Why does git-mergetool use /dev/tty?

git-mergetool.sh, lines 298-302:

    if test $last_status -ne 0; then
        prompt_after_failed_merge < /dev/tty || exit 1
    fi
    printf "\n"
    merge_file "$i" < /dev/tty > /dev/tty

Why does git-mergetool ignore the provided STDIN and STDOUT when not given a path to merge?

This wasn't apparent until bb0a484: "mergetool: Skip autoresolved paths" added a test that doesn't provide a file to merge on the command line.

~~ Brian Gernhardt