PR c++/89024 - ICE with incomplete enum type.

	* call.c (standard_conversion): When converting an
	ARITHMETIC_TYPE_P to an incomplete type, return NULL.
	
	* g++.dg/cpp0x/enum37.C: New test.

From-SVN: r268320

gcc/cp/ChangeLog

+2019-01-27  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/89024 - ICE with incomplete enum type.
+	* call.c (standard_conversion): When converting an
+	ARITHMETIC_TYPE_P to an incomplete type, return NULL.
+	
 2019-01-25  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/88969

gcc/cp/call.c

@@ -1412,6 +1412,13 @@ standard_conversion (tree to, tree from, tree expr, bool c_cast_p,
 	     || (fcode == REAL_TYPE && !(flags & LOOKUP_NO_NON_INTEGRAL)))
           || SCOPED_ENUM_P (from))
 	return NULL;
+
+      /* If we're parsing an enum with no fixed underlying type, we're
+	 dealing with an incomplete type, which renders the conversion
+	 ill-formed.  */
+      if (!COMPLETE_TYPE_P (from))
+	return NULL;
+
       conv = build_conv (ck_std, to, conv);
 
       /* Give this a better rank if it's a promotion.  */

gcc/testsuite/ChangeLog

+2019-01-27  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/89024 - ICE with incomplete enum type.
+	* g++.dg/cpp0x/enum37.C: New test.
+
 2019-01-27  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* gnat.dg/opt75.adb: New test.

gcc/testsuite/g++.dg/cpp0x/enum37.C

+// PR c++/89024
+// { dg-do compile { target c++11 } }
+
+template <class T, class U> struct same;
+template <class T> struct same<T,T> {};
+
+template<class T> T&& declval();
+
+template<typename _To1>
+void __test_aux(_To1);
+
+template<typename _From1, typename _To1,
+        typename = decltype(__test_aux<_To1>(declval<_From1>()))>
+char __test(int);
+
+template<typename, typename>
+int __test(...);
+
+enum E {
+    x = decltype(__test<E, int>(0))(0)
+};
+
+same<E,decltype(x)> s;
+same<unsigned int,__underlying_type(E)> s2;