feat(internal/yaml): add copyright header to yaml file (#3510)

Write a copyright header to yaml file.

Fixes #3508

Author: JoeWang1127

internal/yaml/copyright.go

@@ -0,0 +1,31 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yaml
+
+const copyright = `# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+`

internal/yaml/yaml.go

@@ -72,13 +72,14 @@ func Read[T any](path string) (*T, error) {
 	return Unmarshal[T](data)
 }
 
-// Write marshals a value to YAML, formats it with yamlfmt, and writes it to a
-// file.
+// Write marshals a value to YAML, formats it with yamlfmt, adds a copyright header
+// and writes it to a file.
 func Write(path string, v any) error {
 	data, err := Marshal(v)
 	if err != nil {
 		return err
 	}
+	data = append([]byte(copyright), data...)
 	return os.WriteFile(path, data, 0644)
 }
 

internal/yaml/yaml_test.go

@@ -15,6 +15,7 @@
 package yaml
 
 import (
+	"os"
 	"path/filepath"
 	"testing"
 
@@ -74,6 +75,23 @@ func TestReadWrite(t *testing.T) {
 	}
 }
 
+func TestWrite(t *testing.T) {
+	want := copyright + `name: test
+version: v1.0.0
+`
+	path := filepath.Join(t.TempDir(), "test.yaml")
+	if err := Write(path, &testConfig{Name: "test", Version: "v1.0.0"}); err != nil {
+		t.Fatal(err)
+	}
+	got, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if diff := cmp.Diff(want, string(got)); diff != "" {
+		t.Errorf("mismatch (-want +got):\n%s", diff)
+	}
+}
+
 func TestReadError(t *testing.T) {
 	_, err := Read[testConfig]("/nonexistent/path/file.yaml")
 	if err == nil {