ICE in libsyntax/codemap.rs

[lambda-fairy]

Here's a Christmas present for you all:

$ rustc --version
rustc 0.9-pre (b8c87fd 2013-12-24 01:56:30 -0800)
host: x86_64-unknown-linux-gnu

$ rustc main.rs
task 'rustc' failed at 'assertion failed: bpos == mbc.pos || bpos.to_uint() >= mbc.pos.to_uint() + mbc.bytes', /home/chris/.local/rust/src/libsyntax/codemap.rs:479
error: internal compiler error: unexpected failure
...
task '<main>' failed at 'explicit failure', /home/chris/.local/rust/src/librustc/lib.rs:443

The code that causes it is here. I couldn't reduce it further, so I hope it's clear enough.