Re: git: d549de769055 - main - libc: Remove readdir_r(3) [This broke building rust 1.88]

On Thu, Sep 11, 2025 at 9:01 AM Dag-Erling Smørgrav <des@freebsd.org> wrote:

> Alan Somers <asomers@freebsd.org> writes:
> > Dag-Erling Smørgrav <des@freebsd.org> writes:
> > > Tell that to the Rust developers.  They have been repeatedly warned
> > > against using readdir_r(3) for years, as far back as 2016.
> > Have they?  Looking at rust's github page, I see discussions about
> > using readdir_r on Fuchsia and Linux, but nothing about BSD.
>
> If you look at these tickets, there are people pointing out that
> readdir_r() doesn't work correctly even on platforms where it isn't
> formally deprecated.  The Rust developers chose to fix the Linux case
> because it produced a link-time warning and ignored the rest.  That's on
> them.
>
> They also seem to be providing their own prototype for readdir_r(),
> which suppresses the deprecation warning they should be getting on
> FreeBSD 15, and turns the issue from a failure to compile into a failure
> to link.  That's also on them.
>

Where do you see that?  I suppose you must be talking about this line in
libc.  That's not due to anything special about readdir_r; it's just the
way that Rust links to _every_ libc function.  There is a CI step that
ensures these FFI definitions are accurate.
https://github.com/rust-lang/libc/blob/61b722e2517775cea98428702710ee9ef00f02a0/src/unix/mod.rs#L1769C22-L1769C23


>
> > possibly with the aid of installing misc/compat14x
>
> That won't make any difference since readdir_r() is still in our libc.
>
> DES
> --
> Dag-Erling Smørgrav - des@FreeBSD.org
>

There's another problem that we haven't discussed, which is the ability to
run older Rust toolchains.  Even if we fix Rust 1.89.0 to no longer use
readdir_r, older versions will continue to do so.  And Rust developers
frequently must test with older toolchains.  For example, any change to
Rust's libc requires testing with version 1.63.0, released in August 2022.
We can't remove readdir_r without breaking all of those workflows.  We
could probably remove the prototype, but not the function itself.