c++: non-static member, array bound, sizeof [PR93314]

N2253 allowed referring to non-static data members without an object in
unevaluated operands like that of sizeof, but in a constant-expression
context like an array bound or template argument within such an unevaluated
operand we do actually need a value, so that permission cannot apply.

gcc/cp/ChangeLog:

	PR c++/93314
	* semantics.c (finish_id_expression_1): Clear cp_unevaluated_operand
	for a non-static data member in a constant-expression.

gcc/testsuite/ChangeLog:

	PR c++/93314
	* g++.dg/parse/uneval1.C: New test.

gcc/cp/semantics.c

@@ -4093,6 +4093,12 @@ finish_id_expression_1 (tree id_expression,
 
 	  cp_warn_deprecated_use_scopes (scope);
 
+	  /* In a constant-expression context, turn off cp_unevaluated_operand
+	     so finish_non_static_data_member will complain (93314).  */
+	  auto eval = make_temp_override (cp_unevaluated_operand);
+	  if (integral_constant_expression_p && TREE_CODE (decl) == FIELD_DECL)
+	    cp_unevaluated_operand = 0;
+
 	  if (TYPE_P (scope))
 	    decl = finish_qualified_id_expr (scope,
 					     decl,
@@ -4106,6 +4112,10 @@ finish_id_expression_1 (tree id_expression,
 	}
       else if (TREE_CODE (decl) == FIELD_DECL)
 	{
+	  auto eval = make_temp_override (cp_unevaluated_operand);
+	  if (integral_constant_expression_p)
+	    cp_unevaluated_operand = 0;
+
 	  /* Since SCOPE is NULL here, this is an unqualified name.
 	     Access checking has been performed during name lookup
 	     already.  Turn off checking to avoid duplicate errors.  */

gcc/testsuite/g++.dg/parse/uneval1.C

@@ -0,0 +1,14 @@
+// PR c++/93314
+
+struct S {
+  int m;
+  static int f() {
+    return sizeof(char[m]);	// { dg-error "S::m" }
+  }
+};
+
+int main()
+{
+  return S().f()
+    + sizeof(char[S::m]);	// { dg-error "S::m" }
+}