Don't cache null forever if a singleton isn't available yet

# Conflicts: #	binding_generator.py

Author: Zylann

binding_generator.py

@@ -1453,15 +1453,23 @@ def generate_engine_class_source(class_api, used_classes, fully_used_classes, us
 
  if is_singleton:
  result.append(f"{class_name} *{class_name}::get_singleton() {{")
+ # We assume multi-threaded access is OK because each assignment will assign the same value every time
+ result.append(f"\tstatic {class_name} *singleton = nullptr;")
+ result.append("\tif (unlikely(singleton == nullptr)) {")
+ result.append(f"\t\tconst StringName _gde_class_name = {class_name}::get_class_static();")
  result.append(
- f"\tstatic GDExtensionObjectPtr singleton_obj = internal::gdextension_interface_global_get_singleton({class_name}::get_class_static()._native_ptr());"
+ "\t\tGDExtensionObjectPtr singleton_obj = internal::gdextension_interface_global_get_singleton(_gde_class_name._native_ptr());"
  )
  result.append("#ifdef DEBUG_ENABLED")
- result.append("\tERR_FAIL_COND_V(singleton_obj == nullptr, nullptr);")
+ result.append("\t\tERR_FAIL_COND_V(singleton_obj == nullptr, nullptr);")
  result.append("#endif // DEBUG_ENABLED")
  result.append(
- f"\tstatic {class_name} *singleton = reinterpret_cast<{class_name} *>(internal::gdextension_interface_object_get_instance_binding(singleton_obj, internal::token, &{class_name}::_gde_binding_callbacks));"
+ f"\t\tsingleton = reinterpret_cast<{class_name} *>(internal::gdextension_interface_object_get_instance_binding(singleton_obj, internal::token, &{class_name}::_gde_binding_callbacks));"
  )
+ result.append("#ifdef DEBUG_ENABLED")
+ result.append("\t\tERR_FAIL_COND_V(singleton == nullptr, nullptr);")
+ result.append("#endif // DEBUG_ENABLED")
+ result.append("\t}")
  result.append("\treturn singleton;")
  result.append("}")
  result.append("")