8199429: [lworld] Add error example for CheckExamples test

test/langtools/tools/javac/diags/examples/MustUseValueNotUsed.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2024, 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.method.returned.must.use.value
+// key: compiler.note.preview.filename
+// key: compiler.note.preview.recompile
+// options:  --enable-preview --source 24
+
+value record MustHaveValueNotUsed(int i) {
+
+    @MustUse
+    MustHaveValueNotUsed mutate() {
+        return new MustHaveValueNotUsed(i + 1);
+    }
+
+    static void test() {
+        MustHaveValueNotUsed m = new MustHaveValueNotUsed(1);
+        m.mutate(); // error
+        m = m.mutate(); // ok
+    }
+}