Use gopkg.in/yaml.v2 for Helmfile v0.x (#609)

This should fix #435 for Helmfile v0.x releases since the next v0.150.0.
We introduce a new envvar to opt-in to the new YAML library, so that you can give it a shot before upgrading your Helmfile to v1. The same envvar can be used to opt-out of the new YAML library after you upgrade to Helmfile v1, giving you a more flexible migration story.

Signed-off-by: Yusuke Kuoka <ykuoka@gmail.com>

pkg/runtime/runtime.go

@@ -13,13 +13,23 @@ import (
 var (
 	V1Mode bool
 
+	// GoccyGoYaml is set to true in order to let Helmfile use
+	// goccy/go-yaml instead of gopkg.in/yaml.v2.
+	// It's false by default in Helmfile v0.x and true by default for Helmfile v1.x.
+	GoccyGoYaml bool
+
 	// We set this via ldflags at build-time so that we can use the
 	// value specified at the build time as the runtime default.
 	v1Mode string
 )
 
 func Info() string {
-	return fmt.Sprintf("V1 mode = %v", V1Mode)
+	yamlLib := "gopkg.in/yaml.v2"
+	if GoccyGoYaml {
+		yamlLib = "goccy/go-yaml"
+	}
+
+	return fmt.Sprintf("V1 mode = %v\nYAML library = %v", V1Mode, yamlLib)
 }
 
 func init() {
@@ -34,4 +44,14 @@ func init() {
 	default:
 		V1Mode, _ = strconv.ParseBool(v1Mode)
 	}
+
+	// You can switch the YAML library at runtime via an envvar:
+	switch os.Getenv(envvar.GoccyGoYaml) {
+	case "true":
+		GoccyGoYaml = true
+	case "false":
+		GoccyGoYaml = false
+	default:
+		GoccyGoYaml = V1Mode
+	}
 }