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[ICE]: monomorphization failure #158756

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[ICE]: monomorphization failure#158756
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A-codegenArea: Code generationA-monomorphizationArea: MonomorphizationA-trait-systemArea: Trait systemC-bugCategory: This is a bug.I-ICEIssue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️I-prioritizeIssue needs a team member to assess the impact. Will be replaced by P-{low,medium,high,critical}T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.T-typesRelevant to the types team, which will review and decide on the PR/issue.fixed-by-next-solverFixed by the next-generation trait solver, `-Znext-solver`.regression-from-stable-to-stablePerformance or correctness regression from one stable version to another.

Description

@mumbleskates
mumbleskates
opened on Jul 4, 2026

Code

// no idea how to minimize this one; it doesn't happen when i start paring things down, but i have
// committed it in a branch in case you want to see the horrors

Meta

Crashes similarly in all of the below:
rustc --version --verbose:

rustc 1.98.0-nightly (c397dae80 2026-07-02)
binary: rustc
commit-hash: c397dae808f70caebab1fc4e11b3edf7e59f58c7
commit-date: 2026-07-02
host: x86_64-unknown-linux-gnu
release: 1.98.0-nightly
LLVM version: 22.1.8

rustc 1.97.0-beta.6 (b2282dd56 2026-07-01)
binary: rustc
commit-hash: b2282dd5646a57d570fc86fbe8df0e8826665ef6
commit-date: 2026-07-01
host: x86_64-unknown-linux-gnu
release: 1.97.0-beta.6
LLVM version: 22.1.6

rustc 1.96.1 (31fca3adb 2026-06-26)
binary: rustc
commit-hash: 31fca3adb283cc9dfd56b49cdee9a96eb9c96ffd
commit-date: 2026-06-26
host: x86_64-unknown-linux-gnu
release: 1.96.1
LLVM version: 22.1.2

rustc 1.65.0 (897e37553 2022-11-02)
binary: rustc
commit-hash: 897e37553bba8b42751c67658967889d11ecd120
commit-date: 2022-11-02
host: x86_64-unknown-linux-gnu
release: 1.65.0
LLVM version: 15.0.0

Error output

from stable:

query stack during panic:
#0 [items_of_instance] collecting items used by `_::_::<impl at examples/schema.rs:15:35: 15:42>::register::{closure#0}`
#1 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
error: could not compile `bilrost` (example "schema")

Caused by:
  process didn't exit successfully: `/home/widders/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/rustc --crate-name schema --edition=2021 examples/schema.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=185 --crate-type bin --emit=dep-info,link -C embed-bitcode=no -C debuginfo=2 --cfg 'feature="arrayvec"' --cfg 'feature="auto-optimize"' --cfg 'feature="auto-self-copy-optimization"' --cfg 'feature="auto-unroll-varint-encoding"' --cfg 'feature="bstr"' --cfg 'feature="bytestring"' --cfg 'feature="chrono"' --cfg 'feature="default"' --cfg 'feature="derive"' --cfg 'feature="detailed-errors"' --cfg 'feature="extended-diagnostics"' --cfg 'feature="full-test-suite"' --cfg 'feature="hashbrown"' --cfg 'feature="smallvec"' --cfg 'feature="smol_str"' --cfg 'feature="std"' --cfg 'feature="thin-vec"' --cfg 'feature="third-party-type-support"' --cfg 'feature="threadsafe-schema"' --cfg 'feature="time"' --cfg 'feature="tinyvec"' --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values("arrayvec", "auto-optimize", "auto-self-copy-optimization", "auto-unroll-varint-encoding", "bstr", "bytestring", "chrono", "default", "derive", "detailed-errors", "extended-diagnostics", "forbid-unsafe", "full-test-suite", "hashbrown", "no-recursion-limit", "pprof", "prefer-no-self-copy-optimization", "prefer-no-unroll-varint-encoding", "self-copy-optimization", "smallvec", "smol_str", "std", "test-smolstr-force-noncontiguous", "test-suite-extra", "thin-vec", "third-party-type-support", "threadsafe-schema", "time", "tinyvec", "unroll-varint-encoding"))' -C metadata=34e72ac2315b8ee5 -C extra-filename=-8d74cb51b72d2517 --out-dir /home/widders/repos/bilrost/target/debug/examples -C incremental=/home/widders/repos/bilrost/target/debug/incremental -L dependency=/home/widders/repos/bilrost/target/debug/deps --extern arbitrary=/home/widders/repos/bilrost/target/debug/deps/libarbitrary-0728679b9e5fed63.rlib --extern arrayvec=/home/widders/repos/bilrost/target/debug/deps/libarrayvec-43fb47e4eb494826.rlib --extern bilrost=/home/widders/repos/bilrost/target/debug/deps/libbilrost-bf6a6f201ad1d6ad.rlib --extern bilrost=/home/widders/repos/bilrost/target/debug/deps/libbilrost-bf6a6f201ad1d6ad.rlib --extern bilrost_derive=/home/widders/repos/bilrost/target/debug/deps/libbilrost_derive-49c546cfd470378f.so --extern bilrost_types=/home/widders/repos/bilrost/target/debug/deps/libbilrost_types-9d0cd75059bc5925.rlib --extern bstr=/home/widders/repos/bilrost/target/debug/deps/libbstr-6c79ec6770561b68.rlib --extern bytes=/home/widders/repos/bilrost/target/debug/deps/libbytes-89660b0376fecedf.rlib --extern bytestring=/home/widders/repos/bilrost/target/debug/deps/libbytestring-d5491aa098aff8c8.rlib --extern chrono=/home/widders/repos/bilrost/target/debug/deps/libchrono-15470d385670c818.rlib --extern const_panic=/home/widders/repos/bilrost/target/debug/deps/libconst_panic-a84a675caa466021.rlib --extern criterion=/home/widders/repos/bilrost/target/debug/deps/libcriterion-95d5562a18b272eb.rlib --extern hashbrown=/home/widders/repos/bilrost/target/debug/deps/libhashbrown-5fe99400d436e3d9.rlib --extern itertools=/home/widders/repos/bilrost/target/debug/deps/libitertools-e667890de3b201ca.rlib --extern proptest=/home/widders/repos/bilrost/target/debug/deps/libproptest-ba16e32df9e695e4.rlib --extern rand=/home/widders/repos/bilrost/target/debug/deps/librand-b94da0b99e561c86.rlib --extern smallvec=/home/widders/repos/bilrost/target/debug/deps/libsmallvec-0768e0b6ef61c4d6.rlib --extern smol_str=/home/widders/repos/bilrost/target/debug/deps/libsmol_str-b563041025dd90b3.rlib --extern spin=/home/widders/repos/bilrost/target/debug/deps/libspin-9c58c3f0349ea4df.rlib --extern static_assertions=/home/widders/repos/bilrost/target/debug/deps/libstatic_assertions-b762000ac734cfdb.rlib --extern thin_vec=/home/widders/repos/bilrost/target/debug/deps/libthin_vec-fa529e225a04fbba.rlib --extern time=/home/widders/repos/bilrost/target/debug/deps/libtime-bda0b5b6beb993f2.rlib --extern tinyvec=/home/widders/repos/bilrost/target/debug/deps/libtinyvec-0590a625239ec7c9.rlib --extern yoke=/home/widders/repos/bilrost/target/debug/deps/libyoke-15ebf107e3aab358.rlib --cfg rustc_1_66 --cfg rustc_1_82 --check-cfg 'cfg(rustc_1_66)' --check-cfg 'cfg(rustc_1_82)'` (exit status: 101)
Backtrace 

thread 'rustc' (521520) panicked at /rustc-dev/31fca3adb283cc9dfd56b49cdee9a96eb9c96ffd/compiler/rustc_middle/src/ty/instance.rs:568:21:
Box<dyn Any>
stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
   1: <rustc_errors::diagnostic::BugAbort as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
   2: <rustc_errors::DiagCtxtHandle>::span_bug::<rustc_span::span_encoding::Span, alloc::string::String>
   3: rustc_middle::util::bug::opt_span_bug_fmt::<rustc_span::span_encoding::Span>::{closure#0}
   4: rustc_middle::ty::context::tls::with_opt::<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}
   5: rustc_middle::ty::context::tls::with_context_opt::<rustc_middle::ty::context::tls::with_opt<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
   6: rustc_middle::util::bug::span_bug_fmt::<rustc_span::span_encoding::Span>
   7: <rustc_middle::ty::instance::Instance>::expect_resolve
   8: <rustc_monomorphize::collector::MirUsedCollector as rustc_middle::mir::visit::Visitor>::visit_terminator
   9: rustc_monomorphize::collector::items_of_instance
      [... omitted 1 frame ...]
  10: rustc_monomorphize::collector::collect_items_rec
  11: rustc_monomorphize::collector::collect_items_rec
  12: rustc_monomorphize::collector::collect_items_rec
  13: rustc_monomorphize::collector::collect_items_rec
  14: rustc_monomorphize::collector::collect_crate_mono_items::{closure#1}::{closure#0}
  15: rustc_monomorphize::partitioning::collect_and_partition_mono_items
      [... omitted 1 frame ...]
  16: rustc_codegen_ssa::base::codegen_crate::<rustc_codegen_llvm::LlvmCodegenBackend>
  17: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  18: <rustc_interface::queries::Linker>::codegen_and_build_linker
  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.

Activity

  1. mumbleskates
    added
    I-ICEIssue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    C-bugCategory: This is a bug.
    on Jul 4, 2026
  2. rustbot
    added
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Jul 4, 2026

  3. saethlin commented on Jul 4, 2026

    @saethlin
    saethlin
    on Jul 4, 2026 · Hidden as outdated
  4. saethlin
    added
    S-needs-reproStatus: This issue has no reproduction and needs a reproduction to make progress.
    on Jul 4, 2026

  5. mumbleskates commented on Jul 4, 2026

    @mumbleskates
    mumbleskates
    on Jul 4, 2026 · Hidden as outdated
    Author
  6. saethlin
    removed
    S-needs-reproStatus: This issue has no reproduction and needs a reproduction to make progress.
    on Jul 5, 2026

  7. saethlin commented on Jul 5, 2026

    @saethlin
    saethlin
    on Jul 5, 2026 · Hidden as outdated
  8. saethlin
    added
    A-monomorphizationArea: Monomorphization
    and removed
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Jul 5, 2026
  9. saethlin
    self-assigned this
    on Jul 5, 2026

  10. saethlin commented on Jul 6, 2026

    @saethlin
    saethlin
    on Jul 6, 2026 · Hidden as outdated

  11. zachs18 commented on Jul 6, 2026

    @zachs18
    zachs18
    on Jul 6, 2026
    Contributor

    The ICE seems to not happen under -Znext-solver=globally (RUSTFLAGS="-Znext-solver=globally cargo +nightly -Zscript ./bilrost.rs doesn't ICE for https://github.com/saethlin/bilrost/blob/2526a1e0edcb481a55e8ba1ca48eea0965bca3e5/bilrost.rs)

  12. pitust commented on Jul 6, 2026

    @pitust
    pitust
    on Jul 6, 2026 · Hidden as outdated

  13. 2 remaining items

  14. theemathas
    added
    T-typesRelevant to the types team, which will review and decide on the PR/issue.
    fixed-by-next-solverFixed by the next-generation trait solver, `-Znext-solver`.
    A-trait-systemArea: Trait system
    on Jul 7, 2026

  15. theemathas commented on Jul 7, 2026

    @theemathas
    theemathas
    on Jul 7, 2026
    Contributor

    @lcnr What the caching is happening here? My guess is that it looks related to #t-types/trait-system-refactor > The old solver don't record required depth on cache

  16. mumbleskates commented on Jul 7, 2026

    @mumbleskates
    mumbleskates
    on Jul 7, 2026
    ContributorAuthor

    could these functions be aliasing somehow? like it's storing them under colliding keys and only stores and finds one when both are present in a given compilation?

  17. matthiaskrgr
    added
    regression-from-stable-to-stablePerformance or correctness regression from one stable version to another.
    on Jul 8, 2026
  18. rustbot
    added
    I-prioritizeIssue needs a team member to assess the impact. Will be replaced by P-{low,medium,high,critical}
    on Jul 8, 2026

  19. matthiaskrgr commented on Jul 8, 2026

    @matthiaskrgr
    matthiaskrgr
    on Jul 8, 2026
    Member

    this compiled with nightly-2019-12-11 but ICEs with nightly-2019-12-12

      commit[0] 2019-12-10: Auto merge of #66681 - Mark-Simulacrum:toolstate-into-bootstrap, r=pietroalbini
  commit[1] 2019-12-11: Auto merge of #67198 - Xanewok:update-rls, r=nikomatsakis
  commit[2] 2019-12-11: Auto merge of #67202 - JohnTitor:rollup-0xjm5pz, r=JohnTitor
  commit[3] 2019-12-11: Auto merge of #67220 - Centril:rollup-n3u9wd5, r=Centril
  commit[4] 2019-12-11: Auto merge of #66821 - eddyb:global-trait-caching, r=nikomatsakis
  commit[5] 2019-12-11: Auto merge of #65345 - davidtwco:issue-64130-async-send-sync-error-improvements, r=nikomatsakis
ERROR: no CI builds available between 7dbfb0a8ca4ab74ee3111e57a024f9e6257ce37c and 27d6f55f47e8875e71083a28ed84ea5a88e1b596 within last 167 days

    maybe #66821?

  20. saethlin
    removed their assignment
    on Jul 8, 2026

  21. mumbleskates commented on Jul 9, 2026

    @mumbleskates
    mumbleskates
    on Jul 9, 2026
    ContributorAuthor

    This patch fixes the crash in current main:

    index 440ed2b4632..8de0b5c6644 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1544,7 +1544,7 @@ fn can_use_global_caches(
             //
             // FIXME(#132279): This is still incorrect as we treat opaque types
             // and default associated items differently between these two modes.
-            TypingMode::PostAnalysis | TypingMode::Codegen => true,
+            TypingMode::PostAnalysis | TypingMode::Codegen => false,
         }
     }

    re: #132279

  22. mumbleskates commented on Jul 9, 2026

    @mumbleskates
    mumbleskates
    on Jul 9, 2026
    ContributorAuthor

    in fact, going by my testing (as far as i can tell, i might be holding the rustc builder subtly wrong) each of the following also fix it:

    edit: sorry, there was build caching that CARGO_INCREMENTAL=0 was not taking care of in trying to test this. i've rerun against clean caches:

    this fixes the crash:

    index 440ed2b4632..04ccd0d73e3 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1544,7 +1544,8 @@ fn can_use_global_caches(
             //
             // FIXME(#132279): This is still incorrect as we treat opaque types
             // and default associated items differently between these two modes.
-            TypingMode::PostAnalysis | TypingMode::Codegen => true,
+            TypingMode::PostAnalysis => true,
+            TypingMode::Codegen => false,
         }
     }

    ...and this does not fix it:

    Details 
    index 440ed2b4632..e8126adcf86 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1544,7 +1544,8 @@ fn can_use_global_caches(
             //
             // FIXME(#132279): This is still incorrect as we treat opaque types
             // and default associated items differently between these two modes.
-            TypingMode::PostAnalysis | TypingMode::Codegen => true,
+            TypingMode::PostAnalysis => false,
+            TypingMode::Codegen => true,
         }
     }
  23. theemathas
    added
    A-codegenArea: Code generation
    on Jul 10, 2026

  24. mumbleskates commented on Jul 11, 2026

    @mumbleskates
    mumbleskates
    on Jul 11, 2026
    ContributorAuthor

    i poked around a little bit and the above patch also fixes the crash in #146965
    edit: and #146813

  25. rust-bors
    added 2 commits that reference this issue on Jul 13, 2026

    possible minimal fix for #146965, #146813, and #158756

    1aacef4

    Auto merge of #159209 - mumbleskates:trait-selection-experiment, r=<try>

    06631ed
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    A-codegenArea: Code generationA-monomorphizationArea: MonomorphizationA-trait-systemArea: Trait systemC-bugCategory: This is a bug.I-ICEIssue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️I-prioritizeIssue needs a team member to assess the impact. Will be replaced by P-{low,medium,high,critical}T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.T-typesRelevant to the types team, which will review and decide on the PR/issue.fixed-by-next-solverFixed by the next-generation trait solver, `-Znext-solver`.regression-from-stable-to-stablePerformance or correctness regression from one stable version to another.

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