Check inferred `this` parameter against interface requirement `this: void`

Bug Report

🔎 Search Terms

interface method requirement this: void

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

Playground link with relevant code

💻 Code

interface Foo {
  method(this: void): number;
}
class Example implements Foo {
  x = 3;
  method() { return this.x; } // no error
}

🙁 Actual behavior

No error

🙂 Expected behavior

Error because the method implementation's implicit this: Example is not compatible with the interface requirement this: void.

The @typescript-eslint/unbound-method lint rule uses this: void as an annotation indicating the method is allowed to be used without binding this. However, there seems to be no checking from the TS compiler as to whether an inferred this type in a method implementation matches an interface requirement. Thus the lint rule can help you add this: void to the interface if you intend for functions to be usable when not bound... but neither the linter nor compiler currently help prevent runtime errors resulting from implementations with mismatched this types.