Limit infinite evaluation from recursive extends tags

src/main/java/com/hubspot/jinjava/interpret/JinjavaInterpreter.java

@@ -53,6 +53,7 @@
 import java.io.IOException;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
@@ -308,8 +309,22 @@ public String render(Node root, boolean processExtendRoots) {
 
     // render all extend parents, keeping the last as the root output
     if (processExtendRoots) {
+      Set<String> extendPaths = new HashSet<>();
       Optional<String> extendPath = context.getExtendPathStack().peek();
       while (!extendParentRoots.isEmpty()) {
+        if (extendPaths.contains(extendPath.orElse(""))) {
+          addError(
+            TemplateError.fromException(
+              new ExtendsTagCycleException(
+                extendPath.orElse(""),
+                context.getExtendPathStack().getTopLineNumber(),
+                context.getExtendPathStack().getTopStartPosition()
+              )
+            )
+          );
+          break;
+        }
+        extendPaths.add(extendPath.orElse(""));
         context
           .getCurrentPathStack()
           .push(

src/test/java/com/hubspot/jinjava/lib/tag/ExtendsTagTest.java

@@ -244,6 +244,19 @@ public void itSetsErrorLineNumbersCorrectlyInBlocksFromExtendedTemplateInInclude
       .isEqualTo("/errors/error.html");
   }
 
+  @Test
+  public void itLimitsExtendsWithMultipleLevels() throws IOException {
+    // Previously this would run infinitely
+    RenderResult result = jinjava.renderForResult(
+      locator.fixture("rec1.jinja"),
+      new HashMap<>()
+    );
+    assertThat(result.getOutput().trim()).isEqualTo("foo");
+    assertThat(result.getErrors()).hasSize(1);
+    assertThat(result.getErrors().get(0).getMessage())
+      .contains("ExtendsTagCycleException");
+  }
+
   private static class ExtendsTagTestResourceLocator implements ResourceLocator {
     private RelativePathResolver relativePathResolver = new RelativePathResolver();
 

src/test/resources/tags/extendstag/rec1.jinja

@@ -0,0 +1,4 @@
+{% extends 'rec2.jinja' %}
+{% block body %}
+foo
+{% endblock %}

src/test/resources/tags/extendstag/rec2.jinja

@@ -0,0 +1,4 @@
+{% extends 'rec3.jinja' %}
+{% block body %}
+foobar
+{% endblock %}

src/test/resources/tags/extendstag/rec3.jinja

@@ -0,0 +1,4 @@
+{% extends 'rec3.jinja' %}
+{% block body %}
+baz
+{% endblock %}