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 DefModifiers;
  14 use Module;
  15 use Namespace::{self, TypeNS, ValueNS};
  16 use {NameBinding, NameBindingKind};
  17 use ResolveResult;
  18 use ResolveResult::*;
  19 use Resolver;
  20 use UseLexicalScopeFlag;
  21 use {names_to_string, module_to_string};
  22 use {resolve_error, ResolutionError};
  23
  24 use build_reduced_graph;
  25
  26 use rustc::lint;
  27 use rustc::middle::def::*;
  28 use rustc::middle::privacy::*;
  29
  30 use syntax::ast::{NodeId, Name};
  31 use syntax::attr::AttrMetaMethods;
  32 use syntax::codemap::Span;
  33 use syntax::util::lev_distance::find_best_match_for_name;
  34
  35 use std::mem::replace;
  36
  37 /// Contains data for specific types of import directives.
  38 #[derive(Copy, Clone,Debug)]
  39 pub enum ImportDirectiveSubclass {
  40     SingleImport(Name /* target */, Name /* source */),
  41     GlobImport,
  42 }
  43
  44 /// Whether an import can be shadowed by another import.
  45 #[derive(Debug,PartialEq,Clone,Copy)]
  46 pub enum Shadowable {
  47     Always,
  48     Never,
  49 }
  50
  51 /// One import directive.
  52 #[derive(Debug,Clone)]
  53 pub struct ImportDirective {
  54     pub module_path: Vec<Name>,
  55     pub subclass: ImportDirectiveSubclass,
  56     pub span: Span,
  57     pub id: NodeId,
  58     pub is_public: bool, // see note in ImportResolutionPerNamespace about how to use this
  59     pub shadowable: Shadowable,
  60 }
  61
  62 impl ImportDirective {
  63     pub fn new(module_path: Vec<Name>,
  64                subclass: ImportDirectiveSubclass,
  65                span: Span,
  66                id: NodeId,
  67                is_public: bool,
  68                shadowable: Shadowable)
  69                -> ImportDirective {
  70         ImportDirective {
  71             module_path: module_path,
  72             subclass: subclass,
  73             span: span,
  74             id: id,
  75             is_public: is_public,
  76             shadowable: shadowable,
  77         }
  78     }
  79
  80     // Given the binding to which this directive resolves in a particular namespace,
  81     // this returns the binding for the name this directive defines in that namespace.
  82     fn import<'a>(&self, binding: &'a NameBinding<'a>) -> NameBinding<'a> {
  83         let mut modifiers = match self.is_public {
  84             true => DefModifiers::PUBLIC | DefModifiers::IMPORTABLE,
  85             false => DefModifiers::empty(),
  86         };
  87         if let GlobImport = self.subclass {
  88             modifiers = modifiers | DefModifiers::GLOB_IMPORTED;
  89         }
  90         if self.shadowable == Shadowable::Always {
  91             modifiers = modifiers | DefModifiers::PRELUDE;
  92         }
  93
  94         NameBinding {
  95             kind: NameBindingKind::Import { binding: binding, id: self.id },
  96             span: Some(self.span),
  97             modifiers: modifiers,
  98         }
  99     }
 100 }
 101
 102 #[derive(Clone, Default)]
 103 /// Records information about the resolution of a name in a module.
 104 pub struct NameResolution<'a> {
 105     /// The number of unresolved single imports that could define the name.
 106     pub outstanding_references: usize,
 107     /// The least shadowable known binding for this name, or None if there are no known bindings.
 108     pub binding: Option<&'a NameBinding<'a>>,
 109 }
 110
 111 impl<'a> NameResolution<'a> {
 112     pub fn result(&self, outstanding_globs: usize) -> ResolveResult<&'a NameBinding<'a>> {
 113         // If no unresolved imports (single or glob) can define the name, self.binding is final.
 114         if self.outstanding_references == 0 && outstanding_globs == 0 {
 115             return self.binding.map(Success).unwrap_or(Failed(None));
 116         }
 117
 118         if let Some(binding) = self.binding {
 119             // Single imports will never be shadowable by other single or glob imports.
 120             if !binding.defined_with(DefModifiers::GLOB_IMPORTED) { return Success(binding); }
 121             // Non-PRELUDE glob imports will never be shadowable by other glob imports.
 122             if self.outstanding_references == 0 && !binding.defined_with(DefModifiers::PRELUDE) {
 123                 return Success(binding);
 124             }
 125         }
 126
 127         Indeterminate
 128     }
 129
 130     // Define the name or return the existing binding if there is a collision.
 131     pub fn try_define(&mut self, binding: &'a NameBinding<'a>) -> Result<(), &'a NameBinding<'a>> {
 132         let is_prelude = |binding: &NameBinding| binding.defined_with(DefModifiers::PRELUDE);
 133         let old_binding = match self.binding {
 134             Some(_) if is_prelude(binding) => return Ok(()),
 135             Some(old_binding) if !is_prelude(old_binding) => old_binding,
 136             _ => { self.binding = Some(binding); return Ok(()); }
 137         };
 138
 139         // FIXME #31337: We currently allow items to shadow glob-imported re-exports.
 140         if !old_binding.is_import() && binding.defined_with(DefModifiers::GLOB_IMPORTED) {
 141             if let NameBindingKind::Import { binding, .. } = binding.kind {
 142                 if binding.is_import() { return Ok(()); }
 143             }
 144         }
 145
 146         Err(old_binding)
 147     }
 148 }
 149
 150 struct ImportResolvingError<'a> {
 151     /// Module where the error happened
 152     source_module: Module<'a>,
 153     import_directive: ImportDirective,
 154     span: Span,
 155     help: String,
 156 }
 157
 158 struct ImportResolver<'a, 'b: 'a, 'tcx: 'b> {
 159     resolver: &'a mut Resolver<'b, 'tcx>,
 160 }
 161
 162 impl<'a, 'b:'a, 'tcx:'b> ImportResolver<'a, 'b, 'tcx> {
 163     // Import resolution
 164     //
 165     // This is a fixed-point algorithm. We resolve imports until our efforts
 166     // are stymied by an unresolved import; then we bail out of the current
 167     // module and continue. We terminate successfully once no more imports
 168     // remain or unsuccessfully when no forward progress in resolving imports
 169     // is made.
 170
 171     /// Resolves all imports for the crate. This method performs the fixed-
 172     /// point iteration.
 173     fn resolve_imports(&mut self) {
 174         let mut i = 0;
 175         let mut prev_unresolved_imports = 0;
 176         loop {
 177             debug!("(resolving imports) iteration {}, {} imports left",
 178                    i,
 179                    self.resolver.unresolved_imports);
 180
 181             let module_root = self.resolver.graph_root;
 182             let errors = self.resolve_imports_for_module_subtree(module_root);
 183
 184             if self.resolver.unresolved_imports == 0 {
 185                 debug!("(resolving imports) success");
 186                 break;
 187             }
 188
 189             if self.resolver.unresolved_imports == prev_unresolved_imports {
 190                 // resolving failed
 191                 if errors.len() > 0 {
 192                     for e in errors {
 193                         self.import_resolving_error(e)
 194                     }
 195                 } else {
 196                     // Report unresolved imports only if no hard error was already reported
 197                     // to avoid generating multiple errors on the same import.
 198                     // Imports that are still indeterminate at this point are actually blocked
 199                     // by errored imports, so there is no point reporting them.
 200                     self.resolver.report_unresolved_imports(module_root);
 201                 }
 202                 break;
 203             }
 204
 205             i += 1;
 206             prev_unresolved_imports = self.resolver.unresolved_imports;
 207         }
 208     }
 209
 210     /// Resolves an `ImportResolvingError` into the correct enum discriminant
 211     /// and passes that on to `resolve_error`.
 212     fn import_resolving_error(&self, e: ImportResolvingError<'b>) {
 213         // If it's a single failed import then create a "fake" import
 214         // resolution for it so that later resolve stages won't complain.
 215         if let SingleImport(target, _) = e.import_directive.subclass {
 216             let dummy_binding = self.resolver.new_name_binding(NameBinding {
 217                 modifiers: DefModifiers::PRELUDE,
 218                 kind: NameBindingKind::Def(Def::Err),
 219                 span: None,
 220             });
 221
 222             let _ = e.source_module.try_define_child(target, ValueNS, dummy_binding);
 223             let _ = e.source_module.try_define_child(target, TypeNS, dummy_binding);
 224         }
 225
 226         let path = import_path_to_string(&e.import_directive.module_path,
 227                                          e.import_directive.subclass);
 228
 229         resolve_error(self.resolver,
 230                       e.span,
 231                       ResolutionError::UnresolvedImport(Some((&path, &e.help))));
 232     }
 233
 234     /// Attempts to resolve imports for the given module and all of its
 235     /// submodules.
 236     fn resolve_imports_for_module_subtree(&mut self,
 237                                           module_: Module<'b>)
 238                                           -> Vec<ImportResolvingError<'b>> {
 239         let mut errors = Vec::new();
 240         debug!("(resolving imports for module subtree) resolving {}",
 241                module_to_string(&module_));
 242         let orig_module = replace(&mut self.resolver.current_module, module_);
 243         errors.extend(self.resolve_imports_for_module(module_));
 244         self.resolver.current_module = orig_module;
 245
 246         for (_, child_module) in module_.module_children.borrow().iter() {
 247             errors.extend(self.resolve_imports_for_module_subtree(child_module));
 248         }
 249
 250         errors
 251     }
 252
 253     /// Attempts to resolve imports for the given module only.
 254     fn resolve_imports_for_module(&mut self, module: Module<'b>) -> Vec<ImportResolvingError<'b>> {
 255         let mut errors = Vec::new();
 256
 257         if module.all_imports_resolved() {
 258             debug!("(resolving imports for module) all imports resolved for {}",
 259                    module_to_string(&module));
 260             return errors;
 261         }
 262
 263         let mut imports = module.imports.borrow_mut();
 264         let import_count = imports.len();
 265         let mut indeterminate_imports = Vec::new();
 266         while module.resolved_import_count.get() + indeterminate_imports.len() < import_count {
 267             let import_index = module.resolved_import_count.get();
 268             match self.resolve_import_for_module(module, &imports[import_index]) {
 269                 ResolveResult::Failed(err) => {
 270                     let import_directive = &imports[import_index];
 271                     let (span, help) = match err {
 272                         Some((span, msg)) => (span, format!(". {}", msg)),
 273                         None => (import_directive.span, String::new()),
 274                     };
 275                     errors.push(ImportResolvingError {
 276                         source_module: module,
 277                         import_directive: import_directive.clone(),
 278                         span: span,
 279                         help: help,
 280                     });
 281                 }
 282                 ResolveResult::Indeterminate => {}
 283                 ResolveResult::Success(()) => {
 284                     // count success
 285                     module.resolved_import_count
 286                           .set(module.resolved_import_count.get() + 1);
 287                     continue;
 288                 }
 289             }
 290             // This resolution was not successful, keep it for later
 291             indeterminate_imports.push(imports.swap_remove(import_index));
 292
 293         }
 294
 295         imports.extend(indeterminate_imports);
 296
 297         errors
 298     }
 299
 300     /// Attempts to resolve the given import. The return value indicates
 301     /// failure if we're certain the name does not exist, indeterminate if we
 302     /// don't know whether the name exists at the moment due to other
 303     /// currently-unresolved imports, or success if we know the name exists.
 304     /// If successful, the resolved bindings are written into the module.
 305     fn resolve_import_for_module(&mut self,
 306                                  module_: Module<'b>,
 307                                  import_directive: &ImportDirective)
 308                                  -> ResolveResult<()> {
 309         debug!("(resolving import for module) resolving import `{}::...` in `{}`",
 310                names_to_string(&import_directive.module_path),
 311                module_to_string(&module_));
 312
 313         self.resolver
 314             .resolve_module_path(module_,
 315                                  &import_directive.module_path,
 316                                  UseLexicalScopeFlag::DontUseLexicalScope,
 317                                  import_directive.span)
 318             .and_then(|(containing_module, lp)| {
 319                 // We found the module that the target is contained
 320                 // within. Attempt to resolve the import within it.
 321                 if let SingleImport(target, source) = import_directive.subclass {
 322                     self.resolve_single_import(module_,
 323                                                containing_module,
 324                                                target,
 325                                                source,
 326                                                import_directive,
 327                                                lp)
 328                 } else {
 329                     self.resolve_glob_import(module_, containing_module, import_directive, lp)
 330                 }
 331             })
 332             .and_then(|()| {
 333                 // Decrement the count of unresolved imports.
 334                 assert!(self.resolver.unresolved_imports >= 1);
 335                 self.resolver.unresolved_imports -= 1;
 336
 337                 if let GlobImport = import_directive.subclass {
 338                     module_.dec_glob_count();
 339                     if import_directive.is_public {
 340                         module_.dec_pub_glob_count();
 341                     }
 342                 }
 343                 if import_directive.is_public {
 344                     module_.dec_pub_count();
 345                 }
 346                 Success(())
 347             })
 348     }
 349
 350     fn resolve_single_import(&mut self,
 351                              module_: Module<'b>,
 352                              target_module: Module<'b>,
 353                              target: Name,
 354                              source: Name,
 355                              directive: &ImportDirective,
 356                              lp: LastPrivate)
 357                              -> ResolveResult<()> {
 358         debug!("(resolving single import) resolving `{}` = `{}::{}` from `{}` id {}, last \
 359                 private {:?}",
 360                target,
 361                module_to_string(&target_module),
 362                source,
 363                module_to_string(module_),
 364                directive.id,
 365                lp);
 366
 367         let lp = match lp {
 368             LastMod(lp) => lp,
 369             LastImport {..} => {
 370                 self.resolver
 371                     .session
 372                     .span_bug(directive.span, "not expecting Import here, must be LastMod")
 373             }
 374         };
 375
 376         // If this is a circular import, we temporarily count it as determined so that
 377         // it fails (as opposed to being indeterminate) when nothing else can define it.
 378         if target_module.def_id() == module_.def_id() && source == target {
 379             module_.decrement_outstanding_references_for(target, ValueNS);
 380             module_.decrement_outstanding_references_for(target, TypeNS);
 381         }
 382
 383         // We need to resolve both namespaces for this to succeed.
 384         let value_result =
 385             self.resolver.resolve_name_in_module(target_module, source, ValueNS, false, true);
 386         let type_result =
 387             self.resolver.resolve_name_in_module(target_module, source, TypeNS, false, true);
 388
 389         if target_module.def_id() == module_.def_id() && source == target {
 390             module_.increment_outstanding_references_for(target, ValueNS);
 391             module_.increment_outstanding_references_for(target, TypeNS);
 392         }
 393
 394         match (&value_result, &type_result) {
 395             (&Indeterminate, _) | (_, &Indeterminate) => return Indeterminate,
 396             (&Failed(_), &Failed(_)) => {
 397                 let children = target_module.resolutions.borrow();
 398                 let names = children.keys().map(|&(ref name, _)| name);
 399                 let lev_suggestion = match find_best_match_for_name(names, &source.as_str(), None) {
 400                     Some(name) => format!(". Did you mean to use `{}`?", name),
 401                     None => "".to_owned(),
 402                 };
 403                 let msg = format!("There is no `{}` in `{}`{}",
 404                                   source,
 405                                   module_to_string(target_module), lev_suggestion);
 406                 return Failed(Some((directive.span, msg)));
 407             }
 408             _ => (),
 409         }
 410
 411         match (&value_result, &type_result) {
 412             (&Success(name_binding), _) if !name_binding.is_import() &&
 413                                            directive.is_public &&
 414                                            !name_binding.is_public() => {
 415                 let msg = format!("`{}` is private, and cannot be reexported", source);
 416                 let note_msg = format!("Consider marking `{}` as `pub` in the imported module",
 417                                         source);
 418                 struct_span_err!(self.resolver.session, directive.span, E0364, "{}", &msg)
 419                     .span_note(directive.span, &note_msg)
 420                     .emit();
 421             }
 422
 423             (_, &Success(name_binding)) if !name_binding.is_import() && directive.is_public => {
 424                 if !name_binding.is_public() {
 425                     let msg = format!("`{}` is private, and cannot be reexported", source);
 426                     let note_msg =
 427                         format!("Consider declaring type or module `{}` with `pub`", source);
 428                     struct_span_err!(self.resolver.session, directive.span, E0365, "{}", &msg)
 429                         .span_note(directive.span, &note_msg)
 430                         .emit();
 431                 } else if name_binding.defined_with(DefModifiers::PRIVATE_VARIANT) {
 432                     let msg = format!("variant `{}` is private, and cannot be reexported \
 433                                        (error E0364), consider declaring its enum as `pub`",
 434                                        source);
 435                     self.resolver.session.add_lint(lint::builtin::PRIVATE_IN_PUBLIC,
 436                                                    directive.id,
 437                                                    directive.span,
 438                                                    msg);
 439                 }
 440             }
 441
 442             _ => {}
 443         }
 444
 445         for &(ns, result) in &[(ValueNS, &value_result), (TypeNS, &type_result)] {
 446             if let Success(binding) = *result {
 447                 if !binding.defined_with(DefModifiers::IMPORTABLE) {
 448                     let msg = format!("`{}` is not directly importable", target);
 449                     span_err!(self.resolver.session, directive.span, E0253, "{}", &msg);
 450                 }
 451
 452                 self.define(module_, target, ns, directive.import(binding));
 453             }
 454         }
 455
 456         // Record what this import resolves to for later uses in documentation,
 457         // this may resolve to either a value or a type, but for documentation
 458         // purposes it's good enough to just favor one over the other.
 459         module_.decrement_outstanding_references_for(target, ValueNS);
 460         module_.decrement_outstanding_references_for(target, TypeNS);
 461
 462         let def_and_priv = |binding: &NameBinding| {
 463             let def = binding.def().unwrap();
 464             let last_private = if binding.is_public() { lp } else { DependsOn(def.def_id()) };
 465             (def, last_private)
 466         };
 467         let value_def_and_priv = value_result.success().map(&def_and_priv);
 468         let type_def_and_priv = type_result.success().map(&def_and_priv);
 469
 470         let import_lp = LastImport {
 471             value_priv: value_def_and_priv.map(|(_, p)| p),
 472             value_used: Used,
 473             type_priv: type_def_and_priv.map(|(_, p)| p),
 474             type_used: Used,
 475         };
 476
 477         let write_path_resolution = |(def, _)| {
 478             let path_resolution =
 479                 PathResolution { base_def: def, last_private: import_lp, depth: 0 };
 480             self.resolver.def_map.borrow_mut().insert(directive.id, path_resolution);
 481         };
 482         value_def_and_priv.map(&write_path_resolution);
 483         type_def_and_priv.map(&write_path_resolution);
 484
 485         debug!("(resolving single import) successfully resolved import");
 486         return Success(());
 487     }
 488
 489     // Resolves a glob import. Note that this function cannot fail; it either
 490     // succeeds or bails out (as importing * from an empty module or a module
 491     // that exports nothing is valid). target_module is the module we are
 492     // actually importing, i.e., `foo` in `use foo::*`.
 493     fn resolve_glob_import(&mut self,
 494                            module_: Module<'b>,
 495                            target_module: Module<'b>,
 496                            directive: &ImportDirective,
 497                            lp: LastPrivate)
 498                            -> ResolveResult<()> {
 499         // We must bail out if the node has unresolved imports of any kind (including globs).
 500         if target_module.pub_count.get() > 0 {
 501             debug!("(resolving glob import) target module has unresolved pub imports; bailing out");
 502             return Indeterminate;
 503         }
 504
 505         if module_.def_id() == target_module.def_id() {
 506             // This means we are trying to glob import a module into itself, and it is a no-go
 507             let msg = "Cannot glob-import a module into itself.".into();
 508             return Failed(Some((directive.span, msg)));
 509         }
 510
 511         // Add all children from the containing module.
 512         build_reduced_graph::populate_module_if_necessary(self.resolver, target_module);
 513         target_module.for_each_child(|name, ns, binding| {
 514             if !binding.defined_with(DefModifiers::IMPORTABLE | DefModifiers::PUBLIC) { return }
 515             if binding.is_extern_crate() { return }
 516             self.define(module_, name, ns, directive.import(binding));
 517
 518             if ns == TypeNS && directive.is_public &&
 519                binding.defined_with(DefModifiers::PRIVATE_VARIANT) {
 520                 let msg = format!("variant `{}` is private, and cannot be reexported (error \
 521                                    E0364), consider declaring its enum as `pub`", name);
 522                 self.resolver.session.add_lint(lint::builtin::PRIVATE_IN_PUBLIC,
 523                                                directive.id,
 524                                                directive.span,
 525                                                msg);
 526             }
 527         });
 528
 529         // Record the destination of this import
 530         if let Some(did) = target_module.def_id() {
 531             self.resolver.def_map.borrow_mut().insert(directive.id,
 532                                                       PathResolution {
 533                                                           base_def: Def::Mod(did),
 534                                                           last_private: lp,
 535                                                           depth: 0,
 536                                                       });
 537         }
 538
 539         debug!("(resolving glob import) successfully resolved import");
 540         return Success(());
 541     }
 542
 543     fn define(&mut self,
 544               parent: Module<'b>,
 545               name: Name,
 546               ns: Namespace,
 547               binding: NameBinding<'b>) {
 548         let binding = self.resolver.new_name_binding(binding);
 549         if let Err(old_binding) = parent.try_define_child(name, ns, binding) {
 550             self.report_conflict(name, ns, binding, old_binding);
 551         } else if binding.is_public() { // Add to the export map
 552             if let (Some(parent_def_id), Some(def)) = (parent.def_id(), binding.def()) {
 553                 let parent_node_id = self.resolver.ast_map.as_local_node_id(parent_def_id).unwrap();
 554                 let export = Export { name: name, def_id: def.def_id() };
 555                 self.resolver.export_map.entry(parent_node_id).or_insert(Vec::new()).push(export);
 556             }
 557         }
 558     }
 559
 560     fn report_conflict(&mut self,
 561                        name: Name,
 562                        ns: Namespace,
 563                        binding: &'b NameBinding<'b>,
 564                        old_binding: &'b NameBinding<'b>) {
 565         if old_binding.is_extern_crate() {
 566             let msg = format!("import `{0}` conflicts with imported crate \
 567                                in this module (maybe you meant `use {0}::*`?)",
 568                               name);
 569             span_err!(self.resolver.session, binding.span.unwrap(), E0254, "{}", &msg);
 570         } else if old_binding.is_import() {
 571             let ns_word = match (ns, old_binding.module()) {
 572                 (ValueNS, _) => "value",
 573                 (TypeNS, Some(module)) if module.is_normal() => "module",
 574                 (TypeNS, Some(module)) if module.is_trait() => "trait",
 575                 (TypeNS, _) => "type",
 576             };
 577             let mut err = struct_span_err!(self.resolver.session,
 578                                            binding.span.unwrap(),
 579                                            E0252,
 580                                            "a {} named `{}` has already been imported \
 581                                             in this module",
 582                                            ns_word,
 583                                            name);
 584             err.span_note(old_binding.span.unwrap(),
 585                           &format!("previous import of `{}` here", name));
 586             err.emit();
 587         } else if ns == ValueNS { // Check for item conflicts in the value namespace
 588             let mut err = struct_span_err!(self.resolver.session,
 589                                            binding.span.unwrap(),
 590                                            E0255,
 591                                            "import `{}` conflicts with value in this module",
 592                                            name);
 593             err.span_note(old_binding.span.unwrap(), "conflicting value here");
 594             err.emit();
 595         } else { // Check for item conflicts in the type namespace
 596             let (what, note) = match old_binding.module() {
 597                 Some(ref module) if module.is_normal() =>
 598                     ("existing submodule", "note conflicting module here"),
 599                 Some(ref module) if module.is_trait() =>
 600                     ("trait in this module", "note conflicting trait here"),
 601                 _ => ("type in this module", "note conflicting type here"),
 602             };
 603             let mut err = struct_span_err!(self.resolver.session,
 604                                            binding.span.unwrap(),
 605                                            E0256,
 606                                            "import `{}` conflicts with {}",
 607                                            name,
 608                                            what);
 609             err.span_note(old_binding.span.unwrap(), note);
 610             err.emit();
 611         }
 612     }
 613 }
 614
 615 fn import_path_to_string(names: &[Name], subclass: ImportDirectiveSubclass) -> String {
 616     if names.is_empty() {
 617         import_directive_subclass_to_string(subclass)
 618     } else {
 619         (format!("{}::{}",
 620                  names_to_string(names),
 621                  import_directive_subclass_to_string(subclass)))
 622             .to_string()
 623     }
 624 }
 625
 626 fn import_directive_subclass_to_string(subclass: ImportDirectiveSubclass) -> String {
 627     match subclass {
 628         SingleImport(_, source) => source.to_string(),
 629         GlobImport => "*".to_string(),
 630     }
 631 }
 632
 633 pub fn resolve_imports(resolver: &mut Resolver) {
 634     let mut import_resolver = ImportResolver { resolver: resolver };
 635     import_resolver.resolve_imports();
 636 }