Object spread can lead to unknown properties added [Regression v3.1.6]

[Cellule]

TypeScript Version: 3.6.0-dev.20190719

Search Terms:
spread
type check

Code

// Error as expected, b2 is not a valid key
const foo: {a?: string; b?: string} = {
    //a: "",
    ...{b2: ""}
}
// I meant to overwrite b, but somehow this is accepted
const bar: {a?: string; b?: string} = {
    a: "",
    ...{b2: ""}
}

Expected behavior:
bar should not accept ...{b2: ""}

Actual behavior:
bar has type {a?: string; b?: string}, but at runtime actually has extra property b2

Playground Link:
No problem v3.0.1
Regression v3.1.6

Related Issues:
#30129

[micheleangioni]

I've run into this problem as well. It's still present in 3.7.2

Other example

[hikarino-my]

I've created a PR that will fix this issue.
Could someone check for it please?
#37392

[manast-apsis]

Not sure but seems to me that this issue should have quite a big impact in angular apps that use ngrx, where spread operator is commonly used to copy state properties from one action to the next in the reducers... basically it allows you to put any data on the state without being aware of it.