PR c++/90190 - CTAD with list-constructor.

The passage quoted talks about an initializer list containing a single
expression, but a braced-init-list is not an expression.

	* pt.c (do_class_deduction): Don't try the single element deduction
	if the single element is also a braced list.

From-SVN: r270468

gcc/cp/ChangeLog

 2019-04-19  Jason Merrill  <jason@redhat.com>
 
+	PR c++/90190 - CTAD with list-constructor.
+	* pt.c (do_class_deduction): Don't try the single element deduction
+	if the single element is also a braced list.
+
 	PR c++/90171 - ICE with destroying delete with size_t parm.
 	* call.c (sized_deallocation_fn_p): New.  Use it instead of
 	second_parm_is_size_t in most cases.

gcc/cp/pt.c

@@ -27325,15 +27325,18 @@ do_class_deduction (tree ptype, tree tmpl, tree init, int flags,
 	     where U is a specialization of C or a class derived from a
 	     specialization of C.  */
 	  tree elt = CONSTRUCTOR_ELT (init, 0)->value;
-	  tree etype = TREE_TYPE (elt);
-
-	  tree tparms = INNERMOST_TEMPLATE_PARMS (DECL_TEMPLATE_PARMS (tmpl));
-	  tree targs = make_tree_vec (TREE_VEC_LENGTH (tparms));
-	  int err = unify (tparms, targs, type, etype,
-			   UNIFY_ALLOW_DERIVED, /*explain*/false);
-	  if (err == 0)
-	    try_list_ctor = false;
-	  ggc_free (targs);
+	  if (!BRACE_ENCLOSED_INITIALIZER_P (elt))
+	    {
+	      tree etype = TREE_TYPE (elt);
+	      tree tparms = (INNERMOST_TEMPLATE_PARMS
+			     (DECL_TEMPLATE_PARMS (tmpl)));
+	      tree targs = make_tree_vec (TREE_VEC_LENGTH (tparms));
+	      int err = unify (tparms, targs, type, etype,
+			       UNIFY_ALLOW_DERIVED, /*explain*/false);
+	      if (err == 0)
+		try_list_ctor = false;
+	      ggc_free (targs);
+	    }
 	}
       if (try_list_ctor || is_std_init_list (type))
 	args = make_tree_vector_single (init);

gcc/testsuite/g++.dg/cpp1z/class-deduction65.C

+// PR c++/90190
+// { dg-do compile { target c++17 } }
+
+#include <initializer_list>
+
+enum class X {};
+
+struct Term {
+  double a;
+  X i;
+};
+
+template <class It = const Term *>
+struct sum {
+  sum(std::initializer_list<Term>) {}
+};
+
+int main() {
+  auto c2 = sum{{1, X()}, {2, X()}};
+  auto c1 = sum{{1, X()}};  // fails only this
+  auto c0 = sum{{}};
+}