[vm] Pass snapshot flag to kernel_service

Enable reporting of null safety compilation mode when running
`dart compile aot-snapshot`, `dart compile jit-snapshot`,
and `dart compile kernel`.

Closes flutter#44234

TEST=pkg/dartdev/test/commands/compile_test.dart

Change-Id: I0d4b35c6ccb4167c0c7539a4eb24a5139e29cf53
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/178990
Commit-Queue: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Ben Konyi <bkonyi@google.com>

Author: johnniwinther

pkg/dartdev/test/commands/compile_test.dart

@@ -356,4 +356,145 @@ void main() {}
     expect(File(outFile).existsSync(), true,
         reason: 'File not found: $outFile');
   });
+
+  test('Compile AOT snapshot with sound null safety', () {
+    final p = project(mainSrc: '''void main() {}''');
+    final inFile = path.canonicalize(path.join(p.dirPath, p.relativeFilePath));
+    final outFile = path.canonicalize(path.join(p.dirPath, 'myaot'));
+
+    var result = p.runSync(
+      [
+        'compile',
+        'aot-snapshot',
+        '-o',
+        outFile,
+        inFile,
+      ],
+    );
+
+    expect(result.stdout, contains(soundNullSafetyMessage));
+    expect(result.stderr, isEmpty);
+    expect(result.exitCode, 0);
+    expect(File(outFile).existsSync(), true,
+        reason: 'File not found: $outFile');
+  });
+
+  test('Compile AOT snapshot with unsound null safety', () {
+    final p = project(mainSrc: '''
+// @dart=2.9
+void main() {}
+''');
+    final inFile = path.canonicalize(path.join(p.dirPath, p.relativeFilePath));
+    final outFile = path.canonicalize(path.join(p.dirPath, 'myaot'));
+
+    var result = p.runSync(
+      [
+        'compile',
+        'aot-snapshot',
+        '-o',
+        outFile,
+        inFile,
+      ],
+    );
+
+    expect(result.stdout, contains(unsoundNullSafetyMessage));
+    expect(result.stderr, isEmpty);
+    expect(result.exitCode, 0);
+    expect(File(outFile).existsSync(), true,
+        reason: 'File not found: $outFile');
+  });
+
+  test('Compile kernel with sound null safety', () {
+    final p = project(mainSrc: '''void main() {}''');
+    final inFile = path.canonicalize(path.join(p.dirPath, p.relativeFilePath));
+    final outFile = path.canonicalize(path.join(p.dirPath, 'mydill'));
+
+    var result = p.runSync(
+      [
+        'compile',
+        'kernel',
+        '-o',
+        outFile,
+        inFile,
+      ],
+    );
+
+    expect(result.stdout, contains(soundNullSafetyMessage));
+    expect(result.stderr, isEmpty);
+    expect(result.exitCode, 0);
+    expect(File(outFile).existsSync(), true,
+        reason: 'File not found: $outFile');
+  });
+
+  test('Compile kernel with unsound null safety', () {
+    final p = project(mainSrc: '''
+// @dart=2.9
+void main() {}
+''');
+    final inFile = path.canonicalize(path.join(p.dirPath, p.relativeFilePath));
+    final outFile = path.canonicalize(path.join(p.dirPath, 'mydill'));
+
+    var result = p.runSync(
+      [
+        'compile',
+        'kernel',
+        '-o',
+        outFile,
+        inFile,
+      ],
+    );
+
+    expect(result.stdout, contains(unsoundNullSafetyMessage));
+    expect(result.stderr, isEmpty);
+    expect(result.exitCode, 0);
+    expect(File(outFile).existsSync(), true,
+        reason: 'File not found: $outFile');
+  });
+
+  test('Compile JIT snapshot with sound null safety', () {
+    final p = project(mainSrc: '''void main() {}''');
+    final inFile = path.canonicalize(path.join(p.dirPath, p.relativeFilePath));
+    final outFile = path.canonicalize(path.join(p.dirPath, 'myjit'));
+
+    var result = p.runSync(
+      [
+        'compile',
+        'jit-snapshot',
+        '-o',
+        outFile,
+        inFile,
+      ],
+    );
+
+    expect(result.stdout, contains(soundNullSafetyMessage));
+    expect(result.stderr, isEmpty);
+    expect(result.exitCode, 0);
+    expect(File(outFile).existsSync(), true,
+        reason: 'File not found: $outFile');
+  });
+
+  test('Compile JIT snapshot with unsound null safety', () {
+    final p = project(mainSrc: '''
+// @dart=2.9
+void main() {}
+''');
+    final inFile = path.canonicalize(path.join(p.dirPath, p.relativeFilePath));
+    final outFile = path.canonicalize(path.join(p.dirPath, 'myjit'));
+
+    var result = p.runSync(
+      [
+        'compile',
+        'jit-snapshot',
+        '-o',
+        outFile,
+        inFile,
+      ],
+    );
+
+    expect(result.stdout, contains(unsoundNullSafetyMessage));
+    expect(result.stderr, isEmpty);
+    expect(result.exitCode, 0);
+    expect(File(outFile).existsSync(), true,
+        reason: 'File not found: $outFile');
+  });
 }