[flutter_conductor] pretty-print state JSON file (#87756)

dev/conductor/lib/state.dart

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:convert' show jsonDecode, jsonEncode;
+import 'dart:convert' show JsonEncoder, jsonDecode;
 
 import 'package:file/file.dart' show File;
 import 'package:platform/platform.dart';
@@ -230,10 +230,13 @@ ReleasePhase getNextPhase(ReleasePhase currentPhase) {
   return nextPhase;
 }
 
+// Indent two spaces.
+const JsonEncoder _encoder = JsonEncoder.withIndent('  ');
+
 void writeStateToFile(File file, pb.ConductorState state, List<String> logs) {
   state.logs.addAll(logs);
   file.writeAsStringSync(
-    jsonEncode(state.toProto3Json()),
+    _encoder.convert(state.toProto3Json()),
     flush: true,
   );
 }

dev/conductor/test/state_test.dart

@@ -0,0 +1,68 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:conductor/proto/conductor_state.pb.dart' as pb;
+import 'package:conductor/state.dart';
+import 'package:file/file.dart';
+import 'package:file/memory.dart';
+
+import './common.dart';
+
+void main() {
+  test('writeStateToFile() pretty-prints JSON with 2 spaces', () {
+    final MemoryFileSystem fileSystem = MemoryFileSystem.test();
+    final File stateFile = fileSystem.file('/path/to/statefile.json')
+      ..createSync(recursive: true);
+    const String candidateBranch = 'flutter-2.3-candidate.0';
+    final pb.ConductorState state = pb.ConductorState(
+      releaseChannel: 'stable',
+      releaseVersion: '2.3.4',
+      incrementLevel: 'z',
+      engine: pb.Repository(
+        candidateBranch: candidateBranch,
+        upstream: pb.Remote(
+          name: 'upstream',
+          url: 'https://github.com/flutter/engine.git',
+        ),
+      ),
+      framework: pb.Repository(
+        candidateBranch: candidateBranch,
+        upstream: pb.Remote(
+          name: 'upstream',
+          url: 'https://github.com/flutter/flutter.git',
+        ),
+      ),
+    );
+    writeStateToFile(
+      stateFile,
+      state,
+      <String>['[status] hello world'],
+    );
+    final String serializedState = stateFile.readAsStringSync();
+    const String expectedString = '''
+{
+  "releaseChannel": "stable",
+  "releaseVersion": "2.3.4",
+  "engine": {
+    "candidateBranch": "flutter-2.3-candidate.0",
+    "upstream": {
+      "name": "upstream",
+      "url": "https://github.com/flutter/engine.git"
+    }
+  },
+  "framework": {
+    "candidateBranch": "flutter-2.3-candidate.0",
+    "upstream": {
+      "name": "upstream",
+      "url": "https://github.com/flutter/flutter.git"
+    }
+  },
+  "logs": [
+    "[status] hello world"
+  ],
+  "incrementLevel": "z"
+}''';
+    expect(serializedState, expectedString);
+  });
+}