maybe_auto_unbox hang with uniq

[jruderman]

fn altsimple() { alt ~true { _ { } } }
fn main() { }

Hangs in the alias pass:

#0  upcall_malloc (task=0x1c00df0, nbytes=16, td=0x0) at ../src/rt/rust_upcall.cpp:57
#1  0x002c5563 in middle::mut::expr_root::maybe_auto_unbox ()
#2  0x002c8d16 in middle::mut::expr_root ()
#3  0x002e4124 in middle::alias::expr_root ()
#4  0x002db386 in middle::alias::check_alt ()
#5  0x002cf984 in middle::alias::visit_expr ()
#6  0x005e2ce3 in middle::alias::check_crate::thunk3652 ()
#7  0x002d0be0 in middle::alias::visit_block ()
#8  0x005e2a43 in middle::alias::check_crate::thunk3647 ()
#9  0x002cf38e in middle::alias::visit_fn ()
#10 0x005e2eb7 in middle::alias::check_crate::thunk3655 ()
#11 0x00391b00 in syntax::visit::visit_item ()
#12 0x00605ec2 in syntax::visit::default_visitor::thunk5307 ()
#13 0x0039160b in syntax::visit::visit_mod ()
#14 0x00605d0f in syntax::visit::default_visitor::thunk5304 ()
#15 0x00391332 in syntax::visit::visit_crate ()
#16 0x002ce21a in middle::alias::check_crate ()
#17 0x00643455 in driver::rustc::compile_input::thunk7996 ()
#18 0x0055a8a0 in driver::rustc::time ()
#19 0x00560402 in driver::rustc::compile_input ()
#20 0x005807b8 in driver::rustc::main ()
#21 0x0058230f in _rust_main ()
#22 0x0064852f in _rust_main_wrap ()
#23 0xdeadbeef in ?? ()

I think the problem is that middle::mut::expr_root::maybe_auto_unbox doesn't update "t" in the ty::ty_uniq arm.

[brson]

Yep, that's the problem