Compile time executable calling?

[Timothee Cour]

On Fri, Jul 12, 2013 at 1:42 PM, Tofu Ninja <emmons0 at purdue.edu> wrote:

> So I had an idea recently, wouldn't it be cool to have the ability to call
> an executable at compile time and capture its output. Something like the
> string imports but instead of opening and reading a text file, it run an
> executable, waits for it to finish, and grabs its output.
>
> It would get really cool if you could pass this executable some args and
> then mix in its out put into your own code. It could be used similarly to
> how CTFE are used but with out the overhead of trying to compile that
> function and what not and with out the limitations on what it can do.
>
> I could imagine all sorts of things that would be possible with this that
> is currently not.
>
> Not sure if this is something that could be implemented easily, but seems
> like something that could be done and something that would be really cool.
>

I would definitely love that, and I don't see why this should be hard.
It should be enabled by a compiler switch (dmd -enable_exec) for obvious
safety reasons though (just as string import requires -J).

This enables or simplifies a number of things:

* ctfeWriteln becomes trivial (this feature has been asked a while ago)
* CTFE in situations where current CTFE fails
* do things that would temprarily require malloc
* easily customize compilation process (user would be able to add logging /
profile info without touching the dmd compiler)
* accessing environment variables during compilation

seems to me all that is needed is optionally redirecting stdin/stdout of a
forked process inside dmd compilation, with the exec C function family.
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