// This fix finds nils initializing these types and replaces the nils with 0s.
func cftypefix(f *ast.File) bool {
	return typefix(f, func(s string) bool {
		return strings.HasPrefix(s, "C.") && strings.HasSuffix(s, "Ref") && s != "C.CFAllocatorRef"
	})
}

// typefix replaces nil with 0 for all nils whose type, when passed to badType, returns true.
func typefix(f *ast.File, badType func(string) bool) bool {
	if !imports(f, "C") {
		return false
	}