chore(core/v0): fix chunks constructed with tool calls + chunks (#9256)

Author: hntrl

.changeset/stale-chefs-roll.md

@@ -0,0 +1,5 @@
+---
+"@langchain/core": patch
+---
+
+fix chunks constructed with tool calls + chunks

dependency_range_tests/scripts/langchain/test-with-latest-deps.sh

@@ -22,7 +22,7 @@ cd /app
 node /updater_script/update_resolutions_latest.js
 
 yarn
-yarn add @langchain/core
+yarn add @langchain/core@^0.3
 
 # Check the test command completes successfully
 NODE_OPTIONS=--experimental-vm-modules yarn run jest --testPathIgnorePatterns=\\.int\\.test.ts --testTimeout 30000 --maxWorkers=50%

langchain-core/src/messages/ai.ts

@@ -259,7 +259,10 @@ export class AIMessageChunk extends BaseMessageChunk {
         invalid_tool_calls: [],
         tool_call_chunks: [],
       };
-    } else if (fields.tool_call_chunks === undefined) {
+    } else if (
+      fields.tool_call_chunks === undefined ||
+      fields.tool_call_chunks.length === 0
+    ) {
       initParams = {
         ...fields,
         tool_calls: fields.tool_calls ?? [],
@@ -271,37 +274,35 @@ export class AIMessageChunk extends BaseMessageChunk {
             : undefined,
       };
     } else {
-      const groupedToolCallChunks = fields.tool_call_chunks.reduce(
-        (acc, chunk) => {
-          const matchedChunkIndex = acc.findIndex(([match]) => {
-            // If chunk has an id and index, match if both are present
-            if (
-              "id" in chunk &&
-              chunk.id &&
-              "index" in chunk &&
-              chunk.index !== undefined
-            ) {
-              return chunk.id === match.id && chunk.index === match.index;
-            }
-            // If chunk has an id, we match on id
-            if ("id" in chunk && chunk.id) {
-              return chunk.id === match.id;
-            }
-            // If chunk has an index, we match on index
-            if ("index" in chunk && chunk.index !== undefined) {
-              return chunk.index === match.index;
-            }
-            return false;
-          });
-          if (matchedChunkIndex !== -1) {
-            acc[matchedChunkIndex].push(chunk);
-          } else {
-            acc.push([chunk]);
+      const toolCallChunks = fields.tool_call_chunks ?? [];
+      const groupedToolCallChunks = toolCallChunks.reduce((acc, chunk) => {
+        const matchedChunkIndex = acc.findIndex(([match]) => {
+          // If chunk has an id and index, match if both are present
+          if (
+            "id" in chunk &&
+            chunk.id &&
+            "index" in chunk &&
+            chunk.index !== undefined
+          ) {
+            return chunk.id === match.id && chunk.index === match.index;
           }
-          return acc;
-        },
-        [] as ToolCallChunk[][]
-      );
+          // If chunk has an id, we match on id
+          if ("id" in chunk && chunk.id) {
+            return chunk.id === match.id;
+          }
+          // If chunk has an index, we match on index
+          if ("index" in chunk && chunk.index !== undefined) {
+            return chunk.index === match.index;
+          }
+          return false;
+        });
+        if (matchedChunkIndex !== -1) {
+          acc[matchedChunkIndex].push(chunk);
+        } else {
+          acc.push([chunk]);
+        }
+        return acc;
+      }, [] as ToolCallChunk[][]);
 
       const toolCalls: ToolCall[] = [];
       const invalidToolCalls: InvalidToolCall[] = [];

langchain-core/src/messages/tests/ai.test.ts

@@ -2,6 +2,35 @@ import { describe, it, expect } from "@jest/globals";
 import { AIMessageChunk } from "../ai.js";
 
 describe("AIMessageChunk", () => {
+  describe("constructor", () => {
+    it("can be constructed with tool calls using basic params", () => {
+      const chunk = new AIMessageChunk({
+        content: "",
+        tool_calls: [
+          {
+            name: "get_weather",
+            args: {
+              location: "San Francisco",
+            },
+          },
+        ],
+        invalid_tool_calls: [],
+        tool_call_chunks: [],
+        additional_kwargs: {},
+        response_metadata: {},
+      });
+      expect(chunk.tool_calls).toHaveLength(1);
+      expect(chunk.tool_calls).toEqual([
+        {
+          name: "get_weather",
+          args: {
+            location: "San Francisco",
+          },
+        },
+      ]);
+    });
+  });
+
   it("should properly merge tool call chunks that have matching indices and ids", () => {
     const chunk1 = new AIMessageChunk({
       content: "",