Unable to recreate GDExtension instance with hot reloading enabled

[LouChiSoft]

Godot version

4.3-stable (Double precision)

godot-cpp version

4.3-stable (Double precision)

System information

Windows 10, R9 7900, RX 7900XT

Issue description

Debug compile for Windows 10, using CMake included via FetchContent and enabling hot reloading via GODOT_ENABLE_HOT_RELOAD set to ON or YES results in a Unable to recreate GDExtension instance - does this extension support hot reloading? error when rebuilding the project.

I've verified that the gdextension file has reloading enabled by adding a status message to the godot-cpp cmake file to print out the value of GODOT_ENABLE_HOT_RELOAD and make sure that it propagates from the top level which it does.

Steps to reproduce

• Clone this project: https://github.com/LouChiSoft/GDFlecs
• Optional: Add a status print to the godot-cpp CMakeLists.txt inside the build folder and print the value of GODOT_ENABLE_HOT_RELOAD from inside the CMakeLists to ensure that the value is set properly
• Configure with: cmake -B ./build -DPRECISION="double"
• Build with: cmake --build ./build --config Debug --parallel *desired thread count*
• Run with Godot 4.3.stable.double
• Make a code change and rebuild
• Make Godot the active window and Unable to recreate GDExtension instance - does this extension support hot reloading? should be in the output

Minimal reproduction project

https://github.com/LouChiSoft/GDFlecs

[LouChiSoft]

Hi, I was wondering if anyone had managed to have a look at this yet?

[dsnopek]

It sounds like HOT_RELOAD_ENABLED isn't defined when building your extension. I had thought the cmake configuration in the 4.3 branch did do that, but I haven't had a chance to double check

[LouChiSoft]

Is HOT_RELOAD_ENABLED different from GODOT_ENABLE_HOT_RELOAD? GODOT_ENABLE_HOT_RELOAD is the one in the comments at the top of the CMake file for Godot-cpp

[enetheru]

@LouChiSoft

in CMake:
GODOT_ENABLE_HOT_RELOAD is not a valid flag, and is not used anywhere.

GODOT_USE_HOT_RELOAD is the option for the cmake build, can be specified as part of the cmake configuration process like
cmake <path to source> -DGODOT_HOT_RELOAD=ON or added to your cmake scripts, or in a preset file, etc..

HOT_RELOAD_ENABLED is the cpp define added to the compiler command when compiling the extension, however it may not be the only thing needed to create a hot-reloadable library, for example gcc requires -fno-gnu-unique (After reviewing the build tools it appears to be the only other requirement).

In SCons the equivalent flag is use_hot_reload

[enetheru]

also, if the flag is not specified, then only the template_debug and editor builds define HOT_RELOAD_ENABLED

[LouChiSoft]

GODOT_ENABLE_HOT_RELOAD is not a valid flag, and is not used anywhere.

Are you sure, I literally copied it from the CMakeLists.txt file from within the _deps folder for godot-cpp in my build folder. Screenshot from git tag godot-4.3-stable:

for example gcc requires -fno-gnu-unique (After reviewing the build tools it appears to be the only other requirement).

For now I am using MSVC and Windows, do you know of any MSVC specific flags I need to use?

[enetheru]

Are you sure, I literally copied it from the CMakeLists.txt file from within the _deps folder for godot-cpp in my build folder. Screenshot from git tag godot-4.3-stable:

My bad, I was thinking master branch, sorry.

The old 4.3 and lower cmake code is so bad it was the reason I decided to contribute.

I can offer no help it's that bad, and recommend backporting all cmake/build system related changes from master instead. Fingers crossed it all gets cherry picked in the future. I maintain my own branch of 4.3 with backported changes for this reason.

[LouChiSoft]

Ah, I can see where the confusion came from then. If the CMake for 4.3 is really that bad I will take a look at the main. Although 4.4 might have come out by the time I am free to work on my project again. Hopefully with 4.4 it will be easier to setup

[enetheru]

@LouChiSoft now that 4.4 has been release can you please test again?

[LouChiSoft]

Apologies, I haven't had time to check this until now. Unfortunately it doesn't seem to work. I no longer get the same error message about trying to replace a DLL without hot reloading enabled, but the DLL isn't being reloaded. Am I right in assuming that the new CMake flag to set for hot reloading is GODOTCPP_USE_HOT_RELOAD?

[LouChiSoft]

I did some more digging. If I do a debug build from scratch with no artifacts then hot reloading seems to work as intended as tested by adding and removing a custom node from the extension. I can happily rebuild the extension without having to delete anything in the addon folder.

As soon as I built in release with hot reloading everything seems to break. There are no error messages, but no changes in the code are reflected in the engine. And confusingly it also breaks debug builds. The only way to get it working again is to close the editor, delete the entire addon from the addon folder, rebuild the addon and re-open the editor.

[LouChiSoft]

Hey, me again. I have been trying to get this working but I am unsure what to change. As I mentioned above using Debug builds work as intended, and while for the most part you won't need hot reloading in Release in a pinch where you just need to fix something quick having to restart your entire editor because hot reloading in Release isn't working is a bit of a pain.

Is hot reloading disabled in the CMake for godot-cpp if you build release?

[enetheru]

Not intentionally, it should be independent of release mode, and there is a flag for it to force the issue.
But I haven't tested it myself, if you can whip up a test example that works for scons, and doesnt for cmake that would be handy, otherwise I've been meaning to get to it, just been busy doing other things.