Release Engine after unregistering GDExtensions

[raulsntos]

The Engine is used to retrieve singletons, and GDExtensions may try to retrieve a singleton (e.g.: OS) in their deinitialization.

MRP: GDExtensionSingletonCrash.zip

The MRP shows the following errors and then crashes:

ERROR: Failed to retrieve non-existent singleton 'OS'.
   at: get_singleton_object (core/config/engine.cpp:294)
ERROR: Parameter "singleton_obj" is null.
   at: get_singleton (godot-cpp/gen/src/classes/os.cpp:47)

[dsnopek]

This makes sense to me.

Engine is created before initialize_modules(MODULE_INITIALIZATION_LEVEL_CORE), so it would make sense that it's deleted after uninitialize_modules(MODULE_INITIALIZATION_LEVEL_CORE), since we want to clean things up in basically the reverse order that we created them.

[akien-mga]

Thanks!

[akien-mga]

I noticed we didn't handle the other two cleanup sections in main.cpp with similar code, in the error: goto, and in test_cleanup().

But this change also creates an issue with the StringNames allocated by Engine, which are now not properly freed before calling StringName::cleanup() in unregister_core_types(), see #92726.

[raulsntos]

We could move the memdelete(engine) right before unregister_core_types, I just didn't want to separate the unregister methods.

All that matters to me is that the memdelete(engine) happens after the unregister_core_extensions (and probably also uninitialize_modules because we want godot-cpp and modules to have the same behavior). So something like this could work:

diff --git a/main/main.cpp b/main/main.cpp
index af29e18c46..e4ecbe64c7 100644
--- a/main/main.cpp
+++ b/main/main.cpp
@@ -830,13 +830,15 @@ void Main::test_cleanup() {
 	if (globals) {
 		memdelete(globals);
 	}
-	if (engine) {
-		memdelete(engine);
-	}
 
 	unregister_core_driver_types();
 	unregister_core_extensions();
 	uninitialize_modules(MODULE_INITIALIZATION_LEVEL_CORE);
+
+	if (engine) {
+		memdelete(engine);
+	}
+
 	unregister_core_types();
 
 	OS::get_singleton()->finalize_core();
@@ -2482,15 +2484,17 @@ error:
 	if (globals) {
 		memdelete(globals);
 	}
-	if (engine) {
-		memdelete(engine);
-	}
 	if (packed_data) {
 		memdelete(packed_data);
 	}
 
 	unregister_core_driver_types();
 	unregister_core_extensions();
+
+	if (engine) {
+		memdelete(engine);
+	}
+
 	unregister_core_types();
 
 	OS::get_singleton()->_cmdline.clear();
@@ -4339,12 +4343,13 @@ void Main::cleanup(bool p_force) {
 	unregister_core_driver_types();
 	unregister_core_extensions();
 	uninitialize_modules(MODULE_INITIALIZATION_LEVEL_CORE);
-	unregister_core_types();
 
 	if (engine) {
 		memdelete(engine);
 	}
 
+	unregister_core_types();
+
 	OS::get_singleton()->benchmark_end_measure("Shutdown", "Total");
 	OS::get_singleton()->benchmark_dump();
 

I'll make a PR.