pitivi: Fix build

The latest version is not compatible with Python 3.8,
let's cherry-pick some patches from master.

Also pre-prepare for incoming release of GStreamer 1.18.

pkgs/applications/video/pitivi/default.nix

@@ -1,8 +1,9 @@
 { stdenv
 , fetchFromGitHub
 , fetchurl
+, fetchpatch
 , pkg-config
-, intltool
+, gettext
 , itstool
 , python3
 , wrapGAppsHook
@@ -20,9 +21,8 @@
 }:
 
 let
-  # gst-transcoder will eventually be merged with gstreamer (according to
-  # gst-transcoder 1.8.0 release notes). For now the only user is pitivi so we
-  # don't bother exposing the package to all of nixpkgs.
+  # gst-transcoder was merged with gst-plugins-bad 1.18.
+  # TODO: switch to that once available.
   gst-transcoder = stdenv.mkDerivation rec {
     version = "1.14.1";
     pname = "gst-transcoder";
@@ -61,13 +61,49 @@ in python3Packages.buildPythonApplication rec {
     # and saves them to the generated binary. This would make the build-time
     # dependencies part of the closure so we remove it.
     ./prevent-closure-contamination.patch
+
+    # Port from intltool to gettext.
+    # Needed for the following patches to apply.
+    (fetchpatch {
+      url = "https://gitlab.gnome.org/GNOME/pitivi/commit/89b1053f2516c594f414c5c67c835471bce44b67.patch";
+      sha256 = "8yhArzAtZC+WjHftcSDrstBlT8j6WlGHffU9Nj+ny+c=";
+      excludes = [ "po/POTFILES.in" ];
+    })
+
+    # Complete switching to gst-transcoder in gst-plugins-bad.
+    # Otherwise there will likely be conflics.
+    # TODO: Apply this patch once we are using gst-transcoder from gst-plugins-bad.
+    # (fetchpatch {
+    #   url = "https://gitlab.gnome.org/GNOME/pitivi/commit/51ae6533ee26ffd47e453eb5f5ad8cd46f57d15e.patch";
+    #   sha256 = "zxJm+E5o+oZ3lW6wYNY/ERo2g4NmCjoY8oV+uScq8j8=";
+    # })
+
+    # Generate renderer.so on macOS instead of dylib.
+    # Needed for the following patch to apply.
+    (fetchpatch {
+      url = "https://gitlab.gnome.org/GNOME/pitivi/commit/bcacadcafabf8911efb0fddc8d57329237d08cd1.patch";
+      sha256 = "2BM5acIwOgdr1L9vhtMMN4trrLuqCg/K6v6ZYtD1Fjw=";
+      postFetch = ''
+        sed -i -e "s/1.90.0.1/0.999/g" "$out"
+      '';
+    })
+    (fetchpatch {
+      url = "https://gitlab.gnome.org/GNOME/pitivi/commit/0a3cc054a2c20b59f5aaaaa307de3c9af3c0d270.patch";
+      sha256 = "6DhqRlxFWFFdLwGoFem+vPt8x7v732KMVjMF9fypMK4=";
+      postFetch = ''
+        sed "$out" -i \
+          -e "s/1.90.0.1/0.999/g" \
+          -e "s/\(-python_dep.*\)/\1\n /" \
+          -e "s/-1,9 +1,16/-1,10 +1,17/"
+      '';
+    })
   ];
 
   nativeBuildInputs = [
     meson
     ninja
     pkg-config
-    intltool
+    gettext
     itstool
     python3
     wrapGAppsHook
@@ -106,6 +142,9 @@ in python3Packages.buildPythonApplication rec {
 
   postPatch = ''
     patchShebangs ./getenvvar.py
+
+    # fetchpatch does not support renamings
+    mv data/org.pitivi.Pitivi-mime.xml data/org.pitivi.Pitivi-mime.xml.in
   '';
 
   passthru = {