Add vala 0.26. Will be needed for gnome-terminal 3.14

pkgs/development/compilers/vala/0.26.nix

@@ -0,0 +1,31 @@
+{ stdenv, fetchurl, pkgconfig, flex, bison, libxslt
+, glib, libiconvOrEmpty, libintlOrEmpty
+}:
+
+let
+  major = "0.26";
+  minor = "1";
+  sha256 = "8407abb19ab3a58bbfc0d288abb47666ef81f76d0540258c03965e7545f59e6b";
+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 ]
+    ++ libiconvOrEmpty
+    ++ libintlOrEmpty;
+}

pkgs/top-level/all-packages.nix

@@ -3830,6 +3830,8 @@ let
 
   vala = callPackage ../development/compilers/vala/default.nix { };
 
+  vala_0_26 = callPackage ../development/compilers/vala/0.26.nix { };
+
   visualcpp = callPackage ../development/compilers/visual-c++ { };
 
   vs90wrapper = callPackage ../development/compilers/vs90wrapper { };