Re: [PATCH 8/8] worktree: simplify search for unique worktree

From: "Martin Ågren" <martin.agren@gmail.com>
To: Eric Sunshine <sunshine@sunshineco.com>
Cc: Git List <git@vger.kernel.org>, Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH 8/8] worktree: simplify search for unique worktree
Date: Thu, 10 Sep 2020 21:48:13 +0200	[thread overview]
Message-ID: <CAN0heSrUWiZ_xar3G5rZG-c=8OVp5-eByS6rMXOw9wfTA8kmbA@mail.gmail.com> (raw)
In-Reply-To: <CAPig+cT_VvOiKBCC=E_P0R8SXkoWPVUxxOOLovOmr8N377YNdQ@mail.gmail.com>

On Thu, 10 Sep 2020 at 21:28, Eric Sunshine <sunshine@sunshineco.com> wrote:
>
> On Thu, Sep 10, 2020 at 3:08 PM Martin Ågren <martin.agren@gmail.com> wrote:
> > We track the number of worktrees we've found and break out of the loop
> > early once we hit 2. This is because we're not really interested in the
> > number of matches -- we just want to make sure that we don't find more
> > than one worktree that matches the suffix. This can be done just as well
> > by checking the NULL-ness of the pointer where we collect our
> > answer-to-be. Drop the redundant `nr_found` variable.
> >
> > Signed-off-by: Martin Ågren <martin.agren@gmail.com>
> > ---
> > diff --git a/worktree.c b/worktree.c
> > @@ -172,13 +172,13 @@ static struct worktree *find_worktree_by_suffix(struct worktree **list,
> >                                                 const char *suffix)
> >  {
> > -       for (; *list && nr_found < 2; list++) {
> > +       for (; *list; list++) {
> > @@ -186,11 +186,12 @@ static struct worktree *find_worktree_by_suffix(struct worktree **list,
> >                 if ((!start || (start > 0 && is_dir_sep(path[start - 1]))) &&
> >                     !fspathcmp(suffix, path + start)) {
> > +                       if (found)
> > +                               return NULL;
> >                         found = *list;
> > -                       nr_found++;
> >                 }
> >         }
> > -       return nr_found == 1 ? found : NULL;
> > +       return found;
>
> Although this change appears to be correct and does simplify the code,
> I think it also makes it a bit more opaque. With the explicit
> `nr_found == 1`, it is quite obvious that the function considers
> "success" to be when one and only one entry is found and any other
> number is failure. But with the revised code, it is harder to work out
> precisely what the conditions are.

Thanks for commenting. I found the original trickier than it had to be.
It spreads out the logic in several places and is careful to short-cut
the loop. My first thought was "why doesn't this just use the standard
form?". But I'm open to the idea that it might be a fairly personal
standard form... If there's any risk that someone else comes along and
simplifies this to use a `nr_found` variable, then maybe file this under
code churning?

> Having said that, I think a simple
> comment before the function would suffice to clear up the opaqueness.
> Perhaps something like:
>
>     /* If exactly one worktree matches 'target', return it, else NULL. */

That's a good suggestion regardless.

Thanks
Martin