Node pointers can't be passed into UtilityFunctions::is_instance_valid() to check if they have not been freed; is something needed for this?

[id01]

Godot version

4.2.1.stable

godot-cpp version

4.2.1.stable

System information

Any

Issue description

Currently, is_instance_valid() dereferences object pointers passed to it due to implicit cast to Variant. As such, executing is_instance_valid() on freed nodes, unlike in gdscript, causes a use-after-free crash. Currently, there doesn't seem to be a way to store nodes where UtilityFunctions::is_instance_valid() can work without sacrificing typing (by storing everything as Variant), and the example project simply uses pointers for passing around object pointers as well.

Steps to reproduce

Call UtilityFunctions::is_instance_valid() on a freed node pointer. The program crashes instead of returning false.

Minimal reproduction project

See steps to reproduce.

[dsnopek]

In a C++ module, rather than using is_instance_valid(), in situations where you need to store objects that might get freed, you'd store ObjectID and call ObjectDB::get_instance() to check if it's still valid. This is what I'd recommend doing in godot-cpp as well, since we are attempting to emulate modules (and it doesn't suffer from the problem you're encountering).

Regarding fixing is_instance_valid(): I wonder if we should just not expose it in godot-cpp?

There is no way to check if an Object * has been freed, and trying to create a Variant from a freed Object * will cause a crash. This is exactly what will happen if you call is_instance_valid() with a freed Object * (it's automatically converted to Variant), which that function is practically inviting developers to do. This isn't the first time this issue has come up. :-)