Re: [PATCH 2/8] tag: Refactor the options handling code to be less bizarro

From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Mar 18, 2017, 19:13 UTC
Message-ID: <CACBZZX4Zs=00QXv5eaafQd8-n7OakcL3WeQh8XxiMo-9a+kAzQ@mail.gmail.com>
In-Reply-To: <xmqqr31u301u.fsf@gitster.mtv.corp.google.com>

On Sat, Mar 18, 2017 at 7:35 PM, Junio C Hamano <gitster@pobox.com> wrote:

Show 41 quoted lines

> Ævar Arnfjörð Bjarmason  <avarab@gmail.com> writes:
>
>> diff --git a/builtin/tag.c b/builtin/tag.c
>> index ad29be6923..0bba3fd070 100644
>> --- a/builtin/tag.c
>> +++ b/builtin/tag.c
>> @@ -454,10 +454,10 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
>>       }
>>       create_tag_object = (opt.sign || annotate || msg.given || msgfile);
>>
>> -     if (argc == 0 && !cmdmode)
>> +     if (argc == 0 && !cmdmode && !create_tag_object)
>>               cmdmode = 'l';
>
> So with this change, if we cannot infer that we are creating a tag
> object from other options, we leave cmdmode to its original 0.
>
>> -     if ((create_tag_object || force) && (cmdmode != 0))
>> +     if ((create_tag_object || force) && (cmdmode || (!cmdmode && !argc)))
>>               usage_with_options(git_tag_usage, options);
>
> And then immediately after that, we complain by detecting that we
> know we are creating a tag and a non-zero cmdmode is in effect
> (i.e. 'l', 'd' or 'v', none of which is about creating a tag).  The
> way we used to detect that we are doing something other than tag
> creation was by seeing cmdmode is set to anything.  Because of your
> earlier change, that no longer is true.  You need to separately
> check (!cmdmode && !argc).
>
> By following the logic that way, I can see how this change at this
> step is a no-op, but I have to say that the code with this patch
> looks much more bizarre than the original.
>
> I am not sure why you want to do the first change at this step in
> the first place.  Is it because you'd want to take over (!cmdmode &&
> !argc) condtion to default to 'list'?  With the change in 4/8 and
> 5/8, you are ensuring that cmdmode is set to 'l' for these new cases
> before the code hits the check to call usage_with_options().  And at
> that point, you can use the original "are we creating and !cmdmode
> says we are not?  That's contradiction" logic without making it more
> bizarre with this patch, no?

Nothing about this patch is needed for the rest of the series. I just tried rebasing it out now and all tests pass & everything works as expected.

The reason I'm submitting it is because while this works *now* and there's no cases I can see currently where cmdmode is 'l' after the current `((create_tag_object || force) && (cmdmode != 0))`, during a lengthy debugging session when I was hacking on a subsequent patch in this series it took me a long time to track down a segfault later in the file because surely it was impossible that I was in cmdmode = 'l' with only "git tag -a".

Partly that was late night hacking session blindness after having read the !argc and assuming that the -a would be counted towards argc.

But I thought it was very a very bizarre pattern to set us to cmdmode = 'l' when we're not in that mode at all just to, as can be seen in the diff, get around a slightly more verbose one-time if-check.

So I think it's worth it to include this for less confusion in any subsequent patches to tag.c.