[keyof T] Bug

[fc01]

//Type A ----> Type B
export type A = {
    f1: { x: number, y: number },
    f2: { str: string }
}

export type B =
    { type: 'f1', x: number, y: number } |
    { type: 'f2', str: string }




//error
type GetB<T> = {
    [P in keyof T]: T[P] & { type: P }
}[keyof T]

export type XXX = GetB<A>

/* type XXX is ??

({
    x: number;
    y: number;
} & {
    type: "f1" | "f2";  //<---------------------  ???
}) | ({
    str: string;
} & {
    type: "f1" | "f2";  //<---------------------  ???
})

*/


//right
type GetB2<T> = {
    [P in keyof T]: T[P] & { type: P }
}
export type XXX2 = GetB2<A>[keyof A] 

[jcalz]

Duplicate of #15756. This will be fixed in TypeScript 2.6.