Error message for invalid string literal type could be improved

[NoelAbrahams]

TypeScript Version: 2.0 Beta

Code

// A *self-contained* demonstration of the problem follows...
interface Foo {

    method(value: 'aa'): void;
    method(value: 'bb'): void;
    method(value: 'zz'): void;
    method(value: 'last'): void;
}

const x: Foo = {} as any;

x.method('bar'); // Error line

Expected behavior:

A more meaningful error message, e.g.

Argument of type "'bar'" is not assignable to parameter of type "'aa' | 'bb'|...|'last'"

Actual behavior:

Argument of type "'bar'" is not assignable to parameter of type "'last'"

I am finding this error message confusing, because the compiler picks the value of the last overload in order to report the error, and there is nothing special about the last value.

[DanielRosenwasser]

I've rated this at moderate difficulty because overload resolution isn't the simplest part of the compiler.

For what it's worth, I don't think the suggested error message is the best because it implies you could actually pass in a value of type "aa" | "bb" | ... | "last", but that's not the case.

Also see @sandersn's issue at #6541.