8168774: Polymorhic signature method check crashes javac

Summary: Check for polysig method assumes arity is greater than zero
Reviewed-by: vromero

src/share/classes/com/sun/tools/javac/code/Types.java

@@ -1067,7 +1067,7 @@ public class Types {
        List<Type> argtypes = msym.type.getParameterTypes();
        return (msym.flags_field & NATIVE) != 0 &&
                msym.owner == syms.methodHandleType.tsym &&
-               argtypes.tail.tail == null &&
+               argtypes.length() == 1 &&
                argtypes.head.hasTag(TypeTag.ARRAY) &&
                msym.type.getReturnType().tsym == syms.objectType.tsym &&
                ((ArrayType)argtypes.head).elemtype.tsym == syms.objectType.tsym;

test/tools/javac/meth/BadPolySig.java

+/*
+ * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8168774
+ * @summary Polymorhic signature method check crashes javac
+ * @compile BadPolySig.java
+ */
+
+package java.lang.invoke;
+
+class MethodHandle {
+    native Object m();
+}