Re: [PATCH v2 2/3] parse-options: make OPT_ARGUMENT() more useful

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Mar 15, 2019, 13:24 UTC
Message-ID: <nycvar.QRO.7.76.6.1903151421110.41@tvgsbejvaqbjf.bet>
In-Reply-To: <20190315031553.GB28943@sigill.intra.peff.net>

Hi Peff,

On Thu, 14 Mar 2019, Jeff King wrote:

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> On Thu, Mar 14, 2019 at 04:25:04AM -0700, Johannes Schindelin via GitGitGadget wrote:
> 
> > diff --git a/Documentation/technical/api-parse-options.txt b/Documentation/technical/api-parse-options.txt
> > index 2b036d7838..2e2e7c10c6 100644
> > --- a/Documentation/technical/api-parse-options.txt
> > +++ b/Documentation/technical/api-parse-options.txt
> > @@ -198,8 +198,10 @@ There are some macros to easily define options:
> >  	The filename will be prefixed by passing the filename along with
> >  	the prefix argument of `parse_options()` to `prefix_filename()`.
> >  
> > -`OPT_ARGUMENT(long, description)`::
> > +`OPT_ARGUMENT(long, &int_var, description)`::
> >  	Introduce a long-option argument that will be kept in `argv[]`.
> > +	If this option was seen, `int_var` will be set to one (except
> > +	if a `NULL` pointer was passed).
> 
> So this effectively makes it into a "bool" that we keep.

Almost. It is only a "seen" in the sense that you cannot re-set it to `false`.

But yeah, the difference is subtle.

> I think that's fine. It always uses NOARG, so it is not like we would
> ever need to see "we got --foo, and this is the argument it had".

Yep, I checked that.

> I did wonder if it was possible for "--no-foo" to trigger this (leaving
> the caller who looks at the int unsure if they saw "--foo" or
> "--no-foo"), but it seems that the parse-options code checks for
> OPTION_ARGUMENT before it ever looks at negation.

I checked that, too.

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> Curiously, it also checks it before doing the usual prefix-matching
> magic. So you could otherwise say "--no-inde", but OPT_ARGUMENT() will
> not allow it. I think that's probably sane and not worth thinking
> further about, but it is an interesting quirk that a user could possibly
> run into.

I missed that... ¯\_(ツ)_/¯

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> > diff --git a/parse-options.c b/parse-options.c
> > index cec74522e5..1d57802da0 100644
> > --- a/parse-options.c
> > +++ b/parse-options.c
> > @@ -286,6 +286,8 @@ static enum parse_opt_result parse_long_opt(
> >  					     optname(options, flags));
> >  			if (*rest)
> >  				continue;
> > +			if (options->value)
> > +				*(int *)options->value = options->defval;
> 
> Cute. You could actually assign any defval you like, though of course
> the convenient OPT_ARGUMENT() macro just always uses 1.
> 
> I wondered if you might need another cast for defval itself, but it's an
> intptr_t (so it's the types that use it as a string that need to cast to
> "const char *").

Exactly.

> This looks very clean overall, and I agree it's much nicer than the
> alternatives for your use case.

Thank you! 😊 Dscho