feat (ui): use UI_MESSAGE generic (#6735)

## Background

`useChat` and related types are currently parameterized on message
metadata and data types. This can be simplified to a parameterized ui
message type, from which the other generic parameters can then be
derived.

## Summary

Use a generic `UIMessage` in `Chat` and related types.

## Future Work

* parameterize tool invocations

Author: lgrammel

.changeset/sharp-apes-tickle.md

@@ -0,0 +1,8 @@
+---
+'@ai-sdk/svelte': major
+'@ai-sdk/react': major
+'@ai-sdk/vue': major
+'ai': major
+---
+
+feat (ui): use UI_MESSAGE generic

examples/next-openai/app/use-chat-data-ui-parts/page.tsx

@@ -2,22 +2,26 @@
 
 import ChatInput from '@/component/chat-input';
 import { useChat } from '@ai-sdk/react';
-import { DefaultChatTransport } from 'ai';
-import { z } from 'zod';
+import { DefaultChatTransport, UIMessage } from 'ai';
+
+type MyMessage = UIMessage<
+  never,
+  {
+    weather: {
+      city: string;
+      weather: string;
+      status: 'loading' | 'success';
+    };
+  }
+>;
 
 export default function Chat() {
-  const { error, status, sendMessage, messages, reload, stop } = useChat({
-    transport: new DefaultChatTransport({
-      api: '/api/use-chat-data-ui-parts',
-    }),
-    dataPartSchemas: {
-      weather: z.object({
-        city: z.string(),
-        weather: z.string(),
-        status: z.enum(['loading', 'success']),
+  const { error, status, sendMessage, messages, reload, stop } =
+    useChat<MyMessage>({
+      transport: new DefaultChatTransport({
+        api: '/api/use-chat-data-ui-parts',
       }),
-    },
-  });
+    });
 
   return (
     <div className="flex flex-col w-full max-w-md py-24 mx-auto stretch">

examples/next-openai/app/use-chat-message-metadata/page.tsx

@@ -1,18 +1,19 @@
 'use client';
 
-import { zodSchema } from '@ai-sdk/provider-utils';
-import { useChat } from '@ai-sdk/react';
-import { DefaultChatTransport } from 'ai';
-import { exampleMetadataSchema } from '../api/use-chat-message-metadata/example-metadata-schema';
 import ChatInput from '@/component/chat-input';
+import { useChat } from '@ai-sdk/react';
+import { DefaultChatTransport, UIMessage } from 'ai';
+import { ExampleMetadata } from '../api/use-chat-message-metadata/example-metadata-schema';
+
+type MyMessage = UIMessage<ExampleMetadata>;
 
 export default function Chat() {
-  const { error, status, sendMessage, messages, reload, stop } = useChat({
-    transport: new DefaultChatTransport({
-      api: '/api/use-chat-message-metadata',
-    }),
-    messageMetadataSchema: zodSchema(exampleMetadataSchema),
-  });
+  const { error, status, sendMessage, messages, reload, stop } =
+    useChat<MyMessage>({
+      transport: new DefaultChatTransport({
+        api: '/api/use-chat-message-metadata',
+      }),
+    });
 
   return (
     <div className="flex flex-col w-full max-w-md py-24 mx-auto stretch">

packages/ai/src/ui-message-stream/handle-ui-message-stream-finish.ts

@@ -3,11 +3,7 @@ import {
   processUIMessageStream,
   StreamingUIMessageState,
 } from '../ui/process-ui-message-stream';
-import {
-  InferUIMessageData,
-  InferUIMessageMetadata,
-  UIMessage,
-} from '../ui/ui-messages';
+import { UIMessage } from '../ui/ui-messages';
 import {
   InferUIMessageStreamPart,
   UIMessageStreamPart,
@@ -53,27 +49,16 @@ export function handleUIMessageStreamFinish<UI_MESSAGE extends UIMessage>({
 
   const lastMessage = originalMessages?.[originalMessages.length - 1];
 
-  const state = createStreamingUIMessageState<
-    InferUIMessageMetadata<UI_MESSAGE>,
-    InferUIMessageData<UI_MESSAGE>
-  >({
+  const state = createStreamingUIMessageState<UI_MESSAGE>({
     lastMessage: lastMessage
-      ? (structuredClone(lastMessage) as UIMessage<
-          InferUIMessageMetadata<UI_MESSAGE>,
-          InferUIMessageData<UI_MESSAGE>
-        >)
+      ? (structuredClone(lastMessage) as UI_MESSAGE)
       : undefined,
     messageId, // will be overridden by the stream
   });
 
   const runUpdateMessageJob = async (
     job: (options: {
-      state: StreamingUIMessageState<
-        UIMessage<
-          InferUIMessageMetadata<UI_MESSAGE>,
-          InferUIMessageData<UI_MESSAGE>
-        >
-      >;
+      state: StreamingUIMessageState<UI_MESSAGE>;
       write: () => void;
     }) => Promise<void>,
   ) => {

packages/ai/src/ui/chat-transport.ts

@@ -1,16 +1,13 @@
 import { UIMessageStreamPart } from '../ui-message-stream';
 import { ChatRequestOptions } from './chat';
-import { UIDataTypes, UIMessage } from './ui-messages';
+import { UIMessage } from './ui-messages';
 
-export interface ChatTransport<
-  MESSAGE_METADATA,
-  DATA_TYPES extends UIDataTypes,
-> {
+export interface ChatTransport<UI_MESSAGE extends UIMessage> {
   // TODO better name
   submitMessages: (
     options: {
       chatId: string;
-      messages: UIMessage<MESSAGE_METADATA, DATA_TYPES>[];
+      messages: UI_MESSAGE[];
       abortSignal: AbortSignal | undefined;
       requestType: 'generate' | 'resume'; // TODO have separate functions
     } & ChatRequestOptions,