core.sys.posix.dirent: Add dirfd

[dd86k]

This commit adds the definition of dirfd, a POSIX function.

The pragma is left as-is, as it was (erroneously) defined in Phobos.

extern (D) added because the entire module is otherwise affected by extern (C).

(Take 2, switching branches everywhere gets a little messy, my bad.)

[dlang-bot]

Thanks for your pull request and interest in making D better, @dd86k! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

---

If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.

Bugzilla references

Your PR doesn't reference any Bugzilla issue.

If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog.

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#22750"

[dkorpel]

Doesn't extern(C) already mangle it as dirfd?

[dd86k]

Yep, at least on most platforms (at least POSIX), but I left this as-is because the C extern definition in Phobos (std.process) had it, and I'd hate to break anything here.

Related: dlang/phobos#10976

[dkorpel]

The reason Phobos had it is because it was defined in a function scope, where extern(C) would only affect the ABI and not the mangle. Here it would be more risky to have a special mangle override for this one function rather than make it consistent with the rest.

[dd86k]

Fair, I'll remove it

[ibuclaw]

Did you mean to put the declaration in the middle of a section declaring other functions?

Perhaps add the declaration immediately before Thread-Safe Functions (TSF) ?

[dd86k]

Did you mean to put the declaration in the middle of a section declaring other functions?
Perhaps add the declaration immediately before Thread-Safe Functions (TSF) ?

Oh, yeah, I see that I accidentally put that in-between readdir/closedir.

dirfd is neither TSF or XSI, so I'll move it higher, since it's typically defined rather high up.

It is still POSIX-1.2008, though.

[dd86k]

On second thought.. I did define it after struct DIR; declarations, since NetBSD stuff is the only exception.

Up to anyone if it's preferred to have the binding on every version scope.

[ibuclaw]

On second thought.. I did define it after struct DIR; declarations, since NetBSD stuff is the only exception.

D doesn't care about order of declarations / forward references. Move it higher up if that makes more sense.