Generics with default and $ExpectType value

[malthe]

Consider the following example:

class Foo<T = number> {
    public bar: T;
}

declare const foo: Foo;

// $ExpectType Foo<number>
foo;

Should this be rendered instead as just Foo – ?

There's a situation that might motivate this further than just "it's simpler" which is that perhaps generics have been added to Foo but backwards compatibility is provided through the default type.

If a type is specified using just default types, should the tool drop those types from the output?

[jakebailey]

ExpectType is more or less the same as hovering, and hovering will show the instantiation. We call typeToString, and there doesn't seem to be a formatting flag that would omit type arguments when only defaults were used either.

See also twoslash queries: Playground Link

[malthe]

Some discussion over at Typescript on the behavior of typeToString: microsoft/TypeScript#43988.