re PR c++/89913 (ICE with invalid using declaration)

PR c++/89913

gcc/cp/
	* pt.c (get_underlying_template): Exit loop if the original type
	of the alias is null.

gcc/testsuite/
	* g++.dg/cpp2a/pr89913.C: New test.

From-SVN: r278451

gcc/cp/ChangeLog

+2019-11-15  Andrew Sutton  <asutton@lock3software.com>
+
+	PR c++/89913
+	* pt.c (get_underlying_template): Exit loop if the original type
+	of the alias is null.
+
+2019-11-19  Andrew Sutton  <asutton@lock3software.com>
+
+	PR c++/92078
+	* pt.c (maybe_new_partial_specialization): Apply access to newly
+	created partial specializations. Update comment style.
+
 2019-11-19  Andrew Sutton  <asutton@lock3software.com>
 
 	PR c++/92078

gcc/cp/pt.c

@@ -6395,6 +6395,9 @@ get_underlying_template (tree tmpl)
     {
       /* Determine if the alias is equivalent to an underlying template.  */
       tree orig_type = DECL_ORIGINAL_TYPE (DECL_TEMPLATE_RESULT (tmpl));
+      /* The underlying type may have been ill-formed. Don't proceed.  */
+      if (!orig_type)
+	break;
       tree tinfo = TYPE_TEMPLATE_INFO_MAYBE_ALIAS (orig_type);
       if (!tinfo)
 	break;

gcc/testsuite/ChangeLog

+2019-11-15  Andrew Sutton  <asutton@lock3software.com>
+
+	PR c++/89913
+	* g++.dg/cpp2a/pr89913.C: New test.
+
 2019-11-19  Andrew Sutton  <asutton@lock3software.com>
 
 	PR c++/92078

gcc/testsuite/g++.dg/cpp2a/pr89913.C

+// { dg-do compile { target c++2a } }
+
+template<typename...> using A = auto; // { dg-error "not allowed" }
+// In pre-20, the error is "invalid use of auto"
+
+template<typename... T> using B = A<T...>;