TypeScript incorrectly detects nullable when using Required operator

[LeHibouMT]

🔎 Search Terms

"Required", "Undefined"

🕗 Version & Regression Information

• This changed between versions 5.7.2 and 5.7.3
• This changed in commit or PR _______
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about Required Operator
• I was unable to test this on prior versions because I lacked times

⏯ Playground Link

https://playcode.io/2273403

💻 Code

interface Link {
path: string;
label: string;
subLinks?: [Link, ...Link[]]; // either undefined or defined with at least one element
}

let testRequiredArray: Required[] = [];

const testArray: Link[] = [
{ path: '1', label: '1' },
{ path: '2', label: '2', subLinks: [{ path: '3', label: '3' }] },
];

testArray.map(link => {
if (!link.subLinks) {
console.log('no sublinks!');
} else {
console.log('sublinks!');
// error
testRequiredArray = [...testRequiredArray, link];
// but this work as typescript knows that sublinks is defined and have at least one element
let test = link.subLinks[0];
}
});

🙁 Actual behavior

TypeScript doesn't detect in the "if" block that a value should be defined so it leads to an error when trying to use it for a Required variable.

I have the error: Type 'Link' is not assignable to type 'Required'.
Types of property 'subLinks' are incompatible.
Type '[Link, ...Link[]] | undefined' is not assignable to type '[Link, ...Link[]]'.
Type 'undefined' is not assignable to type '[Link, ...Link[]]'.ts(2322)

🙂 Expected behavior

TypeScript should detect that its defined.

Additional information about the issue

I used it with React but the same error appears with regular TypeScript code.

[MartinJohns]

Duplicate of #42384.

• This changed between versions 5.7.2 and 5.7.3

I doubt that this is true.