Official servers will not load wasm binaries compiled using Rust >=1.70

[shanemadden]

Current nightly builds of rust use new wasm opcodes for sign-extension which will not load under the LLVM running on the official servers. Private servers tested appear to have no problem with the new opcodes.

Errors like Compiling wasm function #1389:<screeps::constants::small_enums::Direction as ... failed: Invalid opcode (enable with --experimental-wasm-se) @+1009670 will occur on attempt to load the module.

Ideally we'll be able to have a setting to control disabling these newer opcodes (possibly integrated into cargo-screeps) but a working workaround has not yet been identified - see rust-lang/rust#109807

[shanemadden]

The workaround that we've identified to this issue using the resources in the linked issue requires nightly rust. To work around:

1. Add build flags with set the target cpu to mvp, and rebuild std, which is usually used from the distribution pre-compiled. Example from my screeps.toml:

    [ptr.build]
     extra_options = ["--features=mmo", "--config", "build.rustflags=['-Ctarget-cpu=mvp']", "-Z", "build-std=std,panic_abort"]
   

2. Additionally (and technically a separate issue), add the --disable-sign-ext to the options passed to wasm-opt, as current versions will add the new opcodes even when rustc does not. Example from my Cargo.toml:

   [package.metadata.wasm-pack.profile.release]
   wasm-opt = ["-O4", "--disable-sign-ext"]
   

[shanemadden]

An alternative workaround identified in the linked rust issue, that doesn't require build-std (but does require wasm-opt), is to add --signext-lowering to your wasm-opt options.