Inferred missing properties use resolved generic types rather than staying generic

TypeScript Version: 3.3.0-dev.20181212

Search Terms: declare property generic missing member

Code

class TestClass<T> {
    // Inferred:
    // otherValue: number;
    public constructor(
        public readonly value: T,
    ) { }
}


const foo = new TestClass<number>(1);

foo.otherValue = foo.value;

Expected behavior:

Declare property 'otherValue' should create otherValue: T;

Actual behavior:

...but it actually creates otherValue: number. Whatever generic type from the place you request the missing property be added will be the type of the property.

Playground Link: http://www.typescriptlang.org/play/#src=class%20TestClass%3CT%3E%20%7B%0D%0A%20%20%20%20%2F%2F%20Inferred%3A%0D%0A%20%20%20%20%2F%2F%20otherValue%3A%20number%3B%0D%0A%20%20%20%20public%20constructor(%0D%0A%20%20%20%20%20%20%20%20public%20readonly%20value%3A%20T%2C%0D%0A%20%20%20%20)%20%7B%20%7D%0D%0A%7D%0D%0A%0D%0A%0D%0Aconst%20foo%20%3D%20new%20TestClass%3Cnumber%3E(1)%3B%0D%0A%0D%0Afoo.otherValue%20%3D%20foo.value%3B%0D%0A

Related Issues: I found a lot of similar bugs but didn't see any that looked related...

Start with the provided TypeScript playground reproduction using typescript@next and verify whether the behavior still occurs. Trace how the missing property is inferred from the generic class and instantiated value. Done means the declared property preserves the generic type T rather than resolving to number, with a regression test covering the example.