Add newline to bash prompt if the last output didn't end with one

.bashrc

# This won't work in PS1, as inside PS1, newlines
# in command substitutions are handled specially.
# Hence, using PROMPT_COMMAND instead.

__conditional_newline() {
    IFS='[;' read -rsd R -p $'\e[6n' _ _ col
    if [ -n "$col" ] && [ "$col" -gt 1 ]; then
        echo -e "\033[01;31m\\missing newline\033[00m"
    fi
}

__add_to_prompt_command() {
    local new_cmd="$1"
    if [[ "$PROMPT_COMMAND" != *"$new_cmd"* ]]; then
        if [ -n "$PROMPT_COMMAND" ]; then
            PROMPT_COMMAND="$new_cmd; $PROMPT_COMMAND"
        else
            PROMPT_COMMAND="$new_cmd"
        fi
    fi
}

__add_to_prompt_command __conditional_newline