Indexed this types don't narrow when their referenced property narrows

[JakeTunaley]

TypeScript Version: 3.1.0-dev.20180829

Search Terms: this index narrowing generics

Code

type Keys = 'string' | 'number';
type Switch<T extends Keys> =
	T extends 'string' ? string :
	T extends 'number' ? number :
	never;

interface Main<T extends Keys> {
	kind: T;
	value: Switch<this['kind']>;
}

let x: Main<Keys> = null as any;

x.kind;
x.value;
if (x.kind === 'string') {
	x.kind; // Narrowed to "string"
	x.value;
} else {
	x.kind; // Narrowed to "number"
	x.value;
}

Expected behavior:
In the first if block, x.value should be of type string. In the second if block, x.value should be of type number.

Actual behavior:
In both cases x.value is not narrowed, despite x.kind narrowing successfully.

Related Issues: #24085