open a file in the diff panel via clide ui open diff

Adds diff as a fourth ui.open target. The diff extension now retains an
app-scoped DiffController and subscribes to its builtin.diff/selection
channel: a selection reveals the diff tab and focuses the file, which
the view scrolls into view and highlights. Retaining the controller in
the extension (not the view) lets a focus survive the tab being
revealed/remounted, mirroring the ReaderNav viewers.

Closes T-233.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/builtin/diff/diff_controller_test.dart

@@ -0,0 +1,88 @@
+/// Tests DiffController's load + focus behaviour (T-233): loading hydrates the
+/// diff list and clears stale focus; focus() records a path, notifies, and
+/// reloads; git.changed refreshes.
+library;
+
+import 'package:clide/builtin/diff/src/diff_controller.dart';
+import 'package:clide/clide.dart';
+import 'package:clide/kernel/kernel.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../../helpers/fake_ipc.dart';
+
+IpcResponse _ok(Map<String, Object?> data) => IpcResponse.ok(id: '', data: data);
+
+Map<String, Object?> _file(String path) => {'path': path, 'hunks': const []};
+
+void main() {
+  late DaemonBus bus;
+  late FakeDaemonClient ipc;
+  late DiffController c;
+  late int diffCalls;
+
+  setUp(() {
+    bus = DaemonBus();
+    ipc = FakeDaemonClient(log: Logger(), events: bus);
+    diffCalls = 0;
+    ipc.stub('git.diff', (_) async {
+      diffCalls++;
+      return _ok({
+        'diffs': [_file('lib/a.dart'), _file('lib/b.dart')],
+      });
+    });
+    c = DiffController(ipc: ipc, events: bus);
+  });
+
+  tearDown(() async {
+    c.dispose();
+    await bus.dispose();
+  });
+
+  test('load hydrates the diff list', () async {
+    await c.load();
+    expect(c.diffs.map((d) => d['path']), ['lib/a.dart', 'lib/b.dart']);
+    expect(c.error, isNull);
+  });
+
+  test('focus records the path, notifies, and reloads', () async {
+    await c.load();
+    final before = diffCalls;
+    var notified = 0;
+    c.addListener(() => notified++);
+
+    c.focus('lib/b.dart');
+    expect(c.focusPath, 'lib/b.dart');
+    expect(notified, greaterThan(0));
+    // focus() reloads so the latest edits to that file are present.
+    await Future<void>.delayed(Duration.zero);
+    expect(diffCalls, greaterThan(before));
+  });
+
+  test('a focus whose file leaves the diff is dropped on reload', () async {
+    c.focus('lib/gone.dart');
+    expect(c.focusPath, 'lib/gone.dart');
+    // The reload triggered by focus() returns a list without that file.
+    await Future<void>.delayed(Duration.zero);
+    expect(c.focusPath, isNull);
+  });
+
+  test('a focus that stays in the diff survives reload', () async {
+    c.focus('lib/a.dart');
+    await Future<void>.delayed(Duration.zero);
+    expect(c.focusPath, 'lib/a.dart');
+  });
+
+  test('git.changed refreshes the diff', () async {
+    await c.load();
+    final before = diffCalls;
+    bus.emit(DaemonEvent(subsystem: 'git', kind: 'git.changed', data: const {}, ts: DateTime.now().toUtc()));
+    await Future<void>.delayed(Duration.zero);
+    expect(diffCalls, greaterThan(before));
+  });
+
+  test('a git.diff error surfaces on the controller', () async {
+    ipc.stub('git.diff', (_) async => IpcResponse.err(id: '', error: IpcError(code: IpcExitCode.toolError, kind: IpcErrorKind.toolError, message: 'boom')));
+    await c.load();
+    expect(c.error, 'boom');
+  });
+}

test/builtin/diff/diff_view_test.dart

@@ -0,0 +1,71 @@
+/// Widget tests for DiffView focus (T-233): an injected controller renders its
+/// diffs, and focusing a file highlights its header with the focus accent.
+library;
+
+import 'package:clide/builtin/diff/src/diff_controller.dart';
+import 'package:clide/builtin/diff/src/diff_view.dart';
+import 'package:clide/clide.dart';
+import 'package:clide/kernel/kernel.dart';
+import 'package:clide/widgets/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../../helpers/fake_ipc.dart';
+import '../../helpers/kernel_fixture.dart';
+import '../../helpers/widget_harness.dart';
+
+IpcResponse _ok(Map<String, Object?> data) => IpcResponse.ok(id: '', data: data);
+Map<String, Object?> _file(String path) => {'path': path, 'hunks': const []};
+
+ClideText _header(WidgetTester tester, String path) => tester.widget<ClideText>(find.byWidgetPredicate((w) => w is ClideText && w.data == path));
+
+void main() {
+  late KernelFixture f;
+  late DaemonBus bus;
+  late FakeDaemonClient ipc;
+  late DiffController c;
+
+  setUp(() async {
+    f = await KernelFixture.create();
+    bus = DaemonBus();
+    ipc = FakeDaemonClient(log: Logger(), events: bus);
+    ipc.stub(
+        'git.diff',
+        (_) async => _ok({
+              'diffs': [_file('lib/a.dart'), _file('lib/b.dart')]
+            }));
+    c = DiffController(ipc: ipc, events: bus);
+  });
+
+  tearDown(() async {
+    c.dispose();
+    await bus.dispose();
+    f.dispose();
+  });
+
+  testWidgets('renders the injected controller\'s diffs', (tester) async {
+    await c.load();
+    await tester.pumpWidget(harness(f, DiffView(controller: c)));
+    await tester.pumpAndSettle();
+    expect(find.byWidgetPredicate((w) => w is ClideText && w.data == 'lib/a.dart'), findsOneWidget);
+    expect(find.byWidgetPredicate((w) => w is ClideText && w.data == 'lib/b.dart'), findsOneWidget);
+  });
+
+  testWidgets('focusing a file highlights its header with the focus accent', (tester) async {
+    await c.load();
+    await tester.pumpWidget(harness(f, DiffView(controller: c)));
+    await tester.pumpAndSettle();
+
+    final ctx = tester.element(find.byType(DiffView));
+    final tokens = ClideTheme.of(ctx).surface;
+    // Before focus: header uses the plain panel-header foreground.
+    expect(_header(tester, 'lib/b.dart').color, tokens.panelHeaderForeground);
+
+    c.focus('lib/b.dart');
+    await tester.pumpAndSettle();
+
+    // After focus: the targeted file's header switches to the focus accent.
+    expect(_header(tester, 'lib/b.dart').color, tokens.globalFocus);
+    // The other file stays unhighlighted.
+    expect(_header(tester, 'lib/a.dart').color, tokens.panelHeaderForeground);
+  });
+}