Subject: Re: [PATCH v2 1/4] wt-status: read HEAD and ORIG_HEAD via the refdb

From: Junio C Hamano <[email-masked]>
Date: Tue, 12 Dec 2023 12:24:24 -0800

Patrick Steinhardt <[email-masked]> writes:

> 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.

"via the refdb" -> "via the refs API" or something here and on the
title, and possibly elsewhere in the proposed log messages and
in-code comments in patches in this series, as I've never seen a
word "refdb" used in the context of this project.

I agree it is bad manners to be intimate with the implementation
details of the how files-backend stores HEAD and ORIG_HEAD.

> 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.

Good to see a rewrite being careful like this.

> 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))
> +		return 0;
> +

This made me wonder if we have changed behaviour when on an unborn
branch.  In such a case, the original most likely would have read
"ref: blah" in "head" and compared it with "rebase_amend", which
would be a good way to ensure they would not match.  I would not
know offhand what the updated code would do, but head_oid would be
uninitialized in such a case, so ...?

>  	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))
>  		split_in_progress = 1;
>  
> -	free(head);
> -	free(orig_head);
>  	free(rebase_amend);
>  	free(rebase_orig_head);