Hi Peff,
On Fri, 9 Nov 2018, Jeff King wrote:
> On Fri, Nov 09, 2018 at 01:34:19AM -0800, Johannes Schindelin via
> GitGitGadget wrote:
>
> > From: Johannes Schindelin <johannes.schinde...@gmx.de>
> >
> > When we converted a `git checkout -q $onto^0` call to use
> > `reset_head()`, we inadvertently incurred a change from a twoway_merge
> > to a oneway_merge, as if we wanted a `git reset --hard` instead.
> >
> > This has performance ramifications under certain, though, as the
> > oneway_merge needs to lstat() every single index entry whereas
> > twoway_merge does not.
> >
> > So let's go back to the old behavior.
>
> Makes sense. I didn't think too hard about any possible gotchas with the
> twoway/oneway switch, but if that's what git-checkout was doing before,
> it seems obviously safe.
Right.
> > diff --git a/builtin/rebase.c b/builtin/rebase.c
> > index 6f6d7de156..c1cc50f3f8 100644
> > --- a/builtin/rebase.c
> > +++ b/builtin/rebase.c
> > @@ -523,11 +523,12 @@ finished_rebase:
> > #define GIT_REFLOG_ACTION_ENVIRONMENT "GIT_REFLOG_ACTION"
> >
> > static int reset_head(struct object_id *oid, const char *action,
> > - const char *switch_to_branch, int detach_head,
> > + const char *switch_to_branch,
> > + int detach_head, int reset_hard,
>
> It might be worth switching to a single flag variable here. It would
> make calls like this:
>
> > - if (reset_head(&options.onto->object.oid, "checkout", NULL, 1,
> > + if (reset_head(&options.onto->object.oid, "checkout", NULL, 1, 0,
> > NULL, msg.buf))
>
> a little more self-documenting (if a little more verbose).
I thought about that, but for just two flags? Well, let me try it and see
whether I like the result ;-)
> > - if (!oid) {
> > - if (get_oid("HEAD", &head_oid)) {
> > - rollback_lock_file(&lock);
> > - return error(_("could not determine HEAD revision"));
> > - }
> > - oid = &head_oid;
> > + if (get_oid("HEAD", &head_oid)) {
> > + rollback_lock_file(&lock);
> > + return error(_("could not determine HEAD revision"));
> > }
>
> This one could actually turn into:
>
> ret = error(...);
> goto leave_reset_head;
>
> now. We don't have to worry about an uninitialized desc.buffer anymore
> (as I mentioned in the previous email), because "nr" would be 0.
>
> It doesn't save any lines, though (but maybe having a single
> cleanup/exit point would make things easier to read; I dunno).
But you're right, of course. Consistency makes for easier-to-read code.
> Take all my comments as observations, not objections. This looks OK to
> me either way.
Actually, you got me thinking about the desc.buffer. And I think there is
one corner case where it could cause a problem: `struct tree_desc desc[2]`
does not initialize the buffers to NULL. And what if
fill_tree_descriptor() function returns NULL? Then the buffer is still
uninitialized.
In practice, our *current* version of fill_tree_descriptor() never returns
NULL if the oid parameter is non-NULL. It would die() in the error case
instead (bad!). So to prepare for a less bad version, I'd rather
initialize the `desc` array and be on the safe (and easier to reason
about) side.
Thank you for your helpful review,
Dscho
