Add an arena for import directives

src/librustc_resolve/build_reduced_graph.rs

@@ -707,9 +707,10 @@ impl<'a, 'b:'a, 'tcx:'b> GraphBuilder<'a, 'b, 'tcx> {
             }
         }
 
-        module_.unresolved_imports
-               .borrow_mut()
-               .push(ImportDirective::new(module_path, subclass, span, id, is_public, shadowable));
+        let directive =
+            ImportDirective::new(module_path, subclass, span, id, is_public, shadowable);
+        let directive = self.resolver.arenas.alloc_import_directive(directive);
+        module_.unresolved_imports.borrow_mut().push(directive);
         self.unresolved_imports += 1;
     }
 }

src/librustc_resolve/lib.rs

@@ -812,7 +812,7 @@ pub struct ModuleS<'a> {
     extern_crate_id: Option<NodeId>,
 
     resolutions: RefCell<HashMap<(Name, Namespace), NameResolution<'a>>>,
-    unresolved_imports: RefCell<Vec<ImportDirective>>,
+    unresolved_imports: RefCell<Vec<&'a ImportDirective>>,
 
     // The module children of this node, including normal modules and anonymous modules.
     // Anonymous children are pseudo-modules that are implicitly created around items
@@ -1167,6 +1167,13 @@ pub struct Resolver<'a, 'tcx: 'a> {
 pub struct ResolverArenas<'a> {
     modules: arena::TypedArena<ModuleS<'a>>,
     name_bindings: arena::TypedArena<NameBinding<'a>>,
+    import_directives: arena::TypedArena<ImportDirective>,
+}
+
+impl<'a> ResolverArenas<'a> {
+    fn alloc_import_directive(&'a self, import_directive: ImportDirective) -> &'a ImportDirective {
+        self.import_directives.alloc(import_directive)
+    }
 }
 
 #[derive(PartialEq)]
@@ -1234,6 +1241,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         ResolverArenas {
             modules: arena::TypedArena::new(),
             name_bindings: arena::TypedArena::new(),
+            import_directives: arena::TypedArena::new(),
         }
     }
 

src/librustc_resolve/resolve_imports.rs

@@ -172,7 +172,7 @@ impl<'a> NameResolution<'a> {
 struct ImportResolvingError<'a> {
     /// Module where the error happened
     source_module: Module<'a>,
-    import_directive: ImportDirective,
+    import_directive: &'a ImportDirective,
     span: Span,
     help: String,
 }
@@ -249,7 +249,7 @@ impl<'a, 'b:'a, 'tcx:'b> ImportResolver<'a, 'b, 'tcx> {
         }
 
         let path = import_path_to_string(&e.import_directive.module_path,
-                                         e.import_directive.subclass);
+                                         &e.import_directive.subclass);
 
         resolve_error(self.resolver,
                       e.span,
@@ -608,7 +608,7 @@ impl<'a, 'b:'a, 'tcx:'b> ImportResolver<'a, 'b, 'tcx> {
     }
 }
 
-fn import_path_to_string(names: &[Name], subclass: ImportDirectiveSubclass) -> String {
+fn import_path_to_string(names: &[Name], subclass: &ImportDirectiveSubclass) -> String {
     if names.is_empty() {
         import_directive_subclass_to_string(subclass)
     } else {
@@ -619,8 +619,8 @@ fn import_path_to_string(names: &[Name], subclass: ImportDirectiveSubclass) -> S
     }
 }
 
-fn import_directive_subclass_to_string(subclass: ImportDirectiveSubclass) -> String {
-    match subclass {
+fn import_directive_subclass_to_string(subclass: &ImportDirectiveSubclass) -> String {
+    match *subclass {
         SingleImport { source, .. } => source.to_string(),
         GlobImport => "*".to_string(),
     }