ICE: src/librustc_typeck/check/generator_interior.rs:204: impossible case reached

[Dirbaio]

Code

Playground

use std::mem;
use std::marker::PhantomData;

pub struct Server<'a> {
    thing: PhantomData<&'a u8>,
}

impl<'a> Server<'a> {
    async fn run_1(&self) {
        let data = &mut [0u8; mem::size_of::<u32>()];
        self.run_2().await
    }

    async fn run_2(&self)  {
    }
}

fn main() {

}

Meta

rustc --version --verbose:

rustc 1.46.0-nightly (826cb062a 2020-06-05)
binary: rustc
commit-hash: 826cb062a659f7b719a8a0ab1497a78229318aab
commit-date: 2020-06-05
host: x86_64-unknown-linux-gnu
release: 1.46.0-nightly
LLVM version: 10.0

Error output

error: internal compiler error: src/librustc_typeck/check/generator_interior.rs:204: impossible case reached

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:907:9
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/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.46.0-nightly (826cb062a 2020-06-05) running on x86_64-unknown-linux-gnu

error: aborting due to previous error

Backtrace

[dirbaio@mars firmware]$ RUST_BACKTRACE=1 rustc --edition 2018 test.rs 
error: internal compiler error: src/librustc_typeck/check/generator_interior.rs:204: impossible case reached

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:907:9
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:1076
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1537
   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:481
  12: std::panicking::begin_panic
  13: rustc_errors::HandlerInner::bug
  14: rustc_errors::Handler::bug
  15: rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}
  16: rustc_middle::ty::context::tls::with_opt::{{closure}}
  17: rustc_middle::ty::context::tls::with_opt
  18: rustc_middle::util::bug::opt_span_bug_fmt
  19: rustc_middle::util::bug::bug_fmt
  20: rustc_typeck::check::generator_interior::resolve_interior
  21: rustc_typeck::check::FnCtxt::resolve_generator_interiors
  22: rustc_middle::ty::context::GlobalCtxt::enter_local
  23: rustc_typeck::check::typeck_tables_of
  24: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::typeck_tables_of>::compute
  25: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  26: rustc_query_system::query::plumbing::get_query_impl
  27: rustc_mir_build::hair::cx::Cx::new
  28: rustc_middle::ty::context::GlobalCtxt::enter_local
  29: rustc_mir_build::build::mir_built
  30: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::mir_built>::compute
  31: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  32: rustc_query_system::query::plumbing::get_query_impl::{{closure}}
  33: rustc_query_system::query::plumbing::get_query_impl
  34: rustc_mir::transform::check_unsafety::unsafety_check_result
  35: 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
  36: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  37: rustc_query_system::query::plumbing::get_query_impl::{{closure}}
  38: rustc_query_system::query::plumbing::get_query_impl
  39: rustc_mir::transform::mir_const
  40: 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
  41: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  42: rustc_query_system::query::plumbing::get_query_impl::{{closure}}
  43: rustc_query_system::query::plumbing::get_query_impl
  44: rustc_mir::transform::mir_validated
  45: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::mir_validated>::compute
  46: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  47: rustc_query_system::query::plumbing::get_query_impl::{{closure}}
  48: rustc_query_system::query::plumbing::get_query_impl
  49: rustc_mir::borrow_check::mir_borrowck
  50: 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
  51: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  52: rustc_data_structures::stack::ensure_sufficient_stack
  53: rustc_query_system::query::plumbing::get_query_impl
  54: rustc_typeck::collect::type_of::type_of
  55: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  56: rustc_data_structures::stack::ensure_sufficient_stack
  57: rustc_query_system::query::plumbing::get_query_impl
  58: rustc_middle::ty::util::<impl rustc_middle::ty::context::TyCtxt>::try_expand_impl_trait_type::OpaqueTypeExpander::expand_opaque_ty
  59: rustc_middle::ty::util::<impl rustc_middle::ty::context::TyCtxt>::try_expand_impl_trait_type
  60: rustc_typeck::check::check_item_type
  61: rustc_middle::hir::map::Map::visit_item_likes_in_module
  62: rustc_typeck::check::check_mod_item_types
  63: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::check_mod_item_types>::compute
  64: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  65: rustc_data_structures::stack::ensure_sufficient_stack
  66: rustc_query_system::query::plumbing::get_query_impl
  67: rustc_query_system::query::plumbing::ensure_query_impl
  68: rustc_session::utils::<impl rustc_session::session::Session>::time
  69: rustc_typeck::check_crate
  70: rustc_interface::passes::analysis
  71: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute
  72: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  73: rustc_query_system::query::plumbing::get_query_impl
  74: rustc_middle::ty::context::tls::enter_global
  75: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  76: rustc_span::with_source_map
  77: rustc_interface::interface::run_compiler_in_existing_thread_pool
  78: scoped_tls::ScopedKey<T>::set
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 1.46.0-nightly (826cb062a 2020-06-05) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [typeck_tables_of] type-checking `Server::<'a>::run_1`
#1 [mir_built] building MIR for `Server::<'a>::run_1`
#2 [unsafety_check_result] unsafety-checking `Server::<'a>::run_1`
#3 [mir_const] processing MIR for `Server::<'a>::run_1`
#4 [mir_validated] processing `Server::<'a>::run_1`
#5 [mir_borrowck] borrow-checking `Server::<'a>::run_1`
#6 [type_of] computing type of `Server<'a>::run_1::{{opaque}}#0`
#7 [check_mod_item_types] checking item types in top-level module
#8 [analysis] running analysis passes on this crate
end of query stack

[jonas-schievink]

rust/src/librustc_typeck/check/generator_interior.rs

Lines 201 to 205 in 826cb06

	// Unify the type variable inside the generator with the new witness
	match fcx.at(&fcx.misc(body.value.span), fcx.param_env).eq(interior, witness) {
	Ok(ok) => fcx.register_infer_ok_obligations(ok),
	_ => bug!(),
	}

[lcnr]

further minimized:

async fn run_1<'a>() {
    let data = &mut [0u8; { 1 + 4 }];
    run_2().await
}

async fn run_2() {}
fn main() {}

Looks like the generator code incorrectly handles ConstKind::Unevaluated somewhere 🤔

[tmandry]

PR is up. I noticed that an old stable rustc doesn't ICE, so marking as such and nominating the PR for beta backport.