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Recursive type alias in union type breaks in 3.8.3 #37344
Description
TypeScript Version: 3.8.3
Search Terms: recursive, recursion
Code
type Action<T, P> = P extends void ? { type : T } : { type: T, payload: P }
enum ActionType {
Foo,
Bar,
Baz,
Batch
}
type ReducerAction =
| Action<ActionType.Bar, number>
| Action<ActionType.Baz, boolean>
| Action<ActionType.Foo, string>
| Action<ActionType.Batch, ReducerAction[]>Expected behavior: compiler does not complain recursive type alias, works fine in 3.7.5
Actual behavior: compiler complains recursive type alias, breaks in 3.8.3
Type arguments for 'Array' circularly reference themselves.
Related Issues:
I'm not sure, if this might be related to #35017.
Activity
stefanvonderkrone commentedon Mar 13, 2020
I must add that the recursive type definition of
ReducerActionseems to break because of the conditionality of theActiontype. If I remove the condition (type Action<T, P> = { type: T, payload: P }) then the type checking succeeds.weswigham commentedon Mar 13, 2020
Aye. The conditional's check for simplifiability makes the circularly referential array type get resolved too soon. We should probably defer simplifying conditionals over deferred type references like we do generics.