Subject: Re: [PATCH v3 6/8] rebase: factor out branch_base calculation

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Thu, 13 Oct 2022 21:21:09 +0200

On Thu, Oct 13 2022, Phillip Wood via GitGitGadget wrote:

> From: Phillip Wood <[email-masked]>
>
> Separate out calculating the merge base between 'onto' and 'HEAD' from
> the check for whether we can fast-forward or not. This means we can skip
> the fast-forward checks when the rebase is forced and avoid calculating
> the merge-base between 'HEAD' and 'onto' when --keep-base is given.
>
> Signed-off-by: Phillip Wood <[email-masked]>
> ---
>  builtin/rebase.c | 34 ++++++++++++++++++++--------------
>  1 file changed, 20 insertions(+), 14 deletions(-)
>
> diff --git a/builtin/rebase.c b/builtin/rebase.c
> index cbafcc41e75..40619a0fb2d 100644
> --- a/builtin/rebase.c
> +++ b/builtin/rebase.c
> @@ -871,13 +871,9 @@ static int can_fast_forward(struct commit *onto, struct commit *upstream,
>  	struct commit_list *merge_bases = NULL;
>  	int res = 0;
>  
> -	merge_bases = get_merge_bases(onto, head);
> -	if (!merge_bases || merge_bases->next) {
> -		oidcpy(branch_base, null_oid());
> -		goto done;
> -	}
> +	if (is_null_oid(branch_base))
> +		goto done; /* fill_branch_base() found multiple merge bases */
>  
> -	oidcpy(branch_base, &merge_bases->item->object.oid);
>  	if (!oideq(branch_base, &onto->object.oid))
>  		goto done;
>  
> @@ -887,7 +883,6 @@ static int can_fast_forward(struct commit *onto, struct commit *upstream,
>  	if (!upstream)
>  		goto done;
>  
> -	free_commit_list(merge_bases);
>  	merge_bases = get_merge_bases(upstream, head);
>  	if (!merge_bases || merge_bases->next)
>  		goto done;
> @@ -902,6 +897,20 @@ done:
>  	return res && is_linear_history(onto, head);
>  }
>  
> +static void fill_branch_base(struct rebase_options *options,
> +			    struct object_id *branch_base)
> +{
> +	struct commit_list *merge_bases = NULL;
> +
> +	merge_bases = get_merge_bases(options->onto, options->orig_head);
> +	if (!merge_bases || merge_bases->next)
> +		oidcpy(branch_base, null_oid());
> +	else
> +		oidcpy(branch_base, &merge_bases->item->object.oid);
> +
> +	free_commit_list(merge_bases);
> +}

I wondered if this could be a bit shorter/less wrap-y with shorter
variable names, anyway, I see it's code copied from above, so nevermind
in advance... :)
	
	static void fill_branch_base(struct rebase_options *o, struct object_id *dst)
	{
		struct commit_list *mb = get_merge_bases(o->onto, o->orig_head);
		const struct object_id *src = (!mb || mb->next) ? null_oid() :
			&mb->item->object.oid;
	
		oidcpy(dst, src);
		free_commit_list(mb);
	}

> @@ -1669,8 +1678,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
>  		if (!options.onto)
>  			die(_("Does not point to a valid commit '%s'"),
>  				options.onto_name);
> +		fill_branch_base(&options, &branch_base);
>  	}
> -
>  	if (options.fork_point > 0)
>  		options.restrict_revision =
>  			get_fork_point(options.upstream_name, options.orig_head);

I wouldn't mind the stray whitespace change, but here it seems
unintentional, in 7/8 your change on top is:
	
	@@ -1680,6 +1691,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
	 				options.onto_name);
	 		fill_branch_base(&options, &branch_base);
	 	}
	+	if (keep_base && options.reapply_cherry_picks)
	+		options.upstream = options.onto;
	+
	 	if (options.fork_point > 0)
	 		options.restrict_revision =
	 			get_fork_point(options.upstream_name, options.orig_head);

Presumably we want to have \n\n spacing for both of those, and to not
remove the spacing here in 6/8, only to add it back?