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::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(binding)
 300                     if !self.is_accessible_from(binding.vis, single_import.parent) => continue,
 301                 Ok(_) | Err(Undetermined) => return Err(Undetermined),
 302             }
 303         }
 304
 305         // So we have a resolution that's from a glob import. This resolution is determined
 306         // if it cannot be shadowed by some new item/import expanded from a macro.
 307         // This happens either if there are no unexpanded macros, or expanded names cannot
 308         // shadow globs (that happens in macro namespace or with restricted shadowing).
 309         //
 310         // Additionally, any macro in any module can plant names in the root module if it creates
 311         // `macro_export` macros, so the root module effectively has unresolved invocations if any
 312         // module has unresolved invocations.
 313         // However, it causes resolution/expansion to stuck too often (#53144), so, to make
 314         // progress, we have to ignore those potential unresolved invocations from other modules
 315         // and prohibit access to macro-expanded `macro_export` macros instead (unless restricted
 316         // shadowing is enabled, see `macro_expanded_macro_export_errors`).
 317         let unexpanded_macros = !module.unresolved_invocations.borrow().is_empty();
 318         if let Some(binding) = resolution.binding {
 319             if !unexpanded_macros || ns == MacroNS || restricted_shadowing {
 320                 return check_usable(self, binding);
 321             } else {
 322                 return Err(Undetermined);
 323             }
 324         }
 325
 326         // --- From now on we have no resolution. ---
 327
 328         // Now we are in situation when new item/import can appear only from a glob or a macro
 329         // expansion. With restricted shadowing names from globs and macro expansions cannot
 330         // shadow names from outer scopes, so we can freely fallback from module search to search
 331         // in outer scopes. To continue search in outer scopes we have to lie a bit and return
 332         // `Determined` to `resolve_lexical_macro_path_segment` even if the correct answer
 333         // for in-module resolution could be `Undetermined`.
 334         if restricted_shadowing {
 335             return Err(Determined);
 336         }
 337
 338         // Check if one of unexpanded macros can still define the name,
 339         // if it can then our "no resolution" result is not determined and can be invalidated.
 340         if unexpanded_macros {
 341             return Err(Undetermined);
 342         }
 343
 344         // Check if one of glob imports can still define the name,
 345         // if it can then our "no resolution" result is not determined and can be invalidated.
 346         for glob_import in module.globs.borrow().iter() {
 347             if !self.is_accessible(glob_import.vis.get()) {
 348                 continue
 349             }
 350             let module = match glob_import.imported_module.get() {
 351                 Some(ModuleOrUniformRoot::Module(module)) => module,
 352                 Some(ModuleOrUniformRoot::UniformRoot(_)) => continue,
 353                 None => return Err(Undetermined),
 354             };
 355             let (orig_current_module, mut ident) = (self.current_module, ident.modern());
 356             match ident.span.glob_adjust(module.expansion, glob_import.span.ctxt().modern()) {
 357                 Some(Some(def)) => self.current_module = self.macro_def_scope(def),
 358                 Some(None) => {}
 359                 None => continue,
 360             };
 361             let result = self.resolve_ident_in_module_unadjusted(
 362                 ModuleOrUniformRoot::Module(module),
 363                 ident,
 364                 ns,
 365                 false,
 366                 false,
 367                 path_span,
 368             );
 369             self.current_module = orig_current_module;
 370
 371             match result {
 372                 Err(Determined) => continue,
 373                 Ok(binding)
 374                     if !self.is_accessible_from(binding.vis, glob_import.parent) => continue,
 375                 Ok(_) | Err(Undetermined) => return Err(Undetermined),
 376             }
 377         }
 378
 379         // No resolution and no one else can define the name - determinate error.
 380         Err(Determined)
 381     }
 382
 383     // Add an import directive to the current module.
 384     pub fn add_import_directive(&mut self,
 385                                 module_path: Vec<Ident>,
 386                                 subclass: ImportDirectiveSubclass<'a>,
 387                                 span: Span,
 388                                 id: NodeId,
 389                                 root_span: Span,
 390                                 root_id: NodeId,
 391                                 vis: ty::Visibility,
 392                                 expansion: Mark,
 393                                 is_uniform_paths_canary: bool) {
 394         let current_module = self.current_module;
 395         let directive = self.arenas.alloc_import_directive(ImportDirective {
 396             parent: current_module,
 397             module_path,
 398             imported_module: Cell::new(None),
 399             subclass,
 400             span,
 401             id,
 402             root_span,
 403             root_id,
 404             vis: Cell::new(vis),
 405             expansion,
 406             used: Cell::new(false),
 407             is_uniform_paths_canary,
 408         });
 409
 410         debug!("add_import_directive({:?})", directive);
 411
 412         self.indeterminate_imports.push(directive);
 413         match directive.subclass {
 414             SingleImport { target, type_ns_only, .. } => {
 415                 self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 416                     let mut resolution = this.resolution(current_module, target, ns).borrow_mut();
 417                     resolution.single_imports.insert(PtrKey(directive));
 418                 });
 419             }
 420             // We don't add prelude imports to the globs since they only affect lexical scopes,
 421             // which are not relevant to import resolution.
 422             GlobImport { is_prelude: true, .. } => {}
 423             GlobImport { .. } => self.current_module.globs.borrow_mut().push(directive),
 424             _ => unreachable!(),
 425         }
 426     }
 427
 428     // Given a binding and an import directive that resolves to it,
 429     // return the corresponding binding defined by the import directive.
 430     pub fn import(&self, binding: &'a NameBinding<'a>, directive: &'a ImportDirective<'a>)
 431                   -> &'a NameBinding<'a> {
 432         let vis = if binding.pseudo_vis().is_at_least(directive.vis.get(), self) ||
 433                      // c.f. `PUB_USE_OF_PRIVATE_EXTERN_CRATE`
 434                      !directive.is_glob() && binding.is_extern_crate() {
 435             directive.vis.get()
 436         } else {
 437             binding.pseudo_vis()
 438         };
 439
 440         if let GlobImport { ref max_vis, .. } = directive.subclass {
 441             if vis == directive.vis.get() || vis.is_at_least(max_vis.get(), self) {
 442                 max_vis.set(vis)
 443             }
 444         }
 445
 446         self.arenas.alloc_name_binding(NameBinding {
 447             kind: NameBindingKind::Import {
 448                 binding,
 449                 directive,
 450                 used: Cell::new(false),
 451             },
 452             span: directive.span,
 453             vis,
 454             expansion: directive.expansion,
 455         })
 456     }
 457
 458     // Define the name or return the existing binding if there is a collision.
 459     pub fn try_define(&mut self,
 460                       module: Module<'a>,
 461                       ident: Ident,
 462                       ns: Namespace,
 463                       binding: &'a NameBinding<'a>)
 464                       -> Result<(), &'a NameBinding<'a>> {
 465         self.update_resolution(module, ident, ns, |this, resolution| {
 466             if let Some(old_binding) = resolution.binding {
 467                 if binding.is_glob_import() {
 468                     if !old_binding.is_glob_import() &&
 469                        !(ns == MacroNS && old_binding.expansion != Mark::root()) {
 470                         resolution.shadowed_glob = Some(binding);
 471                     } else if binding.def() != old_binding.def() {
 472                         resolution.binding = Some(this.ambiguity(old_binding, binding));
 473                     } else if !old_binding.vis.is_at_least(binding.vis, &*this) {
 474                         // We are glob-importing the same item but with greater visibility.
 475                         resolution.binding = Some(binding);
 476                     }
 477                 } else if old_binding.is_glob_import() {
 478                     if ns == MacroNS && binding.expansion != Mark::root() &&
 479                        binding.def() != old_binding.def() {
 480                         resolution.binding = Some(this.ambiguity(binding, old_binding));
 481                     } else {
 482                         resolution.binding = Some(binding);
 483                         resolution.shadowed_glob = Some(old_binding);
 484                     }
 485                 } else if let (&NameBindingKind::Def(_, true), &NameBindingKind::Def(_, true)) =
 486                         (&old_binding.kind, &binding.kind) {
 487
 488                     this.session.buffer_lint_with_diagnostic(
 489                         DUPLICATE_MACRO_EXPORTS,
 490                         CRATE_NODE_ID,
 491                         binding.span,
 492                         &format!("a macro named `{}` has already been exported", ident),
 493                         BuiltinLintDiagnostics::DuplicatedMacroExports(
 494                             ident, old_binding.span, binding.span));
 495
 496                     resolution.binding = Some(binding);
 497                 } else {
 498                     return Err(old_binding);
 499                 }
 500             } else {
 501                 resolution.binding = Some(binding);
 502             }
 503
 504             Ok(())
 505         })
 506     }
 507
 508     pub fn ambiguity(&self, b1: &'a NameBinding<'a>, b2: &'a NameBinding<'a>)
 509                      -> &'a NameBinding<'a> {
 510         self.arenas.alloc_name_binding(NameBinding {
 511             kind: NameBindingKind::Ambiguity { b1, b2 },
 512             vis: if b1.vis.is_at_least(b2.vis, self) { b1.vis } else { b2.vis },
 513             span: b1.span,
 514             expansion: Mark::root(),
 515         })
 516     }
 517
 518     // Use `f` to mutate the resolution of the name in the module.
 519     // If the resolution becomes a success, define it in the module's glob importers.
 520     fn update_resolution<T, F>(&mut self, module: Module<'a>, ident: Ident, ns: Namespace, f: F)
 521                                -> T
 522         where F: FnOnce(&mut Resolver<'a, 'crateloader>, &mut NameResolution<'a>) -> T
 523     {
 524         // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
 525         // during which the resolution might end up getting re-defined via a glob cycle.
 526         let (binding, t) = {
 527             let resolution = &mut *self.resolution(module, ident, ns).borrow_mut();
 528             let old_binding = resolution.binding();
 529
 530             let t = f(self, resolution);
 531
 532             match resolution.binding() {
 533                 _ if old_binding.is_some() => return t,
 534                 None => return t,
 535                 Some(binding) => match old_binding {
 536                     Some(old_binding) if ptr::eq(old_binding, binding) => return t,
 537                     _ => (binding, t),
 538                 }
 539             }
 540         };
 541
 542         // Define `binding` in `module`s glob importers.
 543         for directive in module.glob_importers.borrow_mut().iter() {
 544             let mut ident = ident.modern();
 545             let scope = match ident.span.reverse_glob_adjust(module.expansion,
 546                                                              directive.span.ctxt().modern()) {
 547                 Some(Some(def)) => self.macro_def_scope(def),
 548                 Some(None) => directive.parent,
 549                 None => continue,
 550             };
 551             if self.is_accessible_from(binding.vis, scope) {
 552                 let imported_binding = self.import(binding, directive);
 553                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
 554             }
 555         }
 556
 557         t
 558     }
 559
 560     // Define a "dummy" resolution containing a Def::Err as a placeholder for a
 561     // failed resolution
 562     fn import_dummy_binding(&mut self, directive: &'a ImportDirective<'a>) {
 563         if let SingleImport { target, .. } = directive.subclass {
 564             let dummy_binding = self.dummy_binding;
 565             let dummy_binding = self.import(dummy_binding, directive);
 566             self.per_ns(|this, ns| {
 567                 let _ = this.try_define(directive.parent, target, ns, dummy_binding);
 568             });
 569         }
 570     }
 571 }
 572
 573 pub struct ImportResolver<'a, 'b: 'a, 'c: 'a + 'b> {
 574     pub resolver: &'a mut Resolver<'b, 'c>,
 575 }
 576
 577 impl<'a, 'b: 'a, 'c: 'a + 'b> ::std::ops::Deref for ImportResolver<'a, 'b, 'c> {
 578     type Target = Resolver<'b, 'c>;
 579     fn deref(&self) -> &Resolver<'b, 'c> {
 580         self.resolver
 581     }
 582 }
 583
 584 impl<'a, 'b: 'a, 'c: 'a + 'b> ::std::ops::DerefMut for ImportResolver<'a, 'b, 'c> {
 585     fn deref_mut(&mut self) -> &mut Resolver<'b, 'c> {
 586         self.resolver
 587     }
 588 }
 589
 590 impl<'a, 'b: 'a, 'c: 'a + 'b> ty::DefIdTree for &'a ImportResolver<'a, 'b, 'c> {
 591     fn parent(self, id: DefId) -> Option<DefId> {
 592         self.resolver.parent(id)
 593     }
 594 }
 595
 596 impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
 597     // Import resolution
 598     //
 599     // This is a fixed-point algorithm. We resolve imports until our efforts
 600     // are stymied by an unresolved import; then we bail out of the current
 601     // module and continue. We terminate successfully once no more imports
 602     // remain or unsuccessfully when no forward progress in resolving imports
 603     // is made.
 604
 605     /// Resolves all imports for the crate. This method performs the fixed-
 606     /// point iteration.
 607     pub fn resolve_imports(&mut self) {
 608         let mut prev_num_indeterminates = self.indeterminate_imports.len() + 1;
 609         while self.indeterminate_imports.len() < prev_num_indeterminates {
 610             prev_num_indeterminates = self.indeterminate_imports.len();
 611             for import in mem::replace(&mut self.indeterminate_imports, Vec::new()) {
 612                 match self.resolve_import(&import) {
 613                     true => self.determined_imports.push(import),
 614                     false => self.indeterminate_imports.push(import),
 615                 }
 616             }
 617         }
 618     }
 619
 620     pub fn finalize_imports(&mut self) {
 621         for module in self.arenas.local_modules().iter() {
 622             self.finalize_resolutions_in(module);
 623         }
 624
 625         #[derive(Default)]
 626         struct UniformPathsCanaryResult {
 627             module_scope: Option<Span>,
 628             block_scopes: Vec<Span>,
 629         }
 630         // Collect all tripped `uniform_paths` canaries separately.
 631         let mut uniform_paths_canaries: BTreeMap<
 632             (Span, NodeId),
 633             (Name, PerNS<UniformPathsCanaryResult>),
 634         > = BTreeMap::new();
 635
 636         let mut errors = false;
 637         let mut seen_spans = FxHashSet();
 638         for i in 0 .. self.determined_imports.len() {
 639             let import = self.determined_imports[i];
 640             let error = self.finalize_import(import);
 641
 642             // For a `#![feature(uniform_paths)]` `use self::x as _` canary,
 643             // failure is ignored, while success may cause an ambiguity error.
 644             if import.is_uniform_paths_canary {
 645                 if error.is_some() {
 646                     continue;
 647                 }
 648
 649                 let (name, result) = match import.subclass {
 650                     SingleImport { source, ref result, .. } => (source.name, result),
 651                     _ => bug!(),
 652                 };
 653
 654                 let has_explicit_self =
 655                     import.module_path.len() > 0 &&
 656                     import.module_path[0].name == keywords::SelfValue.name();
 657
 658                 let (prev_name, canary_results) =
 659                     uniform_paths_canaries.entry((import.span, import.id))
 660                         .or_insert((name, PerNS::default()));
 661
 662                 // All the canaries with the same `id` should have the same `name`.
 663                 assert_eq!(*prev_name, name);
 664
 665                 self.per_ns(|_, ns| {
 666                     if let Some(result) = result[ns].get().ok() {
 667                         if has_explicit_self {
 668                             // There should only be one `self::x` (module-scoped) canary.
 669                             assert_eq!(canary_results[ns].module_scope, None);
 670                             canary_results[ns].module_scope = Some(result.span);
 671                         } else {
 672                             canary_results[ns].block_scopes.push(result.span);
 673                         }
 674                     }
 675                 });
 676             } else if let Some((span, err)) = error {
 677                 errors = true;
 678
 679                 if let SingleImport { source, ref result, .. } = import.subclass {
 680                     if source.name == "self" {
 681                         // Silence `unresolved import` error if E0429 is already emitted
 682                         match result.value_ns.get() {
 683                             Err(Determined) => continue,
 684                             _ => {},
 685                         }
 686                     }
 687                 }
 688
 689                 // If the error is a single failed import then create a "fake" import
 690                 // resolution for it so that later resolve stages won't complain.
 691                 self.import_dummy_binding(import);
 692                 if !seen_spans.contains(&span) {
 693                     let path = import_path_to_string(&import.module_path[..],
 694                                                      &import.subclass,
 695                                                      span);
 696                     let error = ResolutionError::UnresolvedImport(Some((span, &path, &err)));
 697                     resolve_error(self.resolver, span, error);
 698                     seen_spans.insert(span);
 699                 }
 700             }
 701         }
 702
 703         for ((span, _), (name, results)) in uniform_paths_canaries {
 704             self.per_ns(|this, ns| {
 705                 let results = &results[ns];
 706
 707                 let has_external_crate =
 708                     ns == TypeNS && this.extern_prelude.contains(&name);
 709
 710                 // An ambiguity requires more than one possible resolution.
 711                 let possible_resultions =
 712                     (has_external_crate as usize) +
 713                     (results.module_scope.is_some() as usize) +
 714                     (!results.block_scopes.is_empty() as usize);
 715                 if possible_resultions <= 1 {
 716                     return;
 717                 }
 718
 719                 errors = true;
 720
 721                 // Special-case the error when `self::x` finds its own `use x;`.
 722                 if has_external_crate &&
 723                    results.module_scope == Some(span) &&
 724                    results.block_scopes.is_empty() {
 725                     let msg = format!("`{}` import is redundant", name);
 726                     this.session.struct_span_err(span, &msg)
 727                         .span_label(span,
 728                             format!("refers to external crate `::{}`", name))
 729                         .span_label(span,
 730                             format!("defines `self::{}`, shadowing itself", name))
 731                         .help(&format!("remove or write `::{}` explicitly instead", name))
 732                         .note("relative `use` paths enabled by `#![feature(uniform_paths)]`")
 733                         .emit();
 734                     return;
 735                 }
 736
 737                 let msg = format!("`{}` import is ambiguous", name);
 738                 let mut err = this.session.struct_span_err(span, &msg);
 739                 let mut suggestion_choices = String::new();
 740                 if has_external_crate {
 741                     write!(suggestion_choices, "`::{}`", name);
 742                     err.span_label(span,
 743                         format!("can refer to external crate `::{}`", name));
 744                 }
 745                 if let Some(span) = results.module_scope {
 746                     if !suggestion_choices.is_empty() {
 747                         suggestion_choices.push_str(" or ");
 748                     }
 749                     write!(suggestion_choices, "`self::{}`", name);
 750                     err.span_label(span,
 751                         format!("can refer to `self::{}`", name));
 752                 }
 753                 for &span in &results.block_scopes {
 754                     err.span_label(span,
 755                         format!("shadowed by block-scoped `{}`", name));
 756                 }
 757                 err.help(&format!("write {} explicitly instead", suggestion_choices));
 758                 err.note("relative `use` paths enabled by `#![feature(uniform_paths)]`");
 759                 err.emit();
 760             });
 761         }
 762
 763         // Report unresolved imports only if no hard error was already reported
 764         // to avoid generating multiple errors on the same import.
 765         if !errors {
 766             for import in &self.indeterminate_imports {
 767                 if import.is_uniform_paths_canary {
 768                     continue;
 769                 }
 770
 771                 let error = ResolutionError::UnresolvedImport(None);
 772                 resolve_error(self.resolver, import.span, error);
 773                 break;
 774             }
 775         }
 776     }
 777
 778     /// Attempts to resolve the given import, returning true if its resolution is determined.
 779     /// If successful, the resolved bindings are written into the module.
 780     fn resolve_import(&mut self, directive: &'b ImportDirective<'b>) -> bool {
 781         debug!("(resolving import for module) resolving import `{}::...` in `{}`",
 782                names_to_string(&directive.module_path[..]),
 783                module_to_string(self.current_module).unwrap_or("???".to_string()));
 784
 785         self.current_module = directive.parent;
 786
 787         let module = if let Some(module) = directive.imported_module.get() {
 788             module
 789         } else {
 790             let vis = directive.vis.get();
 791             // For better failure detection, pretend that the import will not define any names
 792             // while resolving its module path.
 793             directive.vis.set(ty::Visibility::Invisible);
 794             let result = self.resolve_path(
 795                 Some(if directive.is_uniform_paths_canary {
 796                     ModuleOrUniformRoot::Module(directive.parent)
 797                 } else {
 798                     ModuleOrUniformRoot::UniformRoot(keywords::Invalid.name())
 799                 }),
 800                 &directive.module_path[..],
 801                 None,
 802                 false,
 803                 directive.span,
 804                 directive.crate_lint(),
 805             );
 806             directive.vis.set(vis);
 807
 808             match result {
 809                 PathResult::Module(module) => module,
 810                 PathResult::Indeterminate => return false,
 811                 _ => return true,
 812             }
 813         };
 814
 815         directive.imported_module.set(Some(module));
 816         let (source, target, result, type_ns_only) = match directive.subclass {
 817             SingleImport { source, target, ref result, type_ns_only } =>
 818                 (source, target, result, type_ns_only),
 819             GlobImport { .. } => {
 820                 self.resolve_glob_import(directive);
 821                 return true;
 822             }
 823             _ => unreachable!(),
 824         };
 825
 826         let mut indeterminate = false;
 827         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 828             if let Err(Undetermined) = result[ns].get() {
 829                 result[ns].set(this.resolve_ident_in_module(module,
 830                                                             source,
 831                                                             ns,
 832                                                             false,
 833                                                             directive.span));
 834             } else {
 835                 return
 836             };
 837
 838             let parent = directive.parent;
 839             match result[ns].get() {
 840                 Err(Undetermined) => indeterminate = true,
 841                 Err(Determined) => {
 842                     this.update_resolution(parent, target, ns, |_, resolution| {
 843                         resolution.single_imports.remove(&PtrKey(directive));
 844                     });
 845                 }
 846                 Ok(binding) if !binding.is_importable() => {
 847                     let msg = format!("`{}` is not directly importable", target);
 848                     struct_span_err!(this.session, directive.span, E0253, "{}", &msg)
 849                         .span_label(directive.span, "cannot be imported directly")
 850                         .emit();
 851                     // Do not import this illegal binding. Import a dummy binding and pretend
 852                     // everything is fine
 853                     this.import_dummy_binding(directive);
 854                 }
 855                 Ok(binding) => {
 856                     let imported_binding = this.import(binding, directive);
 857                     let conflict = this.try_define(parent, target, ns, imported_binding);
 858                     if let Err(old_binding) = conflict {
 859                         this.report_conflict(parent, target, ns, imported_binding, old_binding);
 860                     }
 861                 }
 862             }
 863         });
 864
 865         !indeterminate
 866     }
 867
 868     // If appropriate, returns an error to report.
 869     fn finalize_import(&mut self, directive: &'b ImportDirective<'b>) -> Option<(Span, String)> {
 870         self.current_module = directive.parent;
 871         let ImportDirective { ref module_path, span, .. } = *directive;
 872
 873         let module_result = self.resolve_path(
 874             Some(if directive.is_uniform_paths_canary {
 875                 ModuleOrUniformRoot::Module(directive.parent)
 876             } else {
 877                 ModuleOrUniformRoot::UniformRoot(keywords::Invalid.name())
 878             }),
 879             &module_path,
 880             None,
 881             true,
 882             span,
 883             directive.crate_lint(),
 884         );
 885         let module = match module_result {
 886             PathResult::Module(module) => module,
 887             PathResult::Failed(span, msg, false) => {
 888                 resolve_error(self, span, ResolutionError::FailedToResolve(&msg));
 889                 return None;
 890             }
 891             PathResult::Failed(span, msg, true) => {
 892                 let (mut self_path, mut self_result) = (module_path.clone(), None);
 893                 let is_special = |ident: Ident| ident.is_path_segment_keyword() &&
 894                                                 ident.name != keywords::CrateRoot.name();
 895                 if !self_path.is_empty() && !is_special(self_path[0]) &&
 896                    !(self_path.len() > 1 && is_special(self_path[1])) {
 897                     self_path[0].name = keywords::SelfValue.name();
 898                     self_result = Some(self.resolve_path(None, &self_path, None, false,
 899                                                          span, CrateLint::No));
 900                 }
 901                 return if let Some(PathResult::Module(..)) = self_result {
 902                     Some((span, format!("Did you mean `{}`?", names_to_string(&self_path[..]))))
 903                 } else {
 904                     Some((span, msg))
 905                 };
 906             },
 907             _ => return None,
 908         };
 909
 910         let (ident, result, type_ns_only) = match directive.subclass {
 911             SingleImport { source, ref result, type_ns_only, .. } => (source, result, type_ns_only),
 912             GlobImport { is_prelude, ref max_vis } => {
 913                 if module_path.len() <= 1 {
 914                     // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
 915                     // 2 segments, so the `resolve_path` above won't trigger it.
 916                     let mut full_path = module_path.clone();
 917                     full_path.push(keywords::Invalid.ident());
 918                     self.lint_if_path_starts_with_module(
 919                         directive.crate_lint(),
 920                         &full_path,
 921                         directive.span,
 922                         None,
 923                     );
 924                 }
 925
 926                 if let ModuleOrUniformRoot::Module(module) = module {
 927                     if module.def_id() == directive.parent.def_id() {
 928                         // Importing a module into itself is not allowed.
 929                         return Some((directive.span,
 930                             "Cannot glob-import a module into itself.".to_string()));
 931                     }
 932                 }
 933                 if !is_prelude &&
 934                    max_vis.get() != ty::Visibility::Invisible && // Allow empty globs.
 935                    !max_vis.get().is_at_least(directive.vis.get(), &*self) {
 936                     let msg = "A non-empty glob must import something with the glob's visibility";
 937                     self.session.span_err(directive.span, msg);
 938                 }
 939                 return None;
 940             }
 941             _ => unreachable!(),
 942         };
 943
 944         let mut all_ns_err = true;
 945         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 946             if let Ok(binding) = result[ns].get() {
 947                 all_ns_err = false;
 948                 if this.record_use(ident, ns, binding, directive.span) {
 949                     if let ModuleOrUniformRoot::Module(module) = module {
 950                         this.resolution(module, ident, ns).borrow_mut().binding =
 951                             Some(this.dummy_binding);
 952                     }
 953                 }
 954             }
 955         });
 956
 957         if all_ns_err {
 958             let mut all_ns_failed = true;
 959             self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
 960                 match this.resolve_ident_in_module(module, ident, ns, true, span) {
 961                     Ok(_) => all_ns_failed = false,
 962                     _ => {}
 963                 }
 964             });
 965
 966             return if all_ns_failed {
 967                 let resolutions = match module {
 968                     ModuleOrUniformRoot::Module(module) =>
 969                         Some(module.resolutions.borrow()),
 970                     ModuleOrUniformRoot::UniformRoot(_) => None,
 971                 };
 972                 let resolutions = resolutions.as_ref().into_iter().flat_map(|r| r.iter());
 973                 let names = resolutions.filter_map(|(&(ref i, _), resolution)| {
 974                     if *i == ident { return None; } // Never suggest the same name
 975                     match *resolution.borrow() {
 976                         NameResolution { binding: Some(name_binding), .. } => {
 977                             match name_binding.kind {
 978                                 NameBindingKind::Import { binding, .. } => {
 979                                     match binding.kind {
 980                                         // Never suggest the name that has binding error
 981                                         // i.e. the name that cannot be previously resolved
 982                                         NameBindingKind::Def(Def::Err, _) => return None,
 983                                         _ => Some(&i.name),
 984                                     }
 985                                 },
 986                                 _ => Some(&i.name),
 987                             }
 988                         },
 989                         NameResolution { ref single_imports, .. }
 990                             if single_imports.is_empty() => None,
 991                         _ => Some(&i.name),
 992                     }
 993                 });
 994                 let lev_suggestion =
 995                     match find_best_match_for_name(names, &ident.as_str(), None) {
 996                         Some(name) => format!(". Did you mean to use `{}`?", name),
 997                         None => String::new(),
 998                     };
 999                 let msg = match module {
1000                     ModuleOrUniformRoot::Module(module) => {
1001                         let module_str = module_to_string(module);
1002                         if let Some(module_str) = module_str {
1003                             format!("no `{}` in `{}`{}", ident, module_str, lev_suggestion)
1004                         } else {
1005                             format!("no `{}` in the root{}", ident, lev_suggestion)
1006                         }
1007                     }
1008                     ModuleOrUniformRoot::UniformRoot(_) => {
1009                         if !ident.is_path_segment_keyword() {
1010                             format!("no `{}` external crate{}", ident, lev_suggestion)
1011                         } else {
1012                             // HACK(eddyb) this shows up for `self` & `super`, which
1013                             // should work instead - for now keep the same error message.
1014                             format!("no `{}` in the root{}", ident, lev_suggestion)
1015                         }
1016                     }
1017                 };
1018                 Some((span, msg))
1019             } else {
1020                 // `resolve_ident_in_module` reported a privacy error.
1021                 self.import_dummy_binding(directive);
1022                 None
1023             }
1024         }
1025
1026         let mut reexport_error = None;
1027         let mut any_successful_reexport = false;
1028         self.per_ns(|this, ns| {
1029             if let Ok(binding) = result[ns].get() {
1030                 let vis = directive.vis.get();
1031                 if !binding.pseudo_vis().is_at_least(vis, &*this) {
1032                     reexport_error = Some((ns, binding));
1033                 } else {
1034                     any_successful_reexport = true;
1035                 }
1036             }
1037         });
1038
1039         // All namespaces must be re-exported with extra visibility for an error to occur.
1040         if !any_successful_reexport {
1041             let (ns, binding) = reexport_error.unwrap();
1042             if ns == TypeNS && binding.is_extern_crate() {
1043                 let msg = format!("extern crate `{}` is private, and cannot be \
1044                                    re-exported (error E0365), consider declaring with \
1045                                    `pub`",
1046                                    ident);
1047                 self.session.buffer_lint(PUB_USE_OF_PRIVATE_EXTERN_CRATE,
1048                                          directive.id,
1049                                          directive.span,
1050                                          &msg);
1051             } else if ns == TypeNS {
1052                 struct_span_err!(self.session, directive.span, E0365,
1053                                  "`{}` is private, and cannot be re-exported", ident)
1054                     .span_label(directive.span, format!("re-export of private `{}`", ident))
1055                     .note(&format!("consider declaring type or module `{}` with `pub`", ident))
1056                     .emit();
1057             } else {
1058                 let msg = format!("`{}` is private, and cannot be re-exported", ident);
1059                 let note_msg =
1060                     format!("consider marking `{}` as `pub` in the imported module", ident);
1061                 struct_span_err!(self.session, directive.span, E0364, "{}", &msg)
1062                     .span_note(directive.span, &note_msg)
1063                     .emit();
1064             }
1065         }
1066
1067         if module_path.len() <= 1 {
1068             // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
1069             // 2 segments, so the `resolve_path` above won't trigger it.
1070             let mut full_path = module_path.clone();
1071             full_path.push(ident);
1072             self.per_ns(|this, ns| {
1073                 if let Ok(binding) = result[ns].get() {
1074                     this.lint_if_path_starts_with_module(
1075                         directive.crate_lint(),
1076                         &full_path,
1077                         directive.span,
1078                         Some(binding),
1079                     );
1080                 }
1081             });
1082         }
1083
1084         // Record what this import resolves to for later uses in documentation,
1085         // this may resolve to either a value or a type, but for documentation
1086         // purposes it's good enough to just favor one over the other.
1087         self.per_ns(|this, ns| if let Some(binding) = result[ns].get().ok() {
1088             let import = this.import_map.entry(directive.id).or_default();
1089             import[ns] = Some(PathResolution::new(binding.def()));
1090         });
1091
1092         debug!("(resolving single import) successfully resolved import");
1093         None
1094     }
1095
1096     fn resolve_glob_import(&mut self, directive: &'b ImportDirective<'b>) {
1097         let module = match directive.imported_module.get().unwrap() {
1098             ModuleOrUniformRoot::Module(module) => module,
1099             ModuleOrUniformRoot::UniformRoot(_) => {
1100                 self.session.span_err(directive.span,
1101                     "cannot glob-import all possible crates");
1102                 return;
1103             }
1104         };
1105
1106         self.populate_module_if_necessary(module);
1107
1108         if let Some(Def::Trait(_)) = module.def() {
1109             self.session.span_err(directive.span, "items in traits are not importable.");
1110             return;
1111         } else if module.def_id() == directive.parent.def_id()  {
1112             return;
1113         } else if let GlobImport { is_prelude: true, .. } = directive.subclass {
1114             self.prelude = Some(module);
1115             return;
1116         }
1117
1118         // Add to module's glob_importers
1119         module.glob_importers.borrow_mut().push(directive);
1120
1121         // Ensure that `resolutions` isn't borrowed during `try_define`,
1122         // since it might get updated via a glob cycle.
1123         let bindings = module.resolutions.borrow().iter().filter_map(|(&ident, resolution)| {
1124             resolution.borrow().binding().map(|binding| (ident, binding))
1125         }).collect::<Vec<_>>();
1126         for ((mut ident, ns), binding) in bindings {
1127             let scope = match ident.span.reverse_glob_adjust(module.expansion,
1128                                                              directive.span.ctxt().modern()) {
1129                 Some(Some(def)) => self.macro_def_scope(def),
1130                 Some(None) => self.current_module,
1131                 None => continue,
1132             };
1133             if self.is_accessible_from(binding.pseudo_vis(), scope) {
1134                 let imported_binding = self.import(binding, directive);
1135                 let _ = self.try_define(directive.parent, ident, ns, imported_binding);
1136             }
1137         }
1138
1139         // Record the destination of this import
1140         self.record_def(directive.id, PathResolution::new(module.def().unwrap()));
1141     }
1142
1143     // Miscellaneous post-processing, including recording re-exports,
1144     // reporting conflicts, and reporting unresolved imports.
1145     fn finalize_resolutions_in(&mut self, module: Module<'b>) {
1146         // Since import resolution is finished, globs will not define any more names.
1147         *module.globs.borrow_mut() = Vec::new();
1148
1149         let mut reexports = Vec::new();
1150
1151         for (&(ident, ns), resolution) in module.resolutions.borrow().iter() {
1152             let resolution = &mut *resolution.borrow_mut();
1153             let binding = match resolution.binding {
1154                 Some(binding) => binding,
1155                 None => continue,
1156             };
1157
1158             if binding.is_import() || binding.is_macro_def() {
1159                 let def = binding.def();
1160                 if def != Def::Err {
1161                     if !def.def_id().is_local() {
1162                         self.cstore.export_macros_untracked(def.def_id().krate);
1163                     }
1164                     reexports.push(Export {
1165                         ident: ident.modern(),
1166                         def: def,
1167                         span: binding.span,
1168                         vis: binding.vis,
1169                     });
1170                 }
1171             }
1172
1173             match binding.kind {
1174                 NameBindingKind::Import { binding: orig_binding, directive, .. } => {
1175                     if ns == TypeNS && orig_binding.is_variant() &&
1176                         !orig_binding.vis.is_at_least(binding.vis, &*self) {
1177                             let msg = match directive.subclass {
1178                                 ImportDirectiveSubclass::SingleImport { .. } => {
1179                                     format!("variant `{}` is private and cannot be re-exported",
1180                                             ident)
1181                                 },
1182                                 ImportDirectiveSubclass::GlobImport { .. } => {
1183                                     let msg = "enum is private and its variants \
1184                                                cannot be re-exported".to_owned();
1185                                     let error_id = (DiagnosticMessageId::ErrorId(0), // no code?!
1186                                                     Some(binding.span),
1187                                                     msg.clone());
1188                                     let fresh = self.session.one_time_diagnostics
1189                                         .borrow_mut().insert(error_id);
1190                                     if !fresh {
1191                                         continue;
1192                                     }
1193                                     msg
1194                                 },
1195                                 ref s @ _ => bug!("unexpected import subclass {:?}", s)
1196                             };
1197                             let mut err = self.session.struct_span_err(binding.span, &msg);
1198
1199                             let imported_module = match directive.imported_module.get() {
1200                                 Some(ModuleOrUniformRoot::Module(module)) => module,
1201                                 _ => bug!("module should exist"),
1202                             };
1203                             let resolutions = imported_module.parent.expect("parent should exist")
1204                                 .resolutions.borrow();
1205                             let enum_path_segment_index = directive.module_path.len() - 1;
1206                             let enum_ident = directive.module_path[enum_path_segment_index];
1207
1208                             let enum_resolution = resolutions.get(&(enum_ident, TypeNS))
1209                                 .expect("resolution should exist");
1210                             let enum_span = enum_resolution.borrow()
1211                                 .binding.expect("binding should exist")
1212                                 .span;
1213                             let enum_def_span = self.session.source_map().def_span(enum_span);
1214                             let enum_def_snippet = self.session.source_map()
1215                                 .span_to_snippet(enum_def_span).expect("snippet should exist");
1216                             // potentially need to strip extant `crate`/`pub(path)` for suggestion
1217                             let after_vis_index = enum_def_snippet.find("enum")
1218                                 .expect("`enum` keyword should exist in snippet");
1219                             let suggestion = format!("pub {}",
1220                                                      &enum_def_snippet[after_vis_index..]);
1221
1222                             self.session
1223                                 .diag_span_suggestion_once(&mut err,
1224                                                            DiagnosticMessageId::ErrorId(0),
1225                                                            enum_def_span,
1226                                                            "consider making the enum public",
1227                                                            suggestion);
1228                             err.emit();
1229                     }
1230                 }
1231                 _ => {}
1232             }
1233         }
1234
1235         if reexports.len() > 0 {
1236             if let Some(def_id) = module.def_id() {
1237                 self.export_map.insert(def_id, reexports);
1238             }
1239         }
1240     }
1241 }
1242
1243 fn import_path_to_string(names: &[Ident],
1244                          subclass: &ImportDirectiveSubclass,
1245                          span: Span) -> String {
1246     let pos = names.iter()
1247         .position(|p| span == p.span && p.name != keywords::CrateRoot.name());
1248     let global = !names.is_empty() && names[0].name == keywords::CrateRoot.name();
1249     if let Some(pos) = pos {
1250         let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
1251         names_to_string(names)
1252     } else {
1253         let names = if global { &names[1..] } else { names };
1254         if names.is_empty() {
1255             import_directive_subclass_to_string(subclass)
1256         } else {
1257             format!("{}::{}",
1258                     names_to_string(names),
1259                     import_directive_subclass_to_string(subclass))
1260         }
1261     }
1262 }
1263
1264 fn import_directive_subclass_to_string(subclass: &ImportDirectiveSubclass) -> String {
1265     match *subclass {
1266         SingleImport { source, .. } => source.to_string(),
1267         GlobImport { .. } => "*".to_string(),
1268         ExternCrate(_) => "<extern crate>".to_string(),
1269         MacroUse => "#[macro_use]".to_string(),
1270     }
1271 }