Re: [PATCH 1/3] merge-ort: add new merge_ort_generic() function

> diff --git a/merge-ort-wrappers.c b/merge-ort-wrappers.c
> index d6f61359965..62834c30e9e 100644
> --- a/merge-ort-wrappers.c
> +++ b/merge-ort-wrappers.c
> @@ -64,3 +68,63 @@ int merge_ort_recursive(struct merge_options *opt,
>  
>  	return tmp.clean;
>  }
> +
> +static struct commit *get_ref(struct repository *repo,
> +			      const struct object_id *oid,
> +			      const char *name)
> +{
> +	struct object *object;
> +
> +	object = deref_tag(repo, parse_object(repo, oid),
> +			   name, strlen(name));
> +	if (!object)
> +		return NULL;
> +	if (object->type == OBJ_TREE)
> +		return make_virtual_commit(repo, (struct tree*)object, name);
> +	if (object->type != OBJ_COMMIT)
> +		return NULL;
> +	if (repo_parse_commit(repo, (struct commit *)object))
> +		return NULL;
> +	return (struct commit *)object;
> +}

> +int merge_ort_generic(struct merge_options *opt,
> +		      const struct object_id *head,
> +		      const struct object_id *merge,
> +		      int num_merge_bases,
> +		      const struct object_id *merge_bases,
> +		      struct commit **result)
> +{
> +	int clean;
> +	struct lock_file lock = LOCK_INIT;
> +	struct commit *head_commit = get_ref(opt->repo, head, opt->branch1);
> +	struct commit *next_commit = get_ref(opt->repo, merge, opt->branch2);
> +	struct commit_list *ca = NULL;
> +
> +	if (merge_bases) {
> +		int i;
> +		for (i = 0; i < num_merge_bases; ++i) {
> +			struct commit *base;
> +			if (!(base = get_ref(opt->repo, &merge_bases[i],
> +					     oid_to_hex(&merge_bases[i]))))
> +				return error(_("Could not parse object '%s'"),
> +					     oid_to_hex(&merge_bases[i]));
> +			commit_list_insert(base, &ca);
> +		}
> +	}
> +
> +	repo_hold_locked_index(opt->repo, &lock, LOCK_DIE_ON_ERROR);
> +	clean = merge_ort_recursive(opt, head_commit, next_commit, ca,
> +				    result);
> +	free_commit_list(ca);
> +	if (clean < 0) {
> +		rollback_lock_file(&lock);
> +		return clean;
> +	}
> +
> +	if (write_locked_index(opt->repo->index, &lock,
> +			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
> +		return error(_("Unable to write index."));
> +
> +	return clean ? 0 : 1;
> +}

> diff --git a/merge-ort.c b/merge-ort.c
> index 46e78c3ffa6..b4ff24403a1 100644
> --- a/merge-ort.c
> +++ b/merge-ort.c
> @@ -5186,6 +5186,8 @@ static void merge_ort_internal(struct merge_options *opt,
>  		ancestor_name = "empty tree";
>  	} else if (merge_bases) {
>  		ancestor_name = "merged common ancestors";
> +	} else if (opt->ancestor) {
> +		ancestor_name = opt->ancestor;
>  	} else {
>  		strbuf_add_unique_abbrev(&merge_base_abbrev,
>  					 &merged_merge_bases->object.oid,
> @@ -5275,8 +5277,13 @@ void merge_incore_recursive(struct merge_options *opt,
>  {
>  	trace2_region_enter("merge", "incore_recursive", opt->repo);
>  
> -	/* We set the ancestor label based on the merge_bases */
> -	assert(opt->ancestor == NULL);
> +	/*
> +	 * We set the ancestor label based on the merge_bases...but we
> +	 * allow one exception through so that builtin/am can override
> +	 * with its constructed fake ancestor.
> +	 */
> +	assert(opt->ancestor == NULL ||
> +	       (merge_bases && !merge_bases->next));
>  
>  	trace2_region_enter("merge", "merge_start", opt->repo);
>  	merge_start(opt, result);