Add UsageError and MissingConf back

z/cmd.go

@@ -525,7 +525,6 @@ func (x *Cmd) Log(format string, a ...any) {
 // convenience. See UseConf.
 func (x *Cmd) C(q string) (string, error) {
 	if Conf == nil {
-		log.Printf("cmd %q requires a configurer (Z.Conf must be assigned)", x.Name)
 		return "", UsesConf{x}
 	}
 	path := x.Path()
@@ -581,6 +580,11 @@ func (x *Cmd) Fill(tmpl string) string {
 	return buf.String()
 }
 
+// UsageError returns IncorrectUsage for self.
+func (x *Cmd) UsageError() error {
+	return IncorrectUsage{x}
+}
+
 // --------------------- bonzai.Command interface ---------------------
 
 // GetName fulfills the bonzai.Command interface. No Fill.

z/errors.go

@@ -26,6 +26,14 @@ func (e WrongNumArgs) Error() string {
 	return fmt.Sprintf("wrong number of args, %v required", e.Cmd.NumArgs)
 }
 
+type MissingConf struct {
+	Path string
+}
+
+func (e MissingConf) Error() string {
+	return fmt.Sprintf("missing conf value for %v", e.Path)
+}
+
 type UsesConf struct {
 	Cmd *Cmd
 }