uim, gtk-exe-env, qt-plugin-env: Add input method modules for GTK+ and Qt

nixos/modules/config/qt-plugin-env.nix

@@ -0,0 +1,37 @@
+{ config, pkgs, lib, ... }:
+
+{
+  imports = [
+  ];
+
+  options = {
+    qtPlugins = lib.mkOption {
+      type = lib.types.listOf lib.types.path;
+      default = [];
+      description = ''
+        Plugin packages for Qt such as input methods.
+      '';
+    };
+  };
+
+  config = {
+    environment.variables = if builtins.length config.qtPlugins > 0
+      then
+        let
+          paths = [ pkgs.qt48 ] ++ config.qtPlugins;
+          env = pkgs.buildEnv {
+            name = "qt-plugin-env";
+
+            inherit paths;
+
+            postBuild = lib.concatStringsSep "\n"
+              (map (d: d.qtPluginEnvPostBuild or "") paths);
+
+            ignoreCollisions = true;
+          };
+        in {
+          QT_PLUGIN_PATH = [ (builtins.toString env) ];
+        }
+      else {};
+  };
+}