command: hide internal commands

This marks commands as internal via a magic usage string.

Signed-off-by: Ophestra <cat@gensokyo.uk>

command/command.go

@@ -6,6 +6,9 @@ import (
 	"strings"
 )
 
+// UsageInternal causes the command to be hidden from help text when set as the usage string.
+const UsageInternal = "internal"
+
 type (
 	// HandlerFunc is called when matching a directly handled subcommand tree.
 	HandlerFunc = func(args []string) error

command/help.go

@@ -44,8 +44,10 @@ func (n *node) writeCommands(w io.Writer) error {
 	if n == nil {
 		return nil
 	}
-	if _, err := fmt.Fprintf(w, "\t%s\t%s\n", n.name, n.usage); err != nil {
+	if n.usage != UsageInternal {
-		return err
+		if _, err := fmt.Fprintf(w, "\t%s\t%s\n", n.name, n.usage); err != nil {
+			return err
+		}
 	}
 	return n.next.writeCommands(w)
 }

command/parse_test.go

@@ -289,6 +289,7 @@ func buildTestCommand(wout, wlog io.Writer) (c command.Command) {
 		})
 
 	c.New("empty", "empty subcommand")
+	c.New("hidden", command.UsageInternal)
 
 	c.New("join", "wraps strings.Join").
 		Command("out", "write result to wout", func(args []string) error {