Compiler error on nightly (since April 28th): librustc/ty/layout.rs:1002: impossible case reached

[cipriancraciun]

I have a "largish" piece of code that fails to build with any nightly compilers since April 28th. The latest to work was April 27th.

The error is:

error: internal compiler error: librustc/ty/layout.rs:1002: impossible case reached
thread 'main' panicked at 'Box<Any>', librustc_errors/lib.rs:554:9
[...]
  99: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
query stack during panic:
#0 [layout_raw] computing layout of `primitives_procedures::ProcedurePrimitive0`
#1 [layout_raw] computing layout of `primitives_procedures::ProcedurePrimitive`
#2 [layout_raw] computing layout of `values_value::Value`
#3 [layout_raw] computing layout of `std::option::Option<values_value::Value>`
#4 [layout_raw] computing layout of `contexts::BindingTemplate`
#5 [layout_raw] computing layout of `std::option::Option<contexts::BindingTemplate>`
#6 [layout_raw] computing layout of `compiler::CompilerBinding`
end of query stack
error: aborting due to previous error

---

In order to reproduce this error, and to check the last nightly that works, bellow are the bash snippets that clone the repository, install the two nightlies via rust-up in the current folder, and execute the compilation:

• get the sources:

git clone --depth=1 -- https://github.com/cipriancraciun/vonuvoli-scheme.git ./vonuvoli-scheme
cd -- ./vonuvoli-scheme

• prepare the rust-up environment:

mkdir -- ./.rust ./.rust/rustup ./.rust/cargo

curl -s -o ./.rust/rustup-init.tmp -- https://static.rust-lang.org/rustup/dist/x86_64-unknown-linux-gnu/rustup-init
mv -n -T -- ./.rust/rustup-init.tmp ./.rust/rustup-init
chmod +x -- ./.rust/rustup-init

export -- RUSTUP_HOME="${PWD}/.rust/rustup"
export -- CARGO_HOME="${PWD}/.rust/cargo"
export -- RUST_BACKTRACE=1

• install the two nightly versions:

./.rust/rustup-init -y --no-modify-path
./.rust/cargo/bin/rustup install nightly-2018-04-27
./.rust/cargo/bin/rustup install nightly-2018-05-04

• compile with success by using the April 27th version of nightly:

./.rust/cargo/bin/cargo +nightly-2018-04-27 build --lib --no-default-features

• compile with failure by using the latest version (at the moment of writing) of nightly:

./.rust/cargo/bin/cargo +nightly-2018-05-04 build --lib --no-default-features

---

The full output obtained from rustc is bellow:

   Compiling vonuvoli-scheme v0.1.0 (file:///home/ciprian/vonuvoli-scheme)
error: internal compiler error: librustc/ty/layout.rs:1002: impossible case reached

thread 'main' panicked at 'Box<Any>', librustc_errors/lib.rs:554:9
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
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:467
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::bug
   8: rustc::session::opt_span_bug_fmt::{{closure}}
   9: rustc::ty::context::tls::with_opt::{{closure}}
  10: rustc::ty::context::tls::with_context_opt
  11: rustc::ty::context::tls::with_opt
  12: rustc::session::opt_span_bug_fmt
  13: rustc::session::bug_fmt
  14: <rustc::ty::layout::LayoutCx<'tcx, rustc::ty::context::TyCtxt<'a, 'tcx, 'tcx>>>::layout_raw_uncached
  15: rustc::ty::context::tls::with_related_context
  16: rustc::ty::layout::layout_raw
  17: rustc::ty::maps::<impl rustc::ty::maps::config::QueryConfig<'tcx> for rustc::ty::maps::queries::layout_raw<'tcx>>::compute
  18: rustc::ty::context::tls::with_context
  19: rustc::dep_graph::graph::DepGraph::with_task_impl
  20: rustc::ty::context::tls::with_related_context
  21: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  22: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  23: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &'a mut F>::call_once
  24: <&'a mut I as core::iter::iterator::Iterator>::next
  25: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  26: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  27: <rustc::ty::layout::LayoutCx<'tcx, rustc::ty::context::TyCtxt<'a, 'tcx, 'tcx>>>::layout_raw_uncached
  28: rustc::ty::context::tls::with_related_context
  29: rustc::ty::layout::layout_raw
  30: rustc::ty::maps::<impl rustc::ty::maps::config::QueryConfig<'tcx> for rustc::ty::maps::queries::layout_raw<'tcx>>::compute
  31: rustc::ty::context::tls::with_context
  32: rustc::dep_graph::graph::DepGraph::with_task_impl
  33: rustc::ty::context::tls::with_related_context
  34: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  35: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  36: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &'a mut F>::call_once
  37: <&'a mut I as core::iter::iterator::Iterator>::next
  38: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  39: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  40: <rustc::ty::layout::LayoutCx<'tcx, rustc::ty::context::TyCtxt<'a, 'tcx, 'tcx>>>::layout_raw_uncached
  41: rustc::ty::context::tls::with_related_context
  42: rustc::ty::layout::layout_raw
  43: rustc::ty::maps::<impl rustc::ty::maps::config::QueryConfig<'tcx> for rustc::ty::maps::queries::layout_raw<'tcx>>::compute
  44: rustc::ty::context::tls::with_context
  45: rustc::dep_graph::graph::DepGraph::with_task_impl
  46: rustc::ty::context::tls::with_related_context
  47: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  48: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  49: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &'a mut F>::call_once
  50: <&'a mut I as core::iter::iterator::Iterator>::next
  51: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  52: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  53: <rustc::ty::layout::LayoutCx<'tcx, rustc::ty::context::TyCtxt<'a, 'tcx, 'tcx>>>::layout_raw_uncached
  54: rustc::ty::context::tls::with_related_context
  55: rustc::ty::layout::layout_raw
  56: rustc::ty::maps::<impl rustc::ty::maps::config::QueryConfig<'tcx> for rustc::ty::maps::queries::layout_raw<'tcx>>::compute
  57: rustc::ty::context::tls::with_context
  58: rustc::dep_graph::graph::DepGraph::with_task_impl
  59: rustc::ty::context::tls::with_related_context
  60: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  61: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  62: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &'a mut F>::call_once
  63: <&'a mut I as core::iter::iterator::Iterator>::next
  64: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  65: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  66: <rustc::ty::layout::LayoutCx<'tcx, rustc::ty::context::TyCtxt<'a, 'tcx, 'tcx>>>::layout_raw_uncached
  67: rustc::ty::context::tls::with_related_context
  68: rustc::ty::layout::layout_raw
  69: rustc::ty::maps::<impl rustc::ty::maps::config::QueryConfig<'tcx> for rustc::ty::maps::queries::layout_raw<'tcx>>::compute
  70: rustc::ty::context::tls::with_context
  71: rustc::dep_graph::graph::DepGraph::with_task_impl
  72: rustc::ty::context::tls::with_related_context
  73: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  74: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  75: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &'a mut F>::call_once
  76: <&'a mut I as core::iter::iterator::Iterator>::next
  77: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  78: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  79: <rustc::ty::layout::LayoutCx<'tcx, rustc::ty::context::TyCtxt<'a, 'tcx, 'tcx>>>::layout_raw_uncached
  80: rustc::ty::context::tls::with_related_context
  81: rustc::ty::layout::layout_raw
  82: rustc::ty::maps::<impl rustc::ty::maps::config::QueryConfig<'tcx> for rustc::ty::maps::queries::layout_raw<'tcx>>::compute
  83: rustc::ty::context::tls::with_context
  84: rustc::dep_graph::graph::DepGraph::with_task_impl
  85: rustc::ty::context::tls::with_related_context
  86: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  87: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  88: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &'a mut F>::call_once
  89: <&'a mut I as core::iter::iterator::Iterator>::next
  90: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  91: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  92: <rustc::ty::layout::LayoutCx<'tcx, rustc::ty::context::TyCtxt<'a, 'tcx, 'tcx>>>::layout_raw_uncached
  93: rustc::ty::context::tls::with_related_context
  94: rustc::ty::layout::layout_raw
  95: rustc::ty::maps::<impl rustc::ty::maps::config::QueryConfig<'tcx> for rustc::ty::maps::queries::layout_raw<'tcx>>::compute
  96: rustc::ty::context::tls::with_context
  97: rustc::dep_graph::graph::DepGraph::with_task_impl
  98: rustc::ty::context::tls::with_related_context
  99: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
query stack during panic:
#0 [layout_raw] computing layout of `primitives_procedures::ProcedurePrimitive0`
#1 [layout_raw] computing layout of `primitives_procedures::ProcedurePrimitive`
#2 [layout_raw] computing layout of `values_value::Value`
#3 [layout_raw] computing layout of `std::option::Option<values_value::Value>`
#4 [layout_raw] computing layout of `contexts::BindingTemplate`
#5 [layout_raw] computing layout of `std::option::Option<contexts::BindingTemplate>`
#6 [layout_raw] computing layout of `compiler::CompilerBinding`
end of query stack
error: aborting due to previous error


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-nightly (e82261dfb 2018-05-03) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=32 -C debuginfo=2 -C incremental --crate-type lib

note: some of the compiler flags provided by cargo are hidden

error: Could not compile `vonuvoli-scheme`.

To learn more, run the command again with --verbose.

---

If need I can try to use a different build, arguments, etc.

Hope it helps in finding the issue,
Ciprian.

[bytwise]

I got the same ICE with rustc 1.27.0-nightly (428ea5f6b 2018-05-06) and could reduce it to the following https://play.rust-lang.org/?gist=2302770d40b839577492d146542b1471&version=nightly&mode=debug

[nikomatsakis]

Is there any chance we can bisect this? The https://github.com/rust-lang-nursery/cargo-bisect-rustc tool may be of use. It'd be great if we could narrow this down to a specific PR. That said, I'll cc @eddyb since they tend to be the owner of the layout code.

[nikomatsakis]

cc @nox

[nikomatsakis]

Well I guess the original poster already narrowed down Apr 27 as the "last working nightly", so that should help (though the cargo-bisect-rustc tool could identify the specific PR)

[nikomatsakis]

@nox thinks this is likely the same issue as #50371, assigning to them.

[nox]

Not the same issue as #50371, but still the same issue as something we found with @eddyb on some other patch that didn't land yet, and we didn't realise it could already happen. I have a patch for it, now I just need to write a test that demonstrates the issue.

[eddyb]

It's something that shouldn't be possible, given the code. I think it could be a compiler miscompilation. In any case, the bug!() should be changed to provide as much information as possible, and the testcase attempted with the changed compiler.

EDIT: nevermind it's "just" uninhabited structs being "unions".
EDIT2: I will mark this as fixed in a PR which changes uninhabited structs to never be unions.

[eddyb]

Minimal reproduction by guessing from the code:

enum Void {}
enum Foo { A(i32), B(Void), C(i32) }

[cipriancraciun]

I confirm that with the latest nightly (2018-05-13) it compiles just fine.
Thanks!