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"This expression is not callable." false positive on union of generic functions where the call is valid for all types in the union #64855
Description
🔎 Search Terms
union generic function "has signatures, but none of those signatures are compatible with each other"
🕗 Version & Regression Information
tested on 6.0.3 and 7.0.2
⏯ Playground Link
💻 Code
declare const foo: (<T>(value: T) => T) | (<T extends number>(value: T) => T)
const asdf = foo(1)🙁 Actual behavior
This expression is not callable.
Each member of the union type '(<T>(value: T) => T) | (<T extends number>(value: T) => T)' has signatures, but none of those signatures are compatible with each other.
🙂 Expected behavior
no error, since the call is valid for both function types in the union
Additional information about the issue
No response
Activity
jcalz commentedon Oct 18, 2026
This is a known limitation of the work in #29011 to address #7294. Currently a union of call signatures can have at most one overloaded member and one generic member. Here you have two generic members, so TS does not try to unify. Not sure if this will be closed as a design limitation, or kept open as a feature request to try again to look at unification, but it's not considered a bug.