RUSTFLAGS in .cargo/config.toml or environment variable is not respected when compiling build scripts

[funnsam]

The changes in #50 does not apply to build scripts. For example, when compiling the chess crate with [build] rustflags = ["-C", "target-cpu=native"] in .cargo/config.toml and running cargo pgo build -- --verbose, it produces several compiler error due to some code not generated in the build script due to missing CPU features when compiling the build script. There are probably more crates that are affected by this.

Edit: was doing RUSTFLAGS="-C target-cpu=native" cargo pgo build -- --verbose, but both are not working

   Compiling chess v4.0.0 (/home/funnsam/Projects/personal/chessbot2/chess)
     Running `/home/funnsam/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc --crate-name build_script_build --edition=2021 chess/src/build.rs --error-format=json --json=diagnostic-rendered-ans
i,artifacts,future-incompat --diagnostic-width=206 --crate-type bin --emit=dep-info,link -C opt-level=3 -C embed-bitcode=no --check-cfg 'cfg(docsrs)' --check-cfg 'cfg(feature, values())' -C metadata=6d17c18
f1e2910a5 -C extra-filename=-6d17c18f1e2910a5 --out-dir /home/funnsam/Projects/personal/chessbot2/target/release/build/chess-6d17c18f1e2910a5 -C strip=debuginfo -L dependency=/home/funnsam/Projects/personal
/chessbot2/target/release/deps --extern const_for=/home/funnsam/Projects/personal/chessbot2/target/release/deps/libconst_for-1ca5b06aeec5f8b6.rlib --extern rand=/home/funnsam/Projects/personal/chessbot2/tar
get/release/deps/librand-1f61f4d4dde8b834.rlib --extern thiserror=/home/funnsam/Projects/personal/chessbot2/target/release/deps/libthiserror-b2960b6fa067cfe0.rlib` (no -C target-cpu=native here!)
     Running `/home/funnsam/Projects/personal/chessbot2/target/release/build/chess-6d17c18f1e2910a5/build-script-build`
     Running `/home/funnsam/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc --crate-name chess --edition=2021 chess/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,fut
ure-incompat --diagnostic-width=206 --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C linker-plugin-lto -C codegen-units=1 --check-cfg 'cfg(docsrs)' --check-cfg 'cfg(feature, values())' -C me
tadata=7dc5e06409290ebf -C extra-filename=-7dc5e06409290ebf --out-dir /home/funnsam/Projects/personal/chessbot2/target/x86_64-unknown-linux-gnu/release/deps --target x86_64-unknown-linux-gnu -C strip=debugi
nfo -L dependency=/home/funnsam/Projects/personal/chessbot2/target/x86_64-unknown-linux-gnu/release/deps -L dependency=/home/funnsam/Projects/personal/chessbot2/target/release/deps --extern arrayvec=/home/f
unnsam/Projects/personal/chessbot2/target/x86_64-unknown-linux-gnu/release/deps/libarrayvec-dbffae55b3fbc857.rmeta --extern const_for=/home/funnsam/Projects/personal/chessbot2/target/x86_64-unknown-linux-gn
u/release/deps/libconst_for-5f58c96a18b272b2.rmeta --extern nodrop=/home/funnsam/Projects/personal/chessbot2/target/x86_64-unknown-linux-gnu/release/deps/libnodrop-375fbaee2b52f7f1.rmeta --extern thiserror=
/home/funnsam/Projects/personal/chessbot2/target/x86_64-unknown-linux-gnu/release/deps/libthiserror-16130579d7cde1cd.rmeta -C target-cpu=native -Cprofile-generate=/home/funnsam/Projects/personal/chessbot2/t
arget/pgo-profiles`
error[E0425]: cannot find value `ROOK_BMI_MASK` in this scope                                                                                                                                               
  --> chess/src/magic.rs:43:27
   |
43 |         let bmi2_magic = *ROOK_BMI_MASK.get_unchecked(sq.to_int() as usize);
   |                           ^^^^^^^^^^^^^ not found in this scope

...

[Kobzol]

Hi! Sorry for the delay, was swamped this week.

The situation with RUSTFLAGS is... complicated, to say the least. cargo-pgo uses [target.'cfg(all())'] instead of [build], because it has a higher precedence.

Could you try replacing [build] rustflags with [target.'cfg(all())'] rustflags? Then the flags should be properly combined.

[Kobzol]

Posted #63 to document this.