Re: [PATCH] merge-recursive.c: Fix case-changing merge bug

[David Turner <dturner@twopensource.com>]

On Tue, 2014-05-06 at 10:07 -0700, Junio C Hamano wrote:
> David Turner <dturner@twopensource.com> writes:
> 
> > On a case-insensitive filesystem, when merging, a file would be
> > wrongly deleted from the working tree if an incoming commit had
> > renamed it changing only its case.  When merging a rename, the file
> > with the old name would be deleted -- but since the filesystem
> > considers the old name to be the same as the new name, the new
> > file would in fact be deleted.
> >
> > We avoid this by not deleting files that have a case-clone in the
> > index at stage 0.
> >
> > Signed-off-by: David Turner <dturner@twitter.com>
> > ---
> >  merge-recursive.c           |  6 ++++++
> >  t/t7063-merge-ignorecase.sh | 32 ++++++++++++++++++++++++++++++++
> >  2 files changed, 38 insertions(+)
> >  create mode 100755 t/t7063-merge-ignorecase.sh
> >
> > diff --git a/merge-recursive.c b/merge-recursive.c
> > index 4177092..cab16fa 100644
> > --- a/merge-recursive.c
> > +++ b/merge-recursive.c
> > @@ -589,6 +589,12 @@ static int remove_file(struct merge_options *o, int clean,
> >  			return -1;
> >  	}
> >  	if (update_working_directory) {
> > +		if (ignore_case) {
> > +			struct cache_entry *ce;
> > +			ce = cache_file_exists(path, strlen(path), ignore_case);
> > +			if (ce && ce_stage(ce) == 0)
> > +				return 0;
> > +		}
> >  		if (remove_path(path))
> >  			return -1;
> >  	}
> 
> Thanks.
> 
> I wonder what happens if you did the same merge using the resolve
> strategy, though.  If you see a similar issue, and the true reason
> of the breakage turns out to be because three-way merge performed by
> unpack_trees() (with opts.update set to 1) considers that these
> paths that only differ in case in "our" tree, in the index and in
> the working tree are different paths (I am not saying that is the
> case, but that was one of my first hunches after seeing the initial
> report) then it may suggest that the above might not be the best
> change to fix the issue.

I changed the test to -s resolve, and it changed from failing to
passing.  So while I still don't know whether this is the right change,
it's at least not wrong for that reason.

> > diff --git a/t/t7063-merge-ignorecase.sh b/t/t7063-merge-ignorecase.sh
> > new file mode 100755
> > index 0000000..6d4959f
> > --- /dev/null
> > +++ b/t/t7063-merge-ignorecase.sh
> 
> Hmmm, did you really have to add a file dedicated for this single
> test?

Would you prefer that I add it to t6022-merge-rename.sh?  Or I could
add it to t7062-wtstatus-ignorecase.sh and rename that file to
t7062-ignorecase.sh.