Make GSettingsSchemaKey public

Take this private API and make it public along with a boxed type and
ref/unref functions.

Future commits will add accessors with new functionality and some that
allow us to deprecate functions on GSettings itself (such as
g_settings_get_range).

https://bugzilla.gnome.org/show_bug.cgi?id=668232

docs/reference/gio/gio-sections.txt

@@ -2406,8 +2406,15 @@ g_settings_schema_unref
 g_settings_schema_get_id
 g_settings_schema_get_path
 
+<SUBSECTION>
+GSettingsSchemaKey
+g_settings_schema_get_key
+g_settings_schema_key_ref
+g_settings_schema_key_unref
+
 <SUBSECTION Private>
 g_settings_schema_get_type
+g_settings_schema_key_get_type
 g_settings_schema_source_get_type
 </SECTION>
 

gio/gsettingsschema-internal.h

@@ -22,7 +22,7 @@
 
 #include "gsettingsschema.h"
 
-typedef struct
+struct _GSettingsSchemaKey
 {
   GSettingsSchema *schema;
   const gchar *name;
@@ -39,7 +39,9 @@ typedef struct
   const GVariantType *type;
   GVariant *minimum, *maximum;
   GVariant *default_value;
-} GSettingsSchemaKey;
+
+  gint ref_count;
+};
 
 const gchar *           g_settings_schema_get_gettext_domain            (GSettingsSchema  *schema);
 GVariantIter *          g_settings_schema_get_value                     (GSettingsSchema  *schema,

gio/gsettingsschema.c

@@ -1076,3 +1076,76 @@ g_settings_schema_key_from_flags (GSettingsSchemaKey *key,
 
   return g_variant_builder_end (&builder);
 }
+
+G_DEFINE_BOXED_TYPE (GSettingsSchemaKey, g_settings_schema_key, g_settings_schema_key_ref, g_settings_schema_key_unref)
+
+/**
+ * g_settings_schema_key_ref:
+ * @key: a #GSettingsSchemaKey
+ *
+ * Increase the reference count of @key, returning a new reference.
+ *
+ * Returns: a new reference to @key
+ *
+ * Since: 2.40
+ **/
+GSettingsSchemaKey *
+g_settings_schema_key_ref (GSettingsSchemaKey *key)
+{
+  g_return_val_if_fail (key != NULL, NULL);
+
+  g_atomic_int_inc (&key->ref_count);
+
+  return key;
+}
+
+/**
+ * g_settings_schema_key_unref:
+ * @key: a #GSettingsSchemaKey
+ *
+ * Decrease the reference count of @key, possibly freeing it.
+ *
+ * Since: 2.40
+ **/
+void
+g_settings_schema_key_unref (GSettingsSchemaKey *key)
+{
+  g_return_if_fail (key != NULL);
+
+  if (g_atomic_int_dec_and_test (&key->ref_count))
+    {
+      g_settings_schema_key_clear (key);
+
+      g_slice_free (GSettingsSchemaKey, key);
+    }
+}
+
+/**
+ * g_settings_schema_get_key:
+ * @schema: a #GSettingsSchema
+ * @name: the name of a key
+ *
+ * Gets the key named @name from @schema.
+ *
+ * It is a programmer error to request a key that does not exist.  See
+ * g_settings_schema_list_keys().
+ *
+ * Returns: (transfer full): the #GSettingsSchemaKey for @name
+ *
+ * Since: 2.40
+ **/
+GSettingsSchemaKey *
+g_settings_schema_get_key (GSettingsSchema *schema,
+                           const gchar     *name)
+{
+  GSettingsSchemaKey *key;
+
+  g_return_val_if_fail (schema != NULL, NULL);
+  g_return_val_if_fail (name != NULL, NULL);
+
+  key = g_slice_new (GSettingsSchemaKey);
+  g_settings_schema_key_init (key, schema, name);
+  key->ref_count = 1;
+
+  return key;
+}

gio/gsettingsschema.h

@@ -27,6 +27,7 @@ G_BEGIN_DECLS
 
 typedef struct _GSettingsSchemaSource                       GSettingsSchemaSource;
 typedef struct _GSettingsSchema                             GSettingsSchema;
+typedef struct _GSettingsSchemaKey                          GSettingsSchemaKey;
 
 #define                 G_TYPE_SETTINGS_SCHEMA_SOURCE                   (g_settings_schema_source_get_type ())
 GLIB_AVAILABLE_IN_2_32
@@ -63,6 +64,18 @@ GLIB_AVAILABLE_IN_2_32
 const gchar *           g_settings_schema_get_id                        (GSettingsSchema        *schema);
 GLIB_AVAILABLE_IN_2_32
 const gchar *           g_settings_schema_get_path                      (GSettingsSchema        *schema);
+GLIB_AVAILABLE_IN_2_40
+GSettingsSchemaKey *    g_settings_schema_get_key                       (GSettingsSchema        *schema,
+                                                                         const gchar            *key);
+
+#define                 G_TYPE_SETTINGS_SCHEMA_KEY                      (g_settings_schema_key_get_type ())
+GLIB_AVAILABLE_IN_2_40
+GType                   g_settings_schema_key_get_type                  (void) G_GNUC_CONST;
+
+GLIB_AVAILABLE_IN_2_40
+GSettingsSchemaKey *    g_settings_schema_key_ref                       (GSettingsSchemaKey     *key);
+GLIB_AVAILABLE_IN_2_40
+void                    g_settings_schema_key_unref                     (GSettingsSchemaKey     *key);
 
 G_END_DECLS