Subject: Re: [PATCH v2 3/3] bundle: remove "ref_list" in favor of string-list.c API

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Thu, 24 Jun 2021 21:31:02 +0200

On Thu, Jun 24 2021, Jeff King wrote:

> On Mon, Jun 21, 2021 at 05:16:14PM +0200, Ævar Arnfjörð Bjarmason wrote:
>
>> Move away from the "struct ref_list" in bundle.c in favor of the
>> almost identical string-list.c API.
>> 
>> That API fits this use-case perfectly, but did not exist in its
>> current form when this code was added in 2e0afafebd (Add git-bundle:
>> move objects and references by archive, 2007-02-22), with hindsight we
>> could have used the path-list API, which later got renamed to
>> string-list. See 8fd2cb4069 (Extract helper bits from
>> c-merge-recursive work, 2006-07-25)
>
> I think this is a good direction, and I didn't see any errors in the
> code. It's slightly sad that we end up with more lines than we started
> with, but I think that's mostly because you're actually freeing the
> memory now.
>
> Two small nitpicks:
>
>> @@ -103,19 +94,22 @@ static int parse_bundle_header(int fd, struct bundle_header *header,
>>  		 * Prerequisites have object name that is optionally
>>  		 * followed by SP and subject line.
>>  		 */
>> -		if (parse_oid_hex_algop(buf.buf, &oid, &p, header->hash_algo) ||
>> +		oid = xmalloc(sizeof(struct object_id));
>> +		if (parse_oid_hex_algop(buf.buf, oid, &p, header->hash_algo) ||
>>  		    (*p && !isspace(*p)) ||
>>  		    (!is_prereq && !*p)) {
>>  			if (report_path)
>>  				error(_("unrecognized header: %s%s (%d)"),
>>  				      (is_prereq ? "-" : ""), buf.buf, (int)buf.len);
>>  			status = -1;
>> +			free(oid);
>>  			break;
>>  		} else {
>
> This would be slightly simpler if you kept a local "struct object_id",
> and then called:
>
>   string_list_append(list, string)->util = oiddup(&oid);
>
> later when you know you want to save it. And then you don't have to
> worry about the extra cleanup here. That does require an extra oidcpy()
> under the hood, but I suspect that is lost in the noise.
>
> I'm OK with it either way.

That sounds simpler indeed, thanks.

>> -			if (is_prereq)
>> -				add_to_ref_list(&oid, "", &header->prerequisites);
>> -			else
>> -				add_to_ref_list(&oid, p + 1, &header->references);
>> +			const char *string = is_prereq ? "" : p + 1;
>> +			struct string_list *list = is_prereq
>> +				? &header->prerequisites
>> +				: &header->references;
>> +			string_list_append(list, string)->util = oid;
>
> I'm usually a big fan of the ternary operator, and using variable
> indirection to make it clear that we always call a function.  But here I
> think it makes things more confusing.  The two sides of the if/else are
> sufficiently simple that it's easy to see they both make the same
> function call. And because there are two variables, we check is_prereq
> twice, making it much harder to see the two cases.
>
> I.e., I think:
>
>   if (is_prereq)
>           string_list_append(&header->prerequisites, "")->util = oid;
>   else
>           string_list_append(&header->references, p + 1)->util = oid;
>
> is much more obvious.

Hah, that's actually the exact code I wrote to begin with, before
thinking "hrm, someone will probably say I should just use a ternary
here". I'll change it back :)