resource: Add g_resource[s]_has_children

These functions avoid allocating the children array when it is
not needed.

gio/gresource.c

@@ -1023,6 +1023,43 @@ g_resource_enumerate_children (GResource             *resource,
   return children;
 }
 
+/**
+ * g_resource_has_children:
+ * @resource: A #GResource
+ * @path: A pathname inside the resource
+ *
+ * Returns whether the specified @path in the resource
+ * has children.
+ *
+ * Returns: %TRUE if @path has children
+ *
+ * Since: 2.84
+ */
+gboolean
+g_resource_has_children (GResource  *resource,
+                         const char *path)
+{
+  /* Size of 256 is arbitrarily chosen based on being large enough
+   * for pretty much everything we come across, but not cumbersome
+   * on the stack. It also matches common cacheline sizes.
+   */
+  char local_str[256];
+  const char *path_with_slash;
+  guint n;
+  char *freeme = NULL;
+
+  if (*path == 0)
+    return FALSE;
+
+  path_with_slash = ensure_slash_suffix (path, local_str, sizeof (local_str), &freeme);
+
+  n = gvdb_table_n_children (resource->table, path_with_slash);
+
+  g_free (freeme);
+
+  return n > 0;
+}
+
 static GRWLock resources_lock;
 static GList *registered_resources;
 
@@ -1301,6 +1338,39 @@ g_resources_enumerate_children (const gchar           *path,
     }
 }
 
+/**
+ * g_resources_has_children:
+ * @path: A pathname
+ *
+ * Returns whether the specified @path in the set of
+ * globally registered resources has children.
+ *
+ * Returns: %TRUE if @patch has children
+ *
+ * Since: 2.84
+ */
+gboolean
+g_resources_has_children (const char *path)
+{
+  register_lazy_static_resources ();
+
+  g_rw_lock_reader_lock (&resources_lock);
+
+  for (GList *l = registered_resources; l != NULL; l = l->next)
+    {
+      GResource *r = l->data;
+
+      if (g_resource_has_children (r, path))
+        {
+          g_rw_lock_reader_unlock (&resources_lock);
+          return TRUE;
+        }
+    }
+
+  g_rw_lock_reader_unlock (&resources_lock);
+  return FALSE;
+}
+
 /**
  * g_resources_get_info:
  * @path: A pathname inside the resource

gio/gresource.h

@@ -119,6 +119,12 @@ gboolean      g_resources_get_info           (const char            *path,
 					      guint32               *flags,
 					      GError               **error);
 
+GIO_AVAILABLE_IN_2_84
+gboolean      g_resource_has_children        (GResource             *resource,
+                                              const char            *path);
+GIO_AVAILABLE_IN_2_84
+gboolean      g_resources_has_children       (const char            *path);
+
 
 GIO_AVAILABLE_IN_2_32
 void          g_static_resource_init          (GStaticResource *static_resource);

gio/tests/resources.c

@@ -1046,6 +1046,29 @@ test_overlay (void)
   g_test_trap_assert_passed ();
 }
 
+static void
+test_resource_has_children (void)
+{
+  GResource *resource;
+  GError *error = NULL;
+
+  g_assert_true (g_resources_has_children ("/auto_loaded"));
+  g_assert_true (g_resources_has_children ("/auto_loaded/"));
+  g_assert_false (g_resources_has_children ("/auto_loaded/test1.txt"));
+  g_assert_false (g_resources_has_children ("/no/such/prefix"));
+
+  resource = g_resource_load (g_test_get_filename (G_TEST_BUILT, "test.gresource", NULL), &error);
+  g_assert_nonnull (resource);
+  g_assert_no_error (error);
+
+  g_assert_true (g_resource_has_children (resource, "/a_prefix"));
+  g_assert_true (g_resource_has_children (resource, "/a_prefix/"));
+  g_assert_false (g_resource_has_children (resource, "/a_prefix/test2.txt"));
+  g_assert_false (g_resource_has_children (resource, "/no/such/prefix"));
+
+  g_resource_unref (resource);
+}
+
 int
 main (int   argc,
       char *argv[])
@@ -1075,6 +1098,7 @@ main (int   argc,
   g_test_add_func ("/resource/64k", test_resource_64k);
   g_test_add_func ("/resource/overlay", test_overlay);
   g_test_add_func ("/resource/digits", test_resource_digits);
+  g_test_add_func ("/resource/has-children", test_resource_has_children);
 
   return g_test_run();
 }