0u8..-1 compiles without warning

[bluss]

0u8..-1 compiles, runs (as 0..255) without warning or error. Debug assertions don't fire.

We error on 0..-1u8 error: unary negation of unsigned integers may be removed in the future.

We can't "fix" this backwards compatibly after 1.0.

0u8..-1 should either warn or trip debug assertions.

[bombless]

Hmm we cannot add warning because of compatibly?
I just want to make sure...

[bluss]

We can add a warning, but to make it a hard error would be breaking.

[nagisa]

I think this should error the same way as 0u8..-1 case errors, for consistency with let x: u8 = -1, which also errors.

[bombless]

FWIW, I think we are contributing to Rust 1.1, so it's fine to break some 1.0 code.

[Stebalien]

@bombless Point releases are not allowed to introduce backwards incompatible changes (except bug fixes). Only major releases (2.0) can do that.

[nagisa]

We could always make it a warning for 1.x series and note it will become an error in next major release.

[bombless]

Hmm if somebody's quick enough to make a patch then we can backport it to beta branch and fix this in time. Also this can be considered a bug anyway.