Mark experimental flags in --help

Prior to this commit, experimental flags were not distinguishable from
regular flags in `--help`

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

util/cobrautil/cobrautil.go

@@ -1,6 +1,10 @@
 package cobrautil
 
-import "github.com/spf13/cobra"
+import (
+	"github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+	"github.com/spf13/pflag"
+)
 
 // HideInheritedFlags hides inherited flags
 func HideInheritedFlags(cmd *cobra.Command, hidden ...string) {
@@ -12,3 +16,38 @@ func HideInheritedFlags(cmd *cobra.Command, hidden ...string) {
 		_ = cmd.Flags().MarkHidden(h)
 	}
 }
+
+const annotationExperimentalCLI = "experimentalCLI"
+
+func MarkFlagExperimental(f *pflag.Flag) {
+	if _, ok := f.Annotations[annotationExperimentalCLI]; ok {
+		return
+	}
+	if f.Annotations == nil {
+		f.Annotations = make(map[string][]string)
+	}
+	f.Annotations[annotationExperimentalCLI] = nil
+	f.Usage += " (EXPERIMENTAL)"
+}
+
+func MarkFlagsExperimental(fs *pflag.FlagSet, names ...string) {
+	for _, name := range names {
+		f := fs.Lookup(name)
+		if f == nil {
+			logrus.Warningf("Unknown flag name %q", name)
+			continue
+		}
+		MarkFlagExperimental(f)
+	}
+}
+
+func MarkCommandExperimental(c *cobra.Command) {
+	if _, ok := c.Annotations[annotationExperimentalCLI]; ok {
+		return
+	}
+	if c.Annotations == nil {
+		c.Annotations = make(map[string]string)
+	}
+	c.Annotations[annotationExperimentalCLI] = ""
+	c.Short += " (EXPERIMENTAL)"
+}