dip1000 and preview in combine to cause extra safety errors

[12345swordy]

On Wednesday, 8 June 2022 at 18:32:41 UTC, Timon Gehr wrote:
> On 6/8/22 19:22, deadalnix wrote:
>> On Wednesday, 8 June 2022 at 17:09:49 UTC, Mathias LANG wrote:
>>> And you'll see the bug, even without `-preview=dip1000`.
>>>
>>> Why is this happening ? You correctly guessed, because the 
>>> frontend wrongfully lets the `string` go on the stack instead 
>>> of allocating with it.
>>> ...
>
> Your code is literally calling this function:
>
> ```d
> string foo(scope string s){ return s; }
> ```
>
> This causes UB, therefore you can't blame the compiler frontend 
> here.

I got to say here, you shouldn't be able to compile that code at 
all if it is going to shoot you in the foot unintentionally.

- Alex