GSettingsBackend API/ABI change

- add list() virtual method
  - add 'default_value' flag to read() call

gio/gdelayedsettingsbackend.c

@@ -42,16 +42,18 @@ G_DEFINE_TYPE (GDelayedSettingsBackend,
 static GVariant *
 g_delayed_settings_backend_read (GSettingsBackend   *backend,
                                  const gchar        *key,
-                                 const GVariantType *expected_type)
+                                 const GVariantType *expected_type,
+                                 gboolean            default_value)
 {
   GDelayedSettingsBackend *delayed = G_DELAYED_SETTINGS_BACKEND (backend);
   GVariant *result;
 
-  if ((result = g_tree_lookup (delayed->priv->delayed, key)))
+  if (!default_value &&
+      (result = g_tree_lookup (delayed->priv->delayed, key)))
     return g_variant_ref (result);
 
   return g_settings_backend_read (delayed->priv->backend,
-                                  key, expected_type);
+                                  key, expected_type, default_value);
 }
 static gboolean
 g_delayed_settings_backend_write (GSettingsBackend *backend,

gio/gio.symbols

@@ -1387,6 +1387,7 @@ g_settings_backend_setup_keyfile
 g_settings_backend_setup
 g_settings_backend_get_type
 g_settings_backend_changed
+g_settings_backend_flatten_tree
 g_settings_backend_keys_changed
 g_settings_backend_path_changed
 g_settings_backend_path_writable_changed

gio/gkeyfilesettingsbackend.c

@@ -54,11 +54,15 @@ struct _GKeyfileSettingsBackendPrivate
 static GVariant *
 g_keyfile_settings_backend_read (GSettingsBackend   *backend,
                                  const gchar        *key,
-                                 const GVariantType *expected_type)
+                                 const GVariantType *expected_type,
+                                 gboolean            default_value)
 {
   GKeyfileSettingsBackend *kf_backend = G_KEYFILE_SETTINGS_BACKEND (backend);
   GVariant *value;
 
+  if (default_value)
+    return NULL;
+
   value = g_hash_table_lookup (kf_backend->priv->table, key);
 
   if (value != NULL)

gio/gmemorysettingsbackend.c

@@ -48,11 +48,14 @@ G_DEFINE_TYPE_WITH_CODE (GMemorySettingsBackend,
 static GVariant *
 g_memory_settings_backend_read (GSettingsBackend   *backend,
                                 const gchar        *key,
-                                const GVariantType *expected_type)
+                                const GVariantType *expected_type,
+                                gboolean            default_value)
 {
+  GMemorySettingsBackend *memory = G_MEMORY_SETTINGS_BACKEND (backend);
   GVariant *value;
 
-  GMemorySettingsBackend *memory = G_MEMORY_SETTINGS_BACKEND (backend);
+  if (default_value)
+    return NULL;
 
   value = g_hash_table_lookup (memory->table, key);
 

gio/gnullsettingsbackend.c

@@ -42,7 +42,8 @@ G_DEFINE_TYPE (GNullSettingsBackend,
 static GVariant *
 g_null_settings_backend_read (GSettingsBackend   *backend,
                               const gchar        *key,
-                              const GVariantType *expected_type)
+                              const GVariantType *expected_type,
+                              gboolean            default_value)
 {
   return NULL;
 }

gio/gsettings.c

@@ -751,7 +751,7 @@ g_settings_get_value (GSettings   *settings,
 
   path = g_strconcat (settings->priv->path, key, NULL);
   type = g_variant_get_type (sval);
-  value = g_settings_backend_read (settings->priv->backend, path, type);
+  value = g_settings_backend_read (settings->priv->backend, path, type, FALSE);
   g_free (path);
 
   if (options != NULL)

gio/gsettingsbackend.c

@@ -368,17 +368,18 @@ g_settings_backend_path_writable_changed (GSettingsBackend *backend,
 
 typedef struct
 {
+  const gchar **keys;
+  GVariant **values;
   gint prefix_len;
   gchar *prefix;
-  gchar **items;
+} FlattenState;
-} GetKeysState;
 
 static gboolean
-tree_get_keys (gpointer key,
+g_settings_backend_flatten_one (gpointer key,
-               gpointer value,
+                                gpointer value,
-               gpointer user_data)
+                                gpointer user_data)
 {
-  GetKeysState *state = user_data;
+  FlattenState *state = user_data;
   const gchar *skey = key;
   gint i;
 
@@ -419,11 +420,60 @@ tree_get_keys (gpointer key,
   /* save the entire item into the array.
    * the prefixes will be removed later.
    */
-  *state->items++ = key;
+  *state->keys++ = key;
+
+  if (state->values)
+    *state->values++ = value;
 
   return FALSE;
 }
 
+/**
+ * g_settings_backend_flatten_tree:
+ * @tree: a #GTree containing the changes
+ * @path: the location to save the path
+ * @keys: the location to save the relative keys
+ * @values: the location to save the values, or %NULL
+ *
+ * Calculate the longest common prefix of all keys in a tree and write
+ * out an array of the key names relative to that prefix and,
+ * optionally, the value to store at each of those keys.
+ *
+ * You must free the value returned in @path, @keys and @values using
+ * g_free().  You should not attempt to free or unref the contents of
+ * @keys or @values.
+ *
+ * Since: 2.26
+ **/
+void
+g_settings_backend_flatten_tree (GTree         *tree,
+                                 gchar        **path,
+                                 const gchar ***keys,
+                                 GVariant    ***values)
+{
+  FlattenState state = { 0, };
+  gsize nnodes;
+  gsize i;
+
+  nnodes = g_tree_nnodes (tree);
+
+  *keys = state.keys = g_new (const gchar *, nnodes + 1);
+  state.keys[nnodes] = NULL;
+
+  if (values != NULL)
+    {
+      *values = state.values = g_new (GVariant *, nnodes + 1);
+      state.values[nnodes] = NULL;
+    }
+
+  g_tree_foreach (tree, g_settings_backend_flatten_one, &state);
+  g_return_if_fail (*keys + nnodes == state.keys);
+
+  *path = state.prefix;
+  for (i = 0; i < nnodes; i++)
+    state.keys[i] += state.prefix_len;
+}
+
 /**
  * g_settings_backend_changed_tree:
  * @backend: a #GSettingsBackend implementation
@@ -442,28 +492,18 @@ g_settings_backend_changed_tree (GSettingsBackend *backend,
                                  gpointer          origin_tag)
 {
   GSettingsBackendWatch *watch;
-  GetKeysState state = { 0, };
+  const gchar **keys;
-  gchar **list;
+  gchar *path;
 
   g_return_if_fail (G_IS_SETTINGS_BACKEND (backend));
 
-  list = g_new (gchar *, g_tree_nnodes (tree) + 1);
+  g_settings_backend_flatten_tree (tree, &path, &keys, NULL);
-  state.items = list;
-
-  g_tree_foreach (tree, tree_get_keys, &state);
-  g_return_if_fail (list + g_tree_nnodes (tree) == state.items);
-  *state.items = NULL;
-
-  while (state.items-- != list)
-    *state.items += state.prefix_len;
 
   for (watch = backend->priv->watches; watch; watch = watch->next)
-    watch->keys_changed (backend, state.prefix,
+    watch->keys_changed (backend, path, keys, origin_tag, watch->user_data);
-                         (const gchar * const *) list,
-                         origin_tag, watch->user_data);
 
-  g_free (list);
+  g_free (path);
-  g_free (state.prefix);
+  g_free (keys);
 }
 
 /*< private >
@@ -487,10 +527,11 @@ g_settings_backend_changed_tree (GSettingsBackend *backend,
 GVariant *
 g_settings_backend_read (GSettingsBackend   *backend,
                          const gchar        *key,
-                         const GVariantType *expected_type)
+                         const GVariantType *expected_type,
+                         gboolean            default_value)
 {
   return G_SETTINGS_BACKEND_GET_CLASS (backend)
-    ->read (backend, key, expected_type);
+    ->read (backend, key, expected_type, default_value);
 }
 
 /*< private >

gio/gsettingsbackend.h

@@ -69,7 +69,11 @@ struct _GSettingsBackendClass
 
   GVariant *  (*read)             (GSettingsBackend    *backend,
                                    const gchar         *key,
-                                   const GVariantType  *expected_type);
+                                   const GVariantType  *expected_type,
+                                   gboolean             default_value);
+  gchar **    (*list)             (GSettingsBackend    *backend,
+                                   const gchar         *path,
+                                   gsize               *length);
   gboolean    (*write)            (GSettingsBackend    *backend,
                                    const gchar         *key,
                                    GVariant            *value,
@@ -112,6 +116,10 @@ void                            g_settings_backend_changed              (GSettin
 void                            g_settings_backend_path_changed         (GSettingsBackend    *backend,
                                                                          const gchar         *path,
                                                                          gpointer             origin_tag);
+void                            g_settings_backend_flatten_tree         (GTree               *tree,
+                                                                         gchar              **path,
+                                                                         const gchar       ***keys,
+                                                                         GVariant          ***values);
 void                            g_settings_backend_keys_changed         (GSettingsBackend    *backend,
                                                                          const gchar         *path,
                                                                          gchar const * const *items,

gio/gsettingsbackendinternal.h

@@ -67,7 +67,8 @@ GTree *                         g_settings_backend_create_tree          (void);
 G_GNUC_INTERNAL
 GVariant *                      g_settings_backend_read                 (GSettingsBackend                     *backend,
                                                                          const gchar                          *key,
-                                                                         const GVariantType                   *expected_type);
+                                                                         const GVariantType                   *expected_type,
+                                                                         gboolean                              default_value);
 G_GNUC_INTERNAL
 gboolean                        g_settings_backend_write                (GSettingsBackend                     *backend,
                                                                          const gchar                          *key,