shell completion --format: only show usable methods

In a template you cann call function that are defined on a type, however
this is only useful if they return one value. If it returns more than
one the template cannot know what value it has to display.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

cmd/podman/common/completion.go

@@ -1084,7 +1084,12 @@ func getStructFields(f reflect.Value, prefix string) []string {
 func getMethodNames(f reflect.Value, prefix string) []string {
 	suggestions := make([]string, 0, f.NumMethod())
 	for j := 0; j < f.NumMethod(); j++ {
-		fname := f.Type().Method(j).Name
+		method := f.Type().Method(j)
+		// in a template we can only run functions with one return value
+		if method.Func.Type().NumOut() != 1 {
+			continue
+		}
+		fname := method.Name
 		if strings.HasPrefix(fname, prefix) {
 			// add method name with closing braces
 			suggestions = append(suggestions, fname+"}}")

cmd/podman/common/completion_test.go

@@ -37,6 +37,10 @@ func (c Car) internal() int {
 	return 0
 }
 
+func (c Car) TwoOut() (string, string) {
+	return "", ""
+}
+
 func TestAutocompleteFormat(t *testing.T) {
 	testStruct := struct {
 		Name string