ICE in _match.rs:1184:21 when building "gfx-backend-metal" on Nightly

[kvark]

We are seeing a new ICE on macOS/Nightly: https://github.com/gfx-rs/wgpu-native/runs/700057380

Meta

rustc 1.45.0-nightly (9310e3bd4 2020-05-21)

Backtrace:

2020-05-22T15:48:09.2856440Z thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0', src/librustc_mir_build/hair/pattern/_match.rs:1184:21
2020-05-22T15:48:09.2859080Z stack backtrace:
2020-05-22T15:48:09.4938590Z    0: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
2020-05-22T15:48:09.4942910Z    1: core::fmt::write
2020-05-22T15:48:09.4952680Z    2: std::io::Write::write_fmt
2020-05-22T15:48:09.4953030Z    3: std::panicking::default_hook::{{closure}}
2020-05-22T15:48:09.5054570Z    4: std::panicking::default_hook
2020-05-22T15:48:09.5155760Z    5: rustc_driver::report_ice
2020-05-22T15:48:09.5172590Z    6: std::panicking::rust_panic_with_hook
2020-05-22T15:48:09.5173000Z    7: rust_begin_unwind
2020-05-22T15:48:09.5173420Z    8: core::panicking::panic_fmt
2020-05-22T15:48:09.5173790Z    9: core::panicking::panic_bounds_check
2020-05-22T15:48:09.5174910Z   10: rustc_mir_build::hair::pattern::_match::Fields::replace_with_fieldpats
2020-05-22T15:48:09.5175400Z   11: rustc_mir_build::hair::pattern::_match::PatStack::specialize_constructor
2020-05-22T15:48:09.5175790Z   12: rustc_mir_build::hair::pattern::_match::is_useful_specialized
2020-05-22T15:48:09.5176130Z   13: <core::iter::adapters::Map<I,F> as core::iter::traits::iterator::Iterator>::try_fold
2020-05-22T15:48:09.5176540Z   14: rustc_mir_build::hair::pattern::_match::is_useful
2020-05-22T15:48:09.5176870Z   15: rustc_mir_build::hair::pattern::_match::is_useful
2020-05-22T15:48:09.5177250Z   16: rustc_mir_build::hair::pattern::_match::is_useful
2020-05-22T15:48:09.5177670Z   17: rustc_mir_build::hair::pattern::_match::is_useful_specialized
2020-05-22T15:48:09.5178050Z   18: <core::iter::adapters::Map<I,F> as core::iter::traits::iterator::Iterator>::try_fold
2020-05-22T15:48:09.5178420Z   19: rustc_mir_build::hair::pattern::_match::is_useful
2020-05-22T15:48:09.5178750Z   20: rustc_mir_build::hair::pattern::check_match::check_not_useful
2020-05-22T15:48:09.5179140Z   21: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
2020-05-22T15:48:09.5179540Z   22: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
2020-05-22T15:48:09.5179930Z   23: rustc_mir_build::hair::pattern::check_match::check_match
2020-05-22T15:48:09.5180310Z   24: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::check_match>::compute
2020-05-22T15:48:09.5180700Z   25: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
2020-05-22T15:48:09.5181080Z   26: rustc_data_structures::stack::ensure_sufficient_stack
2020-05-22T15:48:09.5181460Z   27: rustc_query_system::query::plumbing::get_query_impl
2020-05-22T15:48:09.5181780Z   28: rustc_query_system::query::plumbing::ensure_query_impl
2020-05-22T15:48:09.5182150Z   29: rustc_session::utils::<impl rustc_session::session::Session>::time
2020-05-22T15:48:09.5182740Z   30: rustc_session::utils::<impl rustc_session::session::Session>::time
2020-05-22T15:48:09.5183130Z   31: rustc_interface::passes::analysis
2020-05-22T15:48:09.5183510Z   32: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute
2020-05-22T15:48:09.5184600Z   33: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
2020-05-22T15:48:09.5184980Z   34: rustc_query_system::query::plumbing::get_query_impl
2020-05-22T15:48:09.5185360Z   35: rustc_middle::ty::context::tls::enter_global
2020-05-22T15:48:09.5185690Z   36: rustc_interface::interface::run_compiler_in_existing_thread_pool
2020-05-22T15:48:09.5186050Z   37: scoped_tls::ScopedKey<T>::set
2020-05-22T15:48:09.5186410Z   38: rustc_ast::attr::with_globals
2020-05-22T15:48:09.5186760Z note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
2020-05-22T15:48:09.5187040Z 
2020-05-22T15:48:09.5187400Z error: internal compiler error: unexpected panic
2020-05-22T15:48:09.5187710Z 
2020-05-22T15:48:09.5188010Z note: the compiler unexpectedly panicked. this is a bug.
2020-05-22T15:48:09.5188330Z 
2020-05-22T15:48:09.5189640Z note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
2020-05-22T15:48:09.5190010Z 
2020-05-22T15:48:09.5190810Z note: rustc 1.45.0-nightly (9310e3bd4 2020-05-21) running on x86_64-apple-darwin
2020-05-22T15:48:09.5191130Z 
2020-05-22T15:48:09.5191900Z note: compiler flags: -C embed-bitcode=no -C debuginfo=2 --crate-type lib
2020-05-22T15:48:09.5192280Z 
2020-05-22T15:48:09.5192600Z note: some of the compiler flags provided by cargo are hidden
2020-05-22T15:48:09.5192870Z 
2020-05-22T15:48:09.5193200Z query stack during panic:
2020-05-22T15:48:09.5193530Z #0 [check_match] processing `soft::Own::own_render`
2020-05-22T15:48:09.5194200Z #1 [analysis] running analysis passes on this crate
2020-05-22T15:48:09.5194640Z end of query stack
2020-05-22T15:48:09.5521870Z error: could not compile `gfx-backend-metal`.

[ecstatic-morse]

cc @Nadrieril, who wrote replace_with_fieldpats.

[Nadrieril]

Hmm, I can't figure out what might have gone wrong by just looking at it. I'll try to reduce it over the weekend if no one beats me to it. If it helps, the ICE comes from pattern-matching, and uninhabited types might be involved.

[Nadrieril]

This only appears on MacOS and I've been unable to get the right cross-compilation magic going on my Linux machine :(

[spastorino]

We need to bisect and find an mcve.

@rustbot ping cleanup

[rustbot]

Hey Cleanup Crew ICE-breakers! This bug has been identified as a good
"Cleanup ICE-breaking candidate". In case it's useful, here are some
instructions for tackling these sorts of bugs. Maybe take a look?
Thanks! <3

cc @AminArria @chrissimpkins @contrun @DutchGhost @elshize @ethanboxx @h-michael @HallerPatrick @hdhoang @hellow554 @imtsuki @kanru @KarlK90 @LeSeulArtichaut @MAdrianMattocks @matheus-consoli @mental32 @nmccarty @Noah-Kennedy @pard68 @PeytonT @pierreN @Redblueflame @RobbieClarken @RobertoSnap @robjtede @SarthakSingh31 @senden9 @shekohex @sinato @spastorino @turboladen @woshilapin @yerke

[spastorino]

Assigning P-high as discussed as part of the Prioritization Working Group process and removing I-prioritize.

[Nadrieril]

As mentioned in #72506, I expect that PR to fix this issue. I think it'd make sense to wait for #72506 to be merged before investing too much effort here.

[SimonSapin]

I confirm that servo/servo#26648 does not appear to reproduce in today’s Nightly (with #72506): https://community-tc.services.mozilla.com/tasks/RWtZsX9ERIGSoRkc01VJhQ/runs/0/logs/https%3A%2F%2Fcommunity-tc.services.mozilla.com%2Fapi%2Fqueue%2Fv1%2Ftask%2FRWtZsX9ERIGSoRkc01VJhQ%2Fruns%2F0%2Fartifacts%2Fpublic%2Flogs%2Flive.log#L1978

[Nadrieril]

@kvark Can you confirm this is fixed for you on latest nightly?

[kvark]

Looks to be passing now, thank you!