ada: Fix bogus error with "=" operator on array of private unchecked union

The code is legal and, therefore, must be accepted by the compiler, but it
must raise Program_Error at run time due to operands not having inferable
discriminants and a warning be given at compile time (RM B.3.3(22-23)).

gcc/ada/

	* exp_ch4.adb (Expand_Array_Equality.Component_Equality): Copy the
	Comes_From_Source flag from the original test to the new one, and
	remove obsolete code dealing with unchecked unions.
	* sem_util.adb (Has_Inferable_Discriminants): Return False for an
	incomplete or private nominal subtype.

2 files changed, 14 insertions, 20 deletions

diff --git a/gcc/ada/exp_ch4.adb b/gcc/ada/exp_ch4.adb
index 7349dfc..983f662 100644
--- a/gcc/ada/exp_ch4.adb
+++ b/gcc/ada/exp_ch4.adb
@@ -1570,26 +1570,17 @@ package body Exp_Ch4 is
            (Outer_Type => Typ, Nod => Nod, Comp_Type => Component_Type (Typ),
             Lhs => L, Rhs => R);
 
-         --  If some (sub)component is an unchecked_union, the whole operation
-         --  will raise program error.
+         --  This is necessary to give the warning about Program_Error being
+         --  raised when some (sub)component is an unchecked_union.
 
-         if Nkind (Test) = N_Raise_Program_Error then
+         Preserve_Comes_From_Source (Test, Nod);
 
-            --  This node is going to be inserted at a location where a
-            --  statement is expected: clear its Etype so analysis will set
-            --  it to the expected Standard_Void_Type.
-
-            Set_Etype (Test, Empty);
-            return Test;
-
-         else
-            return
-              Make_Implicit_If_Statement (Nod,
-                Condition       => Make_Op_Not (Loc, Right_Opnd => Test),
-                Then_Statements => New_List (
-                  Make_Simple_Return_Statement (Loc,
-                    Expression => New_Occurrence_Of (Standard_False, Loc))));
-         end if;
+         return
+           Make_Implicit_If_Statement (Nod,
+             Condition       => Make_Op_Not (Loc, Right_Opnd => Test),
+             Then_Statements => New_List (
+               Make_Simple_Return_Statement (Loc,
+                 Expression => New_Occurrence_Of (Standard_False, Loc))));
       end Component_Equality;
 
       ------------------
diff --git a/gcc/ada/sem_util.adb b/gcc/ada/sem_util.adb
index 8425359..4cdac94 100644
--- a/gcc/ada/sem_util.adb
+++ b/gcc/ada/sem_util.adb
@@ -12119,11 +12119,14 @@ package body Sem_Util is
            and then Is_Constrained (Etype (Subtype_Mark (N)));
 
       --  For all other names, it is sufficient to have a constrained
-      --  Unchecked_Union nominal subtype.
+      --  Unchecked_Union nominal subtype, unless it is incomplete or
+      --  private because it cannot have a known discriminant part in
+      --  this case (RM B.3.3 (11/2)).
 
       else
          return Is_Unchecked_Union (Etype (N))
-           and then Is_Constrained (Etype (N));
+           and then Is_Constrained (Etype (N))
+           and then not Is_Incomplete_Or_Private_Type (Etype (N));
       end if;
    end Has_Inferable_Discriminants;