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, CrateLint, Module, PerNS};
  14 use Namespace::{self, TypeNS, MacroNS};
  15 use {NameBinding, NameBindingKind, ToNameBinding, PathResult, PrivacyError};
  16 use Resolver;
  17 use {names_to_string, module_to_string};
  18 use {resolve_error, ResolutionError};
  19
  20 use rustc_data_structures::ptr_key::PtrKey;
  21 use rustc::ty;
  22 use rustc::lint::builtin::BuiltinLintDiagnostics;
  23 use rustc::lint::builtin::{DUPLICATE_MACRO_EXPORTS, PUB_USE_OF_PRIVATE_EXTERN_CRATE};
  24 use rustc::hir::def_id::{CRATE_DEF_INDEX, DefId};
  25 use rustc::hir::def::*;
  26 use rustc::session::DiagnosticMessageId;
  27 use rustc::util::nodemap::{FxHashMap, FxHashSet};
  28
  29 use syntax::ast::{Ident, Name, NodeId, CRATE_NODE_ID};
  30 use syntax::ext::base::Determinacy::{self, Determined, Undetermined};
  31 use syntax::ext::hygiene::Mark;
  32 use syntax::symbol::keywords;
  33 use syntax::util::lev_distance::find_best_match_for_name;
  34 use syntax_pos::Span;
  35
  36 use std::cell::{Cell, RefCell};
  37 use std::{mem, ptr};
  38
  39 /// Contains data for specific types of import directives.
  40 #[derive(Clone, Debug)]
  41 pub enum ImportDirectiveSubclass<'a> {
  42     SingleImport {
  43         target: Ident,
  44         source: Ident,
  45         result: PerNS<Cell<Result<&'a NameBinding<'a>, Determinacy>>>,
  46         type_ns_only: bool,
  47     },
  48     GlobImport {
  49         is_prelude: bool,
  50         max_vis: Cell<ty::Visibility>, // The visibility of the greatest re-export.
  51         // n.b. `max_vis` is only used in `finalize_import` to check for re-export errors.
  52     },
  53     ExternCrate(Option<Name>),
  54     MacroUse,
  55 }
  56
  57 /// One import directive.
  58 #[derive(Debug,Clone)]
  59 pub struct ImportDirective<'a> {
  60     /// The id of the `extern crate`, `UseTree` etc that imported this `ImportDirective`.
  61     ///
  62     /// In the case where the `ImportDirective` was expanded from a "nested" use tree,
  63     /// this id is the id of the leaf tree. For example:
  64     ///
  65     /// ```ignore (pacify the mercilous tidy)
  66     /// use foo::bar::{a, b}
  67     /// ```
  68     ///
  69     /// If this is the import directive for `foo::bar::a`, we would have the id of the `UseTree`
  70     /// for `a` in this field.
  71     pub id: NodeId,
  72
  73     /// The `id` of the "root" use-kind -- this is always the same as
  74     /// `id` except in the case of "nested" use trees, in which case
  75     /// it will be the `id` of the root use tree. e.g., in the example
  76     /// from `id`, this would be the id of the `use foo::bar`
  77     /// `UseTree` node.
  78     pub root_id: NodeId,
  79
  80     /// Span of this use tree.
  81     pub span: Span,
  82
  83     /// Span of the *root* use tree (see `root_id`).
  84     pub root_span: Span,
  85
  86     pub parent: Module<'a>,
  87     pub module_path: Vec<Ident>,
  88     pub imported_module: Cell<Option<Module<'a>>>, // the resolution of `module_path`
  89     pub subclass: ImportDirectiveSubclass<'a>,
  90     pub vis: Cell<ty::Visibility>,
  91     pub expansion: Mark,
  92     pub used: Cell<bool>,
  93 }
  94
  95 impl<'a> ImportDirective<'a> {
  96     pub fn is_glob(&self) -> bool {
  97         match self.subclass { ImportDirectiveSubclass::GlobImport { .. } => true, _ => false }
  98     }
  99
 100     crate fn crate_lint(&self) -> CrateLint {
 101         CrateLint::UsePath { root_id: self.root_id, root_span: self.root_span }
 102     }
 103 }
 104
 105 #[derive(Clone, Default, Debug)]
 106 /// Records information about the resolution of a name in a namespace of a module.
 107 pub struct NameResolution<'a> {
 108     /// Single imports that may define the name in the namespace.
 109     /// Import directives are arena-allocated, so it's ok to use pointers as keys.
 110     single_imports: FxHashSet<PtrKey<'a, ImportDirective<'a>>>,
 111     /// The least shadowable known binding for this name, or None if there are no known bindings.
 112     pub binding: Option<&'a NameBinding<'a>>,
 113     shadowed_glob: Option<&'a NameBinding<'a>>,
 114 }
 115
 116 impl<'a> NameResolution<'a> {
 117     // Returns the binding for the name if it is known or None if it not known.
 118     fn binding(&self) -> Option<&'a NameBinding<'a>> {
 119         self.binding.and_then(|binding| {
 120             if !binding.is_glob_import() ||
 121                self.single_imports.is_empty() { Some(binding) } else { None }
 122         })
 123     }
 124 }
 125
 126 impl<'a> Resolver<'a> {
 127     fn resolution(&self, module: Module<'a>, ident: Ident, ns: Namespace)
 128                   -> &'a RefCell<NameResolution<'a>> {
 129         *module.resolutions.borrow_mut().entry((ident.modern(), ns))
 130                .or_insert_with(|| self.arenas.alloc_name_resolution())
 131     }
 132
 133     /// Attempts to resolve `ident` in namespaces `ns` of `module`.
 134     /// Invariant: if `record_used` is `Some`, expansion and import resolution must be complete.
 135     pub fn resolve_ident_in_module_unadjusted(&mut self,
 136                                               module: Module<'a>,
 137                                               ident: Ident,
 138                                               ns: Namespace,
 139                                               restricted_shadowing: bool,
 140                                               record_used: bool,
 141                                               path_span: Span)
 142                                               -> Result<&'a NameBinding<'a>, Determinacy> {
 143         self.populate_module_if_necessary(module);
 144
 145         let resolution = self.resolution(module, ident, ns)
 146             .try_borrow_mut()
 147             .map_err(|_| Determined)?; // This happens when there is a cycle of imports
 148
 149         if record_used {
 150             if let Some(binding) = resolution.binding {
 151                 if let Some(shadowed_glob) = resolution.shadowed_glob {
 152                     let name = ident.name;
 153                     // Forbid expanded shadowing to avoid time travel.
 154                     if restricted_shadowing &&
 155                        binding.expansion != Mark::root() &&
 156                        ns != MacroNS && // In MacroNS, `try_define` always forbids this shadowing
 157                        binding.def() != shadowed_glob.def() {
 158                         self.ambiguity_errors.push(AmbiguityError {
 159                             span: path_span,
 160                             name,
 161                             lexical: false,
 162                             b1: binding,
 163                             b2: shadowed_glob,
 164                         });
 165                     }
 166                 }
 167                 if self.record_use(ident, ns, binding, path_span) {
 168                     return Ok(self.dummy_binding);
 169                 }
 170                 if !self.is_accessible(binding.vis) {
 171                     self.privacy_errors.push(PrivacyError(path_span, ident.name, binding));
 172                 }
 173             }
 174
 175             return resolution.binding.ok_or(Determined);
 176         }
 177
 178         let check_usable = |this: &mut Self, binding: &'a NameBinding<'a>| {
 179             // `extern crate` are always usable for backwards compatibility, see issue #37020.
 180             let usable = this.is_accessible(binding.vis) || binding.is_extern_crate();
 181             if usable { Ok(binding) } else { Err(Determined) }
 182         };
 183
 184         // Items and single imports are not shadowable, if we have one, then it's determined.
 185         if let Some(binding) = resolution.binding {
 186             if !binding.is_glob_import() {
 187                 return check_usable(self, binding);
 188             }
 189         }
 190
 191         // --- From now on we either have a glob resolution or no resolution. ---
 192
 193         // Check if one of single imports can still define the name,
 194         // if it can then our result is not determined and can be invalidated.
 195         for single_import in &resolution.single_imports {
 196             if !self.is_accessible(single_import.vis.get()) {
 197                 continue;
 198             }
 199             let module = unwrap_or!(single_import.imported_module.get(), return Err(Undetermined));
 200             let ident = match single_import.subclass {
 201                 SingleImport { source, .. } => source,
 202                 _ => unreachable!(),
 203             };
 204             match self.resolve_ident_in_module(module, ident, ns, false, path_span) {
 205                 Err(Determined) => continue,
 206                 Ok(_) | Err(Undetermined) => return Err(Undetermined),
 207             }
 208         }
 209
 210         // So we have a resolution that's from a glob import. This resolution is determined
 211         // if it cannot be shadowed by some new item/import expanded from a macro.
 212         // This happens either if there are no unexpanded macros, or expanded names cannot
 213         // shadow globs (that happens in macro namespace or with restricted shadowing).
 214         let unexpanded_macros = !module.unresolved_invocations.borrow().is_empty() ||
 215                                 (ns == MacroNS && ptr::eq(module, self.graph_root) &&
 216                                  !self.unresolved_invocations_macro_export.is_empty());
 217         if let Some(binding) = resolution.binding {
 218             if !unexpanded_macros || ns == MacroNS || restricted_shadowing {
 219                 return check_usable(self, binding);
 220             } else {
 221                 return Err(Undetermined);
 222             }
 223         }
 224
 225         // --- From now on we have no resolution. ---
 226
 227         // Now we are in situation when new item/import can appear only from a glob or a macro
 228         // expansion. With restricted shadowing names from globs and macro expansions cannot
 229         // shadow names from outer scopes, so we can freely fallback from module search to search
 230         // in outer scopes. To continue search in outer scopes we have to lie a bit and return
 231         // `Determined` to `resolve_lexical_macro_path_segment` even if the correct answer
 232         // for in-module resolution could be `Undetermined`.
 233         if restricted_shadowing {
 234             return Err(Determined);
 235         }
 236
 237         // Check if one of unexpanded macros can still define the name,
 238         // if it can then our "no resolution" result is not determined and can be invalidated.
 239         if unexpanded_macros {
 240             return Err(Undetermined);
 241         }
 242
 243         // Check if one of glob imports can still define the name,
 244         // if it can then our "no resolution" result is not determined and can be invalidated.
 245         for glob_import in module.globs.borrow().iter() {
 246             if !self.is_accessible(glob_import.vis.get()) {
 247                 continue
 248             }
 249             let module = unwrap_or!(glob_import.imported_module.get(), return Err(Undetermined));
 250             let (orig_current_module, mut ident) = (self.current_module, ident.modern());
 251             match ident.span.glob_adjust(module.expansion, glob_import.span.ctxt().modern()) {
 252                 Some(Some(def)) => self.current_module = self.macro_def_scope(def),
 253                 Some(None) => {}
 254                 None => continue,
 255             };
 256             let result = self.resolve_ident_in_module_unadjusted(
 257                 module, ident, ns, false, false, path_span,
 258             );
 259             self.current_module = orig_current_module;
 260             match result {
 261                 Err(Determined) => continue,
 262                 Ok(_) | Err(Undetermined) => return Err(Undetermined),
 263             }
 264         }
 265
 266         // No resolution and no one else can define the name - determinate error.
 267         Err(Determined)
 268     }
 269
 270     // Add an import directive to the current module.
 271     pub fn add_import_directive(&mut self,
 272                                 module_path: Vec<Ident>,
 273                                 subclass: ImportDirectiveSubclass<'a>,
 274                                 span: Span,
 275                                 id: NodeId,
 276                                 root_span: Span,
 277                                 root_id: NodeId,
 278                                 vis: ty::Visibility,
 279                                 expansion: Mark) {
 280         let current_module = self.current_module;
 281         let directive = self.arenas.alloc_import_directive(ImportDirective {
 282             parent: current_module,
 283             module_path,
 284             imported_module: Cell::new(None),
 285             subclass,
 286             span,
 287             id,
 288             root_span,
 289             root_id,
 290             vis: Cell::new(vis),
 291             expansion,
 292             used: Cell::new(false),
 293         });
 294
 295         self.indeterminate_imports.push(directive);
 296         match directive.subclass {
 297             SingleImport { target, type_ns_only, .. } => {
 298                 self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 299                     let mut resolution = this.resolution(current_module, target, ns).borrow_mut();
 300                     resolution.single_imports.insert(PtrKey(directive));
 301                 });
 302             }
 303             // We don't add prelude imports to the globs since they only affect lexical scopes,
 304             // which are not relevant to import resolution.
 305             GlobImport { is_prelude: true, .. } => {}
 306             GlobImport { .. } => self.current_module.globs.borrow_mut().push(directive),
 307             _ => unreachable!(),
 308         }
 309     }
 310
 311     // Given a binding and an import directive that resolves to it,
 312     // return the corresponding binding defined by the import directive.
 313     pub fn import(&self, binding: &'a NameBinding<'a>, directive: &'a ImportDirective<'a>)
 314                   -> &'a NameBinding<'a> {
 315         let vis = if binding.pseudo_vis().is_at_least(directive.vis.get(), self) ||
 316                      // c.f. `PUB_USE_OF_PRIVATE_EXTERN_CRATE`
 317                      !directive.is_glob() && binding.is_extern_crate() {
 318             directive.vis.get()
 319         } else {
 320             binding.pseudo_vis()
 321         };
 322
 323         if let GlobImport { ref max_vis, .. } = directive.subclass {
 324             if vis == directive.vis.get() || vis.is_at_least(max_vis.get(), self) {
 325                 max_vis.set(vis)
 326             }
 327         }
 328
 329         self.arenas.alloc_name_binding(NameBinding {
 330             kind: NameBindingKind::Import {
 331                 binding,
 332                 directive,
 333                 used: Cell::new(false),
 334             },
 335             span: directive.span,
 336             vis,
 337             expansion: directive.expansion,
 338         })
 339     }
 340
 341     // Define the name or return the existing binding if there is a collision.
 342     pub fn try_define(&mut self,
 343                       module: Module<'a>,
 344                       ident: Ident,
 345                       ns: Namespace,
 346                       binding: &'a NameBinding<'a>)
 347                       -> Result<(), &'a NameBinding<'a>> {
 348         self.update_resolution(module, ident, ns, |this, resolution| {
 349             if let Some(old_binding) = resolution.binding {
 350                 if binding.is_glob_import() {
 351                     if !old_binding.is_glob_import() &&
 352                        !(ns == MacroNS && old_binding.expansion != Mark::root()) {
 353                         resolution.shadowed_glob = Some(binding);
 354                     } else if binding.def() != old_binding.def() {
 355                         resolution.binding = Some(this.ambiguity(old_binding, binding));
 356                     } else if !old_binding.vis.is_at_least(binding.vis, &*this) {
 357                         // We are glob-importing the same item but with greater visibility.
 358                         resolution.binding = Some(binding);
 359                     }
 360                 } else if old_binding.is_glob_import() {
 361                     if ns == MacroNS && binding.expansion != Mark::root() &&
 362                        binding.def() != old_binding.def() {
 363                         resolution.binding = Some(this.ambiguity(binding, old_binding));
 364                     } else {
 365                         resolution.binding = Some(binding);
 366                         resolution.shadowed_glob = Some(old_binding);
 367                     }
 368                 } else if let (&NameBindingKind::Def(_, true), &NameBindingKind::Def(_, true)) =
 369                         (&old_binding.kind, &binding.kind) {
 370
 371                     this.session.buffer_lint_with_diagnostic(
 372                         DUPLICATE_MACRO_EXPORTS,
 373                         CRATE_NODE_ID,
 374                         binding.span,
 375                         &format!("a macro named `{}` has already been exported", ident),
 376                         BuiltinLintDiagnostics::DuplicatedMacroExports(
 377                             ident, old_binding.span, binding.span));
 378
 379                     resolution.binding = Some(binding);
 380                 } else {
 381                     return Err(old_binding);
 382                 }
 383             } else {
 384                 resolution.binding = Some(binding);
 385             }
 386
 387             Ok(())
 388         })
 389     }
 390
 391     pub fn ambiguity(&self, b1: &'a NameBinding<'a>, b2: &'a NameBinding<'a>)
 392                      -> &'a NameBinding<'a> {
 393         self.arenas.alloc_name_binding(NameBinding {
 394             kind: NameBindingKind::Ambiguity { b1, b2 },
 395             vis: if b1.vis.is_at_least(b2.vis, self) { b1.vis } else { b2.vis },
 396             span: b1.span,
 397             expansion: Mark::root(),
 398         })
 399     }
 400
 401     // Use `f` to mutate the resolution of the name in the module.
 402     // If the resolution becomes a success, define it in the module's glob importers.
 403     fn update_resolution<T, F>(&mut self, module: Module<'a>, ident: Ident, ns: Namespace, f: F)
 404                                -> T
 405         where F: FnOnce(&mut Resolver<'a>, &mut NameResolution<'a>) -> T
 406     {
 407         // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
 408         // during which the resolution might end up getting re-defined via a glob cycle.
 409         let (binding, t) = {
 410             let resolution = &mut *self.resolution(module, ident, ns).borrow_mut();
 411             let old_binding = resolution.binding();
 412
 413             let t = f(self, resolution);
 414
 415             match resolution.binding() {
 416                 _ if old_binding.is_some() => return t,
 417                 None => return t,
 418                 Some(binding) => match old_binding {
 419                     Some(old_binding) if ptr::eq(old_binding, binding) => return t,
 420                     _ => (binding, t),
 421                 }
 422             }
 423         };
 424
 425         // Define `binding` in `module`s glob importers.
 426         for directive in module.glob_importers.borrow_mut().iter() {
 427             let mut ident = ident.modern();
 428             let scope = match ident.span.reverse_glob_adjust(module.expansion,
 429                                                              directive.span.ctxt().modern()) {
 430                 Some(Some(def)) => self.macro_def_scope(def),
 431                 Some(None) => directive.parent,
 432                 None => continue,
 433             };
 434             if self.is_accessible_from(binding.vis, scope) {
 435                 let imported_binding = self.import(binding, directive);
 436                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
 437             }
 438         }
 439
 440         t
 441     }
 442
 443     // Define a "dummy" resolution containing a Def::Err as a placeholder for a
 444     // failed resolution
 445     fn import_dummy_binding(&mut self, directive: &'a ImportDirective<'a>) {
 446         if let SingleImport { target, .. } = directive.subclass {
 447             let dummy_binding = self.dummy_binding;
 448             let dummy_binding = self.import(dummy_binding, directive);
 449             self.per_ns(|this, ns| {
 450                 let _ = this.try_define(directive.parent, target, ns, dummy_binding);
 451             });
 452         }
 453     }
 454 }
 455
 456 pub struct ImportResolver<'a, 'b: 'a> {
 457     pub resolver: &'a mut Resolver<'b>,
 458 }
 459
 460 impl<'a, 'b: 'a> ::std::ops::Deref for ImportResolver<'a, 'b> {
 461     type Target = Resolver<'b>;
 462     fn deref(&self) -> &Resolver<'b> {
 463         self.resolver
 464     }
 465 }
 466
 467 impl<'a, 'b: 'a> ::std::ops::DerefMut for ImportResolver<'a, 'b> {
 468     fn deref_mut(&mut self) -> &mut Resolver<'b> {
 469         self.resolver
 470     }
 471 }
 472
 473 impl<'a, 'b: 'a> ty::DefIdTree for &'a ImportResolver<'a, 'b> {
 474     fn parent(self, id: DefId) -> Option<DefId> {
 475         self.resolver.parent(id)
 476     }
 477 }
 478
 479 impl<'a, 'b:'a> ImportResolver<'a, 'b> {
 480     // Import resolution
 481     //
 482     // This is a fixed-point algorithm. We resolve imports until our efforts
 483     // are stymied by an unresolved import; then we bail out of the current
 484     // module and continue. We terminate successfully once no more imports
 485     // remain or unsuccessfully when no forward progress in resolving imports
 486     // is made.
 487
 488     /// Resolves all imports for the crate. This method performs the fixed-
 489     /// point iteration.
 490     pub fn resolve_imports(&mut self) {
 491         let mut prev_num_indeterminates = self.indeterminate_imports.len() + 1;
 492         while self.indeterminate_imports.len() < prev_num_indeterminates {
 493             prev_num_indeterminates = self.indeterminate_imports.len();
 494             for import in mem::replace(&mut self.indeterminate_imports, Vec::new()) {
 495                 match self.resolve_import(&import) {
 496                     true => self.determined_imports.push(import),
 497                     false => self.indeterminate_imports.push(import),
 498                 }
 499             }
 500         }
 501     }
 502
 503     pub fn finalize_imports(&mut self) {
 504         for module in self.arenas.local_modules().iter() {
 505             self.finalize_resolutions_in(module);
 506         }
 507
 508         let mut errors = false;
 509         let mut seen_spans = FxHashSet();
 510         for i in 0 .. self.determined_imports.len() {
 511             let import = self.determined_imports[i];
 512             if let Some((span, err)) = self.finalize_import(import) {
 513                 errors = true;
 514
 515                 if let SingleImport { source, ref result, .. } = import.subclass {
 516                     if source.name == "self" {
 517                         // Silence `unresolved import` error if E0429 is already emitted
 518                         match result.value_ns.get() {
 519                             Err(Determined) => continue,
 520                             _ => {},
 521                         }
 522                     }
 523                 }
 524
 525                 // If the error is a single failed import then create a "fake" import
 526                 // resolution for it so that later resolve stages won't complain.
 527                 self.import_dummy_binding(import);
 528                 if !seen_spans.contains(&span) {
 529                     let path = import_path_to_string(&import.module_path[..],
 530                                                      &import.subclass,
 531                                                      span);
 532                     let error = ResolutionError::UnresolvedImport(Some((span, &path, &err)));
 533                     resolve_error(self.resolver, span, error);
 534                     seen_spans.insert(span);
 535                 }
 536             }
 537         }
 538
 539         // Report unresolved imports only if no hard error was already reported
 540         // to avoid generating multiple errors on the same import.
 541         if !errors {
 542             if let Some(import) = self.indeterminate_imports.iter().next() {
 543                 let error = ResolutionError::UnresolvedImport(None);
 544                 resolve_error(self.resolver, import.span, error);
 545             }
 546         }
 547     }
 548
 549     /// Attempts to resolve the given import, returning true if its resolution is determined.
 550     /// If successful, the resolved bindings are written into the module.
 551     fn resolve_import(&mut self, directive: &'b ImportDirective<'b>) -> bool {
 552         debug!("(resolving import for module) resolving import `{}::...` in `{}`",
 553                names_to_string(&directive.module_path[..]),
 554                module_to_string(self.current_module).unwrap_or("???".to_string()));
 555
 556         self.current_module = directive.parent;
 557
 558         let module = if let Some(module) = directive.imported_module.get() {
 559             module
 560         } else {
 561             let vis = directive.vis.get();
 562             // For better failure detection, pretend that the import will not define any names
 563             // while resolving its module path.
 564             directive.vis.set(ty::Visibility::Invisible);
 565             let result = self.resolve_path(&directive.module_path[..], None, false,
 566                                            directive.span, directive.crate_lint());
 567             directive.vis.set(vis);
 568
 569             match result {
 570                 PathResult::Module(module) => module,
 571                 PathResult::Indeterminate => return false,
 572                 _ => return true,
 573             }
 574         };
 575
 576         directive.imported_module.set(Some(module));
 577         let (source, target, result, type_ns_only) = match directive.subclass {
 578             SingleImport { source, target, ref result, type_ns_only } =>
 579                 (source, target, result, type_ns_only),
 580             GlobImport { .. } => {
 581                 self.resolve_glob_import(directive);
 582                 return true;
 583             }
 584             _ => unreachable!(),
 585         };
 586
 587         let mut indeterminate = false;
 588         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 589             if let Err(Undetermined) = result[ns].get() {
 590                 result[ns].set(this.resolve_ident_in_module(module,
 591                                                             source,
 592                                                             ns,
 593                                                             false,
 594                                                             directive.span));
 595             } else {
 596                 return
 597             };
 598
 599             let parent = directive.parent;
 600             match result[ns].get() {
 601                 Err(Undetermined) => indeterminate = true,
 602                 Err(Determined) => {
 603                     this.update_resolution(parent, target, ns, |_, resolution| {
 604                         resolution.single_imports.remove(&PtrKey(directive));
 605                     });
 606                 }
 607                 Ok(binding) if !binding.is_importable() => {
 608                     let msg = format!("`{}` is not directly importable", target);
 609                     struct_span_err!(this.session, directive.span, E0253, "{}", &msg)
 610                         .span_label(directive.span, "cannot be imported directly")
 611                         .emit();
 612                     // Do not import this illegal binding. Import a dummy binding and pretend
 613                     // everything is fine
 614                     this.import_dummy_binding(directive);
 615                 }
 616                 Ok(binding) => {
 617                     let imported_binding = this.import(binding, directive);
 618                     let conflict = this.try_define(parent, target, ns, imported_binding);
 619                     if let Err(old_binding) = conflict {
 620                         this.report_conflict(parent, target, ns, imported_binding, old_binding);
 621                     }
 622                 }
 623             }
 624         });
 625
 626         !indeterminate
 627     }
 628
 629     // If appropriate, returns an error to report.
 630     fn finalize_import(&mut self, directive: &'b ImportDirective<'b>) -> Option<(Span, String)> {
 631         self.current_module = directive.parent;
 632         let ImportDirective { ref module_path, span, .. } = *directive;
 633         let mut warn_if_binding_comes_from_local_crate = false;
 634
 635         // FIXME: Last path segment is treated specially in import resolution, so extern crate
 636         // mode for absolute paths needs some special support for single-segment imports.
 637         if module_path.len() == 1 && (module_path[0].name == keywords::CrateRoot.name() ||
 638                                       module_path[0].name == keywords::Extern.name()) {
 639             let is_extern = module_path[0].name == keywords::Extern.name() ||
 640                             (self.session.features_untracked().extern_absolute_paths &&
 641                              self.session.rust_2018());
 642             match directive.subclass {
 643                 GlobImport { .. } if is_extern => {
 644                     return Some((directive.span,
 645                                  "cannot glob-import all possible crates".to_string()));
 646                 }
 647                 GlobImport { .. } if self.session.features_untracked().extern_absolute_paths => {
 648                     self.lint_path_starts_with_module(
 649                         directive.root_id,
 650                         directive.root_span,
 651                     );
 652                 }
 653                 SingleImport { source, target, .. } => {
 654                     let crate_root = if source.name == keywords::Crate.name() &&
 655                                         module_path[0].name != keywords::Extern.name() {
 656                         if target.name == keywords::Crate.name() {
 657                             return Some((directive.span,
 658                                          "crate root imports need to be explicitly named: \
 659                                           `use crate as name;`".to_string()));
 660                         } else {
 661                             Some(self.resolve_crate_root(source))
 662                         }
 663                     } else if is_extern && !source.is_path_segment_keyword() {
 664                         let crate_id =
 665                             self.resolver.crate_loader.process_use_extern(
 666                                 source.name,
 667                                 directive.span,
 668                                 directive.id,
 669                                 &self.resolver.definitions,
 670                             );
 671                         let crate_root =
 672                             self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
 673                         self.populate_module_if_necessary(crate_root);
 674                         Some(crate_root)
 675                     } else {
 676                         warn_if_binding_comes_from_local_crate = true;
 677                         None
 678                     };
 679
 680                     if let Some(crate_root) = crate_root {
 681                         let binding = (crate_root, ty::Visibility::Public, directive.span,
 682                                        directive.expansion).to_name_binding(self.arenas);
 683                         let binding = self.arenas.alloc_name_binding(NameBinding {
 684                             kind: NameBindingKind::Import {
 685                                 binding,
 686                                 directive,
 687                                 used: Cell::new(false),
 688                             },
 689                             vis: directive.vis.get(),
 690                             span: directive.span,
 691                             expansion: directive.expansion,
 692                         });
 693                         let _ = self.try_define(directive.parent, target, TypeNS, binding);
 694                         return None;
 695                     }
 696                 }
 697                 _ => {}
 698             }
 699         }
 700
 701         let module_result = self.resolve_path(
 702             &module_path,
 703             None,
 704             true,
 705             span,
 706             directive.crate_lint(),
 707         );
 708         let module = match module_result {
 709             PathResult::Module(module) => module,
 710             PathResult::Failed(span, msg, false) => {
 711                 resolve_error(self, span, ResolutionError::FailedToResolve(&msg));
 712                 return None;
 713             }
 714             PathResult::Failed(span, msg, true) => {
 715                 let (mut self_path, mut self_result) = (module_path.clone(), None);
 716                 let is_special = |ident: Ident| ident.is_path_segment_keyword() &&
 717                                                 ident.name != keywords::CrateRoot.name();
 718                 if !self_path.is_empty() && !is_special(self_path[0]) &&
 719                    !(self_path.len() > 1 && is_special(self_path[1])) {
 720                     self_path[0].name = keywords::SelfValue.name();
 721                     self_result = Some(self.resolve_path(&self_path, None, false,
 722                                                          span, CrateLint::No));
 723                 }
 724                 return if let Some(PathResult::Module(..)) = self_result {
 725                     Some((span, format!("Did you mean `{}`?", names_to_string(&self_path[..]))))
 726                 } else {
 727                     Some((span, msg))
 728                 };
 729             },
 730             _ => return None,
 731         };
 732
 733         let (ident, result, type_ns_only) = match directive.subclass {
 734             SingleImport { source, ref result, type_ns_only, .. } => (source, result, type_ns_only),
 735             GlobImport { .. } if module.def_id() == directive.parent.def_id() => {
 736                 // Importing a module into itself is not allowed.
 737                 return Some((directive.span,
 738                              "Cannot glob-import a module into itself.".to_string()));
 739             }
 740             GlobImport { is_prelude, ref max_vis } => {
 741                 if !is_prelude &&
 742                    max_vis.get() != ty::Visibility::Invisible && // Allow empty globs.
 743                    !max_vis.get().is_at_least(directive.vis.get(), &*self) {
 744                     let msg = "A non-empty glob must import something with the glob's visibility";
 745                     self.session.span_err(directive.span, msg);
 746                 }
 747                 return None;
 748             }
 749             _ => unreachable!(),
 750         };
 751
 752         let mut all_ns_err = true;
 753         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 754             if let Ok(binding) = result[ns].get() {
 755                 all_ns_err = false;
 756                 if this.record_use(ident, ns, binding, directive.span) {
 757                     this.resolution(module, ident, ns).borrow_mut().binding =
 758                         Some(this.dummy_binding);
 759                 }
 760             }
 761         });
 762
 763         if all_ns_err {
 764             let mut all_ns_failed = true;
 765             self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 766                 match this.resolve_ident_in_module(module, ident, ns, true, span) {
 767                     Ok(_) => all_ns_failed = false,
 768                     _ => {}
 769                 }
 770             });
 771
 772             return if all_ns_failed {
 773                 let resolutions = module.resolutions.borrow();
 774                 let names = resolutions.iter().filter_map(|(&(ref i, _), resolution)| {
 775                     if *i == ident { return None; } // Never suggest the same name
 776                     match *resolution.borrow() {
 777                         NameResolution { binding: Some(name_binding), .. } => {
 778                             match name_binding.kind {
 779                                 NameBindingKind::Import { binding, .. } => {
 780                                     match binding.kind {
 781                                         // Never suggest the name that has binding error
 782                                         // i.e. the name that cannot be previously resolved
 783                                         NameBindingKind::Def(Def::Err, _) => return None,
 784                                         _ => Some(&i.name),
 785                                     }
 786                                 },
 787                                 _ => Some(&i.name),
 788                             }
 789                         },
 790                         NameResolution { ref single_imports, .. }
 791                             if single_imports.is_empty() => None,
 792                         _ => Some(&i.name),
 793                     }
 794                 });
 795                 let lev_suggestion =
 796                     match find_best_match_for_name(names, &ident.as_str(), None) {
 797                         Some(name) => format!(". Did you mean to use `{}`?", name),
 798                         None => "".to_owned(),
 799                     };
 800                 let module_str = module_to_string(module);
 801                 let msg = if let Some(module_str) = module_str {
 802                     format!("no `{}` in `{}`{}", ident, module_str, lev_suggestion)
 803                 } else {
 804                     format!("no `{}` in the root{}", ident, lev_suggestion)
 805                 };
 806                 Some((span, msg))
 807             } else {
 808                 // `resolve_ident_in_module` reported a privacy error.
 809                 self.import_dummy_binding(directive);
 810                 None
 811             }
 812         }
 813
 814         let mut reexport_error = None;
 815         let mut any_successful_reexport = false;
 816         self.per_ns(|this, ns| {
 817             if let Ok(binding) = result[ns].get() {
 818                 let vis = directive.vis.get();
 819                 if !binding.pseudo_vis().is_at_least(vis, &*this) {
 820                     reexport_error = Some((ns, binding));
 821                 } else {
 822                     any_successful_reexport = true;
 823                 }
 824             }
 825         });
 826
 827         // All namespaces must be re-exported with extra visibility for an error to occur.
 828         if !any_successful_reexport {
 829             let (ns, binding) = reexport_error.unwrap();
 830             if ns == TypeNS && binding.is_extern_crate() {
 831                 let msg = format!("extern crate `{}` is private, and cannot be \
 832                                    re-exported (error E0365), consider declaring with \
 833                                    `pub`",
 834                                    ident);
 835                 self.session.buffer_lint(PUB_USE_OF_PRIVATE_EXTERN_CRATE,
 836                                          directive.id,
 837                                          directive.span,
 838                                          &msg);
 839             } else if ns == TypeNS {
 840                 struct_span_err!(self.session, directive.span, E0365,
 841                                  "`{}` is private, and cannot be re-exported", ident)
 842                     .span_label(directive.span, format!("re-export of private `{}`", ident))
 843                     .note(&format!("consider declaring type or module `{}` with `pub`", ident))
 844                     .emit();
 845             } else {
 846                 let msg = format!("`{}` is private, and cannot be re-exported", ident);
 847                 let note_msg =
 848                     format!("consider marking `{}` as `pub` in the imported module", ident);
 849                 struct_span_err!(self.session, directive.span, E0364, "{}", &msg)
 850                     .span_note(directive.span, &note_msg)
 851                     .emit();
 852             }
 853         }
 854
 855         if warn_if_binding_comes_from_local_crate {
 856             let mut warned = false;
 857             self.per_ns(|this, ns| {
 858                 let binding = match result[ns].get().ok() {
 859                     Some(b) => b,
 860                     None => return
 861                 };
 862                 if let NameBindingKind::Import { directive: d, .. } = binding.kind {
 863                     if let ImportDirectiveSubclass::ExternCrate(..) = d.subclass {
 864                         return
 865                     }
 866                 }
 867                 if warned {
 868                     return
 869                 }
 870                 warned = true;
 871                 this.lint_path_starts_with_module(
 872                     directive.root_id,
 873                     directive.root_span,
 874                 );
 875             });
 876         }
 877
 878         // Record what this import resolves to for later uses in documentation,
 879         // this may resolve to either a value or a type, but for documentation
 880         // purposes it's good enough to just favor one over the other.
 881         self.per_ns(|this, ns| if let Some(binding) = result[ns].get().ok() {
 882             let import = this.import_map.entry(directive.id).or_default();
 883             import[ns] = Some(PathResolution::new(binding.def()));
 884         });
 885
 886         debug!("(resolving single import) successfully resolved import");
 887         None
 888     }
 889
 890     fn resolve_glob_import(&mut self, directive: &'b ImportDirective<'b>) {
 891         let module = directive.imported_module.get().unwrap();
 892         self.populate_module_if_necessary(module);
 893
 894         if let Some(Def::Trait(_)) = module.def() {
 895             self.session.span_err(directive.span, "items in traits are not importable.");
 896             return;
 897         } else if module.def_id() == directive.parent.def_id()  {
 898             return;
 899         } else if let GlobImport { is_prelude: true, .. } = directive.subclass {
 900             self.prelude = Some(module);
 901             return;
 902         }
 903
 904         // Add to module's glob_importers
 905         module.glob_importers.borrow_mut().push(directive);
 906
 907         // Ensure that `resolutions` isn't borrowed during `try_define`,
 908         // since it might get updated via a glob cycle.
 909         let bindings = module.resolutions.borrow().iter().filter_map(|(&ident, resolution)| {
 910             resolution.borrow().binding().map(|binding| (ident, binding))
 911         }).collect::<Vec<_>>();
 912         for ((mut ident, ns), binding) in bindings {
 913             let scope = match ident.span.reverse_glob_adjust(module.expansion,
 914                                                              directive.span.ctxt().modern()) {
 915                 Some(Some(def)) => self.macro_def_scope(def),
 916                 Some(None) => self.current_module,
 917                 None => continue,
 918             };
 919             if self.is_accessible_from(binding.pseudo_vis(), scope) {
 920                 let imported_binding = self.import(binding, directive);
 921                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
 922             }
 923         }
 924
 925         // Record the destination of this import
 926         self.record_def(directive.id, PathResolution::new(module.def().unwrap()));
 927     }
 928
 929     // Miscellaneous post-processing, including recording re-exports,
 930     // reporting conflicts, and reporting unresolved imports.
 931     fn finalize_resolutions_in(&mut self, module: Module<'b>) {
 932         // Since import resolution is finished, globs will not define any more names.
 933         *module.globs.borrow_mut() = Vec::new();
 934
 935         let mut reexports = Vec::new();
 936         let mut exported_macro_names = FxHashMap();
 937         if ptr::eq(module, self.graph_root) {
 938             let macro_exports = mem::replace(&mut self.macro_exports, Vec::new());
 939             for export in macro_exports.into_iter().rev() {
 940                 if let Some(later_span) = exported_macro_names.insert(export.ident.modern(),
 941                                                                       export.span) {
 942                     self.session.buffer_lint_with_diagnostic(
 943                         DUPLICATE_MACRO_EXPORTS,
 944                         CRATE_NODE_ID,
 945                         later_span,
 946                         &format!("a macro named `{}` has already been exported", export.ident),
 947                         BuiltinLintDiagnostics::DuplicatedMacroExports(
 948                             export.ident, export.span, later_span));
 949                 } else {
 950                     reexports.push(export);
 951                 }
 952             }
 953         }
 954
 955         for (&(ident, ns), resolution) in module.resolutions.borrow().iter() {
 956             let resolution = &mut *resolution.borrow_mut();
 957             let binding = match resolution.binding {
 958                 Some(binding) => binding,
 959                 None => continue,
 960             };
 961
 962             if binding.is_import() || binding.is_macro_def() {
 963                 let def = binding.def();
 964                 if def != Def::Err {
 965                     if !def.def_id().is_local() {
 966                         self.cstore.export_macros_untracked(def.def_id().krate);
 967                     }
 968                     if let Def::Macro(..) = def {
 969                         if let Some(&span) = exported_macro_names.get(&ident.modern()) {
 970                             let msg =
 971                                 format!("a macro named `{}` has already been exported", ident);
 972                             self.session.struct_span_err(span, &msg)
 973                                 .span_label(span, format!("`{}` already exported", ident))
 974                                 .span_note(binding.span, "previous macro export here")
 975                                 .emit();
 976                         }
 977                     }
 978                     reexports.push(Export {
 979                         ident: ident.modern(),
 980                         def: def,
 981                         span: binding.span,
 982                         vis: binding.vis,
 983                     });
 984                 }
 985             }
 986
 987             match binding.kind {
 988                 NameBindingKind::Import { binding: orig_binding, directive, .. } => {
 989                     if ns == TypeNS && orig_binding.is_variant() &&
 990                         !orig_binding.vis.is_at_least(binding.vis, &*self) {
 991                             let msg = match directive.subclass {
 992                                 ImportDirectiveSubclass::SingleImport { .. } => {
 993                                     format!("variant `{}` is private and cannot be re-exported",
 994                                             ident)
 995                                 },
 996                                 ImportDirectiveSubclass::GlobImport { .. } => {
 997                                     let msg = "enum is private and its variants \
 998                                                cannot be re-exported".to_owned();
 999                                     let error_id = (DiagnosticMessageId::ErrorId(0), // no code?!
1000                                                     Some(binding.span),
1001                                                     msg.clone());
1002                                     let fresh = self.session.one_time_diagnostics
1003                                         .borrow_mut().insert(error_id);
1004                                     if !fresh {
1005                                         continue;
1006                                     }
1007                                     msg
1008                                 },
1009                                 ref s @ _ => bug!("unexpected import subclass {:?}", s)
1010                             };
1011                             let mut err = self.session.struct_span_err(binding.span, &msg);
1012
1013                             let imported_module = directive.imported_module.get()
1014                                 .expect("module should exist");
1015                             let resolutions = imported_module.parent.expect("parent should exist")
1016                                 .resolutions.borrow();
1017                             let enum_path_segment_index = directive.module_path.len() - 1;
1018                             let enum_ident = directive.module_path[enum_path_segment_index];
1019
1020                             let enum_resolution = resolutions.get(&(enum_ident, TypeNS))
1021                                 .expect("resolution should exist");
1022                             let enum_span = enum_resolution.borrow()
1023                                 .binding.expect("binding should exist")
1024                                 .span;
1025                             let enum_def_span = self.session.codemap().def_span(enum_span);
1026                             let enum_def_snippet = self.session.codemap()
1027                                 .span_to_snippet(enum_def_span).expect("snippet should exist");
1028                             // potentially need to strip extant `crate`/`pub(path)` for suggestion
1029                             let after_vis_index = enum_def_snippet.find("enum")
1030                                 .expect("`enum` keyword should exist in snippet");
1031                             let suggestion = format!("pub {}",
1032                                                      &enum_def_snippet[after_vis_index..]);
1033
1034                             self.session
1035                                 .diag_span_suggestion_once(&mut err,
1036                                                            DiagnosticMessageId::ErrorId(0),
1037                                                            enum_def_span,
1038                                                            "consider making the enum public",
1039                                                            suggestion);
1040                             err.emit();
1041                     }
1042                 }
1043                 _ => {}
1044             }
1045         }
1046
1047         if reexports.len() > 0 {
1048             if let Some(def_id) = module.def_id() {
1049                 self.export_map.insert(def_id, reexports);
1050             }
1051         }
1052     }
1053 }
1054
1055 fn import_path_to_string(names: &[Ident],
1056                          subclass: &ImportDirectiveSubclass,
1057                          span: Span) -> String {
1058     let pos = names.iter()
1059         .position(|p| span == p.span && p.name != keywords::CrateRoot.name());
1060     let global = !names.is_empty() && names[0].name == keywords::CrateRoot.name();
1061     if let Some(pos) = pos {
1062         let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
1063         names_to_string(names)
1064     } else {
1065         let names = if global { &names[1..] } else { names };
1066         if names.is_empty() {
1067             import_directive_subclass_to_string(subclass)
1068         } else {
1069             format!("{}::{}",
1070                     names_to_string(names),
1071                     import_directive_subclass_to_string(subclass))
1072         }
1073     }
1074 }
1075
1076 fn import_directive_subclass_to_string(subclass: &ImportDirectiveSubclass) -> String {
1077     match *subclass {
1078         SingleImport { source, .. } => source.to_string(),
1079         GlobImport { .. } => "*".to_string(),
1080         ExternCrate(_) => "<extern crate>".to_string(),
1081         MacroUse => "#[macro_use]".to_string(),
1082     }
1083 }