What seems to be a borrowchecker regression

borrow-regression.rs

// This compiles without error on stable and beta but gives a borrow
// error on nightly. It worked as of nightly 6e5a32547.

// Replacing the .by_ref() with explicitly taking a &mut ref fixes it.
// Other more dubious things fix it also.

pub type Session = i32;

pub struct StreamParser<'a, T: Iterator<Item=i32>> {
    _tokens: T,
    _session: &'a mut Session,
}

impl<'a, T: Iterator<Item=i32>> StreamParser<'a, T> {
    pub fn thing(&mut self) -> bool { true }
}


pub fn parse_stream<T: Iterator<Item=i32>, U, F>(
        session: &mut Session,
        tokens: T,
        f: F) -> U
    where F: Fn(&mut StreamParser<T>) -> U {

    let mut tokp = StreamParser { _tokens: tokens, _session: session };
    f(&mut tokp)
}

pub fn thing(session: &mut Session) {
    let toks = vec!(1, 2, 3);
    let mut stream = toks.into_iter();

    let _b = parse_stream(session,
                          stream.by_ref(),
                          // If the by_ref is replaced with &mut stream
                          // it works on nightly
                          //&mut stream,
                          |p| p.thing());

}

fn main() {}