[Feature Request]: RUSTC_AR is missing

[lexi-the-cute]

Problem

RUSTC_AR is missing from the available build environment variables in build.rs.

This makes the below code not work.

    cc::Build::new()
        .compiler(PathBuf::from(env::var("RUSTC_LINKER").unwrap()))
        .archiver(PathBuf::from(env::var("RUSTC_AR").unwrap()))
        .file(lib_path.to_str().unwrap())
        .compile("browser");

Proposed Solution

I started work on lexi-the-cute@287fb2a and am currently compiling Cargo in order to make sure the variable works. 4 tests fail, so I temporarily disabled them. The 4 tests are listed below.

cargo test -j 8 build_script::custom_build_ar_bad_host
cargo test -j 8 build_script::custom_build_ar_bad_host_with_arch
cargo test -j 8 build_script::custom_build_ar_host_target_with_bad_host_config
cargo test -j 8 build_script::custom_build_env_var_rustc_ar_bad_host_target

Notes

I based my commit on #5394 and am waiting for approval to make a pull request to add this feature

[weihanglo]

Hello. As far as I can tell

• The codegen option in rustc (-C ar=) has been deprecated long time ago.
• rustc switched to llvm-ar instead of external ar since 2015 — trans: Use LLVM's writeArchive to modify archives rust#26926
• target.<triple>.ar is not used anymore in cargo — Remove config references to the ar tool #2369

Basically it does nothing on rustc/cargo side. I am not sure if this configuration is still useful. Could you elaborate more?

[lexi-the-cute]

That's good to know. I've had my config.toml setup as:

[target.wasm32-unknown-emscripten]
ar = "$WORKSPACE/tools/emsdk/upstream/emscripten/emar"
linker = "$WORKSPACE/tools/emsdk/upstream/emscripten/emcc"
rustflags = ["-L$WORKSPACE/target/libs", "-lSDL2", "-lSDL2_image", "-lSDL2_ttf", "-lSDL2_mixer", "-lpthread"]

The $WORKSPACE variable is replaced by sed in my build script. I was using the ar variable thinking it was telling rust to use emar instead of the default ar tool.

[weihanglo]

Thank you for letting us know.

Unless people are using an extremely old Rust, this should be a no-op. Going in close this out as we don't support archiver configuration anymore. Thanks.