8004504: ListBuffer could reuse List.nil() as the sentinel element

ListBuffer.last now points to the last elements with client data, or null if none.

Reviewed-by: jjg, mcimadamore

langtools/test/tools/javac/util/list/ListBufferTest.java

@@ -0,0 +1,112 @@
+/*
+ * Copyright (c) 2012, 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.
+ */
+
+/*
+ * @test
+ * @bug 8004504
+ * @summary Ensure that ListBuffer is working properly
+ */
+
+import com.sun.tools.javac.util.List;
+import com.sun.tools.javac.util.ListBuffer;
+import java.util.Iterator;
+import java.util.Objects;
+
+public class ListBufferTest {
+    public static void main(String... args) {
+        testRemove();
+        testCopiedEndsWithList_nil();
+    }
+
+    private static void testCopiedEndsWithList_nil() {
+        ListBuffer<String> lb = new ListBuffer<>();
+
+        lb.add("a");
+        lb.add("b");
+        lb.add("c");
+
+        List<String> l1 = lb.toList();
+
+        assertListEquals(l1, "a", "b", "c");
+        assertEndsWithNil(l1);
+
+        lb.add("d");
+
+        List<String> l2 = lb.toList();
+        assertListEquals(l2, "a", "b", "c", "d");
+        assertEndsWithNil(l2);
+        assertListEquals(l1, "a", "b", "c");
+    }
+
+    private static void testRemove() {
+        ListBuffer<String> lb1 = new ListBuffer<>();
+
+        lb1.add("a");
+        lb1.add("b");
+        lb1.add("c");
+
+        assertListEquals(lb1.toList(), "a", "b", "c");
+        assertEquals(lb1.next(), "a");
+        assertListEquals(lb1.toList(), "b", "c");
+        assertEquals(lb1.next(), "b");
+        assertListEquals(lb1.toList(), "c");
+        assertEquals(lb1.next(), "c");
+        assertListEquals(lb1.toList());
+        assertEquals(lb1.next(), null);
+
+        lb1.add("d");
+
+        assertEquals(lb1.next(), "d");
+    }
+
+    private static void assertEndsWithNil(List<?> list) {
+        while (!list.isEmpty()) {
+            list = list.tail;
+        }
+
+        if (list != List.nil()) throw new IllegalStateException("Not ending with List.nil()");
+    }
+
+    private static <T> void assertListEquals(Iterable<T> list, T... data) {
+        int i = 0;
+        Iterator<T> it = list.iterator();
+
+        while (it.hasNext() && i < data.length) {
+            assertEquals(it.next(), data[i++]);
+        }
+
+        if (it.hasNext()) {
+            throw new IllegalStateException("Too many elements in the list");
+        }
+
+        if (i < data.length) {
+            throw new IllegalStateException("Too few elements in the list");
+        }
+    }
+
+    private static void assertEquals(Object expected, Object actual) {
+        if (!Objects.equals(expected, actual)) {
+            throw new IllegalStateException("Incorrect content. Expected: " + expected + ", actual: " + actual);
+        }
+    }
+}