At some point, Google stopped requiring "function" and switched to "user". Vertex requires this, now.

Author: afirstenberg

libs/providers/langchain-google/src/converters/messages.ts

@@ -394,8 +394,8 @@ function convertStandardContentMessageToGeminiContent(
   } else if (AIMessage.isInstance(message)) {
     role = "model";
   } else if (ToolMessage.isInstance(message)) {
-    // Tool messages in Gemini are represented as function responses
-    role = "function";
+    // Tool messages in Gemini were represented as function responses, but now are "user"
+    role = "user";
   } else if (ChatMessage.isInstance(message)) {
     // Map ChatMessage roles to Gemini roles
     const msgRole = message.role.toLowerCase();
@@ -408,7 +408,7 @@ function convertStandardContentMessageToGeminiContent(
     ) {
       role = "model";
     } else if (msgRole === "function" || msgRole === "tool") {
-      role = "function";
+      role = "user";
     } else {
       // Default to user for unknown roles
       role = "user";
@@ -648,8 +648,8 @@ function convertLegacyContentMessageToGeminiContent(
     } else if (AIMessage.isInstance(message)) {
       return "model";
     } else if (ToolMessage.isInstance(message)) {
-      // Tool messages in Gemini are represented as function responses
-      return "function";
+      // Tool messages in Gemini were represented as function responses, but now are "user"
+      return "user";
     } else if (ChatMessage.isInstance(message)) {
       // Map ChatMessage roles to Gemini roles
       const msgRole = message.role.toLowerCase();
@@ -662,7 +662,7 @@ function convertLegacyContentMessageToGeminiContent(
       ) {
         return "model";
       } else if (msgRole === "function" || msgRole === "tool") {
-        return "function";
+        return "user";
       } else {
         // Default to user for unknown roles
         return "user";
@@ -735,11 +735,6 @@ function convertLegacyContentMessageToGeminiContent(
     });
   }
 
-  // Remove non-functionResponse parts if this is a tool response
-  if (role === "function") {
-    parts = parts.filter((part) => "functionResponse" in part);
-  }
-
   // Only add content if we have parts
   if (parts.length > 0) {
     return { role, parts };