ICE: 'broken MIR: bad assignment: NoSolution' on trait with default method and no impls

[LunaAmora]

Code

type Spanned<T> = (T, ());

trait Span<T> {}

impl<T> Span<T> for (T, ()) {}

impl<F, T: From<F>> From<Spanned<F>> for dyn Span<T>
where
    Self: Sized
{
    fn from((from, ()): Spanned<F>) -> Self {
        (T::from(from), ())
    }
}

Meta

rustc --version --verbose:

rustc 1.68.2 (9eb3afe9e 2023-03-27)
binary: rustc
commit-hash: 9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0
commit-date: 2023-03-27
host: x86_64-unknown-linux-gnu
release: 1.68.2
LLVM version: 15.0.6

Error output

error: internal compiler error: no errors encountered even though `delay_span_bug` issued

error: internal compiler error: broken MIR in DefId(0:12 ~ ice_repro[09b7]::{impl#1}::from) (_0 = (move _3, move _5)): bad assignment (dyn Span<T> = (T, ())): NoSolution
  --> src/main.rs:12:9
   |
12 |         (T::from(from), ())
   |         ^^^^^^^^^^^^^^^^^^^
   |
   = note: delayed at    0: <rustc_errors::HandlerInner>::emit_diagnostic
              1: <rustc_errors::Handler>::delay_span_bug::<rustc_span::span_encoding::Span, &str>
              2: <rustc_borrowck::type_check::TypeChecker>::typeck_mir
              3: rustc_borrowck::nll::compute_regions
              4: rustc_borrowck::do_mir_borrowck
              5: rustc_borrowck::mir_borrowck
              6: <rustc_borrowck::provide::{closure#0} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId)>>::call_once
              7: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::mir::query::BorrowCheckResult>
              8: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::queries::mir_borrowck, rustc_query_impl::plumbing::QueryCtxt>
              9: rustc_data_structures::sync::par_for_each_in::<&[rustc_span::def_id::LocalDefId], <rustc_middle::hir::map::Map>::par_body_owners<rustc_interface::passes::analysis::{closure#2}::{closure#0}>::{closure#0}>
             10: <rustc_session::session::Session>::time::<(), rustc_interface::passes::analysis::{closure#2}>
             11: rustc_interface::passes::analysis
             12: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, (), core::result::Result<(), rustc_errors::ErrorGuaranteed>>
             13: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::queries::analysis, rustc_query_impl::plumbing::QueryCtxt>
             14: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::analysis
             15: <rustc_interface::passes::QueryContext>::enter::<rustc_driver::run_compiler::{closure#1}::{closure#2}::{closure#2}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>
             16: rustc_span::with_source_map::<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}::{closure#0}>
             17: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>
             18: std::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>
             19: <<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
             20: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                        at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/alloc/src/boxed.rs:1988:9
             21: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                        at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/alloc/src/boxed.rs:1988:9
             22: std::sys::unix::thread::Thread::new::thread_start
                        at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/sys/unix/thread.rs:108:17
             23: <unknown>
             24: <unknown>
           

note: the compiler unexpectedly panicked. this is a bug.

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: rustc 1.68.2 (9eb3afe9e 2023-03-27) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type bin -C embed-bitcode=no -C debuginfo=2 -C linker=clang -C incremental=[REDACTED] -C link-arg=-fuse-ld=/usr/bin/mold

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

query stack during panic:
end of query stack
error: could not compile `ice_repro`

rustc +nightly --version --verbose:

rustc 1.70.0-nightly (478cbb42b 2023-03-28)
binary: rustc
commit-hash: 478cbb42b730ba4739351b72ce2aa928e78e2f81
commit-date: 2023-03-28
host: x86_64-unknown-linux-gnu
release: 1.70.0-nightly
LLVM version: 16.0.0

Error output (+nightly)

error: internal compiler error: no errors encountered even though `delay_span_bug` issued

error: internal compiler error: broken MIR in DefId(0:12 ~ ice_repro[184d]::{impl#1}::from) (_0 = (move _3, move _5)): bad assignment (dyn Span<T> = (T, ())): NoSolution
  --> src/main.rs:12:9
   |
12 |         (T::from(from), ())
   |         ^^^^^^^^^^^^^^^^^^^
   |
   = note: delayed at    0: <rustc_errors::HandlerInner>::emit_diagnostic
              1: <rustc_errors::Handler>::delay_span_bug::<rustc_span::span_encoding::Span, &str>
              2: <rustc_borrowck::type_check::TypeChecker>::typeck_mir
              3: rustc_borrowck::type_check::type_check
              4: rustc_borrowck::nll::compute_regions
              5: rustc_borrowck::do_mir_borrowck
              6: <rustc_borrowck::provide::{closure#0} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId)>>::call_once
              7: <std::thread::local::LocalKey<core::cell::Cell<*const ()>>>::with::<rustc_middle::ty::context::tls::enter_context<rustc_query_system::query::plumbing::execute_job_incr<rustc_query_impl::queries::mir_borrowck, rustc_query_impl::plumbing::QueryCtxt>::{closure#2}, (&rustc_middle::mir::query::BorrowCheckResult, rustc_query_system::dep_graph::graph::DepNodeIndex)>::{closure#0}, (&rustc_middle::mir::query::BorrowCheckResult, rustc_query_system::dep_graph::graph::DepNodeIndex)>
              8: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::queries::mir_borrowck, rustc_query_impl::plumbing::QueryCtxt>
              9: rustc_data_structures::sync::par_for_each_in::<&[rustc_span::def_id::LocalDefId], <rustc_middle::hir::map::Map>::par_body_owners<rustc_interface::passes::analysis::{closure#2}::{closure#0}>::{closure#0}>
             10: <rustc_session::session::Session>::time::<(), rustc_interface::passes::analysis::{closure#2}>
             11: rustc_interface::passes::analysis
             12: <std::thread::local::LocalKey<core::cell::Cell<*const ()>>>::with::<rustc_middle::ty::context::tls::enter_context<rustc_query_system::query::plumbing::execute_job_incr<rustc_query_impl::queries::analysis, rustc_query_impl::plumbing::QueryCtxt>::{closure#2}, (core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_query_system::dep_graph::graph::DepNodeIndex)>::{closure#0}, (core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_query_system::dep_graph::graph::DepNodeIndex)>
             13: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::queries::analysis, rustc_query_impl::plumbing::QueryCtxt>
             14: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::analysis
             15: <rustc_interface::queries::QueryResult<&rustc_middle::ty::context::GlobalCtxt>>::enter::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#1}::{closure#2}::{closure#4}>
             16: <rustc_interface::interface::Compiler>::enter::<rustc_driver_impl::run_compiler::{closure#1}::{closure#2}, core::result::Result<core::option::Option<rustc_interface::queries::Linker>, rustc_span::ErrorGuaranteed>>
             17: rustc_span::with_source_map::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#1}>::{closure#0}::{closure#0}>
             18: std::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
             19: <<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
             20: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                        at /rustc/478cbb42b730ba4739351b72ce2aa928e78e2f81/library/alloc/src/boxed.rs:1988:9
             21: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                        at /rustc/478cbb42b730ba4739351b72ce2aa928e78e2f81/library/alloc/src/boxed.rs:1988:9
             22: std::sys::unix::thread::Thread::new::thread_start
                        at /rustc/478cbb42b730ba4739351b72ce2aa928e78e2f81/library/std/src/sys/unix/thread.rs:108:17
             23: <unknown>
             24: <unknown>
           

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: rustc 1.70.0-nightly (478cbb42b 2023-03-28) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type bin -C embed-bitcode=no -C debuginfo=2 -C linker=clang -C incremental=[REDACTED] -C link-arg=-fuse-ld=/usr/bin/mold

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

query stack during panic:
end of query stack
error: could not compile `ice_repro` (bin "ice_repro")

Backtrace

(Nothing changes from the previous error)

[LunaAmora]

Update: Found a really minimal case to trigger the ICE

trait Empty<T> {}

impl<T> Default for dyn Empty<T>
where
    Self: Sized,
{
    fn default() -> Self {
        ()
    }
}

And this other case that needs the trivial_bounds feature:

#![feature(trivial_bounds)]
trait Empty {}

impl Default for dyn Empty
where
    Self: Sized,
{
    fn default() -> Self {
        ()
    }
}

[JohnTitor]

Triage: Fixed on the latest nightly, @rustbot labels: +E-needs-test