[clang++] Crash when parsing out-of-class definition of member function with trailing requires clause

[PiliLatiesa]

I'm observing crashes when compiling the following snipped with clang trunk. Clang 19 doesn't crash.

#include <cstdint>

template<typename T>
class TExprBase;

template<std::size_t dim, std::size_t rank, template<std::size_t, std::size_t> typename T>
class TExprBase<T<dim, rank>>
{
public:
  void Curl() const requires (dim == 3u && rank == 1u);
};

template<std::size_t dim, std::size_t rank, template<std::size_t, std::size_t> typename T>
void TExprBase<T<dim, rank>>::Curl() const requires (dim == 3u && rank == 1u)
{
}

[shafik]

Confirmed: https://godbolt.org/z/jevEajn63

Unreachable:

not a non-type template argument
UNREACHABLE executed at /root/llvm-project/clang/lib/Sema/SemaTemplate.cpp:7669!

Backtrace:

PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.	Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -std=c++20 <source>
1.	<source>:15:1: current parser token '{'
 #0 0x0000000003ba9d48 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ba9d48)
 #1 0x0000000003ba7a0c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ba7a0c)
 #2 0x0000000003af4c68 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x000078328da42520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x000078328da969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x000078328da42476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x000078328da287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x0000000003b0053a (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b0053a)
 #8 0x00000000071952a7 clang::Sema::BuildExpressionFromNonTypeTemplateArgument(clang::TemplateArgument const&, clang::SourceLocation) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x71952a7)
 #9 0x00000000073cace3 (anonymous namespace)::TemplateInstantiator::transformNonTypeTemplateParmRef(clang::Decl*, clang::NonTypeTemplateParmDecl const*, clang::SourceLocation, clang::TemplateArgument, std::optional<unsigned int>) SemaTemplateInstantiate.cpp:0:0
#10 0x00000000073dcc6d (anonymous namespace)::TemplateInstantiator::TransformDeclRefExpr(clang::DeclRefExpr*) SemaTemplateInstantiate.cpp:0:0
#11 0x00000000073b1257 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#12 0x00000000073c0540 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformBinaryOperator(clang::BinaryOperator*) SemaTemplateInstantiate.cpp:0:0
#13 0x00000000073b0ede clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#14 0x00000000073c0540 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformBinaryOperator(clang::BinaryOperator*) SemaTemplateInstantiate.cpp:0:0
#15 0x00000000073b0ede clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#16 0x00000000073bba38 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformParenExpr(clang::ParenExpr*) SemaTemplateInstantiate.cpp:0:0
#17 0x00000000073b14d6 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#18 0x00000000073c141f clang::Sema::SubstConstraintExprWithoutSatisfaction(clang::Expr*, clang::MultiLevelTemplateArgumentList const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x73c141f)
#19 0x0000000006924d6b SubstituteConstraintExpressionWithoutSatisfaction(clang::Sema&, clang::Sema::TemplateCompareNewDeclInfo const&, clang::Expr const*) SemaConcept.cpp:0:0
#20 0x000000000693078a clang::Sema::AreConstraintExpressionsEqual(clang::NamedDecl const*, clang::Expr const*, clang::Sema::TemplateCompareNewDeclInfo const&, clang::Expr const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x693078a)
#21 0x00000000070af4a1 IsOverloadOrOverrideImpl(clang::Sema&, clang::FunctionDecl*, clang::FunctionDecl*, bool, bool, bool) SemaOverload.cpp:0:0
#22 0x00000000070af901 clang::Sema::CheckOverload(clang::Scope*, clang::FunctionDecl*, clang::LookupResult const&, clang::NamedDecl*&, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x70af901)
#23 0x0000000006a08570 clang::Sema::CheckFunctionDeclaration(clang::Scope*, clang::FunctionDecl*, clang::LookupResult&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a08570)
#24 0x0000000006a0eb46 clang::Sema::ActOnFunctionDeclarator(clang::Scope*, clang::Declarator&, clang::DeclContext*, clang::TypeSourceInfo*, clang::LookupResult&, llvm::MutableArrayRef<clang::TemplateParameterList*>, bool&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a0eb46)
#25 0x0000000006a13da0 clang::Sema::HandleDeclarator(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef<clang::TemplateParameterList*>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a13da0)
#26 0x0000000006a14750 clang::Sema::ActOnStartOfFunctionDef(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef<clang::TemplateParameterList*>, clang::SkipBodyInfo*, clang::Sema::FnBodyKind) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a14750)
#27 0x0000000006650140 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6650140)
#28 0x00000000066856ed clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66856ed)
#29 0x000000000674eec6 clang::Parser::ParseDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo&, clang::ParsingDeclRAIIObject&, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x674eec6)
#30 0x000000000675c78c clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#31 0x000000000675caaa clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x675caaa)
#32 0x000000000668dc93 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x668dc93)
#33 0x000000000664c6d7 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x664c6d7)
#34 0x000000000664d57d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x664d57d)
#35 0x000000000663fa9a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x663fa9a)
#36 0x0000000004502248 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4502248)
#37 0x00000000047bbb49 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47bbb49)
#38 0x000000000473a6ee clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x473a6ee)
#39 0x00000000048a16be clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48a16be)
#40 0x0000000000cdb8ef cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcdb8ef)
#41 0x0000000000cd35fa ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#42 0x0000000004545f19 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#43 0x0000000003af5114 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3af5114)
#44 0x000000000454650f clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (.part.0) Job.cpp:0:0
#45 0x000000000450be4d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x450be4d)
#46 0x000000000450cf3d clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x450cf3d)
#47 0x0000000004514865 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4514865)
#48 0x0000000000cd87bf clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcd87bf)
#49 0x0000000000ba7d14 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xba7d14)
#50 0x000078328da29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#51 0x000078328da29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#52 0x0000000000cd30ae _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcd30ae)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134

[shafik]

Unreachable added in 5518a9d

CC @bolshakov-a

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (PiliLatiesa)

I'm observing crashes when compiling the following snipped with clang trunk. Clang 19 doesn't crash.

#include <cstdint>

template<typename T>
class TExprBase;

template<std::size_t dim, std::size_t rank, template<std::size_t, std::size_t> typename T>
class TExprBase<T<dim, rank>>
{
public:
  void Curl() const requires (dim == 3u && rank == 1u);
};

template<std::size_t dim, std::size_t rank, template<std::size_t, std::size_t> typename T>
void TExprBase<T<dim, rank>>::Curl() const requires (dim == 3u && rank == 1u)
{
}

[bolshakov-a]

It's not me, it's after #111852.

[shafik]

It's not me, it's after #111852.

Apologies.

CC @sdkrystian

[PiliLatiesa]

Slightly reduced:

template<typename T>
class TBase;

template<int dim, template<int> typename T>
class TBase<T<dim>>
{
  void Curl() const requires (dim == 3u);
};

template<int dim, template<int> typename T>
void TBase<T<dim>>::Curl() const requires (dim == 3u) {} 

[bolshakov-a]

Even this works breaks:

template<int T>
struct Tpl{};

template<typename T>
class TExprBase;

template<int dim>
class TExprBase<Tpl<dim>>
{
public:
  void Curl() const requires (dim == 3u);
};

template<int dim>
void TExprBase<Tpl<dim>>::Curl() const requires (dim == 3u)
{
}

TemplateArgument arg argument of TemplateInstantiator::transformNonTypeTemplateParmRef appears to be Tpl<dim> type template argument of the primary template instead of dim NTTP of the specialization, and the assertion fires correctly.