Allow overriding the default help flags.

By default, help listings exclude unlisted commands and private flags.
Add a setting to Env to allow these defaults to be overridden, affecting the
environment and all its children.

command.go

@@ -40,6 +40,7 @@ type Env struct {
 	ctx    context.Context
 	cancel context.CancelCauseFunc
 	merge  bool
+	hflag  HelpFlags // default: no unlisted commands, no private flags
 }
 
 // Context returns the context associated with e. If e does not have its own
@@ -104,6 +105,12 @@ func (e *Env) SetContext(ctx context.Context) *Env {
 // will shadow the flag for the descendant.
 func (e *Env) MergeFlags(merge bool) *Env { e.merge = merge; return e }
 
+// HelpFlags sets the base help flags for e and returns e.
+//
+// By default, help listings do not include unlisted commands or private flags.
+// This permits the caller to override the default help printing rules.
+func (e *Env) HelpFlags(f HelpFlags) *Env { e.hflag = (f &^ IncludeCommands); return e }
+
 // output returns the log writer for c.
 func (e *Env) output() io.Writer {
 	if e.Log != nil {
@@ -281,7 +288,7 @@ func RunOrFail(env *Env, rawArgs []string) {
 		var uerr UsageError
 		if errors.As(err, &uerr) {
 			log.Printf("Error: %s", uerr.Message)
-			uerr.Env.Command.HelpInfo(0).WriteUsage(uerr.Env)
+			uerr.Env.Command.HelpInfo(env.hflag).WriteUsage(uerr.Env)
 		} else if !errors.Is(err, ErrRequestHelp) {
 			log.Printf("Error: %v", err)
 			os.Exit(1)

help.go

@@ -183,15 +183,15 @@ func writeTopics(w io.Writer, base, label string, topics []HelpInfo) {
 // runLongHelp is a run function that prints long-form help.
 // The topics are additional help topics to include in the output.
 func printLongHelp(env *Env, topics []HelpInfo) error {
-	ht := env.Command.HelpInfo(IncludeCommands)
+	ht := env.Command.HelpInfo(env.hflag | IncludeCommands)
 	ht.Topics = append(ht.Topics, topics...)
 	ht.WriteLong(env)
 	return ErrRequestHelp
 }
 
 // runShortHelp is a run function that prints synopsis help.
 func printShortHelp(env *Env) error {
-	env.Command.HelpInfo(0).WriteSynopsis(env)
+	env.Command.HelpInfo(env.hflag).WriteSynopsis(env)
 	return ErrRequestHelp
 }
 
@@ -202,7 +202,7 @@ func RunHelp(env *Env) error {
 	target := walkArgs(env.Parent, env.Args)
 	if target == env.Parent {
 		// For the parent, include the help command's own topics.
-		return printLongHelp(target, env.Command.HelpInfo(IncludeCommands).Topics)
+		return printLongHelp(target, env.Command.HelpInfo(env.hflag|IncludeCommands).Topics)
 	} else if target != nil {
 		return printLongHelp(target, nil)
 	}