Repository navigation
Assertion function & Type guards for Record types broken on 5.0 #53379
Description
🔎 Search Terms
- asserts
- assertion function
- type guard
- record
🕗 Version & Regression Information
Worked on 4.9, broken since 5.0
Probably introduced by #52984
⏯ Playground Link
Playground link with relevant code
💻 Code
declare function isObject(o: unknown): o is Record<string, any>
declare function assertObject(o: unknown): asserts o is Record<string, any>
let value: {} = null!;
if(isObject(value)) {
value.anything // error since 5.0.2
}
assertObject(value)
value.anything // error since 5.0.2🙁 Actual behavior
Property 'anything' does not exist on type '{}'.(2339)
🙂 Expected behavior
No error, narrowing / assertion should work fine.
Activity
ahejlsberg commentedon Mar 20, 2023
Hmm, looks like the strict subtype relation considers
{}andRecord<string, any>to be mutual subtypes. That's an oversight and apparently we don't have test coverage for that combination. It should be the case that{}is a strict supertype ofRecord<string, any>, similar to{}being a strict supertype ofRecord<string, unknown>(for which we do have test coverage).