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, ModuleOrUniformRoot, 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::collections::BTreeMap;
  38 use std::fmt::Write;
  39 use std::{mem, ptr};
  40
  41 /// Contains data for specific types of import directives.
  42 #[derive(Clone, Debug)]
  43 pub enum ImportDirectiveSubclass<'a> {
  44     SingleImport {
  45         target: Ident,
  46         source: Ident,
  47         result: PerNS<Cell<Result<&'a NameBinding<'a>, Determinacy>>>,
  48         type_ns_only: bool,
  49     },
  50     GlobImport {
  51         is_prelude: bool,
  52         max_vis: Cell<ty::Visibility>, // The visibility of the greatest re-export.
  53         // n.b. `max_vis` is only used in `finalize_import` to check for re-export errors.
  54     },
  55     ExternCrate(Option<Name>),
  56     MacroUse,
  57 }
  58
  59 /// One import directive.
  60 #[derive(Debug,Clone)]
  61 pub struct ImportDirective<'a> {
  62     /// The id of the `extern crate`, `UseTree` etc that imported this `ImportDirective`.
  63     ///
  64     /// In the case where the `ImportDirective` was expanded from a "nested" use tree,
  65     /// this id is the id of the leaf tree. For example:
  66     ///
  67     /// ```ignore (pacify the mercilous tidy)
  68     /// use foo::bar::{a, b}
  69     /// ```
  70     ///
  71     /// If this is the import directive for `foo::bar::a`, we would have the id of the `UseTree`
  72     /// for `a` in this field.
  73     pub id: NodeId,
  74
  75     /// The `id` of the "root" use-kind -- this is always the same as
  76     /// `id` except in the case of "nested" use trees, in which case
  77     /// it will be the `id` of the root use tree. e.g., in the example
  78     /// from `id`, this would be the id of the `use foo::bar`
  79     /// `UseTree` node.
  80     pub root_id: NodeId,
  81
  82     /// Span of this use tree.
  83     pub span: Span,
  84
  85     /// Span of the *root* use tree (see `root_id`).
  86     pub root_span: Span,
  87
  88     pub parent: Module<'a>,
  89     pub module_path: Vec<Ident>,
  90     /// The resolution of `module_path`.
  91     pub imported_module: Cell<Option<ModuleOrUniformRoot<'a>>>,
  92     pub subclass: ImportDirectiveSubclass<'a>,
  93     pub vis: Cell<ty::Visibility>,
  94     pub expansion: Mark,
  95     pub used: Cell<bool>,
  96
  97     /// Whether this import is a "canary" for the `uniform_paths` feature,
  98     /// i.e. `use x::...;` results in an `use self::x as _;` canary.
  99     /// This flag affects diagnostics: an error is reported if and only if
 100     /// the import resolves successfully and an external crate with the same
 101     /// name (`x` above) also exists; any resolution failures are ignored.
 102     pub is_uniform_paths_canary: bool,
 103 }
 104
 105 impl<'a> ImportDirective<'a> {
 106     pub fn is_glob(&self) -> bool {
 107         match self.subclass { ImportDirectiveSubclass::GlobImport { .. } => true, _ => false }
 108     }
 109
 110     crate fn crate_lint(&self) -> CrateLint {
 111         CrateLint::UsePath { root_id: self.root_id, root_span: self.root_span }
 112     }
 113 }
 114
 115 #[derive(Clone, Default, Debug)]
 116 /// Records information about the resolution of a name in a namespace of a module.
 117 pub struct NameResolution<'a> {
 118     /// Single imports that may define the name in the namespace.
 119     /// Import directives are arena-allocated, so it's ok to use pointers as keys.
 120     single_imports: FxHashSet<PtrKey<'a, ImportDirective<'a>>>,
 121     /// The least shadowable known binding for this name, or None if there are no known bindings.
 122     pub binding: Option<&'a NameBinding<'a>>,
 123     shadowed_glob: Option<&'a NameBinding<'a>>,
 124 }
 125
 126 impl<'a> NameResolution<'a> {
 127     // Returns the binding for the name if it is known or None if it not known.
 128     fn binding(&self) -> Option<&'a NameBinding<'a>> {
 129         self.binding.and_then(|binding| {
 130             if !binding.is_glob_import() ||
 131                self.single_imports.is_empty() { Some(binding) } else { None }
 132         })
 133     }
 134 }
 135
 136 impl<'a, 'crateloader> Resolver<'a, 'crateloader> {
 137     fn resolution(&self, module: Module<'a>, ident: Ident, ns: Namespace)
 138                   -> &'a RefCell<NameResolution<'a>> {
 139         *module.resolutions.borrow_mut().entry((ident.modern(), ns))
 140                .or_insert_with(|| self.arenas.alloc_name_resolution())
 141     }
 142
 143     /// Attempts to resolve `ident` in namespaces `ns` of `module`.
 144     /// Invariant: if `record_used` is `Some`, expansion and import resolution must be complete.
 145     pub fn resolve_ident_in_module_unadjusted(&mut self,
 146                                               module: ModuleOrUniformRoot<'a>,
 147                                               ident: Ident,
 148                                               ns: Namespace,
 149                                               restricted_shadowing: bool,
 150                                               record_used: bool,
 151                                               path_span: Span)
 152                                               -> Result<&'a NameBinding<'a>, Determinacy> {
 153         let module = match module {
 154             ModuleOrUniformRoot::Module(module) => module,
 155             ModuleOrUniformRoot::UniformRoot(root) => {
 156                 // HACK(eddyb): `resolve_path` uses `keywords::Invalid` to indicate
 157                 // paths of length 0, and currently these are relative `use` paths.
 158                 let can_be_relative = !ident.is_path_segment_keyword() &&
 159                     root == keywords::Invalid.name();
 160                 if can_be_relative {
 161                     // Relative paths should only get here if the feature-gate is on.
 162                     assert!(self.session.rust_2018() &&
 163                             self.session.features_untracked().uniform_paths);
 164
 165                     // Try first to resolve relatively.
 166                     let mut ctxt = ident.span.ctxt().modern();
 167                     let self_module = self.resolve_self(&mut ctxt, self.current_module);
 168
 169                     let binding = self.resolve_ident_in_module_unadjusted(
 170                         ModuleOrUniformRoot::Module(self_module),
 171                         ident,
 172                         ns,
 173                         restricted_shadowing,
 174                         record_used,
 175                         path_span,
 176                     );
 177
 178                     // FIXME(eddyb) This may give false negatives, specifically
 179                     // if a crate with the same name is found in `extern_prelude`,
 180                     // preventing the check below this one from returning `binding`
 181                     // in all cases.
 182                     //
 183                     // That is, if there's no crate with the same name, `binding`
 184                     // is always returned, which is the result of doing the exact
 185                     // same lookup of `ident`, in the `self` module.
 186                     // But when a crate does exist, it will get chosen even when
 187                     // macro expansion could result in a success from the lookup
 188                     // in the `self` module, later on.
 189                     //
 190                     // NB. This is currently alleviated by the "ambiguity canaries"
 191                     // (see `is_uniform_paths_canary`) that get introduced for the
 192                     // maybe-relative imports handled here: if the false negative
 193                     // case were to arise, it would *also* cause an ambiguity error.
 194                     if binding.is_ok() {
 195                         return binding;
 196                     }
 197
 198                     // Fall back to resolving to an external crate.
 199                     if !(ns == TypeNS && self.extern_prelude.contains(&ident.name)) {
 200                         // ... unless the crate name is not in the `extern_prelude`.
 201                         return binding;
 202                     }
 203                 }
 204
 205                 let crate_root = if
 206                     ns == TypeNS &&
 207                     root != keywords::Extern.name() &&
 208                     (
 209                         ident.name == keywords::Crate.name() ||
 210                         ident.name == keywords::DollarCrate.name()
 211                     )
 212                 {
 213                     self.resolve_crate_root(ident)
 214                 } else if ns == TypeNS && !ident.is_path_segment_keyword() {
 215                     let crate_id =
 216                         self.crate_loader.process_path_extern(ident.name, ident.span);
 217                     self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX })
 218                 } else {
 219                     return Err(Determined);
 220                 };
 221                 self.populate_module_if_necessary(crate_root);
 222                 let binding = (crate_root, ty::Visibility::Public,
 223                                ident.span, Mark::root()).to_name_binding(self.arenas);
 224                 return Ok(binding);
 225             }
 226         };
 227
 228         self.populate_module_if_necessary(module);
 229
 230         let resolution = self.resolution(module, ident, ns)
 231             .try_borrow_mut()
 232             .map_err(|_| Determined)?; // This happens when there is a cycle of imports
 233
 234         if let Some(binding) = resolution.binding {
 235             if !restricted_shadowing && binding.expansion != Mark::root() {
 236                 if let NameBindingKind::Def(_, true) = binding.kind {
 237                     self.macro_expanded_macro_export_errors.insert((path_span, binding.span));
 238                 }
 239             }
 240         }
 241
 242         if record_used {
 243             if let Some(binding) = resolution.binding {
 244                 if let Some(shadowed_glob) = resolution.shadowed_glob {
 245                     let name = ident.name;
 246                     // Forbid expanded shadowing to avoid time travel.
 247                     if restricted_shadowing &&
 248                        binding.expansion != Mark::root() &&
 249                        ns != MacroNS && // In MacroNS, `try_define` always forbids this shadowing
 250                        binding.def() != shadowed_glob.def() {
 251                         self.ambiguity_errors.push(AmbiguityError {
 252                             span: path_span,
 253                             name,
 254                             lexical: false,
 255                             b1: binding,
 256                             b2: shadowed_glob,
 257                         });
 258                     }
 259                 }
 260                 if self.record_use(ident, ns, binding, path_span) {
 261                     return Ok(self.dummy_binding);
 262                 }
 263                 if !self.is_accessible(binding.vis) {
 264                     self.privacy_errors.push(PrivacyError(path_span, ident.name, binding));
 265                 }
 266             }
 267
 268             return resolution.binding.ok_or(Determined);
 269         }
 270
 271         let check_usable = |this: &mut Self, binding: &'a NameBinding<'a>| {
 272             // `extern crate` are always usable for backwards compatibility, see issue #37020.
 273             let usable = this.is_accessible(binding.vis) || binding.is_extern_crate();
 274             if usable { Ok(binding) } else { Err(Determined) }
 275         };
 276
 277         // Items and single imports are not shadowable, if we have one, then it's determined.
 278         if let Some(binding) = resolution.binding {
 279             if !binding.is_glob_import() {
 280                 return check_usable(self, binding);
 281             }
 282         }
 283
 284         // --- From now on we either have a glob resolution or no resolution. ---
 285
 286         // Check if one of single imports can still define the name,
 287         // if it can then our result is not determined and can be invalidated.
 288         for single_import in &resolution.single_imports {
 289             if !self.is_accessible(single_import.vis.get()) {
 290                 continue;
 291             }
 292             let module = unwrap_or!(single_import.imported_module.get(), return Err(Undetermined));
 293             let ident = match single_import.subclass {
 294                 SingleImport { source, .. } => source,
 295                 _ => unreachable!(),
 296             };
 297             match self.resolve_ident_in_module(module, ident, ns, false, path_span) {
 298                 Err(Determined) => continue,
 299                 Ok(_) | Err(Undetermined) => return Err(Undetermined),
 300             }
 301         }
 302
 303         // So we have a resolution that's from a glob import. This resolution is determined
 304         // if it cannot be shadowed by some new item/import expanded from a macro.
 305         // This happens either if there are no unexpanded macros, or expanded names cannot
 306         // shadow globs (that happens in macro namespace or with restricted shadowing).
 307         //
 308         // Additionally, any macro in any module can plant names in the root module if it creates
 309         // `macro_export` macros, so the root module effectively has unresolved invocations if any
 310         // module has unresolved invocations.
 311         // However, it causes resolution/expansion to stuck too often (#53144), so, to make
 312         // progress, we have to ignore those potential unresolved invocations from other modules
 313         // and prohibit access to macro-expanded `macro_export` macros instead (unless restricted
 314         // shadowing is enabled, see `macro_expanded_macro_export_errors`).
 315         let unexpanded_macros = !module.unresolved_invocations.borrow().is_empty();
 316         if let Some(binding) = resolution.binding {
 317             if !unexpanded_macros || ns == MacroNS || restricted_shadowing {
 318                 return check_usable(self, binding);
 319             } else {
 320                 return Err(Undetermined);
 321             }
 322         }
 323
 324         // --- From now on we have no resolution. ---
 325
 326         // Now we are in situation when new item/import can appear only from a glob or a macro
 327         // expansion. With restricted shadowing names from globs and macro expansions cannot
 328         // shadow names from outer scopes, so we can freely fallback from module search to search
 329         // in outer scopes. To continue search in outer scopes we have to lie a bit and return
 330         // `Determined` to `resolve_lexical_macro_path_segment` even if the correct answer
 331         // for in-module resolution could be `Undetermined`.
 332         if restricted_shadowing {
 333             return Err(Determined);
 334         }
 335
 336         // Check if one of unexpanded macros can still define the name,
 337         // if it can then our "no resolution" result is not determined and can be invalidated.
 338         if unexpanded_macros {
 339             return Err(Undetermined);
 340         }
 341
 342         // Check if one of glob imports can still define the name,
 343         // if it can then our "no resolution" result is not determined and can be invalidated.
 344         for glob_import in module.globs.borrow().iter() {
 345             if !self.is_accessible(glob_import.vis.get()) {
 346                 continue
 347             }
 348             let module = match glob_import.imported_module.get() {
 349                 Some(ModuleOrUniformRoot::Module(module)) => module,
 350                 Some(ModuleOrUniformRoot::UniformRoot(_)) => continue,
 351                 None => return Err(Undetermined),
 352             };
 353             let (orig_current_module, mut ident) = (self.current_module, ident.modern());
 354             match ident.span.glob_adjust(module.expansion, glob_import.span.ctxt().modern()) {
 355                 Some(Some(def)) => self.current_module = self.macro_def_scope(def),
 356                 Some(None) => {}
 357                 None => continue,
 358             };
 359             let result = self.resolve_ident_in_module_unadjusted(
 360                 ModuleOrUniformRoot::Module(module),
 361                 ident,
 362                 ns,
 363                 false,
 364                 false,
 365                 path_span,
 366             );
 367             self.current_module = orig_current_module;
 368             match result {
 369                 Err(Determined) => continue,
 370                 Ok(_) | Err(Undetermined) => return Err(Undetermined),
 371             }
 372         }
 373
 374         // No resolution and no one else can define the name - determinate error.
 375         Err(Determined)
 376     }
 377
 378     // Add an import directive to the current module.
 379     pub fn add_import_directive(&mut self,
 380                                 module_path: Vec<Ident>,
 381                                 subclass: ImportDirectiveSubclass<'a>,
 382                                 span: Span,
 383                                 id: NodeId,
 384                                 root_span: Span,
 385                                 root_id: NodeId,
 386                                 vis: ty::Visibility,
 387                                 expansion: Mark,
 388                                 is_uniform_paths_canary: bool) {
 389         let current_module = self.current_module;
 390         let directive = self.arenas.alloc_import_directive(ImportDirective {
 391             parent: current_module,
 392             module_path,
 393             imported_module: Cell::new(None),
 394             subclass,
 395             span,
 396             id,
 397             root_span,
 398             root_id,
 399             vis: Cell::new(vis),
 400             expansion,
 401             used: Cell::new(false),
 402             is_uniform_paths_canary,
 403         });
 404
 405         debug!("add_import_directive({:?})", directive);
 406
 407         self.indeterminate_imports.push(directive);
 408         match directive.subclass {
 409             SingleImport { target, type_ns_only, .. } => {
 410                 self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 411                     let mut resolution = this.resolution(current_module, target, ns).borrow_mut();
 412                     resolution.single_imports.insert(PtrKey(directive));
 413                 });
 414             }
 415             // We don't add prelude imports to the globs since they only affect lexical scopes,
 416             // which are not relevant to import resolution.
 417             GlobImport { is_prelude: true, .. } => {}
 418             GlobImport { .. } => self.current_module.globs.borrow_mut().push(directive),
 419             _ => unreachable!(),
 420         }
 421     }
 422
 423     // Given a binding and an import directive that resolves to it,
 424     // return the corresponding binding defined by the import directive.
 425     pub fn import(&self, binding: &'a NameBinding<'a>, directive: &'a ImportDirective<'a>)
 426                   -> &'a NameBinding<'a> {
 427         let vis = if binding.pseudo_vis().is_at_least(directive.vis.get(), self) ||
 428                      // c.f. `PUB_USE_OF_PRIVATE_EXTERN_CRATE`
 429                      !directive.is_glob() && binding.is_extern_crate() {
 430             directive.vis.get()
 431         } else {
 432             binding.pseudo_vis()
 433         };
 434
 435         if let GlobImport { ref max_vis, .. } = directive.subclass {
 436             if vis == directive.vis.get() || vis.is_at_least(max_vis.get(), self) {
 437                 max_vis.set(vis)
 438             }
 439         }
 440
 441         self.arenas.alloc_name_binding(NameBinding {
 442             kind: NameBindingKind::Import {
 443                 binding,
 444                 directive,
 445                 used: Cell::new(false),
 446             },
 447             span: directive.span,
 448             vis,
 449             expansion: directive.expansion,
 450         })
 451     }
 452
 453     // Define the name or return the existing binding if there is a collision.
 454     pub fn try_define(&mut self,
 455                       module: Module<'a>,
 456                       ident: Ident,
 457                       ns: Namespace,
 458                       binding: &'a NameBinding<'a>)
 459                       -> Result<(), &'a NameBinding<'a>> {
 460         self.update_resolution(module, ident, ns, |this, resolution| {
 461             if let Some(old_binding) = resolution.binding {
 462                 if binding.is_glob_import() {
 463                     if !old_binding.is_glob_import() &&
 464                        !(ns == MacroNS && old_binding.expansion != Mark::root()) {
 465                         resolution.shadowed_glob = Some(binding);
 466                     } else if binding.def() != old_binding.def() {
 467                         resolution.binding = Some(this.ambiguity(old_binding, binding));
 468                     } else if !old_binding.vis.is_at_least(binding.vis, &*this) {
 469                         // We are glob-importing the same item but with greater visibility.
 470                         resolution.binding = Some(binding);
 471                     }
 472                 } else if old_binding.is_glob_import() {
 473                     if ns == MacroNS && binding.expansion != Mark::root() &&
 474                        binding.def() != old_binding.def() {
 475                         resolution.binding = Some(this.ambiguity(binding, old_binding));
 476                     } else {
 477                         resolution.binding = Some(binding);
 478                         resolution.shadowed_glob = Some(old_binding);
 479                     }
 480                 } else if let (&NameBindingKind::Def(_, true), &NameBindingKind::Def(_, true)) =
 481                         (&old_binding.kind, &binding.kind) {
 482
 483                     this.session.buffer_lint_with_diagnostic(
 484                         DUPLICATE_MACRO_EXPORTS,
 485                         CRATE_NODE_ID,
 486                         binding.span,
 487                         &format!("a macro named `{}` has already been exported", ident),
 488                         BuiltinLintDiagnostics::DuplicatedMacroExports(
 489                             ident, old_binding.span, binding.span));
 490
 491                     resolution.binding = Some(binding);
 492                 } else {
 493                     return Err(old_binding);
 494                 }
 495             } else {
 496                 resolution.binding = Some(binding);
 497             }
 498
 499             Ok(())
 500         })
 501     }
 502
 503     pub fn ambiguity(&self, b1: &'a NameBinding<'a>, b2: &'a NameBinding<'a>)
 504                      -> &'a NameBinding<'a> {
 505         self.arenas.alloc_name_binding(NameBinding {
 506             kind: NameBindingKind::Ambiguity { b1, b2 },
 507             vis: if b1.vis.is_at_least(b2.vis, self) { b1.vis } else { b2.vis },
 508             span: b1.span,
 509             expansion: Mark::root(),
 510         })
 511     }
 512
 513     // Use `f` to mutate the resolution of the name in the module.
 514     // If the resolution becomes a success, define it in the module's glob importers.
 515     fn update_resolution<T, F>(&mut self, module: Module<'a>, ident: Ident, ns: Namespace, f: F)
 516                                -> T
 517         where F: FnOnce(&mut Resolver<'a, 'crateloader>, &mut NameResolution<'a>) -> T
 518     {
 519         // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
 520         // during which the resolution might end up getting re-defined via a glob cycle.
 521         let (binding, t) = {
 522             let resolution = &mut *self.resolution(module, ident, ns).borrow_mut();
 523             let old_binding = resolution.binding();
 524
 525             let t = f(self, resolution);
 526
 527             match resolution.binding() {
 528                 _ if old_binding.is_some() => return t,
 529                 None => return t,
 530                 Some(binding) => match old_binding {
 531                     Some(old_binding) if ptr::eq(old_binding, binding) => return t,
 532                     _ => (binding, t),
 533                 }
 534             }
 535         };
 536
 537         // Define `binding` in `module`s glob importers.
 538         for directive in module.glob_importers.borrow_mut().iter() {
 539             let mut ident = ident.modern();
 540             let scope = match ident.span.reverse_glob_adjust(module.expansion,
 541                                                              directive.span.ctxt().modern()) {
 542                 Some(Some(def)) => self.macro_def_scope(def),
 543                 Some(None) => directive.parent,
 544                 None => continue,
 545             };
 546             if self.is_accessible_from(binding.vis, scope) {
 547                 let imported_binding = self.import(binding, directive);
 548                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
 549             }
 550         }
 551
 552         t
 553     }
 554
 555     // Define a "dummy" resolution containing a Def::Err as a placeholder for a
 556     // failed resolution
 557     fn import_dummy_binding(&mut self, directive: &'a ImportDirective<'a>) {
 558         if let SingleImport { target, .. } = directive.subclass {
 559             let dummy_binding = self.dummy_binding;
 560             let dummy_binding = self.import(dummy_binding, directive);
 561             self.per_ns(|this, ns| {
 562                 let _ = this.try_define(directive.parent, target, ns, dummy_binding);
 563             });
 564         }
 565     }
 566 }
 567
 568 pub struct ImportResolver<'a, 'b: 'a, 'c: 'a + 'b> {
 569     pub resolver: &'a mut Resolver<'b, 'c>,
 570 }
 571
 572 impl<'a, 'b: 'a, 'c: 'a + 'b> ::std::ops::Deref for ImportResolver<'a, 'b, 'c> {
 573     type Target = Resolver<'b, 'c>;
 574     fn deref(&self) -> &Resolver<'b, 'c> {
 575         self.resolver
 576     }
 577 }
 578
 579 impl<'a, 'b: 'a, 'c: 'a + 'b> ::std::ops::DerefMut for ImportResolver<'a, 'b, 'c> {
 580     fn deref_mut(&mut self) -> &mut Resolver<'b, 'c> {
 581         self.resolver
 582     }
 583 }
 584
 585 impl<'a, 'b: 'a, 'c: 'a + 'b> ty::DefIdTree for &'a ImportResolver<'a, 'b, 'c> {
 586     fn parent(self, id: DefId) -> Option<DefId> {
 587         self.resolver.parent(id)
 588     }
 589 }
 590
 591 impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
 592     // Import resolution
 593     //
 594     // This is a fixed-point algorithm. We resolve imports until our efforts
 595     // are stymied by an unresolved import; then we bail out of the current
 596     // module and continue. We terminate successfully once no more imports
 597     // remain or unsuccessfully when no forward progress in resolving imports
 598     // is made.
 599
 600     /// Resolves all imports for the crate. This method performs the fixed-
 601     /// point iteration.
 602     pub fn resolve_imports(&mut self) {
 603         let mut prev_num_indeterminates = self.indeterminate_imports.len() + 1;
 604         while self.indeterminate_imports.len() < prev_num_indeterminates {
 605             prev_num_indeterminates = self.indeterminate_imports.len();
 606             for import in mem::replace(&mut self.indeterminate_imports, Vec::new()) {
 607                 match self.resolve_import(&import) {
 608                     true => self.determined_imports.push(import),
 609                     false => self.indeterminate_imports.push(import),
 610                 }
 611             }
 612         }
 613     }
 614
 615     pub fn finalize_imports(&mut self) {
 616         for module in self.arenas.local_modules().iter() {
 617             self.finalize_resolutions_in(module);
 618         }
 619
 620         #[derive(Default)]
 621         struct UniformPathsCanaryResult {
 622             module_scope: Option<Span>,
 623             block_scopes: Vec<Span>,
 624         }
 625         // Collect all tripped `uniform_paths` canaries separately.
 626         let mut uniform_paths_canaries: BTreeMap<
 627             (Span, NodeId),
 628             (Name, PerNS<UniformPathsCanaryResult>),
 629         > = BTreeMap::new();
 630
 631         let mut errors = false;
 632         let mut seen_spans = FxHashSet();
 633         for i in 0 .. self.determined_imports.len() {
 634             let import = self.determined_imports[i];
 635             let error = self.finalize_import(import);
 636
 637             // For a `#![feature(uniform_paths)]` `use self::x as _` canary,
 638             // failure is ignored, while success may cause an ambiguity error.
 639             if import.is_uniform_paths_canary {
 640                 if error.is_some() {
 641                     continue;
 642                 }
 643
 644                 let (name, result) = match import.subclass {
 645                     SingleImport { source, ref result, .. } => (source.name, result),
 646                     _ => bug!(),
 647                 };
 648
 649                 let has_explicit_self =
 650                     import.module_path.len() > 0 &&
 651                     import.module_path[0].name == keywords::SelfValue.name();
 652
 653                 let (prev_name, canary_results) =
 654                     uniform_paths_canaries.entry((import.span, import.id))
 655                         .or_insert((name, PerNS::default()));
 656
 657                 // All the canaries with the same `id` should have the same `name`.
 658                 assert_eq!(*prev_name, name);
 659
 660                 self.per_ns(|_, ns| {
 661                     if let Some(result) = result[ns].get().ok() {
 662                         if has_explicit_self {
 663                             // There should only be one `self::x` (module-scoped) canary.
 664                             assert_eq!(canary_results[ns].module_scope, None);
 665                             canary_results[ns].module_scope = Some(result.span);
 666                         } else {
 667                             canary_results[ns].block_scopes.push(result.span);
 668                         }
 669                     }
 670                 });
 671             } else if let Some((span, err)) = error {
 672                 errors = true;
 673
 674                 if let SingleImport { source, ref result, .. } = import.subclass {
 675                     if source.name == "self" {
 676                         // Silence `unresolved import` error if E0429 is already emitted
 677                         match result.value_ns.get() {
 678                             Err(Determined) => continue,
 679                             _ => {},
 680                         }
 681                     }
 682                 }
 683
 684                 // If the error is a single failed import then create a "fake" import
 685                 // resolution for it so that later resolve stages won't complain.
 686                 self.import_dummy_binding(import);
 687                 if !seen_spans.contains(&span) {
 688                     let path = import_path_to_string(&import.module_path[..],
 689                                                      &import.subclass,
 690                                                      span);
 691                     let error = ResolutionError::UnresolvedImport(Some((span, &path, &err)));
 692                     resolve_error(self.resolver, span, error);
 693                     seen_spans.insert(span);
 694                 }
 695             }
 696         }
 697
 698         for ((span, _), (name, results)) in uniform_paths_canaries {
 699             self.per_ns(|this, ns| {
 700                 let results = &results[ns];
 701
 702                 let has_external_crate =
 703                     ns == TypeNS && this.extern_prelude.contains(&name);
 704
 705                 // An ambiguity requires more than one possible resolution.
 706                 let possible_resultions =
 707                     (has_external_crate as usize) +
 708                     (results.module_scope.is_some() as usize) +
 709                     (!results.block_scopes.is_empty() as usize);
 710                 if possible_resultions <= 1 {
 711                     return;
 712                 }
 713
 714                 errors = true;
 715
 716                 // Special-case the error when `self::x` finds its own `use x;`.
 717                 if has_external_crate &&
 718                    results.module_scope == Some(span) &&
 719                    results.block_scopes.is_empty() {
 720                     let msg = format!("`{}` import is redundant", name);
 721                     this.session.struct_span_err(span, &msg)
 722                         .span_label(span,
 723                             format!("refers to external crate `::{}`", name))
 724                         .span_label(span,
 725                             format!("defines `self::{}`, shadowing itself", name))
 726                         .help(&format!("remove or write `::{}` explicitly instead", name))
 727                         .note("relative `use` paths enabled by `#![feature(uniform_paths)]`")
 728                         .emit();
 729                     return;
 730                 }
 731
 732                 let msg = format!("`{}` import is ambiguous", name);
 733                 let mut err = this.session.struct_span_err(span, &msg);
 734                 let mut suggestion_choices = String::new();
 735                 if has_external_crate {
 736                     write!(suggestion_choices, "`::{}`", name);
 737                     err.span_label(span,
 738                         format!("can refer to external crate `::{}`", name));
 739                 }
 740                 if let Some(span) = results.module_scope {
 741                     if !suggestion_choices.is_empty() {
 742                         suggestion_choices.push_str(" or ");
 743                     }
 744                     write!(suggestion_choices, "`self::{}`", name);
 745                     err.span_label(span,
 746                         format!("can refer to `self::{}`", name));
 747                 }
 748                 for &span in &results.block_scopes {
 749                     err.span_label(span,
 750                         format!("shadowed by block-scoped `{}`", name));
 751                 }
 752                 err.help(&format!("write {} explicitly instead", suggestion_choices));
 753                 err.note("relative `use` paths enabled by `#![feature(uniform_paths)]`");
 754                 err.emit();
 755             });
 756         }
 757
 758         // Report unresolved imports only if no hard error was already reported
 759         // to avoid generating multiple errors on the same import.
 760         if !errors {
 761             for import in &self.indeterminate_imports {
 762                 if import.is_uniform_paths_canary {
 763                     continue;
 764                 }
 765
 766                 let error = ResolutionError::UnresolvedImport(None);
 767                 resolve_error(self.resolver, import.span, error);
 768                 break;
 769             }
 770         }
 771     }
 772
 773     /// Attempts to resolve the given import, returning true if its resolution is determined.
 774     /// If successful, the resolved bindings are written into the module.
 775     fn resolve_import(&mut self, directive: &'b ImportDirective<'b>) -> bool {
 776         debug!("(resolving import for module) resolving import `{}::...` in `{}`",
 777                names_to_string(&directive.module_path[..]),
 778                module_to_string(self.current_module).unwrap_or("???".to_string()));
 779
 780         self.current_module = directive.parent;
 781
 782         let module = if let Some(module) = directive.imported_module.get() {
 783             module
 784         } else {
 785             let vis = directive.vis.get();
 786             // For better failure detection, pretend that the import will not define any names
 787             // while resolving its module path.
 788             directive.vis.set(ty::Visibility::Invisible);
 789             let result = self.resolve_path(
 790                 Some(if directive.is_uniform_paths_canary {
 791                     ModuleOrUniformRoot::Module(directive.parent)
 792                 } else {
 793                     ModuleOrUniformRoot::UniformRoot(keywords::Invalid.name())
 794                 }),
 795                 &directive.module_path[..],
 796                 None,
 797                 false,
 798                 directive.span,
 799                 directive.crate_lint(),
 800             );
 801             directive.vis.set(vis);
 802
 803             match result {
 804                 PathResult::Module(module) => module,
 805                 PathResult::Indeterminate => return false,
 806                 _ => return true,
 807             }
 808         };
 809
 810         directive.imported_module.set(Some(module));
 811         let (source, target, result, type_ns_only) = match directive.subclass {
 812             SingleImport { source, target, ref result, type_ns_only } =>
 813                 (source, target, result, type_ns_only),
 814             GlobImport { .. } => {
 815                 self.resolve_glob_import(directive);
 816                 return true;
 817             }
 818             _ => unreachable!(),
 819         };
 820
 821         let mut indeterminate = false;
 822         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 823             if let Err(Undetermined) = result[ns].get() {
 824                 result[ns].set(this.resolve_ident_in_module(module,
 825                                                             source,
 826                                                             ns,
 827                                                             false,
 828                                                             directive.span));
 829             } else {
 830                 return
 831             };
 832
 833             let parent = directive.parent;
 834             match result[ns].get() {
 835                 Err(Undetermined) => indeterminate = true,
 836                 Err(Determined) => {
 837                     this.update_resolution(parent, target, ns, |_, resolution| {
 838                         resolution.single_imports.remove(&PtrKey(directive));
 839                     });
 840                 }
 841                 Ok(binding) if !binding.is_importable() => {
 842                     let msg = format!("`{}` is not directly importable", target);
 843                     struct_span_err!(this.session, directive.span, E0253, "{}", &msg)
 844                         .span_label(directive.span, "cannot be imported directly")
 845                         .emit();
 846                     // Do not import this illegal binding. Import a dummy binding and pretend
 847                     // everything is fine
 848                     this.import_dummy_binding(directive);
 849                 }
 850                 Ok(binding) => {
 851                     let imported_binding = this.import(binding, directive);
 852                     let conflict = this.try_define(parent, target, ns, imported_binding);
 853                     if let Err(old_binding) = conflict {
 854                         this.report_conflict(parent, target, ns, imported_binding, old_binding);
 855                     }
 856                 }
 857             }
 858         });
 859
 860         !indeterminate
 861     }
 862
 863     // If appropriate, returns an error to report.
 864     fn finalize_import(&mut self, directive: &'b ImportDirective<'b>) -> Option<(Span, String)> {
 865         self.current_module = directive.parent;
 866         let ImportDirective { ref module_path, span, .. } = *directive;
 867
 868         let module_result = self.resolve_path(
 869             Some(if directive.is_uniform_paths_canary {
 870                 ModuleOrUniformRoot::Module(directive.parent)
 871             } else {
 872                 ModuleOrUniformRoot::UniformRoot(keywords::Invalid.name())
 873             }),
 874             &module_path,
 875             None,
 876             true,
 877             span,
 878             directive.crate_lint(),
 879         );
 880         let module = match module_result {
 881             PathResult::Module(module) => module,
 882             PathResult::Failed(span, msg, false) => {
 883                 resolve_error(self, span, ResolutionError::FailedToResolve(&msg));
 884                 return None;
 885             }
 886             PathResult::Failed(span, msg, true) => {
 887                 let (mut self_path, mut self_result) = (module_path.clone(), None);
 888                 let is_special = |ident: Ident| ident.is_path_segment_keyword() &&
 889                                                 ident.name != keywords::CrateRoot.name();
 890                 if !self_path.is_empty() && !is_special(self_path[0]) &&
 891                    !(self_path.len() > 1 && is_special(self_path[1])) {
 892                     self_path[0].name = keywords::SelfValue.name();
 893                     self_result = Some(self.resolve_path(None, &self_path, None, false,
 894                                                          span, CrateLint::No));
 895                 }
 896                 return if let Some(PathResult::Module(..)) = self_result {
 897                     Some((span, format!("Did you mean `{}`?", names_to_string(&self_path[..]))))
 898                 } else {
 899                     Some((span, msg))
 900                 };
 901             },
 902             _ => return None,
 903         };
 904
 905         let (ident, result, type_ns_only) = match directive.subclass {
 906             SingleImport { source, ref result, type_ns_only, .. } => (source, result, type_ns_only),
 907             GlobImport { is_prelude, ref max_vis } => {
 908                 if module_path.len() <= 1 {
 909                     // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
 910                     // 2 segments, so the `resolve_path` above won't trigger it.
 911                     let mut full_path = module_path.clone();
 912                     full_path.push(keywords::Invalid.ident());
 913                     self.lint_if_path_starts_with_module(
 914                         directive.crate_lint(),
 915                         &full_path,
 916                         directive.span,
 917                         None,
 918                     );
 919                 }
 920
 921                 if let ModuleOrUniformRoot::Module(module) = module {
 922                     if module.def_id() == directive.parent.def_id() {
 923                         // Importing a module into itself is not allowed.
 924                         return Some((directive.span,
 925                             "Cannot glob-import a module into itself.".to_string()));
 926                     }
 927                 }
 928                 if !is_prelude &&
 929                    max_vis.get() != ty::Visibility::Invisible && // Allow empty globs.
 930                    !max_vis.get().is_at_least(directive.vis.get(), &*self) {
 931                     let msg = "A non-empty glob must import something with the glob's visibility";
 932                     self.session.span_err(directive.span, msg);
 933                 }
 934                 return None;
 935             }
 936             _ => unreachable!(),
 937         };
 938
 939         let mut all_ns_err = true;
 940         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 941             if let Ok(binding) = result[ns].get() {
 942                 all_ns_err = false;
 943                 if this.record_use(ident, ns, binding, directive.span) {
 944                     if let ModuleOrUniformRoot::Module(module) = module {
 945                         this.resolution(module, ident, ns).borrow_mut().binding =
 946                             Some(this.dummy_binding);
 947                     }
 948                 }
 949             }
 950         });
 951
 952         if all_ns_err {
 953             let mut all_ns_failed = true;
 954             self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 955                 match this.resolve_ident_in_module(module, ident, ns, true, span) {
 956                     Ok(_) => all_ns_failed = false,
 957                     _ => {}
 958                 }
 959             });
 960
 961             return if all_ns_failed {
 962                 let resolutions = match module {
 963                     ModuleOrUniformRoot::Module(module) =>
 964                         Some(module.resolutions.borrow()),
 965                     ModuleOrUniformRoot::UniformRoot(_) => None,
 966                 };
 967                 let resolutions = resolutions.as_ref().into_iter().flat_map(|r| r.iter());
 968                 let names = resolutions.filter_map(|(&(ref i, _), resolution)| {
 969                     if *i == ident { return None; } // Never suggest the same name
 970                     match *resolution.borrow() {
 971                         NameResolution { binding: Some(name_binding), .. } => {
 972                             match name_binding.kind {
 973                                 NameBindingKind::Import { binding, .. } => {
 974                                     match binding.kind {
 975                                         // Never suggest the name that has binding error
 976                                         // i.e. the name that cannot be previously resolved
 977                                         NameBindingKind::Def(Def::Err, _) => return None,
 978                                         _ => Some(&i.name),
 979                                     }
 980                                 },
 981                                 _ => Some(&i.name),
 982                             }
 983                         },
 984                         NameResolution { ref single_imports, .. }
 985                             if single_imports.is_empty() => None,
 986                         _ => Some(&i.name),
 987                     }
 988                 });
 989                 let lev_suggestion =
 990                     match find_best_match_for_name(names, &ident.as_str(), None) {
 991                         Some(name) => format!(". Did you mean to use `{}`?", name),
 992                         None => "".to_owned(),
 993                     };
 994                 let msg = match module {
 995                     ModuleOrUniformRoot::Module(module) => {
 996                         let module_str = module_to_string(module);
 997                         if let Some(module_str) = module_str {
 998                             format!("no `{}` in `{}`{}", ident, module_str, lev_suggestion)
 999                         } else {
1000                             format!("no `{}` in the root{}", ident, lev_suggestion)
1001                         }
1002                     }
1003                     ModuleOrUniformRoot::UniformRoot(_) => {
1004                         if !ident.is_path_segment_keyword() {
1005                             format!("no `{}` external crate{}", ident, lev_suggestion)
1006                         } else {
1007                             // HACK(eddyb) this shows up for `self` & `super`, which
1008                             // should work instead - for now keep the same error message.
1009                             format!("no `{}` in the root{}", ident, lev_suggestion)
1010                         }
1011                     }
1012                 };
1013                 Some((span, msg))
1014             } else {
1015                 // `resolve_ident_in_module` reported a privacy error.
1016                 self.import_dummy_binding(directive);
1017                 None
1018             }
1019         }
1020
1021         let mut reexport_error = None;
1022         let mut any_successful_reexport = false;
1023         self.per_ns(|this, ns| {
1024             if let Ok(binding) = result[ns].get() {
1025                 let vis = directive.vis.get();
1026                 if !binding.pseudo_vis().is_at_least(vis, &*this) {
1027                     reexport_error = Some((ns, binding));
1028                 } else {
1029                     any_successful_reexport = true;
1030                 }
1031             }
1032         });
1033
1034         // All namespaces must be re-exported with extra visibility for an error to occur.
1035         if !any_successful_reexport {
1036             let (ns, binding) = reexport_error.unwrap();
1037             if ns == TypeNS && binding.is_extern_crate() {
1038                 let msg = format!("extern crate `{}` is private, and cannot be \
1039                                    re-exported (error E0365), consider declaring with \
1040                                    `pub`",
1041                                    ident);
1042                 self.session.buffer_lint(PUB_USE_OF_PRIVATE_EXTERN_CRATE,
1043                                          directive.id,
1044                                          directive.span,
1045                                          &msg);
1046             } else if ns == TypeNS {
1047                 struct_span_err!(self.session, directive.span, E0365,
1048                                  "`{}` is private, and cannot be re-exported", ident)
1049                     .span_label(directive.span, format!("re-export of private `{}`", ident))
1050                     .note(&format!("consider declaring type or module `{}` with `pub`", ident))
1051                     .emit();
1052             } else {
1053                 let msg = format!("`{}` is private, and cannot be re-exported", ident);
1054                 let note_msg =
1055                     format!("consider marking `{}` as `pub` in the imported module", ident);
1056                 struct_span_err!(self.session, directive.span, E0364, "{}", &msg)
1057                     .span_note(directive.span, &note_msg)
1058                     .emit();
1059             }
1060         }
1061
1062         if module_path.len() <= 1 {
1063             // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
1064             // 2 segments, so the `resolve_path` above won't trigger it.
1065             let mut full_path = module_path.clone();
1066             full_path.push(ident);
1067             self.per_ns(|this, ns| {
1068                 if let Ok(binding) = result[ns].get() {
1069                     this.lint_if_path_starts_with_module(
1070                         directive.crate_lint(),
1071                         &full_path,
1072                         directive.span,
1073                         Some(binding),
1074                     );
1075                 }
1076             });
1077         }
1078
1079         // Record what this import resolves to for later uses in documentation,
1080         // this may resolve to either a value or a type, but for documentation
1081         // purposes it's good enough to just favor one over the other.
1082         self.per_ns(|this, ns| if let Some(binding) = result[ns].get().ok() {
1083             let import = this.import_map.entry(directive.id).or_default();
1084             import[ns] = Some(PathResolution::new(binding.def()));
1085         });
1086
1087         debug!("(resolving single import) successfully resolved import");
1088         None
1089     }
1090
1091     fn resolve_glob_import(&mut self, directive: &'b ImportDirective<'b>) {
1092         let module = match directive.imported_module.get().unwrap() {
1093             ModuleOrUniformRoot::Module(module) => module,
1094             ModuleOrUniformRoot::UniformRoot(_) => {
1095                 self.session.span_err(directive.span,
1096                     "cannot glob-import all possible crates");
1097                 return;
1098             }
1099         };
1100
1101         self.populate_module_if_necessary(module);
1102
1103         if let Some(Def::Trait(_)) = module.def() {
1104             self.session.span_err(directive.span, "items in traits are not importable.");
1105             return;
1106         } else if module.def_id() == directive.parent.def_id()  {
1107             return;
1108         } else if let GlobImport { is_prelude: true, .. } = directive.subclass {
1109             self.prelude = Some(module);
1110             return;
1111         }
1112
1113         // Add to module's glob_importers
1114         module.glob_importers.borrow_mut().push(directive);
1115
1116         // Ensure that `resolutions` isn't borrowed during `try_define`,
1117         // since it might get updated via a glob cycle.
1118         let bindings = module.resolutions.borrow().iter().filter_map(|(&ident, resolution)| {
1119             resolution.borrow().binding().map(|binding| (ident, binding))
1120         }).collect::<Vec<_>>();
1121         for ((mut ident, ns), binding) in bindings {
1122             let scope = match ident.span.reverse_glob_adjust(module.expansion,
1123                                                              directive.span.ctxt().modern()) {
1124                 Some(Some(def)) => self.macro_def_scope(def),
1125                 Some(None) => self.current_module,
1126                 None => continue,
1127             };
1128             if self.is_accessible_from(binding.pseudo_vis(), scope) {
1129                 let imported_binding = self.import(binding, directive);
1130                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
1131             }
1132         }
1133
1134         // Record the destination of this import
1135         self.record_def(directive.id, PathResolution::new(module.def().unwrap()));
1136     }
1137
1138     // Miscellaneous post-processing, including recording re-exports,
1139     // reporting conflicts, and reporting unresolved imports.
1140     fn finalize_resolutions_in(&mut self, module: Module<'b>) {
1141         // Since import resolution is finished, globs will not define any more names.
1142         *module.globs.borrow_mut() = Vec::new();
1143
1144         let mut reexports = Vec::new();
1145         let mut exported_macro_names = FxHashMap();
1146         if ptr::eq(module, self.graph_root) {
1147             let macro_exports = mem::replace(&mut self.macro_exports, Vec::new());
1148             for export in macro_exports.into_iter().rev() {
1149                 if let Some(later_span) = exported_macro_names.insert(export.ident.modern(),
1150                                                                       export.span) {
1151                     self.session.buffer_lint_with_diagnostic(
1152                         DUPLICATE_MACRO_EXPORTS,
1153                         CRATE_NODE_ID,
1154                         later_span,
1155                         &format!("a macro named `{}` has already been exported", export.ident),
1156                         BuiltinLintDiagnostics::DuplicatedMacroExports(
1157                             export.ident, export.span, later_span));
1158                 } else {
1159                     reexports.push(export);
1160                 }
1161             }
1162         }
1163
1164         for (&(ident, ns), resolution) in module.resolutions.borrow().iter() {
1165             let resolution = &mut *resolution.borrow_mut();
1166             let binding = match resolution.binding {
1167                 Some(binding) => binding,
1168                 None => continue,
1169             };
1170
1171             if binding.is_import() || binding.is_macro_def() {
1172                 let def = binding.def();
1173                 if def != Def::Err {
1174                     if !def.def_id().is_local() {
1175                         self.cstore.export_macros_untracked(def.def_id().krate);
1176                     }
1177                     if let Def::Macro(..) = def {
1178                         if let Some(&span) = exported_macro_names.get(&ident.modern()) {
1179                             let msg =
1180                                 format!("a macro named `{}` has already been exported", ident);
1181                             self.session.struct_span_err(span, &msg)
1182                                 .span_label(span, format!("`{}` already exported", ident))
1183                                 .span_note(binding.span, "previous macro export here")
1184                                 .emit();
1185                         }
1186                     }
1187                     reexports.push(Export {
1188                         ident: ident.modern(),
1189                         def: def,
1190                         span: binding.span,
1191                         vis: binding.vis,
1192                     });
1193                 }
1194             }
1195
1196             match binding.kind {
1197                 NameBindingKind::Import { binding: orig_binding, directive, .. } => {
1198                     if ns == TypeNS && orig_binding.is_variant() &&
1199                         !orig_binding.vis.is_at_least(binding.vis, &*self) {
1200                             let msg = match directive.subclass {
1201                                 ImportDirectiveSubclass::SingleImport { .. } => {
1202                                     format!("variant `{}` is private and cannot be re-exported",
1203                                             ident)
1204                                 },
1205                                 ImportDirectiveSubclass::GlobImport { .. } => {
1206                                     let msg = "enum is private and its variants \
1207                                                cannot be re-exported".to_owned();
1208                                     let error_id = (DiagnosticMessageId::ErrorId(0), // no code?!
1209                                                     Some(binding.span),
1210                                                     msg.clone());
1211                                     let fresh = self.session.one_time_diagnostics
1212                                         .borrow_mut().insert(error_id);
1213                                     if !fresh {
1214                                         continue;
1215                                     }
1216                                     msg
1217                                 },
1218                                 ref s @ _ => bug!("unexpected import subclass {:?}", s)
1219                             };
1220                             let mut err = self.session.struct_span_err(binding.span, &msg);
1221
1222                             let imported_module = match directive.imported_module.get() {
1223                                 Some(ModuleOrUniformRoot::Module(module)) => module,
1224                                 _ => bug!("module should exist"),
1225                             };
1226                             let resolutions = imported_module.parent.expect("parent should exist")
1227                                 .resolutions.borrow();
1228                             let enum_path_segment_index = directive.module_path.len() - 1;
1229                             let enum_ident = directive.module_path[enum_path_segment_index];
1230
1231                             let enum_resolution = resolutions.get(&(enum_ident, TypeNS))
1232                                 .expect("resolution should exist");
1233                             let enum_span = enum_resolution.borrow()
1234                                 .binding.expect("binding should exist")
1235                                 .span;
1236                             let enum_def_span = self.session.codemap().def_span(enum_span);
1237                             let enum_def_snippet = self.session.codemap()
1238                                 .span_to_snippet(enum_def_span).expect("snippet should exist");
1239                             // potentially need to strip extant `crate`/`pub(path)` for suggestion
1240                             let after_vis_index = enum_def_snippet.find("enum")
1241                                 .expect("`enum` keyword should exist in snippet");
1242                             let suggestion = format!("pub {}",
1243                                                      &enum_def_snippet[after_vis_index..]);
1244
1245                             self.session
1246                                 .diag_span_suggestion_once(&mut err,
1247                                                            DiagnosticMessageId::ErrorId(0),
1248                                                            enum_def_span,
1249                                                            "consider making the enum public",
1250                                                            suggestion);
1251                             err.emit();
1252                     }
1253                 }
1254                 _ => {}
1255             }
1256         }
1257
1258         if reexports.len() > 0 {
1259             if let Some(def_id) = module.def_id() {
1260                 self.export_map.insert(def_id, reexports);
1261             }
1262         }
1263     }
1264 }
1265
1266 fn import_path_to_string(names: &[Ident],
1267                          subclass: &ImportDirectiveSubclass,
1268                          span: Span) -> String {
1269     let pos = names.iter()
1270         .position(|p| span == p.span && p.name != keywords::CrateRoot.name());
1271     let global = !names.is_empty() && names[0].name == keywords::CrateRoot.name();
1272     if let Some(pos) = pos {
1273         let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
1274         names_to_string(names)
1275     } else {
1276         let names = if global { &names[1..] } else { names };
1277         if names.is_empty() {
1278             import_directive_subclass_to_string(subclass)
1279         } else {
1280             format!("{}::{}",
1281                     names_to_string(names),
1282                     import_directive_subclass_to_string(subclass))
1283         }
1284     }
1285 }
1286
1287 fn import_directive_subclass_to_string(subclass: &ImportDirectiveSubclass) -> String {
1288     match *subclass {
1289         SingleImport { source, .. } => source.to_string(),
1290         GlobImport { .. } => "*".to_string(),
1291         ExternCrate(_) => "<extern crate>".to_string(),
1292         MacroUse => "#[macro_use]".to_string(),
1293     }
1294 }