Rename of file is causing changes to be lost

Rename of file is causing changes to be lost

[Robert Dailey]

I'm on Windows and core.ignorecase is set to 'true' when I clone/init
a repository. I've got a branch where I started making changes to a
file AND renamed it only to change its case. The changes I've made
were significant enough that git no longer detects a rename, instead
the files show up as "D" and "A" in git status (deleted then added).
To correct this, I do an interactive rebase to add an additional
commit before the first one to rename the file without changing it,
and *then* allow the second commit to change the file. The goal is
that rebase should detect the rename and automatically move the
changes in the (now) second commit to the newly named file. Here's a
MCVE (treat this as a script):

#/bin/bash
git init testgitrepo
cd testgitrepo/
git config core.ignorecase true # This is set by Windows for me, but
hopefully will allow this to repro on linux. Didn't test linux though.
echo "first change" > foo.txt
git add . && git commit -m 'first change'
git checkout -b topic
echo "second change" > foo.txt
git mv foo.txt FOO.txt
git add . && git commit -m 'second change'
git rebase -i master # Move line 1 to line 2, and put "x false" in line 1
git mv foo.txt FOO.txt && git commit -m 'rename foo'
git rebase --continue
git mergetool

After the rebase continue, you will get a conflict like so:

error: could not apply 527d208... second change

When you have resolved this problem, run "git rebase --continue".
If you prefer to skip this patch, run "git rebase --skip" instead.
To check out the original branch and stop rebasing, run "git rebase --abort".

Could not apply 527d208... second change
CONFLICT (rename/delete): foo.txt deleted in 527d208... second change
and renamed to FOO.txt in HEAD. Version HEAD of FOO.txt left in tree.

The last command, `git mergetool` runs, giving you the option to pick
the Created (left) or Deleted (right) version of the file:

Left: The file is created, but selecting this erases the changes from
the "added" version on the remote (which is topic). Basically the
rename of only case confused git, and we lost the changes on the
remote version of the file
Right: File is deleted. Changes are still lost.

The ideal outcome is that the changes from the "added" version of the
file in the 2nd commit get carried over to the "renamed" version of
the file, which when you compare the two are named exactly the same
after the 1st commit is introduced. How can I solve this issue?

Re: Rename of file is causing changes to be lost

[Robert Dailey]

On Thu, Mar 8, 2018 at 10:01 AM, Robert Dailey <rcdailey.lists@gmail.com> wrote:
> I'm on Windows and core.ignorecase is set to 'true' when I clone/init
> a repository. I've got a branch where I started making changes to a
> file AND renamed it only to change its case. The changes I've made
> were significant enough that git no longer detects a rename, instead
> the files show up as "D" and "A" in git status (deleted then added).
> To correct this, I do an interactive rebase to add an additional
> commit before the first one to rename the file without changing it,
> and *then* allow the second commit to change the file. The goal is
> that rebase should detect the rename and automatically move the
> changes in the (now) second commit to the newly named file. Here's a
> MCVE (treat this as a script):
>
> #/bin/bash
> git init testgitrepo
> cd testgitrepo/
> git config core.ignorecase true # This is set by Windows for me, but
> hopefully will allow this to repro on linux. Didn't test linux though.
> echo "first change" > foo.txt
> git add . && git commit -m 'first change'
> git checkout -b topic
> echo "second change" > foo.txt
> git mv foo.txt FOO.txt
> git add . && git commit -m 'second change'
> git rebase -i master # Move line 1 to line 2, and put "x false" in line 1
> git mv foo.txt FOO.txt && git commit -m 'rename foo'
> git rebase --continue
> git mergetool
>
> After the rebase continue, you will get a conflict like so:
>
> error: could not apply 527d208... second change
>
> When you have resolved this problem, run "git rebase --continue".
> If you prefer to skip this patch, run "git rebase --skip" instead.
> To check out the original branch and stop rebasing, run "git rebase --abort".
>
> Could not apply 527d208... second change
> CONFLICT (rename/delete): foo.txt deleted in 527d208... second change
> and renamed to FOO.txt in HEAD. Version HEAD of FOO.txt left in tree.
>
> The last command, `git mergetool` runs, giving you the option to pick
> the Created (left) or Deleted (right) version of the file:
>
> Left: The file is created, but selecting this erases the changes from
> the "added" version on the remote (which is topic). Basically the
> rename of only case confused git, and we lost the changes on the
> remote version of the file
> Right: File is deleted. Changes are still lost.
>
> The ideal outcome is that the changes from the "added" version of the
> file in the 2nd commit get carried over to the "renamed" version of
> the file, which when you compare the two are named exactly the same
> after the 1st commit is introduced. How can I solve this issue?

I wanted to bump this and see if anyone would have a spare few minutes
to help me out with this. I know it's a needlessly complex situation,
but I'd really love to know how to resolve the specific issue, or
perhaps learn a better way to approach this in the future if I'm
shooting myself in the foot here.

Thanks again.

Re: Rename of file is causing changes to be lost

[Elijah Newren]

On Thu, Mar 8, 2018 at 8:01 AM, Robert Dailey <rcdailey.lists@gmail.com> wrote:
> I'm on Windows and core.ignorecase is set to 'true' when I clone/init
> a repository. I've got a branch where I started making changes to a
> file AND renamed it only to change its case. The changes I've made
> were significant enough that git no longer detects a rename, instead
> the files show up as "D" and "A" in git status (deleted then added).
> To correct this, I do an interactive rebase to add an additional
> commit before the first one to rename the file without changing it,
> and *then* allow the second commit to change the file. The goal is
> that rebase should detect the rename and automatically move the
> changes in the (now) second commit to the newly named file. Here's a
> MCVE (treat this as a script):
>
> #/bin/bash
> git init testgitrepo
> cd testgitrepo/
> git config core.ignorecase true # This is set by Windows for me, but
> hopefully will allow this to repro on linux. Didn't test linux though.
> echo "first change" > foo.txt
> git add . && git commit -m 'first change'
> git checkout -b topic
> echo "second change" > foo.txt
> git mv foo.txt FOO.txt
> git add . && git commit -m 'second change'
> git rebase -i master # Move line 1 to line 2, and put "x false" in line 1
> git mv foo.txt FOO.txt && git commit -m 'rename foo'
> git rebase --continue
> git mergetool
>
> After the rebase continue, you will get a conflict like so:
>
> error: could not apply 527d208... second change
>
> When you have resolved this problem, run "git rebase --continue".
> If you prefer to skip this patch, run "git rebase --skip" instead.
> To check out the original branch and stop rebasing, run "git rebase --abort".
>
> Could not apply 527d208... second change
> CONFLICT (rename/delete): foo.txt deleted in 527d208... second change
> and renamed to FOO.txt in HEAD. Version HEAD of FOO.txt left in tree.
>
> The last command, `git mergetool` runs, giving you the option to pick
> the Created (left) or Deleted (right) version of the file:
>
> Left: The file is created, but selecting this erases the changes from
> the "added" version on the remote (which is topic). Basically the
> rename of only case confused git, and we lost the changes on the
> remote version of the file
> Right: File is deleted. Changes are still lost.
>
> The ideal outcome is that the changes from the "added" version of the
> file in the 2nd commit get carried over to the "renamed" version of
> the file, which when you compare the two are named exactly the same
> after the 1st commit is introduced. How can I solve this issue?

Cool, thanks for the testcase.  I don't have a good workaround for
you, but this is clearly a bug in the merge-recursive logic in git.  I
guess it's what might be called a rename/add/delete conflict, which
git just doesn't handle.  Your testcase triggers the bug just fine on
linux, though you can trigger the exact same bug without case
sensitivity using a slightly different setup (and no need for an
interactive rebase):

------
git init foobar
cd foobar
echo "original file" >foo
git add foo
git commit -m "original"
git branch L
git branch R

git checkout L
git rm foo
echo "different file" >bar
git add bar
git commit -m "Remove foo, add bar"

git checkout R
git mv foo bar
git commit -m "rename foo to bar"

git merge L
-------

git has code to handle rename/delete conflicts and rename/add
conflicts, but since one side of history BOTH deleted foo and added an
unrelated bar, that means both types of changes are relevant to the
same path (bar) -- essentially, a rename/delete/add conflict.  Sadly,
git only goes down a codepath that handles one of those two (the
rename/delete), and incorrectly throws away the separate add:

-----
$ git ls-files -s
100644 78fa0f415ae2bdb5c0182c067eacaaf843699b39 2    bar

$ git ls-tree -r master
100644 blob 78fa0f415ae2bdb5c0182c067eacaaf843699b39    foo
$ git ls-tree -r L
100644 blob f286e5cdd97ac6895438ea4548638bb98ac9bd6b    bar
$ git ls-tree -r R
100644 blob 78fa0f415ae2bdb5c0182c067eacaaf843699b39    bar
-----

But the problem is actually a bit bigger than shown here; there are
higher order corner cases here too.  I realized in the past that e.g.
rename/rename(1to2) could also have rename/add conflicts for each
rename (thus making a rename/rename/add/add conflict possible), but I
also felt there were probably some other bad interactions out there.
I figured they were likely theoretical only, so I didn't bother
investigating.  But, combining your example with that other one, we
should also be able to come up with a
rename/rename/add/add/delete/delete conflict.  I wonder if there are
others...

Anyway, I recorded this at
https://bugs.chromium.org/p/git/issues/detail?id=11.  Sorry I don't
have a workaround, but I'll try to eventually get back to this and fix
it.

Re: Rename of file is causing changes to be lost

[Robert Dailey]

On Tue, Mar 13, 2018 at 11:51 AM, Elijah Newren <newren@gmail.com> wrote:
> Anyway, I recorded this at
> https://bugs.chromium.org/p/git/issues/detail?id=11.  Sorry I don't
> have a workaround, but I'll try to eventually get back to this and fix
> it.

Thank you for taking the time to verify this for me. I will keep an
eye on the issue you linked!