Negative numbers in types like-uint

[tredoe]

The compiler should show a warning message when is used a negative number into a like-uint type

let n: u8 = -1;
println!("{}", n); // => 255

[jdm]

Probably related to #2438.

[recrack]

Should this be done in typeck, or is it best done in lint?

[Aatch]

Nominating for production-ready.

[msullivan]

Yeah, I agree with that nomination.

[emberian]

This should really be a lint I think

[graydon]

Relative of #4220 and #5551 so probably milestone #1.

[graydon]

accepted for well-defined milestone

[pcwalton]

Nominating because I believe we decided to not do this for negative numbers and the warning is already implemented for positive numbers. I think this can be closed.

[emberian]

I think we should have a lint for bare -1 when it infers to an unsigned type, but -1u should be allowed. Generally I think the more-obvious construction !0, !0 - 1 etc should be used instead of negative literals.

[fhahn]

Could this lint be combined with the type_overflow lint? The message of that lint ("literal out of range for its type") would fit in my opinion and and it shouldn't be too hard to extend the code of this lint.

[emberian]

I think at this point we've gone whole-hog on accepting that not warning on this is a feature. Nominating for closure.

[pnkfelix]

Lints are not a language backwards-compatibility issue.

Recategorizing as P-low, not 1.0 milestone.