refactor(flags): accept plural flag names through one normalize function

Every command accepts a flag's plural, such as --add-labels for
--add-label (D8), instead of per-command alias maps.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/app.go

@@ -214,19 +214,34 @@ var rootGroups = map[string]string{
 // Commands add other gh verbs, such as new, co, add and get, to their own Aliases.
 var verbAliases = map[string]string{"list": "ls", "delete": "rm"}
 
-// addVerbAliases gives every list and delete command its short name.
+// addVerbAliases gives every list and delete command its short name, and lets its flags be named
+// in the plural.
 func addVerbAliases(cmd *cobra.Command) {
 	if alias, ok := verbAliases[cmd.Name()]; ok && cmd.HasParent() && !slices.Contains(cmd.Aliases, alias) {
 		cmd.Aliases = append(cmd.Aliases, alias)
 	}
+	acceptPlurals(cmd)
 	for _, child := range cmd.Commands() {
 		addVerbAliases(child)
 	}
 }
 
+// acceptPlurals lets the flags of cmd be named in the plural, such as --add-labels for the gh name
+// --add-label (D8), without showing the plural in help.
+func acceptPlurals(cmd *cobra.Command) {
+	names := map[string]bool{}
+	cmd.Flags().VisitAll(func(flag *pflag.Flag) { names[flag.Name] = true })
+	normalize := cmd.Flags().GetNormalizeFunc()
+	cmd.Flags().SetNormalizeFunc(func(flags *pflag.FlagSet, name string) pflag.NormalizedName {
+		if singular, ok := strings.CutSuffix(name, "s"); ok && !names[name] && names[singular] {
+			name = singular
+		}
+		return normalize(flags, name)
+	})
+}
+
 // flagAliases makes the flags of cmd accept each key of aliases as another name of the flag it maps
-// to, without showing it in help. Renamed flags keep their old names working this way, such as the
-// plural --add-labels after the singular gh name --add-label became primary (D8).
+// to, without showing it in help. Renamed flags keep their old names working this way.
 func flagAliases(cmd *cobra.Command, aliases map[string]string) {
 	normalize := cmd.Flags().GetNormalizeFunc()
 	cmd.Flags().SetNormalizeFunc(func(flags *pflag.FlagSet, name string) pflag.NormalizedName {