Re: [PATCH v2 11/11] merge-ort: add implementation of type-changed rename handling

From: Elijah Newren <newren@gmail.com>
To: Derrick Stolee <stolee@gmail.com>
Cc: Elijah Newren via GitGitGadget <gitgitgadget@gmail.com>,
	Git Mailing List <git@vger.kernel.org>,
	Johannes Schindelin <Johannes.Schindelin@gmx.de>
Subject: Re: [PATCH v2 11/11] merge-ort: add implementation of type-changed rename handling
Date: Tue, 15 Dec 2020 09:11:04 -0800	[thread overview]
Message-ID: <CABPp-BGSCeffT-VnniGXM8D8BC=T6YWHr4ei2ij+1-+0ghg8OA@mail.gmail.com> (raw)
In-Reply-To: <fcc6b18e-c5eb-27a1-b6b5-4dcdd97e2b90@gmail.com>

On Tue, Dec 15, 2020 at 6:31 AM Derrick Stolee <stolee@gmail.com> wrote:
>
> On 12/14/2020 11:21 AM, Elijah Newren via GitGitGadget wrote:
> > From: Elijah Newren <newren@gmail.com>
> >
> > Implement cases where renames are involved in type changes (i.e. the
> > side of history that didn't rename the file changed its type from a
> > regular file to a symlink or submodule).  There was some code to handle
> > this in merge-recursive but only in the special case when the renamed
> > file had no content changes.  The code here works differently -- it
> > knows process_entry() can handle mode conflicts, so it does a few
> > minimal tweaks to ensure process_entry() can just finish the job as
> > needed.
> >
> > Signed-off-by: Elijah Newren <newren@gmail.com>
> > ---
> >  merge-ort.c | 33 +++++++++++++++++++++++++++++++--
> >  1 file changed, 31 insertions(+), 2 deletions(-)
> >
> > diff --git a/merge-ort.c b/merge-ort.c
> > index 9aac33c8e31..11e33f56edf 100644
> > --- a/merge-ort.c
> > +++ b/merge-ort.c
> > @@ -778,7 +778,32 @@ static int process_renames(struct merge_options *opt,
> >                        S_ISREG(newinfo->stages[target_index].mode));
> >               if (type_changed && collision) {
> >                       /* special handling so later blocks can handle this */
>
> Perhaps drop this comment, or incorporate it into the lower one?

Will do.

> > -                     die("Not yet implemented");
> > +                     /*
> > +                      * if type_changed && collision are both true, then this
> > +                      * was really a double rename, but one side wasn't
> > +                      * detected due to lack of break detection.  I.e.
> > +                      * something like
> > +                      *    orig: has normal file 'foo'
> > +                      *    side1: renames 'foo' to 'bar', adds 'foo' symlink
> > +                      *    side2: renames 'foo' to 'bar'
> > +                      * In this case, the foo->bar rename on side1 won't be
> > +                      * detected because the new symlink named 'foo' is
> > +                      * there and we don't do break detection.  But we detect
> > +                      * this here because we don't want to merge the content
> > +                      * of the foo symlink with the foo->bar file, so we
> > +                      * have some logic to handle this special case.  The
> > +                      * easiest way to do that is make 'bar' on side1 not
> > +                      * be considered a colliding file but the other part
> > +                      * of a normal rename.  If the file is very different,
> > +                      * well we're going to get content merge conflicts
> > +                      * anyway so it doesn't hurt.  And if the colliding
> > +                      * file also has a different type, that'll be handled
> > +                      * by the content merge logic in process_entry() too.
> > +                      *
> > +                      * See also t6430, 'rename vs. rename/symlink'
>
> I appreciate the callout to a test that exercises this behavior.
>
> > +                      */
> > +                     collision = 0;
> > +             }
>
> Here, we regain that closing curly brace, fixing the compiler errors from
> earlier.

So embarrassing.  I was pretty sure I tested the individual patches,
but maybe I somehow missed this series??  Anyway, yeah, I'll fix it
up.

>
> >               if (source_deleted) {
> >                       if (target_index == 1) {
> >                               rename_branch = opt->branch1;
> > @@ -858,7 +883,11 @@ static int process_renames(struct merge_options *opt,
> >                       newinfo->pathnames[0] = oldpath;
> >                       if (type_changed) {
> >                               /* rename vs. typechange */
> > -                             die("Not yet implemented");
> > +                             /* Mark the original as resolved by removal */
> > +                             memcpy(&oldinfo->stages[0].oid, &null_oid,
> > +                                    sizeof(oldinfo->stages[0].oid));
> > +                             oldinfo->stages[0].mode = 0;
> > +                             oldinfo->filemask &= 0x06;
>
> This matches your explanation in the comment above. I wonder if 0x06
> could be less magical, but we are really deep in the weeds here already.
>
> Thanks,
> -Stolee
>