Re: [PATCH 2/6] commit-graph.h: store object directory in 'struct commit_graph'

From: Taylor Blau <me@ttaylorr.com>
Date: Feb 3, 2020, 03:58 UTC
Message-ID: <20200203035819.GA23625@syl.local>
In-Reply-To: <CAN0heSrrrWjBKnzjMfzEkTMVTge2AfVdwsp6D5Mx==5S8-ZLJQ@mail.gmail.com>

Hi Martin,

Thanks for your review! Your comments were all quite helpful, and I applied all of your suggested changes.

On Fri, Jan 31, 2020 at 07:52:02AM +0100, Martin Ågren wrote:

Show 5 quoted lines

> On Fri, 31 Jan 2020 at 00:03, Taylor Blau <me@ttaylorr.com> wrote:
> > Instead of getting rid of the 'struct object_directory *', store that
> > insead of a 'char *odb' in 'struct commit_graph'. Once the 'struct
>
> s/insead/instead/

Typo. Thanks for noticing. I fixed this in my local copy of this branch.

Show 18 quoted lines

> >         if (open_ok)
> >                 graph = load_commit_graph_one_fd_st(fd, &st);
> > -        else
> > -               graph = read_commit_graph_one(the_repository, opts.obj_dir);
> > +       else {
> > +               struct object_directory *odb;
> > +               if ((odb = find_odb(the_repository, opts.obj_dir)))
> > +                       graph = read_commit_graph_one(the_repository, odb);
> > +       }
>
> I'm a tiny bit allergic to this assignment-within-if. It's wrapped by
> another pair of parentheses, which both compilers and humans know to
> interpret as "trust me, this is not a mistake", but I still find this
> easier to read:
>
>   odb = find_odb(...);
>   if (odb)
>           ....

To be honest, I'm not such a fan of this style myself, but it seemed odd to me to write:

  struct object_directory *odb;
  odb = ...;
  if (odb) {
  }

when we were really only trying to call 'find_odb()' and do something with its result, but only if it was non-NULL. I counted 152 of these assign-if's laying around with:

  $ git grep 'if ((.* =[^=]' | wc -l

but it seems like they are in poor style (as evidenced by your and Junio's response later in the thread). So, I removed this and instead promoted 'odb' to a local variable at the function level, since we do that promotion anyway in a couple of patches later. This reduces the churn, and avoids either an assign-if, or a define/assign/check.

> > --- a/builtin/commit.c
> > +++ b/builtin/commit.c
>
> > +#include "object-store.h"

No; this is a stray left over from some development on this branch. I'll remove it.

Show 11 quoted lines

> This is the only change in this file, which looks a bit odd. I haven't
> actually applied your patches, to be honest, but is this inclusion
> really needed?
>
> > --- a/commit-graph.c
> > +++ b/commit-graph.c
>
> > +struct object_directory *find_odb(struct repository *r, const char *obj_dir)
>
> This doesn't look commit-graph related -- could/should it go somewhere
> else?

I'll respond in more complete detail further down in the thread, but the short answer is "yes, this should go in builtin/commit-graph.c".

Show 30 quoted lines

> > +{
> > +       struct object_directory *odb;
> > +       char *obj_dir_real = real_pathdup(obj_dir, 1);
> > +       int cmp = -1;
> > +
> > +       prepare_alt_odb(r);
> > +       for (odb = r->objects->odb; odb; odb = odb->next) {
> > +               cmp = strcmp(obj_dir_real, real_path(odb->path));
> > +               if (!cmp)
> > +                       break;
> > +       }
>
> At this point, either odb is NULL or cmp is zero. Those are the only two
> ways out of the loop.
>
> > +       free(obj_dir_real);
> > +
> > +       if (cmp)
> > +               odb = NULL;
>
> Meaning that this doesn't do much? If the most recent comparison failed,
> it's because we didn't find anything, so odb will be NULL.
>
> > +       return odb;
> > +}
>
> I think you could drop `cmp` and that final check, and write the loop
> body as "if (!strcmp(...)) break". You could also have an empty loop
> body, but I wouldn't go there -- I'd find that less readable. (Maybe
> that's just me.)

Thanks, I changed this to remove the 'cmp' check outside of the loop, which I agree is unnecessary.

> Martin

Thanks, Taylor