[Discussion] Handling variables in deferred scopes

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

@@ -18,6 +18,7 @@
 
 import com.google.common.collect.HashMultimap;
 import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Maps;
 import com.google.common.collect.SetMultimap;
 import com.hubspot.jinjava.lib.Importable;
 import com.hubspot.jinjava.lib.exptest.ExpTest;
@@ -269,9 +270,21 @@ public void addResolvedFunction(String function) {
   }
 
   public void addDeferredNode(Node node) {
+    addDeferredNodeAndContext(node, 1);
+  }
+
+  //depth is "height" back up the context tree here
+  private void addDeferredNodeAndContext(Node node, int currentDepth) {
     deferredNodes.add(node);
+
+    if (getParent() != null && currentDepth++ == 0) {
+      Map<String, Object> localDifference = Maps
+        .difference(getParent(), this)
+        .entriesOnlyOnRight();
+      getParent().putAll(localDifference);
+    }
     if (getParent() != null) {
-      getParent().addDeferredNode(node);
+      getParent().addDeferredNodeAndContext(node, currentDepth);
     }
   }
 

src/test/java/com/hubspot/jinjava/interpret/DeferredTest.java

@@ -2,6 +2,7 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+import com.google.common.base.Joiner;
 import com.hubspot.jinjava.Jinjava;
 import com.hubspot.jinjava.JinjavaConfig;
 import com.hubspot.jinjava.random.RandomNumberGeneratorStrategy;
@@ -183,4 +184,49 @@ public void itDefersMacro() {
     String output = interpreter.render(deferredOutput);
     assertThat(output).isEqualTo("0,10,15,25");
   }
+
+  @Test
+  public void itPreservesVariablesUsedInDeferredBlock() {
+    String template = "";
+    template += "{% for item in resolved %}";
+    template += "{% set varUsedInForScope = 'outside if statement' %}";
+    template += "   {% if deferred %}";
+    template += "     {{ varUsedInForScope }}";
+    template += "     {% set varUsedInForScope = 'entered if statement' %}";
+    template += "   {% endif %}";
+    template += "   {{ varUsedInForScope }}";
+    template += "{% endfor %}";
+
+    String desiredDeferredOutput =
+      "   {% if deferred %}     {{ varUsedInForScope }}     {% set varUsedInForScope = 'entered if statement' %}   {% endif %}   {{ varUsedInForScope }}";
+    String output = interpreter.render(template);
+    //No Scope Copying:
+    //Interpreter Scope after render:
+    // deferred=com.hubspot.jinjava.interpret.DeferredValue@1af2d44a
+    // resolved=resolvedValue
+    //Note that varUsedInForScope is lost
+    //Output 1st render: {% if deferred %}     {{ varUsedInForScope }}     {% set varUsedInForScope = 'entered if statement' %}   {% endif %}   outside if statement
+    //Output 2nd render:                   outside if statement
+    //Note the missing first print statement from inside the deferred statement. The printed statement is simply preserved from the 1st render and should have the value "entered if statement"
+
+    //With Scope Copying:
+    // resolved=resolvedValue
+    // loop=com.hubspot.jinjava.util.ForLoop@c88a337
+    // varUsedInForScope=outside if statement
+    // item=resolvedValue
+    // deferred=com.hubspot.jinjava.interpret.DeferredValue@5d0a1059
+    //Output 1st render: {% if deferred %}     {{ varUsedInForScope }}     {% set varUsedInForScope = 'entered if statement' %}   {% endif %}   outside if statement
+    //Output 2nd render:         outside if statement           outside if statement
+    //This result is more functional as it allows the var in the if block to be evaluated but it does not have the expected new value for varUsedInForScope
+
+    Joiner.MapJoiner mapJoiner = Joiner.on(",").withKeyValueSeparator("=");
+
+    System.out.println(mapJoiner.join(interpreter.getContext()));
+    //assertThat(output).isEqualTo(desiredDeferredOutput);
+
+    interpreter.getContext().put("deferred", "resolved");
+    String outputWithNoDeferredValues = interpreter.render(output);
+    String expectedOutputWithNoDeferred = "outside if statement    entered if statement";
+    assertThat(outputWithNoDeferredValues).isEqualTo(expectedOutputWithNoDeferred);
+  }
 }