rust-lang / rust-lang/rust

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

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C-bug I-ICE S-needs-info S-needs-repro T-compiler
Dominant language
Rust
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Description

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

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start at compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs near report_similar_impl_candidates, then trace the opaque-future and type-checking paths named in the backtrace. Reproduce the async foo/bar example with the reported toolchain context. Done means this case no longer causes rustc to panic at Option::unwrap() and instead completes compilation or emits a normal diagnostic.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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