fix: Check Agent's prompt template variables and prompt resolver parameters are aligned (#5163)

* Check Agent's prompt template parameters and prompt resolver parameters are aligned

* Lower the logger warning

* Automatically append transcript if needed

* Amend flaky test

haystack/agents/base.py

@@ -396,17 +396,15 @@ class Agent:
         # first resolve prompt template params
         template_params = self.prompt_parameters_resolver(query=query, agent=self, agent_step=current_step)
 
-        # if prompt node has no default prompt template, use agent's prompt template
-        if self.prompt_node.default_prompt_template is None:
-            prepared_prompt = next(self.prompt_template.fill(**template_params))
-            prompt_node_response = self.prompt_node(
-                prepared_prompt, stream_handler=AgentTokenStreamingHandler(self.callback_manager)
-            )
-        # otherwise, if prompt node has default prompt template, use it
-        else:
-            prompt_node_response = self.prompt_node(
-                stream_handler=AgentTokenStreamingHandler(self.callback_manager), **template_params
-            )
+        # check for template parameters mismatch
+        self.check_prompt_template(template_params)
+
+        # invoke via prompt node
+        prompt_node_response = self.prompt_node.prompt(
+            prompt_template=self.prompt_template,
+            stream_handler=AgentTokenStreamingHandler(self.callback_manager),
+            **template_params,
+        )
         return prompt_node_response
 
     def create_agent_step(self, max_steps: Optional[int] = None) -> AgentStep:
@@ -422,3 +420,35 @@ class Agent:
         return {
             k: v if isinstance(v, str) else next(iter(v)) for k, v in kwargs.items() if isinstance(v, (str, Iterable))
         }
+
+    def check_prompt_template(self, template_params: Dict[str, Any]) -> None:
+        """
+        Verifies that the Agent's prompt template is adequately populated with the correct parameters
+        provided by the prompt parameter resolver.
+
+        If template_params contains a parameter that is not specified in the prompt template, a warning is logged
+        at DEBUG level. Sometimes the prompt parameter resolver may provide additional parameters that are not
+        used by the prompt template. However, if the prompt parameter resolver provides a 'transcript'
+        parameter that is not used in the prompt template, an error is logged.
+
+        :param template_params: The parameters provided by the prompt parameter resolver.
+
+        """
+        unused_params = set(template_params.keys()) - set(self.prompt_template.prompt_params)
+
+        if "transcript" in unused_params:
+            logger.warning(
+                "The 'transcript' parameter is missing from the Agent's prompt template. All ReAct agents "
+                "that go through multiple steps to reach a goal require this parameter. Please append {transcript} "
+                "to the end of the Agent's prompt template to ensure its proper functioning. A temporary prompt "
+                "template with {transcript} appended will be used for this run."
+            )
+            new_prompt_text = self.prompt_template.prompt_text + "\n {transcript}"
+            self.prompt_template = PromptTemplate(prompt=new_prompt_text)
+
+        elif unused_params:
+            logger.debug(
+                "The Agent's prompt template does not utilize the following parameters provided by the "
+                "prompt parameter resolver: %s. Note that these parameters are available for use if needed.",
+                list(unused_params),
+            )

test/agents/test_agent.py

@@ -2,18 +2,17 @@ import logging
 import os
 import re
 from typing import Tuple
-from unittest.mock import Mock, patch
-
-from events import Events
-
-from haystack.agents.types import AgentTokenStreamingHandler, AgentToolLogger
-from test.conftest import MockRetriever, MockPromptNode
 from unittest import mock
+from unittest.mock import Mock, patch
+from test.conftest import MockRetriever, MockPromptNode
+
 import pytest
+from events import Events
 
 from haystack import BaseComponent, Answer, Document
 from haystack.agents import Agent, AgentStep
 from haystack.agents.base import Tool, ToolsManager
+from haystack.agents.types import AgentTokenStreamingHandler, AgentToolLogger
 from haystack.nodes import PromptModel, PromptNode, PromptTemplate
 from haystack.pipelines import ExtractiveQAPipeline, DocumentSearchPipeline, BaseStandardPipeline
 
@@ -356,3 +355,77 @@ def test_agent_token_streaming_handler():
 
     assert result == "test"
     mock_callback.assert_called_once_with("test")  # assert that the mock callback was called with "test"
+
+
+@pytest.mark.unit
+def test_agent_prompt_template_parameter_has_transcript(caplog):
+    mock_prompt_node = Mock(spec=PromptNode)
+    prompt = PromptTemplate(prompt="I now have {query} as a template parameter but also {transcript}")
+    mock_prompt_node.get_prompt_template.return_value = prompt
+
+    agent = Agent(prompt_node=mock_prompt_node)
+    agent.check_prompt_template({"query": "test", "transcript": "some fake transcript"})
+    assert "The 'transcript' parameter is missing from the Agent's prompt template" not in caplog.text
+
+
+@pytest.mark.unit
+def test_agent_prompt_template_has_no_transcript(caplog):
+    mock_prompt_node = Mock(spec=PromptNode)
+    prompt = PromptTemplate(prompt="I only have {query} as a template parameter but I am missing transcript variable")
+    mock_prompt_node.get_prompt_template.return_value = prompt
+    agent = Agent(prompt_node=mock_prompt_node)
+
+    # We start with no transcript in the prompt template
+    assert "transcript" not in prompt.prompt_params
+    assert "transcript" not in agent.prompt_template.prompt_params
+
+    agent.check_prompt_template({"query": "test", "transcript": "some fake transcript"})
+    assert "The 'transcript' parameter is missing from the Agent's prompt template" in caplog.text
+
+    # now let's check again after adding the transcript
+    # query was there to begin with
+    assert "query" in agent.prompt_template.prompt_params
+    # transcript was added automatically for this prompt template and run
+    assert "transcript" in agent.prompt_template.prompt_params
+
+
+@pytest.mark.unit
+def test_agent_prompt_template_unused_parameters(caplog):
+    caplog.set_level(logging.DEBUG)
+    mock_prompt_node = Mock(spec=PromptNode)
+    prompt = PromptTemplate(prompt="I now have {query} and {transcript} as template parameters")
+    mock_prompt_node.get_prompt_template.return_value = prompt
+    agent = Agent(prompt_node=mock_prompt_node)
+    agent.check_prompt_template({"query": "test", "transcript": "some fake transcript", "unused": "test"})
+    assert (
+        "The Agent's prompt template does not utilize the following parameters provided by the "
+        "prompt parameter resolver: ['unused']" in caplog.text
+    )
+
+
+@pytest.mark.unit
+def test_agent_prompt_template_multiple_unused_parameters(caplog):
+    caplog.set_level(logging.DEBUG)
+    mock_prompt_node = Mock(spec=PromptNode)
+    prompt = PromptTemplate(prompt="I now have strange {param_1} and {param_2} as template parameters")
+    mock_prompt_node.get_prompt_template.return_value = prompt
+    agent = Agent(prompt_node=mock_prompt_node)
+    agent.check_prompt_template({"query": "test", "unused": "test"})
+    # order of parameters in the list not guaranteed, so we check for preamble of the message
+    assert (
+        "The Agent's prompt template does not utilize the following parameters provided by the "
+        "prompt parameter resolver" in caplog.text
+    )
+
+
+@pytest.mark.unit
+def test_agent_prompt_template_missing_parameters(caplog):
+    # in check_prompt_template we don't check that all prompt template parameters are filled
+    # prompt template resolution will do that and flag the missing parameters
+    # in check_prompt_template we check if some template parameters are not used
+    mock_prompt_node = Mock(spec=PromptNode)
+    prompt = PromptTemplate(prompt="I now have {query} and {transcript} as template parameters")
+    mock_prompt_node.get_prompt_template.return_value = prompt
+    agent = Agent(prompt_node=mock_prompt_node)
+    agent.check_prompt_template({"transcript": "test"})
+    assert not caplog.text