Decorated function parameter types are not inferred

Bug Report

When decorating a class method, the argument types are not inferred from the decorator. When using the decorator method directly, without decorator syntax, the types are inferred correctly.

🔎 Search Terms

decorator, infer, type, argument

🕗 Version & Regression Information

• This happens for decorators introduced in 5.0

⏯ Playground Link

Playground link with relevant code

💻 Code

function decorate(f: (id: number) => void, context?: any): (id: number) => void { return f }

class Foo {
    @decorate
    one(id) { // Parameter 'id' implicitly has an 'any' type.(7006)
        console.log(id as string)
    }

    two = decorate(function two(id) {
        console.log(id as string) // Conversion of type 'number' to type 'string' may be a mistake… (2352)
    })
}

let foo = new Foo();
foo.one("foo")
foo.two("foo") // Argument of type 'string' is not assignable to parameter of type 'number'.(2345)

🙁 Actual behavior

The parameter id for method one is inferred as any

🙂 Expected behavior

The parameter is inferred as number, similar to how it works when calling the decorated function directly for method two.