When you install bash-completion on your system, usually a function is defined to autocomplete make rules for you. It works with all projects, as it does not rely on the rules being specially marked. (https://github.com/scop/bash-completion/blob/master/completi...)

Before I knew about it, I had written a similar thing:

    # Autocomplete make rules
    _make () {
        local cur prev words cword cmdline
        _init_completion || return
    
        # command to generate the rules
        words="$(make  -pRrq |\
            awk -v RS= -F: '/^# File/,/^# Finished Make data base/ {if ($1 !~ "^[#.]") {print $1}}' |\
            sort | egrep -v -e '^[^[:alnum:]]' | xargs)"
    
        COMPREPLY+=( $( compgen -W "$words" -- $cur) )
    }
    if declare -f _init_completion > /dev/null; then
        complete -F _make make
    fi

It relies on `make -pRrq`, that is a very useful command to debug your makefiles, especially in a big project. The option `-p` prints the make data-base, -R and -r removes the implicit rules and variables, and -q indicates only asking make a question about current state, avoid executing anything.

Well, it worked for a time, but the bash-completion one is nicer (though much, much more complex). Very nice however to know about `-pRrq`, definitely helps when working on big projects.