Prevent StackOverflowError when filtering exception cause loops (#1922)

spock-core/src/main/java/org/spockframework/runtime/StackTraceFilter.java

@@ -18,10 +18,14 @@
 import org.spockframework.util.InternalIdentifiers;
 
 import java.util.ArrayList;
+import java.util.IdentityHashMap;
 import java.util.List;
+import java.util.Set;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+import static java.util.Collections.newSetFromMap;
+
 /**
  * Filters an exception's stack trace. Removes internal Groovy and Spock methods, and
  * restores the original names of feature methods (as specified in source code).
@@ -58,6 +62,14 @@ public StackTraceFilter(IMethodNameMapper mapper) {
 
   @Override
   public void filter(Throwable throwable) {
+    filter(throwable, newSetFromMap(new IdentityHashMap<>()));
+  }
+
+  private void filter(Throwable throwable, Set<Throwable> seen) {
+    if (!seen.add(throwable)) {
+      return;
+    }
+
     List<StackTraceElement> filteredTrace = new ArrayList<>();
 
     for (StackTraceElement elem : throwable.getStackTrace()) {
@@ -74,7 +86,7 @@ public void filter(Throwable throwable) {
 
     throwable.setStackTrace(filteredTrace.toArray(STACK_TRACE_ELEMENTS));
 
-    if (throwable.getCause() != null) filter(throwable.getCause());
+    if (throwable.getCause() != null) filter(throwable.getCause(), seen);
   }
 
   private boolean isInitializerOrFixtureMethod(StackTraceElement elem) {

spock-specs/src/test/groovy/org/spockframework/smoke/StackTraceFiltering.groovy

@@ -364,4 +364,33 @@ org.spockframework.runtime.foo.Baz|bar|0
 org.spockframework.runtime.foo.Baz|bar|0
     """
   }
+
+  def "exception cause loops do not cause StackOverflowError"() {
+    when:
+    runner.runFeatureBody """
+when:
+def e = new Exception()
+def cause = new Exception(e)
+e.initCause(cause)
+throw e
+
+then:
+thrown(RuntimeException)
+    """
+
+    then:
+    WrongExceptionThrownError e = thrown()
+
+    stackTraceLooksLike e.cause, """
+apackage.ASpec|a feature|2
+    """
+
+    stackTraceLooksLike e.cause.cause, """
+apackage.ASpec|a feature|3
+    """
+
+    stackTraceLooksLike e.cause.cause.cause, """
+apackage.ASpec|a feature|2
+    """
+  }
 }