Type Checker Fails to Check Outer Type When Spread Operator is used

[MichaelScheffenacker]

Bug Report

The type checker seems to fail to check the outer type when a spread operator is used .

🔎 Search Terms

repo:microsoft/TypeScript spread type not checked array to object

ts spread operator outer type check fails
ts bug spread operator fails when cast to object instead of array

🕗 Version & Regression Information

Tested on the playground with version 5.1.6, 5.0.4, 4.9.5, 3.9.7

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about spread operator or anything regarding to it. FAG Page.

⏯ Playground Link

TS Playground

There is also this Stack Overflow Question about it.

💻 Code

interface ITest {
  value: number;
};

let x: ITest[] = [{  value: 10 }];

x = { ...x };  // no type check error, but is an object instead of an array
x = { ...[{value: 10}] }  // no type check error, but is an object instead of an array
x = { "0": {value: 10} };  // type check error, is correct
x = { "0": {value: 10}, ...[] };  // no type check error, but is an object instead of an array
x = [ {value: 10} ];  //  no type check error, is correct

🙁 Actual behavior

Type checker does ignore the outer object literal when using the spread operator even though the type is supposed to be an array.

🙂 Expected behavior

Type checker should recognise the outer type if the spread operator is used and raise a mismatched type error.

[MartinJohns]

Duplicate of #52060 / #9726.

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.

[MichaelScheffenacker]

@MartinJohns @RyanCavanaugh I see that this is a duplicate of what is discussed in the later parts of #9726 but I do not quite understand why it falls under the same topic as #9726 was initially created for. I see that it might cause the issue in some tangled ways, but would it not still be much easier to fix than the origina #9726 ? The type checker would just have to look at the outer type (Array or Object literal) to decide that there is a type mismatch. The inner type is checked correctly anyways, why not check the out type too? (Sorry, if I have a simplistic view about it, but currently I have no deeper insight about the type checking constraints there ...)