Python: Fix Handlebars messages helper ignoring its argument

python/semantic_kernel/prompt_template/utils/handlebars_system_helpers.py

@@ -10,12 +10,15 @@
 logger: logging.Logger = logging.getLogger(__name__)
 
 
-def _messages(this, options, *args, **kwargs):
+def _messages(this, *args, **kwargs):
     from semantic_kernel.contents.chat_history import ChatHistory
 
-    if not isinstance(this.context["chat_history"], ChatHistory):
+    # Use the argument passed to the helper, e.g. {{messages my_history}}.
+    # Fall back to the "chat_history" variable when no argument is given.
+    chat_history = args[0] if args else this.context.get("chat_history")
+    if not isinstance(chat_history, ChatHistory):
         return ""
-    return this.context["chat_history"].to_prompt()
+    return chat_history.to_prompt()
 
 
 def _message_to_prompt(this, *args, **kwargs):

python/tests/unit/prompt_template/test_handlebars_prompt_template.py

@@ -479,3 +479,37 @@ async def test_safe_types_are_allowed():
 
     assert "42" in result
     assert "true" in result
+
+
+async def test_helpers_chat_history_messages_uses_argument(kernel: Kernel):
+    template = """{{messages history}}"""
+    target = create_handlebars_prompt_template(template, allow_dangerously_set_content=True)
+    chat_history = ChatHistory()
+    chat_history.add_user_message("User message")
+    rendered = await target.render(kernel, KernelArguments(history=chat_history))
+    assert (
+        rendered.strip() == """<chat_history><message role="user"><text>User message</text></message></chat_history>"""
+    )
+
+
+async def test_helpers_chat_history_messages_prefers_argument_over_chat_history_variable(kernel: Kernel):
+    template = """{{messages other}}"""
+    target = create_handlebars_prompt_template(template, allow_dangerously_set_content=True)
+    wrong = ChatHistory()
+    wrong.add_user_message("WRONG")
+    right = ChatHistory()
+    right.add_user_message("RIGHT")
+    rendered = await target.render(kernel, KernelArguments(chat_history=wrong, other=right))
+    assert "RIGHT" in rendered
+    assert "WRONG" not in rendered
+
+
+async def test_helpers_chat_history_messages_without_argument_uses_chat_history_variable(kernel: Kernel):
+    template = """{{messages}}"""
+    target = create_handlebars_prompt_template(template, allow_dangerously_set_content=True)
+    chat_history = ChatHistory()
+    chat_history.add_user_message("User message")
+    rendered = await target.render(kernel, KernelArguments(chat_history=chat_history))
+    assert (
+        rendered.strip() == """<chat_history><message role="user"><text>User message</text></message></chat_history>"""
+    )