Conditional compilation: Cfg option for debug vs. release Cargo(-esque) profile

[minggfeng]

Much like in this Users thread, I would like to be able to target debug builds with cfg!() (in order to hide logging output only on release builds). I have some ways of accomplishing this, but it'd be convenient to have a cfg flag that we could target, independent of debug_assertions.

[fmease]

Well, debug (or rather, dev) and release profiles are Cargo (exclusive) concepts, rustc doesn't know about them. See also: https://doc.rust-lang.org/cargo/reference/profiles.html#profiles.

I don't know why this is a T-lang matter, this seems to be a T-cargo matter (with T-lang as advisor maybe). It's already possible via a Cargo build script (see https://users.rust-lang.org/t/conditional-compilation-for-debug-release/1098/7), so it's a matter of deciding whether to expose it by default.

[weihanglo]

@rustbot transfer cargo

[weihanglo]

[…] It's already possible via a Cargo build script (see users.rust-lang.org/t/conditional-compilation-for-debug-release/1098/7), so it's a matter of deciding whether to expose it by default.

To add, #[cfg(debug_assertions)] is also the de facto way to do so. I don't see any need for exposing new default cfg from cargo. Propose to close this.

@rustbot label +S-propose-close