ICE: deref projection of non-dereferenceable ty with -Zchalk

[matthiaskrgr]

Code

const FOO: &&&u32 = &&&42;

fn main() {
    match unimplemented!() {
        &&&42 => {},
        FOO => {},
        _ => {},
    }
}

Meta

rustc --version --verbose:

rustc 1.50.0-nightly (29e32120c 2020-12-20)
binary: rustc
commit-hash: 29e32120c33d30ff526fc7f4d94ec9fce0dc10c9
commit-date: 2020-12-20
host: x86_64-unknown-linux-gnu
release: 1.50.0-nightly

Error output

rustc ./59996.rs -Zchalk=yes

warning: unreachable arm
 --> ./59996.rs:5:18
  |
4 |     match unimplemented!() {
  |           ---------------- any code following this expression is unreachable
5 |         &&&42 => {},
  |                  ^^ unreachable arm
  |
  = note: `#[warn(unreachable_code)]` on by default

warning: unreachable pattern
 --> ./59996.rs:6:9
  |
6 |         FOO => {},
  |         ^^^
  |
  = note: `#[warn(unreachable_patterns)]` on by default

error: internal compiler error: compiler/rustc_middle/src/mir/tcx.rs:84:25: deref projection of non-dereferenceable ty PlaceTy { ty: (), variant_index: None }

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:958:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.50.0-nightly (29e32120c 2020-12-20) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z chalk=yes

query stack during panic:
#0 [unsafety_check_result] unsafety-checking `main`
#1 [mir_const] processing MIR for `main`
end of query stack
error: aborting due to previous error; 2 warnings emitted

Backtrace

error: internal compiler error: compiler/rustc_middle/src/mir/tcx.rs:84:25: deref projection of non-dereferenceable ty PlaceTy { ty: (), variant_index: None }

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:958:9
stack backtrace:
   0:     0x7fb51ecb06c7 - std::backtrace_rs::backtrace::libunwind::trace::h746c3e9529d524bc
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/std/src/../../backtrace/src/backtrace/libunwind.rs:90:5
   1:     0x7fb51ecb06c7 - std::backtrace_rs::backtrace::trace_unsynchronized::h84373278bfb39e0c
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7fb51ecb06c7 - std::sys_common::backtrace::_print_fmt::h517324efde750597
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/std/src/sys_common/backtrace.rs:67:5
   3:     0x7fb51ecb06c7 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hf594ab77fac89284
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/std/src/sys_common/backtrace.rs:46:22
   4:     0x7fb51ed2128c - core::fmt::write::h3868db8542c90941
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/core/src/fmt/mod.rs:1078:17
   5:     0x7fb51eca2592 - std::io::Write::write_fmt::h3f6656f045fa877f
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/std/src/io/mod.rs:1519:15
   6:     0x7fb51ecb43b5 - std::sys_common::backtrace::_print::hda7655c057c24dcc
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/std/src/sys_common/backtrace.rs:49:5
   7:     0x7fb51ecb43b5 - std::sys_common::backtrace::print::h546a6c8431d46287
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/std/src/sys_common/backtrace.rs:36:9
   8:     0x7fb51ecb43b5 - std::panicking::default_hook::{{closure}}::h006dd083853faf51
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/std/src/panicking.rs:208:50
   9:     0x7fb51ecb3f0a - std::panicking::default_hook::hf0f9afb1017317fc
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/std/src/panicking.rs:225:9
  10:     0x7fb51f555008 - rustc_driver::report_ice::h956234bae73e460f
  11:     0x7fb51ecb4cb6 - std::panicking::rust_panic_with_hook::hb7a19826c029b1d6
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/std/src/panicking.rs:595:17
  12:     0x7fb52273c32d - std::panicking::begin_panic::{{closure}}::he3ac55d11a883a10
  13:     0x7fb52273c1e6 - std::sys_common::backtrace::__rust_end_short_backtrace::h4402bc3ed558879b
  14:     0x7fb52273c2cf - std::panicking::begin_panic::hd2137c659c375844
  15:     0x7fb522777bac - rustc_errors::HandlerInner::bug::hbfb11e3c8ba1475f
  16:     0x7fb5227762c0 - rustc_errors::Handler::bug::ha00f48e1291906a1
  17:     0x7fb522034224 - rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}::h08c1bd52850a380c
  18:     0x7fb52202e24b - rustc_middle::ty::context::tls::with_opt::{{closure}}::h82c056b7e0ea907f
  19:     0x7fb52202e1f2 - rustc_middle::ty::context::tls::with_opt::h001ea91e9a6c9bc0
  20:     0x7fb522034143 - rustc_middle::util::bug::opt_span_bug_fmt::h033dd7c3ae8939b2
  21:     0x7fb5220340b5 - rustc_middle::util::bug::bug_fmt::hededfcfaf49f2715
  22:     0x7fb52237b058 - rustc_middle::mir::tcx::PlaceTy::projection_ty_core::{{closure}}::hac1075f1f0cd4047
  23:     0x7fb52237afe1 - rustc_middle::mir::tcx::PlaceTy::projection_ty::h87a1160b35cc7231
  24:     0x7fb520e6cc34 - <rustc_mir::transform::check_unsafety::UnsafetyChecker as rustc_middle::mir::visit::Visitor>::visit_place::h2d15a4db23d70aa6
  25:     0x7fb520e6bc35 - <rustc_mir::transform::check_unsafety::UnsafetyChecker as rustc_middle::mir::visit::Visitor>::visit_terminator::h4381967093695f68
  26:     0x7fb520e6e386 - rustc_mir::transform::check_unsafety::unsafety_check_result::h1ddc892dff422567
  27:     0x7fb520e2d827 - core::ops::function::FnOnce::call_once::ha8d8172d355466db
  28:     0x7fb520d4daee - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::unsafety_check_result>::compute::hb6fe82b2233d02cd
  29:     0x7fb520c0f598 - rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}}::h0268cac6188a8e01
  30:     0x7fb520ad1b30 - rustc_query_system::query::plumbing::get_query_impl::hc584a3078278359f
  31:     0x7fb520af65fd - rustc_query_system::query::plumbing::ensure_query_impl::hec652927a136abc8
  32:     0x7fb520dd7e7c - rustc_mir::transform::mir_const::hc71de9a5543cad3e
  33:     0x7fb520d4cfb8 - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::mir_const>::compute::h5cc7a945118b6060
  34:     0x7fb520c433e7 - rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}}::hba9971be539dc293
  35:     0x7fb520ac4e14 - rustc_query_system::query::plumbing::get_query_impl::ha55d44f1e62f8ef6
  36:     0x7fb520dd8349 - rustc_mir::transform::mir_promoted::ha74274350b32e48c
  37:     0x7fb520e22168 - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::mir_promoted>::compute::hac7ef20239caa560
  38:     0x7fb520c17a2b - rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}}::h2cea77d31cb86f3f
  39:     0x7fb520ae23c9 - rustc_query_system::query::plumbing::get_query_impl::he14525912feb6126
  40:     0x7fb520e5ac66 - rustc_mir::borrow_check::mir_borrowck::h36a01cec74a149cb
  41:     0x7fb520e2d757 - core::ops::function::FnOnce::call_once::h3404bcb0fed919ad
  42:     0x7fb51f7b4dee - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::mir_borrowck>::compute::h04e812456adfe4b0
  43:     0x7fb51f76dbf0 - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl::h334ed6218328ffbc
  44:     0x7fb51f7b795b - rustc_data_structures::stack::ensure_sufficient_stack::h8775cd94ce51d4fd
  45:     0x7fb51f7600a7 - rustc_query_system::query::plumbing::get_query_impl::hee9a73cf3bb51533
  46:     0x7fb51f762149 - rustc_query_system::query::plumbing::ensure_query_impl::h5a10e70c7461c3bf
  47:     0x7fb51f78c979 - rustc_session::utils::<impl rustc_session::session::Session>::time::h307c9a8ae086a366
  48:     0x7fb51f7d0a32 - rustc_interface::passes::analysis::h1277a6a22a164c98
  49:     0x7fb51f5b02fb - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute::he772285573dcf530
  50:     0x7fb51f5986ed - rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}}::haf660f8b5fc0a8b6
  51:     0x7fb51f530531 - rustc_query_system::query::plumbing::get_query_impl::h9637293c1f2da416
  52:     0x7fb51f5b546f - rustc_interface::passes::QueryContext::enter::h33139460b088ed05
  53:     0x7fb51f5c2ef5 - rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter::h58cc75bad344bc3b
  54:     0x7fb51f57e6f7 - rustc_span::with_source_map::hb087a1c2bc75d8e9
  55:     0x7fb51f5c40eb - rustc_interface::interface::create_compiler_and_run::ha492945fb183c01e
  56:     0x7fb51f592690 - scoped_tls::ScopedKey<T>::set::hf41307147817b997
  57:     0x7fb51f5a3927 - std::sys_common::backtrace::__rust_begin_short_backtrace::h645f3b510f7fe2fd
  58:     0x7fb51f51894a - core::ops::function::FnOnce::call_once{{vtable.shim}}::h19b1a0a715ec4eae
  59:     0x7fb51ecc47ba - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hea1090dbdcecbf5a
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/alloc/src/boxed.rs:1328:9
  60:     0x7fb51ecc47ba - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h8d5723d3912bd325
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/alloc/src/boxed.rs:1328:9
  61:     0x7fb51ecc47ba - std::sys::unix::thread::Thread::new::thread_start::hc17a425ca2995724
                               at /rustc/29e32120c33d30ff526fc7f4d94ec9fce0dc10c9/library/std/src/sys/unix/thread.rs:71:17
  62:     0x7fb51ebb53e9 - start_thread
  63:     0x7fb51ead2293 - __GI___clone
  64:                0x0 - <unknown>

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

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.50.0-nightly (29e32120c 2020-12-20) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z chalk=yes

query stack during panic:
#0 [unsafety_check_result] unsafety-checking `main`
#1 [mir_const] processing MIR for `main`
#2 [mir_promoted] processing `main`
#3 [mir_borrowck] borrow-checking `main`
#4 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error; 2 warnings emitted

[camelid]

Closed by request of @jackh726.

[jackh726]

Just want to leave some reasoning behind closing this: We discussed this in our wg-traits meeting today. We basically agree that right now the chalk-integration is so experimental that things not working is basically expected. Most of the test suite doesn't even pass with compare-mode=chalk. Once we get to a point that nearly all of the test suite passes with -Z chalk, it'll make more sense to keep chalk-related issues around, particularly under the case that it's something we expect to work with Chalk, but not with the rustc trait solver. If it's a test case that doesn't seem to be covered by the test suite as is, I would expect it's better to just add it as a regular test. But that's sometimes hard to know.

(I'm going to post this to all these 4 closed issues)