isValidSpreadType doesn't handle type parameter

TypeScript Version: 2.7.0-dev.20171114

Code

function shallowClone<T extends object>(x: T): T {
    return { ...x };
}

Expected behavior:

No error.

Actual behavior:

src/a.ts(2,14): error TS2698: Spread types may only be created from object types.

@sandersn

[sandersn]

This is by design:

1. ...T is not assignable to T

class C {
  m() {
    return 'hi'
  }
}
shallowClone(new C()).m() // runtime error: 'm' is not a function

2. Typescript doesn't have a spread type because (1) makes it unusable for React without some constraint on T.