snapper-gui: init at 2020-10-20

Existing snapper-gui package at pythonPackages.snapperGUI is outdated for 6 years,
broken (probably for a while) and misplaced. I weren't able to fix it, so I
repackaged it taking gpodder package for inspiration

pkgs/applications/misc/snapper-gui/default.nix

@@ -0,0 +1,49 @@
+{ lib, stdenv, fetchFromGitHub, python3, python3Packages
+, gnome3, gtk3, wrapGAppsHook, gtksourceview3, snapper
+, gobject-introspection
+}:
+
+python3Packages.buildPythonApplication rec {
+  pname = "snapper-gui";
+  version = "2020-10-20";
+
+  src = fetchFromGitHub {
+    owner = "ricardomv";
+    repo = pname;
+    rev = "f0c67abe0e10cc9e2ebed400cf80ecdf763fb1d1";
+    sha256 = "13j4spbi9pxg69zifzai8ifk4207sn0vwh6vjqryi0snd5sylh7h";
+  };
+
+  nativeBuildInputs = [ wrapGAppsHook ];
+
+  buildInputs = [
+    python3
+    gobject-introspection
+    gnome3.adwaita-icon-theme
+  ];
+
+  doCheck = false; # it doesn't have any tests
+
+  propagatedBuildInputs = with python3Packages; [
+    gtk3
+    dbus-python
+    pygobject3
+    setuptools
+    gtksourceview3
+    snapper
+  ];
+
+  meta = with lib; {
+    description = "Graphical interface for snapper";
+    longDescription = ''
+      A graphical user interface for the tool snapper for Linux filesystem
+      snapshot management. It can compare snapshots and revert differences between snapshots.
+      In simple terms, this allows root and non-root users to view older versions of files
+      and revert changes. Currently works with btrfs, ext4 and thin-provisioned LVM volumes.
+    '';
+    homepage = "https://github.com/ricardomv/snapper-gui";
+    license = licenses.gpl2;
+    platforms = platforms.linux;
+    maintainers = with maintainers; [ ahuzik ];
+  };
+}

pkgs/top-level/all-packages.nix

@@ -24825,6 +24825,7 @@ in
   smartdeblur = callPackage ../applications/graphics/smartdeblur { };
 
   snapper = callPackage ../tools/misc/snapper { };
+  snapper-gui = callPackage ../applications/misc/snapper-gui { };
 
   snd = callPackage ../applications/audio/snd { };