Subject: Re: [PATCH v2 02/19] parse-options-cb: implement parse_opt_pass_argv_array()

From: Junio C Hamano <[email-masked]>
Date: Wed, 10 Jun 2015 01:03:54 -0700

Paul Tan <[email-masked]> writes:

> I don't see how it feels iffy.

That is largely a taste thing.  And a good taste matters.

What is iffy is to use strbuf as an external interface between the
implementation of the parse_opt_pass() API function and its users.

I would expect that no users of the parse_opt_pass() would ever take
advantage of the fact that the value they are using is implemented
as a strbuf, allowing them to use the family of functions in the
strbuf API to further manipulate it.  All users you added wants to
use a plain vanilla string, and only because you used strbuf as the
interface element, they have to say "var.buf" to get to the value
they want to use.

> The purpose of using strbufs (and
> argv_arrays) is to avoid error-prone manual memory management.

It is a good idea to use strbuf as an implementation detail of
parse_opt_pass() function.  After all, safer, easier and efficient
manipulation of strings is why we added the strbuf API to the system
in the first place.

But it is a different matter to expose that as an API element when
the recipient is not going to benefit.

In other words, callers of the API designed with a better taste
would look more like this:

	static const char *opt_diffstat;

	static struct option pull_options[] = {
        	...
                { OPTION_CALLBACK, 'n', NULL, &opt_diffstat, NULL,
		  N_("do not show a diffstat at the end of the merge"),
		  PARSE_OPT_NOARG | PARSE_OPT_NONEG, parse_opt_pass
        	},
		...
	};

	static int run_merge(void)
        {
        	...
                if (opt_diffstat)
                	argv_array_push(&args, opt_diffstat);
		...
	}

That way, they do not have to define strbuf variables and
dereference the value as opt_diffstat.buf.

And the implementation of the API element is not all that different
from what you wrote:

	int parse_opt_pass(const struct options *opt, const char *arg, int unset)
	{
		struct strbuf sb = STRBUF_INIT;
		char **value = opt->value;

		if (*value)
                	free(*value);
		if (opt->long_name) {
                	strbuf_addf(&sb, "--%s%s",
                        	    unset ? "no-" : "",
                                    opt->long_name);
			...
                }
                ...
                *value = strbuf_detach(&sb, NULL);
		return 0;
	}