Re: [PATCH v2 3/3] bisect: combine args passed to find_bisection()

From: Junio C Hamano <gitster@pobox.com>
To: Aaron Lipman <alipman88@gmail.com>
Cc: git@vger.kernel.org
Subject: Re: [PATCH v2 3/3] bisect: combine args passed to find_bisection()
Date: Wed, 29 Jul 2020 21:32:14 -0700	[thread overview]
Message-ID: <xmqqr1st7hdd.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <20200730002735.87655-4-alipman88@gmail.com> (Aaron Lipman's message of "Wed, 29 Jul 2020 20:27:35 -0400")

Aaron Lipman <alipman88@gmail.com> writes:

> Now that find_bisection() accepts multiple boolean arguments, these may
> be combined into a single unsigned integer in order to declutter some of
> the code in bisect.c

I'd rather call them "flags" without "bisect_".  If we are passing
two sets of flags, one set about "bisect" and the other set about
something else, it would make quite a lot of sense to call the first
set "bisect_flags", but what we are seeing here is not like that.

> +	if (read_first_parent_option())
> +		bisect_flags |= BISECT_FIRST_PARENT;
> +
> +	if (!!skipped_revs.nr)
> +		bisect_flags |= BISECT_FIND_ALL;
> +

You do not care what kind of "true" you are feeding "if()", so I do
not think you would want to keep !! prefix here.  Older API into
find_bisection() may wanted to say "pass 1 to find_all", in which
case, normalizing with !! prefix may have made perfect sense, but 
that no longer holds here.

> +
> +	revs.first_parent_only = !!(bisect_flags & BISECT_FIRST_PARENT);

On the other hand, this !! may make sense; especially since .first_parent_only
could just be a one-bit unsigned bitfield.

>  	revs.limited = 1;
>  
>  	bisect_common(&revs);
>  
> -	find_bisection(&revs.commits, &reaches, &all, !!skipped_revs.nr, first_parent_only);
> +	find_bisection(&revs.commits, &reaches, &all, bisect_flags);

> @@ -23,6 +23,9 @@ struct commit_list *filter_skipped(struct commit_list *list,
>  #define BISECT_SHOW_ALL		(1<<0)
>  #define REV_LIST_QUIET		(1<<1)
>  
> +#define BISECT_FIND_ALL		(1u<<0)
> +#define BISECT_FIRST_PARENT	(1u<<1)

The set of bits to go to your "bisect_flags" are only these two new
ones, and the existing BISECT_SHOW_ALL does not belong to it (it is
a bit in rev_list_info.flags), but it is not apparent.  I wonder if
there is a good way to help readers easily tell these two sets apart.
These are flags passed to find_bisection(), so perhaps

    #define FIND_BISECTION_ALL (1U<<0)
    #define FIND_BISECTION_FIRST_PARENT_ONLY (1U<<1)

    unsigned flags = 0;
    if (first_parent)
	flags |= FIND_BISECTION_FIRST_PARENT_ONLY;
    ...
    find_bisection(..., flags);

would be a reasonable compromise?

Thanks.