Polymer transformer logs now show on the frontend for pub serve.

pkg/polymer/lib/src/build/wrapped_logger.dart

+// Copyright (c) 2013, 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.
+
+library polymer.src.build.wrapped_logger;
+
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:barback/barback.dart';
+import 'package:source_span/source_span.dart';
+
+import 'common.dart' as common;
+
+/// A simple class to wrap one TransformLogger with another one that writes all
+/// logs to a file and then forwards the calls to the child.
+class WrappedLogger implements TransformLogger {
+  Transform _transform;
+  List<Map> _logs = new List<Map>();
+
+  bool convertErrorsToWarnings;
+
+  WrappedLogger(this._transform, {this.convertErrorsToWarnings: false});
+
+  void info(String message, {AssetId asset, SourceSpan span}) {
+    _transform.logger.info(message, asset: asset, span: span);
+    _addLog(asset, LogLevel.INFO, message, span);
+  }
+
+  void fine(String message, {AssetId asset, SourceSpan span}) {
+    _transform.logger.fine(message, asset: asset, span: span);
+    _addLog(asset, LogLevel.FINE, message, span);
+  }
+
+  void warning(String message, {AssetId asset, SourceSpan span}) {
+    _transform.logger.warning(message, asset: asset, span: span);
+    _addLog(asset, LogLevel.WARNING, message, span);
+  }
+
+  void error(String message, {AssetId asset, SourceSpan span}) {
+    if (convertErrorsToWarnings) {
+      _transform.logger.warning(message, asset: asset, span: span);
+    } else {
+      _transform.logger.error(message, asset: asset, span: span);
+    }
+    _addLog(asset, LogLevel.ERROR, message, span);
+  }
+
+  /// Outputs the log data to a JSON serialized file.
+  Future writeOutput() {
+    return getNextLogAssetPath().then((path) {
+      _transform.addOutput(new Asset.fromString(path, JSON.encode(_logs)));
+    });
+  }
+
+  // Each phase outputs a new log file with an incrementing # appended, this
+  // figures out the next # to use.
+  Future<String> getNextLogAssetPath([int nextNumber = 1]) {
+    var nextAssetPath = _transform.primaryInput.id.addExtension(
+        '${common.LOG_EXTENSION}.$nextNumber');
+    return _transform.hasInput(nextAssetPath).then((exists) {
+      if (!exists) return nextAssetPath;
+      return getNextLogAssetPath(++nextNumber);
+    });
+  }
+
+  // Combines all existing ._buildLogs.* files into a single ._buildLogs file.
+  static Future combineLogFiles(
+      Transform transform, [int nextNumber = 1, List<Map> logs]) {
+    if (logs == null) logs = new List<Map>();
+    var primaryInputId = transform.primaryInput.id;
+    var nextAssetPath =
+        primaryInputId.addExtension('${common.LOG_EXTENSION}.$nextNumber');
+    return transform.readInputAsString(nextAssetPath).then(
+        (data) {
+          logs.addAll(JSON.decode(data));
+          return combineLogFiles(transform, ++nextNumber, logs);
+        },
+        onError: (_) {
+          transform.addOutput(new Asset.fromString(
+              primaryInputId.addExtension(common.LOG_EXTENSION),
+              JSON.encode(logs)));
+        });
+  }
+
+  void _addLog(AssetId assetId, LogLevel level, String message,
+               SourceSpan span) {
+    var data = {
+        'level': level.name,
+        'message': message,
+    };
+    if (assetId != null) {
+      data['assetId'] = {
+          'package': assetId.package,
+          'path': assetId.path,
+      };
+    }
+    if (span != null) {
+      data['span'] = {
+          'location': span.start.toolString,
+          'text': new HtmlEscape().convert(span.text),
+      };
+    }
+    _logs.add(data);
+  }
+}