tanka: add fish and zsh shell completions

  postInstall = ''

    echo "complete -C $out/bin/tk tk" > tk.bash

    installShellCompletion tk.bash

    cat >tk.fish <<EOF

    function __complete_tk

        set -lx COMP_LINE (commandline -cp)

        test -z (commandline -ct)

        and set COMP_LINE "\$COMP_LINE "

        $out/bin/tk

    end

    complete -f -c tk -a "(__complete_tk)"

    EOF

    cat >tk.zsh <<EOF

    #compdef tk

    autoload -U +X bashcompinit && bashcompinit

    complete -o nospace -C $out/bin/tk tk

    EOF

    installShellCompletion \

      --cmd tk \

      --bash tk.bash \

      --fish tk.fish \

      --zsh tk.zsh

  '';

  meta = with lib; {