$ rustc -Z external-macro-backtrace -
error[E0317]: if may be missing an else clause
  --> <assert_eq macros>:5:1
   |
1  |  / ( $ left : expr , $ right : expr ) => (
2  |  | {
3  |  | match ( & $ left , & $ right ) {
4  |  | ( left_val , right_val ) => {
5  | /| if ! ( * left_val == * right_val ) {
6  | || panic ! (
7  | || r#"assertion failed: `(left == right)`
8  | ||   left: `{:?}`,
9  | ||  right: `{:?}`"# ,
10 | || left_val , right_val ) } } } } ) ; ( $ left : expr , $ right : expr , ) => (
   | ||________________________^ expected (), found isize
...   |
20 |  |  right: `{:?}`: {}"# ,
21 |  | left_val , right_val , format_args ! ( $ ( $ arg ) + ) ) } } } } ) ;
   |  |____________________________________________________________________- in this expansion of `assert_eq!`
   | 
  ::: <anon>:3:16
   |
3  |            Drop = assert_eq!(1, 1)
   |                   ---------------- in this macro invocation
   |
   = note: expected type `()`
              found type `isize`

error: internal compiler error: librustc_mir/hair/pattern/mod.rs:465: unexpected type for tuple pattern: TyError
   | 
  ::: <anon>:3:16
   |
3  |              Drop = assert_eq!(1, 1)
   |                     ---------------- in this macro invocation (#1)
   | 
  ::: <panic macros>:1:1
   |
1  |    / (  ) => ( { panic ! ( "explicit panic" ) } ) ; ( $ msg : expr ) => (
2  |    | {
3  |    | $ crate :: rt :: begin_panic (
4  |    | $ msg , & ( file ! (  ) , line ! (  ) , __rust_unstable_column ! (  ) ) ) } )
...     |
9  |    | & format_args ! ( $ fmt , $ ( $ arg ) + ) , & (
10 |    | file ! (  ) , line ! (  ) , __rust_unstable_column ! (  ) ) ) } ) ;
   |    |___________________________________________________________________- in this expansion of `panic!` (#2)
  --> <assert_eq macros>:7:1
   |
1  |   /  ( $ left : expr , $ right : expr ) => (
2  |   |  {
3  |   |  match ( & $ left , & $ right ) {
4  |   |  ( left_val , right_val ) => {
5  |   |  if ! ( * left_val == * right_val ) {
6  |  /|  panic ! (
7  |  ||  r#"assertion failed: `(left == right)`
   |  ||__^
8  | |||    left: `{:?}`,
9  | |||   right: `{:?}`"# ,
   | |||_________________^
10 |  ||  left_val , right_val ) } } } } ) ; ( $ left : expr , $ right : expr , ) => (
   |  ||_______________________- in this macro invocation (#2)
...    |
20 |   |   right: `{:?}`: {}"# ,
21 |   |  left_val , right_val , format_args ! ( $ ( $ arg ) + ) ) } } } } ) ;
   |   |_____________________________________________________________________- in this expansion of `assert_eq!` (#1)

thread 'main' panicked at 'Box<Any>', librustc_errors/lib.rs:499:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at libstd/sys_common/backtrace.rs:59
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: rustc::util::common::panic_hook
             at librustc/util/common.rs:54
   5: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:467
   6: std::panicking::begin_panic
             at /home/vegard/rust/src/libstd/panicking.rs:397
   7: rustc_errors::Handler::span_bug
             at /home/vegard/rust/src/<panic macros>:3
   8: rustc::session::opt_span_bug_fmt::{{closure}}
             at /home/vegard/rust/src/librustc/session/mod.rs:1279
   9: rustc::ty::context::tls::with_opt::{{closure}}
             at /home/vegard/rust/src/librustc/ty/context.rs:1943
  10: rustc::ty::context::tls::with_context_opt
             at /home/vegard/rust/src/librustc/ty/context.rs:1880
  11: rustc::ty::context::tls::with_opt
             at /home/vegard/rust/src/librustc/ty/context.rs:1943
  12: rustc::session::opt_span_bug_fmt
             at /home/vegard/rust/src/librustc/session/mod.rs:1276
  13: rustc::session::span_bug_fmt
             at /home/vegard/rust/src/librustc/session/mod.rs:1267
  14: rustc_mir::hair::pattern::PatternContext::lower_pattern
             at librustc_mir/hair/pattern/mod.rs:465
             at librustc_mir/hair/pattern/mod.rs:344
  15: rustc_mir::hair::pattern::check_match::MatchVisitor::check_match::{{closure}}
             at librustc_mir/hair/pattern/check_match.rs:202
             at /home/vegard/rust/src/libcore/ops/function.rs:271
             at /home/vegard/rust/src/libcore/option.rs:404
             at /home/vegard/rust/src/libcore/iter/mod.rs:1347
             at /home/vegard/rust/src/liballoc/vec.rs:1883
             at /home/vegard/rust/src/liballoc/vec.rs:1866
             at /home/vegard/rust/src/liballoc/vec.rs:1752
             at /home/vegard/rust/src/libcore/iter/iterator.rs:1375
             at librustc_mir/hair/pattern/check_match.rs:198
             at /home/vegard/rust/src/libcore/ops/function.rs:271
             at /home/vegard/rust/src/libcore/option.rs:404
             at /home/vegard/rust/src/libcore/iter/mod.rs:1347
             at /home/vegard/rust/src/liballoc/vec.rs:1883
             at /home/vegard/rust/src/liballoc/vec.rs:1866
             at /home/vegard/rust/src/liballoc/vec.rs:1752
             at /home/vegard/rust/src/libcore/iter/iterator.rs:1375
             at librustc_mir/hair/pattern/check_match.rs:197
  16: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
             at librustc_mir/hair/pattern/_match.rs:166
             at librustc_mir/hair/pattern/check_match.rs:194
             at librustc_mir/hair/pattern/check_match.rs:102
  17: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
             at /home/vegard/rust/src/libsyntax/ptr.rs:0
  18: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
             at /home/vegard/rust/src/<walk_list macros>:2
             at librustc_mir/hair/pattern/check_match.rs:98
  19: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
             at /home/vegard/rust/src/libsyntax/ptr.rs:0
  20: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
             at /home/vegard/rust/src/<walk_list macros>:2
             at librustc_mir/hair/pattern/check_match.rs:98
  21: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
             at /home/vegard/rust/src/<walk_list macros>:2
             at /home/vegard/rust/src/librustc/hir/intravisit.rs:261
             at /home/vegard/rust/src/librustc/hir/intravisit.rs:1018
             at librustc_mir/hair/pattern/check_match.rs:98
  22: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
             at /home/vegard/rust/src/<walk_list macros>:2
             at /home/vegard/rust/src/librustc/hir/intravisit.rs:261
             at /home/vegard/rust/src/librustc/hir/intravisit.rs:1018
             at librustc_mir/hair/pattern/check_match.rs:98
  23: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
             at /home/vegard/rust/src/librustc/hir/intravisit.rs:995
             at librustc_mir/hair/pattern/check_match.rs:98
  24: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
             at /home/vegard/rust/src/<walk_list macros>:2
             at /home/vegard/rust/src/librustc/hir/intravisit.rs:261
             at /home/vegard/rust/src/librustc/hir/intravisit.rs:1018
             at librustc_mir/hair/pattern/check_match.rs:98
  25: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
             at /home/vegard/rust/src/librustc/hir/intravisit.rs:267
             at /home/vegard/rust/src/<walk_list macros>:2
             at librustc_mir/hair/pattern/check_match.rs:98
  26: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
             at /home/vegard/rust/src/<walk_list macros>:2
             at /home/vegard/rust/src/librustc/hir/intravisit.rs:261
             at /home/vegard/rust/src/librustc/hir/intravisit.rs:1018
             at librustc_mir/hair/pattern/check_match.rs:98
  27: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_body
             at /home/vegard/rust/src/librustc/hir/intravisit.rs:400
             at librustc_mir/hair/pattern/check_match.rs:121
  28: rustc_mir::hair::pattern::check_match::check_match
             at librustc_mir/hair/pattern/check_match.rs:70
             at /home/vegard/rust/src/librustc/session/mod.rs:318
             at librustc_mir/hair/pattern/check_match.rs:69
  29: rustc::dep_graph::graph::DepGraph::with_task_impl
             at librustc/ty/maps/plumbing.rs:723
             at librustc/dep_graph/graph.rs:343
  30: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
             at librustc/dep_graph/graph.rs:209
             at librustc/ty/maps/plumbing.rs:530
             at librustc/ty/maps/plumbing.rs:200
             at librustc/ty/context.rs:1844
             at librustc/ty/context.rs:1787
             at librustc/ty/context.rs:1843
             at librustc/ty/maps/plumbing.rs:199
             at librustc/ty/context.rs:1905
             at librustc/ty/context.rs:1889
             at librustc/ty/context.rs:1880
             at librustc/ty/context.rs:1889
             at librustc/ty/context.rs:1900
             at librustc/ty/maps/plumbing.rs:189
             at librustc/ty/maps/plumbing.rs:523
  31: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
             at librustc/ty/maps/plumbing.rs:372
             at librustc/ty/maps/plumbing.rs:599
             at librustc/ty/maps/plumbing.rs:606
  32: rustc_mir::interpret::const_eval::const_eval_provider
             at librustc_mir/interpret/const_eval.rs:451
  33: rustc::dep_graph::graph::DepGraph::with_task_impl
             at librustc/ty/maps/plumbing.rs:723
             at librustc/dep_graph/graph.rs:343
  34: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
             at librustc/dep_graph/graph.rs:209
             at librustc/ty/maps/plumbing.rs:530
             at librustc/ty/maps/plumbing.rs:200
             at librustc/ty/context.rs:1844
             at librustc/ty/context.rs:1787
             at librustc/ty/context.rs:1843
             at librustc/ty/maps/plumbing.rs:199
             at librustc/ty/context.rs:1905
             at librustc/ty/context.rs:1889
             at librustc/ty/context.rs:1880
             at librustc/ty/context.rs:1889
             at librustc/ty/context.rs:1900
             at librustc/ty/maps/plumbing.rs:189
             at librustc/ty/maps/plumbing.rs:523
  35: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_get_query
             at librustc/ty/maps/plumbing.rs:372
             at librustc/ty/maps/plumbing.rs:599
  36: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::const_eval
             at librustc/ty/maps/plumbing.rs:606
             at librustc/ty/maps/plumbing.rs:776
             at librustc/ty/maps/plumbing.rs:769
  37: rustc::ty::AdtDef::eval_explicit_discr
             at /home/vegard/rust/src/librustc/ty/mod.rs:1935
  38: <rustc_typeck::collect::CollectItemTypesVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_item
             at librustc_typeck/collect.rs:486
             at librustc_typeck/collect.rs:388
             at librustc_typeck/collect.rs:111
  39: rustc_typeck::check_crate::{{closure}}::{{closure}}
             at /home/vegard/rust/src/librustc/hir/itemlikevisit.rs:80
             at /home/vegard/rust/src/librustc/hir/mod.rs:711
             at librustc_typeck/collect.rs:61
             at librustc_typeck/lib.rs:316
  40: rustc_typeck::check_crate
             at /home/vegard/rust/src/librustc/util/common.rs:166
             at /home/vegard/rust/src/librustc/util/common.rs:160
             at librustc_typeck/lib.rs:315
             at /home/vegard/rust/src/librustc/session/mod.rs:318
             at librustc_typeck/lib.rs:314
  41: rustc::ty::context::TyCtxt::create_and_enter
             at librustc_driver/driver.rs:1121
             at /home/vegard/rust/src/librustc/ty/context.rs:1867
             at /home/vegard/rust/src/librustc/ty/context.rs:1844
             at /home/vegard/rust/src/librustc/ty/context.rs:1787
             at /home/vegard/rust/src/librustc/ty/context.rs:1843
             at /home/vegard/rust/src/librustc/ty/context.rs:1866
             at /home/vegard/rust/src/librustc/ty/context.rs:1833
             at /home/vegard/rust/src/libstd/thread/local.rs:294
             at /home/vegard/rust/src/libstd/thread/local.rs:248
             at /home/vegard/rust/src/librustc/ty/context.rs:1825
             at /home/vegard/rust/src/libstd/thread/local.rs:294
             at /home/vegard/rust/src/libstd/thread/local.rs:248
             at /home/vegard/rust/src/librustc/ty/context.rs:1817
             at /home/vegard/rust/src/librustc/ty/context.rs:1855
             at /home/vegard/rust/src/librustc/ty/context.rs:1299
  42: rustc_driver::driver::compile_input
             at librustc_driver/driver.rs:1095
             at librustc_driver/driver.rs:231
  43: rustc_driver::run_compiler
             at librustc_driver/lib.rs:540
             at librustc_driver/lib.rs:457
             at /home/vegard/.cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-0.1.1/src/lib.rs:155
             at /home/vegard/rust/src/libsyntax/lib.rs:97
             at /home/vegard/.cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-0.1.1/src/lib.rs:155
             at /home/vegard/rust/src/libsyntax/lib.rs:96
             at librustc_driver/lib.rs:456
  44: rustc_driver::monitor::{{closure}}
             at librustc_driver/lib.rs:1684
             at librustc_driver/lib.rs:174
             at librustc_driver/lib.rs:1598
  45: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  46: rustc_driver::run
             at /home/vegard/rust/src/libstd/panicking.rs:289
             at /home/vegard/rust/src/libstd/panic.rs:374
             at librustc_driver/lib.rs:1530
             at librustc_driver/lib.rs:1597
             at librustc_driver/lib.rs:173
  47: rustc_driver::main
             at librustc_driver/lib.rs:1677
  48: std::rt::lang_start::{{closure}}
             at /home/vegard/rust/src/libstd/rt.rs:74
  49: std::panicking::try::do_call
             at libstd/rt.rs:59
             at libstd/panicking.rs:310
  50: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  51: std::rt::lang_start_internal
             at libstd/panicking.rs:289
             at libstd/panic.rs:374
             at libstd/rt.rs:58
  52: main
  53: __libc_start_main
  54: _start
query stack during panic:
#0 [check_match] processing `main::Foo::Drop::{{initializer}}`
#1 [const_eval] const-evaluating `main::Foo::Drop::{{initializer}}`
end of query stack
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0317`.

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: rustc 1.27.0-dev running on x86_64-unknown-linux-gnu

note: compiler flags: -Z external-macro-backtrace