Re: [PATCH] push: comment on a funny unbalanced option help

From: Jeff King <peff@peff.net>
Date: Aug 2, 2018, 16:54 UTC
Message-ID: <20180802165457.GC15984@sigill.intra.peff.net>
In-Reply-To: <xmqqftzw4weq.fsf@gitster-ct.c.googlers.com>

On Thu, Aug 02, 2018 at 08:31:57AM -0700, Junio C Hamano wrote:

Show 20 quoted lines

> > diff --git a/parse-options.c b/parse-options.c
> > index 7db84227ab..fadfc6a833 100644
> > --- a/parse-options.c
> > +++ b/parse-options.c
> > @@ -660,7 +660,8 @@ int parse_options(int argc, const char **argv, const char *prefix,
> >  static int usage_argh(const struct option *opts, FILE *outfile)
> >  {
> >  	const char *s;
> > -	int literal = (opts->flags & PARSE_OPT_LITERAL_ARGHELP) || !opts->argh;
> > +	int literal = (opts->flags & PARSE_OPT_LITERAL_ARGHELP) || !opts->argh ||
> > +		(opts->argh[0] == '<' && strchr(opts->argh, '>'));
> 
> You are greedier than what I thought ;-) I would have limited this
> magic to the case where argh is surrounded by "<>", but you allow
> one closing ">" anywhere, which allows us to grab more complex cases.
> 
> The lack of escape hatch to decline this auto-literal magic makes me
> somewhat nervous, but I do not offhand think of a reason why I do
> want an arg-help string that _begins_ with '<' to be enclosed by
> another set of "<>", so perhaps this is a good kind of magic.

I think that case is actually easy; once the caller provides a "<>", they are in "literal" mode, so they are free to add extra brackets if you want. I.e., any "<foo>bar" that you do want enclosed could be spelled "<<foo>bar>". It's the opposite that becomes impossible: you do not have an opening bracket and nor do you want one. But as long as we retain LITERAL_ARGHELP for that case, we have an escape hatch.

I was going to suggest that this conversion has the downside of being somewhat one-way. That is, it is easy for us to find affected sites now since they contain the string LITERAL_ARGHELP. Whereas if we wanted to back it out in the future, it is hard to know which sites are depending on this new behavior.

But I am having trouble thinking of a reason we would want to back it out. This makes most cases easier, and has a good escape hatch.

-Peff

PS I actually would have made the rule simply "does it begin with a
   '<'", which seems simpler still. If people accidentally write "<foo",
   forgetting to close their brackets, that is a bug under both the
   old and new behavior (just with slightly different outcomes).