lib: init formats subset

lib/default.nix

@@ -15,6 +15,10 @@ in pkgs.lib.makeExtensible (self:
     math = callLib ./math.nix;
     xdg = callLib ./xdg.nix;
 
+    # Just like from its inspiration, this contains Nix-representable data
+    # formats and won't have any attributes exported at the top-level.
+    formats = callLib ./formats.nix;
+
     # For future references, these are the only attributes that are going to be
     # exported as part of nixpkgs overlay.
     fetchers = callLib ./fetchers;

lib/formats.nix

@@ -0,0 +1,21 @@
+{ lib, pkgs, self }:
+
+{
+  # The gnome-session config files uses one from GLib. See the following link
+  # at <https://docs.gtk.org/glib/struct.KeyFile.html> for details about the
+  # keyfile formatting and possibly the Desktop Entry specification at
+  # <https://freedesktop.org/wiki/Specifications/desktop-entry-spec>.
+  glibKeyfile = {}: {
+    type = with lib.types;
+      let
+        valueType = oneOf [ bool float int str (listOf valueType) ] // {
+          description =
+            "GLib keyfile atom (bool, int, float, string, or a list of the previous atoms)";
+        };
+      in attrsOf (attrsOf valueType);
+
+    generate = name: value:
+      pkgs.callPackage
+      ({ lib, writeText }: writeText name (lib.generators.toDconfINI value));
+  };
+}