1 files changed, 15 insertions, 1 deletions
diff --git a/gcc/ada/a-cdlili.adb b/gcc/ada/a-cdlili.adb
index 326c74b0785..8b513222ef8 100644
--- a/gcc/ada/a-cdlili.adb
+++ b/gcc/ada/a-cdlili.adb
@@ -515,10 +515,24 @@ package body Ada.Containers.Doubly_Linked_Lists is
          LI, RI : Cursor;
 
       begin
-         if Target'Address = Source'Address then
+
+         --  The semantics of Merge changed slightly per AI05-0021. It was
+         --  originally the case that if Target and Source denoted the same
+         --  container object, then the GNAT implementation of Merge did
+         --  nothing. However, it was argued that RM05 did not precisely
+         --  specify the semantics for this corner case. The decision of the
+         --  ARG was that if Target and Source denote the same non-empty
+         --  container object, then Program_Error is raised.
+
+         if Source.Is_Empty then
             return;
          end if;
 
+         if Target'Address = Source'Address then
+            raise Program_Error with
+              "Target and Source denote same non-empty container";
+         end if;
+
          if Target.Busy > 0 then
             raise Program_Error with
               "attempt to tamper with cursors of Target (list is busy)";