[BUG] git-rebase: reword squashes commits in case of merge-conflicts

Hi all!

During a recent rebase operation on one of my repositories a number of commits unexpectedly ended up getting squashed into other commits. After some experiments it turned out that the 'reword' instruction seems to squash the referenced commit into the preceding commit if there's a merge-conflict.

Here's a small reproduction recipe to illustrate the behavior:

   1. Create a small test repository using the following Bash script:

----
function add_file()
{
     echo "$1" > "$2"
     git add "$2"
     git commit -m "$3"
}

git init .

add_file "test" "file-1" "master"

git checkout -b stuff

add_file "aaa" "file-2" "feature_a" add_file "bbb" "file-2" "fixup! feature_a" add_file "ccc" "file-2" "fixup! feature_a"

add_file "ddd" "file-2" "feature_b" add_file "eee" "file-2" "fixup! feature_b" add_file "fff" "file-2" "fixup! feature_b" ----

   2. Run

        $ git rebase --autosquash --interactive --onto master master stuff

      to interactively rebase 'stuff' onto 'master'. This should generate the
      following todo-stream:

---- pick ... feature_a fixup ... fixup! feature_a fixup <hash_1> fixup! feature_a pick <hash_2> feature_b fixup ... fixup! feature_b fixup ... fixup! feature_b ----

   3. Remove the fixup line right before the second pick (i.e. 'fixup <hash_1>')
      in order to enforce a merge-conflict later when applying commit <hash_2>.

   4. Replace the second pick instruction (i.e. 'pick <hash_2>') with a reword.

   5. Launch the rebase operation. It should fail at the 'reword <hash_2>'
      instruction due to a merge-conflict.

   6. Resolve the conflict by taking the remote-side (i.e. 'ddd'), add the
      change to the index with git-add and run

        $ git rebase --continue

      This should spawn the commit message editor and after saving and quitting
      the rebase should finish cleanly.

After the rebase the 'stuff' branch only has a single commit even though I'd expect there to be two according to the instructions that were passed to git-rebase. It works as expected if there's either no merge-conflict at the reword or if the conflicting commit is applied as 'pick'.

I'm running git version 2.17.1.windows.2. I also tried native git version 2.7.4 via WSL (running Ubuntu 16.04.4 LTS) and this version does not exhibit this behavior.

- ch