Strict typing for object spread in higher order function.

[ccorcos]

TypeScript Version: 2.9.2
Search Terms: strict object literal higher order function object spread
Code

// A *self-contained* demonstration of the problem follows...
// Test this by running `tsc` on the command-line, rather than through another build tool such as Gulp, Webpack, etc.

Expected behavior:

type A = { x: number, y: number }

const x: A = { x: 1, y: 2 }

const y: A = {...x, b: 10} // Error ✅

function hoc(fn: (a: A) => A) { }

hoc(a => ({a: 1, y: 2, b: 10})) // Error ✅

hoc(a => ({ ...a, b: 10 })) // No Error ❌

Actual behavior:

I would expect the hoc(a => ({ ...a, b: 10 })) to throw an error.

Playground Link: playground

[mhegazy]

Duplicate of #12632

[ccorcos]

Thanks!