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Extend {} type checking failureΒ #55546
Description
π Search Terms
type checking on extending generics
π Version & Regression Information
- This changed between versions 5.1.6 and 5.2.2
β― Playground Link
No response
π» Code
export interface ItemDef<T extends {}, K extends keyof T> {
id: keyof T extends string ? keyof T : never;
subItem?: keyof T;
children?: T[K] extends Array<infer U> ? ItemDef<U extends {} ? U : never, keyof U> : ItemDef<T[K], keyof T[K]>;
render: (props: RenderPropsItem<T>) => ReactNode;
renderBody?: (props: RenderPropsItem<T>) => ReactNode;
}
interface RenderProps {
id: string;
[key: string]: unknown;
}
export type RenderPropsItem<T> = T & RenderProps;
export interface RenderItem {
id: string;
data: unknown;
render: (...args: unknown[]) => ReactNode;
renderBody?: (...args: unknown[]) => ReactNode;
subItems?: RenderItem[];
isExpanded?: boolean;
isExpandable?: boolean;
toggleExpanded: () => void;
}π Actual behavior
In the new 5.2 version the children property on type checking returns an error
Type error: Type 'T[K]' does not satisfy the constraint '{}'.
Type 'T[keyof T]' is not assignable to type '{}'.
Type 'T[string] | T[number] | T[symbol]' is not assignable to type '{}'.
Type 'T[string]' is not assignable to type '{}'.
on line children?: T[K] extends Array<infer U> ? ItemDef<U extends {} ? U : never, keyof U> : ItemDef<T[K], keyof T[K]>;
while in the previous version the type check was fine
π Expected behavior
Not sure if it was an error on previous version (5.1.6) or it's a regression.
If a regression to work fine
Additional information about the issue
No response
Activity
Andarist commentedon Aug 28, 2023
Bisected it to this diff which clearly points to #54845 .
This code didn't typecheck with 5.0 and the fact that it did typecheck ok with 5.1 was a bug. This works as intended.
You need to find a way to add the appropriate constraint to
T[K]there. I see that you are already doing thisItemDef<U extends {} ? U : never, keyof U>in the array-related branch of this conditional type. A similar thing would do the trick in the branch that doesn't typecheck today:ItemDef<T[K] extends {} ? T[K] : never, keyof T[K]>. That said, I'd probably try to improve theT's constraint on your place.typescript-bot commentedon Aug 31, 2023
This issue has been marked as "Working as Intended" and has seen no recent activity. It has been automatically closed for house-keeping purposes.