diff -r fd16c54261b3 -r 06bc494ca11e langtools/src/share/classes/com/sun/tools/javac/comp/Env.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/langtools/src/share/classes/com/sun/tools/javac/comp/Env.java	Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,150 @@
+/*
+ * Copyright 1999-2006 Sun Microsystems, Inc.  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.  Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+package com.sun.tools.javac.comp;
+
+import com.sun.tools.javac.util.*;
+import com.sun.tools.javac.tree.*;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+/** A class for environments, instances of which are passed as
+ *  arguments to tree visitors.  Environments refer to important ancestors
+ *  of the subtree that's currently visited, such as the enclosing method,
+ *  the enclosing class, or the enclosing toplevel node. They also contain
+ *  a generic component, represented as a type parameter, to carry further
+ *  information specific to individual passes.
+ *
+ *  <p><b>This is NOT part of any API supported by Sun Microsystems.  If
+ *  you write code that depends on this, you do so at your own risk.
+ *  This code and its internal interfaces are subject to change or
+ *  deletion without notice.</b>
+ */
+public class Env<A> implements Iterable<Env<A>> {
+
+    /** The next enclosing environment.
+     */
+    public Env<A> next;
+
+    /** The environment enclosing the current class.
+     */
+    public Env<A> outer;
+
+    /** The tree with which this environment is associated.
+     */
+    public JCTree tree;
+
+    /** The enclosing toplevel tree.
+     */
+    public JCTree.JCCompilationUnit toplevel;
+
+    /** The next enclosing class definition.
+     */
+    public JCTree.JCClassDecl enclClass;
+
+    /** The next enclosing method definition.
+     */
+    public JCTree.JCMethodDecl enclMethod;
+
+    /** A generic field for further information.
+     */
+    public A info;
+
+    /** Is this an environment for evaluating a base clause?
+     */
+    public boolean baseClause = false;
+
+    /** Create an outermost environment for a given (toplevel)tree,
+     *  with a given info field.
+     */
+    public Env(JCTree tree, A info) {
+        this.next = null;
+        this.outer = null;
+        this.tree = tree;
+        this.toplevel = null;
+        this.enclClass = null;
+        this.enclMethod = null;
+        this.info = info;
+    }
+
+    /** Duplicate this environment, updating with given tree and info,
+     *  and copying all other fields.
+     */
+    public Env<A> dup(JCTree tree, A info) {
+        return dupto(new Env<A>(tree, info));
+    }
+
+    /** Duplicate this environment into a given Environment,
+     *  using its tree and info, and copying all other fields.
+     */
+    public Env<A> dupto(Env<A> that) {
+        that.next = this;
+        that.outer = this.outer;
+        that.toplevel = this.toplevel;
+        that.enclClass = this.enclClass;
+        that.enclMethod = this.enclMethod;
+        return that;
+    }
+
+    /** Duplicate this environment, updating with given tree,
+     *  and copying all other fields.
+     */
+    public Env<A> dup(JCTree tree) {
+        return dup(tree, this.info);
+    }
+
+    /** Return closest enclosing environment which points to a tree with given tag.
+     */
+    public Env<A> enclosing(int tag) {
+        Env<A> env1 = this;
+        while (env1 != null && env1.tree.getTag() != tag) env1 = env1.next;
+        return env1;
+    }
+
+    public String toString() {
+        return "Env[" + info + (outer == null ? "" : ",outer=" + outer) + "]";
+    }
+
+    public Iterator<Env<A>> iterator() {
+        return new Iterator<Env<A>>() {
+            Env<A> next = Env.this;
+            public boolean hasNext() {
+                return next.outer != null;
+            }
+            public Env<A> next() {
+                if (hasNext()) {
+                    Env<A> current = next;
+                    next = current.outer;
+                    return current;
+                }
+                throw new NoSuchElementException();
+
+            }
+            public void remove() {
+                throw new UnsupportedOperationException();
+            }
+        };
+    }
+}