[ddc] Add tests for '--reload-delta-kernel' and '--reload-last-accepted-kernel' flags.

Change-Id: I643957dcd8cc6611108c9ff67a9610bb19475af4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/408924
Commit-Queue: Nate Biggs <[email protected]>
Reviewed-by: Nicholas Shahan <[email protected]>

Author: natebiggs

pkg/dev_compiler/test/hot_reload_delta_flags_test.dart

@@ -0,0 +1,142 @@
+// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+import 'package:test/test.dart';
+
+const String program1 = '''
+class A {
+  final int i;
+  const A(this.i);
+}
+void main() {
+  final a = A(1);
+}
+''';
+
+const String program2Valid = '''
+class A {
+  final int i;
+  const A(this.i);
+}
+void main() {
+  final a = A(2);
+}
+''';
+
+const String program2Error = '''
+class A {
+  const A();
+}
+void main() {
+  final a = A();
+}
+''';
+
+String _resolvePath(String executableRelativePath) {
+  return Uri.file(Platform.resolvedExecutable)
+      .resolve(executableRelativePath)
+      .toFilePath();
+}
+
+Future<void> main() async {
+  group('hot reload flags', () {
+    late Directory tmp;
+    late File outputJs;
+    late File deltaDill;
+    late File lastAcceptedDill;
+    setUp(() {
+      File file(String path) => File.fromUri(tmp.uri.resolve(path));
+
+      tmp = Directory.systemTemp.createTempSync('hot_reload_flags_test');
+      outputJs = file('output.js');
+      deltaDill = file('delta.dill');
+      lastAcceptedDill = file('lastAccepted.dill');
+    });
+
+    tearDown(() {
+      tmp.deleteSync(recursive: true);
+    });
+
+    void runDDC(List<String> flags, String programSource,
+        {String? expectError}) async {
+      final sdkPath = p.dirname(Platform.executable);
+      final dartAotRuntime = p.absolute(sdkPath,
+          Platform.isWindows ? 'dartaotruntime.exe' : 'dartaotruntime');
+      final snapshotName = _resolvePath('snapshots/dartdevc_aot.dart.snapshot');
+      final outlinePath = _resolvePath('../lib/_internal/ddc_outline.dill');
+
+      final sourceFile = File.fromUri(tmp.uri.resolve('main.dart'));
+      sourceFile.writeAsStringSync(programSource);
+
+      final args = <String>[
+        snapshotName,
+        '--dart-sdk-summary',
+        outlinePath,
+        '-o',
+        outputJs.path,
+        ...flags,
+        sourceFile.path,
+      ];
+
+      final process = Process.runSync(dartAotRuntime, args);
+      if (expectError != null) {
+        expect(process.exitCode, isNonNegative);
+        expect(process.stderr, contains(expectError));
+      } else {
+        if (process.exitCode != 0) {
+          print(process.stdout);
+          print(process.stderr);
+        }
+        expect(process.exitCode, 0);
+      }
+    }
+
+    test('providing no flag skips inspector', () {
+      runDDC(const [], program1);
+      expect(outputJs.existsSync(), isTrue);
+      expect(outputJs.statSync().size, isNonNegative);
+    });
+
+    test('providing only delta output flag does not error', () {
+      runDDC(['--reload-delta-kernel=${deltaDill.path}'], program1);
+      expect(deltaDill.existsSync(), isTrue);
+      expect(deltaDill.statSync().size, isNonNegative);
+      expect(outputJs.existsSync(), isTrue);
+      expect(outputJs.statSync().size, isNonNegative);
+    });
+
+    test('providing delta output and last accepted input flag valid change',
+        () {
+      runDDC(['--reload-delta-kernel=${lastAcceptedDill.path}'], program1);
+      expect(lastAcceptedDill.existsSync(), isTrue);
+      expect(lastAcceptedDill.statSync().size, isNonNegative);
+
+      runDDC([
+        '--reload-last-accepted-kernel=${lastAcceptedDill.path}',
+        '--reload-delta-kernel=${deltaDill.path}'
+      ], program2Valid);
+      expect(lastAcceptedDill.existsSync(), isTrue);
+      expect(lastAcceptedDill.statSync().size, isNonNegative);
+      expect(deltaDill.existsSync(), isTrue);
+      expect(deltaDill.statSync().size, isNonNegative);
+      expect(outputJs.existsSync(), isTrue);
+      expect(outputJs.statSync().size, isNonNegative);
+    });
+
+    test('providing delta output and last accepted input flag invalid change',
+        () {
+      runDDC(['--reload-delta-kernel=${lastAcceptedDill.path}'], program1);
+      runDDC([
+        '--reload-last-accepted-kernel=${lastAcceptedDill.path}',
+        '--reload-delta-kernel=${deltaDill.path}'
+      ], program2Error, expectError: 'Const class cannot remove fields');
+      expect(lastAcceptedDill.existsSync(), isTrue);
+      expect(lastAcceptedDill.statSync().size, isNonNegative);
+      expect(deltaDill.existsSync(), isFalse);
+    });
+  });
+}