bad behaviour while using git rebase -i -p

[Jan Viktorin <viktorin@rehivetech.com>]

Hello,

since Git 2.16.1, I've noticed a bad behaviour of git rebase -i -p. It
screws up merge commits created with --log (or config merge.log = true)
in my history. A good merge commit with message like:

    Merge branch 'test'
    
    * test:
      c
      b

is changed after rebase (without touching that commit in any way) into:

    Merge branch 'test' a git-rebase-p-test.sh test: c b

It seems, like the commit message is interpreted somehow - the '*'
character is expanded to the list of files in the current directory and
the original spacing is removed. This happens during my regular work.

Here is a code that seems to be reproducing this behaviour well:

git init

touch a
git add a
git commit -m a

git checkout -b test
# a new branch made to merge back to master later

touch b
git add b
git commit -m b

touch c
git add c
git commit -m c

git checkout master
git merge --no-edit --log test
git log -1
# everything looks good at this point

export GIT_SEQUENCE_EDITOR='sed "1s/pick/reword/" -i'
# we are rewording only the first commit...
export EDITOR='sed "s/b/x/" -i'
# ...and changing its message from "b" to "x"

git rebase -i HEAD^1 -p
git log -1
# here, you can see the bad merge commit message

Regards
Jan