Using !Unpin (perhaps improperly) results in compiler crash #150466

   Compiling chest v0.1.0 (/extra/src/github.com/trunk-os/chest)
error[E0412]: cannot find type `PipeWriter` in this scope
  --> src/pipe.rs:33:25
   |
33 |     writers: Arc<Mutex<Vec<PipeWriter>>>,
   |                            ^^^^^^^^^^ not found in this scope
   |
help: consider importing this struct
   |
20 + use std::io::PipeWriter;
   |

error: negative bounds are not supported
  --> src/pipe.rs:38:70
   |
38 |         mut input: PipeReader, mut output: Pin<Box<dyn AsyncWrite + Send + !Unpin>>,
   |                                                                            ^

error: negative bounds are not supported
  --> src/pipe.rs:41:42
   |
41 |             Vec::<Pin<Box<dyn AsyncWrite + Send + !Unpin>>>::new(),
   |                                                   ^

warning: unused import: `AsyncBufReadExt`
  --> src/http/handlers.rs:12:20
   |
12 | use futures_util::{AsyncBufReadExt, FutureExt, TryStreamExt};
   |                    ^^^^^^^^^^^^^^^
   |
   = note: `#[warn(unused_imports)]` (part of `#[warn(unused)]`) on by default

warning: unused import: `tokio::io::AsyncRead`
  --> src/http/handlers.rs:14:5
   |
14 | use tokio::io::AsyncRead;
   |     ^^^^^^^^^^^^^^^^^^^^


thread 'rustc' (1748428) panicked at compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_trait.rs:425:17:
assertion `left == right` failed
  left: Negative
 right: Positive
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::assert_failed_inner
   3: core::panicking::assert_failed::<rustc_type_ir::predicate::PredicatePolarity, rustc_type_ir::predicate::PredicatePolarity>
   4: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_trait_object_ty::{closure#0}
   5: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_ty::{closure#0}
   6: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_resolved_ty_path
   7: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_ty::{closure#0}
   8: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_resolved_ty_path
   9: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_ty::{closure#0}
  10: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_fn_ty
  11: rustc_hir_analysis::collect::lower_fn_sig_recovering_infer_ret_ty
  12: rustc_hir_analysis::collect::fn_sig
      [... omitted 2 frames ...]
  13: rustc_hir_analysis::check::check::check_item_type
  14: rustc_hir_analysis::check::wfcheck::check_well_formed
      [... omitted 1 frame ...]
  15: rustc_hir_analysis::check::wfcheck::check_type_wf
      [... omitted 1 frame ...]
  16: rustc_hir_analysis::check_crate
  17: rustc_interface::passes::analysis
      [... omitted 1 frame ...]
  18: <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} as core::ops::function::FnOnce<(&rustc_session::session::Session, rustc_middle::ty::context::CurrentGcx, alloc::sync::Arc<rustc_data_structures::jobserver::Proxy>, &std::sync::once_lock::OnceLock<rustc_middle::ty::context::GlobalCtxt>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_middle::arena::Arena>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_hir::Arena>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  19: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: 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 1.92.0 (ded5c06cf 2025-12-08) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -C embed-bitcode=no -C debuginfo=2 -C incremental=[REDACTED]

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

query stack during panic:
#0 [fn_sig] computing function signature of `pipe::<impl at src/pipe.rs:36:1: 36:10>::new`
#1 [check_well_formed] checking that `pipe::<impl at src/pipe.rs:36:1: 36:10>::new` is well-formed
#2 [check_type_wf] checking that types are well-formed
#3 [analysis] running analysis passes on this crate
end of query stack
For more information about this error, try `rustc --explain E0412`.
warning: `chest` (lib) generated 2 warnings
error: could not compile `chest` (lib) due to 3 previous errors; 2 warnings emitted