extend pragma(msg) with writing to file

[TheGag96]

On Thursday, 6 October 2022 at 12:08:16 UTC, bauss wrote:
> It's a very controversial topic because there's a huge security 
> risk in allowing third-parties access to your filesystem, 
> especially without executing an application or anything and 
> simply from building source code or it being a dependency of 
> some other package.

But we've already basically been there for decades through:

* `configure` scripts from autotools
* Makefiles
* Ad-hoc shell/Python build scripts
* `dub.json`/`dub.sdl` calling out to shell

If you're willing to trust any of these, I don't see why you 
shouldn't be able to trust code from the program you're building.

D has always been my true language love, but I'm honestly very 
excited for Jai simply because it has [unrestricted compile-time 
execution](https://youtu.be/De0Am_QcZiQ?t=1582) that it uses to 
replace the need for external build scripts (and cases like OP 
desires). Hope he gets it out of private beta soon because I'd 
really like to see how the "Write your build script in the same 
language your program is in" idea pays off. Zig does something 
similar with its `build.zig` stuff, but this seems more 
comprehensive.