self in expanded macro erroneously talks about static methods

[TimNN]

The following code (playpen):

macro_rules! slf { () => (self;) }

struct Foo;

impl Foo {
    fn bar(self) {
        slf!();
    }
}

causes the error:

`self` is not available in a static method. Maybe a `self` argument is missing?

which is obviously incorrect (and probably caused by a specialized error message if self is an unknown identifier, I would imagine).

[TimNN]

Dupe of #26946.