On Mon, Jun 14 2021, Thorsten Wilms wrote:

> +(define-public mda-lv2
> +  (package
> +   (name "mda-lv2")
> +   (version "1.2.6")
> +   (source
> +    (origin
> +     (method url-fetch)
> +     (uri
> +      ;; Tarball from gitlab lacks waflib directory content, so take it from
> +      ;; drobilla.net.
> +      (string-append "http://download.drobilla.net/mda-lv2-"
> +		     version ".tar.bz2"))

The waflib directory is a submodule in the Git repo, something like this
should work (untested):

  (git-reference
    (url "https://gitlab.com/drobilla/mda-lv2")
    (commit (string-append "v" version))
    (recursive? #t))
  
> +     (sha256
> +      (base32 "1nspk2j11l65m5r9z5isw8j749vh9a89wgx8mkrrq15f4iq12rnd"))))
> +   (build-system waf-build-system)
> +   (arguments
> +    `(#:tests? #f  ; There are no tests.
> +      #:configure-flags
> +      (list (string-append "--prefix="
> +			   (assoc-ref %outputs "out")))))
> +   (inputs
> +    `(("lv2" ,lv2)))
> +   (native-inputs
> +    `(("pkg-config" ,pkg-config)))
> +   (native-search-paths
> +    (list (search-path-specification
> +           (variable "LV2_PATH")
> +           (files '("lib/lv2")))))
> +   (home-page "https://drobilla.net/software/mda-lv2")
> +   (synopsis "Audio plug-in pack for LV2")
> +   (description
> +    "A port of the MDA VST plugins to LV2. Includes effects and a few
> +instruments.")

The description should consist of one or more full sentences, and use
double spaces between sentences.  Maybe something like this:

  MDA-LV2 is an LV2 port of the MDA plugins.  It includes effects and
  a few instrument plugins.
  
> +   (license (list license:gpl3+ license:gpl3+))))

The two licenses are the same, simply ‘license:gpl3+’ would do.

Could you send an updated patch?