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Bug from #23592 - Type 'keyof U & K' does not satisfy the constraint 'string | number | symbol' #23648
Description
TypeScript Version: 2.9.0-dev.20180424
Search Terms:
keyof, intersection, conditional types
Code
type Example<T, U> = { [K in keyof T]: K extends keyof U ? UnexpectedError<K> : NoErrorHere<K> }
type UnexpectedError<T extends PropertyKey> = T
type NoErrorHere<T extends PropertyKey> = TExpected behavior:
No errors.
Actual behavior:
Error on K in UnexpectedError<K> with message
Type 'keyof U & K' does not satisfy the constraint 'string | number | symbol'.
Type 'keyof U & K' is not assignable to type 'symbol'.
Playground Link:
Link (no error in playground)
Related Issues:
#23592
Activity
ahejlsberg commentedon Apr 24, 2018
The issue here is that we don't lift constraints over intersection types. Here's a simpler repro:
We need to lift the individual constraints of
TandUsuch that the intersection typeT & Uappears to have the constraintstring | number(formed by intersecting the individual constraints ofTandU).ahejlsberg commentedon Apr 24, 2018
The reason this shows up with #23592 is that we now have union type constraints for
keyof T.ahejlsberg commentedon Apr 24, 2018
Mohamed Hegazy (@mhegazy) Do you recall if we already have an issue for this?
mhegazy commentedon Apr 25, 2018
do not think i have seen this one before.