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

[Richard (Rikki) Andrew Cattermole]

On 21/02/2025 1:38 PM, Richard (Rikki) Andrew Cattermole wrote:
> On 21/02/2025 8:44 AM, Steven Schveighoffer wrote:
>> On Thursday, 20 February 2025 at 17:42:25 UTC, Ilya wrote:
>>
>>     On Thursday, 20 February 2025 at 15:50:33 UTC, Steven Schveighoffer
>>     wrote:
>>
>>         This has been proposed before, and it doesn't require language
>>         changes:
>>
>>         |void foo() { assert(__ctfe); } |
>>
>>     Yes, I've seen that. But did it go anywhere? I think on the thread
>>     I've found there are some discussions with no conclusion.
>>
>> It has not gone anywhere, but if we were to consider a language 
>> change, I'd want to evaluate whether this is a better option, since 
>> it's a de- facto standard.
> 
> I wouldn't call it any kind of standard.
> 
> But since it cannot work at runtime, and can be seen during compilation 
> it doesn't need a DIP to see this statement and turn off codegen for the 
> function.
> 
> Hmm, I should be able to implement it, gimmie a bit.

Not possible.

assert gets processed during semantic 3, but things like variable 
declarations are seen during semantic 2.

It has to be an attribute seeable on the function declaration.

```d
extern(C) void main() {
	__gshared global = func; // Error: cannot use non-constant CTFE pointer 
in an initializer `func()
	func; // Error: undefined reference to `void start.func()`
}

int* func() {
	assert(__ctfe);
	return new int;
}
```