Inline source maps as part of each script.

pkg/dev_compiler/lib/src/compiler/compiler.dart

 // Copyright (c) 2016, 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.
 
 import 'dart:collection' show HashSet, Queue;
 import 'dart:convert' show BASE64, JSON, UTF8;
 import 'dart:io' show File;
 
 import 'package:analyzer/analyzer.dart'
     show AnalysisError, CompilationUnit, ErrorSeverity;
@@ skipping 425 matching lines @@
   /// module.
   final JS.Program moduleTree;
 
   /// The compiler options used to generate this module.
   final CompilerOptions options;
 
   /// The binary contents of the API summary file, including APIs from each of
   /// the libraries in this module.
   final List<int> summaryBytes;
 
+  /// Unique identifier indicating hole to inline the source map.
+  ///
+  /// We cannot generate the source map before the script it is for is
+  /// generated so we have generate the script including this id and then
+  /// replace the ID once the source map is generated.
+  static String sourceMapHoleID = 'SourceMap3G5a8h6JVhHfdGuDxZr1EF9GQC8y0e6u';
+
   JSModuleFile(
       this.name, this.errors, this.options, this.moduleTree, this.summaryBytes);
 
   JSModuleFile.invalid(this.name, this.errors, this.options)
       : moduleTree = null,
         summaryBytes = null;
 
   /// True if this library was successfully compiled.
   bool get isValid => moduleTree != null;
 
@@ skipping 22 matching lines @@
 
     var tree =
         transformModuleFormat(format, moduleTree, singleOutFile: singleOutFile);
     tree.accept(
         new JS.Printer(opts, printer, localNamer: new JS.TemporaryNamer(tree)));
 
     Map builtMap;
     if (options.sourceMap && sourceMap != null) {
       builtMap =
           placeSourceMap(sourceMap.build(jsUrl), mapUrl, options.bazelMapping);
-
+      if (name == 'dart_sdk') {
+        builtMap = cleanupSdkSourcemap(builtMap);
+      }
       if (options.sourceMapComment) {
         var relativeMapUrl = path
             .toUri(
                 path.relative(path.fromUri(mapUrl), from: path.dirname(jsUrl)))
             .toString();
         assert(path.dirname(jsUrl) == path.dirname(mapUrl));
         printer.emit('\n//# sourceMappingURL=');
-        if (options.inlineSourceMap) {
-          var bytes = UTF8.encode(JSON.encode(builtMap));
-          var base64 = BASE64.encode(bytes);
-          printer..emit('data:application/json;base64,')..emit(base64);
-        } else {
-          printer.emit(relativeMapUrl);
-        }
+        printer.emit(relativeMapUrl);
         printer.emit('\n');
       }
     }
 
-    return new JSModuleCode(printer.getText(), builtMap);
+    var text = printer.getText();
+    var rawSourceMap = options.inlineSourceMap ? JSON.encode(builtMap) : null;
+    // Encode the sourcemap as an escaped string rather than JSON
+    // as Dart code using the sourcemap can't take advantage of it being JS
+    // JSON so we might as well encode it as a String which should be quicker
+    // to parse.
+    text = text.replaceFirst(sourceMapHoleID, JSON.encode(rawSourceMap));
+
+    return new JSModuleCode(text, builtMap);
   }
 
   /// Similar to [getCode] but immediately writes the resulting files.
   ///
   /// If [mapPath] is not supplied but [options.sourceMap] is set, mapPath
   /// will default to [jsPath].map.
   void writeCodeSync(ModuleFormat format, String jsPath,
       {bool singleOutFile: false}) {
     String mapPath = jsPath + '.map';
     var code = getCode(format, jsPath, mapPath, singleOutFile: singleOutFile);
@@ skipping 59 matching lines @@
     // Fall back to a relative path.
     return path.toUri(path.relative(path.fromUri(uri), from: dir)).toString();
   }
 
   for (int i = 0; i < list.length; i++) {
     list[i] = transformUri(list[i]);
   }
   map['file'] = transformUri(map['file']);
   return map;
 }
+
+/// Cleanup the dart_sdk source map.
+///
+/// Strip out files that should not be included in the sdk sourcemap as they
+/// are implementation details that would just confuse users.
+/// Normalize sdk urls to use "dart:" for more understandable stack traces.
+Map cleanupSdkSourcemap(Map sourceMap) {
+  var map = new Map.from(sourceMap);
+  var list = new List.from(map['sources']);
+  map['sources'] = map['sources']
+      .map((url) => url.contains('/_internal/') ? null : url)
+      .toList();
+  return map;
+}