rust-lang / rust-lang/rust

ICE: type flags said there was an error, but now there is not

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C-bug I-ICE S-needs-repro T-compiler
Dominant language
Rust
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PR metrics pending

Description

Code

I encountered this during trying to re-build my rustc natively after bootstrapping it from x86_64. It compiles just fine until rustc_middle, which triggered this error.

I'm not sure how to reduce a rustc-internal crate for a MRE.

Meta

rustc --version --verbose:

rustc 1.88.0 (6b00bc388 2025-06-23) (Alpine Linux 1.88.0-r0)
binary: rustc
commit-hash: 6b00bc3880198600130e1cf62b8f8a93494488cc
commit-date: 2025-06-23
host: mips64-alpine-linux-musl
release: 1.88.0
LLVM version: 20.1.7
Error output
thread 'rustc' panicked at /rustc/6b00bc3880198600130e1cf62b8f8a93494488cc/compiler/rustc_type_ir/src/visit.rs:369:17:
type flags said there was an error, but now there is not
stack backtrace:
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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

note: using internal features is not supported and expected to cause internal compiler errors when used incorrectly

note: please attach the file at `/home/bootstrapper/aports/main/rust/src/rustc-1.88.0-src/rustc-ice-2025-07-04T08_43_28-5019.txt` to your bug report

note: compiler flags: --crate-type lib -C opt-level=3 -C embed-bitcode=no -C codegen-units=1 -C linker=cc -C symbol-mangling-version=v0 -Z unstable-options -Z macro-backtrace -C split-debuginfo=off -C target-feature=-crt-static -C link-args=-Wl,-z,origin -C link-args=-Wl,-rpath,$ORIGIN/../lib -Z on-broken-pipe=kill -Z binary-dep-depinfo -Z tls-model=initial-exec -Z force-unstable-if-unmarked

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

query stack during panic:
#0 [type_op_prove_predicate] evaluating `type_op_prove_predicate` `ProvePredicate { predicate: Binder { value: TraitPredicate(<core::result::Result<ty::generic_args::GenericArg<'_>, rustc_type_ir::solve::NoSolution> as core::marker::Copy>, polarity:Positive), bound_vars: [] } }`
#1 [mir_borrowck] borrow-checking `query::queries::try_normalize_generic_arg_after_erasing_regions::provided_to_erased`
#2 [analysis] running analysis passes on this crate
end of query stack
Backtrace 

thread 'rustc' panicked at /rustc/6b00bc3880198600130e1cf62b8f8a93494488cc/compiler/rustc_type_ir/src/visit.rs:369:17:
type flags said there was an error, but now there is not
stack backtrace:
   0:       0xfff2f0a654 - <unknown>
   1:       0xfff2f0a54c - std::backtrace::Backtrace::force_capture::h7bc806466c7ada4c
   2:       0xffef2e6988 - <unknown>
   3:       0xfff2f39070 - std::panicking::rust_panic_with_hook::ha141d1e29aebdf4d
   4:       0xfff2f38ab0 - <unknown>
   5:       0xfff2f32cac - <unknown>
   6:       0xfff2f384a8 - __rustc[30f31e44393b6d21]::rust_begin_unwind
   7:       0xffef262fd4 - core::panicking::panic_fmt::hd9c04f9652809349
   8:       0xfff1ab40b4 - <unknown>
   9:       0xfff1d7809c - <unknown>
  10:       0xfff095ce44 - rustc_traits[d78d3f2be068cdcf]::type_op::type_op_prove_predicate
  11:       0xfff17a6c94 - <unknown>
  12:       0xfff1745764 - <unknown>
  13:       0xfff14cfa34 - rustc_query_system[4b7b70bec177b8ee]::query::plumbing::try_execute_query::<rustc_query_impl[525c5d0a46a8a31e]::DynamicConfig<rustc_query_system[4b7b70bec177b8ee]::query::caches::DefaultCache<rustc_type_ir[33d8f32a7726b8f7]::canonical::CanonicalQueryInput<rustc_middle[6a2df7201115868e]::ty::context::TyCtxt, rustc_middle[6a2df7201115868e]::ty::ParamEnvAnd<rustc_middle[6a2df7201115868e]::traits::query::type_op::DropckOutlives>>, rustc_middle[6a2df7201115868e]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[525c5d0a46a8a31e]::plumbing::QueryCtxt, false>
  14:       0xfff1848f64 - <unknown>
  15:       0xfff1d915f4 - <rustc_middle[6a2df7201115868e]::traits::query::type_op::ProvePredicate as rustc_trait_selection[ec4bad5e88d7b903]::traits::query::type_op::QueryTypeOp>::perform_query
  16:       0xfff0849a64 - <unknown>
  17:       0xfff080ef04 - <rustc_borrowck[a79de11e43ea584b]::type_check::TypeChecker as rustc_middle[6a2df7201115868e]::mir::visit::Visitor>::visit_place
  18:       0xfff0861264 - <rustc_borrowck[a79de11e43ea584b]::type_check::TypeChecker as rustc_middle[6a2df7201115868e]::mir::visit::Visitor>::visit_operand
  19:       0xfff085b3ec - <rustc_borrowck[a79de11e43ea584b]::type_check::TypeChecker as rustc_middle[6a2df7201115868e]::mir::visit::Visitor>::visit_rvalue
  20:       0xfff0855e2c - <rustc_borrowck[a79de11e43ea584b]::type_check::TypeChecker as rustc_middle[6a2df7201115868e]::mir::visit::Visitor>::visit_statement
  21:       0xfff0854ea0 - <rustc_borrowck[a79de11e43ea584b]::type_check::TypeChecker as rustc_middle[6a2df7201115868e]::mir::visit::Visitor>::visit_body
  22:       0xfff0806284 - <unknown>
  23:       0xfff08650e8 - <unknown>
  24:       0xfff08169e4 - rustc_borrowck[a79de11e43ea584b]::mir_borrowck
  25:       0xfff179bff4 - <unknown>
  26:       0xfff16f59a4 - <unknown>
  27:       0xfff15754fc - rustc_query_system[4b7b70bec177b8ee]::query::plumbing::try_execute_query::<rustc_query_impl[525c5d0a46a8a31e]::DynamicConfig<rustc_data_structures[cd03c0ffb1296099]::vec_cache::VecCache<rustc_hir[8d450c4f8d2e80a4]::hir_id::OwnerId, rustc_middle[6a2df7201115868e]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[4b7b70bec177b8ee]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[525c5d0a46a8a31e]::plumbing::QueryCtxt, false>
  28:       0xfff17e9ea8 - <unknown>
  29:       0xffef5d08c0 - <unknown>
  30:       0xffef685db4 - <unknown>
  31:       0xffef68a7b0 - rustc_interface[a6ec810f99644e35]::passes::analysis
  32:       0xfff17aa570 - <unknown>
  33:       0xfff17617dc - <unknown>
  34:       0xfff14a6c70 - rustc_query_system[4b7b70bec177b8ee]::query::plumbing::try_execute_query::<rustc_query_impl[525c5d0a46a8a31e]::DynamicConfig<rustc_query_system[4b7b70bec177b8ee]::query::caches::SingleCache<rustc_middle[6a2df7201115868e]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[525c5d0a46a8a31e]::plumbing::QueryCtxt, false>
  35:       0xfff17bccac - <unknown>
  36:       0xffef2f3074 - <unknown>
  37:       0xffef2ced44 - <unknown>
  38:       0xffef2ecbd8 - <unknown>
  39:       0xffef2d198c - <unknown>
  40:       0xffef2efc68 - <unknown>
  41:       0xfff2f3d434 - <unknown>
  42:       0xfff3ebcaa4 - <unknown>


rustc version: 1.88.0 (6b00bc388 2025-06-23) (Alpine Linux 1.88.0-r0)
platform: mips64-alpine-linux-musl

query stack during panic:
#0 [type_op_prove_predicate] evaluating `type_op_prove_predicate` `ProvePredicate { predicate: Binder { value: TraitPredicate(<core::result::Result<ty::generic_args::GenericArg<'_>, rustc_type_ir::solve::NoSolution> as core::marker::Copy>, polarity:Positive), bound_vars: [] } }`
#1 [mir_borrowck] borrow-checking `query::queries::try_normalize_generic_arg_after_erasing_regions::provided_to_erased`
#2 [analysis] running analysis passes on this crate
end of query stack

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the native rustc bootstrap on mips64 Alpine and reading compiler/rustc_type_ir/src/visit.rs:369. Trace the type_op_prove_predicate and mir_borrowck query entries shown in the panic, then reduce the rustc_middle trigger to a reproducible test. Done means the compiler no longer panics and a regression test covers the failure.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
25/100

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