Re: [PATCH v3 1/3] ref-filter: add worktreepath atom

[Nickolai Belakovski <nbelakovski@gmail.com>]

On Tue, Dec 18, 2018 at 9:22 AM Jeff King <peff@peff.net> wrote:
>
> On Sun, Dec 16, 2018 at 01:57:57PM -0800, nbelakovski@gmail.com wrote:
>
> > From: Nickolai Belakovski <nbelakovski@gmail.com>
> >
> > Add an atom proving the path of the linked worktree where this ref is
> > checked out, if it is checked out in any linked worktrees, and empty
> > string otherwise.
>
> I stumbled over the word "proving" here. Maybe "showing" would be more
> clear?

Oops, providing

> > +worktreepath::
> > +     The absolute path to the worktree in which the ref is checked
> > +     out, if it is checked out in any linked worktree. ' ' otherwise.
> > +
>
> Also, why are we replacing it with a single space? Wouldn't the empty
> string be more customary (and work with the other "if empty, then do
> this" formatting options)?

I was just following what was done for HEAD, but overall I agree that
empty is preferable to single space, will change.

> Minor style nit: we put the "*" in a pointer declaration next to the
> variable name, without intervening whitespace. Like:
>
>   static struct worktree **worktrees;

Gotcha, will do, thanks for pointing it out.


To sum up the hashmap comments:
-I hadn't thought to re-use the head_ref of worktree as the key.
That's clever. I like the readability of having separate entries for
key and value, but I can see the benefit of not having to do an extra
allocation. I can make up for the readability hit with a comment.
-Actually, for any valid use case there will only be one instance of
the map since the entries of used_atom are cached, but regardless it
makes sense to keep per-atom info in used_atom and global context
somewhere else, so I'll make that change to make it a static variable
outside of used_atom.
-Will change the lookup logic to remove the extra allocation. Since
I'm letting the hashmap use its internal comparison function on the
hash, I don't need to provide a comparison function.

> What's this extra strncmp about? If we're _not_ a worktreepath atom,
> we'd still do the lookup only to put nothing in the string?

Leftover from an earlier iteration where I was going to support
getting more info out of the worktree struct. I decided to limit scope
to just the info I really needed for the branch change. I left it like
this because I thought it would make the code more readable for
someone who wanted to come in and add that extra info, but I think
you're right that it ends up just reading kind of awkwardly.

>
> > @@ -2013,7 +2076,14 @@ void ref_array_clear(struct ref_array *array)
> >       int i;
> >
> >       for (i = 0; i < used_atom_cnt; i++)
> > +     {
> > +             if (!strncmp(used_atom[i].name, "worktreepath", strlen("worktreepath")))
> > +             {
> > +                     hashmap_free(&(used_atom[i].u.reftoworktreeinfo_map), 1);
> > +                     free_worktrees(worktrees);
> > +             }
>
> And if we move the mapping out to a static global, then this only has to
> be done once, not once per atom. In fact, I think this could double-free
> "worktrees" with your current patch if you have two "%(worktree)"
> placeholders, since "worktrees" already is a global.

Only if someone put a colon on one of the %(worktree) atoms, otherwise
they're all cached, but as you say moot point anyway if the map is
moved outside the used_atom structure.

>
> It's probably worth testing that the path we get is actually sane, too.
> I.e., expect something more like:
>
>    cat >expect <<-\EOF
>    master: $PWD
>    master: $PWD/worktree
>    side: not checked out
>    EOF
>    git for-each-ref \
>      --format="%(refname:short): %(if)%(worktreepath)%(then)%(worktreepath)%(else)not checked %out%(end)
>
> (I wish there was a way to avoid that really long line, but I don't
> think there is).
>

Yea good call, can do.

Thanks for all the feedback, will try to turn these around quickly.