4.9 regression: unexpected error using in operator on generic object intersected with {}

[OliverJAsh]

Bug Report

🔎 Search Terms

• in operator
• generic
• object

🕗 Version & Regression Information

• This changed between versions 4.8 and 4.9

⏯ Playground Link

Playground link with relevant code

💻 Code

const f = <P extends object>(a: P & {}) => {
    // Unexpected error:
    // Type 'P & {}' may represent a primitive value, which is not permitted as the right operand of the 'in' operator.ts(2638)
    "foo" in a;
};

🙁 Actual behavior

See code comment above.

🙂 Expected behavior

See code comment above.

[fatcerberus]

Duplicate of #51501 (NonNullable<T> is defined as T & {} so it's the same issue) and the fix is #51502

[Andarist]

I can confirm that my PR fixes this issue. I've pushed out this repro case as an additional test case: 42ac98e