Is this a bug?

[Elfstone]

On Thursday, 16 March 2023 at 04:31:11 UTC, Elfstone wrote:
> On Thursday, 16 March 2023 at 04:04:51 UTC, Elfstone wrote:
>> On Thursday, 16 March 2023 at 03:44:19 UTC, Elfstone wrote:
>>> [...]
>>
>> Correction.
>>
>> With or without comments, mostly it doesn't compile, 
>> occasionally it does!
>> I have no idea.
>
> I can't get it to compile anymore, it must be some mistake from 
> me. Maybe I forgot to save   while modifying the code.
>
> So the `S` declared in `is` expression can contaminate the 
> scope? Is this supposed to happen?

Never mind, I just found out this is supposed to happen, `S` is 
supposed to be available later.

https://dlang.org/spec/expression.html#is-parameter-list