fix: append runtime meta to ChatMessage's extracted meta in AnswerBuilder (#8544)

* append runtime meta to extracted meta

* add pylint ignore flag to .run()

* explicitly convert reply to string

haystack/components/builders/answer_builder.py

@@ -58,7 +58,7 @@ class AnswerBuilder:
         self.reference_pattern = reference_pattern
 
     @component.output_types(answers=List[GeneratedAnswer])
-    def run(
+    def run(  # pylint: disable=too-many-positional-arguments
         self,
         query: str,
         replies: Union[List[str], List[ChatMessage]],
@@ -111,10 +111,13 @@ class AnswerBuilder:
         pattern = pattern or self.pattern
         reference_pattern = reference_pattern or self.reference_pattern
         all_answers = []
-        for reply, metadata in zip(replies, meta):
+        for reply, given_metadata in zip(replies, meta):
             # Extract content from ChatMessage objects if reply is a ChatMessages, else use the string as is
-            extracted_reply: str = reply.content if isinstance(reply, ChatMessage) else reply  # type: ignore
+            extracted_reply = reply.content if isinstance(reply, ChatMessage) else str(reply)
-            extracted_metadata = reply.meta if isinstance(reply, ChatMessage) else metadata
+            extracted_metadata = reply.meta if isinstance(reply, ChatMessage) else {}
+
+            extracted_metadata = {**extracted_metadata, **given_metadata}
+
             referenced_docs = []
             if documents:
                 if reference_pattern:

releasenotes/notes/merge_runtime_meta_in_answerbuilder-4103b4ca4590aea5.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    When meta is passed into AnswerBuilder.run(), it is now merged into GeneratedAnswer meta

test/components/builders/test_answer_builder.py

@@ -36,6 +36,16 @@ class TestAnswerBuilder:
         assert answers[0].documents == []
         assert isinstance(answers[0], GeneratedAnswer)
 
+    def test_run_with_meta(self):
+        component = AnswerBuilder()
+        output = component.run(query="query", replies=["reply1"], meta=[{"test": "meta"}])
+        answers = output["answers"]
+        assert answers[0].data == "reply1"
+        assert answers[0].meta == {"test": "meta"}
+        assert answers[0].query == "query"
+        assert answers[0].documents == []
+        assert isinstance(answers[0], GeneratedAnswer)
+
     def test_run_without_pattern(self):
         component = AnswerBuilder()
         output = component.run(query="test query", replies=["Answer: AnswerString"], meta=[{}])
@@ -272,3 +282,45 @@ class TestAnswerBuilder:
         assert answers[0].query == "test query"
         assert answers[0].documents == []
         assert isinstance(answers[0], GeneratedAnswer)
+
+    def test_run_with_chat_message_replies_with_meta_set_at_run_time(self):
+        component = AnswerBuilder()
+        replies = [
+            ChatMessage(
+                content="AnswerString",
+                role=ChatRole.ASSISTANT,
+                name=None,
+                meta={
+                    "model": "gpt-4o-mini",
+                    "index": 0,
+                    "finish_reason": "stop",
+                    "usage": {"prompt_tokens": 32, "completion_tokens": 153, "total_tokens": 185},
+                },
+            )
+        ]
+        output = component.run(query="test query", replies=replies, meta=[{"test": "meta"}])
+        answers = output["answers"]
+        assert len(answers) == 1
+        assert answers[0].data == "AnswerString"
+        assert answers[0].meta == {
+            "model": "gpt-4o-mini",
+            "index": 0,
+            "finish_reason": "stop",
+            "usage": {"prompt_tokens": 32, "completion_tokens": 153, "total_tokens": 185},
+            "test": "meta",
+        }
+        assert answers[0].query == "test query"
+        assert answers[0].documents == []
+        assert isinstance(answers[0], GeneratedAnswer)
+
+    def test_run_with_chat_message_no_meta_with_meta_set_at_run_time(self):
+        component = AnswerBuilder()
+        replies = [ChatMessage(content="AnswerString", role=ChatRole.ASSISTANT, name=None, meta={})]
+        output = component.run(query="test query", replies=replies, meta=[{"test": "meta"}])
+        answers = output["answers"]
+        assert len(answers) == 1
+        assert answers[0].data == "AnswerString"
+        assert answers[0].meta == {"test": "meta"}
+        assert answers[0].query == "test query"
+        assert answers[0].documents == []
+        assert isinstance(answers[0], GeneratedAnswer)