Two nREPL clients connected to same server attempting to eval at same time crash the server

[timmw]

Issue Description

As the title says. It doesn't seem to matter what is being evaluated via the nREPL.

Discovered, investigated and minimal repro created with a coding agent. Stack traces from coredumpctl info and demangled with c++filt.

Reproduction Steps

Run this script:
nrepl_concurrency_bug.sh

The script runs an nREPL server, connects 2 clients, tries to eval (+ 1 1) with each client and fails consistently.

jank health check

─ system ──────────────────────────────────────────────────────────────────────
─ ✅ operating system: linux
─ ✅ default triple: x86_64-unknown-linux-gnu

─ jank install ────────────────────────────────────────────────────────────────
─ ✅ jank version: jank-0.1-alpha
─ ✅ jank cmake build type: Release
─ ✅ jank resource dir: ../lib/jank/0.1
─ ✅ jank resolved resource dir: /home/tim/.local/bin/../lib/jank/0.1 (found)
─ ✅ jank user cache dir: /home/tim/.cache/jank/x86_64-unknown-linux-gnu-f3d5d4bf0d952cd60c105ecd8c4ecbab1de6a8cb5d2278f3abe20df6353238e4 (found)

─ clang install ───────────────────────────────────────────────────────────────
─ ✅ configured clang path: /nix/store/yjvbvb8rm3pbws3hap8csf62jf9cgvfc-clang-wrapper-23.0.0-unstable-2026-06-21/bin/clang++ (found)
─ ✅ configured clang resource dir: /nix/store/yjvbvb8rm3pbws3hap8csf62jf9cgvfc-clang-wrapper-23.0.0-unstable-2026-06-21/resource-root (found)

─ jank runtime ────────────────────────────────────────────────────────────────
─ ✅ jank runtime initialized
─ ✅ jank pch path: /home/tim/.cache/jank/x86_64-unknown-linux-gnu-f3d5d4bf0d952cd60c105ecd8c4ecbab1de6a8cb5d2278f3abe20df6353238e4 (found)
─ ✅ jank can jit compile c++
─ ✅ jank can aot compile working binaries

─ support ─────────────────────────────────────────────────────────────────────
If you're having issues with jank, please either ask the jank community on the Clojurians Slack or report the issue on Github.

─ Slack: https://clojurians.slack.com/archives/C03SRH97FDK
─ Github: https://github.com/jank-lang/jank

Stack trace

Main thread

#0  __syscall_cancel_arch
#1  __internal_syscall_cancel
#2  __syscall_cancel
#3  read
#4  _IO_file_underflow@@GLIBC_2.2.5
#5  _IO_default_uflow
#6  _IO_getc
#7  __gnu_cxx::stdio_sync_filebuf<char, std::char_traits<char>>::underflow()
#8  std::getline<char, std::char_traits<char>, std::allocator<char>>(std::basic_istream<char, ...>&, std::__cxx11::basic_string<char, ...>&, char)
#9  jank::terminal_repl::read_line(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>> const&)
#10 jank::terminal_repl::repl()
#11 main::$_0::__invoke(int, char const**)
#12 jank_init_dynamic
#13 __libc_start_call_main
#14 __libc_start_main@@GLIBC_2.34
#15 _start


Crashing thread

#0  clang::Sema::EmitDiagnostic(unsigned int, clang::DiagnosticBuilder const&)
#1  clang::SemaBase::ImmediateDiagBuilder::~ImmediateDiagBuilder()
#2  clang::SemaBase::SemaDiagnosticBuilder::~SemaDiagnosticBuilder()
#3  (anonymous namespace)::ConstraintSatisfactionChecker::Evaluate(clang::AtomicConstraint const&, clang::MultiLevelTemplateArgumentList const&)
#4  (anonymous namespace)::ConstraintSatisfactionChecker::Evaluate(clang::ConceptIdConstraint const&, clang::MultiLevelTemplateArgumentList const&)
#5  CheckConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::AssociatedConstraint>, clang::MultiLevelTemplateArgumentList const&, clang::SourceRange, clang::ConstraintSatisfaction&, clang::Expr**, clang::ConceptReference const*)
#6  clang::Sema::CheckConstraintSatisfaction(llvm::PointerUnion<clang::NamedDecl const*, clang::concepts::NestedRequirement const*>, llvm::ArrayRef<clang::AssociatedConstraint>, clang::MultiLevelTemplateArgumentList const&, clang::SourceRange, clang::ConstraintSatisfaction&, clang::ConceptReference const*, clang::Expr**)
#7  clang::Sema::CheckConceptTemplateId(clang::CXXScopeSpec const&, clang::SourceLocation, clang::DeclarationNameInfo const&, clang::NamedDecl*, clang::TemplateDecl*, clang::TemplateArgumentListInfo const*, bool)
#8  clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformConceptSpecializationExpr(clang::ConceptSpecializationExpr*)
#9  clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCXXFoldExpr(clang::CXXFoldExpr*)
#10 clang::Sema::SubstConstraintExpr(clang::Expr*, clang::MultiLevelTemplateArgumentList const&)
#11 (anonymous namespace)::ConstraintSatisfactionChecker::Evaluate(clang::AtomicConstraint const&, clang::MultiLevelTemplateArgumentList const&)
#12 (anonymous namespace)::ConstraintSatisfactionChecker::Evaluate(clang::ConceptIdConstraint const&, clang::MultiLevelTemplateArgumentList const&)
#13 CheckConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::AssociatedConstraint>, clang::MultiLevelTemplateArgumentList const&, clang::SourceRange, clang::ConstraintSatisfaction&, clang::Expr**, clang::ConceptReference const*)
#14 clang::Sema::CheckConstraintSatisfaction(llvm::PointerUnion<clang::NamedDecl const*, clang::concepts::NestedRequirement const*>, llvm::ArrayRef<clang::AssociatedConstraint>, clang::MultiLevelTemplateArgumentList const&, clang::SourceRange, clang::ConstraintSatisfaction&, clang::ConceptReference const*, clang::Expr**)
#15 CheckDeducedArgumentConstraints(clang::Sema&, clang::NamedDecl*, llvm::ArrayRef<clang::TemplateArgument>, llvm::ArrayRef<clang::TemplateArgument>, clang::sema::TemplateDeductionInfo&)
#16 FinishTemplateArgumentDeduction(clang::Sema&, clang::NamedDecl*, clang::TemplateParameterList*, clang::TemplateDecl*, bool, llvm::ArrayRef<clang::TemplateArgumentLoc>, llvm::ArrayRef<clang::TemplateArgument>, llvm::SmallVectorImpl<clang::DeducedTemplateArgument>&, clang::sema::TemplateDeductionInfo&, bool)
#17 void llvm::function_ref<void ()>::callback_fn<DeduceTemplateArguments<clang::ClassTemplatePartialSpecializationDecl>(...)::{lambda()#1}>(long)
#18 clang::StackExhaustionHandler::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>)
#19 DeduceTemplateArguments<clang::ClassTemplatePartialSpecializationDecl>(clang::Sema&, clang::ClassTemplatePartialSpecializationDecl*, llvm::ArrayRef<clang::TemplateArgument>, clang::sema::TemplateDeductionInfo&)
#20 getPatternForClassTemplateSpecialization(clang::Sema&, clang::SourceLocation, clang::ClassTemplateSpecializationDecl*, clang::TemplateSpecializationKind, bool) [clone .isra.0]
#21 clang::Sema::InstantiateClassTemplateSpecialization(clang::SourceLocation, clang::ClassTemplateSpecializationDecl*, clang::TemplateSpecializationKind, bool, bool)
#22 void llvm::function_ref<void ()>::callback_fn<clang::Sema::RequireCompleteTypeImpl(...)::{lambda()#1}>(long)
#23 clang::StackExhaustionHandler::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>)
#24 clang::Sema::RequireCompleteTypeImpl(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser*)
#25 clang::Sema::RequireCompleteType(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser&)
#26 clang::Sema::RequireCompleteType(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, unsigned int)
#27 CppImpl::InstantiateTemplate(clang::TemplateDecl*, llvm::ArrayRef<clang::TemplateArgument>, clang::Sema&, bool)
#28 CppImpl::InstantiateTemplate(CppInternal::Interpreter&, void*, CppImpl::TemplateArgInfo const*, unsigned long, bool)
#29 jank::analyze::cpp_util::is_trait_convertible(jtl::ptr<void>)
#30 jank::analyze::cpp_util::determine_implicit_conversion(jtl::ptr<void>, jtl::ptr<void>)
#31 jank::analyze::apply_implicit_conversion(jtl::ref<jank::analyze::expression>, jtl::ptr<void>, jtl::ptr<void>, folly::fbvector<jank::runtime::oref<jank::runtime::object>, gc_allocator<...> > const&)
#32 jank::runtime::visit_map_like<...analyze_map(...)::$_0>(..., jank::runtime::oref<jank::runtime::object>)
#33 jank::analyze::processor::analyze(...)::$_0::operator()<jank::runtime::oref<jank::runtime::obj::persistent_array_map>>(...) const
#34 jank::analyze::processor::analyze(jank::runtime::oref<jank::runtime::object>, jtl::ptr<jank::analyze::local_frame>, jank::analyze::expression_position, jtl::option<jtl::ref<jank::analyze::expr::function_context>> const&, bool)
#35 jank::runtime::visit_map_like<...analyze_map(...)::$_0>(..., jank::runtime::oref<jank::runtime::object>)
#36 jank::analyze::processor::analyze(...)::$_0::operator()<jank::runtime::oref<jank::runtime::obj::persistent_array_map>>(...) const
#37 jank::analyze::processor::analyze(jank::runtime::oref<jank::runtime::object>, jtl::ptr<jank::analyze::local_frame>, jank::analyze::expression_position, jtl::option<jtl::ref<jank::analyze::expr::function_context>> const&, bool)
#38 jank::analyze::processor::analyze(jank::runtime::oref<jank::runtime::object>, jank::analyze::expression_position)
#39 jank::runtime::context::eval(jank::runtime::oref<jank::runtime::object>)
#40 _jank_eval_str(char const*)
#41 jank_nrepl_server_capture_with_capture_118_1
#42 jank_nrepl_server_handler_eval_do_eval_117_6
#43 jank_nrepl_server_handler_eval_fn_137_1
#44 jank::runtime::obj::multi_function::call(jank::runtime::oref<jank::runtime::object>) const
#45 jank_nrepl_server_core_handle_client_195_1
#46 std::thread::_State_impl<std::thread::_Invoker<std::tuple<jank::runtime::future(jank::runtime::oref<jank::runtime::object>)::$_0>>>::_M_run()
#47 execute_native_thread_routine
#48 start_thread
#49 __clone3

OS Version Information

Fedora 43

I acknowledge that:

• I have searched the jank repository (both open and closed Discussions and Issues) and confirm this is not a duplicate of an existing issue or discussion.
• I have checked the "Preview" tab on all text fields to ensure that everything looks right, and have wrapped all configuration and code in code blocks with a group of three backticks (```) on separate lines.