difftool fails with dangling symlinks, writes to targets outside of the repository

[Philippe <bqobctqyemmeacqxbrsaury3l4ka@quarantine.de>]

Hi all,


I'm using a git repository for configuration management which contains
several dangling symlinks (which only make sense on the to be deployed
system, fwiw). Now, using git 2.23, I ran into a problem regarding the
difftool, which fails when such a symlink is involved in a changeset.

The best way to describe that problem is probably to provide an example.

> #!/bin/bash
> tmp=$(mktemp -d)
> trap "rm -rf ${tmp}" 0 1 2 15
> 
> set -x
> 
> cd ${tmp}
> git init
> ln -s ../doesnot/exist myfile
> git add myfile ; git commit -m "initial checkin" myfile
> 
> git checkout -b mybranch
> rm -f myfile ; echo "foo" > myfile
> git commit -am "typechange"
> 
> git difftool -d master..mybranch

The last call fails with:

> fatal: could not open '/tmp/git-difftool.2wHaR9/left/myfile' for writing: No such file or directory

Neither specifying "--symlinks" nor "--no-symlinks" resolves that.

Playing around with this issue lead me to another strange behaviour.
Difftool might overwrite symlink targets that are not part of the
repository. Please take a look at the following script:

> #!/bin/bash
> tmp=$(mktemp -d)
> trap "rm -rf ${tmp}" 0 1 2 15
> 
> set -x
> 
> echo "hello world" > /tmp/testfile
> cat /tmp/testfile
> 
> cd ${tmp}
> git init
> ln -s /tmp/testfile myfile
> git add myfile ; git commit -m "initial checkin" myfile
> 
> git checkout -b mybranch
> rm -f myfile ; echo "foo" > myfile
> git commit -am "typechange"
> 
> git difftool -d master..mybranch
> 
> cat /tmp/testfile

Here, difftool overwrites the /tmp/testfile's content "hello world" with
"/tmp/testfile".

Did I run into a bug or is it a layer 8 problem?


Regards,

Philippe