Changes NoArgs to report invalid argument

NoArgs currently reports "unknown command", which is a little
misleading to the user. Change it to report "invalid argument" as
a more appropriate return error. This should be appropriate for
both root and sub-commands.

Author: neurocline

args.go

@@ -26,7 +26,7 @@ func legacyArgs(cmd *Command, args []string) error {
 // NoArgs returns an error if any args are included.
 func NoArgs(cmd *Command, args []string) error {
 	if len(args) > 0 {
-		return fmt.Errorf("unknown command %q for %q", args[0], cmd.CommandPath())
+		return fmt.Errorf("invalid argument %q for %q", args[0], cmd.CommandPath())
 	}
 	return nil
 }

args_test.go

@@ -26,7 +26,7 @@ func TestNoArgsWithArgs(t *testing.T) {
 	}
 
 	got := err.Error()
-	expected := `unknown command "illegal" for "c"`
+	expected := `invalid argument "illegal" for "c"`
 	if got != expected {
 		t.Errorf("Expected: %q, got: %q", expected, got)
 	}
@@ -223,7 +223,7 @@ func TestChildTakesNoArgs(t *testing.T) {
 	}
 
 	got := err.Error()
-	expected := `unknown command "illegal" for "root child"`
+	expected := `invalid argument "illegal" for "root child"`
 	if !strings.Contains(got, expected) {
 		t.Errorf("expected %q, got %q", expected, got)
 	}