fix(transformer): Don't hang on bad urls and log better errors

closes https://github.com/angular/angular/issues/2605

modules/angular2/src/transform/common/xhr_impl.dart

@@ -16,9 +16,14 @@ class XhrImpl implements XHR {
   Future<String> get(String url) async {
     var assetId = uriToAssetId(_entryPoint, url, logger, null /* span */,
         errorOnAbsolute: false);
+    if (assetId == null) {
+      logger.error(
+          'Uri $url not supported from $_entryPoint, could not build AssetId');
+      return null;
+    }
     var templateExists = await _reader.hasInput(assetId);
     if (!templateExists) {
-      logger.error('Could not read template at uri $url from $_entryPoint');
+      logger.error('Could not read asset at uri $url from $_entryPoint');
       return null;
     }
     return await _reader.readAsString(assetId);

modules/angular2/src/transform/directive_processor/visitors.dart

@@ -1,5 +1,6 @@
 library angular2.transform.directive_processor.visitors;
 
+import 'dart:async';
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/src/generated/java_core.dart';
 import 'package:angular2/src/render/xhr.dart' show XHR;
@@ -263,7 +264,7 @@ class AnnotationsTransformVisitor extends ToSourceVisitor {
       var url = node.expression.accept(_evaluator);
       if (url is String) {
         writer.print("template: r'''");
-        writer.asyncPrint(_xhr.get(url));
+        writer.asyncPrint(_readOrEmptyString(url));
         writer.print("'''");
         return null;
       } else {
@@ -276,7 +277,7 @@ class AnnotationsTransformVisitor extends ToSourceVisitor {
       for (var url in urls) {
         if (url is String) {
           writer.print("r'''");
-          writer.asyncPrint(_xhr.get(url));
+          writer.asyncPrint(_readOrEmptyString(url));
           writer.print("''', ");
         } else {
           logger.warning('style url is not a String ${url}');
@@ -287,4 +288,14 @@ class AnnotationsTransformVisitor extends ToSourceVisitor {
     }
     return super.visitNamedExpression(node);
   }
+
+  /// Attempts to read the content from {@link url}, if it returns null then
+  /// just return the empty string.
+  Future<String> _readOrEmptyString(String url) async {
+    var content = await _xhr.get(url);
+    if (content == null) {
+      content = '';
+    }
+    return content;
+  }
 }

modules/angular2/test/transform/directive_processor/all_tests.dart

@@ -4,6 +4,8 @@ import 'package:barback/barback.dart';
 import 'package:angular2/src/transform/directive_processor/rewriter.dart';
 import 'package:angular2/src/transform/common/annotation_matcher.dart';
 import 'package:angular2/src/transform/common/asset_reader.dart';
+import 'package:angular2/src/transform/common/logging.dart' as log;
+import 'package:code_transformers/messages/build_logger.dart';
 import 'package:dart_style/dart_style.dart';
 import 'package:guinness/guinness.dart';
 import 'package:path/path.dart' as path;
@@ -67,12 +69,29 @@ void allTests() {
 
   _testNgDeps('should not include superclasses in `interfaces`.',
       'superclass_files/soup.dart');
+
+  _testNgDeps(
+      'should not throw/hang on invalid urls', 'invalid_url_files/hello.dart',
+      expectedLogs: [
+    'ERROR: Uri /bad/absolute/url.html not supported from angular2|test/'
+        'transform/directive_processor/invalid_url_files/hello.dart, could not '
+        'build AssetId',
+    'ERROR: Could not read asset at uri package:invalid/package.css from '
+        'angular2|test/transform/directive_processor/invalid_url_files/'
+        'hello.dart',
+    'ERROR: Could not read asset at uri bad_relative_url.css from angular2|'
+        'test/transform/directive_processor/invalid_url_files/hello.dart'
+  ]);
 }
 
 void _testNgDeps(String name, String inputPath,
     {List<AnnotationDescriptor> customDescriptors: const [], AssetId assetId,
-    AssetReader reader}) {
+    AssetReader reader, List<String> expectedLogs}) {
   it(name, () async {
+    if (expectedLogs != null) {
+      log.setLogger(new RecordingLogger());
+    }
+
     var inputId = _assetIdForPath(inputPath);
     if (reader == null) {
       reader = new TestAssetReader();
@@ -93,8 +112,35 @@ void _testNgDeps(String name, String inputPath,
       expect(formatter.format(output))
           .toEqual((await reader.readAsString(expectedId)).replaceAll('\r\n', '\n'));
     }
+
+    if (expectedLogs != null) {
+      expect((log.logger as RecordingLogger).logs, expectedLogs);
+    }
   });
 }
 
 AssetId _assetIdForPath(String path) =>
     new AssetId('angular2', 'test/transform/directive_processor/$path');
+
+class RecordingLogger implements BuildLogger {
+  @override
+  final String detailsUri = '';
+  @override
+  final bool convertErrorsToWarnings = false;
+
+  List<String> logs = [];
+
+  void _record(prefix, msg) => logs.add('$prefix: $msg');
+
+  void info(msg, {AssetId asset, SourceSpan span}) => _record('INFO', msg);
+
+  void fine(msg, {AssetId asset, SourceSpan span}) => _record('FINE', msg);
+
+  void warning(msg, {AssetId asset, SourceSpan span}) => _record('WARN', msg);
+
+  void error(msg, {AssetId asset, SourceSpan span}) => _record('ERROR', msg);
+
+  Future writeOutput() => throw new UnimplementedError();
+  Future addLogFilesFromAsset(AssetId id, [int nextNumber = 1]) =>
+      throw new UnimplementedError();
+}

modules/angular2/test/transform/directive_processor/invalid_url_files/expected/hello.ng_deps.dart

@@ -0,0 +1,20 @@
+library test.transform.directive_processor.url_expression_files.hello.ng_deps.dart;
+
+import 'hello.dart';
+import 'package:angular2/angular2.dart'
+    show bootstrap, Component, Directive, View, NgElement;
+
+var _visited = false;
+void initReflector(reflector) {
+  if (_visited) return;
+  _visited = true;
+  reflector
+    ..registerType(HelloCmp, {
+      'factory': () => new HelloCmp(),
+      'parameters': const [],
+      'annotations': const [
+        const Component(selector: 'hello-app'),
+        const View(template: r'''''', styles: const [r'''''', r'''''',])
+      ]
+    });
+}

modules/angular2/test/transform/directive_processor/invalid_url_files/hello.dart

@@ -0,0 +1,13 @@
+library test.transform.directive_processor.url_expression_files.hello;
+
+import 'package:angular2/angular2.dart'
+show bootstrap, Component, Directive, View, NgElement;
+
+@Component(selector: 'hello-app')
+@View(
+    templateUrl: '/bad/absolute/url.html',
+    styleUrls: const [
+      'package:invalid/package.css',
+      'bad_relative_url.css'
+    ])
+class HelloCmp {}