ConstructorParameters makes mapped tuple type lose its array capabilities

[shy fog]

type ArrMap<T extends any[]> = {[Index in keyof T]: [T[Index], number]};
type Type<T> = new (...args: any[]) => T;

class Test {
    constructor(a: number) {}
}

function testOne<T extends Type<any>>(arr: ArrMap<[T]>) {
    const res = arr.map(item => item[0]); // Works with T[] as result
}

function testTwo<T extends Type<any>>(arr: ArrMap<ConstructorParameters<T>>) {
    arr.map(item => item[0]); // Doesn't even compile
}

function testThree<T extends Type<any>>(arr: ArrMap<[...ConstructorParameters<T>]>) {
    const res = arr.map(item => item[0]); // For some reason ConstructorParameters<T>[number][]
}

How can I make testTwo work like testOne?

[vagrant bramble]

that works:

type ArrMap<T> = T extends readonly any[] ? { [Index in keyof T]: [T[Index], number]; } : never;

I guess its because you could pass an union and then all array properties like .map also get mapped to [T[Index], number] (not 100% sure tho)
https://www.typescriptlang.org/docs/handbook/advanced-types.html#distributive-conditional-types