--- a/langtools/src/share/classes/com/sun/tools/javac/code/Types.java	Wed Aug 31 16:11:28 2011 +0100
+++ b/langtools/src/share/classes/com/sun/tools/javac/code/Types.java	Wed Aug 31 16:15:19 2011 +0100
@@ -2119,6 +2119,8 @@
             }
         }
 
+        List<TypeSymbol> seenTypes = List.nil();
+
         /** members closure visitor methods **/
 
         public CompoundScope visitType(Type t, Boolean skipInterface) {
@@ -2127,21 +2129,33 @@
 
         @Override
         public CompoundScope visitClassType(ClassType t, Boolean skipInterface) {
-            ClassSymbol csym = (ClassSymbol)t.tsym;
-            Entry e = _map.get(csym);
-            if (e == null || !e.matches(skipInterface)) {
-                CompoundScope membersClosure = new CompoundScope(csym);
-                if (!skipInterface) {
-                    for (Type i : interfaces(t)) {
-                        membersClosure.addSubScope(visit(i, skipInterface));
+            if (seenTypes.contains(t.tsym)) {
+                //this is possible when an interface is implemented in multiple
+                //superclasses, or when a classs hierarchy is circular - in such
+                //cases we don't need to recurse (empty scope is returned)
+                return new CompoundScope(t.tsym);
+            }
+            try {
+                seenTypes = seenTypes.prepend(t.tsym);
+                ClassSymbol csym = (ClassSymbol)t.tsym;
+                Entry e = _map.get(csym);
+                if (e == null || !e.matches(skipInterface)) {
+                    CompoundScope membersClosure = new CompoundScope(csym);
+                    if (!skipInterface) {
+                        for (Type i : interfaces(t)) {
+                            membersClosure.addSubScope(visit(i, skipInterface));
+                        }
                     }
+                    membersClosure.addSubScope(visit(supertype(t), skipInterface));
+                    membersClosure.addSubScope(csym.members());
+                    e = new Entry(skipInterface, membersClosure);
+                    _map.put(csym, e);
                 }
-                membersClosure.addSubScope(visit(supertype(t), skipInterface));
-                membersClosure.addSubScope(csym.members());
-                e = new Entry(skipInterface, membersClosure);
-                _map.put(csym, e);
+                return e.compoundScope;
             }
-            return e.compoundScope;
+            finally {
+                seenTypes = seenTypes.tail;
+            }
         }
 
         @Override

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/langtools/test/tools/javac/7079713/TestCircularClassfile.java	Wed Aug 31 16:15:19 2011 +0100
@@ -0,0 +1,167 @@
+/*
+ * Copyright (c) 2011, 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 7079713
+ * @summary javac hangs when compiling a class that references a cyclically inherited class
+ * @run main TestCircularClassfile
+ */
+
+import java.io.*;
+import java.net.URI;
+import java.util.Arrays;
+import javax.tools.JavaCompiler;
+import javax.tools.JavaFileObject;
+import javax.tools.SimpleJavaFileObject;
+import javax.tools.StandardJavaFileManager;
+import javax.tools.StandardLocation;
+import javax.tools.ToolProvider;
+
+import com.sun.source.util.JavacTask;
+
+public class TestCircularClassfile {
+
+    enum SourceKind {
+        A_EXTENDS_B("class B {} class A extends B { void m() {} }"),
+        B_EXTENDS_A("class A { void m() {} } class B extends A {}");
+
+        String sourceStr;
+
+        private SourceKind(String sourceStr) {
+            this.sourceStr = sourceStr;
+        }
+
+        SimpleJavaFileObject getSource() {
+            return new SimpleJavaFileObject(URI.create("myfo:/Test.java"), JavaFileObject.Kind.SOURCE) {
+                @Override
+                public CharSequence getCharContent(boolean ignoreEncodingErrors) throws IOException {
+                    return sourceStr;
+                }
+            };
+        }
+    }
+
+    enum TestKind {
+        REPLACE_A("A.class"),
+        REPLACE_B("B.class");
+
+        String targetClass;
+
+        private TestKind(String targetClass) {
+            this.targetClass = targetClass;
+        }
+    }
+
+    enum ClientKind {
+        METHOD_CALL1("A a = null; a.m();"),
+        METHOD_CALL2("B b = null; b.m();"),
+        CONSTR_CALL1("new A();"),
+        CONSTR_CALL2("new B();"),
+        ASSIGN1("A a = null; B b = a;"),
+        ASSIGN2("B b = null; A a = b;");
+
+        String mainMethod;
+
+        private ClientKind(String mainMethod) {
+            this.mainMethod = mainMethod;
+        }
+
+        SimpleJavaFileObject getSource() {
+            return new SimpleJavaFileObject(URI.create("myfo:/Test.java"), JavaFileObject.Kind.SOURCE) {
+                @Override
+                public CharSequence getCharContent(boolean ignoreEncodingErrors) throws IOException {
+                    return "class Test { public static void main(String[] args) { #M } }"
+                            .replace("#M", mainMethod);
+                }
+            };
+        }
+    }
+
+    public static void main(String... args) throws Exception {
+        JavaCompiler comp = ToolProvider.getSystemJavaCompiler();
+        StandardJavaFileManager fm = comp.getStandardFileManager(null, null, null);
+        int count = 0;
+        for (SourceKind sk1 : SourceKind.values()) {
+            for (SourceKind sk2 : SourceKind.values()) {
+                for (TestKind tk : TestKind.values()) {
+                    for (ClientKind ck : ClientKind.values()) {
+                        new TestCircularClassfile("sub_"+count++, sk1, sk2, tk, ck).check(comp, fm);
+                    }
+                }
+            }
+        }
+    }
+
+    static String workDir = System.getProperty("user.dir");
+
+    String destPath;
+    SourceKind sk1;
+    SourceKind sk2;
+    TestKind tk;
+    ClientKind ck;
+
+    TestCircularClassfile(String destPath, SourceKind sk1, SourceKind sk2, TestKind tk, ClientKind ck) {
+        this.destPath = destPath;
+        this.sk1 = sk1;
+        this.sk2 = sk2;
+        this.tk = tk;
+        this.ck = ck;
+    }
+
+    void check(JavaCompiler comp, StandardJavaFileManager fm) throws Exception {
+        //step 1: compile first source code in the test subfolder
+        File destDir = new File(workDir, destPath); destDir.mkdir();
+        //output dir must be set explicitly as we are sharing the fm (see bug 7026941)
+        fm.setLocation(javax.tools.StandardLocation.CLASS_OUTPUT, Arrays.asList(destDir));
+        JavacTask ct = (JavacTask)comp.getTask(null, fm, null,
+                null, null, Arrays.asList(sk1.getSource()));
+        ct.generate();
+
+        //step 2: compile second source code in a temp folder
+        File tmpDir = new File(destDir, "tmp"); tmpDir.mkdir();
+        //output dir must be set explicitly as we are sharing the fm (see bug 7026941)
+        fm.setLocation(javax.tools.StandardLocation.CLASS_OUTPUT, Arrays.asList(tmpDir));
+        ct = (JavacTask)comp.getTask(null, fm, null,
+                null, null, Arrays.asList(sk2.getSource()));
+        ct.generate();
+
+        //step 3: move a classfile from the temp folder to the test subfolder
+        File fileToMove = new File(tmpDir, tk.targetClass);
+        File target = new File(destDir, tk.targetClass);
+        boolean success = fileToMove.renameTo(target);
+
+        if (!success) {
+            throw new AssertionError("error when moving file " + tk.targetClass);
+        }
+
+        //step 4: compile the client class against the classes in the test subfolder
+        //input/output dir must be set explicitly as we are sharing the fm (see bug 7026941)
+        fm.setLocation(StandardLocation.CLASS_OUTPUT, Arrays.asList(destDir));
+        fm.setLocation(StandardLocation.CLASS_PATH, Arrays.asList(destDir));
+        ct = (JavacTask)comp.getTask(null, fm, null,
+                null, null, Arrays.asList(ck.getSource()));
+
+        ct.generate();
+    }
+}