ICE on 'requires' for recursive function template

[rollbear]

The following invalid code ICEs Clang++ 16.0.6. This is a reduction from a case I believe to be valid, and that was accepted by Clang++-15 (https://godbolt.org/z/axxY8TGWz)

auto c(auto, auto ... fs){return [](auto) requires(c(fs...)){};}
auto f = c([]{})(5);

with the backtrace:

$ clang++-16 -std=c++2b err.cpp
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: /usr/lib/llvm-16/bin/clang -cc1 -triple x86_64-pc-linux-gnu -emit-obj -mrelax-all -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name err.cpp -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=all -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -mllvm -treat-scalable-fixed-error-as-warning -debugger-tuning=gdb -fcoverage-compilation-dir=/ -resource-dir /usr/lib/llvm-16/lib/clang/16 -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12 -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/x86_64-linux-gnu/c++/12 -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/backward -internal-isystem /usr/lib/llvm-16/lib/clang/16/include -internal-isystem /usr/local/include -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -std=c++2b -fdeprecated-macro -fdebug-compilation-dir=/ -ferror-limit 19 -fgnuc-version=4.2.1 -fno-implicit-modules -fcxx-exceptions -fexceptions -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/err-6f78a7.o -x c++ err.cpp
1.      err.cpp:2:19: current parser token ')'
 #0 0x00007f899cf08c16 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/usr/lib/llvm-16/bin/../lib/libLLVM-16.so.1+0xfc1c16)
 #1 0x00007f899cf06e60 llvm::sys::RunSignalHandlers() (/usr/lib/llvm-16/bin/../lib/libLLVM-16.so.1+0xfbfe60)
 #2 0x00007f899cf093eb (/usr/lib/llvm-16/bin/../lib/libLLVM-16.so.1+0xfc23eb)
 #3 0x00007f899b9ff4b0 (/lib/x86_64-linux-gnu/libc.so.6+0x3c4b0)
 #4 0x00007f89a500b3ee 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>&) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x1aa13ee)
 #5 0x00007f89a4fa2571 (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x1a38571)
 #6 0x00007f89a4fa85ab (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x1a3e5ab)
 #7 0x00007f89a4fa1f82 clang::Sema::SubstConstraintExpr(clang::Expr*, clang::MultiLevelTemplateArgumentList const&) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x1a37f82)
 #8 0x00007f89a49cf387 (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x1465387)
 #9 0x00007f89a49ce279 (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x1464279)
#10 0x00007f89a49c94df (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x145f4df)
#11 0x00007f89a49c8e8c clang::Sema::CheckConstraintSatisfaction(clang::NamedDecl const*, llvm::ArrayRef<clang::Expr const*>, llvm::SmallVectorImpl<clang::Expr*>&, clang::MultiLevelTemplateArgumentList const&, clang::SourceRange, clang::ConstraintSatisfaction&) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x145ee8c)
#12 0x00007f89a49cb785 clang::Sema::CheckInstantiatedFunctionTemplateConstraints(clang::SourceLocation, clang::FunctionDecl*, llvm::ArrayRef<clang::TemplateArgument>, clang::ConstraintSatisfaction&) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x1461785)
#13 0x00007f89a4f415df clang::Sema::FinishTemplateArgumentDeduction(clang::FunctionTemplateDecl*, llvm::SmallVectorImpl<clang::DeducedTemplateArgument>&, unsigned int, clang::FunctionDecl*&, clang::sema::TemplateDeductionInfo&, llvm::SmallVectorImpl<clang::Sema::OriginalCallArg> const*, bool, llvm::function_ref<bool ()>) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x19d75df)
#14 0x00007f89a4f94ab7 (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x1a2aab7)
#15 0x00007f89a48966dd clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x132c6dd)
#16 0x00007f89a4f42a81 clang::Sema::DeduceTemplateArguments(clang::FunctionTemplateDecl*, clang::TemplateArgumentListInfo*, llvm::ArrayRef<clang::Expr*>, clang::FunctionDecl*&, clang::sema::TemplateDeductionInfo&, bool, llvm::function_ref<bool (llvm::ArrayRef<clang::QualType>)>) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x19d8a81)
#17 0x00007f89a4e1f5f0 clang::Sema::AddMethodTemplateCandidate(clang::FunctionTemplateDecl*, clang::DeclAccessPair, clang::CXXRecordDecl*, clang::TemplateArgumentListInfo*, clang::QualType, clang::Expr::Classification, llvm::ArrayRef<clang::Expr*>, clang::OverloadCandidateSet&, bool, bool, clang::OverloadCandidateParamOrder) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x18b55f0)
#18 0x00007f89a4e1ffc3 clang::Sema::AddMethodCandidate(clang::DeclAccessPair, clang::QualType, clang::Expr::Classification, llvm::ArrayRef<clang::Expr*>, clang::OverloadCandidateSet&, bool, clang::OverloadCandidateParamOrder) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x18b5fc3)
#19 0x00007f89a4e36e67 clang::Sema::BuildCallToObjectOfClassType(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x18cce67)
#20 0x00007f89a4b50681 clang::Sema::BuildCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*, bool, bool) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x15e6681)
#21 0x00007f89a4b687fd clang::Sema::ActOnCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x15fe7fd)
#22 0x00007f89a417fa4c clang::Parser::ParsePostfixExpressionSuffix(clang::ActionResult<clang::Expr*, true>) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0xc15a4c)
#23 0x00007f89a4180965 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0xc16965)
#24 0x00007f89a417cbe1 clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0xc12be1)
#25 0x00007f89a414f26b clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0xbe526b)
#26 0x00007f89a414c637 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0xbe2637)
#27 0x00007f89a41fc557 clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0xc92557)
#28 0x00007f89a41fbf79 clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0xc91f79)
#29 0x00007f89a41fb217 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0xc91217)
#30 0x00007f89a41f95be clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0xc8f5be)
#31 0x00007f89a413933e clang::ParseAST(clang::Sema&, bool, bool) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0xbcf33e)
#32 0x00007f89a5d503b5 clang::FrontendAction::Execute() (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x27e63b5)
#33 0x00007f89a5ccac94 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x2760c94)
#34 0x00007f89a5dc9434 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/usr/lib/llvm-16/bin/../lib/libclang-cpp.so.16+0x285f434)
#35 0x000055dc45f3b116 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/usr/lib/llvm-16/bin/clang+0x15116)
#36 0x000055dc45f38280 (/usr/lib/llvm-16/bin/clang+0x12280)
#37 0x000055dc45f37f89 clang_main(int, char**) (/usr/lib/llvm-16/bin/clang+0x11f89)
#38 0x00007f899b9e6a90 (/lib/x86_64-linux-gnu/libc.so.6+0x23a90)
#39 0x00007f899b9e6b49 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x23b49)
#40 0x000055dc45f348b5 _start (/usr/lib/llvm-16/bin/clang+0xe8b5)
clang: error: unable to execute command: Segmentation fault (core dumped)
clang: error: clang frontend command failed due to signal (use -v to see invocation)
Ubuntu clang version 16.0.6 (++20230710042020+7cbf1a259152-1~exp1~20230710162037.55)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/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/err-c1b700.cpp
clang: note: diagnostic msg: /tmp/err-c1b700.sh
clang: note: diagnostic msg: 

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

/tmp/err-c1b700.cpp:

# 1 "err.cpp"
# 1 "<built-in>" 1
# 1 "<built-in>" 3
# 451 "<built-in>" 3
# 1 "<command line>" 1
# 1 "<built-in>" 2
# 1 "err.cpp" 2
auto c(auto, auto ... fs){return [](auto) requires(c(fs...)){};}
auto f = c([]{})(5);

/tmp/err-c1b700.sh:

# Crash reproducer for Ubuntu clang version 16.0.6 (++20230710042020+7cbf1a259152-1~exp1~20230710162037.55)
# Driver args: "--driver-mode=g++" "-std=c++2b" "err.cpp"
# Original command:  "/usr/lib/llvm-16/bin/clang" "-cc1" "-triple" "x86_64-pc-linux-gnu" "-emit-obj" "-mrelax-all" "-disable-free" "-clear-ast-before-backend" "-disable-llvm-verifier" "-discard-value-names" "-main-file-name" "err.cpp" "-mrelocation-model" "pic" "-pic-level" "2" "-pic-is-pie" "-mframe-pointer=all" "-fmath-errno" "-ffp-contract=on" "-fno-rounding-math" "-mconstructor-aliases" "-funwind-tables=2" "-target-cpu" "x86-64" "-tune-cpu" "generic" "-mllvm" "-treat-scalable-fixed-error-as-warning" "-debugger-tuning=gdb" "-fcoverage-compilation-dir=/" "-resource-dir" "/usr/lib/llvm-16/lib/clang/16" "-internal-isystem" "/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12" "-internal-isystem" "/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/x86_64-linux-gnu/c++/12" "-internal-isystem" "/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/backward" "-internal-isystem" "/usr/lib/llvm-16/lib/clang/16/include" "-internal-isystem" "/usr/local/include" "-internal-isystem" "/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../x86_64-linux-gnu/include" "-internal-externc-isystem" "/usr/include/x86_64-linux-gnu" "-internal-externc-isystem" "/include" "-internal-externc-isystem" "/usr/include" "-std=c++2b" "-fdeprecated-macro" "-fdebug-compilation-dir=/" "-ferror-limit" "19" "-fgnuc-version=4.2.1" "-fno-implicit-modules" "-fcxx-exceptions" "-fexceptions" "-faddrsig" "-D__GCC_HAVE_DWARF2_CFI_ASM=1" "-o" "/tmp/err-6f78a7.o" "-x" "c++" "err.cpp"
 "/usr/lib/llvm-16/bin/clang" "-cc1" "-triple" "x86_64-pc-linux-gnu" "-emit-obj" "-mrelax-all" "-disable-free" "-clear-ast-before-backend" "-disable-llvm-verifier" "-discard-value-names" "-main-file-name" "err.cpp" "-mrelocation-model" "pic" "-pic-level" "2" "-pic-is-pie" "-mframe-pointer=all" "-fmath-errno" "-ffp-contract=on" "-fno-rounding-math" "-mconstructor-aliases" "-funwind-tables=2" "-target-cpu" "x86-64" "-tune-cpu" "generic" "-mllvm" "-treat-scalable-fixed-error-as-warning" "-debugger-tuning=gdb" "-fcoverage-compilation-dir=/" "-std=c++2b" "-fdeprecated-macro" "-fdebug-compilation-dir=/" "-ferror-limit" "19" "-fgnuc-version=4.2.1" "-fno-implicit-modules" "-fcxx-exceptions" "-fexceptions" "-faddrsig" "-D__GCC_HAVE_DWARF2_CFI_ASM=1" "-x" "c++" "err-c1b700.cpp"

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[0x59616e]

The first bad commit is babdef2, but the diagnostic message before this commit is weird, as it doesn't point out that the substitution failure is due to the unsatisfied constraint. So this may not be a regression. The issue has always been there, but had not been exhumed until now.

I will keep investigating.

[0x59616e]

By the way, should we add a C++20 tag ?

[EugeneZelenko]

Godbolt reproducer is compiled with C++23.

[AaronBallman]

Reduced slightly more:

inline constexpr auto neg = []<typename T>(T t) { return -t; };

inline constexpr auto add = []<typename T, typename ... Ts>(T t, Ts ... ts) {
        return (t + ... + ts);
};

template <typename F, typename ... Fs>
constexpr decltype(auto) compose(F f, Fs ... fs)
{
    if constexpr (sizeof...(fs) == 0)
    {
        return [f]<typename T>(T&& t) { f(t); };
    }
    else
    {
        return [=]<typename T>(T&& t) requires(requires{f(compose(fs...)(t));}) { return f(compose(fs...)(t)); };
    }
};

constexpr auto x = compose(add(3), neg)(-5);

https://godbolt.org/z/f6Garf4rE

[llvmbot]

@llvm/issue-subscribers-c-20

[0x59616e]

My conjecture is that Sema::SetupConstraintScope does not do its job comprehensively.

Also, I want to kindly ask where in the C++ standard has the specification of checking the contraint of a lambda defined within a template function.

Thanks !