rust-lang / rust-lang/rust

memory allocation crash, freeze. compiler bug, reproducible

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C-bug fixed-by-next-solver I-compilemem needs-triage
Dominant language
Rust
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PR metrics pending

Description

I tried this code:


pub trait TraitItem {}
pub trait TraitInner {
    type Encoder;
}
trait Trait {
    type X<T>: TraitInner;
    fn a<T: TraitItem>() -> <Self::X<T> as TraitInner>::Encoder {
        todo!()
    }
}
fn a<T: Trait>() {
    T::a(); // missing a generic argument.
}

fn main() {}

I expected to see this happen:
compilation fail. T::a(); needs a generic argument.

Instead, this happened:
Freeze and crash after 3~5mins.
output> memory allocation of 12884901888 bytes failed

Meta

rustc --version --verbose:

rustc 1.94.0-nightly (4f14395c3 2025-12-22)
binary: rustc
commit-hash: 4f14395c37db4c1be874e6b0ace6721674223c22
commit-date: 2025-12-22
host: x86_64-pc-windows-msvc
release: 1.94.0-nightly
LLVM version: 21.1.8

I also tried it on stable 1.92.0

Backtrace 

memory allocation of 25769803776 bytes failed
stack backtrace:
   0:     0x7fff8d23bda2 - std::backtrace_rs::backtrace::win64::trace
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\std\src\..\..\backtrace\src\backtrace\win64.rs:85
   1:     0x7fff8d23bda2 - std::backtrace_rs::backtrace::trace_unsynchronized
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\std\src\..\..\backtrace\src\backtrace\mod.rs:66
   2:     0x7fff8d23bda2 - std::sys::backtrace::_print_fmt
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\std\src\sys\backtrace.rs:74
   3:     0x7fff8d23bda2 - std::sys::backtrace::impl$0::print::impl$0::fmt
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\std\src\sys\backtrace.rs:44
   4:     0x7fff8d263bb1 - core::fmt::write
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\core\src\fmt\mod.rs:0
   5:     0x7fff8d24bf94 - std::io::default_write_fmt
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\std\src\io\mod.rs:639
   6:     0x7fff8d24bf94 - std::io::Write::write_fmt<std::sys::stdio::windows::Stderr>
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\std\src\io\mod.rs:1994
   7:     0x7fff8d22f18f - std::sys::backtrace::BacktraceLock::print
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\std\src\sys\backtrace.rs:47
   8:     0x7fff8d22f18f - std::alloc::default_alloc_error_hook
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\std\src\alloc.rs:397
   9:     0x7fff8d21596c - std::alloc::rust_oom::closure$0
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\std\src\alloc.rs:428
  10:     0x7fff8d21301f - std::sys::backtrace::__rust_end_short_backtrace<std::alloc::rust_oom::closure_env$0,never$>
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\std\src\sys\backtrace.rs:182
  11:     0x7fff8d22f21b - std::alloc::rust_oom
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\std\src\alloc.rs:424
  12:     0x7fff8d216898 - std::alloc::_::__rust_alloc_error_handler
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\std\src\alloc.rs:423
  13:     0x7fff9144d8c6 - alloc::alloc::handle_alloc_error::rt_error
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\alloc\src\alloc.rs:407
  14:     0x7fff9144d8c6 - alloc::alloc::handle_alloc_error
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\alloc\src\alloc.rs:413
  15:     0x7fff9144d8e0 - alloc::raw_vec::handle_error
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\alloc\src\raw_vec\mod.rs:845
  16:     0x7fff8ca5f118 - <alloc[32b78c042131820c]::raw_vec::RawVec<rustc_infer[2ef3fe7b5af6d2ef]::traits::Obligation<rustc_middle[4507aa17c3a234da]::ty::predicate::Predicate>>>::grow_one
  17:     0x7fff8e43fc72 - <rustc_infer[2ef3fe7b5af6d2ef]::infer::type_variable::TypeVariableTable>::equate
  18:     0x7fff8e4641e9 - <rustc_infer[2ef3fe7b5af6d2ef]::infer::relate::type_relating::TypeRelating as rustc_type_ir[c154d49aa2decc6a]::relate::TypeRelation<rustc_middle[4507aa17c3a234da]::ty::context::TyCtxt>>::tys
  19:     0x7fff8e3a207e - <rustc_trait_selection[7cf490ea1d8c21b5]::traits::fulfill::FulfillProcessor as rustc_data_structures[a277ee3cb8020c61]::obligation_forest::ObligationProcessor>::process_obligation
  20:     0x7fff8e21c7fc - <rustc_data_structures[a277ee3cb8020c61]::obligation_forest::ObligationForest<rustc_trait_selection[7cf490ea1d8c21b5]::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection[7cf490ea1d8c21b5]::traits::fulfill::FulfillProcessor>
  21:     0x7fff8e397b0f - <rustc_trait_selection[7cf490ea1d8c21b5]::traits::dyn_compatibility::IllegalRpititVisitor as rustc_type_ir[c154d49aa2decc6a]::visit::TypeVisitor<rustc_middle[4507aa17c3a234da]::ty::context::TyCtxt>>::visit_ty
  22:     0x7fff90bf5c97 - <rustc_trait_selection[7cf490ea1d8c21b5]::error_reporting::traits::on_unimplemented::IgnoredDiagnosticOption>::maybe_emit_warning
  23:     0x7fff90c0fef5 - <rustc_trait_selection[7cf490ea1d8c21b5]::error_reporting::TypeErrCtxt>::report_fulfillment_errors
  24:     0x7fff8d3f87bd - <hashbrown[9136093051120b50]::raw::RawTable<usize>>::reserve_rehash::<indexmap[ec73d677b2bddae6]::map::core::get_hash<(rustc_middle[4507aa17c3a234da]::ty::predicate::Predicate, rustc_middle[4507aa17c3a234da]::traits::ObligationCause), ()>::{closure#0}>
  25:     0x7fff8d402190 - rustc_hir_typeck[f794fe6d5536baf2]::typeck
  26:     0x7fff8e07ea1b - RINvMs6_NtCsjEjIgJm70IZ_9hashbrown3rawINtB6_8RawTableTTNtNtNtCs5VrzBvHPef6_12rustc_middle2ty8instance8InstanceNtNtNtBX_3mir4mono14CollectionModeETINtNtNtBX_5query5erase6ErasedAhj20_ENtNtNtCshNWRC7hgUh2_18rustc_query_system9dep_graph5graph12DepNodeIndexEEE1
  27:     0x7fff8e1220b2 - RINvNtNtCshNWRC7hgUh2_18rustc_query_system5query8plumbing17try_execute_queryINtCskqlstfJzFev_16rustc_query_impl13DynamicConfigINtNtCsdWOAk63c2pV_21rustc_data_structures9vec_cache8VecCacheNtNtCsgIZ5R5sjmKO_10rustc_span6def_id10LocalDefIdINtNtNtCs5VrzBvHPef6
  28:     0x7fff8e157cb2 - rustc_query_impl[ede6e18130cd7241]::plumbing::query_key_hash_verify_all
  29:     0x7fff8d5b3ead - rustc_hir_analysis[a4f86372022e8a93]::check_crate
  30:     0x7fff8d2968c2 - rustc_interface[4ed039da73a99626]::passes::analysis
  31:     0x7fff8cc9297a - <rustc_lint[f03cfdcd39272055]::builtin::SpecialModuleName as rustc_lint[f03cfdcd39272055]::passes::EarlyLintPass>::check_crate
  32:     0x7fff8cc9cba3 - RINvNtNtCshNWRC7hgUh2_18rustc_query_system5query8plumbing17try_execute_queryINtCskqlstfJzFev_16rustc_query_impl13DynamicConfigINtNtB4_6caches11SingleCacheINtNtNtCs5VrzBvHPef6_12rustc_middle5query5erase6ErasedAhj0_EEKb0_KB3s_KB3s_ENtNtB1f_8plumbing9QueryCtx
  33:     0x7fff8cd7bad3 - rustc_query_impl[ede6e18130cd7241]::profiling_support::alloc_self_profile_query_strings
  34:     0x7fff8a7ba8b1 - std[c408b2fec0bd27e4]::sys::backtrace::__rust_begin_short_backtrace::<std[c408b2fec0bd27e4]::thread::lifecycle::spawn_unchecked<ctrlc[f1ecb5857ba832a7]::set_handler_inner<rustc_driver_impl[28ea21ef32bc2990]::install_ctrlc_handler::{closure#0}>::{closure#0}, ()>::{closure#1}::{closure#0}::{closure#0}, ()>
  35:     0x7fff8a7b52bf - RINvNtNtCsgPu1A1epAMW_3std3sys9backtrace28___rust_begin_short_backtraceNCNCINvNtCs6LwlKu3Lu2U_15rustc_interface4util26run_in_thread_with_globalsNCINvB1e_31run_in_thread_pool_with_globalsNCINvNtB1g_9interface12run_compileruNCNvCs3vMOzKSVgQu_17rustc_driver_i
  36:     0x7fff8a7c11e9 - std[c408b2fec0bd27e4]::sys::backtrace::__rust_begin_short_backtrace::<std[c408b2fec0bd27e4]::thread::lifecycle::spawn_unchecked<ctrlc[f1ecb5857ba832a7]::set_handler_inner<rustc_driver_impl[28ea21ef32bc2990]::install_ctrlc_handler::{closure#0}>::{closure#0}, ()>::{closure#1}::{closure#0}::{closure#0}, ()>
  37:     0x7fff8d2392a8 - std::sys::thread::windows::impl$0::new::thread_start
                               at /rustc/4f14395c37db4c1be874e6b0ace6721674223c22/library\std\src\sys\thread\windows.rs:58
  38:     0x7ff85a63e8d7 - BaseThreadInitThunk
  39:     0x7ff85bccc48c - RtlUserThreadStart

Contributor guide

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First steps

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  4. Open a pull request that references the issue number.

Research direction

Compile the provided reproducer on the reported stable and nightly versions, then use the backtrace to begin in rustc_hir_typeck::typeck and the rustc_infer and rustc_trait_selection frames. Confirm the problematic case reaches the reported allocation growth; done means rustc promptly reports the missing generic argument instead of freezing or exhausting memory.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
48/100

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