[bug] React hooks with streaming always return non-nullable types

[aboqasem]

Product

BAML

Describe the bug

From the docs:

But the React hooks are always returning the non-nullable types.

Reproduction Steps

Given the following BAML:

class MessageTest {
  // MessageTest won't stream until type is known
  type "error" | "success" | "info" @stream.not_null

  // MessageTest will only stream when title is known
  title string @stream.done @stream.not_null

  // Timestamp will only appear when fully complete, until then it will be null
  timestamp string @stream.done

  // will stream token by token, and include completion state
  content string @stream.with_state

  // will stream token by token
  other string
}

function GetMessageTest(input: string) -> MessageTest {
  client CustomGPT5
  prompt #"
  "#
}

It generates two types:

// types.ts
export interface MessageTest {
  type: "error" | "success" | "info"
  title: string
  timestamp: string
  content: string
  other: string
  
}

// partial_types.ts
    interface MessageTest {
      type: "error" | "success" | "info"
      title: string
      timestamp?: string | null
      content?: StreamState<string | null>
      other?: string | null
    }

Then the hook's return type is:

// const data: {
//     type: "error" | "success" | "info";
//     title: string;
//     timestamp: string;
//     content: string;
//     other: string;
// } | undefined
// const data: MessageTest | undefined

const { data } = useGetMessageTest({ stream: true });

Shouldn't it be partial_types.MessageTest? Because it is actually returning null in the nullable fields, which is causing Cannot access property on ... bugs.

BAML Version

0.211.2

Language/Framework

React

LLM Provider

None

LLM Model

No response

Operating System

macOS

Browser

Firefox

Code Editor

VS Code

[linear[bot]]

BAML-520

[imalsogreg]

Thanks for the report! I believe you're right that the data field of the hook should contain the partial type in your case, and we'll look into that.

In the meantime, you can work around the issue by using the streamData field (of the same hook) - does that work as expected for you?