Handle circular references.

core/src/main/java/hudson/Functions.java

@@ -156,6 +156,8 @@ import com.google.common.base.Predicate;
 import com.google.common.base.Predicates;
 import hudson.model.PasswordParameterDefinition;
 import hudson.util.RunList;
+import java.util.HashSet;
+import java.util.Set;
 import java.util.concurrent.atomic.AtomicLong;
 import javax.annotation.CheckForNull;
 import javax.annotation.Nonnull;
@@ -1453,10 +1455,14 @@ public class Functions {
             return Messages.Functions_NoExceptionDetails();
         }
         StringBuilder s = new StringBuilder();
-        doPrintStackTrace(s, t, null, "");
+        doPrintStackTrace(s, t, null, "", new HashSet<Throwable>());
         return s.toString();
     }
-    private static void doPrintStackTrace(@Nonnull StringBuilder s, @Nonnull Throwable t, @CheckForNull Throwable higher, @Nonnull String prefix) {
+    private static void doPrintStackTrace(@Nonnull StringBuilder s, @Nonnull Throwable t, @CheckForNull Throwable higher, @Nonnull String prefix, @Nonnull Set<Throwable> encountered) {
+        if (!encountered.add(t)) {
+            s.append("<cycle to ").append(t).append(">\n");
+            return;
+        }
         if (Util.isOverridden(Throwable.class, t.getClass(), "printStackTrace", PrintWriter.class)) {
             StringWriter sw = new StringWriter();
             t.printStackTrace(new PrintWriter(sw));
@@ -1465,11 +1471,11 @@ public class Functions {
         }
         Throwable lower = t.getCause();
         if (lower != null) {
-            doPrintStackTrace(s, lower, t, prefix);
+            doPrintStackTrace(s, lower, t, prefix, encountered);
         }
         for (Throwable suppressed : t.getSuppressed()) {
             s.append(prefix).append("Also:   ");
-            doPrintStackTrace(s, suppressed, t, prefix + "\t");
+            doPrintStackTrace(s, suppressed, t, prefix + "\t", encountered);
         }
         if (lower != null) {
             s.append(prefix).append("Caused: ");

core/src/test/java/hudson/FunctionsTest.java

@@ -501,6 +501,22 @@ public class FunctionsTest {
                 s.println("Some custom exception");
             }
         }, "Some custom exception\n", "Some custom exception\n");
+        // Circular references:
+        Stack stack1 = new Stack("p.Exc1", "p.C.method1:17");
+        Stack stack2 = new Stack("p.Exc2", "p.C.method2:27");
+        stack1.cause(stack2);
+        stack2.cause(stack1);
+        assertPrintThrowable(stack1,
+            "p.Exc1\n" +
+            "\tat p.C.method1(C.java:17)\n" +
+            "Caused by: p.Exc2\n" +
+            "\tat p.C.method2(C.java:27)\n" +
+            "\t[CIRCULAR REFERENCE:p.Exc1]\n",
+            "<cycle to p.Exc1>\n" +
+            "Caused: p.Exc2\n" +
+            "\tat p.C.method2(C.java:27)\n" +
+            "Caused: p.Exc1\n" +
+            "\tat p.C.method1(C.java:17)\n");
     }
     private static void assertPrintThrowable(Throwable t, String traditional, String custom) {
         StringWriter sw = new StringWriter();