Declaration emit inlines types incorrectly

🔎 Search Terms

declaration emit inline

🕗 Version & Regression Information

I was unable to test this prior to 4.4 since React types are no longer compatible with that version.

⏯ Playground Link

No response

💻 Code

import * as React from "react";

export class Component extends React.Component<{ children: React.ReactNode }> {
  render() {
    if (Math.random()) {
      return <div>{this.props.children}</div>;
    } else {
      return this.props.children;
    }
  }
}

Full repro: https://github.com/eps1lon/ts-module-auto-export/tree/bad-inline

🙁 Actual behavior

Return value from render() is not referencing React.ReactNode but inlines its (incomplete) union members:

import * as React from "react";
export declare class Component extends React.Component<{
    children: React.ReactNode;
}> {
    render(): string | number | boolean | Iterable<React.ReactNode> | import("react/jsx-runtime").JSX.Element;
}

🙂 Expected behavior

Return type references the type alias. Inlining union members is incorrect (we may add or remove members or treat members as internal, local types) generally and here specially not even using all members.

export declare class Component extends React.Component<{
  children: React.ReactNode;
}> {
  render(): React.ReactNode | import("react/jsx-runtime").JSX.Element;
}

Additional information about the issue

The fact that it inlines the type here is a special case of https://github.com/microsoft/TypeScript/issues/37151. https://github.com/microsoft/TypeScript/issues/37151 is a more general since it's not always clear when inlining is correct or not. I'd be curious to know what would break if TS would not stop inlining in this special case.

But this issue is also broader since the inline is incomplete.

Bắt đầu với bản tái hiện bad-inline được liên kết của ts-module-auto-export và kiểm tra đầu ra declaration emit của TypeScript cho Component.render. So sánh kiểu trả về được phát ra với tham chiếu React.ReactNode mong đợi, sau đó sử dụng issue #37151 để hiểu hành vi inlining liên quan; được xem là hoàn tất khi union được phát ra đầy đủ và thông qua type alias như được minh họa.