Opaque Future Type crashed compiler :) Called `Option::unwrap()` on a `None` value

[Token-Thinker]

This is curiosity of our friends that will overthrow us AI :)

" The ICE is happening when the compiler tries to type-check async fn foo(...) -> ! (and its call into the generic bar) and ends up in a busted report_similar_impl_candidates path.

Code

Concretely, this signature:

#[embassy_executor::task]
async fn foo(A: SomeTypeIMatching) -> ! {
    bar(A).await
}

—combined with your generic async method

pub async fn Bar<A: OtherGenericType + 'static>(a: A) -> ! { … }

—produces an opaque future type that the compiler can’t correctly resolve, and that eventually hits an internal None.unwrap().

Solution (work around -.-)

I explicitly defined the types (though i didn't want to) within the module that is being called. This no longer has the error because of that.

Meta

I'm using container...

FROM espressif/idf-rust:esp32_latest
USER root
WORKDIR /owb
COPY . /owb
RUN chown -R esp:esp /owb
USER esp

ENV PATH="/home/esp/.rustup/toolchains/esp/xtensa-esp-elf/esp-14.2.0_20240906/xtensa-esp-elf/bin:/home/esp/.cargo/bin:$PATH"

CMD ["/bin/bash"]

Error output

thread 'rustc' panicked at compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs:1824:44:
called `Option::unwrap()` on a `None` value

Backtrace

thread 'rustc' panicked at compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs:1824:44:
called `Option::unwrap()` on a `None` value
stack backtrace:
   0:     0x7c13b4b5d604 - std::backtrace::Backtrace::create::hc917666e49edcc67
   1:     0x7c13b4b5d555 - std::backtrace::Backtrace::force_capture::h0456361e9223ac44
   2:     0x7c13ada3864f - <alloc[326f412a89e5869a]::boxed::Box<rustc_driver_impl[11120e4604616cb8]::install_ice_hook::{closure#0}> as core[19c24f2bf64da68c]::ops::function::Fn<(&dyn for<'a, 'b> core[19c24f2bf64da68c]::ops::function::Fn<(&'a std[3c1f75e497f5fe1]::panic::PanicHookInfo<'b>,), Output = ()> + core[19c24f2bf64da68c]::marker::Send + core[19c24f2bf64da68c]::marker::Sync, &std[3c1f75e497f5fe1]::panic::PanicHookInfo)>>::call
   3:     0x7c13b4b5f40d - std::panicking::rust_panic_with_hook::h81634076ecf27e23
   4:     0x7c13b4b47216 - std::panicking::begin_panic_handler::{{closure}}::hc739c40ce3082128
   5:     0x7c13b4b46ee9 - std::sys::backtrace::__rust_end_short_backtrace::h1aa68d986880e1b9
   6:     0x7c13b4b5eecc - rust_begin_unwind
   7:     0x7c13b4bea690 - core::panicking::panic_fmt::ha0d34e63f154cecc
   8:     0x7c13b4bea71c - core::panicking::panic::h80c9defdaf74510a
   9:     0x7c13b4be5e69 - core::option::unwrap_failed::h6a0ccd5c3d009ffb
  10:     0x7c13b37e6f08 - <rustc_trait_selection[a8595092de99c364]::error_reporting::TypeErrCtxt>::report_similar_impl_candidates
  11:     0x7c13b3811e8a - <rustc_trait_selection[a8595092de99c364]::error_reporting::TypeErrCtxt>::report_fulfillment_errors
  12:     0x7c13b188c491 - <rustc_hir_typeck[c37f261e904b2689]::fn_ctxt::FnCtxt>::report_ambiguity_errors
  13:     0x7c13b1b1da72 - rustc_hir_typeck[c37f261e904b2689]::typeck
  14:     0x7c13b3008ca0 - rustc_query_impl[139339c607ef3f83]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[139339c607ef3f83]::query_impl::typeck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 8usize]>>
  15:     0x7c13b332260c - <rustc_query_impl[139339c607ef3f83]::query_impl::typeck::dynamic_query::{closure#2} as core[19c24f2bf64da68c]::ops::function::FnOnce<(rustc_middle[8ac56485c6056ae4]::ty::context::TyCtxt, rustc_span[6216dc77597e7c6d]::def_id::LocalDefId)>>::call_once
  16:     0x7c13b310423c - rustc_query_system[58145ffb095b1890]::query::plumbing::try_execute_query::<rustc_query_impl[139339c607ef3f83]::DynamicConfig<rustc_data_structures[7490c3560e13ac19]::vec_cache::VecCache<rustc_span[6216dc77597e7c6d]::def_id::LocalDefId, rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[58145ffb095b1890]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[139339c607ef3f83]::plumbing::QueryCtxt, false>
  17:     0x7c13b3205a16 - rustc_query_impl[139339c607ef3f83]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
  18:     0x7c13b1de4e85 - rustc_middle[8ac56485c6056ae4]::query::plumbing::query_get_at::<rustc_data_structures[7490c3560e13ac19]::vec_cache::VecCache<rustc_span[6216dc77597e7c6d]::def_id::LocalDefId, rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[58145ffb095b1890]::dep_graph::graph::DepNodeIndex>>
  19:     0x7c13b1e0d864 - rustc_hir_analysis[f2f24cae42e238bb]::collect::type_of::opaque::find_opaque_ty_constraints_for_rpit
  20:     0x7c13b1e57f7a - rustc_hir_analysis[f2f24cae42e238bb]::collect::type_of::type_of_opaque
  21:     0x7c13b30029c5 - rustc_query_impl[139339c607ef3f83]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[139339c607ef3f83]::query_impl::type_of_opaque::dynamic_query::{closure#2}::{closure#0}, rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 8usize]>>
  22:     0x7c13b33d62c0 - <rustc_query_impl[139339c607ef3f83]::query_impl::type_of_opaque::dynamic_query::{closure#2} as core[19c24f2bf64da68c]::ops::function::FnOnce<(rustc_middle[8ac56485c6056ae4]::ty::context::TyCtxt, rustc_span[6216dc77597e7c6d]::def_id::DefId)>>::call_once
  23:     0x7c13b30575d8 - rustc_query_system[58145ffb095b1890]::query::plumbing::try_execute_query::<rustc_query_impl[139339c607ef3f83]::DynamicConfig<rustc_query_system[58145ffb095b1890]::query::caches::DefIdCache<rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[139339c607ef3f83]::plumbing::QueryCtxt, false>
  24:     0x7c13b31f12f9 - rustc_query_impl[139339c607ef3f83]::query_impl::type_of_opaque::get_query_non_incr::__rust_end_short_backtrace
  25:     0x7c13b1e351cc - rustc_middle[8ac56485c6056ae4]::query::plumbing::query_get_at::<rustc_query_system[58145ffb095b1890]::query::caches::DefIdCache<rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 8usize]>>>
  26:     0x7c13b1e565d9 - rustc_hir_analysis[f2f24cae42e238bb]::collect::type_of::type_of
  27:     0x7c13b3008d42 - rustc_query_impl[139339c607ef3f83]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[139339c607ef3f83]::query_impl::type_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 8usize]>>
  28:     0x7c13b31ed340 - <rustc_query_impl[139339c607ef3f83]::query_impl::type_of::dynamic_query::{closure#2} as core[19c24f2bf64da68c]::ops::function::FnOnce<(rustc_middle[8ac56485c6056ae4]::ty::context::TyCtxt, rustc_span[6216dc77597e7c6d]::def_id::DefId)>>::call_once
  29:     0x7c13b30575d8 - rustc_query_system[58145ffb095b1890]::query::plumbing::try_execute_query::<rustc_query_impl[139339c607ef3f83]::DynamicConfig<rustc_query_system[58145ffb095b1890]::query::caches::DefIdCache<rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[139339c607ef3f83]::plumbing::QueryCtxt, false>
  30:     0x7c13b31f0d39 - rustc_query_impl[139339c607ef3f83]::query_impl::type_of::get_query_non_incr::__rust_end_short_backtrace
  31:     0x7c13b1de61dc - rustc_middle[8ac56485c6056ae4]::query::plumbing::query_get_at::<rustc_query_system[58145ffb095b1890]::query::caches::DefIdCache<rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 8usize]>>>
  32:     0x7c13b1df664d - rustc_hir_analysis[f2f24cae42e238bb]::check::check::check_item_type
  33:     0x7c13b1e473ad - rustc_hir_analysis[f2f24cae42e238bb]::check::wfcheck::check_well_formed
  34:     0x7c13b3003ff0 - rustc_query_impl[139339c607ef3f83]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[139339c607ef3f83]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 1usize]>>
  35:     0x7c13b32e504c - <rustc_query_impl[139339c607ef3f83]::query_impl::check_well_formed::dynamic_query::{closure#2} as core[19c24f2bf64da68c]::ops::function::FnOnce<(rustc_middle[8ac56485c6056ae4]::ty::context::TyCtxt, rustc_span[6216dc77597e7c6d]::def_id::LocalDefId)>>::call_once
  36:     0x7c13b30fc6cd - rustc_query_system[58145ffb095b1890]::query::plumbing::try_execute_query::<rustc_query_impl[139339c607ef3f83]::DynamicConfig<rustc_data_structures[7490c3560e13ac19]::vec_cache::VecCache<rustc_span[6216dc77597e7c6d]::def_id::LocalDefId, rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 1usize]>, rustc_query_system[58145ffb095b1890]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[139339c607ef3f83]::plumbing::QueryCtxt, false>
  37:     0x7c13b321882d - rustc_query_impl[139339c607ef3f83]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
  38:     0x7c13b1d631b3 - rustc_middle[8ac56485c6056ae4]::query::plumbing::query_ensure_error_guaranteed::<rustc_data_structures[7490c3560e13ac19]::vec_cache::VecCache<rustc_span[6216dc77597e7c6d]::def_id::LocalDefId, rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 1usize]>, rustc_query_system[58145ffb095b1890]::dep_graph::graph::DepNodeIndex>, ()>
  39:     0x7c13b1d571bf - <rustc_middle[8ac56485c6056ae4]::hir::ModuleItems>::par_opaques::<rustc_hir_analysis[f2f24cae42e238bb]::check::wfcheck::check_mod_type_wf::{closure#4}>
  40:     0x7c13b1e50a5b - rustc_hir_analysis[f2f24cae42e238bb]::check::wfcheck::check_mod_type_wf
  41:     0x7c13b3003fc0 - rustc_query_impl[139339c607ef3f83]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[139339c607ef3f83]::query_impl::check_mod_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 1usize]>>
  42:     0x7c13b32c5ffc - <rustc_query_impl[139339c607ef3f83]::query_impl::check_mod_type_wf::dynamic_query::{closure#2} as core[19c24f2bf64da68c]::ops::function::FnOnce<(rustc_middle[8ac56485c6056ae4]::ty::context::TyCtxt, rustc_span[6216dc77597e7c6d]::def_id::LocalModDefId)>>::call_once
  43:     0x7c13b30a780c - rustc_query_system[58145ffb095b1890]::query::plumbing::try_execute_query::<rustc_query_impl[139339c607ef3f83]::DynamicConfig<rustc_query_system[58145ffb095b1890]::query::caches::DefaultCache<rustc_span[6216dc77597e7c6d]::def_id::LocalModDefId, rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[139339c607ef3f83]::plumbing::QueryCtxt, false>
  44:     0x7c13b320544d - rustc_query_impl[139339c607ef3f83]::query_impl::check_mod_type_wf::get_query_non_incr::__rust_end_short_backtrace
  45:     0x7c13b1d5891d - <rustc_data_structures[7490c3560e13ac19]::sync::parallel::ParallelGuard>::run::<(), rustc_data_structures[7490c3560e13ac19]::sync::parallel::par_for_each_in<&rustc_hir[5d3ee39a220d4a50]::hir_id::OwnerId, &[rustc_hir[5d3ee39a220d4a50]::hir_id::OwnerId], <rustc_middle[8ac56485c6056ae4]::hir::map::Map>::par_for_each_module<rustc_hir_analysis[f2f24cae42e238bb]::check_crate::{closure#0}::{closure#0}>::{closure#0}>::{closure#0}::{closure#1}::{closure#0}>
  46:     0x7c13b1c43cde - <rustc_session[ae442a1a39ad9b5f]::session::Session>::time::<(), rustc_hir_analysis[f2f24cae42e238bb]::check_crate::{closure#0}>
  47:     0x7c13b1b58f8f - rustc_hir_analysis[f2f24cae42e238bb]::check_crate
  48:     0x7c13adccce29 - rustc_interface[fa0ba49808ba01a1]::passes::analysis
  49:     0x7c13b3008d7e - rustc_query_impl[139339c607ef3f83]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[139339c607ef3f83]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 1usize]>>
  50:     0x7c13b33885e8 - <rustc_query_impl[139339c607ef3f83]::query_impl::analysis::dynamic_query::{closure#2} as core[19c24f2bf64da68c]::ops::function::FnOnce<(rustc_middle[8ac56485c6056ae4]::ty::context::TyCtxt, ())>>::call_once
  51:     0x7c13b3061a6c - rustc_query_system[58145ffb095b1890]::query::plumbing::try_execute_query::<rustc_query_impl[139339c607ef3f83]::DynamicConfig<rustc_query_system[58145ffb095b1890]::query::caches::SingleCache<rustc_middle[8ac56485c6056ae4]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[139339c607ef3f83]::plumbing::QueryCtxt, false>
  52:     0x7c13b31f2243 - rustc_query_impl[139339c607ef3f83]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  53:     0x7c13ad9a5bfe - <rustc_middle[8ac56485c6056ae4]::ty::context::GlobalCtxt>::enter::<rustc_driver_impl[11120e4604616cb8]::run_compiler::{closure#0}::{closure#1}::{closure#6}, core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>>
  54:     0x7c13ad9eed65 - <rustc_interface[fa0ba49808ba01a1]::interface::Compiler>::enter::<rustc_driver_impl[11120e4604616cb8]::run_compiler::{closure#0}::{closure#1}, core[19c24f2bf64da68c]::result::Result<core[19c24f2bf64da68c]::option::Option<rustc_interface[fa0ba49808ba01a1]::queries::Linker>, rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>>
  55:     0x7c13ada70ff2 - <scoped_tls[4cdd8087fbbd96d6]::ScopedKey<rustc_span[6216dc77597e7c6d]::SessionGlobals>>::set::<rustc_interface[fa0ba49808ba01a1]::util::run_in_thread_with_globals<rustc_interface[fa0ba49808ba01a1]::util::run_in_thread_pool_with_globals<rustc_interface[fa0ba49808ba01a1]::interface::run_compiler<core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>, rustc_driver_impl[11120e4604616cb8]::run_compiler::{closure#0}>::{closure#1}, core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>>::{closure#0}, core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>>::{closure#0}::{closure#0}::{closure#0}, core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>>
  56:     0x7c13ada25a9c - rustc_span[6216dc77597e7c6d]::create_session_globals_then::<core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>, rustc_interface[fa0ba49808ba01a1]::util::run_in_thread_with_globals<rustc_interface[fa0ba49808ba01a1]::util::run_in_thread_pool_with_globals<rustc_interface[fa0ba49808ba01a1]::interface::run_compiler<core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>, rustc_driver_impl[11120e4604616cb8]::run_compiler::{closure#0}>::{closure#1}, core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>>::{closure#0}, core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>>::{closure#0}::{closure#0}::{closure#0}>
  57:     0x7c13ada798e2 - std[3c1f75e497f5fe1]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[fa0ba49808ba01a1]::util::run_in_thread_with_globals<rustc_interface[fa0ba49808ba01a1]::util::run_in_thread_pool_with_globals<rustc_interface[fa0ba49808ba01a1]::interface::run_compiler<core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>, rustc_driver_impl[11120e4604616cb8]::run_compiler::{closure#0}>::{closure#1}, core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>>::{closure#0}, core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>>
  58:     0x7c13ada563c1 - <<std[3c1f75e497f5fe1]::thread::Builder>::spawn_unchecked_<rustc_interface[fa0ba49808ba01a1]::util::run_in_thread_with_globals<rustc_interface[fa0ba49808ba01a1]::util::run_in_thread_pool_with_globals<rustc_interface[fa0ba49808ba01a1]::interface::run_compiler<core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>, rustc_driver_impl[11120e4604616cb8]::run_compiler::{closure#0}>::{closure#1}, core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>>::{closure#0}, core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[19c24f2bf64da68c]::result::Result<(), rustc_span[6216dc77597e7c6d]::ErrorGuaranteed>>::{closure#1} as core[19c24f2bf64da68c]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  59:     0x7c13b4b9c5bb - std::sys::pal::unix::thread::Thread::new::thread_start::hba5155a029b79976
  60:     0x7c13aa3df1c4 - <unknown>
  61:     0x7c13aa45eac0 - __clone
  62:                0x0 - <unknown>


rustc version: 1.84.0-nightly (b0bd11bcc 2025-01-10) (1.84.0.0)
platform: x86_64-unknown-linux-gnu

query stack during panic:
#0 [typeck] type-checking `__led_task_task`
#1 [type_of_opaque] computing type of opaque `__led_task_task::{opaque#0}`
#2 [type_of] computing type of `__led_task_task::{opaque#0}`
#3 [check_well_formed] checking that `__led_task_task::{opaque#0}` is well-formed
#4 [check_mod_type_wf] checking that types are well-formed in top-level module
#5 [analysis] running analysis passes on this crate
end of query stack

[jieyouxu]

rustc version: 1.84.0-nightly (b0bd11b 2025-01-10) (1.84.0.0)

This is not the latest stable or nightly version. Does this reproduce on the latest nightly?

[jieyouxu]

In particular, this might be #132920 that was fixed in a stable point release 1.84.1?

[Token-Thinker]

rustc version: 1.84.0-nightly (b0bd11b 2025-01-10) (1.84.0.0)

This is not the latest stable or nightly version. Does this reproduce on the latest nightly?

Checking now....it might be that espup is out of date itself because the env i'm running is the below but i use espup to generate the binary.

rustc 1.88.0-nightly (2fa8b11f0 2025-04-06)
binary: rustc
commit-hash: 2fa8b11f0933dae9b4e5d287cc10c989218e8b36
commit-date: 2025-04-06
host: x86_64-unknown-linux-gnu
release: 1.88.0-nightly
LLVM version: 20.1.2