This tarball kills rustc with the above error:
www.leptoquark.net/~elly/rustsocket-nematch.tar
The stack trace is:
#0 upcall_fail (task=0x87239e4, expr=0x86e3630 "non-exhaustive match failure",
file=0x86e3650 "src/comp/middle/resolve.rs", line=1148) at ./src/rt/rust_upcall.cpp:237
#1 0x08145af3 in middle::resolve::map_crate::index_i ()
#2 0x0868f50c in middle::resolve::map_crate::thunk2985 ()
#3 0x0833bc3e in syntax::visit::visit_mod ()
#4 0x086b0007 in syntax::visit::default_visitor::thunk5346 ()
#5 0x0813fbf1 in middle::resolve::resolve_crate ()
#6 0x086cffe8 in driver::rustc::compile_input::thunk7925 ()
#7 0x0861bcd3 in driver::rustc::time ()
#8 0x0861e978 in driver::rustc::compile_input ()
#9 0x0865d934 in _rust_main ()
#10 0x086d6a2c in _rust_main_wrap ()
#11 0xf7fca6e1 in task_start_wrapper (a=0xf65a600c) at ./src/rt/rust_task.cpp:128