From 836647231346e5d113fffaf33566ea3f618dbc9c Mon Sep 17 00:00:00 2001
From: Tamas Cservenak <tamas@cservenak.net>
Date: Wed, 5 Jun 2024 15:26:02 +0200
Subject: [PATCH 1/2] [MNG-8066] Default exception handler does not handle
 recursion

If there is a recursion in throwable causes, Maven will
hang forever, instead to return.

---

https://issues.apache.org/jira/browse/MNG-8066
---
 .../exception/DefaultExceptionHandler.java    | 24 ++++++++++++++-----
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/maven-core/src/main/java/org/apache/maven/exception/DefaultExceptionHandler.java b/maven-core/src/main/java/org/apache/maven/exception/DefaultExceptionHandler.java
index 32c289c6699a..997656b30f0d 100644
--- a/maven-core/src/main/java/org/apache/maven/exception/DefaultExceptionHandler.java
+++ b/maven-core/src/main/java/org/apache/maven/exception/DefaultExceptionHandler.java
@@ -22,7 +22,10 @@
 import java.net.ConnectException;
 import java.net.UnknownHostException;
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.IdentityHashMap;
 import java.util.List;
+import java.util.Set;
 
 import org.apache.maven.lifecycle.LifecycleExecutionException;
 import org.apache.maven.model.building.ModelProblem;
@@ -87,13 +90,13 @@
  */
 @Component(role = ExceptionHandler.class)
 public class DefaultExceptionHandler implements ExceptionHandler {
-
+    @Override
     public ExceptionSummary handleException(Throwable exception) {
         return handle("", exception);
     }
 
     private ExceptionSummary handle(String message, Throwable exception) {
-        String reference = getReference(exception);
+        String reference = getReference(Collections.newSetFromMap(new IdentityHashMap<>()), exception);
 
         List<ExceptionSummary> children = null;
 
@@ -153,8 +156,11 @@ private ExceptionSummary handle(ModelProblem problem, String projectId) {
         }
     }
 
-    private String getReference(Throwable exception) {
+    private String getReference(Set<Throwable> dejaVu, Throwable exception) {
         String reference = "";
+        if (!dejaVu.add(exception)) {
+            return reference;
+        }
 
         if (exception != null) {
             if (exception instanceof MojoExecutionException) {
@@ -186,14 +192,14 @@ private String getReference(Throwable exception) {
                 }
 
                 if (StringUtils.isEmpty(reference)) {
-                    reference = getReference(cause);
+                    reference = getReference(dejaVu, cause);
                 }
 
                 if (StringUtils.isEmpty(reference)) {
                     reference = exception.getClass().getSimpleName();
                 }
             } else if (exception instanceof LifecycleExecutionException) {
-                reference = getReference(exception.getCause());
+                reference = getReference(dejaVu, exception.getCause());
             } else if (isNoteworthyException(exception)) {
                 reference = exception.getClass().getSimpleName();
             }
@@ -222,7 +228,8 @@ private boolean isNoteworthyException(Throwable exception) {
     private String getMessage(String message, Throwable exception) {
         String fullMessage = (message != null) ? message : "";
 
-        // To break out of possible endless loop when getCause returns "this"
+        // To break out of possible endless loop when getCause returns "this", or dejaVu for n-level recursion (n>1)
+        Set<Throwable> dejaVu = Collections.newSetFromMap(new IdentityHashMap<>());
         for (Throwable t = exception; t != null && t != t.getCause(); t = t.getCause()) {
             String exceptionMessage = t.getMessage();
 
@@ -246,6 +253,11 @@ private String getMessage(String message, Throwable exception) {
             } else if (!fullMessage.contains(exceptionMessage)) {
                 fullMessage = join(fullMessage, exceptionMessage);
             }
+
+            if (!dejaVu.add(t)) {
+                fullMessage = join(fullMessage, "[CIRCULAR REFERENCE]");
+                break;
+            }
         }
 
         return fullMessage.trim();

From 6c6505044cfbe6ca55e5f54c118e105cf0d99256 Mon Sep 17 00:00:00 2001
From: Tamas Cservenak <tamas@cservenak.net>
Date: Thu, 6 Jun 2024 11:30:47 +0200
Subject: [PATCH 2/2] Add UT

---
 .../exception/DefaultExceptionHandlerTest.java   | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/maven-core/src/test/java/org/apache/maven/exception/DefaultExceptionHandlerTest.java b/maven-core/src/test/java/org/apache/maven/exception/DefaultExceptionHandlerTest.java
index 33fe83c21d6b..6a14ffa1a848 100644
--- a/maven-core/src/test/java/org/apache/maven/exception/DefaultExceptionHandlerTest.java
+++ b/maven-core/src/test/java/org/apache/maven/exception/DefaultExceptionHandlerTest.java
@@ -124,4 +124,20 @@ public synchronized Throwable getCause() {
         String expectedReference = "http://cwiki.apache.org/confluence/display/MAVEN/PluginContainerException";
         assertEquals(expectedReference, summary.getReference());
     }
+
+    @Test
+    public void testHandleExceptionSelfReferencing() {
+        RuntimeException boom3 = new RuntimeException("BOOM3");
+        RuntimeException boom2 = new RuntimeException("BOOM2", boom3);
+        RuntimeException boom1 = new RuntimeException("BOOM1", boom2);
+        boom3.initCause(boom1);
+
+        DefaultExceptionHandler handler = new DefaultExceptionHandler();
+        ExceptionSummary summary = handler.handleException(boom1);
+
+        assertEquals("BOOM1: BOOM2: BOOM3: [CIRCULAR REFERENCE]", summary.getMessage());
+        assertEquals("", summary.getReference());
+        assertEquals(0, summary.getChildren().size());
+        assertEquals(boom1, summary.getException());
+    }
 }