Implement argument handling in macro caller functionality

src/main/java/com/hubspot/jinjava/lib/tag/CallTag.java

@@ -65,20 +65,40 @@ public String getName() {
 
   @Override
   public String interpret(TagNode tagNode, JinjavaInterpreter interpreter) {
-    String macroExpr = "{{" + tagNode.getHelpers().trim() + "}}";
+    String macroCallExpr = tagNode.getHelpers().trim();
+
+    LinkedHashMap<String, Object> argNamesWithDefaults = new LinkedHashMap<>();
+
+    if (macroCallExpr.startsWith("(")) {
+      int closeIdx = macroCallExpr.indexOf(')');
+      if (closeIdx != -1) {
+        String params = macroCallExpr.substring(1, closeIdx).trim();
+        if (!params.isEmpty()) {
+          MacroTag.populateArgNames(
+            tagNode.getLineNumber(),
+            interpreter,
+            params,
+            argNamesWithDefaults
+          );
+        }
+        macroCallExpr = macroCallExpr.substring(closeIdx + 1).trim();
+      }
+    }
+
+    String macroExpr = "{{" + macroCallExpr + "}}";
 
     try (InterpreterScopeClosable c = interpreter.enterNonStackingScope()) {
-      LinkedHashMap<String, Object> args = new LinkedHashMap<>();
       MacroFunction caller = new MacroFunction(
         tagNode.getChildren(),
         "caller",
-        args,
+        argNamesWithDefaults,
         true,
         interpreter.getContext(),
         interpreter.getLineNumber(),
         interpreter.getPosition()
       );
       interpreter.getContext().addGlobalMacro(caller);
+      interpreter.getContext().put(caller.getName(), caller);
 
       return interpreter.render(macroExpr);
     }

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

@@ -45,6 +45,13 @@ public void itDoesNotDoubleCountCallTagTowardsDepth() throws IOException {
     }
   }
 
+  @Test
+  public void testCallerArgsFn() {
+    String result = interpreter.render(fixture("caller_args"));
+    System.out.println(result);
+    assertThat(result).isEqualTo(fixture("caller_args.expected"));
+  }
+
   private String fixture(String name) {
     try {
       return Resources.toString(

src/test/resources/tags/calltag/caller_args.expected.jinja

@@ -0,0 +1,9 @@
+start
+before
+    #a b c#
+after
+
+before
+    caller is undefined => #a b#
+after
+stop

src/test/resources/tags/calltag/caller_args.jinja

@@ -0,0 +1,17 @@
+start
+{% macro test(arg1, arg2) -%}
+before
+{%- if caller is undefined %}
+    caller is undefined => #{{ arg1 }} {{ arg2 }}#
+{%- else %}
+    {{ caller(arg1, arg2) }}
+{%- endif %}
+after
+{%- endmacro -%}
+
+{% call(arg1, arg2, arg3 = "c") test({"a_key": "a"}, "b") -%}
+#{{ arg1.a_key }} {{ arg2 }} {{ arg3 }}#
+{%- endcall %}
+
+{{ test("a", "b") }}
+stop