[BUG] rebase --interactive silently overwrites ignored files

I'm using git 2.20.1 from Debian. Git is usually careful not to overwrite untracked files, including ignored files. But interactive rebase doesn't detect this (non-interactive rebase works fine).

Reproduction: -----

#!/bin/sh mkdir upstream cd upstream git init echo 1 >feature-1 git add feature-1 git commit -m "feature 1"

cd .. git clone upstream local cd local # write some tools for our own convenience echo ours >tools echo /tools >>.git/info/exclude # start working on a feature git checkout -b f2 echo wip >feature-2 git add feature-2 git commit -m "wip"

cd ../upstream # official tools are available echo theirs >tools git add tools git commit -m "tools"

cd ../local git fetch ../upstream master

# this would be okay #git rebase FETCH_HEAD

# problem: overwrites tools silently GIT_EDITOR=true git rebase -i FETCH_HEAD

cat tools

-----

Expected: `git rebase -i` fails because it would have to overwrite the
untracked "tools" file. Contents of tools file remains `ours`.

Actual: Contents of tools file becomes `theirs`.