Handle field collisions in class merger

Change-Id: Ica3207e70d7860826632ca4af6b29179f3fdda73
diff --git a/src/test/examples/classmerging/FieldCollisionTest.java b/src/test/examples/classmerging/FieldCollisionTest.java
new file mode 100644
index 0000000..5bb2260
--- /dev/null
+++ b/src/test/examples/classmerging/FieldCollisionTest.java
@@ -0,0 +1,43 @@
+// Copyright (c) 2018, the R8 project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+package classmerging;
+
+public class FieldCollisionTest {
+
+  private static final B SENTINEL_A = new B("A");
+  private static final B SENTINEL_B = new B("B");
+
+  public static void main(String[] args) {
+    B obj = new B();
+    System.out.println(obj.toString());
+  }
+
+  // Will be merged into B.
+  public static class A {
+
+    // After class merging, this field will have the same name and type as the field B.obj,
+    // unless we handle the collision.
+    protected final A obj = SENTINEL_A;
+  }
+
+  public static class B extends A {
+
+    protected final String message;
+    protected final B obj = SENTINEL_B;
+
+    public B() {
+      this(null);
+    }
+
+    public B(String message) {
+      this.message = message;
+    }
+
+    @Override
+    public String toString() {
+      return obj.message + System.lineSeparator() + ((B) super.obj).message;
+    }
+  }
+}