str = module_to_string(module);
 722                 let msg = if &module_str == "???" {
 723                     format!("no `{}` in the root{}", ident, lev_suggestion)
 724                 } else {
 725                     format!("no `{}` in `{}`{}", ident, module_str, lev_suggestion)
 726                 };
 727                 Some((span, msg))
 728             } else {
 729                 // `resolve_ident_in_module` reported a privacy error.
 730                 self.import_dummy_binding(directive);
 731                 None
 732             }
 733         }
 734
 735         let mut reexport_error = None;
 736         let mut any_successful_reexport = false;
 737         self.per_ns(|this, ns| {
 738             if let Ok(binding) = result[ns].get() {
 739                 let vis = directive.vis.get();
 740                 if !binding.pseudo_vis().is_at_least(vis, &*this) {
 741                     reexport_error = Some((ns, binding));
 742                 } else {
 743                     any_successful_reexport = true;
 744                 }
 745             }
 746         });
 747
 748         // All namespaces must be re-exported with extra visibility for an error to occur.
 749         if !any_successful_reexport {
 750             let (ns, binding) = reexport_error.unwrap();
 751             if ns == TypeNS && binding.is_extern_crate() {
 752                 let msg = format!("extern crate `{}` is private, and cannot be reexported \
 753                                    (error E0365), consider declaring with `pub`",
 754                                    ident);
 755                 self.session.buffer_lint(PUB_USE_OF_PRIVATE_EXTERN_CRATE,
 756                                          directive.id,
 757                                          directive.span,
 758                                          &msg);
 759             } else if ns == TypeNS {
 760                 struct_span_err!(self.session, directive.span, E0365,
 761                                  "`{}` is private, and cannot be reexported", ident)
 762                     .span_label(directive.span, format!("reexport of private `{}`", ident))
 763                     .note(&format!("consider declaring type or module `{}` with `pub`", ident))
 764                     .emit();
 765             } else {
 766                 let msg = format!("`{}` is private, and cannot be reexported", ident);
 767                 let note_msg =
 768                     format!("consider marking `{}` as `pub` in the imported module", ident);
 769                 struct_span_err!(self.session, directive.span, E0364, "{}", &msg)
 770                     .span_note(directive.span, &note_msg)
 771                     .emit();
 772             }
 773         }
 774
 775         // Record what this import resolves to for later uses in documentation,
 776         // this may resolve to either a value or a type, but for documentation
 777         // purposes it's good enough to just favor one over the other.
 778         self.per_ns(|this, ns| if let Some(binding) = result[ns].get().ok() {
 779             this.def_map.entry(directive.id).or_insert(PathResolution::new(binding.def()));
 780         });
 781
 782         debug!("(resolving single import) successfully resolved import");
 783         None
 784     }
 785
 786     fn resolve_glob_import(&mut self, directive: &'b ImportDirective<'b>) {
 787         let module = directive.imported_module.get().unwrap();
 788         self.populate_module_if_necessary(module);
 789
 790         if let Some(Def::Trait(_)) = module.def() {
 791             self.session.span_err(directive.span, "items in traits are not importable.");
 792             return;
 793         } else if module.def_id() == directive.parent.def_id()  {
 794             return;
 795         } else if let GlobImport { is_prelude: true, .. } = directive.subclass {
 796             self.prelude = Some(module);
 797             return;
 798         }
 799
 800         // Add to module's glob_importers
 801         module.glob_importers.borrow_mut().push(directive);
 802
 803         // Ensure that `resolutions` isn't borrowed during `try_define`,
 804         // since it might get updated via a glob cycle.
 805         let bindings = module.resolutions.borrow().iter().filter_map(|(&ident, resolution)| {
 806             resolution.borrow().binding().map(|binding| (ident, binding))
 807         }).collect::<Vec<_>>();
 808         for ((mut ident, ns), binding) in bindings {
 809             let scope = match ident.ctxt.reverse_glob_adjust(module.expansion,
 810                                                              directive.span.ctxt().modern()) {
 811                 Some(Some(def)) => self.macro_def_scope(def),
 812                 Some(None) => self.current_module,
 813                 None => continue,
 814             };
 815             if self.is_accessible_from(binding.pseudo_vis(), scope) {
 816                 let imported_binding = self.import(binding, directive);
 817                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
 818             }
 819         }
 820
 821         // Record the destination of this import
 822         self.record_def(directive.id, PathResolution::new(module.def().unwrap()));
 823     }
 824
 825     // Miscellaneous post-processing, including recording reexports,
 826     // reporting conflicts, and reporting unresolved imports.
 827     fn finalize_resolutions_in(&mut self, module: Module<'b>) {
 828         // Since import resolution is finished, globs will not define any more names.
 829         *module.globs.borrow_mut() = Vec::new();
 830
 831         let mut reexports = Vec::new();
 832         let mut exported_macro_names = FxHashMap();
 833         if module as *const _ == self.graph_root as *const _ {
 834             let macro_exports = mem::replace(&mut self.macro_exports, Vec::new());
 835             for export in macro_exports.into_iter().rev() {
 836                 if exported_macro_names.insert(export.ident.modern(), export.span).is_none() {
 837                     reexports.push(export);
 838                 }
 839             }
 840         }
 841
 842         for (&(ident, ns), resolution) in module.resolutions.borrow().iter() {
 843             let resolution = &mut *resolution.borrow_mut();
 844             let binding = match resolution.binding {
 845                 Some(binding) => binding,
 846                 None => continue,
 847             };
 848
 849             if binding.vis == ty::Visibility::Public &&
 850                (binding.is_import() || binding.is_macro_def()) {
 851                 let def = binding.def();
 852                 if def != Def::Err {
 853                     if !def.def_id().is_local() {
 854                         self.cstore.export_macros_untracked(def.def_id().krate);
 855                     }
 856                     if let Def::Macro(..) = def {
 857                         if let Some(&span) = exported_macro_names.get(&ident.modern()) {
 858                             let msg =
 859                                 format!("a macro named `{}` has already been exported", ident);
 860                             self.session.struct_span_err(span, &msg)
 861                                 .span_label(span, format!("`{}` already exported", ident))
 862                                 .span_note(binding.span, "previous macro export here")
 863                                 .emit();
 864                         }
 865                     }
 866                     reexports.push(Export { ident: ident.modern(), def: def, span: binding.span });
 867                 }
 868             }
 869
 870             match binding.kind {
 871                 NameBindingKind::Import { binding: orig_binding, directive, .. } => {
 872                     if ns == TypeNS && orig_binding.is_variant() &&
 873                         !orig_binding.vis.is_at_least(binding.vis, &*self) {
 874                             let msg = match directive.subclass {
 875                                 ImportDirectiveSubclass::SingleImport { .. } => {
 876                                     format!("variant `{}` is private and cannot be reexported",
 877                                             ident)
 878                                 },
 879                                 ImportDirectiveSubclass::GlobImport { .. } => {
 880                                     let msg = "enum is private and its variants \
 881                                                cannot be reexported".to_owned();
 882                                     let error_id = (DiagnosticMessageId::ErrorId(0), // no code?!
 883                                                     Some(binding.span),
 884                                                     msg.clone());
 885                                     let fresh = self.session.one_time_diagnostics
 886                                         .borrow_mut().insert(error_id);
 887                                     if !fresh {
 888                                         continue;
 889                                     }
 890                                     msg
 891                                 },
 892                                 ref s @ _ => bug!("unexpected import subclass {:?}", s)
 893                             };
 894                             let mut err = self.session.struct_span_err(binding.span, &msg);
 895
 896                             let imported_module = directive.imported_module.get()
 897                                 .expect("module should exist");
 898                             let resolutions = imported_module.parent.expect("parent should exist")
 899                                 .resolutions.borrow();
 900                             let enum_path_segment_index = directive.module_path.len() - 1;
 901                             let enum_ident = directive.module_path[enum_path_segment_index].node;
 902
 903                             let enum_resolution = resolutions.get(&(enum_ident, TypeNS))
 904                                 .expect("resolution should exist");
 905                             let enum_span = enum_resolution.borrow()
 906                                 .binding.expect("binding should exist")
 907                                 .span;
 908                             let enum_def_span = self.session.codemap().def_span(enum_span);
 909                             let enum_def_snippet = self.session.codemap()
 910                                 .span_to_snippet(enum_def_span).expect("snippet should exist");
 911                             // potentially need to strip extant `crate`/`pub(path)` for suggestion
 912                             let after_vis_index = enum_def_snippet.find("enum")
 913                                 .expect("`enum` keyword should exist in snippet");
 914                             let suggestion = format!("pub {}",
 915                                                      &enum_def_snippet[after_vis_index..]);
 916
 917                             self.session
 918                                 .diag_span_suggestion_once(&mut err,
 919                                                            DiagnosticMessageId::ErrorId(0),
 920                                                            enum_def_span,
 921                                                            "consider making the enum public",
 922                                                            suggestion);
 923                             err.emit();
 924                     }
 925                 }
 926                 NameBindingKind::Ambiguity { b1, b2, .. }
 927                         if b1.is_glob_import() && b2.is_glob_import() => {
 928                     let (orig_b1, orig_b2) = match (&b1.kind, &b2.kind) {
 929                         (&NameBindingKind::Import { binding: b1, .. },
 930                          &NameBindingKind::Import { binding: b2, .. }) => (b1, b2),
 931                         _ => continue,
 932                     };
 933                     let (b1, b2) = match (orig_b1.vis, orig_b2.vis) {
 934                         (ty::Visibility::Public, ty::Visibility::Public) => continue,
 935                         (ty::Visibility::Public, _) => (b1, b2),
 936                         (_, ty::Visibility::Public) => (b2, b1),
 937                         _ => continue,
 938                     };
 939                     resolution.binding = Some(self.arenas.alloc_name_binding(NameBinding {
 940                         kind: NameBindingKind::Ambiguity { b1: b1, b2: b2, legacy: true }, ..*b1
 941                     }));
 942                 }
 943                 _ => {}
 944             }
 945         }
 946
 947         if reexports.len() > 0 {
 948             if let Some(def_id) = module.def_id() {
 949                 self.export_map.insert(def_id, reexports);
 950             }
 951         }
 952     }
 953 }
 954
 955 fn import_path_to_string(names: &[SpannedIdent],
 956                          subclass: &ImportDirectiveSubclass,
 957                          span: Span) -> String {
 958     let pos = names.iter()
 959         .position(|p| span == p.span && p.node.name != keywords::CrateRoot.name());
 960     let global = !names.is_empty() && names[0].node.name == keywords::CrateRoot.name();
 961     if let Some(pos) = pos {
 962         let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
 963         names_to_string(names)
 964     } else {
 965         let names = if global { &names[1..] } else { names };
 966         if names.is_empty() {
 967             import_directive_subclass_to_string(subclass)
 968         } else {
 969             (format!("{}::{}",
 970                      names_to_string(names),
 971                      import_directive_subclass_to_string(subclass)))
 972         }
 973     }
 974 }
 975
 976 fn import_directive_subclass_to_string(subclass: &ImportDirectiveSubclass) -> String {
 977     match *subclass {
 978         SingleImport { source, .. } => source.to_string(),
 979         GlobImport { .. } => "*".to_string(),
 980         ExternCrate(_) => "<extern crate>".to_string(),
 981         MacroUse => "#[macro_use]".to_string(),
 982     }
 983 }