Maintain freshness on the result of onbject spread operator

[mhegazy]

interface I { 
    a: number;
    b: string;
}

var obj = { c: true };

var i: I = { a: 0, b: "s", c: obj.c };// Error, unknown property c
var i: I = { a: 0, b: "s", ...obj } // No error here.

[mhegazy]

As noted in #2103 (comment), spreading a symbolic name is different from adding the property definition in the object literal. in the later, an excess property is likely an error; in the earlier it is not necessarily one.

[aaronbeall]

@mhegazy

Why was this closed? Maybe I didn't understand but this is still an issue:

interface Foo {
  a: number;
  b: string;
}

declare const stuff: any;

const a: Foo = { a: 1, b: "b" } // Ok
const b: Foo = { a: 1, b: "b", c: "c" } // Error - Ok
const c: Foo = { a: 1, b: "b", c: "c", ...stuff } // No Error - not Ok!

I don't understand why the presence of ...stuff makes the unknown typed property c become allowed. If it was part of stuff I understand this is a "bag or properties" you don't want to error on unknown properties, but why does it allow previous errors to become allowed?

[markudevelop]

I'm facing the same issue why was that declined?

[mhegazy]

An update on this issue. we have revisited the original decision (more in #14853), and some of the patterns involving spread should be flagged now as errors in TS 2.4, see #15908.

[aaronbeall]

@mhegazy That's great news! Thanks for the update!