[flutter_tools] ensure all source maps load correctly for release and profile (#50702)

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

@@ -400,6 +400,7 @@ class _ResidentWebRunner extends ResidentWebRunner {
       urlTunneller: urlTunneller,
       buildMode: debuggingOptions.buildInfo.mode,
       enableDwds: _enableDwds,
+      entrypoint: globals.fs.file(target).uri,
     );
     final Uri url = await device.devFS.create();
     if (debuggingOptions.buildInfo.isDebug) {

packages/flutter_tools/lib/src/web/devfs_web.dart

@@ -53,6 +53,7 @@ class WebAssetServer implements AssetReader {
     UrlTunneller urlTunneller,
     BuildMode buildMode,
     bool enableDwds,
+    Uri entrypoint,
   ) async {
     try {
       final InternetAddress address = (await InternetAddress.lookup(hostname)).first;
@@ -63,7 +64,7 @@ class WebAssetServer implements AssetReader {
 
       // In release builds deploy a simpler proxy server.
       if (buildMode != BuildMode.debug) {
-        final ReleaseAssetServer releaseAssetServer = ReleaseAssetServer();
+        final ReleaseAssetServer releaseAssetServer = ReleaseAssetServer(entrypoint);
         shelf.serveRequests(httpServer, releaseAssetServer.handle);
         return server;
       }
@@ -318,8 +319,10 @@ class WebDevFS implements DevFS {
     @required this.urlTunneller,
     @required this.buildMode,
     @required this.enableDwds,
+    @required this.entrypoint,
   });
 
+  final Uri entrypoint;
   final String hostname;
   final int port;
   final String packagesFilePath;
@@ -385,6 +388,7 @@ class WebDevFS implements DevFS {
       urlTunneller,
       buildMode,
       enableDwds,
+      entrypoint,
     );
     return Uri.parse('http://$hostname:$port');
   }
@@ -552,15 +556,22 @@ String _filePathToUriFragment(String path) {
 }
 
 class ReleaseAssetServer {
+  ReleaseAssetServer(this.entrypoint);
+
+  final Uri entrypoint;
+
   // Locations where source files, assets, or source maps may be located.
   final List<Uri> _searchPaths = <Uri>[
     globals.fs.directory(getWebBuildDirectory()).uri,
-    globals.fs.directory(Cache.flutterRoot).parent.uri,
-    globals.fs.currentDirectory.childDirectory('lib').uri,
+    globals.fs.directory(Cache.flutterRoot).uri,
+    globals.fs.currentDirectory.uri,
   ];
 
   Future<shelf.Response> handle(shelf.Request request) async {
     Uri fileUri;
+    if (request.url.toString() == 'main.dart') {
+      fileUri = entrypoint;
+    } else {
       for (final Uri uri in _searchPaths) {
         final Uri potential = uri.resolve(request.url.path);
         if (potential == null || !globals.fs.isFileSync(potential.toFilePath())) {
@@ -569,7 +580,7 @@ class ReleaseAssetServer {
         fileUri = potential;
         break;
       }
-
+    }
     if (fileUri != null) {
       final File file = globals.fs.file(fileUri);
       final Uint8List bytes = file.readAsBytesSync();

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

@@ -289,6 +289,7 @@ void main() {
         urlTunneller: null,
         buildMode: BuildMode.debug,
         enableDwds: false,
+        entrypoint: Uri.base,
       );
       webDevFS.requireJS.createSync(recursive: true);
       webDevFS.dartSdk.createSync(recursive: true);

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

@@ -40,7 +40,7 @@ void main() {
   });
 
   test('release asset server serves correct mime type and content length for png', () => testbed.run(() async {
-    final ReleaseAssetServer assetServer = ReleaseAssetServer();
+    final ReleaseAssetServer assetServer = ReleaseAssetServer(Uri.base);
     globals.fs.file(globals.fs.path.join('build', 'web', 'assets', 'foo.png'))
       ..createSync(recursive: true)
       ..writeAsBytesSync(kTransparentImage);
@@ -54,7 +54,7 @@ void main() {
   }));
 
   test('release asset server serves correct mime type and content length for JavaScript', () => testbed.run(() async {
-    final ReleaseAssetServer assetServer = ReleaseAssetServer();
+    final ReleaseAssetServer assetServer = ReleaseAssetServer(Uri.base);
     globals.fs.file(globals.fs.path.join('build', 'web', 'assets', 'foo.js'))
       ..createSync(recursive: true)
       ..writeAsStringSync('function main() {}');
@@ -68,7 +68,7 @@ void main() {
   }));
 
   test('release asset server serves correct mime type and content length for html', () => testbed.run(() async {
-    final ReleaseAssetServer assetServer = ReleaseAssetServer();
+    final ReleaseAssetServer assetServer = ReleaseAssetServer(Uri.base);
     globals.fs.file(globals.fs.path.join('build', 'web', 'assets', 'foo.html'))
       ..createSync(recursive: true)
       ..writeAsStringSync('<!doctype html><html></html>');
@@ -82,7 +82,7 @@ void main() {
   }));
 
   test('release asset server serves content from flutter root', () => testbed.run(() async {
-    final ReleaseAssetServer assetServer = ReleaseAssetServer();
+    final ReleaseAssetServer assetServer = ReleaseAssetServer(Uri.base);
     globals.fs.file(globals.fs.path.join('flutter', 'bar.dart'))
       ..createSync(recursive: true)
       ..writeAsStringSync('void main() { }');
@@ -93,8 +93,8 @@ void main() {
   }));
 
   test('release asset server serves content from project directory', () => testbed.run(() async {
-    final ReleaseAssetServer assetServer = ReleaseAssetServer();
-    globals.fs.file(globals.fs.path.join('lib', 'bar.dart'))
+    final ReleaseAssetServer assetServer = ReleaseAssetServer(Uri.base);
+    globals.fs.file(globals.fs.path.join('bar.dart'))
       ..createSync(recursive: true)
       ..writeAsStringSync('void main() { }');
     final Response response = await assetServer