Re: git commit file completion recently broke

> On Wed, Dec 06, 2017 at 04:38:29PM -0800, Jacob Keller wrote:
>
>> >> But nope, it looks like the culprit is f7923a5ece (diff: use
>> >> skip_to_optional_val(), 2017-12-04), which switched over parsing of
>> >> "--relative".
>> >
>> > Oh, actually, I guess I was half-right. It feeds &options->prefix as the
>> > "default", meaning that we overwrite it with the empty string. I don't
>> > think "--relative" works for the semantics of skip_to_optional_value,
>> > since it needs:
>> >
>> >   --relative=foo: set prefix to "foo"
>> >
>> >   --relative: leave prefix untouched
>> >
>> > -Peff
>>
>> Yep, and apparently our test suite completely lacked any tests of
>> --relative on its own.
>>
>> I've sent a patch to add some tests.
>
> Great. I was also saddened by our lack of tests.
>
>> I don't know the exact best way to fix this, I guess we could just
>> revert it the changes to relative... but maybe we could add or modify
>> the semantics of skip_to_optional_val()?? What if it was changed so
>> that it left the value alone if no value was provided? This would
>> require callers to pre-set the value they want as default, but that
>> would solve relative's problem.
>
> I think that would work for this case. But just looking at others from
> the same series, I think they'd get pretty awkward. For instance we now
> have:
>

>   else if (!strcmp(arg, "--color))
>         options->use_color = 1;
>   else if (skip_prefix(arg, "--color=", &arg))
>         /* parse "arg" as colorbool */
>
> which became:
>
>   else if (skip_to_optional_val_default(arg, "--color", &arg, "always"))
>         /* parse "arg" as colorbool */
>
> How would that look with the "leave it alone instead of assigning a
> default" semantics? It gets pretty clumsy, because you have to
> pre-assign "always" to some pointer. But then we can't reuse "arg", so
> we end up with something more like:
>
>   const char *color_val = "always";
>   ...
>   else if (skip_to_optional_val(arg, "--color", &color_val))
>

> But we need one such "color_val" for every option we test for, and we
> have to set all of them up before any matches (because we don't know
> which one we'll actually match). Yuck.
>
> I think we'd do better to just assign NULL when there's "=", so we can
> tell the difference between "--relative", "--relative=", and
> "--relative=foo" (all of which are distinct).
>
> I think that's possible with the current scheme by doing:
>
>   else if (skip_to_optional_val_default(arg, "--relative", &arg, NULL)) {
>         options->flags.relative_name = 1;
>         if (arg)
>                 options->prefix = arg;
>   }
>
> IOW, the problem isn't in the design of the skip function, but just how
> it was used in this particular case. I do think it may make sense for
> the "short" one to use NULL, like:
>
>   skip_to_optional_val(arg, "--relative, &arg)
>
> but maybe some other callers would be more inconvenienced (they may have
> to current NULL back into the empty string if they want to string
> "--foo" the same as "--foo=").
>
> -Peff