Variadic friend `operator==` + modules causes "Assertion `Name.isIdentifier() && "Name is not a simple identifier"' failed"

[davidstone]

Given a.cpp:

export module a;

template<typename, typename>
concept c = true;

export template<typename... Ts>
struct a {
	template<typename... Us> requires(... and c<Ts, Us>)
	friend bool operator==(a, a<Us...>) {
		return true;
	}
};

template struct a<>;

and b.cpp:

import a;

template struct a<int>;

When compiled with

clang++ -std=c++20 -x c++-module -fmodule-output=a.pcm --precompile -c a.cpp
clang++ -std=c++20 -fmodule-file=a=a.pcm -c b.cpp

causes clang to fail with

a.cpp:8:36: error: pack expansion contains parameter packs 'Ts' and 'Us' that have different lengths (0 vs. 1)
    8 |         template<typename... Us> requires(... and c<Ts, Us>)
      |                                           ^         ~~  ~~
clang++: llvm/clang/include/clang/AST/Decl.h:276: StringRef clang::NamedDecl::getName() const: Assertion `Name.isIdentifier() && "Name is not a simple identifier"' failed.
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: clang++ -std=c++20 -fmodule-file=a=a.pcm -c b.cpp
1.      b.cpp:3:23: current parser token ';'
2.      b.cpp:3:17: instantiating class definition 'a<int>'
 #0 0x000055dfe453ffc2 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (clang+++0x4598fc2)
 #1 0x000055dfe453d9ce llvm::sys::RunSignalHandlers() (clang+++0x45969ce)
 #2 0x000055dfe44843a9 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007fa344a5c710 (/usr/lib/libc.so.6+0x3e710)
 #4 0x00007fa344aac83c (/usr/lib/libc.so.6+0x8e83c)
 #5 0x00007fa344a5c668 gsignal (/usr/lib/libc.so.6+0x3e668)
 #6 0x00007fa344a444b8 abort (/usr/lib/libc.so.6+0x264b8)
 #7 0x00007fa344a443dc (/usr/lib/libc.so.6+0x263dc)
 #8 0x00007fa344a54d26 (/usr/lib/libc.so.6+0x36d26)
 #9 0x000055dfe74e2dba clang::Sema::PrintInstantiationStack() (clang+++0x753bdba)
#10 0x000055dfe6b4978d clang::Sema::EmitCurrentDiagnostic(unsigned int) (clang+++0x6ba278d)
#11 0x000055dfe6b4a677 clang::Sema::ImmediateDiagBuilder::~ImmediateDiagBuilder() Sema.cpp:0:0
#12 0x000055dfe6b4a7e8 clang::Sema::SemaDiagnosticBuilder::~SemaDiagnosticBuilder() (clang+++0x6ba37e8)
#13 0x000055dfe758b31a clang::Sema::CheckParameterPacksForExpansion(clang::SourceLocation, clang::SourceRange, llvm::ArrayRef<std::pair<llvm::PointerUnion<clang::TemplateTypeParmType const*, clang::NamedDecl*>, clang::SourceLocation>>, clang::MultiLevelTemplateArgumentList const&, bool&, bool&, std::optional<unsigned int>&) (clang+++0x75e431a)
#14 0x000055dfe74fd6d9 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCXXFoldExpr(clang::CXXFoldExpr*) SemaTemplateInstantiate.cpp:0:0
#15 0x000055dfe74ec36c clang::Sema::SubstConstraintExprWithoutSatisfaction(clang::Expr*, clang::MultiLevelTemplateArgumentList const&) (clang+++0x754536c)
#16 0x000055dfe6cc2882 SubstituteConstraintExpressionWithoutSatisfaction(clang::Sema&, clang::Sema::TemplateCompareNewDeclInfo const&, clang::Expr const*) SemaConcept.cpp:0:0
#17 0x000055dfe6cc2606 clang::Sema::AreConstraintExpressionsEqual(clang::NamedDecl const*, clang::Expr const*, clang::Sema::TemplateCompareNewDeclInfo const&, clang::Expr const*) (clang+++0x6d1b606)
#18 0x000055dfe7364961 clang::Sema::TemplateParameterListsAreEqual(clang::Sema::TemplateCompareNewDeclInfo const&, clang::TemplateParameterList*, clang::NamedDecl const*, clang::TemplateParameterList*, bool, clang::Sema::TemplateParameterListEqualKind, clang::SourceLocation) (clang+++0x73bd961)
#19 0x000055dfe72b88df IsOverloadOrOverrideImpl(clang::Sema&, clang::FunctionDecl*, clang::FunctionDecl*, bool, bool, bool) SemaOverload.cpp:0:0
#20 0x000055dfe72b8385 clang::Sema::CheckOverload(clang::Scope*, clang::FunctionDecl*, clang::LookupResult const&, clang::NamedDecl*&, bool) (clang+++0x7311385)
#21 0x000055dfe6d4dd02 clang::Sema::CheckFunctionDeclaration(clang::Scope*, clang::FunctionDecl*, clang::LookupResult&, bool, bool) (clang+++0x6da6d02)
#22 0x000055dfe753f31d clang::TemplateDeclInstantiator::VisitFunctionDecl(clang::FunctionDecl*, clang::TemplateParameterList*, clang::TemplateDeclInstantiator::RewriteKind) (clang+++0x759831d)
#23 0x000055dfe753c79c clang::TemplateDeclInstantiator::VisitFunctionTemplateDecl(clang::FunctionTemplateDecl*) (clang+++0x759579c)
#24 0x000055dfe75398b6 clang::TemplateDeclInstantiator::VisitFriendDecl(clang::FriendDecl*) (clang+++0x75928b6)
#25 0x000055dfe74e7c05 clang::Sema::InstantiateClass(clang::SourceLocation, clang::CXXRecordDecl*, clang::CXXRecordDecl*, clang::MultiLevelTemplateArgumentList const&, clang::TemplateSpecializationKind, bool) (clang+++0x7540c05)
#26 0x000055dfe74e9e7b clang::Sema::InstantiateClassTemplateSpecialization(clang::SourceLocation, clang::ClassTemplateSpecializationDecl*, clang::TemplateSpecializationKind, bool) (clang+++0x7542e7b)
#27 0x000055dfe7385234 clang::Sema::ActOnExplicitInstantiation(clang::Scope*, clang::SourceLocation, clang::SourceLocation, unsigned int, clang::SourceLocation, clang::CXXScopeSpec const&, clang::OpaquePtr<clang::TemplateName>, clang::SourceLocation, clang::SourceLocation, llvm::MutableArrayRef<clang::ParsedTemplateArgument>, clang::SourceLocation, clang::ParsedAttributesView const&) (clang+++0x73de234)
#28 0x000055dfe69cd590 clang::Parser::ParseClassSpecifier(clang::tok::TokenKind, clang::SourceLocation, clang::DeclSpec&, clang::Parser::ParsedTemplateInfo const&, clang::AccessSpecifier, bool, clang::Parser::DeclSpecContext, clang::ParsedAttributes&) (clang+++0x6a26590)
#29 0x000055dfe69a8bf8 clang::Parser::ParseDeclarationSpecifiers(clang::DeclSpec&, clang::Parser::ParsedTemplateInfo const&, clang::AccessSpecifier, clang::Parser::DeclSpecContext, clang::Parser::LateParsedAttrList*, clang::ImplicitTypenameContext) (clang+++0x6a01bf8)
#30 0x000055dfe6a673fe clang::Parser::ParseSingleDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo const&, clang::ParsingDeclRAIIObject&, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (clang+++0x6ac03fe)
#31 0x000055dfe6a65bf4 clang::Parser::ParseExplicitInstantiation(clang::DeclaratorContext, clang::SourceLocation, clang::SourceLocation, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (clang+++0x6abebf4)
#32 0x000055dfe6a65aa7 clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (clang+++0x6abeaa7)
#33 0x000055dfe69a2147 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (clang+++0x69fb147)
#34 0x000055dfe6a79fa4 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (clang+++0x6ad2fa4)
#35 0x000055dfe6a78416 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (clang+++0x6ad1416)
#36 0x000055dfe698a2ee clang::ParseAST(clang::Sema&, bool, bool) (clang+++0x69e32ee)
#37 0x000055dfe528035d clang::FrontendAction::Execute() (clang+++0x52d935d)
#38 0x000055dfe51e6add clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (clang+++0x523fadd)
#39 0x000055dfe531e2ee clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (clang+++0x53772ee)
#40 0x000055dfe2caab71 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (clang+++0x2d03b71)
#41 0x000055dfe2ca6ede ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#42 0x000055dfe4fbd2f9 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::$_0>(long) Job.cpp:0:0
#43 0x000055dfe44840a6 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (clang+++0x44dd0a6)
#44 0x000055dfe4fbc993 clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (clang+++0x5015993)
#45 0x000055dfe4f76d1d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (clang+++0x4fcfd1d)
#46 0x000055dfe4f76ff7 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (clang+++0x4fcfff7)
#47 0x000055dfe4f99ec9 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (clang+++0x4ff2ec9)
#48 0x000055dfe2ca6351 clang_main(int, char**, llvm::ToolContext const&) (clang+++0x2cff351)
#49 0x000055dfe2cb7ad2 main (clang+++0x2d10ad2)
#50 0x00007fa344a45cd0 (/usr/lib/libc.so.6+0x27cd0)
#51 0x00007fa344a45d8a __libc_start_main (/usr/lib/libc.so.6+0x27d8a)
#52 0x000055dfe2ca32e5 _start (clang+++0x2cfc2e5)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
clang version 18.0.0git (https://github.com/llvm/llvm-project.git fc6faa1113e9069f41b5500db051210af0eea843)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: llvm/build/bin
clang++: note: diagnostic msg: 
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang++: note: diagnostic msg: /tmp/b-55bc08.cpp
clang++: note: diagnostic msg: /tmp/b-55bc08.sh
clang++: note: diagnostic msg: 

********************

This started happening within the past two weeks or so.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: David Stone (davidstone)

Given a.cpp:

export module a;

template<typename, typename>
concept c = true;

export template<typename... Ts>
struct a {
	template<typename... Us> requires(... and c<Ts, Us>)
	friend bool operator==(a, a<Us...>) {
		return true;
	}
};

template struct a<>;

and b.cpp:

import a;

template struct a<int>;

When compiled with

clang++ -std=c++20 -x c++-module -fmodule-output=a.pcm --precompile -c a.cpp
clang++ -std=c++20 -fmodule-file=a=a.pcm -c b.cpp

causes clang to fail with

a.cpp:8:36: error: pack expansion contains parameter packs 'Ts' and 'Us' that have different lengths (0 vs. 1)
    8 |         template<typename... Us> requires(... and c<Ts, Us>)
      |                                           ^         ~~  ~~
clang++: llvm/clang/include/clang/AST/Decl.h:276: StringRef clang::NamedDecl::getName() const: Assertion `Name.isIdentifier() && "Name is not a simple identifier"' failed.
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: clang++ -std=c++20 -fmodule-file=a=a.pcm -c b.cpp
1.      b.cpp:3:23: current parser token ';'
2.      b.cpp:3:17: instantiating class definition 'a<int>'
 #<!-- -->0 0x000055dfe453ffc2 llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;, int) (clang+++0x4598fc2)
 #<!-- -->1 0x000055dfe453d9ce llvm::sys::RunSignalHandlers() (clang+++0x45969ce)
 #<!-- -->2 0x000055dfe44843a9 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #<!-- -->3 0x00007fa344a5c710 (/usr/lib/libc.so.6+0x3e710)
 #<!-- -->4 0x00007fa344aac83c (/usr/lib/libc.so.6+0x8e83c)
 #<!-- -->5 0x00007fa344a5c668 gsignal (/usr/lib/libc.so.6+0x3e668)
 #<!-- -->6 0x00007fa344a444b8 abort (/usr/lib/libc.so.6+0x264b8)
 #<!-- -->7 0x00007fa344a443dc (/usr/lib/libc.so.6+0x263dc)
 #<!-- -->8 0x00007fa344a54d26 (/usr/lib/libc.so.6+0x36d26)
 #<!-- -->9 0x000055dfe74e2dba clang::Sema::PrintInstantiationStack() (clang+++0x753bdba)
#<!-- -->10 0x000055dfe6b4978d clang::Sema::EmitCurrentDiagnostic(unsigned int) (clang+++0x6ba278d)
#<!-- -->11 0x000055dfe6b4a677 clang::Sema::ImmediateDiagBuilder::~ImmediateDiagBuilder() Sema.cpp:0:0
#<!-- -->12 0x000055dfe6b4a7e8 clang::Sema::SemaDiagnosticBuilder::~SemaDiagnosticBuilder() (clang+++0x6ba37e8)
#<!-- -->13 0x000055dfe758b31a clang::Sema::CheckParameterPacksForExpansion(clang::SourceLocation, clang::SourceRange, llvm::ArrayRef&lt;std::pair&lt;llvm::PointerUnion&lt;clang::TemplateTypeParmType const*, clang::NamedDecl*&gt;, clang::SourceLocation&gt;&gt;, clang::MultiLevelTemplateArgumentList const&amp;, bool&amp;, bool&amp;, std::optional&lt;unsigned int&gt;&amp;) (clang+++0x75e431a)
#<!-- -->14 0x000055dfe74fd6d9 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformCXXFoldExpr(clang::CXXFoldExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->15 0x000055dfe74ec36c clang::Sema::SubstConstraintExprWithoutSatisfaction(clang::Expr*, clang::MultiLevelTemplateArgumentList const&amp;) (clang+++0x754536c)
#<!-- -->16 0x000055dfe6cc2882 SubstituteConstraintExpressionWithoutSatisfaction(clang::Sema&amp;, clang::Sema::TemplateCompareNewDeclInfo const&amp;, clang::Expr const*) SemaConcept.cpp:0:0
#<!-- -->17 0x000055dfe6cc2606 clang::Sema::AreConstraintExpressionsEqual(clang::NamedDecl const*, clang::Expr const*, clang::Sema::TemplateCompareNewDeclInfo const&amp;, clang::Expr const*) (clang+++0x6d1b606)
#<!-- -->18 0x000055dfe7364961 clang::Sema::TemplateParameterListsAreEqual(clang::Sema::TemplateCompareNewDeclInfo const&amp;, clang::TemplateParameterList*, clang::NamedDecl const*, clang::TemplateParameterList*, bool, clang::Sema::TemplateParameterListEqualKind, clang::SourceLocation) (clang+++0x73bd961)
#<!-- -->19 0x000055dfe72b88df IsOverloadOrOverrideImpl(clang::Sema&amp;, clang::FunctionDecl*, clang::FunctionDecl*, bool, bool, bool) SemaOverload.cpp:0:0
#<!-- -->20 0x000055dfe72b8385 clang::Sema::CheckOverload(clang::Scope*, clang::FunctionDecl*, clang::LookupResult const&amp;, clang::NamedDecl*&amp;, bool) (clang+++0x7311385)
#<!-- -->21 0x000055dfe6d4dd02 clang::Sema::CheckFunctionDeclaration(clang::Scope*, clang::FunctionDecl*, clang::LookupResult&amp;, bool, bool) (clang+++0x6da6d02)
#<!-- -->22 0x000055dfe753f31d clang::TemplateDeclInstantiator::VisitFunctionDecl(clang::FunctionDecl*, clang::TemplateParameterList*, clang::TemplateDeclInstantiator::RewriteKind) (clang+++0x759831d)
#<!-- -->23 0x000055dfe753c79c clang::TemplateDeclInstantiator::VisitFunctionTemplateDecl(clang::FunctionTemplateDecl*) (clang+++0x759579c)
#<!-- -->24 0x000055dfe75398b6 clang::TemplateDeclInstantiator::VisitFriendDecl(clang::FriendDecl*) (clang+++0x75928b6)
#<!-- -->25 0x000055dfe74e7c05 clang::Sema::InstantiateClass(clang::SourceLocation, clang::CXXRecordDecl*, clang::CXXRecordDecl*, clang::MultiLevelTemplateArgumentList const&amp;, clang::TemplateSpecializationKind, bool) (clang+++0x7540c05)
#<!-- -->26 0x000055dfe74e9e7b clang::Sema::InstantiateClassTemplateSpecialization(clang::SourceLocation, clang::ClassTemplateSpecializationDecl*, clang::TemplateSpecializationKind, bool) (clang+++0x7542e7b)
#<!-- -->27 0x000055dfe7385234 clang::Sema::ActOnExplicitInstantiation(clang::Scope*, clang::SourceLocation, clang::SourceLocation, unsigned int, clang::SourceLocation, clang::CXXScopeSpec const&amp;, clang::OpaquePtr&lt;clang::TemplateName&gt;, clang::SourceLocation, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::ParsedTemplateArgument&gt;, clang::SourceLocation, clang::ParsedAttributesView const&amp;) (clang+++0x73de234)
#<!-- -->28 0x000055dfe69cd590 clang::Parser::ParseClassSpecifier(clang::tok::TokenKind, clang::SourceLocation, clang::DeclSpec&amp;, clang::Parser::ParsedTemplateInfo const&amp;, clang::AccessSpecifier, bool, clang::Parser::DeclSpecContext, clang::ParsedAttributes&amp;) (clang+++0x6a26590)
#<!-- -->29 0x000055dfe69a8bf8 clang::Parser::ParseDeclarationSpecifiers(clang::DeclSpec&amp;, clang::Parser::ParsedTemplateInfo const&amp;, clang::AccessSpecifier, clang::Parser::DeclSpecContext, clang::Parser::LateParsedAttrList*, clang::ImplicitTypenameContext) (clang+++0x6a01bf8)
#<!-- -->30 0x000055dfe6a673fe clang::Parser::ParseSingleDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo const&amp;, clang::ParsingDeclRAIIObject&amp;, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::AccessSpecifier) (clang+++0x6ac03fe)
#<!-- -->31 0x000055dfe6a65bf4 clang::Parser::ParseExplicitInstantiation(clang::DeclaratorContext, clang::SourceLocation, clang::SourceLocation, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::AccessSpecifier) (clang+++0x6abebf4)
#<!-- -->32 0x000055dfe6a65aa7 clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::AccessSpecifier) (clang+++0x6abeaa7)
#<!-- -->33 0x000055dfe69a2147 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::SourceLocation*) (clang+++0x69fb147)
#<!-- -->34 0x000055dfe6a79fa4 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec*) (clang+++0x6ad2fa4)
#<!-- -->35 0x000055dfe6a78416 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&lt;clang::DeclGroupRef&gt;&amp;, clang::Sema::ModuleImportState&amp;) (clang+++0x6ad1416)
#<!-- -->36 0x000055dfe698a2ee clang::ParseAST(clang::Sema&amp;, bool, bool) (clang+++0x69e32ee)
#<!-- -->37 0x000055dfe528035d clang::FrontendAction::Execute() (clang+++0x52d935d)
#<!-- -->38 0x000055dfe51e6add clang::CompilerInstance::ExecuteAction(clang::FrontendAction&amp;) (clang+++0x523fadd)
#<!-- -->39 0x000055dfe531e2ee clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (clang+++0x53772ee)
#<!-- -->40 0x000055dfe2caab71 cc1_main(llvm::ArrayRef&lt;char const*&gt;, char const*, void*) (clang+++0x2d03b71)
#<!-- -->41 0x000055dfe2ca6ede ExecuteCC1Tool(llvm::SmallVectorImpl&lt;char const*&gt;&amp;, llvm::ToolContext const&amp;) driver.cpp:0:0
#<!-- -->42 0x000055dfe4fbd2f9 void llvm::function_ref&lt;void ()&gt;::callback_fn&lt;clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const::$_0&gt;(long) Job.cpp:0:0
#<!-- -->43 0x000055dfe44840a6 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref&lt;void ()&gt;) (clang+++0x44dd0a6)
#<!-- -->44 0x000055dfe4fbc993 clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const (clang+++0x5015993)
#<!-- -->45 0x000055dfe4f76d1d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&amp;, clang::driver::Command const*&amp;, bool) const (clang+++0x4fcfd1d)
#<!-- -->46 0x000055dfe4f76ff7 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;, bool) const (clang+++0x4fcfff7)
#<!-- -->47 0x000055dfe4f99ec9 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;) (clang+++0x4ff2ec9)
#<!-- -->48 0x000055dfe2ca6351 clang_main(int, char**, llvm::ToolContext const&amp;) (clang+++0x2cff351)
#<!-- -->49 0x000055dfe2cb7ad2 main (clang+++0x2d10ad2)
#<!-- -->50 0x00007fa344a45cd0 (/usr/lib/libc.so.6+0x27cd0)
#<!-- -->51 0x00007fa344a45d8a __libc_start_main (/usr/lib/libc.so.6+0x27d8a)
#<!-- -->52 0x000055dfe2ca32e5 _start (clang+++0x2cfc2e5)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
clang version 18.0.0git (https://github.com/llvm/llvm-project.git fc6faa1113e9069f41b5500db051210af0eea843)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: llvm/build/bin
clang++: note: diagnostic msg: 
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang++: note: diagnostic msg: /tmp/b-55bc08.cpp
clang++: note: diagnostic msg: /tmp/b-55bc08.sh
clang++: note: diagnostic msg: 

********************

This started happening within the past two weeks or so.

[llvmbot]

@llvm/issue-subscribers-c-20

Author: David Stone (davidstone)

Given a.cpp:

export module a;

template<typename, typename>
concept c = true;

export template<typename... Ts>
struct a {
	template<typename... Us> requires(... and c<Ts, Us>)
	friend bool operator==(a, a<Us...>) {
		return true;
	}
};

template struct a<>;

and b.cpp:

import a;

template struct a<int>;

When compiled with

clang++ -std=c++20 -x c++-module -fmodule-output=a.pcm --precompile -c a.cpp
clang++ -std=c++20 -fmodule-file=a=a.pcm -c b.cpp

causes clang to fail with

a.cpp:8:36: error: pack expansion contains parameter packs 'Ts' and 'Us' that have different lengths (0 vs. 1)
    8 |         template<typename... Us> requires(... and c<Ts, Us>)
      |                                           ^         ~~  ~~
clang++: llvm/clang/include/clang/AST/Decl.h:276: StringRef clang::NamedDecl::getName() const: Assertion `Name.isIdentifier() && "Name is not a simple identifier"' failed.
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: clang++ -std=c++20 -fmodule-file=a=a.pcm -c b.cpp
1.      b.cpp:3:23: current parser token ';'
2.      b.cpp:3:17: instantiating class definition 'a<int>'
 #<!-- -->0 0x000055dfe453ffc2 llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;, int) (clang+++0x4598fc2)
 #<!-- -->1 0x000055dfe453d9ce llvm::sys::RunSignalHandlers() (clang+++0x45969ce)
 #<!-- -->2 0x000055dfe44843a9 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #<!-- -->3 0x00007fa344a5c710 (/usr/lib/libc.so.6+0x3e710)
 #<!-- -->4 0x00007fa344aac83c (/usr/lib/libc.so.6+0x8e83c)
 #<!-- -->5 0x00007fa344a5c668 gsignal (/usr/lib/libc.so.6+0x3e668)
 #<!-- -->6 0x00007fa344a444b8 abort (/usr/lib/libc.so.6+0x264b8)
 #<!-- -->7 0x00007fa344a443dc (/usr/lib/libc.so.6+0x263dc)
 #<!-- -->8 0x00007fa344a54d26 (/usr/lib/libc.so.6+0x36d26)
 #<!-- -->9 0x000055dfe74e2dba clang::Sema::PrintInstantiationStack() (clang+++0x753bdba)
#<!-- -->10 0x000055dfe6b4978d clang::Sema::EmitCurrentDiagnostic(unsigned int) (clang+++0x6ba278d)
#<!-- -->11 0x000055dfe6b4a677 clang::Sema::ImmediateDiagBuilder::~ImmediateDiagBuilder() Sema.cpp:0:0
#<!-- -->12 0x000055dfe6b4a7e8 clang::Sema::SemaDiagnosticBuilder::~SemaDiagnosticBuilder() (clang+++0x6ba37e8)
#<!-- -->13 0x000055dfe758b31a clang::Sema::CheckParameterPacksForExpansion(clang::SourceLocation, clang::SourceRange, llvm::ArrayRef&lt;std::pair&lt;llvm::PointerUnion&lt;clang::TemplateTypeParmType const*, clang::NamedDecl*&gt;, clang::SourceLocation&gt;&gt;, clang::MultiLevelTemplateArgumentList const&amp;, bool&amp;, bool&amp;, std::optional&lt;unsigned int&gt;&amp;) (clang+++0x75e431a)
#<!-- -->14 0x000055dfe74fd6d9 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformCXXFoldExpr(clang::CXXFoldExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->15 0x000055dfe74ec36c clang::Sema::SubstConstraintExprWithoutSatisfaction(clang::Expr*, clang::MultiLevelTemplateArgumentList const&amp;) (clang+++0x754536c)
#<!-- -->16 0x000055dfe6cc2882 SubstituteConstraintExpressionWithoutSatisfaction(clang::Sema&amp;, clang::Sema::TemplateCompareNewDeclInfo const&amp;, clang::Expr const*) SemaConcept.cpp:0:0
#<!-- -->17 0x000055dfe6cc2606 clang::Sema::AreConstraintExpressionsEqual(clang::NamedDecl const*, clang::Expr const*, clang::Sema::TemplateCompareNewDeclInfo const&amp;, clang::Expr const*) (clang+++0x6d1b606)
#<!-- -->18 0x000055dfe7364961 clang::Sema::TemplateParameterListsAreEqual(clang::Sema::TemplateCompareNewDeclInfo const&amp;, clang::TemplateParameterList*, clang::NamedDecl const*, clang::TemplateParameterList*, bool, clang::Sema::TemplateParameterListEqualKind, clang::SourceLocation) (clang+++0x73bd961)
#<!-- -->19 0x000055dfe72b88df IsOverloadOrOverrideImpl(clang::Sema&amp;, clang::FunctionDecl*, clang::FunctionDecl*, bool, bool, bool) SemaOverload.cpp:0:0
#<!-- -->20 0x000055dfe72b8385 clang::Sema::CheckOverload(clang::Scope*, clang::FunctionDecl*, clang::LookupResult const&amp;, clang::NamedDecl*&amp;, bool) (clang+++0x7311385)
#<!-- -->21 0x000055dfe6d4dd02 clang::Sema::CheckFunctionDeclaration(clang::Scope*, clang::FunctionDecl*, clang::LookupResult&amp;, bool, bool) (clang+++0x6da6d02)
#<!-- -->22 0x000055dfe753f31d clang::TemplateDeclInstantiator::VisitFunctionDecl(clang::FunctionDecl*, clang::TemplateParameterList*, clang::TemplateDeclInstantiator::RewriteKind) (clang+++0x759831d)
#<!-- -->23 0x000055dfe753c79c clang::TemplateDeclInstantiator::VisitFunctionTemplateDecl(clang::FunctionTemplateDecl*) (clang+++0x759579c)
#<!-- -->24 0x000055dfe75398b6 clang::TemplateDeclInstantiator::VisitFriendDecl(clang::FriendDecl*) (clang+++0x75928b6)
#<!-- -->25 0x000055dfe74e7c05 clang::Sema::InstantiateClass(clang::SourceLocation, clang::CXXRecordDecl*, clang::CXXRecordDecl*, clang::MultiLevelTemplateArgumentList const&amp;, clang::TemplateSpecializationKind, bool) (clang+++0x7540c05)
#<!-- -->26 0x000055dfe74e9e7b clang::Sema::InstantiateClassTemplateSpecialization(clang::SourceLocation, clang::ClassTemplateSpecializationDecl*, clang::TemplateSpecializationKind, bool) (clang+++0x7542e7b)
#<!-- -->27 0x000055dfe7385234 clang::Sema::ActOnExplicitInstantiation(clang::Scope*, clang::SourceLocation, clang::SourceLocation, unsigned int, clang::SourceLocation, clang::CXXScopeSpec const&amp;, clang::OpaquePtr&lt;clang::TemplateName&gt;, clang::SourceLocation, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::ParsedTemplateArgument&gt;, clang::SourceLocation, clang::ParsedAttributesView const&amp;) (clang+++0x73de234)
#<!-- -->28 0x000055dfe69cd590 clang::Parser::ParseClassSpecifier(clang::tok::TokenKind, clang::SourceLocation, clang::DeclSpec&amp;, clang::Parser::ParsedTemplateInfo const&amp;, clang::AccessSpecifier, bool, clang::Parser::DeclSpecContext, clang::ParsedAttributes&amp;) (clang+++0x6a26590)
#<!-- -->29 0x000055dfe69a8bf8 clang::Parser::ParseDeclarationSpecifiers(clang::DeclSpec&amp;, clang::Parser::ParsedTemplateInfo const&amp;, clang::AccessSpecifier, clang::Parser::DeclSpecContext, clang::Parser::LateParsedAttrList*, clang::ImplicitTypenameContext) (clang+++0x6a01bf8)
#<!-- -->30 0x000055dfe6a673fe clang::Parser::ParseSingleDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo const&amp;, clang::ParsingDeclRAIIObject&amp;, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::AccessSpecifier) (clang+++0x6ac03fe)
#<!-- -->31 0x000055dfe6a65bf4 clang::Parser::ParseExplicitInstantiation(clang::DeclaratorContext, clang::SourceLocation, clang::SourceLocation, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::AccessSpecifier) (clang+++0x6abebf4)
#<!-- -->32 0x000055dfe6a65aa7 clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::AccessSpecifier) (clang+++0x6abeaa7)
#<!-- -->33 0x000055dfe69a2147 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::SourceLocation*) (clang+++0x69fb147)
#<!-- -->34 0x000055dfe6a79fa4 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec*) (clang+++0x6ad2fa4)
#<!-- -->35 0x000055dfe6a78416 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&lt;clang::DeclGroupRef&gt;&amp;, clang::Sema::ModuleImportState&amp;) (clang+++0x6ad1416)
#<!-- -->36 0x000055dfe698a2ee clang::ParseAST(clang::Sema&amp;, bool, bool) (clang+++0x69e32ee)
#<!-- -->37 0x000055dfe528035d clang::FrontendAction::Execute() (clang+++0x52d935d)
#<!-- -->38 0x000055dfe51e6add clang::CompilerInstance::ExecuteAction(clang::FrontendAction&amp;) (clang+++0x523fadd)
#<!-- -->39 0x000055dfe531e2ee clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (clang+++0x53772ee)
#<!-- -->40 0x000055dfe2caab71 cc1_main(llvm::ArrayRef&lt;char const*&gt;, char const*, void*) (clang+++0x2d03b71)
#<!-- -->41 0x000055dfe2ca6ede ExecuteCC1Tool(llvm::SmallVectorImpl&lt;char const*&gt;&amp;, llvm::ToolContext const&amp;) driver.cpp:0:0
#<!-- -->42 0x000055dfe4fbd2f9 void llvm::function_ref&lt;void ()&gt;::callback_fn&lt;clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const::$_0&gt;(long) Job.cpp:0:0
#<!-- -->43 0x000055dfe44840a6 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref&lt;void ()&gt;) (clang+++0x44dd0a6)
#<!-- -->44 0x000055dfe4fbc993 clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const (clang+++0x5015993)
#<!-- -->45 0x000055dfe4f76d1d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&amp;, clang::driver::Command const*&amp;, bool) const (clang+++0x4fcfd1d)
#<!-- -->46 0x000055dfe4f76ff7 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;, bool) const (clang+++0x4fcfff7)
#<!-- -->47 0x000055dfe4f99ec9 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;) (clang+++0x4ff2ec9)
#<!-- -->48 0x000055dfe2ca6351 clang_main(int, char**, llvm::ToolContext const&amp;) (clang+++0x2cff351)
#<!-- -->49 0x000055dfe2cb7ad2 main (clang+++0x2d10ad2)
#<!-- -->50 0x00007fa344a45cd0 (/usr/lib/libc.so.6+0x27cd0)
#<!-- -->51 0x00007fa344a45d8a __libc_start_main (/usr/lib/libc.so.6+0x27d8a)
#<!-- -->52 0x000055dfe2ca32e5 _start (clang+++0x2cfc2e5)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
clang version 18.0.0git (https://github.com/llvm/llvm-project.git fc6faa1113e9069f41b5500db051210af0eea843)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: llvm/build/bin
clang++: note: diagnostic msg: 
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang++: note: diagnostic msg: /tmp/b-55bc08.cpp
clang++: note: diagnostic msg: /tmp/b-55bc08.sh
clang++: note: diagnostic msg: 

********************

This started happening within the past two weeks or so.

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: David Stone (davidstone)

Given a.cpp:

export module a;

template<typename, typename>
concept c = true;

export template<typename... Ts>
struct a {
	template<typename... Us> requires(... and c<Ts, Us>)
	friend bool operator==(a, a<Us...>) {
		return true;
	}
};

template struct a<>;

and b.cpp:

import a;

template struct a<int>;

When compiled with

clang++ -std=c++20 -x c++-module -fmodule-output=a.pcm --precompile -c a.cpp
clang++ -std=c++20 -fmodule-file=a=a.pcm -c b.cpp

causes clang to fail with

a.cpp:8:36: error: pack expansion contains parameter packs 'Ts' and 'Us' that have different lengths (0 vs. 1)
    8 |         template<typename... Us> requires(... and c<Ts, Us>)
      |                                           ^         ~~  ~~
clang++: llvm/clang/include/clang/AST/Decl.h:276: StringRef clang::NamedDecl::getName() const: Assertion `Name.isIdentifier() && "Name is not a simple identifier"' failed.
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: clang++ -std=c++20 -fmodule-file=a=a.pcm -c b.cpp
1.      b.cpp:3:23: current parser token ';'
2.      b.cpp:3:17: instantiating class definition 'a<int>'
 #<!-- -->0 0x000055dfe453ffc2 llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;, int) (clang+++0x4598fc2)
 #<!-- -->1 0x000055dfe453d9ce llvm::sys::RunSignalHandlers() (clang+++0x45969ce)
 #<!-- -->2 0x000055dfe44843a9 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #<!-- -->3 0x00007fa344a5c710 (/usr/lib/libc.so.6+0x3e710)
 #<!-- -->4 0x00007fa344aac83c (/usr/lib/libc.so.6+0x8e83c)
 #<!-- -->5 0x00007fa344a5c668 gsignal (/usr/lib/libc.so.6+0x3e668)
 #<!-- -->6 0x00007fa344a444b8 abort (/usr/lib/libc.so.6+0x264b8)
 #<!-- -->7 0x00007fa344a443dc (/usr/lib/libc.so.6+0x263dc)
 #<!-- -->8 0x00007fa344a54d26 (/usr/lib/libc.so.6+0x36d26)
 #<!-- -->9 0x000055dfe74e2dba clang::Sema::PrintInstantiationStack() (clang+++0x753bdba)
#<!-- -->10 0x000055dfe6b4978d clang::Sema::EmitCurrentDiagnostic(unsigned int) (clang+++0x6ba278d)
#<!-- -->11 0x000055dfe6b4a677 clang::Sema::ImmediateDiagBuilder::~ImmediateDiagBuilder() Sema.cpp:0:0
#<!-- -->12 0x000055dfe6b4a7e8 clang::Sema::SemaDiagnosticBuilder::~SemaDiagnosticBuilder() (clang+++0x6ba37e8)
#<!-- -->13 0x000055dfe758b31a clang::Sema::CheckParameterPacksForExpansion(clang::SourceLocation, clang::SourceRange, llvm::ArrayRef&lt;std::pair&lt;llvm::PointerUnion&lt;clang::TemplateTypeParmType const*, clang::NamedDecl*&gt;, clang::SourceLocation&gt;&gt;, clang::MultiLevelTemplateArgumentList const&amp;, bool&amp;, bool&amp;, std::optional&lt;unsigned int&gt;&amp;) (clang+++0x75e431a)
#<!-- -->14 0x000055dfe74fd6d9 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformCXXFoldExpr(clang::CXXFoldExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->15 0x000055dfe74ec36c clang::Sema::SubstConstraintExprWithoutSatisfaction(clang::Expr*, clang::MultiLevelTemplateArgumentList const&amp;) (clang+++0x754536c)
#<!-- -->16 0x000055dfe6cc2882 SubstituteConstraintExpressionWithoutSatisfaction(clang::Sema&amp;, clang::Sema::TemplateCompareNewDeclInfo const&amp;, clang::Expr const*) SemaConcept.cpp:0:0
#<!-- -->17 0x000055dfe6cc2606 clang::Sema::AreConstraintExpressionsEqual(clang::NamedDecl const*, clang::Expr const*, clang::Sema::TemplateCompareNewDeclInfo const&amp;, clang::Expr const*) (clang+++0x6d1b606)
#<!-- -->18 0x000055dfe7364961 clang::Sema::TemplateParameterListsAreEqual(clang::Sema::TemplateCompareNewDeclInfo const&amp;, clang::TemplateParameterList*, clang::NamedDecl const*, clang::TemplateParameterList*, bool, clang::Sema::TemplateParameterListEqualKind, clang::SourceLocation) (clang+++0x73bd961)
#<!-- -->19 0x000055dfe72b88df IsOverloadOrOverrideImpl(clang::Sema&amp;, clang::FunctionDecl*, clang::FunctionDecl*, bool, bool, bool) SemaOverload.cpp:0:0
#<!-- -->20 0x000055dfe72b8385 clang::Sema::CheckOverload(clang::Scope*, clang::FunctionDecl*, clang::LookupResult const&amp;, clang::NamedDecl*&amp;, bool) (clang+++0x7311385)
#<!-- -->21 0x000055dfe6d4dd02 clang::Sema::CheckFunctionDeclaration(clang::Scope*, clang::FunctionDecl*, clang::LookupResult&amp;, bool, bool) (clang+++0x6da6d02)
#<!-- -->22 0x000055dfe753f31d clang::TemplateDeclInstantiator::VisitFunctionDecl(clang::FunctionDecl*, clang::TemplateParameterList*, clang::TemplateDeclInstantiator::RewriteKind) (clang+++0x759831d)
#<!-- -->23 0x000055dfe753c79c clang::TemplateDeclInstantiator::VisitFunctionTemplateDecl(clang::FunctionTemplateDecl*) (clang+++0x759579c)
#<!-- -->24 0x000055dfe75398b6 clang::TemplateDeclInstantiator::VisitFriendDecl(clang::FriendDecl*) (clang+++0x75928b6)
#<!-- -->25 0x000055dfe74e7c05 clang::Sema::InstantiateClass(clang::SourceLocation, clang::CXXRecordDecl*, clang::CXXRecordDecl*, clang::MultiLevelTemplateArgumentList const&amp;, clang::TemplateSpecializationKind, bool) (clang+++0x7540c05)
#<!-- -->26 0x000055dfe74e9e7b clang::Sema::InstantiateClassTemplateSpecialization(clang::SourceLocation, clang::ClassTemplateSpecializationDecl*, clang::TemplateSpecializationKind, bool) (clang+++0x7542e7b)
#<!-- -->27 0x000055dfe7385234 clang::Sema::ActOnExplicitInstantiation(clang::Scope*, clang::SourceLocation, clang::SourceLocation, unsigned int, clang::SourceLocation, clang::CXXScopeSpec const&amp;, clang::OpaquePtr&lt;clang::TemplateName&gt;, clang::SourceLocation, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::ParsedTemplateArgument&gt;, clang::SourceLocation, clang::ParsedAttributesView const&amp;) (clang+++0x73de234)
#<!-- -->28 0x000055dfe69cd590 clang::Parser::ParseClassSpecifier(clang::tok::TokenKind, clang::SourceLocation, clang::DeclSpec&amp;, clang::Parser::ParsedTemplateInfo const&amp;, clang::AccessSpecifier, bool, clang::Parser::DeclSpecContext, clang::ParsedAttributes&amp;) (clang+++0x6a26590)
#<!-- -->29 0x000055dfe69a8bf8 clang::Parser::ParseDeclarationSpecifiers(clang::DeclSpec&amp;, clang::Parser::ParsedTemplateInfo const&amp;, clang::AccessSpecifier, clang::Parser::DeclSpecContext, clang::Parser::LateParsedAttrList*, clang::ImplicitTypenameContext) (clang+++0x6a01bf8)
#<!-- -->30 0x000055dfe6a673fe clang::Parser::ParseSingleDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo const&amp;, clang::ParsingDeclRAIIObject&amp;, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::AccessSpecifier) (clang+++0x6ac03fe)
#<!-- -->31 0x000055dfe6a65bf4 clang::Parser::ParseExplicitInstantiation(clang::DeclaratorContext, clang::SourceLocation, clang::SourceLocation, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::AccessSpecifier) (clang+++0x6abebf4)
#<!-- -->32 0x000055dfe6a65aa7 clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::AccessSpecifier) (clang+++0x6abeaa7)
#<!-- -->33 0x000055dfe69a2147 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::SourceLocation*) (clang+++0x69fb147)
#<!-- -->34 0x000055dfe6a79fa4 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec*) (clang+++0x6ad2fa4)
#<!-- -->35 0x000055dfe6a78416 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&lt;clang::DeclGroupRef&gt;&amp;, clang::Sema::ModuleImportState&amp;) (clang+++0x6ad1416)
#<!-- -->36 0x000055dfe698a2ee clang::ParseAST(clang::Sema&amp;, bool, bool) (clang+++0x69e32ee)
#<!-- -->37 0x000055dfe528035d clang::FrontendAction::Execute() (clang+++0x52d935d)
#<!-- -->38 0x000055dfe51e6add clang::CompilerInstance::ExecuteAction(clang::FrontendAction&amp;) (clang+++0x523fadd)
#<!-- -->39 0x000055dfe531e2ee clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (clang+++0x53772ee)
#<!-- -->40 0x000055dfe2caab71 cc1_main(llvm::ArrayRef&lt;char const*&gt;, char const*, void*) (clang+++0x2d03b71)
#<!-- -->41 0x000055dfe2ca6ede ExecuteCC1Tool(llvm::SmallVectorImpl&lt;char const*&gt;&amp;, llvm::ToolContext const&amp;) driver.cpp:0:0
#<!-- -->42 0x000055dfe4fbd2f9 void llvm::function_ref&lt;void ()&gt;::callback_fn&lt;clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const::$_0&gt;(long) Job.cpp:0:0
#<!-- -->43 0x000055dfe44840a6 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref&lt;void ()&gt;) (clang+++0x44dd0a6)
#<!-- -->44 0x000055dfe4fbc993 clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const (clang+++0x5015993)
#<!-- -->45 0x000055dfe4f76d1d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&amp;, clang::driver::Command const*&amp;, bool) const (clang+++0x4fcfd1d)
#<!-- -->46 0x000055dfe4f76ff7 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;, bool) const (clang+++0x4fcfff7)
#<!-- -->47 0x000055dfe4f99ec9 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;) (clang+++0x4ff2ec9)
#<!-- -->48 0x000055dfe2ca6351 clang_main(int, char**, llvm::ToolContext const&amp;) (clang+++0x2cff351)
#<!-- -->49 0x000055dfe2cb7ad2 main (clang+++0x2d10ad2)
#<!-- -->50 0x00007fa344a45cd0 (/usr/lib/libc.so.6+0x27cd0)
#<!-- -->51 0x00007fa344a45d8a __libc_start_main (/usr/lib/libc.so.6+0x27d8a)
#<!-- -->52 0x000055dfe2ca32e5 _start (clang+++0x2cfc2e5)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
clang version 18.0.0git (https://github.com/llvm/llvm-project.git fc6faa1113e9069f41b5500db051210af0eea843)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: llvm/build/bin
clang++: note: diagnostic msg: 
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang++: note: diagnostic msg: /tmp/b-55bc08.cpp
clang++: note: diagnostic msg: /tmp/b-55bc08.sh
clang++: note: diagnostic msg: 

********************

This started happening within the past two weeks or so.

[cor3ntin]

@ChuanqiXu9 any idea?

[davidstone]

Note that I get the same assertion failure for operator<=> and the same error message but no assertion failure when the function is some arbitrary function, for instance, f.

[davidstone]

@cor3ntin Looks like this was introduced by 69066ab

[ChuanqiXu9]

@ChuanqiXu9 any idea?

I took a look at 69066ab but I didn't find any thing related with modules. Given #78101 reported the same commit. So I feel maybe there are something internal bad with Sema.

I feel we can revert that one first and add these 2 tests to make things more stable.

[cor3ntin]

@ChuanqiXu9 I'm working on a fix, which I should have shortly, thanks for looking!
We were comparing constraints of function in unrelated incomplete contexts and for some reason that was causing issues during instantiation (I haven't dug too much into that, but I'm fixing the symptoms)