Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/56592

@liuxingbaoyu Thank you for the swift fix!
I looked briefly at the PR and I have a feeling that it won't generate the same TS code in these cases:

type Foo2 = { [key in Bar]? };
type Foo3 = { [key in keyof Bar]-? };
type Foo4 = { [key in keyof Bar]+? };

You are right, thank you! I will open a new PR.

Ugh, til that's valid TS 😬

Suprisingly it is 😂