[Ada] Bit_Order cannot be defined for record extensions

[Pierre-Marie de Rodat]

This patch allows the compiler to report an error on Bit_Order when
defined for a record extension.

Tested on x86_64-pc-linux-gnu, committed on trunk

2018-07-16  Javier Miranda  <mira...@adacore.com>

gcc/ada/

        * sem_ch13.adb (Analyze_Attribute_Definition_Clause): Report an error
        on Bit_Order when defined for a record extension.

gcc/testsuite/

        * gnat.dg/bit_order1.adb: New testcase.
--- gcc/ada/sem_ch13.adb
+++ gcc/ada/sem_ch13.adb
@@ -5331,6 +5331,12 @@ package body Sem_Ch13 is
                Error_Msg_N
                  ("Bit_Order can only be defined for record type", Nam);
 
+            elsif Is_Tagged_Type (U_Ent)
+               and then Is_Derived_Type (U_Ent)
+            then
+               Error_Msg_N
+                 ("Bit_Order cannot be defined for record extensions", Nam);
+
             elsif Duplicate_Clause then
                null;
 

--- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/bit_order1.adb
@@ -0,0 +1,18 @@
+--  { dg-do compile }
+
+with System;
+
+procedure Bit_Order1 is
+
+   type Sample_Ttype is tagged record
+      Data : Natural;
+   end record;
+
+   type Other_Type is new Sample_Ttype with record
+      Other_Data : String (1 .. 100);
+   end record;
+
+   for Other_Type'Bit_Order use System.High_Order_First; --  { dg-error "Bit_Order cannot be defined for record extensions" }
+begin
+   null;
+end;