warning: relaxing a default bound only does something for `?Sized`; all other traits are not bound by default --> /tmp/icemaker_global_tempdir.qzKHRUKhhL4b/rustc_testrunner_tmpdir_reporting.uYhpe96WGOAh/mvce.rs:1:18 | 1 | fn foo() -> impl ?Future<Output = impl Send> { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ warning: function `foo` is never used --> /tmp/icemaker_global_tempdir.qzKHRUKhhL4b/rustc_testrunner_tmpdir_reporting.uYhpe96WGOAh/mvce.rs:1:4 | 1 | fn foo() -> impl ?Future<Output = impl Send> { | ^^^ | = note: `#[warn(dead_code)]` on by default warning: 2 warnings emitted note: no errors encountered even though delayed bugs were created note: those delayed bugs will now be shown as internal compiler errors error: internal compiler error: could not unify `()` with revealed type: expected opaque type, found `()` --> /tmp/icemaker_global_tempdir.qzKHRUKhhL4b/rustc_testrunner_tmpdir_reporting.uYhpe96WGOAh/mvce.rs:1:35 | 1 | fn foo() -> impl ?Future<Output = impl Send> { | ^^^^^^^^^ | note: delayed at compiler/rustc_hir_analysis/src/check/check.rs:396:34 0: <rustc_errors::DiagCtxtInner>::emit_diagnostic 1: <rustc_errors::DiagCtxtHandle>::emit_diagnostic 2: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee 3: <rustc_errors::DiagCtxtHandle>::span_delayed_bug::<rustc_span::span_encoding::Span, alloc::string::String> 4: rustc_hir_analysis::check::check::check_item_type 5: rustc_hir_analysis::check::wfcheck::check_well_formed 6: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>> 7: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 1]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false> 8: rustc_query_impl::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace 9: rustc_middle::query::plumbing::query_ensure_error_guaranteed::<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 1]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, ()> 10: rustc_hir_analysis::check::wfcheck::check_mod_type_wf 11: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_mod_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>> 12: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalModDefId, rustc_middle::query::erase::Erased<[u8; 1]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false> 13: rustc_query_impl::query_impl::check_mod_type_wf::get_query_non_incr::__rust_end_short_backtrace 14: rustc_hir_analysis::check_crate 15: rustc_interface::passes::run_required_analyses 16: rustc_interface::passes::analysis 17: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 0]>> 18: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 0]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false> 19: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace 20: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0} 21: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1} 22: std::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()> 23: <<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0} 24: std::sys::pal::unix::thread::Thread::new::thread_start 25: <unknown> 26: <unknown> --> /tmp/icemaker_global_tempdir.qzKHRUKhhL4b/rustc_testrunner_tmpdir_reporting.uYhpe96WGOAh/mvce.rs:1:35 | 1 | fn foo() -> impl ?Future<Output = impl Send> { | ^^^^^^^^^ 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: please make sure that you have updated to the latest nightly note: rustc 1.86.0-nightly (678e669cc 2025-01-19) running on x86_64-unknown-linux-gnu note: compiler flags: -Z dump-mir-dir=dir query stack during panic: end of query stack