A hot-reloaded extension never releases its bindings on engine singletons, so the editor crashes at quit #2084

Godot version

4.8-dev7 (official Windows build)

godot-cpp version or commit hash

694a264 (also reproduced at 5ed72a0; the code involved is unchanged in master at e103d34)

System information

Windows 11, MSVC, x86_64, editor build of the extension

Issue description

After an editor hot reload of a reloadable extension, the editor crashes with an access violation (0xC0000005) at quit. This happens every time, provided the reloaded image has touched any engine singleton.

The cause. godot-cpp releases the instance bindings it put on engine singletons (Time, ResourceUID, IP, Engine, anything reached through get_singleton()) only in ClassDB::deinitialize(GDEXTENSION_INITIALIZATION_CORE) (src/core/class_db.cpp:447-461). That call is reached only when the CORE level's initialisation count returns to zero (src/godot.cpp:212-215, :244-248).

• A first load works. It initialises from CORE, so at quit the count goes from 1 to 0 and the bindings are released.
• A reloaded image does not. The engine initialises it from the extension's minimum level, not from CORE (core/extension/gdextension_manager.cpp:47-56). At quit its CORE count goes from 0 to -1, so the release is skipped.

The bindings therefore stay on the engine's objects. Godot closes the library in unregister_core_types (core/register_core_types.cpp:440, gdextension.cpp:877-880) and only afterwards deletes ResourceUID, IP and Time (:442, :444, :492). ~Object then calls each binding's free_callback (core/object/object.cpp:2353-2357), which is godot-cpp's _gde_binding_free_callback in an image that is no longer mapped.

The engine clears a reloadable extension's tracked bindings on a reload (gdextension_manager.cpp:185-189), but never at shutdown.

Steps to reproduce

1. Build an extension with entry_symbol minimum level SCENE and reloadable = true. Make it call something like godot::Time::get_singleton()->get_ticks_msec() after it is initialised.
2. Open its project in the editor, then run GDExtensionManager.reload_extension("res://<its .gdextension>") (or trigger a hot reload by rebuilding).
3. Quit the editor. It exits with 0xC0000005. Without the reload it exits with 0.

We saw it in 3 of 3 runs at 694a264 and 5 of 5 at 5ed72a0.

Workaround

The extension's terminator calls godot::ClassDB::deinitialize(GDEXTENSION_INITIALIZATION_CORE) itself when the image never received a CORE initialisation. With that, the same runs exit 0 (10 of 10). A second call after a normal release does nothing, because engine_singletons is already empty (src/core/class_db.cpp:451-455).

Suggested fix

Either of these:

• In deinitialize_level, release the singleton bindings when the library's last initialised level is torn down, whatever that level is.
• Have the engine initialise a reloaded library from CORE.

Minimal reproduction project (MRP)

Not attached. The steps above are the whole of it: any reloadable extension that touches an engine singleton reproduces it.