Test case:

fn main() {}

struct A;

impl A {
    fn b(&mut self) {
        self.a()
    }
}

trait Foo {}
trait Bar {
    fn a(&self);
}

impl Foo for A {}
impl<T> Bar for T where T: Foo {
    fn a(&self) {}
}

rustc output:

a.rs:7:9: 7:17 error: the trait `Foo` is not implemented for the type `&mut A`
a.rs:7         self.a()
               ^~~~~~~~
error: aborting due to previous error

Expected behavior: &mut self is automatically converted to &self in the self.a() call.

The bug disappears if fn b is changed to take &self, if fn a is changed to take &mut self, or if the call is changed to (&*self).a().

CC @aturon