gnu: python-gst: Fix build with Python 3.8.

Add a patch based on an upstream commit [1].

1: 10707f437f2fc3632067c6a0efa4432f7ebaf362

* gnu/packages/patches/python-gst-fix-build-with-python-3.8.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/gstreamer.scm (python-gst)[source]: Use the patch.

gnu/local.mk

@@ -1394,6 +1394,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/python2-larch-coverage-4.0a6-compatibility.patch \
   %D%/packages/patches/python-configobj-setuptools.patch	\
   %D%/packages/patches/python-flask-restful-werkzeug-compat.patch	\
+  %D%/packages/patches/python-gst-fix-build-with-python-3.8.patch	\
   %D%/packages/patches/python-keras-integration-test.patch	\
   %D%/packages/patches/python-pep8-stdlib-tokenize-compat.patch \
   %D%/packages/patches/python-pyfakefs-remove-bad-test.patch	\

gnu/packages/gstreamer.scm

@@ -521,7 +521,9 @@ (define-public python-gst
                     "gst-python-" version ".tar.xz"))
               (sha256
                (base32
-                "1a48ca66izmm8hnp608jv5isg3jxb0vlfmhns0bg9nbkilag7390"))))
+                "1a48ca66izmm8hnp608jv5isg3jxb0vlfmhns0bg9nbkilag7390"))
+              (patches
+               (search-patches "python-gst-fix-build-with-python-3.8.patch"))))
     (build-system meson-build-system)
     (arguments
      `(#:modules ((guix build meson-build-system)

gnu/packages/patches/python-gst-fix-build-with-python-3.8.patch

@@ -0,0 +1,36 @@
+Fix build with Python 3.8 by also checking for python-3.X-embed.pc. Since
+Python 3.8 the normal checks don't include the Python libraries anymore and
+linking of the gst-python module would fail.
+
+See also https://github.com/mesonbuild/meson/issues/5629
+Fixes https://gitlab.freedesktop.org/gstreamer/gst-python/issues/28
+
+Patch based on upstream commit:
+
+https://gitlab.freedesktop.org/gstreamer/gst-python/-/commit/10707f437f2fc3632067c6a0efa4432f7ebaf362
+
+diff --git a/meson.build b/meson.build
+index 5f13b48..d7c7e66 100644
+--- a/meson.build
++++ b/meson.build
+@@ -23,7 +23,17 @@ pygobject_dep = dependency('pygobject-3.0', fallback: ['pygobject', 'pygobject_d
+ 
+ pymod = import('python')
+ python = pymod.find_installation(get_option('python'))
+-python_dep = python.dependency(required : true)
++pythonver = python.language_version()
++if pythonver.version_compare('<3.0')
++   error('Python2 is not supported anymore, please port your code to python3 (@0@ specified)'.format(python.language_version()))
++endif
++
++# Workaround for https://github.com/mesonbuild/meson/issues/5629
++# https://gitlab.freedesktop.org/gstreamer/gst-python/issues/28
++python_dep = dependency('python-@0@-embed'.format(pythonver), version: '>=3', required: false)
++if not python_dep.found()
++  python_dep = python.dependency(required : true)
++endif
+ 
+ python_abi_flags = python.get_variable('ABIFLAGS', '')
+ pylib_loc = get_option('libpython-dir')
+-- 
+2.26.2