Fix(Chat): Always ensure Anthropic user message comes first (not just when token_limits are provided)

CHANGELOG.md

@@ -9,9 +9,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Bug fixes
 
-* Fixed a bug with `Chat()` sometimes silently dropping errors. (#1672)
-
-* Fixed a bug with `Chat()` sometimes not removing it's loading icon (on error or a `None` transform). (#1679)
+* A few fixes for `ui.Chat()`, including: 
+  * Fixed a bug with `Chat()` sometimes silently dropping errors. (#1672)
+  * Fixed a bug with `Chat()` sometimes not removing it's loading icon (on error or a `None` transform). (#1679)
+  * `.messages(format="anthropic")` correctly removes non-user starting messages (once again). (#1685)
 
 * `shiny create` now uses the template `id` rather than the directory name as the default directory. (#1666)
 

shiny/templates/chat/production/anthropic/app.py

@@ -52,8 +52,14 @@
 
 @chat.on_user_submit
 async def _():
-    messages = chat.messages(format="openai", token_limits=MODEL_INFO["token_limits"])
-    response = await llm.chat.completions.create(
-        model=MODEL_INFO["name"], messages=messages, stream=True
+    messages = chat.messages(
+        format="anthropic",
+        token_limits=MODEL_INFO["token_limits"],
+    )
+    response = await llm.messages.create(
+        model=MODEL_INFO["name"],
+        messages=messages,
+        stream=True,
+        max_tokens=MODEL_INFO["token_limits"][1],
     )
     await chat.append_message_stream(response)

shiny/ui/_chat.py

@@ -471,6 +471,11 @@ def messages(
         """
 
         messages = self._messages()
+
+        # Anthropic requires a user message first and no system messages
+        if format == "anthropic":
+            messages = self._trim_anthropic_messages(messages)
+
         if token_limits is not None:
             messages = self._trim_messages(messages, token_limits, format)
 
@@ -868,17 +873,6 @@ def _trim_messages(
                 messages2.append(m)
                 n_other_messages2 += 1
 
-        # Anthropic doesn't support `role: system` and requires a user message to come 1st
-        if format == "anthropic":
-            if n_system_messages > 0:
-                raise ValueError(
-                    "Anthropic requires a system prompt to be specified in it's `.create()` method "
-                    "(not in the chat messages with `role: system`)."
-                )
-            while n_other_messages2 > 0 and messages2[-1]["role"] != "user":
-                messages2.pop()
-                n_other_messages2 -= 1
-
         messages2.reverse()
 
         if len(messages2) == n_system_messages and n_other_messages2 > 0:
@@ -890,6 +884,22 @@ def _trim_messages(
 
         return tuple(messages2)
 
+    def _trim_anthropic_messages(
+        self,
+        messages: tuple[TransformedMessage, ...],
+    ) -> tuple[TransformedMessage, ...]:
+
+        if any(m["role"] == "system" for m in messages):
+            raise ValueError(
+                "Anthropic requires a system prompt to be specified in it's `.create()` method "
+                "(not in the chat messages with `role: system`)."
+            )
+        for i, m in enumerate(messages):
+            if m["role"] == "user":
+                return messages[i:]
+
+        return ()
+
     def _get_token_count(
         self,
         content: str,