RFC: cfg_os_version_min

[ChrisDenton]

This RFC is largely the work of @rylev and @chriswailes. As suggested by @tmandry I have stripped it down to an MVP that just adds os_version_min.

Rendered

[bjorn3]

So there is no way for the user to configure which minimum API version they want to use? That would make it impossible for eg the libc crate to gate api's behind #[cfg(os_version_min)] corresponding to the libc version that introduced the API in question.

[ChrisDenton]

Yes. One of the issues with the original proposals was there was too much going on. This RFC aims to add the minimally useful feature. Adding compiler flags and Cargo configs to control the minimum version can be a future extension.

With this RFC it is still possible for libc to gate APIs like that. However, you'd need a new target in order to set a different minimal libc version.

[Aloso]

The idea is great, but I think the syntax can be improved. It makes more sense to have this feature under the existing target_os config, so here's an idea:

cfg(target_os("windows", min_version = "..."))

Another idea:

cfg(target_os = "windows >= ...")

[ChrisDenton]

That may work for windows but not, for example, Linux where you may want to cfg on the kernel version or the libc version (or even both).

libc isn't really a target_os.

[Aloso]

Right, so this could be done with a target_libc attribute, like

cfg(target_libc("glibc", min_version = "..."))

But of course this would add more complexity.