Subject: Re: [PATCH 1/4] wt-status: read HEAD and ORIG_HEAD via the refdb

From: Taylor Blau <[email-masked]>
Date: Wed, 29 Nov 2023 16:45:00 -0500

On Wed, Nov 29, 2023 at 09:14:12AM +0100, Patrick Steinhardt wrote:
> We read both the HEAD and ORIG_HEAD references directly from the
> filesystem in order to figure out whether we're currently splitting a
> commit. If both of the following are true:
>
>   - HEAD points to the same object as "rebase-merge/amend".
>
>   - ORIG_HEAD points to the same object as "rebase-merge/orig-head".
>
> Then we are currently splitting commits.
>
> The current code only works by chance because we only have a single
> reference backend implementation. Refactor it to instead read both refs
> via the refdb layer so that we'll also be compatible with alternate
> reference backends.
>
> Note that we pass `RESOLVE_REF_NO_RECURSE` to `read_ref_full()`. This is
> because we didn't resolve symrefs before either, and in practice none of
> the refs in "rebase-merge/" would be symbolic. We thus don't want to
> resolve symrefs with the new code either to retain the old behaviour.
>
> Signed-off-by: Patrick Steinhardt <[email-masked]>
> ---
>  wt-status.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/wt-status.c b/wt-status.c
> index 9f45bf6949..fe9e590b80 100644
> --- a/wt-status.c
> +++ b/wt-status.c
> @@ -1295,26 +1295,27 @@ static char *read_line_from_git_path(const char *filename)
>  static int split_commit_in_progress(struct wt_status *s)
>  {
>  	int split_in_progress = 0;
> -	char *head, *orig_head, *rebase_amend, *rebase_orig_head;
> +	struct object_id head_oid, orig_head_oid;
> +	char *rebase_amend, *rebase_orig_head;
>
>  	if ((!s->amend && !s->nowarn && !s->workdir_dirty) ||
>  	    !s->branch || strcmp(s->branch, "HEAD"))
>  		return 0;
>
> -	head = read_line_from_git_path("HEAD");
> -	orig_head = read_line_from_git_path("ORIG_HEAD");
> +	if (read_ref_full("HEAD", RESOLVE_REF_NO_RECURSE, &head_oid, NULL) ||
> +	    read_ref_full("ORIG_HEAD", RESOLVE_REF_NO_RECURSE, &orig_head_oid, NULL))

Switching to read_ref_full() here is going to have some slightly
different behavior than just reading out the contents of
"$GIT_DIR/HEAD", but I think that it should be OK.

Before we would not have complained, if, for example, the contents of
"$GIT_DIR/HEAD" were malformed, but now we will. I think that's OK,
especially given that if that file is bogus, we'll have other problems
before we get here ;-).

Are there any other gotchas that we should be thinking about?

> +		return 0;
> +
>  	rebase_amend = read_line_from_git_path("rebase-merge/amend");
>  	rebase_orig_head = read_line_from_git_path("rebase-merge/orig-head");
>
> -	if (!head || !orig_head || !rebase_amend || !rebase_orig_head)
> +	if (!rebase_amend || !rebase_orig_head)
>  		; /* fall through, no split in progress */
>  	else if (!strcmp(rebase_amend, rebase_orig_head))
> -		split_in_progress = !!strcmp(head, rebase_amend);
> -	else if (strcmp(orig_head, rebase_orig_head))
> +		split_in_progress = !!strcmp(oid_to_hex(&head_oid), rebase_amend);
> +	else if (strcmp(oid_to_hex(&orig_head_oid), rebase_orig_head))

I did a double take at these strcmp(oid_to_hex(...)) calls, but I think
that they are the best that we can do given that we're still reading the
contents of "rebase-merge/amend" and "rebase-merge/orig-head" directly.

I suppose we could go the other way and turn their contents into
object_ids and then use oidcmp(), but it doesn't seem worth it IMHO.

Thanks,
Taylor