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Circularity error in intersection of object with index signature #38672
Description
TypeScript Version: 4.0.0-dev
Code
type Foo1 = { x: string } & { [x: number]: Foo1 }; // Circularity error
type Foo2 = { x: string } & { [K in number]: Foo2 }; // No errorExpected behavior:
No errors.
Actual behavior:
Error: Type alias 'Foo1' circularly references itself.
Playground Link:
Activity
ahejlsberg commentedon May 20, 2020
Noticed this as I was writing some code. Issue is we check for empty object types in intersections, which currently causes resolution of object type members, which in turn causes unexpected circularities when the types have index signatures. We need to revise the empty object type check to not require member resolution (which really isn't necessary).
DanielRosenwasser commentedon May 20, 2020
Brian Terlson (@bterlson) I think you ran into some weird code that wasn't working here. Check out the packed playground when it's ready over at #38673 (comment)
DanielRosenwasser commentedon May 20, 2020
Glad this was a bug, others on the team were telling me this behavior was expected which made no sense because...well, it was a big feature in 3.7!