Subject: Re: [PATCH v6? 15/17] refs API: make resolve_ref_unsafe() not set errno

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Wed, 14 Jul 2021 10:32:38 +0200

On Tue, Jul 13 2021, Han-Wen Nienhuys wrote:

> On Sun, Jul 11, 2021 at 6:30 PM Ævar Arnfjörð Bjarmason
> <[email-masked]> wrote:
>> +       refs = get_main_ref_store(the_repository);
>> +       head = refs_resolve_ref_unsafe_with_errno(refs, "HEAD", 0, NULL, NULL,
>> +                                                 &resolve_errno);
>> +       if (!head) {
>> +               errno = resolve_errno;
>
> This adds another place where we'd use global errno to communicate.
> Isn't there a die() function that takes an errno value explicitly?

No, not that I know of. I suppose we could refactor fmt_with_err() in
usage.c to somehow be exposed and add e.g. a:

    die_saved_errno(&saved_errno, "msg %s", ....);

But I really don't see the point.

The trouble with using errno is generally introducing undesired action
at a distance, here we're setting it immediately before calling
die_errno(), so there's not much action or distance we should/could be
worried about.

E.g. xmkstemp() in wrapper.c uses this pattern, i.e.:

    errno = saved_errno;
    die_errno(...)