Compiler panic with a Box<dyn std::error::Error> in a future #143618
Description
Code
Change this block of code to the following:
let stream = stream.then(move |res| {
let client = client.clone();
async move {
if let Some(err) = res.err() {
const STREAM_ERR_MSG: &str = "Stream ended before generation completed";
if format!("{:?}", err) == STREAM_ERR_MSG {
client.report_instance_down(instance_id).await;
}
}
res
}
});which essentially access the err, that should be typed Box<dyn std::error::Error>, inside the future block.
Meta
rustc --version --verbose:
rustc 1.87.0 (17067e9ac 2025-05-09)
binary: rustc
commit-hash: 17067e9ac6d7ecb70e50f92c1944e545188d2359
commit-date: 2025-05-09
host: x86_64-unknown-linux-gnu
release: 1.87.0
LLVM version: 20.1.1
Nightly version used for reproducing:
rustc version: 1.90.0-nightly (a84ab0ce6 2025-07-06)
platform: x86_64-unknown-linux-gnu
Error output
At the root directory of the repository, compile the code with
RUST_BACKTRACE=1 cargo +nightly build --release --locked --workspace
Output:
thread 'rustc' panicked at compiler/rustc_mir_transform/src/validate.rs:80:25:
broken MIR in Item(DefId(0:947 ~ dynamo_runtime[774d]::pipeline::network::egress::push_router::{impl#1}::generate_with_fault_detection::{closure#0})) (after phase change to runtime-optimized) at bb19[0]:
Unsize coercion, but `std::pin::Pin<std::boxed::Box<tokio_stream::adapters::Then<std::pin::Pin<std::boxed::Box<dyn engine::AsyncEngineStream<U>>>, {async block@lib/runtime/src/pipeline/network/egress/push_router.rs:200:21: 200:31}, {closure@lib/runtime/src/pipeline/network/egress/push_router.rs:198:42: 198:52}>>>` isn't coercible to `std::pin::Pin<std::boxed::Box<dyn futures::Stream<Item = U> + std::marker::Send + std::marker::Sync>>`
stack backtrace:
0: __rustc::rust_begin_unwind
1: core::panicking::panic_fmt
2: <rustc_mir_transform::validate::CfgChecker>::fail::<alloc::string::String>
3: <rustc_mir_transform::validate::Validator as rustc_mir_transform::pass_manager::MirPass>::run_pass
4: rustc_mir_transform::run_optimization_passes
5: rustc_mir_transform::optimized_mir
[... omitted 1 frame ...]
6: <rustc_middle::ty::context::TyCtxt>::coroutine_layout
7: rustc_ty_utils::layout::layout_of_uncached
8: rustc_ty_utils::layout::layout_of
[... omitted 1 frame ...]
9: <rustc_mir_transform::known_panics_lint::KnownPanicsLint as rustc_mir_transform::pass_manager::MirLint>::run_lint
10: rustc_mir_transform::run_analysis_to_runtime_passes
11: rustc_mir_transform::mir_drops_elaborated_and_const_checked
[... omitted 1 frame ...]
12: <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface::passes::run_required_analyses::{closure#1}::{closure#0}>::{closure#0}
13: rustc_interface::passes::analysis
[... omitted 1 frame ...]
14: 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}
15: 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: please make sure that you have updated to the latest nightly
note: please attach the file at `/workspace/rustc-ice-2025-07-07T22_40_06-29919.txt` to your bug report
note: compiler flags: --crate-type lib -C opt-level=3 -C linker-plugin-lto -C codegen-units=1 -C strip=debuginfo
note: some of the compiler flags provided by cargo are hidden
Backtrace
Full output
RUST_BACKTRACE=1 cargo +nightly build --release --locked --workspace
Compiling dynamo-runtime v0.3.1 (/workspace/lib/runtime)
warning: [email protected]: Building with CUDA KV off
warning: [email protected]: CUDA not enabled, re-run with `--features cuda`
thread 'rustc' panicked at compiler/rustc_mir_transform/src/validate.rs:80:25:
broken MIR in Item(DefId(0:947 ~ dynamo_runtime[774d]::pipeline::network::egress::push_router::{impl#1}::generate_with_fault_detection::{closure#0})) (after phase change to runtime-optimized) at bb19[0]:
Unsize coercion, but `std::pin::Pin<std::boxed::Box<tokio_stream::adapters::Then<std::pin::Pin<std::boxed::Box<dyn engine::AsyncEngineStream<U>>>, {async block@lib/runtime/src/pipeline/network/egress/push_router.rs:200:21: 200:31}, {closure@lib/runtime/src/pipeline/network/egress/push_router.rs:198:42: 198:52}>>>` isn't coercible to `std::pin::Pin<std::boxed::Box<dyn futures::Stream<Item = U> + std::marker::Send + std::marker::Sync>>`
stack backtrace:
0: __rustc::rust_begin_unwind
1: core::panicking::panic_fmt
2: <rustc_mir_transform::validate::CfgChecker>::fail::<alloc::string::String>
3: <rustc_mir_transform::validate::Validator as rustc_mir_transform::pass_manager::MirPass>::run_pass
4: rustc_mir_transform::run_optimization_passes
5: rustc_mir_transform::optimized_mir
[... omitted 1 frame ...]
6: <rustc_middle::ty::context::TyCtxt>::coroutine_layout
7: rustc_ty_utils::layout::layout_of_uncached
8: rustc_ty_utils::layout::layout_of
[... omitted 1 frame ...]
9: <rustc_mir_transform::known_panics_lint::KnownPanicsLint as rustc_mir_transform::pass_manager::MirLint>::run_lint
10: rustc_mir_transform::run_analysis_to_runtime_passes
11: rustc_mir_transform::mir_drops_elaborated_and_const_checked
[... omitted 1 frame ...]
12: <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface::passes::run_required_analyses::{closure#1}::{closure#0}>::{closure#0}
13: rustc_interface::passes::analysis
[... omitted 1 frame ...]
14: 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}
15: 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: please make sure that you have updated to the latest nightly
note: please attach the file at `/workspace/rustc-ice-2025-07-07T22_40_06-29919.txt` to your bug report
note: compiler flags: --crate-type lib -C opt-level=3 -C linker-plugin-lto -C codegen-units=1 -C strip=debuginfo
note: some of the compiler flags provided by cargo are hidden
query stack during panic:
#0 [optimized_mir] optimizing MIR for `pipeline::network::egress::push_router::<impl at lib/runtime/src/pipeline/network/egress/push_router.rs:96:1: 99:54>::generate_with_fault_detection::{closure#0}`
#1 [layout_of] computing layout of `{async fn body of pipeline::network::egress::push_router::<impl at lib/runtime/src/pipeline/network/egress/push_router.rs:96:1: 99:54>::generate_with_fault_detection()}`
#2 [mir_drops_elaborated_and_const_checked] elaborating drops for `pipeline::network::egress::push_router::<impl at lib/runtime/src/pipeline/network/egress/push_router.rs:96:1: 99:54>::generate_with_fault_detection`
#3 [analysis] running analysis passes on this crate
end of query stack
error: future cannot be sent between threads safely
--> lib/runtime/src/pipeline/network/egress/push_router.rs:210:40
|
210 | Ok(ResponseStream::new(Box::pin(stream), engine_ctx))
| ^^^^^^^^^^^^^^^^ future created by async block is not `Send`
|
= help: the trait `std::marker::Send` is not implemented for `dyn StdError`
note: future is not `Send` as this value is used across an await
--> lib/runtime/src/pipeline/network/egress/push_router.rs:204:74
|
201 | if let Some(err) = res.err() {
| --- has type `Box<dyn StdError>` which is not `Send`
...
204 | client.report_instance_down(instance_id).await;
| ^^^^^ await occurs here, with `err` maybe used later
= note: required for the cast from `Pin<Box<Then<Pin<Box<dyn AsyncEngineStream<U>>>, ..., ...>>>` to `Pin<Box<dyn futures::Stream<Item = U> + std::marker::Send + Sync>>`
= note: the full name for the type has been written to '/workspace/target/release/deps/dynamo_runtime-c73794161cb63689.long-type-6849251775564483029.txt'
= note: consider using `--verbose` to print the full type name to the console
error: future cannot be shared between threads safely
--> lib/runtime/src/pipeline/network/egress/push_router.rs:210:40
|
210 | Ok(ResponseStream::new(Box::pin(stream), engine_ctx))
| ^^^^^^^^^^^^^^^^ future created by async block is not `Sync`
|
= help: the trait `Sync` is not implemented for `dyn StdError`
note: future is not `Sync` as this value is used across an await
--> lib/runtime/src/pipeline/network/egress/push_router.rs:204:74
|
201 | if let Some(err) = res.err() {
| --- has type `Box<dyn StdError>` which is not `Sync`
...
204 | client.report_instance_down(instance_id).await;
| ^^^^^ await occurs here, with `err` maybe used later
= note: required for the cast from `Pin<Box<Then<Pin<Box<dyn AsyncEngineStream<U>>>, ..., ...>>>` to `Pin<Box<dyn futures::Stream<Item = U> + std::marker::Send + Sync>>`
= note: the full name for the type has been written to '/workspace/target/release/deps/dynamo_runtime-c73794161cb63689.long-type-6849251775564483029.txt'
= note: consider using `--verbose` to print the full type name to the console
error: could not compile `dynamo-runtime` (lib) due to 2 previous errors
rustc-ice-2025-07-07T22_40_06-29919.txt
thread 'rustc' panicked at compiler/rustc_mir_transform/src/validate.rs:80:25:
broken MIR in Item(DefId(0:947 ~ dynamo_runtime[774d]::pipeline::network::egress::push_router::{impl#1}::generate_with_fault_detection::{closure#0})) (after phase change to runtime-optimized) at bb19[0]:
Unsize coercion, but `std::pin::Pin<std::boxed::Box<tokio_stream::adapters::Then<std::pin::Pin<std::boxed::Box<dyn engine::AsyncEngineStream<U>>>, {async block@lib/runtime/src/pipeline/network/egress/push_router.rs:200:21: 200:31}, {closure@lib/runtime/src/pipeline/network/egress/push_router.rs:198:42: 198:52}>>>` isn't coercible to `std::pin::Pin<std::boxed::Box<dyn futures::Stream<Item = U> + std::marker::Send + std::marker::Sync>>`
stack backtrace:
0: 0x78b87430cac5 - std::backtrace::Backtrace::create::hafc9430f4c5b7bca
1: 0x78b87430ca15 - std::backtrace::Backtrace::force_capture::h638ed5ec06317f78
2: 0x78b8733f3bfc - std[5392b2688ccf6c11]::panicking::update_hook::<alloc[6097bca32dba2b22]::boxed::Box<rustc_driver_impl[486328ec49f3cc14]::install_ice_hook::{closure#1}>>::{closure#0}
3: 0x78b874326aab - std::panicking::rust_panic_with_hook::he4807f33a3524f43
4: 0x78b8743267aa - std::panicking::begin_panic_handler::{{closure}}::heb653abb954cf289
5: 0x78b874322e29 - std::sys::backtrace::__rust_end_short_backtrace::hb1b8fb13fadd2724
6: 0x78b87432648d - __rustc[c0c724db799d4e69]::rust_begin_unwind
7: 0x78b870aa83a0 - core::panicking::panic_fmt::hfcd28465d10d6ced
8: 0x78b8721de3a2 - <rustc_mir_transform[c14be100631af529]::validate::CfgChecker>::fail::<alloc[6097bca32dba2b22]::string::String>
9: 0x78b875ce0799 - <rustc_mir_transform[c14be100631af529]::validate::Validator as rustc_mir_transform[c14be100631af529]::pass_manager::MirPass>::run_pass
10: 0x78b874a103d0 - rustc_mir_transform[c14be100631af529]::run_optimization_passes
11: 0x78b8756adc60 - rustc_mir_transform[c14be100631af529]::optimized_mir
12: 0x78b8756ad435 - rustc_query_impl[dc4ccaf3cfeb0260]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[dc4ccaf3cfeb0260]::query_impl::optimized_mir::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e63663f80c63ef31]::query::erase::Erased<[u8; 8usize]>>
13: 0x78b874a375e5 - rustc_query_system[65e39bd11f71302c]::query::plumbing::try_execute_query::<rustc_query_impl[dc4ccaf3cfeb0260]::DynamicConfig<rustc_query_system[65e39bd11f71302c]::query::caches::DefIdCache<rustc_middle[e63663f80c63ef31]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[dc4ccaf3cfeb0260]::plumbing::QueryCtxt, false>
14: 0x78b874a36adb - rustc_query_impl[dc4ccaf3cfeb0260]::query_impl::optimized_mir::get_query_non_incr::__rust_end_short_backtrace
15: 0x78b875e28a09 - <rustc_middle[e63663f80c63ef31]::ty::context::TyCtxt>::coroutine_layout
16: 0x78b875161f3d - rustc_ty_utils[7ffa9575db8c2558]::layout::layout_of_uncached
17: 0x78b875154bd4 - rustc_ty_utils[7ffa9575db8c2558]::layout::layout_of
18: 0x78b875154b40 - rustc_query_impl[dc4ccaf3cfeb0260]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[dc4ccaf3cfeb0260]::query_impl::layout_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e63663f80c63ef31]::query::erase::Erased<[u8; 16usize]>>
19: 0x78b875153962 - rustc_query_system[65e39bd11f71302c]::query::plumbing::try_execute_query::<rustc_query_impl[dc4ccaf3cfeb0260]::DynamicConfig<rustc_query_system[65e39bd11f71302c]::query::caches::DefaultCache<rustc_middle[e63663f80c63ef31]::ty::PseudoCanonicalInput<rustc_middle[e63663f80c63ef31]::ty::Ty>, rustc_middle[e63663f80c63ef31]::query::erase::Erased<[u8; 16usize]>>, false, true, false>, rustc_query_impl[dc4ccaf3cfeb0260]::plumbing::QueryCtxt, false>
20: 0x78b8751535a4 - rustc_query_impl[dc4ccaf3cfeb0260]::query_impl::layout_of::get_query_non_incr::__rust_end_short_backtrace
21: 0x78b87599ccb2 - <rustc_mir_transform[c14be100631af529]::known_panics_lint::KnownPanicsLint as rustc_mir_transform[c14be100631af529]::pass_manager::MirLint>::run_lint
22: 0x78b874a0aa63 - rustc_mir_transform[c14be100631af529]::run_analysis_to_runtime_passes
23: 0x78b874bb858d - rustc_mir_transform[c14be100631af529]::mir_drops_elaborated_and_const_checked
24: 0x78b874bb7e31 - rustc_query_impl[dc4ccaf3cfeb0260]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[dc4ccaf3cfeb0260]::query_impl::mir_drops_elaborated_and_const_checked::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e63663f80c63ef31]::query::erase::Erased<[u8; 8usize]>>
25: 0x78b874bbe2ee - rustc_query_system[65e39bd11f71302c]::query::plumbing::try_execute_query::<rustc_query_impl[dc4ccaf3cfeb0260]::DynamicConfig<rustc_data_structures[7fa2acbf0e33eb94]::vec_cache::VecCache<rustc_span[5b31911843326824]::def_id::LocalDefId, rustc_middle[e63663f80c63ef31]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[65e39bd11f71302c]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[dc4ccaf3cfeb0260]::plumbing::QueryCtxt, false>
26: 0x78b874bbda55 - rustc_query_impl[dc4ccaf3cfeb0260]::query_impl::mir_drops_elaborated_and_const_checked::get_query_non_incr::__rust_end_short_backtrace
27: 0x78b874bbce3d - <rustc_middle[e63663f80c63ef31]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface[b1f97b06592f8920]::passes::run_required_analyses::{closure#1}::{closure#0}>::{closure#0}
28: 0x78b874bba610 - rustc_interface[b1f97b06592f8920]::passes::analysis
29: 0x78b874bb9acb - rustc_query_impl[dc4ccaf3cfeb0260]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[dc4ccaf3cfeb0260]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e63663f80c63ef31]::query::erase::Erased<[u8; 0usize]>>
30: 0x78b875a70b3c - rustc_query_system[65e39bd11f71302c]::query::plumbing::try_execute_query::<rustc_query_impl[dc4ccaf3cfeb0260]::DynamicConfig<rustc_query_system[65e39bd11f71302c]::query::caches::SingleCache<rustc_middle[e63663f80c63ef31]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[dc4ccaf3cfeb0260]::plumbing::QueryCtxt, false>
31: 0x78b875a70706 - rustc_query_impl[dc4ccaf3cfeb0260]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
32: 0x78b875be6ad6 - rustc_interface[b1f97b06592f8920]::passes::create_and_enter_global_ctxt::<core[919d75d9604c1f70]::option::Option<rustc_interface[b1f97b06592f8920]::queries::Linker>, rustc_driver_impl[486328ec49f3cc14]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
33: 0x78b875cf29c3 - rustc_interface[b1f97b06592f8920]::interface::run_compiler::<(), rustc_driver_impl[486328ec49f3cc14]::run_compiler::{closure#0}>::{closure#1}
34: 0x78b875c07e78 - std[5392b2688ccf6c11]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[b1f97b06592f8920]::util::run_in_thread_with_globals<rustc_interface[b1f97b06592f8920]::util::run_in_thread_pool_with_globals<rustc_interface[b1f97b06592f8920]::interface::run_compiler<(), rustc_driver_impl[486328ec49f3cc14]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
35: 0x78b875c07b56 - <<std[5392b2688ccf6c11]::thread::Builder>::spawn_unchecked_<rustc_interface[b1f97b06592f8920]::util::run_in_thread_with_globals<rustc_interface[b1f97b06592f8920]::util::run_in_thread_pool_with_globals<rustc_interface[b1f97b06592f8920]::interface::run_compiler<(), rustc_driver_impl[486328ec49f3cc14]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[919d75d9604c1f70]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
36: 0x78b875c0617d - std::sys::pal::unix::thread::Thread::new::thread_start::h746b9bcf86250858
37: 0x78b86f68aaa4 - <unknown>
38: 0x78b86f717a34 - clone
39: 0x0 - <unknown>
rustc version: 1.90.0-nightly (a84ab0ce6 2025-07-06)
platform: x86_64-unknown-linux-gnu
query stack during panic:
#0 [optimized_mir] optimizing MIR for `pipeline::network::egress::push_router::<impl at lib/runtime/src/pipeline/network/egress/push_router.rs:96:1: 99:54>::generate_with_fault_detection::{closure#0}`
#1 [layout_of] computing layout of `{async fn body of pipeline::network::egress::push_router::<impl at lib/runtime/src/pipeline/network/egress/push_router.rs:96:1: 99:54>::generate_with_fault_detection()}`
#2 [mir_drops_elaborated_and_const_checked] elaborating drops for `pipeline::network::egress::push_router::<impl at lib/runtime/src/pipeline/network/egress/push_router.rs:96:1: 99:54>::generate_with_fault_detection`
#3 [analysis] running analysis passes on this crate
end of query stack
This issue is not a blocker for our work, but it would be nice to know whether this is a bug in the Rust code that was not handled gracefully by the compiler or the Rust code is well-formed that the compiler just failed to compile.
cc @ryanolson @grahamking if you are also interested in this issue.