Junio C Hamano <junkio@xxxxxxx> writes:
> However.
>
> I usually have "[apply] whitespace = strip" in my ~/.gitconfig,
> but during this verification run, I disabled it to keep rebase
> from falling back to 3-way merge using merge-recursive. If I
> turn it on, rebase still fails and I strongly suspect "rebase
> -m" would fail the same way, although I haven't tried it (it
> takes too much time).
>
> I'll be somewhat busy this weekend, so I would welcome anybody
> else beating me to fixing the problem in merge-recursive.
Yuck. merge-recursive does seem to have problem with D/F
conflict in general; I suspect this is not limited to cases that
involve symbolic links.
First, the setup.
$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/hpa/linux-2.6-newsetup.git/
$ cd linux-2.6-newsetup.git
$ git fetch git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git/
$ git branch other b2ad90f4969226fe8cf3edc5330711ed5fc20105
$ git branch ancestor other^1
$ git reset --hard ancestor
$ echo >>Makefile ; git add Makefile ; git commit -m 'change one'
$ git branch try
To see that the underlying read-tree is working as expected (and
do not have to be debugged), we can first try the usual three-way
read tree:
$ git read-tree -m -u ancestor HEAD other
$ git ls-files -u --abbrev arch/x86-64
This would show...
120000 ad3f146 3 arch/x86_64/boot
100644 495f20c 1 arch/x86_64/boot/.gitignore
100644 495f20c 2 arch/x86_64/boot/.gitignore
100644 ee6f650 1 arch/x86_64/boot/Makefile
100644 ee6f650 2 arch/x86_64/boot/Makefile
...
The current HEAD (the one that we tagged as 'try') has the
directory arch/x86_64/boot/, but all of its files are unchanged
from the "common ancestor", so they all have identical stages 1
and 2, with stage 3 missing. The other tree has boot/ as a
symlink. These "One-side removes other side does not touch" and
"one-side adds" cases are left unmerged by "read-tree -m -u", as
that is how merge-recursive can find renames to begin with.
Now we've seen what the read-tree (which is the same machinery
used as git_merge_trees() in mege-recursive) does with these
three trees, let's see how merge-recursive finishes this off:
$ git reset --hard try
$ git merge-recursive ancestor -- HEAD other
CONFLICT (directory/file): There is a directory with name arch/x86_64/boot in HEAD. Added arch/x86_64/boot as arch/x86_64/boot~other
Removed arch/x86_64/boot/.gitignore
Removed arch/x86_64/boot/Makefile
Removed arch/x86_64/boot/bootsect.S
Removed arch/x86_64/boot/compressed/Makefile
Removed arch/x86_64/boot/compressed/head.S
Removed arch/x86_64/boot/compressed/misc.c
Removed arch/x86_64/boot/compressed/vmlinux.lds
Removed arch/x86_64/boot/compressed/vmlinux.scr
Removed arch/x86_64/boot/install.sh
Removed arch/x86_64/boot/mtools.conf.in
Removed arch/x86_64/boot/setup.S
Removed arch/x86_64/boot/tools/.gitignore
Removed arch/x86_64/boot/tools/build.c
There is no rename, so rename detection does not interfere, but
the D/F conflict detection code in merge-recursive thinks that
arch/x86_64/boot is a directory in one tree (yes, it is true in
the original tree, but it goes away as all files under it), and
a non-directory in another. And instead of replacing the boot/
directory that becomes empty with a new symlink boot/, it
creates the boot~funny-name symlink and fails the operation.
When it actually is checking out arch/x86_64/boot out of the
resolved index, it should notice that (1) arch/x86_64/boot
directory is unnecessary to house anything in the resulting
index anymore, and that (2) there is no locally created
untracked file that is 'precious' [*1*]. Then it can rmdir()
and create the boot/ symlink in its place. To fix this, it may
be necessary to update its checkout code to perform the "remove
first then create" two-pass process git-apply does.
It is unfortunate that for merge-recursive it is probably too
cumbersome to always do the right thing, but I think it should
at least notice that arch/x86_64/boot whose files all disappear
does not conflict with creation of the new symlink.
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