Hot reload final steps

[kkolyan]

I just checked hot reload with Godot and gdext latest master branches and instead of loading new class, I have a Extension marked as reloadable, but attempted to register class 'SuperPlayer' which doesn't support reloading. Perhaps your language binding don't support it? Reloading disabled for this extension.

The place where error generated:
https://github.com/godotengine/godot/blob/4c3dc26367518e006f8555c12f5d2df0b8a28192/core/extension/gdextension.cpp#L431

Seems like we need to supply recreate_instance_func. Also, seems like that requires migration from deprecated _register_extension_class to _register_extension_class2.

Steps to reproduce a problem:

1. get Godot sources and build them. I use scons dev_build=yes debug_symbols=yes platform=windows compiledb=yes -j8 for debugging from CLion.
2. set GODOT4_BIN to the path of result executable
3. select some working gdext project (dodge-the-creeps from examples is ok)
4. add reloadable = true to the configuration section of .gdextension file
5. comment out some class
6. run cargo build --package dodge-the-creeps--lib --features custom-godot
7. run Godot executable with --editor --path <path to dodge-the-creeps Godot folder>, wait it for loading scene
8. run cargo build --package dodge-the-creeps--lib --features custom-godot again
9. switch back to Godot editor and see error in console.

[Bromeon]

Yes, it's simply not implemented yet.

The equivalent for godot-cpp: godotengine/godot-cpp#1200

[kkolyan]

blocked for Windows 10 by upstream godotengine/godot#82601

[kkolyan]

Current problems:

1. GDExtension reload spam on Windows 10 due to inconsistent last_modified_time handling godotengine/godot#82601, hot-fixed locally, PR in upstream.

2. errors in console after DLL change:

 Attempt to register extension class 'SuperPlayer', which appears to be already registered.
  Cannot get class ''.
  Attempt to register extension class 'SuperPlayer', which appears to be already registered.
  Attempt to register extension method 'get_x' for unexisting class 'SuperPlayer'.
  Attempt to register extension method 'set_x' for unexisting class 'SuperPlayer'.
  Attempt to register extension class property 'x' for unexisting class 'SuperPlayer'.
  Attempt to register extension method 'get_y' for unexisting class 'SuperPlayer'.
  Attempt to register extension method 'set_y' for unexisting class 'SuperPlayer'.
  Attempt to register extension class property 'y' for unexisting class 'SuperPlayer'.
  Attempt to register extension method 'get_z' for unexisting class 'SuperPlayer'.
  Attempt to register extension method 'set_z' for unexisting class 'SuperPlayer'.
  Attempt to register extension class property 'z' for unexisting class 'SuperPlayer'.

[kkolyan]

Ready for testing :) To really work well, depends on the pull request mentioned in godotengine/godot#82601.

[kkolyan]

upstream PR merged to master!