Asset server fix for sourcemaps (#44017)

packages/flutter_tools/lib/src/build_runner/web_fs.dart

@@ -442,37 +442,49 @@ class DebugAssetServer extends AssetServer {
       return Response.ok(file.readAsBytesSync(), headers: <String, String>{
         'Content-Type': 'text/javascript',
       });
-    } else if (request.url.path.endsWith('dart_sdk.js')) {
+    } else if (request.url.path.endsWith('dart_sdk.js.map')) {
       final File file = fs.file(fs.path.join(
         artifacts.getArtifactPath(Artifact.flutterWebSdk),
         'kernel',
         'amd',
-        'dart_sdk.js',
+        'dart_sdk.js.map',
       ));
-      return Response.ok(file.readAsBytesSync(), headers: <String, String>{
-        'Content-Type': 'text/javascript',
-      });
-    } else if (request.url.path.endsWith('dart_sdk.js.map')) {
+      return Response.ok(file.readAsBytesSync());
+    } else if (request.url.path.endsWith('dart_sdk.js')) {
       final File file = fs.file(fs.path.join(
         artifacts.getArtifactPath(Artifact.flutterWebSdk),
         'kernel',
         'amd',
-        'dart_sdk.js.map',
+        'dart_sdk.js',
       ));
-      return Response.ok(file.readAsBytesSync());
+      return Response.ok(file.readAsBytesSync(), headers: <String, String>{
+        'Content-Type': 'text/javascript',
+      });
     } else if (request.url.path.endsWith('.dart')) {
       // This is likely a sourcemap request. The first segment is the
       // package name, and the rest is the path to the file relative to
       // the package uri. For example, `foo/bar.dart` would represent a
       // file at a path like `foo/lib/bar.dart`. If there is no leading
       // segment, then we assume it is from the current package.
+      String basePath = request.url.path;
+      basePath = basePath.replaceFirst('packages/build_web_compilers/', '');
+      basePath = basePath.replaceFirst('packages/', '');
 
       // Handle sdk requests that have mangled urls from engine build.
-      if (request.url.path.contains('flutter_web_sdk')) {
+      if (request.url.path.contains('dart-sdk')) {
         // Note: the request is a uri and not a file path, so they always use `/`.
-        final String sdkPath = fs.path.joinAll(request.url.path.split('flutter_web_sdk/').last.split('/'));
-        final String webSdkPath = artifacts.getArtifactPath(Artifact.flutterWebSdk);
-        return Response.ok(fs.file(fs.path.join(webSdkPath, sdkPath)).readAsBytesSync());
+        final String sdkPath = fs.path.joinAll(request.url.path.split('dart-sdk/').last.split('/'));
+        final String dartSdkPath = artifacts.getArtifactPath(Artifact.engineDartSdkPath);
+        final File candidateFile = fs.file(fs.path.join(dartSdkPath, sdkPath));
+        return Response.ok(candidateFile.readAsBytesSync());
+      }
+
+      // See if it is a flutter sdk path.
+      final String webSdkPath = artifacts.getArtifactPath(Artifact.flutterWebSdk);
+      final File candidateFile = fs.file(fs.path.join(webSdkPath,
+        basePath.split('/').join(platform.pathSeparator)));
+      if (candidateFile.existsSync()) {
+        return Response.ok(candidateFile.readAsBytesSync());
       }
 
       final String packageName = request.url.pathSegments.length == 1

packages/flutter_tools/test/general.shard/web/asset_server_test.dart

@@ -2,8 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/build_runner/web_fs.dart';
+import 'package:flutter_tools/src/globals.dart';
 import 'package:flutter_tools/src/project.dart';
 import 'package:shelf/shelf.dart';
 
@@ -52,6 +54,35 @@ void main() {
     expect(await response.readAsString(), 'hello');
   }));
 
+  test('can serve a sourcemap from dart:ui', () => testbed.run(() async {
+    final String flutterWebSdkPath = artifacts.getArtifactPath(Artifact.flutterWebSdk);
+    final File windowSourceFile = fs.file(fs.path.join(flutterWebSdkPath, 'lib', 'ui', 'src', 'ui', 'window.dart'))
+      ..createSync(recursive: true)
+      ..writeAsStringSync('test');
+    final Response response = await assetServer
+      .handle(Request('GET', Uri.parse('http://localhost:8080/packages/build_web_compilers/lib/ui/src/ui/window.dart')));
+
+    expect(response.headers, <String, String>{
+      'content-length': windowSourceFile.lengthSync().toString(),
+    });
+    expect(await response.readAsString(), 'test');
+  }));
+
+  test('can serve a sourcemap from the dart:sdk', () => testbed.run(() async {
+    final String dartSdkPath = artifacts.getArtifactPath(Artifact.engineDartSdkPath);
+    final File listSourceFile = fs.file(fs.path.join(dartSdkPath, 'lib', 'core', 'list.dart'))
+      ..createSync(recursive: true)
+      ..writeAsStringSync('test');
+
+    final Response response = await assetServer
+      .handle(Request('GET', Uri.parse('http://localhost:8080/packages/dart-sdk/lib/core/list.dart')));
+
+    expect(response.headers, <String, String>{
+      'content-length': listSourceFile.lengthSync().toString(),
+    });
+    expect(await response.readAsString(), 'test');
+  }));
+
   test('can serve an asset with a png content type', () => testbed.run(() async {
     final Response response = await assetServer
       .handle(Request('GET', Uri.parse('http://localhost:8080/assets/foo.png')));