r? @Amanieu

rustbot has assigned @Amanieu.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

@sayantn
I'd like to ask how do we know that unknown cfg errors are fixed (and/or which CI failures to track) to know the right timing to revert this PR.
Just making documentation seems working on my local environment so I think there is a failing configuration.

These unknown cfg errors are obtained when stdarch is built as a part of libstd, by itself stdarch should compile fine - the bootstrapping architecture of rustc creates the problem because the stage0 compiler doesn't yet know about those new target features.

It should be good to revert once a stdarch update gets merged, or the bootstrap version gets bumped

It should be good to revert once a stdarch update gets merged, or the bootstrap version gets bumped

I think this could be handled by the special bootstrap cfg set by the rust-lang/rust build-system.

afaik this repo doesn't use cfg(bootstrap) because the update cfgs commit (which removes all cfg(bootstrap) items after the bootstrap bump) wouldn't work here because this is still a submodule, not a subtree. Using cfg(bootstrap) here will require a PR here after bootstrap bump, and a stdarch submodule update in rustc, which might create a lot of problems, because stdarch updates are typically problematic as stdarch CI and rustc CI don't match perfectly