ICE: panicked at 'Box<Any>'

[vadimcn]

#![feature(unboxed_closures)]
fn main() {
    let _: Box<FnOnce<(),()>> = box move|&mut:|{};
}

error: internal compiler error: argument to function with "rust-call" ABI is neither a tuple nor unit
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' panicked at 'Box<Any>', /build/rust-git/src/rust/src/libsyntax/diagnostic.rs:175

Playpen

[bkoropoff]

Looks like substitutions weren't being applied in all places, resulting in it choking on an unsubstituted type parameter. The fix should hopefully be easy.