new annotation or pragma to mark functions that are intended to be only used during compile time

[Ilya]

On Thursday, 13 February 2025 at 22:26:02 UTC, Quirin Schroll 
wrote:
> The easiest and in fact backwards compatible solution for this 
> is to detect `in(__ctfe)` as a [function precondition 
> contract](https://dlang.org/spec/function.html#preconditions) 
> and make the compiler not emit the function into the object

Oh, that's a brilliant idea actually! Thanks, I should have 
experimented with it before trying to introduce my own attribute. 
It seems like it would do _almost_ what I want to achieve. The 
two missing bits would be:

1. Static check, as you pointed out we could even generalize it 
to static contract violation.
2. Skipping codegen of functions that have `in(__ctfe)` in 
preconditions.

Both seem like smaller changes in comparison to what I suggested, 
I really like that. They probably could also be submitted 
independently.

I have some reservations though:
- I really-really-really need to skip codegen of these functions 
in the release build, that's really important for us. But I think 
contracts are ignored in release builds, would that even work?
- (less important) Ideally I'd also like to skip codegen for 
high-order templates using these functions, like in the `map` 
example above. Probably if I implement skipping codegen via 
setting `skipCodegen` bit on the function, it will be propagated 
to the callers with the existing `skipCodegen` implementation, 
but I'm not entirely sure.

> file. If for some reason you don’t like that, I suggest 
> re-using the `__ctfe` keyword for that purpose.

Ok, I've already got the same suggestion on my PR, so I guess we 
have a leader :)