Fixes

langchain-ai · Mar 30, 2024 · 1a84b7c · 1a84b7c
1 parent 534c00b
commit 1a84b7c
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Showing 3 changed files with 42 additions and 56 deletions.
diff --git a/langchain-core/src/messages/index.ts b/langchain-core/src/messages/index.ts
@@ -35,8 +35,7 @@ export type MessageType =
   | "generic"
   | "system"
   | "function"
-  | "tool"
-  | "placeholder";
+  | "tool";
 
 type ImageDetail = "auto" | "low" | "high";
 
@@ -406,39 +405,6 @@ export class AIMessageChunk extends BaseMessageChunk {
   }
 }
 
-export class PlaceholderMessage extends BaseMessage {
-  static lc_name() {
-    return "PlaceholderMessage";
-  }
-
-  _getType(): MessageType {
-    return "placeholder";
-  }
-}
-
-export class PlaceholderMessageChunk extends BaseMessageChunk {
-  static lc_name() {
-    return "PlaceholderMessageChunk";
-  }
-
-  _getType(): MessageType {
-    return "placeholder";
-  }
-
-  concat(chunk: PlaceholderMessageChunk) {
-    return new PlaceholderMessageChunk({
-      content: mergeContent(this.content, chunk.content),
-      additional_kwargs: _mergeDicts(
-        this.additional_kwargs,
-        chunk.additional_kwargs
-      ),
-      response_metadata: _mergeDicts(
-        this.response_metadata,
-        chunk.response_metadata
-      ),
-    });
-  }
-}
 /**
  * Represents a system message in a conversation.
  */
@@ -664,7 +630,12 @@ export class ChatMessage
 
 export type BaseMessageLike =
   | BaseMessage
-  | [StringWithAutocomplete<MessageType | "user" | "assistant">, MessageContent]
+  | [
+      StringWithAutocomplete<
+        MessageType | "user" | "assistant" | "placeholder"
+      >,
+      MessageContent
+    ]
   | string;
 
 export function isBaseMessage(
@@ -697,8 +668,6 @@ export function coerceMessageLikeToMessage(
     return new AIMessage({ content });
   } else if (type === "system") {
     return new SystemMessage({ content });
-  } else if (type === "placeholder") {
-    return new PlaceholderMessage({ content });
   } else {
     throw new Error(
       `Unable to coerce message from array: only human, AI, or system message coercion is currently supported.`

diff --git a/langchain-core/src/prompts/chat.ts b/langchain-core/src/prompts/chat.ts
@@ -6,7 +6,6 @@ import {
   AIMessage,
   HumanMessage,
   SystemMessage,
-  PlaceholderMessage,
   BaseMessage,
   ChatMessage,
   type BaseMessageLike,
@@ -348,8 +347,7 @@ interface _ImageTemplateParam {
 type MessageClass =
   | typeof HumanMessage
   | typeof AIMessage
-  | typeof SystemMessage
-  | typeof PlaceholderMessage;
+  | typeof SystemMessage;
 
 type ChatMessageClass = typeof ChatMessage;
 
@@ -644,19 +642,6 @@ export class SystemMessagePromptTemplate<
   }
 }
 
-export class MessagesPlaceholderPromptTemplate<
-  // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  RunInput extends InputValues = any
-> extends MessagesPlaceholder<RunInput> {
-  static _messageClass(): typeof PlaceholderMessage {
-    return PlaceholderMessage;
-  }
-
-  static lc_name() {
-    return "MessagesPlaceholderPromptTemplate";
-  }
-}
-
 /**
  * Interface for the input of a ChatPromptTemplate.
  */
@@ -701,15 +686,30 @@ function _coerceMessagePromptTemplateLike(
   ) {
     return messagePromptTemplateLike;
   }
+  if (
+    Array.isArray(messagePromptTemplateLike) &&
+    messagePromptTemplateLike[0] === "placeholder"
+  ) {
+    const messageContent = messagePromptTemplateLike[1];
+    if (
+      typeof messageContent !== "string" ||
+      messageContent[0] !== "{" ||
+      messageContent[messageContent.length - 1] !== "}"
+    ) {
+      throw new Error(
+        `Invalid placeholder template: "${messagePromptTemplateLike[1]}". Expected a variable name surrounded by curly braces.`
+      );
+    }
+    const variableName = messageContent.slice(1, -1);
+    return new MessagesPlaceholder({ variableName, optional: true });
+  }
   const message = coerceMessageLikeToMessage(messagePromptTemplateLike);
   if (message._getType() === "human") {
     return HumanMessagePromptTemplate.fromTemplate(message.content);
   } else if (message._getType() === "ai") {
     return AIMessagePromptTemplate.fromTemplate(message.content);
   } else if (message._getType() === "system") {
     return SystemMessagePromptTemplate.fromTemplate(message.content);
-  } else if (message._getType() === "placeholder") {
-    return new MessagesPlaceholderPromptTemplate(message.content as string);
   } else if (ChatMessage.isInstance(message)) {
     return ChatMessagePromptTemplate.fromTemplate(
       message.content as string,

diff --git a/langchain-core/src/prompts/tests/chat.test.ts b/langchain-core/src/prompts/tests/chat.test.ts
@@ -306,6 +306,23 @@ test("Test MessagesPlaceholder not optional", async () => {
   );
 });
 
+test.only("Test MessagesPlaceholder shorthand in a chat prompt template should throw for invalid syntax", async () => {
+  expect(() =>
+    ChatPromptTemplate.fromMessages([["placeholder", "foo"]])
+  ).toThrow();
+});
+
+test.only("Test MessagesPlaceholder shorthand in a chat prompt template", async () => {
+  const prompt = ChatPromptTemplate.fromMessages([["placeholder", "{foo}"]]);
+  const messages = await prompt.formatMessages({
+    foo: [new HumanMessage("Hi there!"), new AIMessage("how r u")],
+  });
+  expect(messages).toEqual([
+    new HumanMessage("Hi there!"),
+    new AIMessage("how r u"),
+  ]);
+});
+
 test("Test using partial", async () => {
   const userPrompt = new PromptTemplate({
     template: "{foo}{bar}",