Support wasm32-unknown-emscripten target

With WebAssembly support being added to the engine, this should be a priority for the next release.

Unfortunately, this cannot be done right now since Rust is still using LLVM 11, which is no longer supported by the version of emscripten that Godot requires (2.0.10). Rust only updates LLVM on new releases, so we'll have to wait for a few months until LLVM is updated upstream.

Until then, it might be a good idea to clarify the state of WASM support in documentation.

[deep-gaurav]

Any updates on this?

@deep-gaurav Not yet, still blocked by rustc :(

[remissio]

With Version 1.52 we got LLVM 12 Support:

https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1520-2021-05-06

[orion78fr]

Just FYI I successfully compiled for wasm with various hacks : https://github.com/orion78fr/godot_keepass_rust_totp
Example : https://orion78.fr/godot_test/keepassTotp.html (it has a simple script that change the button text according to a function call in rust, but I may update things so it may not work as of now)

@orion78fr That's wonderful! Last time I checked there was some miscompilation around i128/u128, but glad to see that the ar trick is working now! Could you add a license on the emcc-test files so we can actually put the workaround in our docs for other people?

[orion78fr]

I've put the repository under MIT License, that should be OK.
The whole steps are here : https://github.com/orion78fr/godot_keepass_rust_totp/actions/runs/900998393/workflow#L255

Some things I had to do :

• Don't forget to set export type to GDNative in the export template (or it won't even try to load the wasm silently) :
  
• Pass -all to wasm-opt because it's automatically called by emcc but doesn't seem to pass the correct wasm feature flags and fails
• Disable stack unwinding because C exceptions is still in spec : https://github.com/WebAssembly/exception-handling (CARGO_PROFILE_RELEASE_PANIC: abort, maybe the other flags for overflow / assertions are necessary but I did so many testing I don't remember).
• Need to compile with PIC to allow the linker to relocate code : RUSTFLAGS: -C link-args=-fPIC -C relocation-model=pic

Maybe something else, I don't remember x)

@orion78fr Thanks. The workflow file is very helpful!

[extrawurst]

@orion78fr thanks so much for looking into this. did you try to run your Web export in safari? on Firefox, chrome it seems to work fine.

I have the same issue with my demo, so I was wondering

[orion78fr]

Yeah I only tested Chrome / Firefox on Windows and Android (as I mainly focus on APK export atm, can't figure out how I could make Android java calls to open files).

Seems like it's some part of the specs that are not supported on Safari.

CanIuse list shared memory as not supported, but I don't know if it's this in particular. Note that I had emcc complaining about shared memory though so maybe it's this.

[extrawurst]

@orion78fr I can export a regular WebGL app via godot and it runs in the browser: https://jontopielski.itch.io/puzzle-sigma (just an example)

so I am still a little hopeful we can figure out how to build a gdnative lib so that safari can load it aswell - after all the above shows that godot itself manages to compile to something safari is able to take and run. it must be some crazy param that i am missing to pass to emcc