Why does intpromote spew warnings for ~ operator?

[Steven Schveighoffer]

On 9/13/21 6:27 PM, Alexey wrote:
> On Monday, 13 September 2021 at 21:03:41 UTC, Guillaume Piolat wrote:
>> On Sunday, 12 September 2021 at 14:14:03 UTC, Steven Schveighoffer wrote:
> 
> It's also not exactly clear why:
> 1. D should be backward compatible with C, which is 50 years old soon.
> 2. why exactly somebody should copy / paste (how many? thousands?) many 
> lines of code without thinking and rechecking. Probably D can't be and 
> shouldn't be compatible with C / C++ to that distinct.
> 3. Is really backward comparability with C/C++ so important?

This is missing the point.

Yes, part of the rationale of intpromote (which despite its flaws, I 
happen to agree with the main thrust of), is that we want D code that 
looks like C and compiles to behave like C. But also, the C behavior is 
what people who have no cares about C would expect.

In other words, if you have:

```d
ushort x = 500;
int y = -x;
```

you would expect y to be -500. But in D it's 65036. Which makes almost 
no sense at all.

Another alternative would be to disable negation on unsigned types. That 
would be also extremely disruptive.

We have a chance here to

1. Make D compatible with C
2. Continue to compile code that is correct in C, and makes sense in D 
(i.e. `short y = -someShort`)
3. Warn and fix surprising results that are 99% likely bugs.

If we do it smartly.

-Steve