Spread operator should work with generic types

[falsandtru]

TypeScript Version: master

Code

function f<a extends Object>() {
	return {...<a>{}};
}
function g<a extends object>() {
	return {...<a>{}};
}

Expected behavior:

ok

Actual behavior:

index.ts(2,10): error TS2698: Spread types may only be created from object types.
index.ts(5,10): error TS2698: Spread types may only be created from object types.

[HerringtonDarkholme]

Another example, it's quite hard for TypeScript to prove a type constraint is spreadable given structural typing

class NonPrimitive {
 private cannotBePrimitiveBrand
}
function t<T extends NonPrimitive>(a: T, b: NonPrimitive) {
 var c = { ...a }
 var d = { ...b }
}

#2103 (comment)

[billba]

Another example:

interface Foo {
 foo: string;
}

const addBar = <F extends Foo>(input: F) => ({
 ... input,
 bar: 5
});

Build 2.3.0-dev.20170424 gives error TS2698: Spread types may only be created from object types. on ...input,

[mhegazy]

Duplicate of #10727. Fixed by #13288

[billba]

Mohamed Hegazy (@mhegazy) This is still happening in the current build.

[mhegazy]

yes. #13288 is not merged yet. we do not have an ETA at the moment.

[billba]

Aha, thanks.

[LKay]

When it will be fixed finally? The problem persists and it's breaking code all over the place!

[devlato]

Any plans fixing this?