implicit 'any' in method with parameter of inferred generic type

🔎 Search Terms

implicit 'any' method parameter inferred generic type

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about type inference

⏯ Playground Link

https://www.typescriptlang.org/play/?suppressImplicitAnyIndexErrors=true&ts=5.5.0-dev.20240531#code/C4TwDgpgBAwg9gOwM7AE4FcDGw6oDwAqAfFALxQDeAUFFAhAO5QAUAdOwIaoDmSAXHQgA3CKgDaAXQCUAggG4qAXwVUAlgmCiAZh0zQA4hHqpVmAApcOAWySES1WgCMuA5sFlSyJIXFUATBUUqKlBIKAAZVRRCKAgAD00EPyQoVAgOP0QAGxBKRUkScgcoMQBpKHUoAGsIEDgtKAIJATF4ZDQsHHwCMokiABooQ2NTC1RrWx7SvolAlT8ITCyuaC10BGxVRCgtODgY+MTk1PTMhBy8guYwSxsBSOixdlYmohkoH38VJY4kFIAxPaUGhQTQoZieChBII-P5QABCXDywQA9CioABJBBaURGPQ7DiqLJIKi7ODMMRUNEAPQA-CCxIC4IMKM5UG5IcFaIpFBJ+gzEagWWyOcCQTyJFRpKj0VicWkNtAGLgqiSyRSGUzhVxRcVaMBWGDgBCFNzeVKpMF1JpUDp8QA5dBWRyiMYTOzApwuFjuOhOl2oTykby+AJKYKhaAPYAAJgOCSMxzSGWyuShBTInpK5UqNTqDSaLTaKAw2FwhF6Aygjudrtuk0rsyU80WyzSO3Wm22ZLjBFiCaSKWTZwu6b613r9yisbwT3Yr3enzDVNl2NxiqgytQqtJexjGrRUDpmr22vZwE54t5-NoYkFZ91XKgEotQA

💻 Code

type Constructor<T> = {
  new (...args: never[]): T;
};

interface GenericParams<T> {
  bar: (t: T) => void;
}

type List<T extends readonly {}[]> = {
  [K in keyof T]: [Constructor<T[K]>, GenericParams<T[K]>];
};

declare function foo<T extends readonly {}[]>(params: List<[...T]>): void;

class Foo {
  test() {}
}
class Bar {}

// Inference fails
foo([
//^?
  [Foo, {bar(t) {

  }}],
  [Bar, {bar(t) {

  }}]
])

// Inference works
foo([
  [Foo, {bar(t) {
    t.test();
  }}]
])

interface NumberParams<T> {
  bar: (t: number) => void;
}

type List2<T extends readonly {}[]> = {
  [K in keyof T]: [Constructor<T[K]>, NumberParams<T[K]>];
};

declare function foo2<T extends readonly {}[]>(params: List2<[...T]>): void;

// Inference works
foo2([
// ^?
  [Foo, {bar(t) {

  }}],
  [Bar, {bar(t) {

  }}]
])

🙁 Actual behavior

In the foo example, the parameter t in the associated bar methods are inferred as type any. It seems that TypeScript should be able to infer the actual types of the parameters.

🙂 Expected behavior

t is inferred as type T in each case, i.e. t should be Foo in the Foo case, and Bar in the Bar case.

There are two additional cases provided here: one with a single element in the provided array, and one where the parameters are not generic (number). In both cases, type inference does assign the correct non-any type. It's unclear what exactly the issue is in the first case.

Additional information about the issue

It's possible this is related to #47599, though I don't have enough knowledge of the internals to say whether or not it's the same class of bug. I haven't found another issue reporting this same behaviour.

Bắt đầu với bản tái hiện TypeScript Playground được liên kết và so sánh các lệnh gọi foo generic với các trường hợp một phần tử và non-generic của foo2. Theo dõi hành vi suy luận kiểu xung quanh kiểu List được ánh xạ; hoàn thành khi mỗi tham số bar được suy luận là Foo hoặc Bar thay vì any, trong khi các trường hợp khác vẫn chính xác.