Subject: Re: [PATCH 5/6] refs: stop resolving ref corresponding to reflogs

From: Junio C Hamano <[email-masked]>
Date: Mon, 19 Feb 2024 16:14:21 -0800

Patrick Steinhardt <[email-masked]> writes:

> Refactor the code to call `check_refname_format()` directly instead of
> trying to resolve the ref. This is significantly more efficient given
> that we don't have to hit the object database anymore to list reflogs.
> And second, it ensures that we end up showing reflogs of broken refs,
> which will help to make the reflog more useful.

And the user would notice corrupt ones among those reflogs listed
when using "rev-list -g" on the reflog anyway?  Which sounds like a
sensible thing to do.

> Note that this really only impacts the case where the corresponding ref
> is corrupt. Reflogs for nonexistent refs would have been returned to the
> caller beforehand already as we did not pass `RESOLVE_REF_READING` to
> the function, and thus `refs_resolve_ref_unsafe()` would have returned
> successfully in that case.

What do "Reflogs for nonexistent refs" really mean?  With the files
backend, if "git branch -d main" that removed the "main" branch
somehow forgot to remove the ".git/logs/refs/heads/main" file, the
reflog entries in such a file is for nonexistent ref.  Is that what
you meant?  As a tool to help diagnosing and correcting minor repo
breakages, finding such a leftover file that should not exist is a
good idea, I would think.

Would we see missing reflog for a ref that exists in the iteration?
I guess we shouldn't, as the reflog iterator that recursively
enumerates files under "$GIT_DIR/logs/" would not see such a missing
reflog by definition.

> diff --git a/refs/files-backend.c b/refs/files-backend.c
> index 2b3c99b00d..741148087d 100644
> --- a/refs/files-backend.c
> +++ b/refs/files-backend.c
> @@ -2130,17 +2130,9 @@ static int files_reflog_iterator_advance(struct ref_iterator *ref_iterator)
>  	while ((ok = dir_iterator_advance(diter)) == ITER_OK) {
>  		if (!S_ISREG(diter->st.st_mode))
>  			continue;
> -		if (diter->basename[0] == '.')
> +		if (check_refname_format(diter->basename,
> +					 REFNAME_ALLOW_ONELEVEL))
>  			continue;

A tangent.

I've never liked the code arrangement in the check_refname_format()
that assumes that each level can be separately checked with exactly
the same logic, and the only thing ALLOW_ONELEVEL does is to include
pseudorefs and HEAD; this makes such assumption even more ingrained.
I am not sure what to think about it, but let's keep reading.

> -		if (ends_with(diter->basename, ".lock"))
> -			continue;

This can safely go, as it is rejected by check_refname_format().

> -		if (!refs_resolve_ref_unsafe(iter->ref_store,
> -					     diter->relative_path, 0,
> -					     NULL, NULL)) {
> -			error("bad ref for %s", diter->path.buf);
> -			continue;
> -		}

This is the focus of this step in the series.  We did not abort the
iteration before, but now we no longer issue any error message.

>  		iter->base.refname = diter->relative_path;
>  		return ITER_OK;
> diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
> index 889bb1f1ba..efbbf23c72 100644
> --- a/refs/reftable-backend.c
> +++ b/refs/reftable-backend.c
> @@ -1659,11 +1659,9 @@ static int reftable_reflog_iterator_advance(struct ref_iterator *ref_iterator)
>  		if (iter->last_name && !strcmp(iter->log.refname, iter->last_name))
>  			continue;
>  
> -		if (!refs_resolve_ref_unsafe(&iter->refs->base, iter->log.refname,
> -					     0, NULL, NULL)) {
> -			error(_("bad ref for %s"), iter->log.refname);
> +		if (check_refname_format(iter->log.refname,
> +					 REFNAME_ALLOW_ONELEVEL))
>  			continue;
> -		}

This side is much more straight-forward.  Looking good.

>  
>  		free(iter->last_name);
>  		iter->last_name = xstrdup(iter->log.refname);