Unexpected excess property error with intersection of index signatures

[jcalz]

Bug Report

🔎 Search Terms

index signature, intersection, excess property checking

🕗 Version & Regression Information

• This changed between versions 4.8.0-dev.20220613 and 4.8.0-dev.20220614

⏯ Playground Link

Playground link with relevant code

💻 Code

let x: { [k: string]: { a: 0 } } & { [k: string]: { b: 0 } };

x = { y: { a: 0, b: 0 } } // error!
//               ~~~~  
// Object literal may only specify known properties, 
// and 'b' does not exist in type '{ a: 0; }'

x = { y: { a: 0 } } // error!
//    ~
// Property 'b' is missing in type '{ a: 0; }'

🙁 Actual behavior

The object literal { a: 0, b: 0 } is considered to have an excess property of b, but if you remove b then the compiler will complain that b is missing. It's a catch-22!

🙂 Expected behavior

The object literal { a:0, b: 0 } should be accepted.

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This came from this Stack Overflow question. Looks like it started with #49503.

[fatcerberus]

Property b is missing in type { a: 0; }

Nice.