Improve metadata resolution timing in assistant app's say method

slack_bolt/context/assistant/assistant_utilities.py

@@ -63,14 +63,17 @@ def set_suggested_prompts(self) -> SetSuggestedPrompts:
 
     @property
     def say(self) -> Say:
+        def build_metadata() -> Optional[dict]:
+            thread_context = self.get_thread_context()
+            if thread_context is not None:
+                return {"event_type": "assistant_thread_context", "event_payload": thread_context}
+            return None
+
         return Say(
             self.client,
             channel=self.channel_id,
             thread_ts=self.thread_ts,
-            metadata={
-                "event_type": "assistant_thread_context",
-                "event_payload": self.get_thread_context(),
-            },
+            build_metadata=build_metadata,
         )
 
     @property

slack_bolt/context/say/say.py

@@ -1,4 +1,4 @@
-from typing import Optional, Union, Dict, Sequence
+from typing import Optional, Union, Dict, Sequence, Callable
 
 from slack_sdk import WebClient
 from slack_sdk.models.attachments import Attachment
@@ -15,18 +15,21 @@ class Say:
     channel: Optional[str]
     thread_ts: Optional[str]
     metadata: Optional[Union[Dict, Metadata]]
+    build_metadata: Optional[Callable[[], Optional[Union[Dict, Metadata]]]]
 
     def __init__(
         self,
         client: Optional[WebClient],
         channel: Optional[str],
         thread_ts: Optional[str] = None,
         metadata: Optional[Union[Dict, Metadata]] = None,
+        build_metadata: Optional[Callable[[], Optional[Union[Dict, Metadata]]]] = None,
     ):
         self.client = client
         self.channel = channel
         self.thread_ts = thread_ts
         self.metadata = metadata
+        self.build_metadata = build_metadata
 
     def __call__(
         self,
@@ -52,6 +55,8 @@ def __call__(
             text_or_whole_response: Union[str, dict] = text
             if isinstance(text_or_whole_response, str):
                 text = text_or_whole_response
+                if metadata is None:
+                    metadata = self.build_metadata() if self.build_metadata is not None else self.metadata
                 return self.client.chat_postMessage(  # type: ignore[union-attr]
                     channel=channel or self.channel,  # type: ignore[arg-type]
                     text=text,
@@ -68,7 +73,7 @@ def __call__(
                     mrkdwn=mrkdwn,
                     link_names=link_names,
                     parse=parse,
-                    metadata=metadata or self.metadata,
+                    metadata=metadata,
                     **kwargs,
                 )
             elif isinstance(text_or_whole_response, dict):
@@ -78,7 +83,8 @@ def __call__(
                 if "thread_ts" not in message:
                     message["thread_ts"] = thread_ts or self.thread_ts
                 if "metadata" not in message:
-                    message["metadata"] = metadata or self.metadata
+                    metadata = self.build_metadata() if self.build_metadata is not None else self.metadata
+                    message["metadata"] = metadata
                 return self.client.chat_postMessage(**message)  # type: ignore[union-attr]
             else:
                 raise ValueError(f"The arg is unexpected type ({type(text_or_whole_response)})")