fix(anthropic): Handle parallel tool result blocks

libs/langchain-anthropic/src/tests/chat_models-tools.int.test.ts

@@ -625,3 +625,64 @@ test("Can bound and invoke different tool types", async () => {
   );
   expect(result.tool_calls?.length).toBeGreaterThanOrEqual(1);
 });
+
+test("Can call and use two tool calls at once", async () => {
+  const tool = {
+    name: "generate_random_joke",
+    description: "Generate a random joke.",
+    schema: z.object({
+      prompt: z.string().describe("The prompt to generate the joke for."),
+    }),
+  };
+  const largeModel = new ChatAnthropic({
+    model: "claude-3-5-sonnet-latest",
+    temperature: 0,
+  }).bindTools([tool]);
+
+  const inputMessage = new HumanMessage(
+    "Generate three (3) random jokes. Please use the generate_random_joke tool, and call it three times in your response to me. Ensure you call the tool three times before responding to me. This is very important."
+  );
+
+  const result = await largeModel.invoke([inputMessage]);
+  expect(result.tool_calls).toHaveLength(3);
+
+  const toolResult1 = new ToolMessage({
+    tool_call_id: result.tool_calls?.[0].id || "",
+    name: "generate_random_joke",
+    content: [
+      {
+        type: "text",
+        text: "This is a joke.",
+      },
+    ],
+  });
+  const toolResult2 = new ToolMessage({
+    tool_call_id: result.tool_calls?.[1].id || "",
+    name: "generate_random_joke",
+    content: [
+      {
+        type: "text",
+        text: "This is the second joke!!",
+      },
+    ],
+  });
+  const toolResult3 = new ToolMessage({
+    tool_call_id: result.tool_calls?.[2].id || "",
+    name: "generate_random_joke",
+    content: "This is the third joke!!",
+  });
+
+  const responseHumanMessage = new HumanMessage(
+    "Please rate all these jokes on a scale of 1-10. Rate them on how funny you think they are."
+  );
+  const result2 = await largeModel.invoke([
+    inputMessage,
+    result,
+    toolResult1,
+    toolResult2,
+    toolResult3,
+    responseHumanMessage,
+  ]);
+
+  expect(result2.content.length).toBeGreaterThan(5);
+});

libs/langchain-anthropic/src/types.ts

@@ -29,3 +29,8 @@ export type AnthropicToolChoice =
   | "none"
   | string;
 export type ChatAnthropicToolType = AnthropicTool | BindToolsInput;
+export type AnthropicTextBlockParam = Anthropic.Messages.TextBlockParam;
+export type AnthropicImageBlockParam = Anthropic.Messages.ImageBlockParam;
+export type AnthropicToolUseBlockParam = Anthropic.Messages.ToolUseBlockParam;
+export type AnthropicToolResultBlockParam =
+  Anthropic.Messages.ToolResultBlockParam;

libs/langchain-anthropic/src/utils/message_inputs.ts

@@ -12,8 +12,12 @@ import {
 } from "@langchain/core/messages";
 import { ToolCall } from "@langchain/core/messages/tool";
 import {
+  AnthropicImageBlockParam,
   AnthropicMessageCreateParams,
+  AnthropicTextBlockParam,
   AnthropicToolResponse,
+  AnthropicToolResultBlockParam,
+  AnthropicToolUseBlockParam,
 } from "../types.js";
 
 function _formatImage(imageUrl: string) {
@@ -250,7 +254,79 @@ export function _convertMessagesToAnthropicPayload(
     }
   });
   return {
-    messages: formattedMessages,
+    messages: mergeMessages(formattedMessages),
     system,
   } as AnthropicMessageCreateParams;
 }
+
+function mergeMessages(messages: AnthropicMessageCreateParams["messages"]) {
+  if (!messages || messages.length <= 1) {
+    return messages;
+  }
+
+  const result: AnthropicMessageCreateParams["messages"] = [];
+  let currentMessage = messages[0];
+
+  const normalizeContent = (
+    content:
+      | string
+      | Array<
+          | AnthropicTextBlockParam
+          | AnthropicImageBlockParam
+          | AnthropicToolUseBlockParam
+          | AnthropicToolResultBlockParam
+        >
+  ): Array<
+    | AnthropicTextBlockParam
+    | AnthropicImageBlockParam
+    | AnthropicToolUseBlockParam
+    | AnthropicToolResultBlockParam
+  > => {
+    if (typeof content === "string") {
+      return [
+        {
+          type: "text",
+          text: content,
+        },
+      ];
+    }
+    return content;
+  };
+
+  const isToolResultMessage = (msg: (typeof messages)[0]) => {
+    if (msg.role !== "user") return false;
+
+    if (typeof msg.content === "string") {
+      return false;
+    }
+
+    return (
+      Array.isArray(msg.content) &&
+      msg.content.every((item) => item.type === "tool_result")
+    );
+  };
+
+  for (let i = 1; i < messages.length; i += 1) {
+    const nextMessage = messages[i];
+
+    if (
+      isToolResultMessage(currentMessage) &&
+      isToolResultMessage(nextMessage)
+    ) {
+      // Merge the messages by combining their content arrays
+      currentMessage = {
+        ...currentMessage,
+        content: [
+          ...normalizeContent(currentMessage.content),
+          ...normalizeContent(nextMessage.content),
+        ],
+      };
+    } else {
+      result.push(currentMessage);
+      currentMessage = nextMessage;
+    }
+  }
+
+  result.push(currentMessage);
+  return result;
+}