Re: bug: git pull may delete untracked files in submodule without notice

>
> Hi,
>
> I found a bug where Git may delete untracked files without notice in
> certain situations. This bug effects Git 2.21.0 both on Linux and Windows.
> In summary this happens when git pull merges a commit that replaces a
> submodule folder with a symlink. Any files within the folder are deleted
> without notice.

> Check out the script below for details.
>
> This happend on some developer's machine and deleted a repository
> containing about 200GiB of files and tons of uncommited local scripts,
> log files and whatever, just because some other dev accidentally
> commited a temporary change.
>
> Greetings,
> Christian Spanier
>
> ##### PREPARATION #####
>
> # New empty repository #1
> mkdir rep1
> cd rep1
> git init --bare .
> cd ..
>
> # New empty repository #2
> mkdir rep2
> cd rep2
> git init --bare .
> cd ..
>
> # Clone repository #1 and create initial commit
> git clone rep1 clone_rep1_user1
> cd clone_rep1_user1
> touch README
> git add README
> git commit -m "initial commit"
> git push
> cd ..
>
> # Clone repository #2 and create initial commit
> git clone rep2 clone_rep2
> cd clone_rep2
> touch README
> git add README
> git commit -m "initial commit"
> git push
> cd ..
>
> # Add repository #2 as a submodule to repository #1
> cd clone_rep1_user1
> git submodule add ../rep2
> git commit -m "add submodule"
> git push
> cd ..
>
> # User 2 also clones repository #1 and #2 recursively
> git clone --recursive rep1 clone_rep1_user2
>
> # User 2 starts working in his folder and adds an important local file
> which is
> # not yet committed inside the submodule folder.
> cd clone_rep1_user2/rep2
> echo "important work" > uncommitted_file
> cd ../../
>
> # Meanwhile, user 1 temporarily switch out folder /clone_rep1_user1/rep2
> with a
> # symbolic link to a different folder (for whatever reason, maybe a copy
> of an
> # older version or anything).
> mkdir rep2_alternative
> cd clone_rep1_user1
> mv rep2 ../rep2_backup
> ln -s ../rep2_alternative rep2
> # On Windows this can be done with 'mklink /D rep2 ../rep2_alternative',
> # which requires admin privileges. The bug is not reproducible when
> # using a directory junction with 'mklink /D /J ...'.
>
> # He does some work on rep1 but then accidently adds the symbolic link
> to his
> # next commit and pushes the changes. Notice the typechange of rep2.
> echo "some" > work
> git status
> # On branch master
> # Your branch is up to date with 'origin/master'.
> #
> # Changes not staged for commit:
> #   (use "git add <file>..." to update what will be committed)
> #   (use "git checkout -- <file>..." to discard changes in working
> directory)
> #
> #         typechange: rep2
> #
> # Untracked files:
> #   (use "git add <file>..." to include in what will be committed)
> #
> #         work
> #
> # no changes added to commit (use "git add" and/or "git commit -a")
> git add .
> git commit -m "do some work"
> git push
> cd ..
>
> # NOW THE BUG:
>
> # User 2 pulls the changes and loses his important work in
> # rep2/uncommitted_file because Git replaces the folder with a symlink
> # without checking for modified or uncommited files!
> # He should get an error in this case!
> cd clone_rep1_user2
> git pull
> cat rep2/uncommitted_file
> # cat: rep2/uncommitted_file: Not a directory
> # "important work" in rep2/uncommitted_file is gone :(