Fix type of length returned by gvdb_table_get_names()

It should not be unsigned. The type in the on-disk format is gint32, so
we need to return something at least as wide as that. However, we
should not expose the implementation detail that the on-disk format is
specifically gint32. Use a gsize, since that’s the normal type for array
lengths — but check that we’re not on a platform where (somehow) gsize
is smaller than gint32.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

gvdb-reader.c

@@ -348,7 +348,7 @@ gvdb_table_list_from_item (GvdbTable                    *table,
  **/
 gchar **
 gvdb_table_get_names (GvdbTable *table,
-                      gint      *length)
+                      gsize     *length)
 {
   gchar **names;
   gint n_names;
@@ -474,7 +474,10 @@ gvdb_table_get_names (GvdbTable *table,
     }
 
   if (length)
-    *length = n_names;
+    {
+      G_STATIC_ASSERT (sizeof (*length) >= sizeof (n_names));
+      *length = n_names;
+    }
 
   return names;
 }

gvdb-reader.h

@@ -38,7 +38,7 @@ G_GNUC_INTERNAL
 void                    gvdb_table_free                                 (GvdbTable    *table);
 G_GNUC_INTERNAL
 gchar **                gvdb_table_get_names                            (GvdbTable    *table,
-                                                                         gint         *length);
+                                                                         gsize        *length);
 G_GNUC_INTERNAL
 gchar **                gvdb_table_list                                 (GvdbTable    *table,
                                                                          const gchar  *key);