> Bash forgot to reset errno before the call. For about 30 years, no one noticed

I have to say, this part of the POSIX API is maddening!

99% of the time, you don't need to set errno = 0 before making a call. You check for a non-zero return, and only then look at errno.

But SOMETIMES you need to set errno = 0, because in this case readdir() returns NULL on both error and EOF.

I actually didn't realize this before working on https://oils.pub/

---

And it should go without saying: Oils simply uses libc - we don't need to support system with a broken getcwd()!

Although a funny thing is that I just fixed a bug related to $PWD that AT&T ksh (the original shell, that bash is based on) hasn't fixed for 30+ years too!

(and I didn't realize it was still maintained)

https://www.illumos.org/issues/17442

https://github.com/oils-for-unix/oils/issues/2058

There is a subtle issue with respect to:

1) "trusting" the $PWD value you inherit from another process

2) Respecting symlinks - this is the reason the shell can't just call getcwd() !

    if (*p != '/' || stat(p, &st1) || stat(".", &st2) ||
        st1.st_dev != st2.st_dev || st1.st_ino != st2.st_ino)
        p = 0;

Instead there's objections on the basis "filesystems shouldn't work like that".

Here it is: https://lists.gnu.org/archive/html/bug-bash/2025-06/msg00149...

[1] https://github.com/NixOS/nixpkgs/commit/dff0ba38a243603534c9...

For a long time, inode numbers from readdir() had certain semantics. Supporting overlay filesystems required changing those semantics. Piles of software were written against the old semantics; and even some of the most common have not been upgraded.

It looks easy on the surface to roll down support for any kind of operating system there is, based on auto-detection and then #if HAVE_THIS or #if HAVE_THAT, but it breaks in ways that maybe really hard to untangle later.

I'd rather have a limited set set of configurations targeting specific platforms/flavors, and knowing that no matter how I compile it, I would know what is `#define`-d and what is not, instead of guessing on what the "host" might have.