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

From: René Scharfe <l.s.r@web.de>
Date: Aug 2, 2018, 15:06 UTC
Message-ID: <e7e5f54d-04b6-4d0f-0bcb-692801f0719c@web.de>
In-Reply-To: <87ftzwu9wg.fsf@evledraar.gmail.com>

Am 02.08.2018 um 16:21 schrieb Ævar Arnfjörð Bjarmason:

Show 51 quoted lines

> 
> On Thu, Aug 02 2018, René Scharfe wrote:
> 
>> Am 02.08.2018 um 00:31 schrieb Ævar Arnfjörð Bjarmason:
>>> But looking at this again it looks like this whole thing should just be
>>> replaced by:
>>>
>>>       diff --git a/builtin/push.c b/builtin/push.c
>>>       index 9cd8e8cd56..b8fa15c101 100644
>>>       --- a/builtin/push.c
>>>       +++ b/builtin/push.c
>>>       @@ -558,9 +558,10 @@ int cmd_push(int argc, const char **argv, const char *prefix)
>>>                       OPT_BIT( 0,  "porcelain", &flags, N_("machine-readable output"), TRANSPORT_PUSH_PORCELAIN),
>>>                       OPT_BIT('f', "force", &flags, N_("force updates"), TRANSPORT_PUSH_FORCE),
>>>                       { OPTION_CALLBACK,
>>>       -                 0, CAS_OPT_NAME, &cas, N_("refname>:<expect"),
>>>       +                 0, CAS_OPT_NAME, &cas, N_("<refname>:<expect>"),
>>>                         N_("require old value of ref to be at this value"),
>>>       -                 PARSE_OPT_OPTARG, parseopt_push_cas_option },
>>>       +                 PARSE_OPT_OPTARG | PARSE_OPT_LITERAL_ARGHELP,
>>>       +                 parseopt_push_cas_option },
>>>                       { OPTION_CALLBACK, 0, "recurse-submodules", &recurse_submodules, "check|on-demand|no",
>>>                               N_("control recursive pushing of submodules"),
>>>                               PARSE_OPT_OPTARG, option_parse_recurse_submodules },
>>>
>>> I.e. the reason this is confusing is because the code originally added
>>> in 28f5d17611 ("remote.c: add command line option parser for
>>> "--force-with-lease"", 2013-07-08) didn't use PARSE_OPT_LITERAL_ARGHELP,
>>> which I also see is what read-tree etc. use already to not end up with
>>> these double <>'s, see also 29f25d493c ("parse-options: add
>>> PARSE_OPT_LITERAL_ARGHELP for complicated argh's", 2009-05-21).
>>
>> We could check if argh comes with its own angle brackets already and
>> not add a second pair in that case, making PARSE_OPT_LITERAL_ARGHELP
>> redundant in most cases, including the one above.  Any downsides?
>> Too magical?
> 
> I'm more inclined to say that we should stop using
> PARSE_OPT_LITERAL_ARGHELP in some of these cases, and change
> "refname>:<expect" to "<refname>:<expect>" in push.c, so that the help
> we emit is --force-with-lease[=<<refname>:<expect>>].
> 
> As noted in 29f25d493c this facility wasn't added with the intent
> turning --refspec=<<refspec>> into --refspec=<refspec>, but to do stuff
> like --option=<val1>[,<val2>] for options that take comma-delimited
> options.
> 
> If we're magically removing <>'s we have no consistent convention to
> tell apart --opt=<a|b|c> meaning "one of a, b or c", --refspec=<refspec>
> meaning "the literal string 'refspec'" and --refspec=<<refspec>> meaning
> add a <refspec> string, i.e. fill in your refspec here.

The notation for requiring a literal string is to use no special markers:

	--option=literal_string

Alternatives can be grouped with parentheses:

	--option=(either|or)

In both cases you'd need PARSE_OPT_LITERAL_ARGHELP.

I haven't seen double angle brackets before in command line help strings. The commit message of 29f25d493c doesn't mention them either. A single pair is used to indicate that users need to fill in a value of a certain type:

	--refspec=<refspec>

Multi-part options aren't special in this syntax:

	--force-with-lease=<refname>:<expect>

NB: The "--refspec=" in the example before that is a literal string, so
this is also already a multi-part option if you will.

According to its manpage the option should rather be shown like this:

	--force-with-lease[=<refname>[:<expect>]]

... to indicate that all three forms are valid:

	--force-with-lease
	--force-with-lease=some_ref
	--force-with-lease=some_ref:but_not_this

The current code doesn't allow that to be expressed, while it's possible with my patch. And nothing is removed -- you can specify as many angle brackets as you like, if that turns out to be useful; parseopt just won't add any more on top automatically anymore if you do that.

Side note: The remaining user of PARSE_OPT_LITERAL_ARGHELP in builtin/update-index.c uses a slash for alternatives; we should probably use pipe instead:

	{OPTION_CALLBACK, 0, "chmod", &set_executable_bit, N_("(+/-)x"),
		N_("override the executable bit of the listed files"),
		PARSE_OPT_NONEG | PARSE_OPT_LITERAL_ARGHELP,
		chmod_callback},

René