Make all DDC internal stack traces apply source maps.

pkg/dev_compiler/web/stack_trace_mapper.dart

Index: pkg/dev_compiler/web/stack_trace_mapper.dart
diff --git a/pkg/dev_compiler/web/stack_trace_mapper.dart b/pkg/dev_compiler/web/stack_trace_mapper.dart
new file mode 100644
index 0000000000000000000000000000000000000000..557e6fd6ddf1e4db0aaf3e67a442de81140b8549
--- /dev/null
+++ b/pkg/dev_compiler/web/stack_trace_mapper.dart
@@ -0,0 +1,134 @@
+// Copyright (c) 2017, 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.
+
+/// Standalone utility that manages loading source maps for all Dart scripts
+/// on the page compiled with DDC.
+///
+/// Example JavaScript usage:
+/// $dartStackTraceUtility.addLoadedListener(function() {
+///   // All Dart source maps are now loaded. It is now safe to start your
+///   // Dart application compiled with DDC.
+///   dart_library.start('your_dart_application');
+/// })
+///
+/// If $dartStackTraceUtility is set, the dart:core StackTrace class calls
+/// $dartStackTraceUtility.mapper(someJSStackTrace)
+/// to apply source maps.
+///
+/// This utility can be compiled to JavaScript using Dart2JS while the rest
+/// of the application is compiled with DDC or could be compiled with DDC.
+
+@JS()
+library stack_trace_mapper;
+
+import 'dart:async';
+import 'dart:html';
+
+import 'package:js/js.dart';
+import 'package:path/path.dart' as path;
+import 'package:source_map_stack_trace/source_map_stack_trace.dart';
+import 'package:source_maps/source_maps.dart';
+import 'package:source_span/source_span.dart';
+import 'package:stack_trace/stack_trace.dart';
+
+typedef void ReadyCallback();
+
+/// Global object DDC uses to see if a stack trace utility has been registered.
+@JS(r'$dartStackTraceUtility')
+external set dartStackTraceUtility(DartStackTraceUtility value);
+
+typedef String StackTraceMapper(String stackTrace);
+typedef dynamic LoadSourceMaps(List<String> scripts, ReadyCallback callback);
+
+@JS()
+@anonymous
+class DartStackTraceUtility {
+  external factory DartStackTraceUtility(
+      {StackTraceMapper mapper, LoadSourceMaps loadSourceMaps});
+}
+
+/// Source mapping that is waits to parse source maps until they match the uri
+/// of a requested source map.
+///
+/// This improves startup performance compared to using MappingBundle directly.
+/// The unparsed data for the source maps must still be loaded before
+/// LazyMapping is used.
+class LazyMapping extends Mapping {
+  MappingBundle _bundle = new MappingBundle();
+
+  /// Map from url to unparsed source map.
+  Map<String, String> _sourceMaps;
+
+  LazyMapping(this._sourceMaps) {}
+
+  List toJson() => _bundle.toJson();
+
+  SourceMapSpan spanFor(int line, int column,
+      {Map<String, SourceFile> files, String uri}) {
+    if (uri == null) {
+      throw new ArgumentError.notNull('uri');
+    }
+    var rawMap = _sourceMaps[uri];
+
+    if (rawMap != null && rawMap.isNotEmpty && !_bundle.containsMapping(uri)) {
+      SingleMapping mapping = parse(rawMap);
+      mapping
+        ..targetUrl = uri
+        ..sourceRoot = '${path.dirname(uri)}/';
+      _bundle.addMapping(mapping);
+    }
+
+    return _bundle.spanFor(line, column, files: files, uri: uri);
+  }
+}
+
+String _toSourceMapLocation(String url) {
+  // The url may have cache busting query parameters which we need to maintain
+  // in the source map url.
+  // For example:
+  //   http://localhost/foo.js?cachebusting=23419
+  // Should get source map
+  //   http://localhost/foo.js.map?cachebusting=23419
+  var uri = Uri.parse(url);
+  return uri.replace(path: '${uri.path}.map').toString();
+}
+
+/// Load a source map for the specified url.
+///
+/// Returns a null string rather than reporting an error if the file cannot be
+/// found as we don't want to throw errors if a few source maps are missing.
+Future<String> loadSourceMap(String url) async {
+  try {
+    return await HttpRequest.getString(_toSourceMapLocation(url));
+  } catch (e) {
+    return null;
+  }
+}
+
+LazyMapping _mapping;
+
+String mapper(String rawStackTrace) {
+  if (_mapping == null) {
+    // This should not happen if the user has waited for the ReadyCallback
+    // to start the application.
+    throw new StateError('Source maps are not done loading.');
+  }
+  return mapStackTrace(_mapping, new Trace.parse(rawStackTrace)).toString();
+}
+
+Future<Null> loadSourceMaps(
+    List<String> scripts, ReadyCallback callback) async {
+  List<Future<String>> sourceMapFutures =
+      scripts.map((script) => loadSourceMap(script)).toList();
+  List<String> sourceMaps = await Future.wait(sourceMapFutures);
+  _mapping = new LazyMapping(new Map.fromIterables(scripts, sourceMaps));
+  callback();
+}
+
+main() {
+  // Register with DDC.
+  dartStackTraceUtility = new DartStackTraceUtility(
+      mapper: allowInterop(mapper),
+      loadSourceMaps: allowInterop(loadSourceMaps));
+}