Merge pull request #1150 from abarrafo/ab-debug-undefined

Debug Undefined Feature to echo back Uknown tokens.

Author: jasmith-hs

src/main/java/com/hubspot/jinjava/lib/expression/DefaultExpressionStrategy.java

@@ -1,5 +1,6 @@
 package com.hubspot.jinjava.lib.expression;
 
+import com.hubspot.jinjava.features.FeatureActivationStrategy;
 import com.hubspot.jinjava.interpret.JinjavaInterpreter;
 import com.hubspot.jinjava.lib.filter.EscapeFilter;
 import com.hubspot.jinjava.objects.SafeString;
@@ -11,6 +12,7 @@
 public class DefaultExpressionStrategy implements ExpressionStrategy {
 
   private static final long serialVersionUID = 436239440273704843L;
+  public static final String ECHO_UNDEFINED = "echoUndefined";
 
   public RenderedOutputNode interpretOutput(
     ExpressionToken master,
@@ -20,6 +22,16 @@ public RenderedOutputNode interpretOutput(
       master.getExpr(),
       master.getLineNumber()
     );
+
+    final FeatureActivationStrategy feat = interpreter
+      .getConfig()
+      .getFeatures()
+      .getActivationStrategy(ECHO_UNDEFINED);
+
+    if (var == null && feat.isActive(interpreter.getContext())) {
+      return new RenderedOutputNode(master.getImage());
+    }
+
     String result = interpreter.getAsString(var);
 
     if (interpreter.getConfig().isNestedInterpretationEnabled()) {

src/test/java/com/hubspot/jinjava/tree/ExpressionNodeTest.java

@@ -1,12 +1,15 @@
 package com.hubspot.jinjava.tree;
 
+import static com.hubspot.jinjava.lib.expression.DefaultExpressionStrategy.ECHO_UNDEFINED;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
 import com.google.common.io.Resources;
 import com.hubspot.jinjava.BaseInterpretingTest;
 import com.hubspot.jinjava.Jinjava;
 import com.hubspot.jinjava.JinjavaConfig;
+import com.hubspot.jinjava.features.FeatureConfig;
+import com.hubspot.jinjava.features.FeatureStrategies;
 import com.hubspot.jinjava.interpret.Context;
 import com.hubspot.jinjava.interpret.JinjavaInterpreter;
 import com.hubspot.jinjava.interpret.UnknownTokenException;
@@ -129,6 +132,29 @@ public void itRendersStringRange() throws Exception {
     assertThat(node.render(interpreter).toString()).isEqualTo("345");
   }
 
+  @Test
+  public void itRenderEchoUndefined() {
+    final JinjavaConfig config = JinjavaConfig
+      .newBuilder()
+      .withFeatureConfig(
+        FeatureConfig.newBuilder().add(ECHO_UNDEFINED, FeatureStrategies.ACTIVE).build()
+      )
+      .build();
+    final JinjavaInterpreter jinjavaInterpreter = new Jinjava(config).newInterpreter();
+    jinjavaInterpreter.getContext().put("subject", "this");
+
+    String template =
+      "{{ subject | capitalize() }} expression {{ testing.template('hello_world') }} " +
+      "has a {{ unknown | lower() }} " +
+      "token but {{ unknown | default(\"replaced\") }} and empty {{ '' }}";
+    Node node = new TreeParser(jinjavaInterpreter, template).buildTree();
+    assertThat(jinjavaInterpreter.render(node))
+      .isEqualTo(
+        "This expression {{ testing.template('hello_world') }} " +
+        "has a {{ unknown | lower() }} token but replaced and empty "
+      );
+  }
+
   @Test
   public void itFailsOnUnknownTokensVariables() throws Exception {
     final JinjavaConfig config = JinjavaConfig