emsdkHack.cmake variables not propagated outside the godot-cpp library

[lechaosx]

Godot version

v4.4.1.stable.nixpkgs [49a5bc7b6]

godot-cpp version

godot-4.4.1-stable

System information

NixOS 25.05.20250721.92c2e04 (Warbler)

Issue description

I'm unable to properly compile GDExtension project for web with CMake. It seems that the variables from emsdkHack.cmake should enable compilation of shared libraries with emscripten, but the variables are set to the godot-cpp project directory scope, not at the top-level GDExtension project scope where it's needed and expected. The only thing that is properly set is the TARGET_SUPPORTS_SHARED_LIBS global property as global properties do not follow directory scopes. This way, the project compiles with warning

em++: warning: linking a library with `-shared` will emit a static object file.  This is a form of emulation to support existing build systems.  If you want to build a runtime shared library use the SIDE_MODULE setting. [-Wemcc]

and the output library is unusable with godot. If I manually include the emsdkHack.cmake file after my top level project call, the compilation passes without a problem. Even with library generated this way, the Remote Deploy -> Run in Browser is not loading and returning Uncaught (in promise) undefined in Firefox console. This might be unrelated issue or result of invalid compilation.

Steps to reproduce

0. Either enter dev environment via nix develop or have prerequisites defined in flake.nix in your PATH via your favourite approach.

To reproduce the failing build:

1. emcmake cmake --preset default -B build-emscripten
2. cmake --build build-emscripten
3. Uncomment the include in top level CMakeLists.txt and compile again for successful build

To try the extension in the editor, also compile it natively:
4. cmake --preset default
5. cmake --build build
6. Open the editor and run the main scene, or alternatively Remote Deploy -> Run in Browser

Minimal reproduction project

gdextension-emscripten-cmake-repro.zip

[enetheru]

I'll have a look as soon as I can, life is chaos right now, so might take me a week.
In the meantime, what version of emscripten are you running? same as listed for godot? https://docs.godotengine.org/en/stable/contributing/development/compiling/compiling_for_web.html
edit: actually as per my own comments on that page, I ended up matching the github actions version of 3.1.64

[lechaosx]

I use emscripten 4.0.8, which might cause the secondary issue where the web preview won't load. I will try it with 3.1.64.
EDIT: I can now confirm that it behaves exactly the same with 3.1.64 on my setup
EDIT 2: In pursue to resolve the secondary issue, I tried to recompile also the export templates with emscripten 3.1.64. This failed because the nix package for this version seems to be bundled with incompatible version of binaryen. This issue seem to originate from accidentally misstagged commit emscripten-core/emscripten#22249. I tried to compile both the export templates and the gdextension with emscripten 3.1.73. The compilation passes, but both Chrome and Firefox won't load the project with Uncaught (in promise) undefined in console.