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Confusing missing property error in a circular situation #62180
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Domain: Mapped TypesThe issue relates to mapped typesThe issue relates to mapped typesHelp WantedYou can do thisYou can do thisPossible ImprovementThe current behavior isn't wrong, but it's possible to see that it might be better in some casesThe current behavior isn't wrong, but it's possible to see that it might be better in some cases
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🔎 Search Terms
missing property mapped type getter deferred
🕗 Version & Regression Information
- This is the behavior in every version I tried
⏯ Playground Link
💻 Code
interface ZodType<T> {
optional: "true" | "false";
output: T;
}
interface ZodString extends ZodType<string> {
optional: "false";
}
type ZodShape = Record<string, any>;
type Prettify<T> = { [K in keyof T]: T[K] } & {};
type InferObjectType<Shape extends ZodShape> = Prettify<
{
[k in keyof Shape as Shape[k] extends { optional: "true" }
? k
: never]?: Shape[k]["output"];
} & {
[k in keyof Shape as Shape[k] extends { optional: "true" }
? never
: k]: Shape[k]["output"];
}
>;
interface ZodObject<T extends ZodShape> extends ZodType<InferObjectType<T>> {
optional: "false";
}
interface ZodOptional<T extends ZodType<any>>
extends ZodType<T["output"] | undefined> {
optional: "true";
}
declare function object<T extends ZodShape>(shape: T): ZodObject<T>;
declare function string(): ZodString;
declare function optional<T extends ZodType<any>>(schema: T): ZodOptional<T>;
const Category = object({
name: string(),
get parent() {
// Argument of type 'ZodObject<{ name: ZodString; readonly parent: ZodOptional<ZodType<any>>; }>' is not assignable to parameter of type 'ZodType<any>'.
// Property 'output' is missing in type 'ZodObject<{ name: ZodString; readonly parent: ZodOptional<ZodType<any>>; }>' but required in type 'ZodType<any>'.(2345)
return optional(Category);
},
});
export const output = Category.output;🙁 Actual behavior
A very confusing error is produced here. A ZodObject extends ZodType and that has an output property so how it can be missing?
🙂 Expected behavior
I don't expect to see this error
Additional information about the issue
Note that if we remove export const output = Category.output; then we can see a new error appearing:
'parent' implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions.(7023)
And this one makes sense (but I'd argue the other one shouldn't appear at all in this scenario).
This has changed with #58337 , before this PR the circularity error was present with and without export const output = Category.output;
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Domain: Mapped TypesThe issue relates to mapped typesThe issue relates to mapped typesHelp WantedYou can do thisYou can do thisPossible ImprovementThe current behavior isn't wrong, but it's possible to see that it might be better in some casesThe current behavior isn't wrong, but it's possible to see that it might be better in some cases
Activity
Fix ghost errors when relating a type whose inherited members are bei…
ahejlsberg commentedon Sep 18, 2026
The issue here is that in
resolveObjectTypeMemberswe first temporarily resolve to the declared members of the type and then incrementally add the inherited members until we reach the fully resolved type. This means that it is possible to observe members missing during base class resolution. I'm going to experiment with stricter enforcement of idempotent resolution, but I already know it will cause some breaks. For example, I've observed interfaces that pass themselves as type parameters to their base interfaces such that they can iterate ofkeyof Tfor the finalT.