error: internal compiler error: src/librustc_mir_build/hair/pattern/_match.rs:318: cannot deref ByRef

[jyn514]

Code

use std::sync::atomic::{AtomicPtr, Ordering};

const P: &dyn T = &S as &dyn T;
static mut LOGGER: AtomicPtr<&dyn T> = AtomicPtr::new(&mut P);

pub trait T {}
struct S;
impl T for S {}

pub fn f() {
    match *LOGGER.load(Ordering::SeqCst) {
        P | _ => {}
    }
}

Meta

rustc --version --verbose:

rustc 1.44.0-nightly (77621317d 2020-03-28)
binary: rustc
commit-hash: 77621317d643cc5d13da60b26ab68b057668e688
commit-date: 2020-03-28
host: x86_64-unknown-linux-gnu
release: 1.44.0-nightly
LLVM version: 9.0

Note that the error is also present on stable (1.42.0).

Error output

error: internal compiler error: src/librustc_mir_build/hair/pattern/_match.rs:318: cannot deref ByRef {
    alloc: Allocation {
        bytes: [
            0,
            0,
            0,
            0,
            0,
            0,
            0,
            0,
            0,
            0,
            0,
            0,
            0,
            0,
            0,
            0,
        ],
        relocations: Relocations(
            SortedMap {
                data: [
                    (
                        Size {
                            raw: 0,
                        },
                        (
                            (),
                            alloc2,
                        ),
                    ),
                    (
                        Size {
                            raw: 8,
                        },
                        (
                            (),
                            alloc4,
                        ),
                    ),
                ],
            },
        ),
        undef_mask: UndefMask {
            blocks: [
                65535,
            ],
            len: Size {
                raw: 16,
            },
        },
        size: Size {
            raw: 16,
        },
        align: Align {
            pow2: 3,
        },
        mutability: Not,
        extra: (),
    },
    offset: Size {
        raw: 0,
    },
}, dyn T -> dyn T

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:880:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Backtrace

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:880:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:78
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:59
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1069
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1439
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:62
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:198
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:218
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:515
  12: std::panicking::begin_panic
  13: rustc_errors::HandlerInner::bug
  14: rustc_errors::Handler::bug
  15: rustc::util::bug::opt_span_bug_fmt::{{closure}}
  16: rustc::ty::context::tls::with_opt::{{closure}}
  17: rustc::ty::context::tls::with_opt
  18: rustc::util::bug::opt_span_bug_fmt
  19: rustc::util::bug::bug_fmt
  20: <rustc_mir_build::hair::pattern::_match::LiteralExpander as rustc_mir_build::hair::pattern::PatternFolder>::fold_pattern
  21: rustc_mir_build::hair::pattern::PatternFoldable::fold_with
  22: <rustc_mir_build::hair::pattern::PatKind as rustc_mir_build::hair::pattern::PatternFoldable>::super_fold_with
  23: <rustc_mir_build::hair::pattern::_match::LiteralExpander as rustc_mir_build::hair::pattern::PatternFolder>::fold_pattern
  24: rustc_mir_build::hair::pattern::check_match::MatchVisitor::lower_pattern
  25: <core::iter::adapters::Map<I,F> as core::iter::traits::iterator::Iterator>::fold
  26: rustc_mir_build::hair::pattern::_match::MatchCheckCtxt::create_and_enter
  27: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
  28: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
  29: rustc_mir_build::hair::pattern::check_match::check_match
  30: rustc::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc::ty::context::TyCtxt> for rustc::ty::query::queries::check_match>::compute
  31: rustc::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc::dep_graph::dep_node::DepKind>::with_deps
  32: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  33: rustc_query_system::query::plumbing::get_query
  34: rustc_query_system::query::plumbing::ensure_query
  35: rustc_session::utils::<impl rustc_session::session::Session>::time
  36: rustc_session::utils::<impl rustc_session::session::Session>::time
  37: rustc_interface::passes::analysis
  38: rustc::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc::ty::context::TyCtxt> for rustc::ty::query::queries::analysis>::compute
  39: rustc::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc::dep_graph::dep_node::DepKind>::with_deps
  40: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  41: rustc_query_system::query::plumbing::get_query
  42: rustc::ty::context::tls::enter_global
  43: rustc_interface::interface::run_compiler_in_existing_thread_pool
  44: scoped_tls::ScopedKey<T>::set
  45: rustc_ast::attr::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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 1.44.0-nightly (77621317d 2020-03-28) running on x86_64-unknown-linux-gnu

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

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

query stack during panic:
#0 [check_match] processing `f`
#1 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

[Centril]

cc @eddyb @varkor @oli-obk @Nadrieril

[eddyb]

cc @pnkfelix I don't think dyn Trait should be structurally matchable.

[jyn514]

Note that this isn't matching on dyn T, it's matching on &'static dyn T. There's a double pointer indirection because AtomicPtr requires T to be Sized.

[eddyb]

@jyn514 References match by their pointee value, unlike raw pointers. You should use *const dyn T if you want to actually compare the pointers.