Type check and Object key completion on overloaded functions with generic types defined in a class are incorrect #58226

🔎 Search Terms

generic overload class

I found an issue #53734 similar to the problem I had, but I am not quite sure if the root cause is the same. Therefore, I am opening this issue.

🕗 Version & Regression Information

This is the behavior in every version I tried, and I reviewed the FAQ for entries about Functions and Generics .

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.4.5#code/JYOwLgpgTgZghgYwgAgEJysg3gKGckOAWwgC5kBnMKUAcwG4cBfHAEwgQBsMUu4KKyAGIB7EdjzJOIuKwA8AFWQQAHpBCtB6KAG0AugD4AFJ2BVyVGiFr6AlOQAKUEUTMRFBxvmmzFytRAaWhjGhCQW1HT2yE4ubh6MkgD0ScgAkjDpyFAQAG7QYMhgABYoIvlQPqzI7DCgwGDAIiAANMgNlI2cnDUiEIIgIoUA7iJQANbI-P4ADhyQrAB0yalVfqrqmmghRmFknVa00bGuFO4KnitSMvJKG4Fb2vrGpuYHdHaOzqfnlyw4CGaVGQMDEyAAvAQIMNhGIjLYcDhQSJFmsnoYjDoAORYvS2ZApZAAYTGOQQhTAAE85sgEKUEOMkWJUTc5NpjDj8YS5ABaPk89IgQFQMkU6m8emTUo5RbIBSlZAzDDECCQTBUmkUYoiACunGqACMUKAYNActVpgADSx0S3IA06wpmZDWyLWfSW5Y4IA

💻 Code

interface Bar {
  name: string;
}
declare class Foo {
  load<T extends Bar[]>(list: string[]): Promise<T>;
  load<T extends Bar>(name: string): Promise<T>;

  // If I revert the overload definition, it still does not work as expected.
  // load<T extends Bar>(name: string): Promise<T>;
  // load<T extends Bar[]>(list: string[]): Promise<T>;
}

const foo = new Foo()

foo.load<Bar[]>(['']) // Correct type check
foo.load<Bar>('') // <---- Incorrect type check here. The parameter type should be inferred as `string` but is `string[]`.

🙁 Actual behavior

When overload function in class with generic type(One is an array and the other is a normal type), Typescript could not match the correct type.

I know that Typescript check the overloaded function from top-to-down, but it still not working even if i revert the definition.

🙂 Expected behavior

Should match the correct type in that case.

Additional information about the issue

No response