Implement modular compilation

lib/src/js_ast/nodes.dart

Index: lib/src/js_ast/nodes.dart
diff --git a/lib/src/js/nodes.dart b/lib/src/js_ast/nodes.dart
similarity index 97%
rename from lib/src/js/nodes.dart
rename to lib/src/js_ast/nodes.dart
index cd0e807a9542a3cf4c5cb13da93722b2f49473a4..be1e764806eee0f05a38179aba939dda738b9d91 100644
--- a/lib/src/js/nodes.dart
+++ b/lib/src/js_ast/nodes.dart
@@ -311,7 +311,12 @@ class Program extends Node {
   /// Top-level statements in the program.
   final List<ModuleItem> body;
 
-  Program(this.body, {this.scriptTag});
+  /// The module's own name.
+  ///
+  /// This is not used in ES6, but is provided to allow module lowering.
+  final String name;
+
+  Program(this.body, {this.scriptTag, this.name});
 
   accept(NodeVisitor visitor) => visitor.visitProgram(this);
   void visitChildren(NodeVisitor visitor) {
@@ -741,7 +746,10 @@ class LiteralExpression extends Expression {
  * AST.
  */
 class VariableDeclarationList extends Expression {
-  /** The `var` or `let` keyword used for this variable declaration list. */
+  /**
+   * The `var` or `let` or `const` keyword used for this variable declaration
+   * list.
+   */
   final String keyword;
   final List<VariableInitialization> declarations;
 
@@ -1733,15 +1741,17 @@ class ImportDeclaration extends ModuleItem {
 
   final LiteralString from;
 
-  ImportDeclaration({this.defaultBinding, this.namedImports, this.from});
+  ImportDeclaration({this.defaultBinding, this.namedImports, this.from}) {
+    assert(from != null);
+  }
 
   /** The `import "name.js"` form of import */
   ImportDeclaration.all(LiteralString module) : this(from: module);
 
   /** If this import has `* as name` returns the name, otherwise null. */
-  String get importStarAs {
+  Identifier get importStarAs {
     if (namedImports != null && namedImports.length == 1 &&
-        namedImports[0].name == '*') {
+        namedImports[0].isStar) {
       return namedImports[0].asName;
     }
     return null;
@@ -1780,6 +1790,26 @@ class ExportDeclaration extends ModuleItem {
               exported is ExportClause);
   }
 
+  /// Gets the list of names exported by this export declaration, or `null`
+  /// if this is an `export *`.
+  ///
+  /// This can be useful for lowering to other module formats.
+  List<Identifier> get exportedNames {
+    if (isDefault) return [new Identifier('default')];
+
+    var exported = this.exported;
+    if (exported is ClassDeclaration) return [exported.classExpr.name];
+    if (exported is FunctionDeclaration) return [exported.name];
+    if (exported is VariableDeclarationList) {
+      return exported.declarations.map((i) => i.declaration).toList();
+    }
+    if (exported is ExportClause) {
+      if (exported.exportStar) return null;
+      return exported.exports.map((e) => e.name).toList();
+    }
+    throw new StateError('invalid export declaration');
+  }
+
   accept(NodeVisitor visitor) => visitor.visitExportDeclaration(this);
   visitChildren(NodeVisitor visitor) => exported.accept(visitor);
   ExportDeclaration _clone() =>
@@ -1794,10 +1824,10 @@ class ExportClause extends Node {
 
   /** The `export * from 'name.js'` form. */
   ExportClause.star(LiteralString from)
-      : this([new NameSpecifier('*')], from: from);
+      : this([new NameSpecifier.star()], from: from);
 
   /** True if this is an `export *`. */
-  bool get exportStar => exports.length == 1 && exports[0].name == '*';
+  bool get exportStar => exports.length == 1 && exports[0].isStar;
 
   accept(NodeVisitor visitor) => visitor.visitExportClause(this);
   void visitChildren(NodeVisitor visitor) {
@@ -1809,11 +1839,14 @@ class ExportClause extends Node {
 
 /** An import or export specifier. */
 class NameSpecifier extends Node {
-  // TODO(jmesserly): should we wrap this in a node of some sort?
-  final String name;
-  final String asName; // Can be null.
+  final Identifier name;
+  final Identifier asName; // Can be null.
 
   NameSpecifier(this.name, {this.asName});
+  NameSpecifier.star() : this(null);
+
+  /** True if this is a `* as someName` specifier. */
+  bool get isStar => name == null;
 
   accept(NodeVisitor visitor) => visitor.visitNameSpecifier(this);
   void visitChildren(NodeVisitor visitor) {}