Subject: Re: [PATCH v3 0/2] patch-id for merges

From: Junio C Hamano <[email-masked]>
Date: Mon, 12 Sep 2016 10:18:33 -0700

Jeff King <[email-masked]> writes:

> That looks like the patch below (as a replacement for patch 2), which is
> even less invasive. It also performs a little better on my example case,
> because we avoid adding merges to the hashmap entirely.

After reading it, I did not find [v3 2/2] is too bad either, but
this is even better ;-)

> diff --git a/patch-ids.c b/patch-ids.c
> index 77e4663..5d2d96a 100644
> --- a/patch-ids.c
> +++ b/patch-ids.c
> @@ -7,10 +7,12 @@
>  int commit_patch_id(struct commit *commit, struct diff_options *options,
>  		    unsigned char *sha1, int diff_header_only)
>  {
> -	if (commit->parents)
> +	if (commit->parents) {
> +		if (commit->parents->next)
> +			return -1;
>  		diff_tree_sha1(commit->parents->item->object.oid.hash,
>  			       commit->object.oid.hash, "", options);
> -	else
> +	} else
>  		diff_root_tree_sha1(commit->object.oid.hash, "", options);

This looks familiar ;-)

> @@ -72,11 +74,20 @@ static int init_patch_id_entry(struct patch_id *patch,
>  	return 0;
>  }
>  
> +static int patch_id_defined(struct commit *commit)
> +{
> +	/* must be 0 or 1 parents */
> +	return !commit->parents || !commit->parents->next;
> +}

If we make the first hunk begin like so:

> +	if (commit->parents) {
> +		if (!patch_id_defined(commit))
> +			return -1;

I wonder if the compiler gives us the same code.

>  struct patch_id *has_commit_patch_id(struct commit *commit,
>  				     struct patch_ids *ids)
>  {
>  	struct patch_id patch;
>  
> +	if (!patch_id_defined(commit))
> +		return NULL;
> +
>  	memset(&patch, 0, sizeof(patch));
>  	if (init_patch_id_entry(&patch, commit, ids))
>  		return NULL;
> @@ -89,6 +100,9 @@ struct patch_id *add_commit_patch_id(struct commit *commit,
>  {
>  	struct patch_id *key = xcalloc(1, sizeof(*key));
>  
> +	if (!patch_id_defined(commit))
> +		return NULL;
> +
>  	if (init_patch_id_entry(key, commit, ids)) {
>  		free(key);
>  		return NULL;

Yup, these two hunks look a lot nicer.

> I'd probably do a preparatory patch to drop the return value from
> add_commit_patch_id(). No callers actually look at it.

Thanks.