Re: [PATCH 2/2] built-in rebase: reinstate `checkout -q` behavior where appropriate
- From
Johannes Schindelin <johannes.schindelin@gmx.de>
- Date
- Nov 9, 2018, 17:21 UTC
- Message-ID
- <nycvar.QRO.7.76.6.1811091813140.39@tvgsbejvaqbjf.bet>
- In-Reply-To
- <20181109101148.GB7410@sigill.intra.peff.net>
Hi Peff,
On Fri, 9 Nov 2018, Jeff King wrote:
Show 17 quoted lines
> On Fri, Nov 09, 2018 at 01:34:19AM -0800, Johannes Schindelin via GitGitGadget wrote: > > > From: Johannes Schindelin <johannes.schindelin@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.
Show 20 quoted lines
> > 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 ;-)
Show 21 quoted lines
> > - 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