Repository navigation
Generic functions combining a conditional type and an intersection are not assignable to themselves #51399
Description
🔎 Search Terms
"same type assignable"
"Two different types with this name exist, but they are unrelated."
🕗 Version & Regression Information
Please keep and fill in the line that best applies:
- This is a crash
- This is the behavior in every version I tried (3.3.3 to nightly), and I reviewed the FAQ for entries about it
⏯ Playground Link
Playground link with relevant code
💻 Code
declare let a: <T>() => (T extends true ? true : false) & boolean
declare let b: <T>() => (T extends true ? true : false) & boolean
a = b🙁 Actual behavior
This produces the following error message:
Type '<T>() => (T extends true ? true : false) & boolean' is not assignable to
type '<T>() => (T extends true ? true : false) & boolean'.
Two different types with this name exist, but they are unrelated.
Type 'false' is not assignable to type '(T extends true ? true : false) & boolean'.
Also, the following unexpectedly removes the error message:
- Removing
& boolean - Replacing
T extends true ? true : falsebytrue - Replacing
T extends true ? true : falsebyT extends true ? true : true - Replacing
b's type bytypeof a
🙂 Expected behavior
Since the two types are identical, a and b should be assignable to each other.
Activity
ahejlsberg commentedon Nov 4, 2022
Hmm, yeah, this looks like an issue in type inference between similar intersections.
ehmicky commentedon Nov 5, 2022
Thanks a lot Anders Hejlsberg (@ahejlsberg) for the quick fix! 🚀
FrameMuse commentedon Jan 12, 2023
Sorry for a bit unrelated comment (it's too long to search for similar issues and I'm too lazy to create a new one), but similar thing happening here when I try to return
1and2. It throws error sayingType '1' is not assignable to type 'Options["enabled"] extends true ? 1 : 2'.ts(2322).RyanCavanaugh commentedon Jan 12, 2023
Valery Zinchenko (@FrameMuse) see #33912