!!

    # Add this to your ~/.config/fish/config.fish
    # Syntax:
    # To just rerun your last command, simply type '!!'
    # This forked version supports "sudo !!" via two functions.
    function !!
        eval $history[1] $argv
    end function
    
    function sudo
    if test $argv
        if test $argv = "!!"
            eval /usr/bin/sudo $history[1]
        else
            eval /usr/bin/sudo $argv
        end
    end
end

Would be a good idea to modify the command in history, replacing !! with the original command.

As it stands:

~> echo ''

~> !!

~> sudo !!
sudo: !!: command not found

A more realistic case when this might occur would be repeated execution of the last command - if you can only do it once then you'd be better off with up+return in your muscle memory than use this !! function.