[Regression] Circular reference error when passing a class expression with non-primitive static properties to a generic function

🔎 Search Terms

class expression static type

🕗 Version & Regression Information

• This changed between versions 4.0.5 and 4.1.5

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=4.1.5#code/CYUwxgNghgTiAEAzArgOzAFwJYHtXzg2RlQElUAHZDAHgBUA+ACi0uoC546BKTugbgBQgsHgDOGeFHgBeAiCIlyVDE0hQxY+AEF4Ab0EBICVGxgkOHLP0BfQTe5A

💻 Code

declare function returnInput<T>(input: T): T;

const a = returnInput(class A {
	static foo = {}
//              ^?
})

🙁 Actual behavior

A.foo: any
Error: 'foo' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.(7022)

And also note that this bug only happens when the type of foo is not a primitive type.

🙂 Expected behavior

A.foo: {}, as it works in 4.0.5

Additional information about the issue

To define a React class component, it is a common practice to include its "sub-components" as private static properties. I also use a "observer" function to make the state change auto observed. So the real-world code may look like:

import { observer } from 'mobx-react';
import { styled } from 'styled-components';

@observer
class ListView extends React.Component {
    // render method here...
    private static readonly Item = observer(class Item extends React.Component {
        private static readonly Header = styled.h4` // <- Cannot infer the type of Header
        // CSS style here...
        `;
    })
}

A workaround is to use static block to initialize the static property but it's cumbersome:

const a = returnInput(class A {
	static foo
//              ^? OK
	static { this.foo = {}; }
})

リンクされた TypeScript Playground から始め、ジェネリック関数とクラス式の例を使って、バージョン 4.0.5 と 4.1.5 の間のリグレッションを比較してください。非プリミティブな静的プロパティがなぜ any と推論されるのかを調査し、ドキュメント化された workaround の動作を維持したまま、例がエラー 7022 なしで A.foo を {} と報告すれば Issue は完了としてください。