Added support for exports and re-exports.

lib/compiler/implementation/tree/nodes.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 abstract class Visitor<R> {
   const Visitor();
 
   abstract R visitNode(Node node);
 
   R visitBlock(Block node) => visitStatement(node);
@@ skipping 1662 matching lines @@
 
   accept(Visitor visitor) => visitor.visitLibraryName(this);
 
   visitChildren(Visitor visitor) => name.accept(visitor);
 
   Token getBeginToken() => libraryKeyword;
 
   Token getEndToken() => name.getEndToken().next;
 }
 
-class Import extends LibraryTag {
+/**
+ * This tag describes a dependency between one library and the exported
+ * identifiers of another library. The other library is specified by the [uri].
+ * Combinators filter away some identifiers from the other library.
+ */
+abstract class LibraryDependency extends LibraryTag {
   final LiteralString uri;
-  final Identifier prefix;
   final NodeList combinators;
 
+  LibraryDependency(this.uri, this.combinators);
+}
+
+/**
+ * An [:import:] library tag.
+ *
+ * An import tag is dependency on another library where the exported identifiers
+ * are put into the import scope of the importing library. The import scope is
+ * only visible inside the library.
+ */
+class Import extends LibraryDependency {
+  final Identifier prefix;
   final Token importKeyword;
 
-  Import(this.importKeyword, this.uri, this.prefix, this.combinators);
+  Import(this.importKeyword, LiteralString uri,
+         this.prefix, NodeList combinators)
+      : super(uri, combinators);
 
   bool get isImport => true;
 
   Import asImport() => this;
 
   Token get asKeyword => prefix == null ? null : uri.getEndToken().next;
 
   accept(Visitor visitor) => visitor.visitImport(this);
 
   visitChildren(Visitor visitor) {
     uri.accept(visitor);
     if (prefix !== null) prefix.accept(visitor);
     if (combinators !== null) combinators.accept(visitor);
   }
 
   Token getBeginToken() => importKeyword;
 
   Token getEndToken() {
     if (combinators !== null) return combinators.getEndToken().next;
     if (prefix !== null) return prefix.getEndToken().next;
     return uri.getEndToken().next;
   }
 }
 
-class Export extends LibraryTag {
-  final LiteralString uri;
-  final NodeList combinators;
-
+/**
+ * An [:export:] library tag.
+ *
+ * An export tag is dependency on another library where the exported identifiers
+ * are put into the export scope of the exporting library. The export scope is
+ * not visible inside the library.
+ */
+class Export extends LibraryDependency {
   final Token exportKeyword;
 
-  Export(this.exportKeyword, this.uri, this.combinators);
+  Export(this.exportKeyword, LiteralString uri, NodeList combinators)
+      : super(uri, combinators);
 
   bool get isExport => true;
 
   Export asExport() => this;
 
   accept(Visitor visitor) => visitor.visitExport(this);
 
   visitChildren(Visitor visitor) {
     uri.accept(visitor);
     if (combinators !== null) combinators.accept(visitor);
@@ skipping 245 matching lines @@
  * argument).
  *
  * TODO(ahe): This method is controversial, the team needs to discuss
  * if top-level methods are acceptable and what naming conventions to
  * use.
  */
 initializerDo(Node node, f(Node node)) {
   SendSet send = node.asSendSet();
   if (send !== null) return f(send.arguments.head);
 }