Can't get InstanceType of own property within class method

[Alacrit]

TypeScript Version: 3.6.4

Search Terms:
InstanceType of this

Code

class Test {

    public prop: StringConstructor = String;
    public test!: InstanceType<this['prop']>;

    public fn() {
        let v1: InstanceType<StringConstructor>,
            v2: InstanceType<this['prop']>,
            v3: this['prop'];

        v1 = 'str'; // OK
        v2 = 'str'; // Type '"str"' is not assignable to type 'InstanceType<this["prop"]>'.
        v3 = String; // OK, TS knows type of this['prop']
        this.test = 'str'; // Type '"str"' is not assignable to type 'InstanceType<this["prop"]>'.
    }

}

let obj = new Test();
obj.test = 'str'; // OK

Expected behavior:
InstanceType<this['prop']> as String

Actual behavior:
Error: Type '"str"' is not assignable to type 'InstanceType<this["prop"]>'.

[RyanCavanaugh]

This is the intended behavioral difference between a this types and the alternative name Test['prop'] - a subtype of Test might have a more specific type of prop

[typescript-bot]

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.