ICE: sequence_element_type called on non-sequence value: Box<str>

[insideable]

Code:

struct Foo {
    name: Box<str>
}

impl Foo {
    fn new(name: Box<str>) -> Foo {
        Foo { name: name }
    }
}

fn main() {}

Compilation fails with ICE:

error: internal compiler error: sequence_element_type called on non-sequence value: Box<str>
note: the compiler hit an unexpected failure path. 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' failed at 'Box<Any>', /home/matrix/github/rust/src/libsyntax/diagnostic.rs:169

$ rustc -v
rustc 0.12.0-dev (9a2286d3a 2014-10-03 07:33:26 +0000)

[insideable]

Simplified example with same result:

fn f(s: Box<str>) -> Box<str> {
    s
}

fn main() {}

[ghost]

Fixed in #17762. Closing.