diff -r 88502b1cf76f -r 7799a51dbe30 test/langtools/tools/javac/diags/examples/PatternBindingMayNotBeAssigned.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/langtools/tools/javac/diags/examples/PatternBindingMayNotBeAssigned.java	Wed Nov 27 09:00:01 2019 +0100
@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2017, 2019, 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.
+ *
+ * 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.
+ */
+
+// key: compiler.err.pattern.binding.may.not.be.assigned
+// key: compiler.note.preview.filename
+// key: compiler.note.preview.recompile
+// options: --enable-preview -source ${jdk.version}
+
+class ResourceMayNotBeAssigned {
+    void m(Object o) {
+        if (o instanceof String s) {
+            s = "";
+        }
+    }
+}