PR c++/88820 - ICE with CTAD and member template used in DMI.

Here the problem was that in order to form a FUNCTION_DECL for foo<int> in
the uninstantiated template, we were trying to deduce template args for S
from the template parm itself, and failing.

	* pt.c (do_class_deduction): Handle parm used as its own arg.

From-SVN: r269463

gcc/cp/ChangeLog

+2019-03-07  Jason Merrill  <jason@redhat.com>
+
+	PR c++/88820 - ICE with CTAD and member template used in DMI.
+	* pt.c (do_class_deduction): Handle parm used as its own arg.
+
 2019-03-07  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/89585

gcc/cp/pt.c

@@ -27184,6 +27184,9 @@ do_class_deduction (tree ptype, tree tmpl, tree init, int flags,
 	error ("non-class template %qT used without template arguments", tmpl);
       return error_mark_node;
     }
+  if (init && TREE_TYPE (init) == ptype)
+    /* Using the template parm as its own argument.  */
+    return ptype;
 
   tree type = TREE_TYPE (tmpl);
 

gcc/testsuite/g++.dg/cpp1z/class-deduction64.C

+// PR c++/88820
+// { dg-do compile { target c++17 } }
+
+template <int> struct S;
+
+template <S> struct W {
+  template <typename> static int foo();
+  bool b = foo<int>();
+};