Make array.includes () work with discriminated union type inference work

[wenq1]

I find it hard to get Array.includes () as a method to type-guard or narrowing discriminated unions

interface Circle {
        kind:           "circle";
        radius:         number;
}

interface Square {
        kind:           "square";
        sideLength:     number;
}

type Shape = Circle | Square;


// "Improved" Array.includes, reference: https://fettblog.eu/typescript-array-includes/
// However, still not working with the parent type
function elementBelongsToArr2<T>(value: unknown, allowedValues: ReadonlyArray<T>): value is T {
        return (allowedValues as ReadonlyArray<unknown>).includes (value);
}

function getArea (shape: Shape) {
        let     area;
        // Attempt 1 - ok
        if (shape.kind === 'circle') {
                let     kind1  = shape.kind;
                //      ^? ("circle"), correct type
                area    = Math.PI * shape.radius ** 2;
                //                  ^? (Circle), correct type
        }

        let     circleKinds     = ["circle"] as const;
        // Attempt 2 - fail
        if (circleKinds.includes (shape.kind)) {        // won't compile here
                let     kind1   = shape.kind;           
                //      ^? ("circle"|"squared"), wrong type
                area    = Math.PI * shape.radius ** 2; 
                //                  ^? (Shape), wrong type
        }

        // Attempt 3 - fail
        if (elementBelongsToArr2 (shape.kind, circleKinds)) {
                let     kind1   = shape.kind;           // correct kind
                //      ^? ("circle"), correct type
                area    = Math.PI * shape.radius ** 2;  // still incorrect shape
                //                  ^? (Shape), wrong type
        }
}

[MartinJohns]

• You forgot to fill out the issue template for feature requests.
• This is a duplicate of .includes or .indexOf does not narrow the type #36275.

[wenq1]

Thanks, close for now.