Subject: Re: [PATCH 1/3] factor out refresh_and_write_cache function

From: Thomas Gummerer <[email-masked]>
Date: Thu, 29 Aug 2019 18:59:10 +0100

On 08/28, Martin Ågren wrote:
> On Tue, 27 Aug 2019 at 12:14, Thomas Gummerer <[email-masked]> wrote:
> >
> > Getting the lock for the index, refreshing it and then writing it is a
> > pattern that happens more than once throughout the codebase.  Factor
> > out the refresh_and_write_cache function from builtin/am.c to
> > read-cache.c, so it can be re-used in other places in a subsequent
> > commit.
> 
> > +/*
> > + * Refresh the index and write it to disk.
> > + *
> > + * Return 1 if refreshing the cache failed, -1 if writing the cache to
> > + * disk failed, 0 on success.
> > + */
> 
> Thank you for documenting. :-) Should we say something about how this
> doesn't explicitly print any error in case refreshing fails (that is, we
> leave it to `refresh_index()`), but that we *do* explicitly print an
> error if writing the index fails? That caught me off-guard as I looked
> at how you convert the callers.
> 
> And do we actually want that asymmetry? Maybe we do.

I think I needed the error for something while I went through a few
iterations of how to best structure this function, but I don't
remember for what exactly now.  I think it might actually be better to
just return -1 here, and let the caller distinguish and show the error
message if they need to.  That also avoids duplicating the error in
case the caller wants to die on error.

> Might be worth pointing out as you convert the callers how some (all?)
> of them now emit different error messages from before, but that it
> shouldn't matter(?) and it makes sense to unify those messages.

Yeah, I don't think changing the error message should matter, but
unifying them is not actually a goal of this series.  So with what you
pointed out above, I think I'll leave them as they are.

> > +int repo_refresh_and_write_index(struct repository*, unsigned int refresh_flags, unsigned int write_flags, const struct pathspec *, char *seen, const char *header_msg);
> 
> > +int repo_refresh_and_write_index(struct  repository *repo,
> > +                                unsigned int refresh_flags,
> > +                                unsigned int write_flags,
> > +                                const struct pathspec *pathspec,
> > +                                char *seen, const char *header_msg)
> > +{
> > +       struct lock_file lock_file = LOCK_INIT;
> > +
> > +       repo_hold_locked_index(repo, &lock_file, LOCK_DIE_ON_ERROR);
> > +       if (refresh_index(repo->index, refresh_flags, pathspec, seen, header_msg))
> > +               return 1;
> > +       if (write_locked_index(repo->index, &lock_file, write_flags))
> > +               return error(_("unable to write index file"));
> > +       return 0;
> > +}
> 
> If `flags` doesn't contain `COMMIT_LOCK`, the lockfile will be closed
> "gently", meaning we still need to either commit it, or roll it back. Or
> let the exit handler roll it back, which is what would happen here, no?
> We lose our handle on the stack and there's no way for anyone to say
> "ok, now I'm done, commit it please" (or "roll it back").
> 
> In short, I think calling this function without providing `COMMIT_LOCK`
> would be useless at best. We should probably let this function provide
> `COMMIT_LOCK | write_flags` or `COMMIT_LOCK | extra_write_flags` or
> whatever. Most callers would just provide "0". Hm?
> 
> Or, we could BUG if the COMMIT_LOCK bit isn't set, but that seems like a
> less good choice to me. If we're so adamant about the bit being set --
> which we should be, IMHO -- we might as well set it ourselves.

Yeah, you're right, making this function use `COMMIT_LOCK | write_flags`
would probably be the best option.  I'll change that, and document it
as well.

Thanks for your review!

> Martin