TypeScript: Inconsistent TS2345 error when using function generics
Bug Report
🔎 Search Terms
- Inconsistent 2345
- function generics
- extends 2345
- generics 2345
🕗 Version & Regression Information
- This changed from version 4.7.4+ and above
⏯ Playground Link
Playground link with relevant code
💻 Code
function func<T extends { foo: 1 }>(arg: T): void {}
func({ foo: 1, bar: 1 });
🙁 Actual behavior
bar property sometimes displayed as valid and sometimes produce an error:
Argument of type '{ foo: 1; bar: number; }' is not assignable to parameter of type '{ foo: 1; }'.
Object literal may only specify known properties, and 'bar' does not exist in type '{ foo: 1; }'.(2345)
When playing with the code live and change bar to bar222 or ba sometimes the error shown and sometimes not.
Refreshing the playground link with the changes always remove the error.
https://user-images.githubusercontent.com/534911/190869020-376ff387-56ff-48b3-83e4-43261b2b4d78.mov
🙂 Expected behavior
Always display as valid without any error.
{ foo: 1, bar: 1 } is a valid subtype of { foo: 1 } and so can legally be used to instantiate T.
Maybe related to https://github.com/microsoft/TypeScript/issues/49490
About this issue
- Original URL
- State: closed
- Created 2 years ago
- Comments: 18 (10 by maintainers)
I was using the editor with TS built from different commits. I was doing that within the TS repo itself so I could pretty easily jump between commits/builds
@OxleyS unfortunately, this looks like a different problem, especially given the call stack shared here
The correct behavior is for there to be no error here: excess property checks aren’t intended to apply to generic constraints.
{ foo: 1, bar: 1 }is a valid subtype of{ foo: 1 }and so can legally be used to instantiateT.