Ideas for PromptTemplate composition and type safety improvements

langchain-core/src/prompts/chat.ts

@@ -17,7 +17,7 @@ import {
  type ChatPromptValueInterface,
  ChatPromptValue,
 } from "../prompt_values.js";
-import type { InputValues, PartialValues } from "../utils/types/index.js";
+import type { InputValues, InputValues_FSTRING, PartialValues } from "../utils/types/index.js";
 import { Runnable } from "../runnables/base.js";
 import { BaseStringPromptTemplate } from "./string.js";
 import {
@@ -29,6 +29,11 @@ import { PromptTemplate, type ParamsFromFString } from "./prompt.js";
 import { ImagePromptTemplate } from "./image.js";
 import { parseFString } from "./template.js";
 
+
+type ObjectTupleIntersection<A, T extends [...unknown[]]> = T['length'] extends 0
+ ? A
+ : ObjectTupleIntersection<A & T[0], T extends [unknown, ...infer R] ? R : []>;
+
 /**
  * Abstract class that serves as a base for creating message prompt
  * templates. It defines how to format messages for different roles in a
@@ -86,12 +91,11 @@ export interface MessagesPlaceholderFields<T extends string> {
  * extends the BaseMessagePromptTemplate.
  */
 export class MessagesPlaceholder<
-  // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  RunInput extends InputValues = any
- >
+ // eslint-disable-next-line @typescript-eslint/no-explicit-any
+ RunInput extends InputValues = any
+>
  extends BaseMessagePromptTemplate<RunInput>
- implements MessagesPlaceholderFields<Extract<keyof RunInput, string>>
-{
+ implements MessagesPlaceholderFields<Extract<keyof RunInput, string>> {
  static lc_name() {
  return "MessagesPlaceholder";
  }
@@ -209,12 +213,12 @@ export abstract class BaseMessageStringPromptTemplate<
  constructor(
  fields:
  | MessageStringPromptTemplateFields<
-  InputValues<Extract<keyof RunInput, string>>
-  >
+ InputValues<Extract<keyof RunInput, string>>
+ >
  | BaseStringPromptTemplate<
-  InputValues<Extract<keyof RunInput, string>>,
-  string
-  >
+ InputValues<Extract<keyof RunInput, string>>,
+ string
+ >
  ) {
  if (!("prompt" in fields)) {
  // eslint-disable-next-line no-param-reassign
@@ -312,8 +316,8 @@ export class ChatMessagePromptTemplate<
  constructor(
  fields:
  | ChatMessagePromptTemplateFields<
-  InputValues<Extract<keyof RunInput, string>>
-  >
+ InputValues<Extract<keyof RunInput, string>>
+ >
  | BaseStringPromptTemplate<InputValues<Extract<keyof RunInput, string>>>,
  role?: string
  ) {
@@ -351,6 +355,25 @@ type MessageClass =
 
 type ChatMessageClass = typeof ChatMessage;
 
+type _StringImageMessagePromptTemplatePrompt<RunInput extends InputValues> =
+ | BaseStringPromptTemplate<
+ RunInput,
+ string
+ > | PromptTemplate<RunInput>
+ | Array<
+ | BaseStringPromptTemplate<
+ RunInput,
+ string
+ >
+ | ImagePromptTemplate<
+ RunInput,
+ string
+ >
+ | MessageStringPromptTemplateFields<
+ RunInput
+ >
+ >;
+
 class _StringImageMessagePromptTemplate<
  // eslint-disable-next-line @typescript-eslint/no-explicit-any
  RunInput extends InputValues = any,
@@ -360,28 +383,11 @@ class _StringImageMessagePromptTemplate<
 
  lc_serializable = true;
 
- inputVariables: Array<Extract<keyof RunInput, string>> = [];
-
  additionalOptions: Record<string, unknown> = {};
 
- prompt:
- | BaseStringPromptTemplate<
- InputValues<Extract<keyof RunInput, string>>,
- string
- >
- | Array<
- | BaseStringPromptTemplate<
- InputValues<Extract<keyof RunInput, string>>,
- string
- >
- | ImagePromptTemplate<
- InputValues<Extract<keyof RunInput, string>>,
- string
- >
- | MessageStringPromptTemplateFields<
- InputValues<Extract<keyof RunInput, string>>
- >
- >;
+ prompt: _StringImageMessagePromptTemplatePrompt<RunInput>;
+
+ inputVariables: Array<Extract<keyof RunInput, string>> = [];
 
  protected messageClass?: MessageClass;
 
@@ -396,9 +402,12 @@ class _StringImageMessagePromptTemplate<
  protected chatMessageClass?: ChatMessageClass;
 
  constructor(
- /** @TODO When we come up with a better way to type prompt templates, fix this */
- // eslint-disable-next-line @typescript-eslint/no-explicit-any
- fields: any,
+ fields:
+ | {
+ prompt: _StringImageMessagePromptTemplatePrompt<RunInput>;
+ additionalOptions?: Record<string, unknown>;
+ }
+ | _StringImageMessagePromptTemplatePrompt<RunInput>,
  additionalOptions?: Record<string, unknown>
  ) {
  if (!("prompt" in fields)) {
@@ -454,15 +463,16 @@ class _StringImageMessagePromptTemplate<
  }
  }
 
- static fromTemplate(
+ // eslint-disable-next-line @typescript-eslint/no-explicit-any
+ static fromTemplate<RunInput extends InputValues = any>(
  template: string | Array<string | _TextTemplateParam | _ImageTemplateParam>,
  additionalOptions?: Record<string, unknown>
  ) {
  if (typeof template === "string") {
- return new this(PromptTemplate.fromTemplate(template));
+ return new this(PromptTemplate.fromTemplate<RunInput>(template));
  }
  const prompt: Array<
- PromptTemplate<InputValues> | ImagePromptTemplate<InputValues>
+ PromptTemplate<RunInput> | ImagePromptTemplate<RunInput>
  > = [];
  for (const item of template) {
  if (
@@ -475,10 +485,10 @@ class _StringImageMessagePromptTemplate<
  } else if (typeof item.text === "string") {
  text = item.text ?? "";
  }
- prompt.push(PromptTemplate.fromTemplate(text));
+ prompt.push(PromptTemplate.fromTemplate(text) as typeof prompt[number]);
  } else if (typeof item === "object" && "image_url" in item) {
  let imgTemplate = item.image_url ?? "";
- let imgTemplateObject: ImagePromptTemplate<InputValues>;
+ let imgTemplateObject: ImagePromptTemplate;
  let inputVariables: string[] = [];
  if (typeof imgTemplate === "string") {
  const parsedTemplate = parseFString(imgTemplate);
@@ -498,7 +508,7 @@ class _StringImageMessagePromptTemplate<
  }
 
  imgTemplate = { url: imgTemplate };
- imgTemplateObject = new ImagePromptTemplate<InputValues>({
+ imgTemplateObject = new ImagePromptTemplate({
  template: imgTemplate,
  inputVariables,
  });
@@ -511,7 +521,7 @@ class _StringImageMessagePromptTemplate<
  } else {
  inputVariables = [];
  }
- imgTemplateObject = new ImagePromptTemplate<InputValues>({
+ imgTemplateObject = new ImagePromptTemplate({
  template: imgTemplate,
  inputVariables,
  });
@@ -664,8 +674,13 @@ export interface ChatPromptTemplateInput<
  validateTemplate?: boolean;
 }
 
-export type BaseMessagePromptTemplateLike =
- | BaseMessagePromptTemplate
+type ChatPromptTemplateLike<RunInput extends InputValues> =
+ | ChatPromptTemplate<RunInput, string>
+ | BaseMessagePromptTemplateLike<RunInput>;
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export type BaseMessagePromptTemplateLike<RunInput extends InputValues = any> =
+ | BaseMessagePromptTemplate<RunInput>
  | BaseMessageLike;
 
 function _isBaseMessagePromptTemplate(
@@ -765,14 +780,13 @@ function isMessagesPlaceholder(
  * ```
  */
 export class ChatPromptTemplate<
-  // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  RunInput extends InputValues = any,
-  // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  PartialVariableName extends string = any
- >
+ // eslint-disable-next-line @typescript-eslint/no-explicit-any
+ RunInput extends InputValues = any,
+ // eslint-disable-next-line @typescript-eslint/no-explicit-any
+ PartialVariableName extends string = any
+>
  extends BaseChatPromptTemplate<RunInput, PartialVariableName>
- implements ChatPromptTemplateInput<RunInput, PartialVariableName>
-{
+ implements ChatPromptTemplateInput<RunInput, PartialVariableName> {
  static lc_name() {
  return "ChatPromptTemplate";
  }
@@ -944,14 +958,14 @@ export class ChatPromptTemplate<
  */
  static fromTemplate<
  // eslint-disable-next-line @typescript-eslint/ban-types
- RunInput extends InputValues = Symbol,
+ RunInput extends InputValues = InputValues_FSTRING,
  T extends string = string
  >(template: T) {
- const prompt = PromptTemplate.fromTemplate(template);
+ const prompt = PromptTemplate.fromTemplate<RunInput>(template);
  const humanTemplate = new HumanMessagePromptTemplate({ prompt });
  return this.fromMessages<
  // eslint-disable-next-line @typescript-eslint/ban-types
- RunInput extends Symbol ? ParamsFromFString<T> : RunInput
+ RunInput extends InputValues_FSTRING ? ParamsFromFString<T> : RunInput
  >([humanTemplate]);
  }
 
@@ -1012,6 +1026,16 @@ export class ChatPromptTemplate<
  });
  }
 
+ // eslint-disable-next-line @typescript-eslint/no-explicit-any
+ static fromTypedMessages<const Prompts extends ChatPromptTemplateLike<any>[]>(messages: Prompts): ChatPromptTemplate<
+ // eslint-disable-next-line @typescript-eslint/ban-types
+ ObjectTupleIntersection<{}, {
+ [P in keyof Prompts]: Prompts[P] extends ChatPromptTemplateLike<infer I> ? I : never
+ }>
+ > {
+ return this.fromMessages(messages);
+ }
+
  /** @deprecated Renamed to .fromMessages */
  // eslint-disable-next-line @typescript-eslint/no-explicit-any
  static fromPromptMessages<RunInput extends InputValues = any>(

langchain-core/src/prompts/prompt.ts

@@ -13,7 +13,11 @@ import {
  type TemplateFormat,
 } from "./template.js";
 import type { SerializedPromptTemplate } from "./serde.js";
-import type { InputValues, PartialValues } from "../utils/types/index.js";
+import type {
+ InputValues,
+ InputValues_FSTRING,
+ PartialValues,
+} from "../utils/types/index.js";
 import { MessageContent } from "../messages/index.js";
 
 /**
@@ -183,7 +187,7 @@ export class PromptTemplate<
  */
  static fromTemplate<
  // eslint-disable-next-line @typescript-eslint/ban-types
- RunInput extends InputValues = Symbol,
+ RunInput extends InputValues = InputValues_FSTRING,
  T extends string = string
  >(
  template: T,
@@ -203,7 +207,7 @@ export class PromptTemplate<
  });
  return new PromptTemplate<
  // eslint-disable-next-line @typescript-eslint/ban-types
- RunInput extends Symbol ? ParamsFromFString<T> : RunInput
+ RunInput extends InputValues_FSTRING ? ParamsFromFString<T> : RunInput
  >({
  // Rely on extracted types
  // eslint-disable-next-line @typescript-eslint/no-explicit-any

langchain-core/src/prompts/tests/chat.test.ts

@@ -568,3 +568,29 @@ test("Multi-modal, multi part chat prompt works with instances of BaseMessage",
  });
  expect(messages).toMatchSnapshot();
 });
+
+test("fromTypedMessages combines message input types", () => {
+ const x = new SystemMessagePromptTemplate<{ x: string }>({
+ prompt: PromptTemplate.fromTemplate(""),
+ });
+ const y = new SystemMessagePromptTemplate<{ y: string }>({
+ prompt: PromptTemplate.fromTemplate(""),
+ });
+
+ const xy = ChatPromptTemplate.fromTypedMessages([x, y]);
+ ((test: ChatPromptTemplate<{ x: string; y: string }>) => test)(xy);
+});
+
+test("_StringImageMessagePromptTemplate infers RunInput from child prompt", () => {
+ const x = new SystemMessagePromptTemplate({
+ prompt: PromptTemplate.fromTemplate<{ x: number; y: boolean }>(""),
+ });
+
+ ((test: SystemMessagePromptTemplate<{ x: number; y: boolean }>) => test)(x);
+
+ // @ts-expect-error - nope
+ ((test: SystemMessagePromptTemplate<{ x: number; z: number }>) => test)(x);
+
+ // @ts-expect-error - nope
+ ((test: SystemMessagePromptTemplate<{ x: string; y: string }>) => test)(x);
+});

langchain-core/src/utils/types/index.ts

@@ -7,7 +7,9 @@ export * from "./is_zod_schema.js";
 export type StringWithAutocomplete<T> = T | (string & Record<never, never>);
 
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
-export type InputValues<K extends string = string> = Record<K, any>;
+export type InputValues<K extends string = string, V = any> = Record<K, V>;
+
+export type InputValues_FSTRING = InputValues & { __FSTRING: true };
 
 export type PartialValues<K extends string = string> = Record<
  K,

langchain/src/experimental/prompts/custom_format.ts

@@ -6,6 +6,8 @@ import {
  TypedPromptInputValues,
 } from "@langchain/core/prompts";
 
+export type InputValues_FSTRING = InputValues & { __FSTRING: true }; 
+
 export type CustomFormatPromptTemplateInput<RunInput extends InputValues> =
  Omit<PromptTemplateInput<RunInput, string>, "templateFormat"> & {
  customParser: (template: string) => ParsedFStringNode[];
@@ -74,7 +76,7 @@ export class CustomFormatPromptTemplate<
  }
  }
  // eslint-disable-next-line @typescript-eslint/ban-types
- return new this<RunInput extends Symbol ? never : RunInput>({
+ return new this<RunInput extends InputValues_FSTRING ? never : RunInput>({
  // eslint-disable-next-line @typescript-eslint/no-explicit-any
  inputVariables: [...names] as any[],
  template,