Flags not passed to rustc

[human-0]

When cargo-pgo is used, the [build.rustflags] of .cargo\config.toml are ignored. Lto in cargo.toml seems to be ignored as well, judging by performance. The only way to pass flags seems to be through the RUSTFLAGS environment variable.

[Kobzol]

The only thing that cargo-pgo does when you execute cargo pgo build is basically that it runs

$ RUSTFLAGS="-Cprofile-generate=..." cargo build

so values from config.toml and Cargo.toml should be respected.

That being said, it looks like if you use RUSTFLAGS , it will override the [build.rustflags] section (rust-lang/cargo#5376). This is the standard behaviour of cargo, so I'm not sure whether we can do anything about it. cargo-pgo could in theory parse the config.toml file, but that would reimplement what cargo does and it would deviate from the default behaviour of cargo.

For now I think that your best bet is to pass these flags using RUSTFLAGS. In any case, the LTO section from Cargo.toml should definitely be applied, if it's not, something is wrong.

[human-0]

I can't reproduce the LTO issue anymore. It was probably just a benchmark inconsistency. (I couldn't find any way to check directly.) The RUSTFLAGS issue is definitely real, but I will probably just use the environment variable.