ICE building Servo with 1.14.0-nightly (0491a2317 2016-11-08)

[nox]

± RUST_BACKTRACE=1 ./mach build -d
   Compiling glutin_app v0.0.1 (file:///Users/nox/src/servo/ports/glutin)
error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'already borrowed: BorrowMutError', ../src/libcore/result.rs:837
stack backtrace:
   1:        0x104829faa - std::sys::imp::backtrace::tracing::imp::write::he3d1bfbdbf113480
   2:        0x104839d6f - std::panicking::default_hook::{{closure}}::h575f1b40d2e88f07
   3:        0x104836e35 - std::panicking::default_hook::h3d5dccce8125d0cf
   4:        0x104837566 - std::panicking::rust_panic_with_hook::h00b81bb3dcbd51f2
   5:        0x104837404 - std::panicking::begin_panic::ha6a0d553db9869ff
   6:        0x104837322 - std::panicking::begin_panic_fmt::h24d113aee3ee4081
   7:        0x104837287 - rust_begin_unwind
   8:        0x104879c10 - core::panicking::panic_fmt::he441b2ea2036b98a
   9:        0x101196f1e - core::result::unwrap_failed::h643f371f836203d8
  10:        0x1013a0d92 - rustc::ty::context::TyCtxt::node_type_insert::h433372d17c14c1dd
  11:        0x10078125b - rustc_metadata::astencode::decode_inlined_item::hd19adf628ddcc1a4
  12:        0x1007a306d - rustc_metadata::decoder::<impl rustc_metadata::cstore::CrateMetadata>::maybe_get_item_ast::h552d81f5f050a70e
  13:        0x1007abb6f - rustc_metadata::cstore_impl::<impl rustc::middle::cstore::CrateStore<'tcx> for rustc_metadata::cstore::CStore>::maybe_get_item_ast::he46c1ec4b2a4b7a1
  14:        0x101103847 - rustc_const_eval::eval::lookup_const_by_id::h2d28364fed06a8ed
  15:        0x101121b29 - rustc_const_eval::pattern::PatternContext::lower_pattern::h22fcc4813d357489
  16:        0x101102338 - <collections::vec::Vec<T> as core::iter::traits::FromIterator<T>>::from_iter::hb3721f06cfebe3d5
  17:        0x101121421 - rustc_const_eval::pattern::PatternContext::lower_pattern::h22fcc4813d357489
  18:        0x1011001da - <core::iter::Map<I, F> as core::iter::iterator::Iterator>::next::h1d00f2eb0a94dd65
  19:        0x101100923 - <core::iter::Map<I, F> as core::iter::iterator::Iterator>::next::h2d56eea4c4b18aae
  20:        0x10111c610 - rustc_const_eval::check_match::MatchVisitor::check_match::hd1f5b608683119ec
  21:        0x10111b1f4 - <rustc_const_eval::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'v>>::visit_fn::h6973aaef1076bcf8
  22:        0x101119bb9 - <rustc_const_eval::check_match::OuterVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'v>>::visit_fn::h88018547ff5e89ca
  23:        0x101119a6e - <rustc_const_eval::check_match::OuterVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'v>>::visit_impl_item::hb3245687d1fcb98c
  24:        0x10111a69a - rustc_const_eval::check_match::check_crate::h7c305da7ebc33f6b
  25:        0x10014fe3e - rustc_driver::driver::phase_3_run_analysis_passes::{{closure}}::hb062c53ab7b33bac
  26:        0x10011c8d6 - rustc_driver::driver::phase_3_run_analysis_passes::h016090d638ff1d7f
  27:        0x10010f6d5 - rustc_driver::driver::compile_input::h21840cdf516c3ab1
  28:        0x10013a009 - rustc_driver::run_compiler::h81a62653df4e7b03
  29:        0x100071d18 - std::panicking::try::do_call::h54deb93462da3a7f
  30:        0x10483a32a - __rust_maybe_catch_panic
  31:        0x100091eef - <F as alloc::boxed::FnBox<A>>::call_box::h2181ecf694b72547
  32:        0x1048363d4 - std::sys::imp::thread::Thread::new::thread_start::h990fb082eb5abe34
  33:     0x7fffc5133aaa - _pthread_body
  34:     0x7fffc51339f6 - _pthread_start

error: Could not compile `glutin_app`.

To learn more, run the command again with --verbose.
Build FAILED in 0:00:03

[eddyb]

My bad, there's a temporary tcx.tables() that ended up in a match discriminant. Minimal testcase:

fn main() {
    match (0, 0) {
        (std::usize::MIN, std::usize::MAX) => {}
        _ => {}
    }
}

The faulty code can be fixed by pulling it out into a variable, like for PatKind::Slice.