Is there a special 'hack' for operators and string literal types? #6505

type WeekDay = "Monday" | "Tuesday" | "Wednesday" | "Thursday" | "Friday" | "Saturday" | "Sunday";

function doFun(a: WeekDay | WeekDay[]) {
    a = "Monday";  // string literal is contextually typed, so it has string literal type "Monday" => no type mismatch
    if (a === "Monday") { // string literal is NOT contextually typed and has type 'string' => should be type mismatch error

    }
}

Type mismatch error in the second case should be because:

1. we're comparing 'string' with "Monday" | "Tuesday" | "Wednesday" | "Thursday" | "Friday" | "Saturday" | "Sunday" | ("Monday" | "Tuesday" | "Wednesday" | "Thursday" | "Friday" | "Saturday" | "Sunday")[] for assignability in both directions
2. according to the spec, in direction 'string' => the-other-type, we're comparing 'string' with all union type constituents, and it's not assignable to any of them => fail
3. according to the spec, in direction the-other-type => 'string', all constituents of the-other-type should be assignable to 'string', but obviously Array is not assignable to it => fail
4. both conditions fail => type mismatch error for '===' operator

But by some reason the compiler doesn't show any errors here.

Is there some special handling of string literal types with operators like '===', switch labels, etc?