pt.c (tsubst_copy_and_build): Get LAMBDA_EXPR_RETURN_TYPE from the instantiated closure.

	* pt.c (tsubst_copy_and_build) [LAMBDA_EXPR]: Get
	LAMBDA_EXPR_RETURN_TYPE from the instantiated closure.

From-SVN: r233955

gcc/cp/ChangeLog

 2016-03-03  Jason Merrill  <jason@redhat.com>
 
+	* pt.c (tsubst_copy_and_build) [LAMBDA_EXPR]: Get
+	LAMBDA_EXPR_RETURN_TYPE from the instantiated closure.
+
 	PR c++/67164
 	* pt.c (copy_template_args): New.
 	(tsubst_pack_expansion): Use it.

gcc/cp/pt.c

@@ -17103,8 +17103,6 @@ tsubst_copy_and_build (tree t,
 	else
 	  gcc_unreachable ();
 	LAMBDA_EXPR_EXTRA_SCOPE (r) = scope;
-	LAMBDA_EXPR_RETURN_TYPE (r)
-	  = tsubst (LAMBDA_EXPR_RETURN_TYPE (t), args, complain, in_decl);
 
 	gcc_assert (LAMBDA_EXPR_THIS_CAPTURE (t) == NULL_TREE
 		    && LAMBDA_EXPR_PENDING_PROXIES (t) == NULL);
@@ -17115,6 +17113,9 @@ tsubst_copy_and_build (tree t,
 	   declaration of the op() for later calls to lambda_function.  */
 	complete_type (type);
 
+	if (tree fn = lambda_function (type))
+	  LAMBDA_EXPR_RETURN_TYPE (r) = TREE_TYPE (TREE_TYPE (fn));
+
 	LAMBDA_EXPR_THIS_CAPTURE (r) = NULL_TREE;
 
 	insert_pending_capture_proxies ();

gcc/testsuite/g++.dg/cpp1y/lambda-generic-trailing1.C

+// { dg-do compile { target c++14 } }
+
+template <class T>
+void f()
+{
+  auto lam = [](auto a)->decltype(++a) { return a; };
+}
+
+int main()
+{
+  f<int>();
+}