print settings: Add api to serialize to a GVariant

This will be useful for portalized print support.

https://bugzilla.gnome.org/show_bug.cgi?id=768499

docs/reference/gtk/gtk3-sections.txt

@@ -7269,10 +7269,12 @@ GTK_PRINT_SETTINGS_WIN32_DRIVER_VERSION
 <SUBSECTION Serialization>
 gtk_print_settings_new_from_file
 gtk_print_settings_new_from_key_file
+gtk_print_settings_new_from_gvariant
 gtk_print_settings_load_file
 gtk_print_settings_load_key_file
 gtk_print_settings_to_file
 gtk_print_settings_to_key_file
+gtk_print_settings_to_gvariant
 
 <SUBSECTION Standard>
 GTK_TYPE_PRINT_SETTINGS

gtk/gtkprintsettings.c

@@ -1941,3 +1941,68 @@ gtk_print_settings_to_key_file (GtkPrintSettings  *settings,
 			      (GtkPrintSettingsFunc) add_value_to_key_file,
 			      &data);
 }
+
+static void
+add_to_variant (const gchar *key,
+                const gchar *value,
+                gpointer     data)
+{
+  GVariantBuilder *builder = data;
+  g_variant_builder_add (builder, "{sv}", key, g_variant_new_string (value));
+}
+
+/**
+ * gtk_print_settings_to_gvariant:
+ * @settings: a #GtkPrintSettings
+ *
+ * Serialize print settings to an a{sv} variant.
+ *
+ * Returns: (transfer none): a new, floating, #GVariant
+ *
+ * Since: 3.22
+ */
+GVariant *
+gtk_print_settings_to_gvariant (GtkPrintSettings *settings)
+{
+  GVariantBuilder builder;
+
+  g_variant_builder_init (&builder, G_VARIANT_TYPE_VARDICT);
+  gtk_print_settings_foreach (settings, add_to_variant, &builder);
+
+  return g_variant_builder_end (&builder);
+}
+
+/**
+ * gtk_print_settings_new_from_gvariant:
+ * @variant: an a{sv} #GVariant
+ *
+ * Deserialize print settings from an a{sv} variant in
+ * the format produced by gtk_print_settings_to_gvariant().
+ *
+ * Returns: (transfer full): a new #GtkPrintSettings object
+ *
+ * Since: 3.22
+ */
+GtkPrintSettings *
+gtk_print_settings_new_from_gvariant (GVariant *variant)
+{
+  GtkPrintSettings *settings;
+  int i;
+
+  g_return_val_if_fail (g_variant_is_of_type (variant, G_VARIANT_TYPE_VARDICT), NULL);
+
+  settings = gtk_print_settings_new ();
+
+  for (i = 0; i < g_variant_n_children (variant); i++)
+    {
+      const char *key;
+      GVariant *v;
+
+      g_variant_get_child (variant, i, "{&sv}", &key, &v);
+      if (g_variant_is_of_type (v, G_VARIANT_TYPE_STRING))
+        gtk_print_settings_set (settings, key, g_variant_get_string (v, NULL));
+      g_variant_unref (v);
+    }
+
+  return settings;
+}

gtk/gtkprintsettings.h

@@ -344,6 +344,12 @@ GDK_AVAILABLE_IN_ALL
 void                  gtk_print_settings_set_output_bin        (GtkPrintSettings   *settings,
 								const gchar        *output_bin);
 
+GDK_AVAILABLE_IN_3_22
+GVariant             *gtk_print_settings_to_gvariant           (GtkPrintSettings   *settings);
+GDK_AVAILABLE_IN_3_22
+GtkPrintSettings     *gtk_print_settings_new_from_gvariant     (GVariant           *variant);
+
+
 G_END_DECLS
 
 #endif /* __GTK_PRINT_SETTINGS_H__ */