Re: [PATCH v3 06/11] merge_bases_many(): pass on errors from `paint_down_to_common()`

> From: Johannes Schindelin <johannes.schindelin@gmx.de>
>
> The `paint_down_to_common()` function was just taught to indicate
> parsing errors, and now the `merge_bases_many()` function is aware of
> that, too.
>
> One tricky aspect is that `merge_bases_many()` parses commits of its
> own, but wants to gracefully handle the scenario where NULL is passed as
> a merge head, returning the empty list of merge bases. The way this was
> handled involved calling `repo_parse_commit(NULL)` and relying on it to
> return an error. This has to be done differently now so that we can
> handle missing commits correctly by producing a fatal error.
>
> Next step: adjust the caller of `merge_bases_many()`:
> `get_merge_bases_many_0()`.
>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>  commit-reach.c | 35 ++++++++++++++++++++++-------------
>  1 file changed, 22 insertions(+), 13 deletions(-)

>
> diff --git a/commit-reach.c b/commit-reach.c
> index 9148a7dcbc0..2c74583c8e0 100644
> --- a/commit-reach.c
> +++ b/commit-reach.c
> @@ -131,41 +131,49 @@ static int paint_down_to_common(struct repository *r,
>  	return 0;
>  }
>  
> -static struct commit_list *merge_bases_many(struct repository *r,
> -					    struct commit *one, int n,
> -					    struct commit **twos)
> +static int merge_bases_many(struct repository *r,
> +			    struct commit *one, int n,
> +			    struct commit **twos,
> +			    struct commit_list **result)
>  {
>  	struct commit_list *list = NULL;
> -	struct commit_list *result = NULL;
>  	int i;
>  
>  	for (i = 0; i < n; i++) {
> -		if (one == twos[i])
> +		if (one == twos[i]) {
>  			/*
>  			 * We do not mark this even with RESULT so we do not
>  			 * have to clean it up.
>  			 */
> -			return commit_list_insert(one, &result);
> +			*result = commit_list_insert(one, result);
> +			return 0;
> +		}
>  	}
>  
> +	if (!one)
> +		return 0;
>  	if (repo_parse_commit(r, one))
> -		return NULL;
> +		return error(_("could not parse commit %s"),
> +			     oid_to_hex(&one->object.oid));
>  	for (i = 0; i < n; i++) {
> +		if (!twos[i])
> +			return 0;
>  		if (repo_parse_commit(r, twos[i]))
> -			return NULL;
> +			return error(_("could not parse commit %s"),
> +				     oid_to_hex(&twos[i]->object.oid));
>  	}
>  
>  	if (paint_down_to_common(r, one, n, twos, 0, 0, &list) < 0) {
>  		free_commit_list(list);
> -		return NULL;
> +		return -1;
>  	}
>  
>  	while (list) {
>  		struct commit *commit = pop_commit(&list);
>  		if (!(commit->object.flags & STALE))
> -			commit_list_insert_by_date(commit, &result);
> +			commit_list_insert_by_date(commit, result);
>  	}
> -	return result;
> +	return 0;
>  }
>  
>  struct commit_list *get_octopus_merge_bases(struct commit_list *in)
> @@ -410,10 +418,11 @@ static struct commit_list *get_merge_bases_many_0(struct repository *r,
>  {
>  	struct commit_list *list;
>  	struct commit **rslt;
> -	struct commit_list *result;
> +	struct commit_list *result = NULL;
>  	int cnt, i;
>  
> -	result = merge_bases_many(r, one, n, twos);
> +	if (merge_bases_many(r, one, n, twos, &result) < 0)
> +		return NULL;
>  	for (i = 0; i < n; i++) {
>  		if (one == twos[i])
>  			return result;