negate_unsigned feature gate warning should be changed to feature gate.

[nagisa]

negate_unsigned feature gate (librustc_lint/builtin.rs) currently emits a warning instead of actual feature_gate due to backwards compatibility concerns. After some time passes this warning should be converted to feature gate.

Basically, reverting the “Convert negate_unsigned feature gate to a warning” commit (0ca8e49) from #27026 and fixing up conflicts (if any) should do.

Note to any people who are planning to do this: ask somebody from language team whether enough time has passed since we started to emit the warning before submitting a PR.

[steveklabnik]

/cc @rust-lang/lang

[pnkfelix]

I think once the next beta has been released (that is, when the current nightly has been shifted over to beta as part of the release train) we can go ahead and apply this change to nightly.

[steveklabnik]

Did this end up happening?

[steveklabnik]

/cc @rust-lang/libs

[nagisa]

This has not been done yet.

I’ve asked @pnkfelix several times on IRC which shift he had in mind (1.3 to beta or 1.4 to beta), because his comment was posted on the day of such shift, but never got a response.

EDIT: well, it won’t hurt more doing this later (after 1.4 shifts to beta) than sooner (now).