Implement the VM service getFlagList API (#2438)

Author: elliette

Diff for: dwds/CHANGELOG.md

@@ -3,6 +3,7 @@
 - Fix bug where debugging clients are not aware of service extensions when connecting to a new web app. - [#2388](https://github.com/dart-lang/webdev/pull/2388)
 - Respect the value of `pause_isolates_on_start` during page-refreshes. - [#2431](https://github.com/dart-lang/webdev/pull/2431)
 - Fix issue where DAP clients wouldn't resume after a restart. - [#2441](https://github.com/dart-lang/webdev/pull/2441)
+- Add implementation for the VM Service's `getFlagList` API. - [#2438](https://github.com/dart-lang/webdev/pull/2438)
 
 ## 24.0.0
 

Diff for: dwds/lib/src/services/chrome_proxy_service.dart

@@ -92,12 +92,17 @@ class ChromeProxyService implements VmServiceInterface {
 
   StreamSubscription<ConsoleAPIEvent>? _consoleSubscription;
 
-  bool _pauseIsolatesOnStart = false;
+  /// The flags that can be set at runtime via [setFlag] and their respective
+  /// values.
+  final Map<String, bool> _currentVmServiceFlags = {
+    _pauseIsolatesOnStartFlag: false,
+  };
 
   /// The value of the [_pauseIsolatesOnStartFlag].
   ///
   /// This value can be updated at runtime via [setFlag].
-  bool get pauseIsolatesOnStart => _pauseIsolatesOnStart;
+  bool get pauseIsolatesOnStart =>
+      _currentVmServiceFlags[_pauseIsolatesOnStartFlag] ?? false;
 
   /// Whether or not the connected app has a pending restart.
   bool get hasPendingRestart => _resumeAfterRestartEventsController.hasListener;
@@ -775,9 +780,22 @@ ${globalToolConfiguration.loadStrategy.loadModuleSnippet}("dart_sdk").developer.
   }
 
   @override
-  Future<FlagList> getFlagList() async {
-    // VM flags do not apply to web apps.
-    return FlagList(flags: []);
+  Future<FlagList> getFlagList() {
+    return wrapInErrorHandlerAsync(
+      'getFlagList',
+      _getFlagList,
+    );
+  }
+
+  Future<FlagList> _getFlagList() {
+    final flags = _currentVmServiceFlags.entries.map<Flag>(
+      (entry) => Flag(
+        name: entry.key,
+        valueAsString: '${entry.value}',
+      ),
+    );
+
+    return Future.value(FlagList(flags: flags.toList()));
   }
 
   @override
@@ -1231,14 +1249,12 @@ ${globalToolConfiguration.loadStrategy.loadModuleSnippet}("dart_sdk").developer.
       );
 
   Future<Success> _setFlag(String name, String value) async {
-    if (!_supportedVmServiceFlags.contains(name)) {
+    if (!_currentVmServiceFlags.containsKey(name)) {
       return _rpcNotSupportedFuture('setFlag');
     }
 
-    if (name == _pauseIsolatesOnStartFlag) {
-      assert(value == 'true' || value == 'false');
-      _pauseIsolatesOnStart = value == 'true';
-    }
+    assert(value == 'true' || value == 'false');
+    _currentVmServiceFlags[name] = value == 'true';
 
     return Success();
   }
@@ -1716,8 +1732,3 @@ const _stderrTypes = ['error'];
 const _stdoutTypes = ['log', 'info', 'warning'];
 
 const _pauseIsolatesOnStartFlag = 'pause_isolates_on_start';
-
-/// The flags that can be set at runtime via [setFlag].
-const _supportedVmServiceFlags = {
-  _pauseIsolatesOnStartFlag,
-};

Diff for: dwds/test/chrome_proxy_service_test.dart

@@ -2097,6 +2097,38 @@ void main() {
       });
     });
 
+    group('getFlagList', () {
+      List<String> stringifyFlags(FlagList flagList) {
+        return flagList.flags
+                ?.map((flag) => '${flag.name} -> ${flag.valueAsString}')
+                .toList() ??
+            [];
+      }
+
+      test('returns expected default values', () async {
+        final service = context.service;
+        final flagList = await service.getFlagList();
+        expect(
+          stringifyFlags(flagList),
+          containsAll([
+            'pause_isolates_on_start -> false',
+          ]),
+        );
+      });
+
+      test('returns any modified flag values', () async {
+        final service = context.service;
+        await service.setFlag('pause_isolates_on_start', 'true');
+        final flagList = await service.getFlagList();
+        expect(
+          stringifyFlags(flagList),
+          containsAll([
+            'pause_isolates_on_start -> true',
+          ]),
+        );
+      });
+    });
+
     group('streamListen/onEvent', () {
       late ChromeProxyService service;