release_config: make the code more sharable

This will allow the `build-flag` command to use release_config_lib code.

Bug: 328495189
Test: manual
Change-Id: If068597b1d68c52c941788931997b7f77c73d2b3

cmd/release_config/release_config_lib/flag_value.go

@@ -0,0 +1,56 @@
+// Copyright 2024 Google Inc. All rights reserved.
+//
+// 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
+//
+//     http://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 release_config_lib
+
+import (
+	"android/soong/cmd/release_config/release_config_proto"
+)
+
+type FlagValue struct {
+	// The path providing this value.
+	path string
+
+	// Protobuf
+	proto release_config_proto.FlagValue
+}
+
+func FlagValueFactory(protoPath string) (fv *FlagValue) {
+	fv = &FlagValue{path: protoPath}
+	if protoPath != "" {
+		LoadTextproto(protoPath, &fv.proto)
+	}
+	return fv
+}
+
+func MarshalValue(value *release_config_proto.Value) string {
+	switch val := value.Val.(type) {
+	case *release_config_proto.Value_UnspecifiedValue:
+		// Value was never set.
+		return ""
+	case *release_config_proto.Value_StringValue:
+		return val.StringValue
+	case *release_config_proto.Value_BoolValue:
+		if val.BoolValue {
+			return "true"
+		}
+		// False ==> empty string
+		return ""
+	case *release_config_proto.Value_Obsolete:
+		return " #OBSOLETE"
+	default:
+		// Flagged as error elsewhere, so return empty string here.
+		return ""
+	}
+}