[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 = {}; }
})

Commencez par le TypeScript Playground lié et comparez la régression entre les versions 4.0.5 et 4.1.5 à l’aide de l’exemple de fonction générique et d’expression de classe. Cherchez pourquoi la propriété statique non primitive est inférée comme any, et considérez l’issue comme terminée lorsque l’exemple signale A.foo comme {} sans l’erreur 7022, tout en préservant le comportement documenté du workaround.