If you make a change to a submodule and use the alternative formatting for submodules in git diff, arcanist fails to parse the diff output.
Repro steps:
# enable git diff --submodule=log by default $ git config --global diff.submodule log # now make a change to a submodule (e.g. updating it) $ cd my-git-submodule $ git checkout master $ git pull $ cd .. # invoke a command that tries to parse the git diff output $ arc lint # most notably this affects arc diff $ git commit -am 'updating my-git-submodule' $ arc diff # fill in review details, submit for review # see: "Diff Parse Exception: ..."