[glib: 4/6] gsettings: Clarify that g_settings_get_child() inherits delay-apply

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 0101ccba16419ab20ebfc2cbd5aa91924494f890
Author: Philip Withnall <pwithnall endlessos org>
Date:   Tue Oct 26 14:10:19 2021 +0100

    gsettings: Clarify that g_settings_get_child() inherits delay-apply
    
    Previously, the delay-apply status of the parent `GSettings` object
    would be partially inherited: `settings->priv->backend` in the child
    `GSettings` object would point to a `GDelayedSettingsBackend`, but
    `settings->priv->delayed` would be `NULL`.
    
    The expectation from https://bugzilla.gnome.org/show_bug.cgi?id=720891
    was that `get_child()` would fully inherit delay-apply status.
    
    So, ensure that `settings->priv->delayed` is correctly set to point to
    the delayed backend when constructing any `GSettings`. Update the tests
    to work again (presumably the inverted test was an oversight in the
    original changes).
    
    Signed-off-by: Philip Withnall <pwithnall endlessos org>
    
    Fixes: #2426

 gio/gsettings.c       | 16 +++++++++++++++-
 gio/tests/gsettings.c |  7 ++++++-
 2 files changed, 21 insertions(+), 2 deletions(-)
---
diff --git a/gio/gsettings.c b/gio/gsettings.c
index 5ebac1170..711929cff 100644
--- a/gio/gsettings.c
+++ b/gio/gsettings.c
@@ -604,6 +604,11 @@ g_settings_set_property (GObject      *object,
 
     case PROP_BACKEND:
       settings->priv->backend = g_value_dup_object (value);
+      if (G_IS_DELAYED_SETTINGS_BACKEND (settings->priv->backend))
+        {
+          g_assert (settings->priv->delayed == NULL);
+          settings->priv->delayed = G_DELAYED_SETTINGS_BACKEND (settings->priv->backend);
+        }
       break;
 
     default:
@@ -680,7 +685,13 @@ g_settings_constructed (GObject *object)
     }
 
   if (settings->priv->backend == NULL)
-    settings->priv->backend = g_settings_backend_get_default ();
+    {
+      settings->priv->backend = g_settings_backend_get_default ();
+
+      /* The default had better not be delayed, otherwise we also need to set
+       * settings->priv->delayed. */
+      g_assert (!G_IS_DELAYED_SETTINGS_BACKEND (settings->priv->backend));
+    }
 
   g_settings_backend_watch (settings->priv->backend,
                             &listener_vtable, G_OBJECT (settings),
@@ -2426,6 +2437,9 @@ g_settings_is_writable (GSettings   *settings,
  * The schema for the child settings object must have been declared
  * in the schema of @settings using a `<child>` element.
  *
+ * The created child settings object will inherit the #GSettings:delay-apply
+ * mode from @settings.
+ *
  * Returns: (not nullable) (transfer full): a 'child' settings object
  *
  * Since: 2.26
diff --git a/gio/tests/gsettings.c b/gio/tests/gsettings.c
index 0b19f2a67..dad1623b7 100644
--- a/gio/tests/gsettings.c
+++ b/gio/tests/gsettings.c
@@ -619,7 +619,7 @@ test_delay_child (void)
   g_assert_nonnull (child);
 
   g_object_get (child, "delay-apply", &delay, NULL);
-  g_assert_false (delay);
+  g_assert_true (delay);
 
   g_settings_get (child, "test-byte", "y", &byte);
   g_assert_cmpuint (byte, ==, 36);
@@ -630,6 +630,11 @@ test_delay_child (void)
   g_settings_get (base, "test-byte", "y", &byte);
   g_assert_cmpuint (byte, ==, 36);
 
+  /* apply the child and the changes should be saved */
+  g_settings_apply (child);
+  g_settings_get (base, "test-byte", "y", &byte);
+  g_assert_cmpuint (byte, ==, 42);
+
   g_object_unref (child);
   g_object_unref (settings);
   g_object_unref (base);