From: Phillip Wood <phillip.wood@talktalk.net>
Date: Sun, 04 Nov 2018 21:12:53 GMT
Subject: Re: [PATCH/RFC] sequencer.c: record revert/cherry-pick commit with trailer lines
Message-ID: <1a667e9c-3944-4bc3-fb60-68e79dff0c34@talktalk.net>
In-Reply-To: <CACsJy8CAw6yR5vbsFJbSd+UTR_1UpS=8PP3hEtbSNSi3SkMNag@mail.gmail.com>

Hi Duy

On 04/11/2018 17:41, Duy Nguyen wrote:
> On Sun, Nov 4, 2018 at 5:45 PM Phillip Wood <phillip.wood@talktalk.net> wrote:
>>
>> On 04/11/2018 07:22, Nguyễn Thái Ngọc Duy wrote:
>>> When a commit is reverted (or cherry-picked with -x) we add an English
>>> sentence recording that commit id in the new commit message. Make
>>> these real trailer lines instead so that they are more friendly to
>>> parsers (especially "git interpret-trailers").
>>>
>>> A reverted commit will have a new trailer
>>>
>>>       Revert: <commit-id>
>>>
>>> Similarly a cherry-picked commit with -x will have
>>>
>>>       Cherry-Pick: <commit-id>
>>
>> I think this is a good idea though I wonder if it will break someones
>> script that is looking for the messages generated by -x at the moment.
> 
> It will [1] but I still think it's worth the trouble. The script will
> be less likely to break after, and you can use git-interpret-trailers
> instead of plain grep.
> 
> [1] https://public-inbox.org/git/20181017143921.GR270328@devbig004.ftw2.facebook.com/
> 
>>> @@ -1758,16 +1757,10 @@ static int do_pick_commit(enum todo_command command, struct commit *commit,
>>>                base_label = msg.label;
>>>                next = parent;
>>>                next_label = msg.parent_label;
>>> -             strbuf_addstr(&msgbuf, "Revert \"");
>>> -             strbuf_addstr(&msgbuf, msg.subject);
>>> -             strbuf_addstr(&msgbuf, "\"\n\nThis reverts commit ");
>>> -             strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
>>> -
>>> -             if (commit->parents && commit->parents->next) {
>>> -                     strbuf_addstr(&msgbuf, ", reversing\nchanges made to ");
>>> -                     strbuf_addstr(&msgbuf, oid_to_hex(&parent->object.oid));
>>> -             }
>>
>> As revert currently records the parent given on the command line when
>> reverting a merge commit it would probably be a good idea to add that
>> either as a separate trailer or to the Revert: trailer and possibly also
>> generate it for cherry picks.
> 
> My mistake. I didn't read carefully and thought it was logging
> commit->parents, which is pointless.
> 
> So what should be the trailer for this (I don't think putting it in
> Revert: is a good idea, too much to parse)? Revert-parent: ?
> Revert-merge: ?

I think Revert-parent: is good, though you seem to have gone for 
including it the Revert: trailer in v2.
>>> -             strbuf_addstr(&msgbuf, ".\n");
>>> +             strbuf_addf(&msgbuf, "Revert \"%s\"\n\n", msg.subject);
>>
>> If the message already contains trailers then should we just append the
>> Revert trailer those rather than inserting "\n\n"?
> 
> Umm.. but this \n\n is for separating the subject and the body. I
> think we need it anyway, trailer or not.

Ah you're right, I had forgotten that the revert message body is empty, 
unlike cherry-pick where the message is copied (and that does the right 
thing already when there are existing trailers).

Best wishes

Phillip


>>> @@ -1784,9 +1777,8 @@ static int do_pick_commit(enum todo_command command, struct commit *commit,
>>>                        strbuf_complete_line(&msgbuf);
>>>                        if (!has_conforming_footer(&msgbuf, NULL, 0))
>>>                                strbuf_addch(&msgbuf, '\n');
>>> -                     strbuf_addstr(&msgbuf, cherry_picked_prefix);
>>> -                     strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
>>> -                     strbuf_addstr(&msgbuf, ")\n");
>>> +                     strbuf_addf(&msgbuf, "Cherry-Pick: %s\n",
>>> +                                 oid_to_hex(&commit->object.oid));
> 
> I will probably make this "Cherry-picked-from:" to match our S-o-b style.
>