fix(ci): force rust to use legacy symbol mangling

[Akinator31]

Problem

The CI was failing during the frontend WASM build with the following error:

Uncaught SyntaxError: Identifier
'wasm_bindgen_4f453e33dd9327c9___convert__closures________invoke___web_sys_a88f6bde22b957e9___features__gen_Event__Event_____'
has already been declared

This error indicates that a JavaScript identifier is declared twice in the code generated by wasm-bindgen.

Root Cause

The project uses Rust nightly (see rust-toolchain.toml), which enables the new v0 symbol mangling scheme by default.

The problem occurs during the following transformation chain:

1. Rust compiles the code with v0 mangling → generates unique WASM symbols
2. wasm-bindgen processes the WASM and uses rustc-demangle to convert symbols into JavaScript names
3. rustc-demangle doesn't handle v0 mangling correctly → two different symbols (e.g., closures with Fn vs FnMut) are
   demangled to the same JavaScript name
4. The final JS contains duplicate identifiers → SyntaxError

This issue is documented in wasm-bindgen issue #4820: wasm-bindgen/wasm-bindgen#4820

Solution

Force Rust to use legacy symbol mangling (instead of v0) by adding the following RUSTFLAGS during frontend builds:

env:
  RUSTFLAGS: '-Csymbol-mangling-version=legacy -Zunstable-options'

Legacy mangling is properly supported by rustc-demangle, thus avoiding name collisions.

Changes

• Added RUSTFLAGS in .github/workflows/release-ci.yml to both frontend build steps:
  • build_and_test job (pre-release tests)
  • upload-assets job (release binaries build)

Notes

This solution is a temporary workaround until rustc-demangle and wasm-bindgen properly support v0 mangling. We can remove these flags once issue #4820 is resolved.

References

• wasm-bindgen issue #4820: The latest nightly rustc will break the wasm build wasm-bindgen/wasm-bindgen#4820