Re: Octopus merge: unique (?) to git, but is it useful?

> diff --git a/builtin-commit.c b/builtin-commit.c
> index b294c1f..1d8d208 100644
> --- a/builtin-commit.c
> +++ b/builtin-commit.c
> @@ -883,10 +883,19 @@ static void add_parent(struct strbuf *sb, const unsigned char *sha1)
>  {
>  	struct object *obj = parse_object(sha1);
>  	const char *parent = sha1_to_hex(sha1);
> +	const char *cp;
> +
>  	if (!obj)
>  		die("Unable to find commit parent %s", parent);
>  	if (obj->type != OBJ_COMMIT)
>  		die("Parent %s isn't a proper commit", parent);
> +	cp = strstr(sb->buf, parent);
> +	if (cp &&
> +	    sb->buf + 8 <= cp && !memcmp(cp - 8, "\nparent ", 8) &&
> +	    cp[40] == '\n') {
> +		error("duplicate parent %s ignored", parent);
> +		return;
> +	}