1 files changed, 40 insertions, 16 deletions

diff --git a/src/backend/nodes/list.c b/src/backend/nodes/list.c
index 083538f70a1..f3e18007086 100644
--- a/src/backend/nodes/list.c
+++ b/src/backend/nodes/list.c
@@ -1250,41 +1250,65 @@ list_copy_tail(const List *oldlist, int nskip)
 }
 
 /*
- * Sort a list using qsort. A sorted list is built but the cells of the
- * original list are re-used.  The comparator function receives arguments of
- * type ListCell **
+ * Sort a list as though by qsort.
+ *
+ * A new list is built and returned.  Like list_copy, this doesn't make
+ * fresh copies of any pointed-to data.
+ *
+ * The comparator function receives arguments of type ListCell **.
  */
 List *
 list_qsort(const List *list, list_qsort_comparator cmp)
 {
-	ListCell   *cell;
-	int			i;
 	int			len = list_length(list);
 	ListCell  **list_arr;
-	List	   *new_list;
+	List	   *newlist;
+	ListCell   *newlist_prev;
+	ListCell   *cell;
+	int			i;
 
+	/* Empty list is easy */
 	if (len == 0)
 		return NIL;
 
+	/* Flatten list cells into an array, so we can use qsort */
+	list_arr = (ListCell **) palloc(sizeof(ListCell *) * len);
 	i = 0;
-	list_arr = palloc(sizeof(ListCell *) * len);
 	foreach(cell, list)
 		list_arr[i++] = cell;
 
 	qsort(list_arr, len, sizeof(ListCell *), cmp);
 
-	new_list = (List *) palloc(sizeof(List));
-	new_list->type = list->type;
-	new_list->length = len;
-	new_list->head = list_arr[0];
-	new_list->tail = list_arr[len - 1];
+	/* Construct new list (this code is much like list_copy) */
+	newlist = new_list(list->type);
+	newlist->length = len;
+
+	/*
+	 * Copy over the data in the first cell; new_list() has already allocated
+	 * the head cell itself
+	 */
+	newlist->head->data = list_arr[0]->data;
+
+	newlist_prev = newlist->head;
+	for (i = 1; i < len; i++)
+	{
+		ListCell   *newlist_cur;
+
+		newlist_cur = (ListCell *) palloc(sizeof(*newlist_cur));
+		newlist_cur->data = list_arr[i]->data;
+		newlist_prev->next = newlist_cur;
 
-	for (i = 0; i < len - 1; i++)
-		list_arr[i]->next = list_arr[i + 1];
+		newlist_prev = newlist_cur;
+	}
 
-	list_arr[len - 1]->next = NULL;
+	newlist_prev->next = NULL;
+	newlist->tail = newlist_prev;
+
+	/* Might as well free the workspace array */
 	pfree(list_arr);
-	return new_list;
+
+	check_list_invariants(newlist);
+	return newlist;
 }
 
 /*