[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 = {}; }
})

Beginnen Sie mit dem verknüpften TypeScript Playground und vergleichen Sie die Regression zwischen den Versionen 4.0.5 und 4.1.5 anhand des Beispiels mit der generischen Funktion und dem Klassenausdruck. Untersuchen Sie, warum die nicht-primitive statische Eigenschaft als any inferiert wird, und betrachten Sie das Issue als erledigt, wenn das Beispiel A.foo ohne Fehler 7022 als {} meldet und dabei das dokumentierte Workaround-Verhalten erhalten bleibt.