Fix: validate input or throw when using MessagesPlaceholder (langchai…

…n-ai#2874) * fix: validate types or throw when using MessagesPlaceholder class * chore: lint files * fix: better error message and account for null/undefined values * chore: lint files * fix: upate isBaseMessage method explicitly * chore: lint files * fix: error messahe * chore: lint files * fix: tests, give error name * chore: lint files * fix: cleaner check * Disallow nullish values * Fix test --------- Co-authored-by: jacoblee93 <[email protected]>
r13v · Oct 12, 2023 · 2039f07 · 2039f07
1 parent afc01bb
commit 2039f07
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Showing 3 changed files with 83 additions and 4 deletions.
diff --git a/langchain/src/prompts/chat.ts b/langchain/src/prompts/chat.ts
@@ -158,10 +158,40 @@ export class MessagesPlaceholder<
     return [this.variableName];
   }
 
-  formatMessages(
+  validateInputOrThrow(
+    input: Array<unknown>,
+    variableName: Extract<keyof RunInput, string>
+  ): input is BaseMessage[] {
+    let isInputBaseMessage = false;
+
+    if (Array.isArray(input)) {
+      isInputBaseMessage = input.every((message) =>
+        isBaseMessage(message as BaseMessage)
+      );
+    } else {
+      isInputBaseMessage = isBaseMessage(input as BaseMessage);
+    }
+
+    if (!isInputBaseMessage) {
+      const readableInput =
+        typeof input === "string" ? input : JSON.stringify(input, null, 2);
+
+      const error = new Error(
+        `Error: Field "${variableName}" in prompt uses a MessagesPlaceholder, which expects an array of BaseMessages as an input value. Received: ${readableInput}`
+      );
+      error.name = "InputFormatError";
+      throw error;
+    }
+
+    return true;
+  }
+
+  async formatMessages(
     values: TypedPromptInputValues<RunInput>
   ): Promise<BaseMessage[]> {
-    return Promise.resolve(values[this.variableName] as BaseMessage[]);
+    this.validateInputOrThrow(values[this.variableName], this.variableName);
+
+    return values[this.variableName];
   }
 }
 

diff --git a/langchain/src/prompts/tests/chat.test.ts b/langchain/src/prompts/tests/chat.test.ts
@@ -304,3 +304,52 @@ test("Test BaseMessage", async () => {
     new FunctionMessage({ content: "{}", name: "get_weather" }),
   ]);
 });
+
+test("Throws if trying to pass non BaseMessage inputs to MessagesPlaceholder", async () => {
+  const prompt = ChatPromptTemplate.fromMessages([
+    ["system", "some string"],
+    new MessagesPlaceholder("chatHistory"),
+    ["human", "{question}"],
+  ]);
+  const value = "this is not a valid input type!";
+
+  try {
+    await prompt.formatMessages({
+      chatHistory: value,
+      question: "What is the meaning of life?",
+    });
+  } catch (e) {
+    // eslint-disable-next-line no-instanceof/no-instanceof
+    if (e instanceof Error) {
+      expect(e.name).toBe("InputFormatError");
+    } else {
+      throw e;
+    }
+  }
+});
+
+test("Does not throws if null or undefined is passed as input to MessagesPlaceholder", async () => {
+  const prompt = ChatPromptTemplate.fromMessages([
+    ["system", "some string"],
+    new MessagesPlaceholder("chatHistory"),
+    new MessagesPlaceholder("chatHistory2"),
+    ["human", "{question}"],
+  ]);
+  const value1 = null;
+  const value2 = undefined;
+
+  try {
+    await prompt.formatMessages({
+      chatHistory: value1,
+      chatHistory2: value2,
+      question: "What is the meaning of life?",
+    });
+  } catch (e) {
+    // eslint-disable-next-line no-instanceof/no-instanceof
+    if (e instanceof Error) {
+      expect(e.name).toBe("InputFormatError");
+    } else {
+      throw e;
+    }
+  }
+});
diff --git a/langchain/src/schema/index.ts b/langchain/src/schema/index.ts
@@ -459,9 +459,9 @@ export type BaseMessageLike =
   | string;
 
 export function isBaseMessage(
-  messageLike: BaseMessageLike
+  messageLike?: unknown
 ): messageLike is BaseMessage {
-  return typeof (messageLike as BaseMessage)._getType === "function";
+  return typeof (messageLike as BaseMessage)?._getType === "function";
 }
 
 export function coerceMessageLikeToMessage(