Add vala 0.28

pkgs/development/compilers/vala/0.28.nix

···
+{ stdenv, fetchurl, pkgconfig, flex, bison, libxslt
+, glib, libiconv, libintlOrEmpty
+}:
+
+let
+  major = "0.28";
+  minor = "0";
+  sha256 = "0zwpzhkhfk3piya14m7p2hl2vaabahprphppfm46ci91z39kp7hd";
+in
+stdenv.mkDerivation rec {
+  name = "vala-${major}.${minor}";
+
+  meta = {
+    description = "Compiler for GObject type system";
+    homepage = "http://live.gnome.org/Vala";
+    license = stdenv.lib.licenses.lgpl21Plus;
+    platforms = stdenv.lib.platforms.unix;
+    maintainers = with stdenv.lib.maintainers; [ antono lethalman ];
+  };
+
+  src = fetchurl {
+    url = "mirror://gnome/sources/vala/${major}/${name}.tar.xz";
+    inherit sha256;
+  };
+
+  nativeBuildInputs = [ pkgconfig flex bison libxslt ];
+
+  buildInputs = [ glib libiconv ]
+    ++ libintlOrEmpty;
+}

pkgs/top-level/all-packages.nix

···
 
   vala_0_26 = callPackage ../development/compilers/vala/0.26.nix { };
 
+  vala_0_28 = callPackage ../development/compilers/vala/0.28.nix { };
+
   visualcpp = callPackage ../development/compilers/visual-c++ { };
 
   vs90wrapper = callPackage ../development/compilers/vs90wrapper { };