[gtk/wip/otte/listview: 902/1040] sortlistmodel: Make sort stable

[Benjamin Otte <otte src gnome org>]

commit 2e47575cd800117692ebc1da795d8cc25c6401dc
Author: Benjamin Otte <otte redhat com>
Date:   Wed Dec 11 01:22:20 2019 +0100

    sortlistmodel: Make sort stable
    
    The sort of the sortlistmodel is now stable with respect to the original
    list model.
    
    That means that if the sorter compares items as equal, the model
    will make sure those items keep the order they were in in the original
    model.
    
    Or in other words: The model guarantees a total order based on the
    item's position in the original model.

 gtk/gtksortlistmodel.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)
---
diff --git a/gtk/gtksortlistmodel.c b/gtk/gtksortlistmodel.c
index 2fa9de9944..5444ee74ae 100644
--- a/gtk/gtksortlistmodel.c
+++ b/gtk/gtksortlistmodel.c
@@ -181,8 +181,14 @@ _sort_func (gconstpointer item1,
 {
   GtkSortListEntry *entry1 = (GtkSortListEntry *) item1;
   GtkSortListEntry *entry2 = (GtkSortListEntry *) item2;
+  GtkOrdering result;
 
-  return gtk_sorter_compare (GTK_SORTER (data), entry1->item, entry2->item);
+  result = gtk_sorter_compare (GTK_SORTER (data), entry1->item, entry2->item);
+
+  if (result == GTK_ORDERING_EQUAL)
+    result = g_sequence_iter_compare (entry1->unsorted_iter, entry2->unsorted_iter);
+
+  return result;
 }
 
 static void