feat(dart/transform): Generate DirectiveMetadata for exports

For all files that export another library, include `DirectiveMetadata`
for the exported library in that file's associated `ng_meta.json` file.

modules/angular2/src/transform/directive_metadata_extractor/extractor.dart

@@ -2,20 +2,59 @@ library angular2.transform.directive_metadata_extractor.extractor;
 
 import 'dart:async';
 
+import 'package:analyzer/analyzer.dart';
 import 'package:angular2/src/render/api.dart';
 import 'package:angular2/src/transform/common/asset_reader.dart';
 import 'package:angular2/src/transform/common/directive_metadata_reader.dart';
+import 'package:angular2/src/transform/common/logging.dart';
+import 'package:angular2/src/transform/common/names.dart';
 import 'package:angular2/src/transform/common/parser.dart';
 import 'package:barback/barback.dart';
+import 'package:code_transformers/assets.dart';
 
 /// Returns a map from a class name (that is, its `Identifier` stringified)
-/// to its [DirectiveMetadata].
-/// Will return `null` if there are no `Directive`-annotated classes in
+/// to [DirectiveMetadata] for all `Directive`-annotated classes  visible
+/// in a file importing `entryPoint`. That is, this includes all
+/// `Directive` annotated classes in `entryPoint` and any assets which it
+/// `export`s.
+/// Returns `null` if there are no `Directive`-annotated classes in
 /// `entryPoint`.
 Future<Map<String, DirectiveMetadata>> extractDirectiveMetadata(
     AssetReader reader, AssetId entryPoint) async {
-  var parser = new Parser(reader);
-  NgDeps ngDeps = await parser.parse(entryPoint);
+  return _extractDirectiveMetadataRecursive(
+      reader, new Parser(reader), entryPoint);
+}
+
+var _nullFuture = new Future.value(null);
+
+Future<Map<String, DirectiveMetadata>> _extractDirectiveMetadataRecursive(
+    AssetReader reader, Parser parser, AssetId entryPoint) async {
+  if (!(await reader.hasInput(entryPoint))) return null;
+
+  var ngDeps = await parser.parse(entryPoint);
+  var baseMap = _metadataMapFromNgDeps(ngDeps);
+
+  return Future.wait(ngDeps.exports.map((export) {
+    var uri = stringLiteralToString(export.uri);
+    if (uri.startsWith('dart:')) return _nullFuture;
+
+    uri = toDepsExtension(uri);
+    var assetId = uriToAssetId(entryPoint, uri, logger, null /* span */);
+    if (assetId == entryPoint) return _nullFuture;
+    return _extractDirectiveMetadataRecursive(reader, parser, assetId)
+        .then((exportMap) {
+      if (exportMap != null) {
+        if (baseMap == null) {
+          baseMap = exportMap;
+        } else {
+          baseMap.addAll(exportMap);
+        }
+      }
+    });
+  })).then((_) => baseMap);
+}
+
+Map<String, DirectiveMetadata> _metadataMapFromNgDeps(NgDeps ngDeps) {
   if (ngDeps == null || ngDeps.registeredTypes.isEmpty) return null;
   var retVal = <String, DirectiveMetadata>{};
   ngDeps.registeredTypes.forEach((rType) {

modules/angular2/src/transform/directive_metadata_extractor/transformer.dart

@@ -36,7 +36,7 @@ class DirectiveMetadataExtractor extends Transformer {
           jsonMap[k] = directiveMetadataToMap(v);
         });
         transform.addOutput(new Asset.fromString(
-            _outputAssetId(fromAssetId), '// ${JSON.encode(jsonMap)}'));
+            _outputAssetId(fromAssetId), JSON.encode(jsonMap)));
       }
     } catch (ex, stackTrace) {
       log.logger.error('Extracting ng metadata failed.\n'
@@ -49,8 +49,5 @@ class DirectiveMetadataExtractor extends Transformer {
 
 AssetId _outputAssetId(AssetId inputAssetId) {
   assert(inputAssetId.path.endsWith(DEPS_EXTENSION));
-  var pathIn = inputAssetId.path;
-  return new AssetId(inputAssetId.package,
-      '${pathIn.substring(0, pathIn.length - DEPS_EXTENSION.length)}'
-      '${META_EXTENSION}');
+  return new AssetId(inputAssetId.package, toMetaExtension(inputAssetId.path));
 }