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Check order dependence with mutually-recursive non-unary generics #44572
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It's reproducible on the playground: Playground link Deleting the unused |
Simplified and cleaned up a little to make the violation more apparent interface Parent<A> {
child: Child<A> | null;
parent: Parent<A> | null;
}
interface Child<A, B = unknown> extends Parent<A> {
readonly a: A;
// This field isn't necessary to the repro, but the
// type parameter is, so including it
readonly b: B;
}
function fn<A>(inp: Child<A>) {
// This assignability check defeats the later one
const a: Child<unknown> = inp;
}
// Allowed initialization of pu
const pu: Parent<unknown> = { child: { a: 0, b: 0, child: null, parent: null }, parent: null };
// Should error
const notString: Parent<string> = pu;
// Unsound read on .child.a
const m: string = notString.child!.a; |
Debugging notes: variance measurement for I'm not sure if any of those comparisons ever actually looked at |
@weswigham, I may need some help/advice on this one. |
We should probably make a |
The |
IIRC, when |
I've spent the last 1.5 days debugging something that looks awfully like this one. This is way beyond my head and the understanding of the type system so I can't fully assess if my issue is exactly the same or just similar. Therefore I'm going to post it, for the time being, to avoid creating a new issue that might be a duplicate of this one. code from the playgrounddeclare class StateNode<TContext, TEvent extends { type: string }> {
// if I comment out this property then error is never reported
_storedEvent: TEvent
// if I comment out this property then error is always reported
_action: ActionObject<TEvent>
// if I comment out this property then error is always reported
_state: StateNode<TContext, any>;
}
interface ActionObject<TEvent extends { type: string }> {
exec: (meta: StateNode<any, TEvent>) => void
}
export declare function createMachine<
TEvent extends { type: string }
>(action: ActionObject<TEvent>): StateNode<any, any>
export declare const execute: <TEvent extends { type: string }>(
handler: (event: TEvent) => any
) => ActionObject<TEvent>;
export declare function interpret<TContext>(
machine: StateNode<TContext, any>
): void
// uncomment to get a correct report in the `createMachine` call below
// const test: ActionObject<{ type: "PLAY"; value: number } | { type: "RESET" }> =
// {} as ActionObject<{
// type: "PLAY";
// value: number;
// }>;
const machine = createMachine({} as any);
// comment out to get a correct report in the `createMachine` call below
interpret(machine);
createMachine<{ type: "PLAY"; value: number } | { type: "RESET" }>(
execute((ev: { type: "PLAY"; value: number }) => {
console.log(ev);
})
); I've also found out that this has changed between 3.7 and 3.8. More accurately - between I know that at this point I'm probably just reiterating what you probably already know but since I've already done this detective work I'm posting this here as a reference, just in case. I also have a hunch that another issue that I've posted some months ago might be related to this one: #45859 (I would have to confirm this when this one here gets fixed) |
Bug Report
Adding an implementation of an interface allows an invalid assignability check of the interface to pass
🔎 Search Terms
assignability, unnecessary implementation
🕗 Version & Regression Information
It's still present in all versions including nightly.
⏯ Playground Link
Playground link with relevant code
Thanks @MartinJohns for the link
💻 Code
The final assignment should not pass. It accurately errors in 3.7.5, if the
Impl
class is removed (or any aspect of theiter
implementation is modified), or by adding a sentinel type likesentinel?: A
to theParent
interface to aid in type checking.🙁 Actual behavior
No error is thrown in the final assignment.
🙂 Expected behavior
A n error is throw:
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