target_pointer_width in proc-macro crates provides build-time width, but some clients want runtime width

[liranringel]

I'm trying to add cross compilation (to compile 32bit) to my crate, and target_pointer_width is 64 in the proc-macro crate (like the host), and 32 in the root crate (like the target):

How can I get the real target_pointer_width in a proc-macro crate?

[est31]

The target_pointer_width at the build time of the proc-macro crate is not incorrect as the proc macro crate has to run on the build host, not the target.

[est31]

I think it should work if you read the TARGET env var at runtime, see more here: https://github.com/rust-lang/cargo/blob/master/src/doc/environment-variables.md

[liranringel]

@est31 I agree the "incorrect" is a bit incorrect :)
Is there an easy way to get the target pointer width? Because the TARGET env var is the target triple, and I don't want to transform it to the target pointer width on my own.

[nagisa]

CARGO_CFG environment variables might work if you’re using cargo; otherwise you’ll have to implement a scheme similar to the one used in rustc-cfg or target_build_utils.

[nagisa]

I guess this is a feature request for proc macro API to expose such info.

[est31]

cc @jseyfried

[liranringel]

@est31 @nagisa I've just checked, and the "TARGET"/"CARGO_CFG_TARGET_POINTER_WIDTH" env vars in the proc-macro crate (in its build script) is determined by the host, not the final target, so I don't see a way to get the target pointer width.