isValidSpreadType doesn't handle type parameter

Nathan Shively-Sanders (@sandersn)

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.

This is by design:

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

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

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