Wrong bounds for macro named the same as a type parameter

[dtolnay]

use std::marker::PhantomData;

#[macro_use]
extern crate serde_derive;

macro_rules! T {
    () => { () };
}

// generates impl<T> Serialize for A<T>
#[derive(Serialize)]
struct A<T> {
    f: (),
    t: PhantomData<T>,
}

// generates impl<T> Serialize for A<T> where T: Serialize
#[derive(Serialize)]
struct B<T> {
    f: T!(),
    t: PhantomData<T>,
}

fn main() {}

When expanding B<T> we see T being used as a "path" in the macro and mistakenly conclude that the type parameter needs to be serializable.