Re: [PATCH v2 2/3] strbuf: set errno to 0 after strbuf_getcwd

[Eric Sunshine <sunshine@sunshineco.com>]

On Fri, Aug 2, 2024 at 5:32 PM Junio C Hamano <gitster@pobox.com> wrote:
> > [...]
> > Set `errno = 0;` prior to exiting from `strbuf_getcwd` successfully.
> > This matches the behavior in functions like `run_transaction_hook`
> > (refs.c:2176) and `read_ref_internal` (refs/files-backend.c:564).
>
> I am still uneasy to see this unconditional clearing, which looks
> more like spreading the bad practice from two places you identified
> than following good behaviour modelled after these two places.
>
> But I'll let it pass.
>
> As long as our programmers understand that across strbuf_getcwd(),
> errno will *not* be preserved, even if the function returns success,
> it would be OK.  As the usual convention around errno is that a
> successful call would leave errno intact, not clear it to 0, it
> would make it a bit harder to learn our API for newcomers, though.

For what it's worth, I share your misgivings about this change and
consider the suggestion[*] to make it save/restore `errno` upon
success more sensible. It would also be a welcome change to see the
function documentation in strbuf.h updated to mention that it follows
the usual convention of leaving `errno` untouched upon success and
clobbered upon error.

[*]: https://lore.kernel.org/git/xmqqv80jeza5.fsf@gitster.g/