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, 'crateloader> Resolver<'a, 'crateloader> {
 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 let Some(binding) = resolution.binding {
 150             if !restricted_shadowing && binding.expansion != Mark::root() {
 151                 if let NameBindingKind::Def(_, true) = binding.kind {
 152                     self.macro_expanded_macro_export_errors.insert((path_span, binding.span));
 153                 }
 154             }
 155         }
 156
 157         if record_used {
 158             if let Some(binding) = resolution.binding {
 159                 if let Some(shadowed_glob) = resolution.shadowed_glob {
 160                     let name = ident.name;
 161                     // Forbid expanded shadowing to avoid time travel.
 162                     if restricted_shadowing &&
 163                        binding.expansion != Mark::root() &&
 164                        ns != MacroNS && // In MacroNS, `try_define` always forbids this shadowing
 165                        binding.def() != shadowed_glob.def() {
 166                         self.ambiguity_errors.push(AmbiguityError {
 167                             span: path_span,
 168                             name,
 169                             lexical: false,
 170                             b1: binding,
 171                             b2: shadowed_glob,
 172                         });
 173                     }
 174                 }
 175                 if self.record_use(ident, ns, binding, path_span) {
 176                     return Ok(self.dummy_binding);
 177                 }
 178                 if !self.is_accessible(binding.vis) {
 179                     self.privacy_errors.push(PrivacyError(path_span, ident.name, binding));
 180                 }
 181             }
 182
 183             return resolution.binding.ok_or(Determined);
 184         }
 185
 186         let check_usable = |this: &mut Self, binding: &'a NameBinding<'a>| {
 187             // `extern crate` are always usable for backwards compatibility, see issue #37020.
 188             let usable = this.is_accessible(binding.vis) || binding.is_extern_crate();
 189             if usable { Ok(binding) } else { Err(Determined) }
 190         };
 191
 192         // Items and single imports are not shadowable, if we have one, then it's determined.
 193         if let Some(binding) = resolution.binding {
 194             if !binding.is_glob_import() {
 195                 return check_usable(self, binding);
 196             }
 197         }
 198
 199         // --- From now on we either have a glob resolution or no resolution. ---
 200
 201         // Check if one of single imports can still define the name,
 202         // if it can then our result is not determined and can be invalidated.
 203         for single_import in &resolution.single_imports {
 204             if !self.is_accessible(single_import.vis.get()) {
 205                 continue;
 206             }
 207             let module = unwrap_or!(single_import.imported_module.get(), return Err(Undetermined));
 208             let ident = match single_import.subclass {
 209                 SingleImport { source, .. } => source,
 210                 _ => unreachable!(),
 211             };
 212             match self.resolve_ident_in_module(module, ident, ns, false, path_span) {
 213                 Err(Determined) => continue,
 214                 Ok(_) | Err(Undetermined) => return Err(Undetermined),
 215             }
 216         }
 217
 218         // So we have a resolution that's from a glob import. This resolution is determined
 219         // if it cannot be shadowed by some new item/import expanded from a macro.
 220         // This happens either if there are no unexpanded macros, or expanded names cannot
 221         // shadow globs (that happens in macro namespace or with restricted shadowing).
 222         //
 223         // Additionally, any macro in any module can plant names in the root module if it creates
 224         // `macro_export` macros, so the root module effectively has unresolved invocations if any
 225         // module has unresolved invocations.
 226         // However, it causes resolution/expansion to stuck too often (#53144), so, to make
 227         // progress, we have to ignore those potential unresolved invocations from other modules
 228         // and prohibit access to macro-expanded `macro_export` macros instead (unless restricted
 229         // shadowing is enabled, see `macro_expanded_macro_export_errors`).
 230         let unexpanded_macros = !module.unresolved_invocations.borrow().is_empty();
 231         if let Some(binding) = resolution.binding {
 232             if !unexpanded_macros || ns == MacroNS || restricted_shadowing {
 233                 return check_usable(self, binding);
 234             } else {
 235                 return Err(Undetermined);
 236             }
 237         }
 238
 239         // --- From now on we have no resolution. ---
 240
 241         // Now we are in situation when new item/import can appear only from a glob or a macro
 242         // expansion. With restricted shadowing names from globs and macro expansions cannot
 243         // shadow names from outer scopes, so we can freely fallback from module search to search
 244         // in outer scopes. To continue search in outer scopes we have to lie a bit and return
 245         // `Determined` to `resolve_lexical_macro_path_segment` even if the correct answer
 246         // for in-module resolution could be `Undetermined`.
 247         if restricted_shadowing {
 248             return Err(Determined);
 249         }
 250
 251         // Check if one of unexpanded macros can still define the name,
 252         // if it can then our "no resolution" result is not determined and can be invalidated.
 253         if unexpanded_macros {
 254             return Err(Undetermined);
 255         }
 256
 257         // Check if one of glob imports can still define the name,
 258         // if it can then our "no resolution" result is not determined and can be invalidated.
 259         for glob_import in module.globs.borrow().iter() {
 260             if !self.is_accessible(glob_import.vis.get()) {
 261                 continue
 262             }
 263             let module = unwrap_or!(glob_import.imported_module.get(), return Err(Undetermined));
 264             let (orig_current_module, mut ident) = (self.current_module, ident.modern());
 265             match ident.span.glob_adjust(module.expansion, glob_import.span.ctxt().modern()) {
 266                 Some(Some(def)) => self.current_module = self.macro_def_scope(def),
 267                 Some(None) => {}
 268                 None => continue,
 269             };
 270             let result = self.resolve_ident_in_module_unadjusted(
 271                 module, ident, ns, false, false, path_span,
 272             );
 273             self.current_module = orig_current_module;
 274             match result {
 275                 Err(Determined) => continue,
 276                 Ok(_) | Err(Undetermined) => return Err(Undetermined),
 277             }
 278         }
 279
 280         // No resolution and no one else can define the name - determinate error.
 281         Err(Determined)
 282     }
 283
 284     // Add an import directive to the current module.
 285     pub fn add_import_directive(&mut self,
 286                                 module_path: Vec<Ident>,
 287                                 subclass: ImportDirectiveSubclass<'a>,
 288                                 span: Span,
 289                                 id: NodeId,
 290                                 root_span: Span,
 291                                 root_id: NodeId,
 292                                 vis: ty::Visibility,
 293                                 expansion: Mark) {
 294         let current_module = self.current_module;
 295         let directive = self.arenas.alloc_import_directive(ImportDirective {
 296             parent: current_module,
 297             module_path,
 298             imported_module: Cell::new(None),
 299             subclass,
 300             span,
 301             id,
 302             root_span,
 303             root_id,
 304             vis: Cell::new(vis),
 305             expansion,
 306             used: Cell::new(false),
 307         });
 308
 309         self.indeterminate_imports.push(directive);
 310         match directive.subclass {
 311             SingleImport { target, type_ns_only, .. } => {
 312                 self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 313                     let mut resolution = this.resolution(current_module, target, ns).borrow_mut();
 314                     resolution.single_imports.insert(PtrKey(directive));
 315                 });
 316             }
 317             // We don't add prelude imports to the globs since they only affect lexical scopes,
 318             // which are not relevant to import resolution.
 319             GlobImport { is_prelude: true, .. } => {}
 320             GlobImport { .. } => self.current_module.globs.borrow_mut().push(directive),
 321             _ => unreachable!(),
 322         }
 323     }
 324
 325     // Given a binding and an import directive that resolves to it,
 326     // return the corresponding binding defined by the import directive.
 327     pub fn import(&self, binding: &'a NameBinding<'a>, directive: &'a ImportDirective<'a>)
 328                   -> &'a NameBinding<'a> {
 329         let vis = if binding.pseudo_vis().is_at_least(directive.vis.get(), self) ||
 330                      // c.f. `PUB_USE_OF_PRIVATE_EXTERN_CRATE`
 331                      !directive.is_glob() && binding.is_extern_crate() {
 332             directive.vis.get()
 333         } else {
 334             binding.pseudo_vis()
 335         };
 336
 337         if let GlobImport { ref max_vis, .. } = directive.subclass {
 338             if vis == directive.vis.get() || vis.is_at_least(max_vis.get(), self) {
 339                 max_vis.set(vis)
 340             }
 341         }
 342
 343         self.arenas.alloc_name_binding(NameBinding {
 344             kind: NameBindingKind::Import {
 345                 binding,
 346                 directive,
 347                 used: Cell::new(false),
 348             },
 349             span: directive.span,
 350             vis,
 351             expansion: directive.expansion,
 352         })
 353     }
 354
 355     // Define the name or return the existing binding if there is a collision.
 356     pub fn try_define(&mut self,
 357                       module: Module<'a>,
 358                       ident: Ident,
 359                       ns: Namespace,
 360                       binding: &'a NameBinding<'a>)
 361                       -> Result<(), &'a NameBinding<'a>> {
 362         self.update_resolution(module, ident, ns, |this, resolution| {
 363             if let Some(old_binding) = resolution.binding {
 364                 if binding.is_glob_import() {
 365                     if !old_binding.is_glob_import() &&
 366                        !(ns == MacroNS && old_binding.expansion != Mark::root()) {
 367                         resolution.shadowed_glob = Some(binding);
 368                     } else if binding.def() != old_binding.def() {
 369                         resolution.binding = Some(this.ambiguity(old_binding, binding));
 370                     } else if !old_binding.vis.is_at_least(binding.vis, &*this) {
 371                         // We are glob-importing the same item but with greater visibility.
 372                         resolution.binding = Some(binding);
 373                     }
 374                 } else if old_binding.is_glob_import() {
 375                     if ns == MacroNS && binding.expansion != Mark::root() &&
 376                        binding.def() != old_binding.def() {
 377                         resolution.binding = Some(this.ambiguity(binding, old_binding));
 378                     } else {
 379                         resolution.binding = Some(binding);
 380                         resolution.shadowed_glob = Some(old_binding);
 381                     }
 382                 } else if let (&NameBindingKind::Def(_, true), &NameBindingKind::Def(_, true)) =
 383                         (&old_binding.kind, &binding.kind) {
 384
 385                     this.session.buffer_lint_with_diagnostic(
 386                         DUPLICATE_MACRO_EXPORTS,
 387                         CRATE_NODE_ID,
 388                         binding.span,
 389                         &format!("a macro named `{}` has already been exported", ident),
 390                         BuiltinLintDiagnostics::DuplicatedMacroExports(
 391                             ident, old_binding.span, binding.span));
 392
 393                     resolution.binding = Some(binding);
 394                 } else {
 395                     return Err(old_binding);
 396                 }
 397             } else {
 398                 resolution.binding = Some(binding);
 399             }
 400
 401             Ok(())
 402         })
 403     }
 404
 405     pub fn ambiguity(&self, b1: &'a NameBinding<'a>, b2: &'a NameBinding<'a>)
 406                      -> &'a NameBinding<'a> {
 407         self.arenas.alloc_name_binding(NameBinding {
 408             kind: NameBindingKind::Ambiguity { b1, b2 },
 409             vis: if b1.vis.is_at_least(b2.vis, self) { b1.vis } else { b2.vis },
 410             span: b1.span,
 411             expansion: Mark::root(),
 412         })
 413     }
 414
 415     // Use `f` to mutate the resolution of the name in the module.
 416     // If the resolution becomes a success, define it in the module's glob importers.
 417     fn update_resolution<T, F>(&mut self, module: Module<'a>, ident: Ident, ns: Namespace, f: F)
 418                                -> T
 419         where F: FnOnce(&mut Resolver<'a, 'crateloader>, &mut NameResolution<'a>) -> T
 420     {
 421         // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
 422         // during which the resolution might end up getting re-defined via a glob cycle.
 423         let (binding, t) = {
 424             let resolution = &mut *self.resolution(module, ident, ns).borrow_mut();
 425             let old_binding = resolution.binding();
 426
 427             let t = f(self, resolution);
 428
 429             match resolution.binding() {
 430                 _ if old_binding.is_some() => return t,
 431                 None => return t,
 432                 Some(binding) => match old_binding {
 433                     Some(old_binding) if ptr::eq(old_binding, binding) => return t,
 434                     _ => (binding, t),
 435                 }
 436             }
 437         };
 438
 439         // Define `binding` in `module`s glob importers.
 440         for directive in module.glob_importers.borrow_mut().iter() {
 441             let mut ident = ident.modern();
 442             let scope = match ident.span.reverse_glob_adjust(module.expansion,
 443                                                              directive.span.ctxt().modern()) {
 444                 Some(Some(def)) => self.macro_def_scope(def),
 445                 Some(None) => directive.parent,
 446                 None => continue,
 447             };
 448             if self.is_accessible_from(binding.vis, scope) {
 449                 let imported_binding = self.import(binding, directive);
 450                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
 451             }
 452         }
 453
 454         t
 455     }
 456
 457     // Define a "dummy" resolution containing a Def::Err as a placeholder for a
 458     // failed resolution
 459     fn import_dummy_binding(&mut self, directive: &'a ImportDirective<'a>) {
 460         if let SingleImport { target, .. } = directive.subclass {
 461             let dummy_binding = self.dummy_binding;
 462             let dummy_binding = self.import(dummy_binding, directive);
 463             self.per_ns(|this, ns| {
 464                 let _ = this.try_define(directive.parent, target, ns, dummy_binding);
 465             });
 466         }
 467     }
 468 }
 469
 470 pub struct ImportResolver<'a, 'b: 'a, 'c: 'a + 'b> {
 471     pub resolver: &'a mut Resolver<'b, 'c>,
 472 }
 473
 474 impl<'a, 'b: 'a, 'c: 'a + 'b> ::std::ops::Deref for ImportResolver<'a, 'b, 'c> {
 475     type Target = Resolver<'b, 'c>;
 476     fn deref(&self) -> &Resolver<'b, 'c> {
 477         self.resolver
 478     }
 479 }
 480
 481 impl<'a, 'b: 'a, 'c: 'a + 'b> ::std::ops::DerefMut for ImportResolver<'a, 'b, 'c> {
 482     fn deref_mut(&mut self) -> &mut Resolver<'b, 'c> {
 483         self.resolver
 484     }
 485 }
 486
 487 impl<'a, 'b: 'a, 'c: 'a + 'b> ty::DefIdTree for &'a ImportResolver<'a, 'b, 'c> {
 488     fn parent(self, id: DefId) -> Option<DefId> {
 489         self.resolver.parent(id)
 490     }
 491 }
 492
 493 impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
 494     // Import resolution
 495     //
 496     // This is a fixed-point algorithm. We resolve imports until our efforts
 497     // are stymied by an unresolved import; then we bail out of the current
 498     // module and continue. We terminate successfully once no more imports
 499     // remain or unsuccessfully when no forward progress in resolving imports
 500     // is made.
 501
 502     /// Resolves all imports for the crate. This method performs the fixed-
 503     /// point iteration.
 504     pub fn resolve_imports(&mut self) {
 505         let mut prev_num_indeterminates = self.indeterminate_imports.len() + 1;
 506         while self.indeterminate_imports.len() < prev_num_indeterminates {
 507             prev_num_indeterminates = self.indeterminate_imports.len();
 508             for import in mem::replace(&mut self.indeterminate_imports, Vec::new()) {
 509                 match self.resolve_import(&import) {
 510                     true => self.determined_imports.push(import),
 511                     false => self.indeterminate_imports.push(import),
 512                 }
 513             }
 514         }
 515     }
 516
 517     pub fn finalize_imports(&mut self) {
 518         for module in self.arenas.local_modules().iter() {
 519             self.finalize_resolutions_in(module);
 520         }
 521
 522         let mut errors = false;
 523         let mut seen_spans = FxHashSet();
 524         for i in 0 .. self.determined_imports.len() {
 525             let import = self.determined_imports[i];
 526             if let Some((span, err)) = self.finalize_import(import) {
 527                 errors = true;
 528
 529                 if let SingleImport { source, ref result, .. } = import.subclass {
 530                     if source.name == "self" {
 531                         // Silence `unresolved import` error if E0429 is already emitted
 532                         match result.value_ns.get() {
 533                             Err(Determined) => continue,
 534                             _ => {},
 535                         }
 536                     }
 537                 }
 538
 539                 // If the error is a single failed import then create a "fake" import
 540                 // resolution for it so that later resolve stages won't complain.
 541                 self.import_dummy_binding(import);
 542                 if !seen_spans.contains(&span) {
 543                     let path = import_path_to_string(&import.module_path[..],
 544                                                      &import.subclass,
 545                                                      span);
 546                     let error = ResolutionError::UnresolvedImport(Some((span, &path, &err)));
 547                     resolve_error(self.resolver, span, error);
 548                     seen_spans.insert(span);
 549                 }
 550             }
 551         }
 552
 553         // Report unresolved imports only if no hard error was already reported
 554         // to avoid generating multiple errors on the same import.
 555         if !errors {
 556             if let Some(import) = self.indeterminate_imports.iter().next() {
 557                 let error = ResolutionError::UnresolvedImport(None);
 558                 resolve_error(self.resolver, import.span, error);
 559             }
 560         }
 561     }
 562
 563     /// Attempts to resolve the given import, returning true if its resolution is determined.
 564     /// If successful, the resolved bindings are written into the module.
 565     fn resolve_import(&mut self, directive: &'b ImportDirective<'b>) -> bool {
 566         debug!("(resolving import for module) resolving import `{}::...` in `{}`",
 567                names_to_string(&directive.module_path[..]),
 568                module_to_string(self.current_module).unwrap_or("???".to_string()));
 569
 570         self.current_module = directive.parent;
 571
 572         let module = if let Some(module) = directive.imported_module.get() {
 573             module
 574         } else {
 575             let vis = directive.vis.get();
 576             // For better failure detection, pretend that the import will not define any names
 577             // while resolving its module path.
 578             directive.vis.set(ty::Visibility::Invisible);
 579             let result = self.resolve_path(&directive.module_path[..], None, false,
 580                                            directive.span, directive.crate_lint());
 581             directive.vis.set(vis);
 582
 583             match result {
 584                 PathResult::Module(module) => module,
 585                 PathResult::Indeterminate => return false,
 586                 _ => return true,
 587             }
 588         };
 589
 590         directive.imported_module.set(Some(module));
 591         let (source, target, result, type_ns_only) = match directive.subclass {
 592             SingleImport { source, target, ref result, type_ns_only } =>
 593                 (source, target, result, type_ns_only),
 594             GlobImport { .. } => {
 595                 self.resolve_glob_import(directive);
 596                 return true;
 597             }
 598             _ => unreachable!(),
 599         };
 600
 601         let mut indeterminate = false;
 602         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 603             if let Err(Undetermined) = result[ns].get() {
 604                 result[ns].set(this.resolve_ident_in_module(module,
 605                                                             source,
 606                                                             ns,
 607                                                             false,
 608                                                             directive.span));
 609             } else {
 610                 return
 611             };
 612
 613             let parent = directive.parent;
 614             match result[ns].get() {
 615                 Err(Undetermined) => indeterminate = true,
 616                 Err(Determined) => {
 617                     this.update_resolution(parent, target, ns, |_, resolution| {
 618                         resolution.single_imports.remove(&PtrKey(directive));
 619                     });
 620                 }
 621                 Ok(binding) if !binding.is_importable() => {
 622                     let msg = format!("`{}` is not directly importable", target);
 623                     struct_span_err!(this.session, directive.span, E0253, "{}", &msg)
 624                         .span_label(directive.span, "cannot be imported directly")
 625                         .emit();
 626                     // Do not import this illegal binding. Import a dummy binding and pretend
 627                     // everything is fine
 628                     this.import_dummy_binding(directive);
 629                 }
 630                 Ok(binding) => {
 631                     let imported_binding = this.import(binding, directive);
 632                     let conflict = this.try_define(parent, target, ns, imported_binding);
 633                     if let Err(old_binding) = conflict {
 634                         this.report_conflict(parent, target, ns, imported_binding, old_binding);
 635                     }
 636                 }
 637             }
 638         });
 639
 640         !indeterminate
 641     }
 642
 643     // If appropriate, returns an error to report.
 644     fn finalize_import(&mut self, directive: &'b ImportDirective<'b>) -> Option<(Span, String)> {
 645         self.current_module = directive.parent;
 646         let ImportDirective { ref module_path, span, .. } = *directive;
 647         let mut warn_if_binding_comes_from_local_crate = false;
 648
 649         // FIXME: Last path segment is treated specially in import resolution, so extern crate
 650         // mode for absolute paths needs some special support for single-segment imports.
 651         if module_path.len() == 1 && (module_path[0].name == keywords::CrateRoot.name() ||
 652                                       module_path[0].name == keywords::Extern.name()) {
 653             let is_extern = module_path[0].name == keywords::Extern.name() ||
 654                             (self.session.features_untracked().extern_absolute_paths &&
 655                              self.session.rust_2018());
 656             match directive.subclass {
 657                 GlobImport { .. } if is_extern => {
 658                     return Some((directive.span,
 659                                  "cannot glob-import all possible crates".to_string()));
 660                 }
 661                 GlobImport { .. } if self.session.features_untracked().extern_absolute_paths => {
 662                     self.lint_path_starts_with_module(
 663                         directive.root_id,
 664                         directive.root_span,
 665                     );
 666                 }
 667                 SingleImport { source, target, .. } => {
 668                     let crate_root = if source.name == keywords::Crate.name() &&
 669                                         module_path[0].name != keywords::Extern.name() {
 670                         if target.name == keywords::Crate.name() {
 671                             return Some((directive.span,
 672                                          "crate root imports need to be explicitly named: \
 673                                           `use crate as name;`".to_string()));
 674                         } else {
 675                             Some(self.resolve_crate_root(source))
 676                         }
 677                     } else if is_extern && !source.is_path_segment_keyword() {
 678                         let crate_id =
 679                             self.resolver.crate_loader.process_use_extern(
 680                                 source.name,
 681                                 directive.span,
 682                                 directive.id,
 683                                 &self.resolver.definitions,
 684                             );
 685                         let crate_root =
 686                             self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
 687                         self.populate_module_if_necessary(crate_root);
 688                         Some(crate_root)
 689                     } else {
 690                         warn_if_binding_comes_from_local_crate = true;
 691                         None
 692                     };
 693
 694                     if let Some(crate_root) = crate_root {
 695                         let binding = (crate_root, ty::Visibility::Public, directive.span,
 696                                        directive.expansion).to_name_binding(self.arenas);
 697                         let binding = self.arenas.alloc_name_binding(NameBinding {
 698                             kind: NameBindingKind::Import {
 699                                 binding,
 700                                 directive,
 701                                 used: Cell::new(false),
 702                             },
 703                             vis: directive.vis.get(),
 704                             span: directive.span,
 705                             expansion: directive.expansion,
 706                         });
 707                         let _ = self.try_define(directive.parent, target, TypeNS, binding);
 708                         let import = self.import_map.entry(directive.id).or_default();
 709                         import[TypeNS] = Some(PathResolution::new(binding.def()));
 710                         return None;
 711                     }
 712                 }
 713                 _ => {}
 714             }
 715         }
 716
 717         let module_result = self.resolve_path(
 718             &module_path,
 719             None,
 720             true,
 721             span,
 722             directive.crate_lint(),
 723         );
 724         let module = match module_result {
 725             PathResult::Module(module) => module,
 726             PathResult::Failed(span, msg, false) => {
 727                 resolve_error(self, span, ResolutionError::FailedToResolve(&msg));
 728                 return None;
 729             }
 730             PathResult::Failed(span, msg, true) => {
 731                 let (mut self_path, mut self_result) = (module_path.clone(), None);
 732                 let is_special = |ident: Ident| ident.is_path_segment_keyword() &&
 733                                                 ident.name != keywords::CrateRoot.name();
 734                 if !self_path.is_empty() && !is_special(self_path[0]) &&
 735                    !(self_path.len() > 1 && is_special(self_path[1])) {
 736                     self_path[0].name = keywords::SelfValue.name();
 737                     self_result = Some(self.resolve_path(&self_path, None, false,
 738                                                          span, CrateLint::No));
 739                 }
 740                 return if let Some(PathResult::Module(..)) = self_result {
 741                     Some((span, format!("Did you mean `{}`?", names_to_string(&self_path[..]))))
 742                 } else {
 743                     Some((span, msg))
 744                 };
 745             },
 746             _ => return None,
 747         };
 748
 749         let (ident, result, type_ns_only) = match directive.subclass {
 750             SingleImport { source, ref result, type_ns_only, .. } => (source, result, type_ns_only),
 751             GlobImport { .. } if module.def_id() == directive.parent.def_id() => {
 752                 // Importing a module into itself is not allowed.
 753                 return Some((directive.span,
 754                              "Cannot glob-import a module into itself.".to_string()));
 755             }
 756             GlobImport { is_prelude, ref max_vis } => {
 757                 if !is_prelude &&
 758                    max_vis.get() != ty::Visibility::Invisible && // Allow empty globs.
 759                    !max_vis.get().is_at_least(directive.vis.get(), &*self) {
 760                     let msg = "A non-empty glob must import something with the glob's visibility";
 761                     self.session.span_err(directive.span, msg);
 762                 }
 763                 return None;
 764             }
 765             _ => unreachable!(),
 766         };
 767
 768         let mut all_ns_err = true;
 769         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 770             if let Ok(binding) = result[ns].get() {
 771                 all_ns_err = false;
 772                 if this.record_use(ident, ns, binding, directive.span) {
 773                     this.resolution(module, ident, ns).borrow_mut().binding =
 774                         Some(this.dummy_binding);
 775                 }
 776             }
 777         });
 778
 779         if all_ns_err {
 780             let mut all_ns_failed = true;
 781             self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 782                 match this.resolve_ident_in_module(module, ident, ns, true, span) {
 783                     Ok(_) => all_ns_failed = false,
 784                     _ => {}
 785                 }
 786             });
 787
 788             return if all_ns_failed {
 789                 let resolutions = module.resolutions.borrow();
 790                 let names = resolutions.iter().filter_map(|(&(ref i, _), resolution)| {
 791                     if *i == ident { return None; } // Never suggest the same name
 792                     match *resolution.borrow() {
 793                         NameResolution { binding: Some(name_binding), .. } => {
 794                             match name_binding.kind {
 795                                 NameBindingKind::Import { binding, .. } => {
 796                                     match binding.kind {
 797                                         // Never suggest the name that has binding error
 798                                         // i.e. the name that cannot be previously resolved
 799                                         NameBindingKind::Def(Def::Err, _) => return None,
 800                                         _ => Some(&i.name),
 801                                     }
 802                                 },
 803                                 _ => Some(&i.name),
 804                             }
 805                         },
 806                         NameResolution { ref single_imports, .. }
 807                             if single_imports.is_empty() => None,
 808                         _ => Some(&i.name),
 809                     }
 810                 });
 811                 let lev_suggestion =
 812                     match find_best_match_for_name(names, &ident.as_str(), None) {
 813                         Some(name) => format!(". Did you mean to use `{}`?", name),
 814                         None => "".to_owned(),
 815                     };
 816                 let module_str = module_to_string(module);
 817                 let msg = if let Some(module_str) = module_str {
 818                     format!("no `{}` in `{}`{}", ident, module_str, lev_suggestion)
 819                 } else {
 820                     format!("no `{}` in the root{}", ident, lev_suggestion)
 821                 };
 822                 Some((span, msg))
 823             } else {
 824                 // `resolve_ident_in_module` reported a privacy error.
 825                 self.import_dummy_binding(directive);
 826                 None
 827             }
 828         }
 829
 830         let mut reexport_error = None;
 831         let mut any_successful_reexport = false;
 832         self.per_ns(|this, ns| {
 833             if let Ok(binding) = result[ns].get() {
 834                 let vis = directive.vis.get();
 835                 if !binding.pseudo_vis().is_at_least(vis, &*this) {
 836                     reexport_error = Some((ns, binding));
 837                 } else {
 838                     any_successful_reexport = true;
 839                 }
 840             }
 841         });
 842
 843         // All namespaces must be re-exported with extra visibility for an error to occur.
 844         if !any_successful_reexport {
 845             let (ns, binding) = reexport_error.unwrap();
 846             if ns == TypeNS && binding.is_extern_crate() {
 847                 let msg = format!("extern crate `{}` is private, and cannot be \
 848                                    re-exported (error E0365), consider declaring with \
 849                                    `pub`",
 850                                    ident);
 851                 self.session.buffer_lint(PUB_USE_OF_PRIVATE_EXTERN_CRATE,
 852                                          directive.id,
 853                                          directive.span,
 854                                          &msg);
 855             } else if ns == TypeNS {
 856                 struct_span_err!(self.session, directive.span, E0365,
 857                                  "`{}` is private, and cannot be re-exported", ident)
 858                     .span_label(directive.span, format!("re-export of private `{}`", ident))
 859                     .note(&format!("consider declaring type or module `{}` with `pub`", ident))
 860                     .emit();
 861             } else {
 862                 let msg = format!("`{}` is private, and cannot be re-exported", ident);
 863                 let note_msg =
 864                     format!("consider marking `{}` as `pub` in the imported module", ident);
 865                 struct_span_err!(self.session, directive.span, E0364, "{}", &msg)
 866                     .span_note(directive.span, &note_msg)
 867                     .emit();
 868             }
 869         }
 870
 871         if warn_if_binding_comes_from_local_crate {
 872             let mut warned = false;
 873             self.per_ns(|this, ns| {
 874                 let binding = match result[ns].get().ok() {
 875                     Some(b) => b,
 876                     None => return
 877                 };
 878                 if let NameBindingKind::Import { directive: d, .. } = binding.kind {
 879                     if let ImportDirectiveSubclass::ExternCrate(..) = d.subclass {
 880                         return
 881                     }
 882                 }
 883                 if warned {
 884                     return
 885                 }
 886                 warned = true;
 887                 this.lint_path_starts_with_module(
 888                     directive.root_id,
 889                     directive.root_span,
 890                 );
 891             });
 892         }
 893
 894         // Record what this import resolves to for later uses in documentation,
 895         // this may resolve to either a value or a type, but for documentation
 896         // purposes it's good enough to just favor one over the other.
 897         self.per_ns(|this, ns| if let Some(binding) = result[ns].get().ok() {
 898             let import = this.import_map.entry(directive.id).or_default();
 899             import[ns] = Some(PathResolution::new(binding.def()));
 900         });
 901
 902         debug!("(resolving single import) successfully resolved import");
 903         None
 904     }
 905
 906     fn resolve_glob_import(&mut self, directive: &'b ImportDirective<'b>) {
 907         let module = directive.imported_module.get().unwrap();
 908         self.populate_module_if_necessary(module);
 909
 910         if let Some(Def::Trait(_)) = module.def() {
 911             self.session.span_err(directive.span, "items in traits are not importable.");
 912             return;
 913         } else if module.def_id() == directive.parent.def_id()  {
 914             return;
 915         } else if let GlobImport { is_prelude: true, .. } = directive.subclass {
 916             self.prelude = Some(module);
 917             return;
 918         }
 919
 920         // Add to module's glob_importers
 921         module.glob_importers.borrow_mut().push(directive);
 922
 923         // Ensure that `resolutions` isn't borrowed during `try_define`,
 924         // since it might get updated via a glob cycle.
 925         let bindings = module.resolutions.borrow().iter().filter_map(|(&ident, resolution)| {
 926             resolution.borrow().binding().map(|binding| (ident, binding))
 927         }).collect::<Vec<_>>();
 928         for ((mut ident, ns), binding) in bindings {
 929             let scope = match ident.span.reverse_glob_adjust(module.expansion,
 930                                                              directive.span.ctxt().modern()) {
 931                 Some(Some(def)) => self.macro_def_scope(def),
 932                 Some(None) => self.current_module,
 933                 None => continue,
 934             };
 935             if self.is_accessible_from(binding.pseudo_vis(), scope) {
 936                 let imported_binding = self.import(binding, directive);
 937                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
 938             }
 939         }
 940
 941         // Record the destination of this import
 942         self.record_def(directive.id, PathResolution::new(module.def().unwrap()));
 943     }
 944
 945     // Miscellaneous post-processing, including recording re-exports,
 946     // reporting conflicts, and reporting unresolved imports.
 947     fn finalize_resolutions_in(&mut self, module: Module<'b>) {
 948         // Since import resolution is finished, globs will not define any more names.
 949         *module.globs.borrow_mut() = Vec::new();
 950
 951         let mut reexports = Vec::new();
 952         let mut exported_macro_names = FxHashMap();
 953         if ptr::eq(module, self.graph_root) {
 954             let macro_exports = mem::replace(&mut self.macro_exports, Vec::new());
 955             for export in macro_exports.into_iter().rev() {
 956                 if let Some(later_span) = exported_macro_names.insert(export.ident.modern(),
 957                                                                       export.span) {
 958                     self.session.buffer_lint_with_diagnostic(
 959                         DUPLICATE_MACRO_EXPORTS,
 960                         CRATE_NODE_ID,
 961                         later_span,
 962                         &format!("a macro named `{}` has already been exported", export.ident),
 963                         BuiltinLintDiagnostics::DuplicatedMacroExports(
 964                             export.ident, export.span, later_span));
 965                 } else {
 966                     reexports.push(export);
 967                 }
 968             }
 969         }
 970
 971         for (&(ident, ns), resolution) in module.resolutions.borrow().iter() {
 972             let resolution = &mut *resolution.borrow_mut();
 973             let binding = match resolution.binding {
 974                 Some(binding) => binding,
 975                 None => continue,
 976             };
 977
 978             if binding.is_import() || binding.is_macro_def() {
 979                 let def = binding.def();
 980                 if def != Def::Err {
 981                     if !def.def_id().is_local() {
 982                         self.cstore.export_macros_untracked(def.def_id().krate);
 983                     }
 984                     if let Def::Macro(..) = def {
 985                         if let Some(&span) = exported_macro_names.get(&ident.modern()) {
 986                             let msg =
 987                                 format!("a macro named `{}` has already been exported", ident);
 988                             self.session.struct_span_err(span, &msg)
 989                                 .span_label(span, format!("`{}` already exported", ident))
 990                                 .span_note(binding.span, "previous macro export here")
 991                                 .emit();
 992                         }
 993                     }
 994                     reexports.push(Export {
 995                         ident: ident.modern(),
 996                         def: def,
 997                         span: binding.span,
 998                         vis: binding.vis,
 999                     });
1000                 }
1001             }
1002
1003             match binding.kind {
1004                 NameBindingKind::Import { binding: orig_binding, directive, .. } => {
1005                     if ns == TypeNS && orig_binding.is_variant() &&
1006                         !orig_binding.vis.is_at_least(binding.vis, &*self) {
1007                             let msg = match directive.subclass {
1008                                 ImportDirectiveSubclass::SingleImport { .. } => {
1009                                     format!("variant `{}` is private and cannot be re-exported",
1010                                             ident)
1011                                 },
1012                                 ImportDirectiveSubclass::GlobImport { .. } => {
1013                                     let msg = "enum is private and its variants \
1014                                                cannot be re-exported".to_owned();
1015                                     let error_id = (DiagnosticMessageId::ErrorId(0), // no code?!
1016                                                     Some(binding.span),
1017                                                     msg.clone());
1018                                     let fresh = self.session.one_time_diagnostics
1019                                         .borrow_mut().insert(error_id);
1020                                     if !fresh {
1021                                         continue;
1022                                     }
1023                                     msg
1024                                 },
1025                                 ref s @ _ => bug!("unexpected import subclass {:?}", s)
1026                             };
1027                             let mut err = self.session.struct_span_err(binding.span, &msg);
1028
1029                             let imported_module = directive.imported_module.get()
1030                                 .expect("module should exist");
1031                             let resolutions = imported_module.parent.expect("parent should exist")
1032                                 .resolutions.borrow();
1033                             let enum_path_segment_index = directive.module_path.len() - 1;
1034                             let enum_ident = directive.module_path[enum_path_segment_index];
1035
1036                             let enum_resolution = resolutions.get(&(enum_ident, TypeNS))
1037                                 .expect("resolution should exist");
1038                             let enum_span = enum_resolution.borrow()
1039                                 .binding.expect("binding should exist")
1040                                 .span;
1041                             let enum_def_span = self.session.codemap().def_span(enum_span);
1042                             let enum_def_snippet = self.session.codemap()
1043                                 .span_to_snippet(enum_def_span).expect("snippet should exist");
1044                             // potentially need to strip extant `crate`/`pub(path)` for suggestion
1045                             let after_vis_index = enum_def_snippet.find("enum")
1046                                 .expect("`enum` keyword should exist in snippet");
1047                             let suggestion = format!("pub {}",
1048                                                      &enum_def_snippet[after_vis_index..]);
1049
1050                             self.session
1051                                 .diag_span_suggestion_once(&mut err,
1052                                                            DiagnosticMessageId::ErrorId(0),
1053                                                            enum_def_span,
1054                                                            "consider making the enum public",
1055                                                            suggestion);
1056                             err.emit();
1057                     }
1058                 }
1059                 _ => {}
1060             }
1061         }
1062
1063         if reexports.len() > 0 {
1064             if let Some(def_id) = module.def_id() {
1065                 self.export_map.insert(def_id, reexports);
1066             }
1067         }
1068     }
1069 }
1070
1071 fn import_path_to_string(names: &[Ident],
1072                          subclass: &ImportDirectiveSubclass,
1073                          span: Span) -> String {
1074     let pos = names.iter()
1075         .position(|p| span == p.span && p.name != keywords::CrateRoot.name());
1076     let global = !names.is_empty() && names[0].name == keywords::CrateRoot.name();
1077     if let Some(pos) = pos {
1078         let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
1079         names_to_string(names)
1080     } else {
1081         let names = if global { &names[1..] } else { names };
1082         if names.is_empty() {
1083             import_directive_subclass_to_string(subclass)
1084         } else {
1085             format!("{}::{}",
1086                     names_to_string(names),
1087                     import_directive_subclass_to_string(subclass))
1088         }
1089     }
1090 }
1091
1092 fn import_directive_subclass_to_string(subclass: &ImportDirectiveSubclass) -> String {
1093     match *subclass {
1094         SingleImport { source, .. } => source.to_string(),
1095         GlobImport { .. } => "*".to_string(),
1096         ExternCrate(_) => "<extern crate>".to_string(),
1097         MacroUse => "#[macro_use]".to_string(),
1098     }
1099 }