ICE: error[E0782]: trait objects must include the `dyn` keyword

[matthiaskrgr]

auto-reduced (treereduce-rust):

#![feature(object_safe_for_dispatch)]

trait B {
    fn bar(&self, x: &Self);
}

trait A {
    fn g(new: B) -> B;
}

fn main() {}

original:

// revisions: old new
//[old] edition:2015
//[new] edition:2021
trait B { fn bar(&self, x: &Self); }
//~^ ERROR the trait `A` cannot be made into an object
// revisions: old new
//[old]~| WARN trait objects without an explicit `dyn` are deprecated
//[old]~| WARN trait objects without an explicit `dyn` are deprecated
//[old]~| WARN this is accepted in the current edition
// other object safety *hard errors* to be suppressed, because we currently
//[old]~| WARN this is accepted in the current edition
trait A { fn g(new: B) -> B; }
//~^ ERROR the trait `B` cannot be made into an object
//[old]~| WARN trait objects without an explicit `dyn` are deprecated
//[old]~| WARN trait objects without an explicit `dyn` are deprecated
//[old]~| WARN trait objects without an explicit `dyn` are deprecated
//[old]~| WARN this is accepted in the current edition
//[old]~| WARN this is accepted in the current edition
//[old]~| WARN this is accepted in the current edition
fn main() {}

Version information

rustc 1.77.0-nightly (af08c64e3 2024-01-29)
binary: rustc
commit-hash: af08c64e3800fd15f0afdb8651de8fa7dacc0026
commit-date: 2024-01-29
host: x86_64-unknown-linux-gnu
release: 1.77.0-nightly
LLVM version: 17.0.6

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zcrate-attr=feature(object_safe_for_dispatch) --edition=2021

Program output

note: no errors encountered even though `span_delayed_bug` issued

note: those delayed bugs will now be shown as internal compiler errors

error: internal compiler error[E0782]: trait objects must include the `dyn` keyword
 --> /tmp/icemaker_global_tempdir.FSnI1dXGl0xd/rustc_testrunner_tmpdir_reporting.ycftxsMipEYM/mvce.rs:6:15
  |
6 |     fn g(new: B) -> B;
  |               ^
  |
  = note: `B` it is not object safe, so it can't be `dyn`
note: delayed at compiler/rustc_hir_analysis/src/astconv/lint.rs:228:21
         0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
         1: <rustc_errors::DiagCtxtInner>::emit_stashed_diagnostics
         2: <rustc_errors::DiagCtxt>::print_error_count
         3: <rustc_session::session::Session>::finish_diagnostics
         4: rustc_interface::interface::run_compiler::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}
         5: std::sys_common::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<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
         6: <<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<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{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}
         7: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                   at /rustc/af08c64e3800fd15f0afdb8651de8fa7dacc0026/library/alloc/src/boxed.rs:2015:9
         8: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                   at /rustc/af08c64e3800fd15f0afdb8651de8fa7dacc0026/library/alloc/src/boxed.rs:2015:9
         9: std::sys::pal::unix::thread::Thread::new::thread_start
                   at /rustc/af08c64e3800fd15f0afdb8651de8fa7dacc0026/library/std/src/sys/pal/unix/thread.rs:108:17
        10: <unknown>
        11: <unknown>
 --> /tmp/icemaker_global_tempdir.FSnI1dXGl0xd/rustc_testrunner_tmpdir_reporting.ycftxsMipEYM/mvce.rs:6:15
  |
6 |     fn g(new: B) -> B;
  |               ^
help: use a new generic type parameter, constrained by `B`
  |
6 |     fn g<T: B>(new: T) -> B;
  |         ++++++      ~
help: you can also use an opaque type, but users won't be able to specify the type parameter when calling the `fn`, having to rely exclusively on type inference
  |
6 |     fn g(new: impl B) -> B;
  |               ++++

error: internal compiler error[E0782]: trait objects must include the `dyn` keyword
 --> /tmp/icemaker_global_tempdir.FSnI1dXGl0xd/rustc_testrunner_tmpdir_reporting.ycftxsMipEYM/mvce.rs:6:21
  |
6 |     fn g(new: B) -> B;
  |                     ^
  |
note: delayed at compiler/rustc_hir_analysis/src/astconv/lint.rs:228:21
         0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
         1: <rustc_errors::DiagCtxtInner>::emit_stashed_diagnostics
         2: <rustc_errors::DiagCtxt>::print_error_count
         3: <rustc_session::session::Session>::finish_diagnostics
         4: rustc_interface::interface::run_compiler::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}
         5: std::sys_common::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<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
         6: <<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<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{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}
         7: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                   at /rustc/af08c64e3800fd15f0afdb8651de8fa7dacc0026/library/alloc/src/boxed.rs:2015:9
         8: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                   at /rustc/af08c64e3800fd15f0afdb8651de8fa7dacc0026/library/alloc/src/boxed.rs:2015:9
         9: std::sys::pal::unix::thread::Thread::new::thread_start
                   at /rustc/af08c64e3800fd15f0afdb8651de8fa7dacc0026/library/std/src/sys/pal/unix/thread.rs:108:17
        10: <unknown>
        11: <unknown>
 --> /tmp/icemaker_global_tempdir.FSnI1dXGl0xd/rustc_testrunner_tmpdir_reporting.ycftxsMipEYM/mvce.rs:6:21
  |
6 |     fn g(new: B) -> B;
  |                     ^
help: `B` is not object safe, use `impl B` to return an opaque type, as long as you return a single underlying type
  |
6 |     fn g(new: B) -> impl B;
  |                     ++++

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 1.77.0-nightly (af08c64e3 2024-01-29) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z crate-attr=feature(object_safe_for_dispatch) -Z dump-mir-dir=dir

query stack during panic:
end of query stack

[matthiaskrgr]

cc @estebank 😅

[estebank]

💀

[nnethercote]

I can't reproduce this on the auto-reduced version, only on the original. The presence of the #![feature(object_safe_for_dispatch)] prevents the ICE.

Also, I can reproduce this on a Nightly from January 25, so it's not related to #120828.

[matthiaskrgr]

Sorry, what I mean is that with rustc 1.78.0-nightly (98aa3624b 2024-02-08) this reports

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[E0782]: trait objects must include the `dyn` keyword
 --> stash.rs:8:15
  |
8 |     fn g(new: B) -> B;
....

but with master f4cfd87 , this talks about stashed errors now in the first ice segment

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: some stashed error is waiting for use
  |
  = note: delayed at compiler/rustc_interface/src/passes.rs:784:31
             0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
             1: <rustc_errors::DiagCtxt>::emit_diagnostic
             2: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic_builder::EmissionGuarantee>::emit_producing_guarantee
             3: rustc_interface::passes::analysis
             4: 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; 1]>>
             5: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 1]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
             6: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
             7: rustc_interface::interface::run_compiler::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}
             8: std::sys_common::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<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
             9: <<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<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{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}
            10: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                       at /rustc/f4cfd872028398da2b2d85c368c51f4d007dc6af/library/alloc/src/boxed.rs:2015:9
            11: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                       at /rustc/f4cfd872028398da2b2d85c368c51f4d007dc6af/library/alloc/src/boxed.rs:2015:9
            12: std::sys::pal::unix::thread::Thread::new::thread_start
                       at /rustc/f4cfd872028398da2b2d85c368c51f4d007dc6af/library/std/src/sys/pal/unix/thread.rs:108:17
            13: <unknown>
            14: <unknown>


error: internal compiler error[E0782]: trait objects must include the `dyn` keyword
 --> stash.rs:8:15
  |
8 |     fn g(new: B) -> B;

which made me think of your PR.

[matthiaskrgr]

I can't reproduce this on the auto-reduced version, only on the original.

did you pass --edition=2021? (this is kinda hidden in the Command line...