Deprecate implicit conversion between signed and unsigned integers

[Dom DiSc]

On Tuesday, 14 May 2024 at 06:59:16 UTC, Dom DiSc wrote:
> We have a working solution that always returns the correct 
> result (see https://issues.dlang.org/show_bug.cgi?id=259).

And by the way: This solution doesn't involve integer propagation 
at all and also works for comparison of long with ulong.
For beginners this is by far the worst bug in D, and its there 
since 18 (in words: eightteen) years - feels like lingering there 
longer than D itself.
This is so distracting.

It's ten lines of code and costs nothing (except if you indeed 
compare differnt signed types, and then it's still very cheep):

```d
int opCmp(T, U)(const(T) a, const(U) b) pure @safe @nogc nothrow
    if(isIntegral!T && isIntegral!U && is(Unqual!T != Unqual!U))
{
    static if(isSigned!T && isUnsigned!U && T.sizeof <= U.sizeof)
       return (a < 0) ? -1 : opCmp(cast(U)a, b);
    else static if(isUnsigned!T && isSigned!U && T.sizeof >= 
U.sizeof)
       return (b < 0) ? 1 : opCmp(a, cast(T)b);
    else // use common type as ever:
       return opCmp(cast(CommonType!(T, U))a, cast(CommonType!(T, 
U))b);
}
```