fish-shell/share/functions/__fish_commandline_test.fish

function __fish_commandline_test

    set -l is_function no
    for i in (commandline -poc)
        switch $i
            case -f --f --fu --fun --func --funct --functi --functio --function
            set is_function yes

            case --
            break


        end
    end

    switch $is_function
        case yes
        return 0
    end
    return 1

end