[flutter_tools] support hot reload of font assets (#109091)

Author: Jonah Williams

packages/flutter_tools/lib/src/devfs.dart

@@ -20,6 +20,8 @@ import 'compile.dart';
 import 'convert.dart' show base64, utf8;
 import 'vmservice.dart';
 
+const String _kFontManifest = 'FontManifest.json';
+
 class DevFSConfig {
   /// Should DevFS assume that symlink targets are stable?
   bool cacheSymlinks = false;
@@ -485,6 +487,9 @@ class DevFS {
   // A flag to indicate whether we have called `setAssetDirectory` on the target device.
   bool hasSetAssetDirectory = false;
 
+  /// Whether the font manifest was uploaded during [update].
+  bool didUpdateFontManifest = false;
+
   List<Uri> sources = <Uri>[];
   DateTime? lastCompiled;
   DateTime? _previousCompiled;
@@ -589,6 +594,7 @@ class DevFS {
     assert(trackWidgetCreation != null);
     assert(generator != null);
     final DateTime candidateCompileTime = DateTime.now();
+    didUpdateFontManifest = false;
     lastPackageConfig = packageConfig;
     _widgetCacheOutputFile = _fileSystem.file('$dillOutputPath.incremental.dill.widget_cache');
 
@@ -644,6 +650,11 @@ class DevFS {
         if (deviceUri.path.startsWith(assetBuildDirPrefix)) {
           archivePath = deviceUri.path.substring(assetBuildDirPrefix.length);
         }
+        // If the font manifest is updated, mark this as true so the hot runner
+        // can invoke a service extension to force the engine to reload fonts.
+        if (archivePath == _kFontManifest) {
+          didUpdateFontManifest = true;
+        }
 
         if (bundle.entryKinds[archivePath] == AssetKind.shader) {
           final Future<DevFSContent?> pending = shaderCompiler.recompileShader(content);

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

@@ -677,6 +677,9 @@ class WebDevFS implements DevFS {
   @override
   bool hasSetAssetDirectory = false;
 
+  @override
+  bool didUpdateFontManifest = false;
+
   Future<DebugConnection>? _cachedExtensionFuture;
   StreamSubscription<void>? _connectedApps;
 

packages/flutter_tools/lib/src/run_hot.dart

@@ -1032,7 +1032,7 @@ class HotRunner extends ResidentRunner {
 
   @visibleForTesting
   Future<void> evictDirtyAssets() async {
-    final List<Future<Map<String, dynamic>?>> futures = <Future<Map<String, dynamic>>>[];
+    final List<Future<void>> futures = <Future<void>>[];
     for (final FlutterDevice? device in flutterDevices) {
       if (device!.devFS!.assetPathsToEvict.isEmpty && device.devFS!.shaderPathsToEvict.isEmpty) {
         continue;
@@ -1060,6 +1060,14 @@ class HotRunner extends ResidentRunner {
         globals.printError('Application isolate not found for $device');
         continue;
       }
+
+      if (device.devFS!.didUpdateFontManifest) {
+        futures.add(device.vmService!.reloadAssetFonts(
+            isolateId: views.first.uiIsolate!.id!,
+            viewId: views.first.id,
+        ));
+      }
+
       for (final String assetPath in device.devFS!.assetPathsToEvict) {
         futures.add(
           device.vmService!
@@ -1081,7 +1089,7 @@ class HotRunner extends ResidentRunner {
       device.devFS!.assetPathsToEvict.clear();
       device.devFS!.shaderPathsToEvict.clear();
     }
-    await Future.wait<Map<String, Object?>?>(futures);
+    await Future.wait<void>(futures);
   }
 
   @override

packages/flutter_tools/lib/src/vmservice.dart

@@ -24,6 +24,7 @@ const String kListViewsMethod = '_flutter.listViews';
 const String kScreenshotSkpMethod = '_flutter.screenshotSkp';
 const String kScreenshotMethod = '_flutter.screenshot';
 const String kRenderFrameWithRasterStatsMethod = '_flutter.renderFrameWithRasterStats';
+const String kReloadAssetFonts = '_flutter.reloadAssetFonts';
 
 /// The error response code from an unrecoverable compilation failure.
 const int kIsolateReloadBarred = 1005;
@@ -880,6 +881,20 @@ class FlutterVmService {
     }
   }
 
+  /// Tell the provided flutter view that the font manifest has been updated
+  /// and asset fonts should be reloaded.
+  Future<void> reloadAssetFonts({
+    required String isolateId,
+    required String viewId,
+  }) async {
+    await callMethodWrapper(
+      kReloadAssetFonts,
+      isolateId: isolateId, args: <String, Object?>{
+        'viewId': viewId,
+      },
+    );
+  }
+
   /// Waits for a signal from the VM service that [extensionName] is registered.
   ///
   /// Looks at the list of loaded extensions for first Flutter view, as well as

packages/flutter_tools/test/general.shard/devfs_test.dart

@@ -643,6 +643,57 @@ void main() {
       FileSystem: () => fileSystem,
       ProcessManager: () => processManager,
     });
+
+    testUsingContext('DevFS tracks when FontManifest is updated', () async {
+      final FakeVmServiceHost fakeVmServiceHost = FakeVmServiceHost(
+        requests: <VmServiceExpectation>[createDevFSRequest],
+        httpAddress: Uri.parse('http://localhost'),
+      );
+      final BufferLogger logger = BufferLogger.test();
+      final DevFS devFS = DevFS(
+        fakeVmServiceHost.vmService,
+        'test',
+        fileSystem.currentDirectory,
+        fileSystem: fileSystem,
+        logger: logger,
+        osUtils: FakeOperatingSystemUtils(),
+        httpClient: FakeHttpClient.any(),
+      );
+
+      await devFS.create();
+
+      expect(devFS.didUpdateFontManifest, false);
+
+      final FakeResidentCompiler residentCompiler = FakeResidentCompiler()
+        ..onRecompile = (Uri mainUri, List<Uri>? invalidatedFiles) async {
+          fileSystem.file('lib/foo.dill')
+            ..createSync(recursive: true)
+            ..writeAsBytesSync(<int>[1, 2, 3, 4, 5]);
+          return const CompilerOutput('lib/foo.dill', 0, <Uri>[]);
+        };
+      final FakeBundle bundle = FakeBundle()
+        ..entries['FontManifest.json'] = DevFSByteContent(<int>[1, 2, 3, 4]);
+
+      final UpdateFSReport report = await devFS.update(
+        mainUri: Uri.parse('lib/main.dart'),
+        generator: residentCompiler,
+        dillOutputPath: 'lib/foo.dill',
+        pathToReload: 'lib/foo.txt.dill',
+        trackWidgetCreation: false,
+        invalidatedFiles: <Uri>[],
+        packageConfig: PackageConfig.empty,
+        shaderCompiler: const FakeShaderCompiler(),
+        bundle: bundle,
+      );
+
+      expect(report.success, true);
+      expect(devFS.shaderPathsToEvict, <String>{});
+      expect(devFS.assetPathsToEvict, <String>{'FontManifest.json'});
+      expect(devFS.didUpdateFontManifest, true);
+    }, overrides: <Type, Generator>{
+      FileSystem: () => fileSystem,
+      ProcessManager: () => processManager,
+    });
   });
 }
 

packages/flutter_tools/test/general.shard/resident_runner_test.dart

@@ -2633,6 +2633,9 @@ class FakeDevFS extends Fake implements DevFS {
   @override
   Set<String> shaderPathsToEvict = <String>{};
 
+  @override
+  bool didUpdateFontManifest = false;
+
   UpdateFSReport nextUpdateReport = UpdateFSReport(success: true);
 
   @override