[Clang][concepts] Clang may fail to match the appropriate partial specialization if contrained by a requires expression containing lambdas

[erinacio]

This issue is first found on clangd 17 shipped with CLion 2023.1.2 (22d9828), and reproduced on x86_64 clang trunk on compiler explorer (0a02f76) and clang-17 from apt.llvm.org (6875424).

This issue seems to only occur when:

1. There's a class template (template <class T> struct A).
2. There's a constrained partial specialization (template <C T> struct A<T>).
3. That is effectively contrained by a requires expression (template <class T> concept C = requires ...;).
4. That requires expression contains a lambda expression.
5. That contraint is not tested before.

Given a type T which satisfies that constraint (i.e. static_assert(C<T>)), clang trunk will fail to match the partial specialization template <C T> struct A<T> if the constraint is not explicitly tested before (including static_assert(C<T>)), and any test to the constraint will fail afterwards.

MRE#1: https://godbolt.org/z/rEfP7PcPc, lambda used as a simple requirement.
MRE#2: https://godbolt.org/z/GhqdnqMGb, lambda used inside parameter list with decltype.

A slightly longer but more meaningful example: https://godbolt.org/z/xfGjrq7db.

[erinacio]

Note that this may not be a Clang 17 regression. The same code would trigger an assertion failure with Clang 15 if enable all debug assertions. Taking MRE#1 as example:

Clang 15 assertion failure stacktrace

clang: /tmp/build/src/llvm-project-15.0.7.src/clang/lib/AST/ExprConstant.cpp:15088: bool clang::Expr::EvaluateAsConstantExpr(EvalResult&, const clang::ASTContext&, ConstantExprKind) const: Assertion `!isValueDependent() && "Expression evaluator can't be called on a dependent expression."' 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 -c test.cc
1.      test.cc:24:39: current parser token ')'
 #0 0x0000556d0680fc26 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/llvm15/bin/clang-15+0x3a8ec26)
 #1 0x0000556d0680d97f llvm::sys::RunSignalHandlers() (/opt/llvm15/bin/clang-15+0x3a8c97f)
 #2 0x0000556d06764409 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007f076f969f50 (/usr/lib/libc.so.6+0x38f50)
 #4 0x00007f076f9b88ec (/usr/lib/libc.so.6+0x878ec)
 #5 0x00007f076f969ea8 raise (/usr/lib/libc.so.6+0x38ea8)
 #6 0x00007f076f95353d abort (/usr/lib/libc.so.6+0x2253d)
 #7 0x00007f076f95345c (/usr/lib/libc.so.6+0x2245c)
 #8 0x00007f076f9629f6 (/usr/lib/libc.so.6+0x319f6)
 #9 0x0000556d0975a57c (/opt/llvm15/bin/clang-15+0x69d957c)
#10 0x0000556d08b1a80f bool calculateConstraintSatisfaction<calculateConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceLocation, clang::MultiLevelTemplateArgumentList&, clang::Expr const*, clang::ConstraintSatisfaction&)::'lambda'(clang::Expr const*)>(clang::Sema&, clang::Expr const*, clang::ConstraintSatisfaction&, calculateConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceLocation, clang::MultiLevelTemplateArgumentList&, clang::Expr const*, clang::ConstraintSatisfaction&)::'lambda'(clang::Expr const*)&&) SemaConcept.cpp:0:0
#11 0x0000556d08b1abbc CheckConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::Expr const*>, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceRange, clang::ConstraintSatisfaction&) SemaConcept.cpp:0:0
#12 0x0000556d08b1ad90 clang::Sema::CheckConstraintSatisfaction(clang::NamedDecl const*, llvm::ArrayRef<clang::Expr const*>, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceRange, clang::ConstraintSatisfaction&) (/opt/llvm15/bin/clang-15+0x5d99d90)
#13 0x0000556d0913a236 clang::Sema::CheckConceptTemplateId(clang::CXXScopeSpec const&, clang::SourceLocation, clang::DeclarationNameInfo const&, clang::NamedDecl*, clang::ConceptDecl*, clang::TemplateArgumentListInfo const*) (/opt/llvm15/bin/clang-15+0x63b9236)
#14 0x0000556d092577d8 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformConceptSpecializationExpr(clang::ConceptSpecializationExpr*) SemaTemplateInstantiate.cpp:0:0
#15 0x0000556d0924599c clang::Sema::SubstExpr(clang::Expr*, clang::MultiLevelTemplateArgumentList const&) (/opt/llvm15/bin/clang-15+0x64c499c)
#16 0x0000556d08b1950b calculateConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceLocation, clang::MultiLevelTemplateArgumentList&, clang::Expr const*, clang::ConstraintSatisfaction&)::'lambda'(clang::Expr const*)::operator()(clang::Expr const*) const SemaConcept.cpp:0:0
#17 0x0000556d08b1a783 bool calculateConstraintSatisfaction<calculateConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceLocation, clang::MultiLevelTemplateArgumentList&, clang::Expr const*, clang::ConstraintSatisfaction&)::'lambda'(clang::Expr const*)>(clang::Sema&, clang::Expr const*, clang::ConstraintSatisfaction&, calculateConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceLocation, clang::MultiLevelTemplateArgumentList&, clang::Expr const*, clang::ConstraintSatisfaction&)::'lambda'(clang::Expr const*)&&) SemaConcept.cpp:0:0
#18 0x0000556d08b1abbc CheckConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::Expr const*>, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceRange, clang::ConstraintSatisfaction&) SemaConcept.cpp:0:0
#19 0x0000556d08b1ad90 clang::Sema::CheckConstraintSatisfaction(clang::NamedDecl const*, llvm::ArrayRef<clang::Expr const*>, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceRange, clang::ConstraintSatisfaction&) (/opt/llvm15/bin/clang-15+0x5d99d90)
#20 0x0000556d091cec7e _Z31FinishTemplateArgumentDeductionIN5clang38ClassTemplatePartialSpecializationDeclEENSt9enable_ifIXsr23IsPartialSpecializationIT_E5valueENS0_4Sema23TemplateDeductionResultEE4typeERS6_PS4_bRKNS0_20TemplateArgumentListERN4llvm15SmallVectorImplINS0_23DeducedTemplateArgumentEEERNS0_4sema21TemplateDeductionInfoE SemaTemplateDeduction.cpp:0:0
#21 0x0000556d091cedf9 void llvm::function_ref<void ()>::callback_fn<clang::Sema::DeduceTemplateArguments(clang::ClassTemplatePartialSpecializationDecl*, clang::TemplateArgumentList const&, clang::sema::TemplateDeductionInfo&)::'lambda'()>(long) SemaTemplateDeduction.cpp:0:0
#22 0x0000556d089e94e4 clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) (/opt/llvm15/bin/clang-15+0x5c684e4)
#23 0x0000556d0920500f clang::Sema::DeduceTemplateArguments(clang::ClassTemplatePartialSpecializationDecl*, clang::TemplateArgumentList const&, clang::sema::TemplateDeductionInfo&) (/opt/llvm15/bin/clang-15+0x648400f)
#24 0x0000556d092325c9 getPatternForClassTemplateSpecialization(clang::Sema&, clang::SourceLocation, clang::ClassTemplateSpecializationDecl*, clang::TemplateSpecializationKind) (.constprop.0) SemaTemplateInstantiate.cpp:0:0
#25 0x0000556d0926e52b clang::Sema::InstantiateClassTemplateSpecialization(clang::SourceLocation, clang::ClassTemplateSpecializationDecl*, clang::TemplateSpecializationKind, bool) (/opt/llvm15/bin/clang-15+0x64ed52b)
#26 0x0000556d092ef504 void llvm::function_ref<void ()>::callback_fn<clang::Sema::RequireCompleteTypeImpl(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser*)::'lambda'()>(long) SemaType.cpp:0:0
#27 0x0000556d089e94e4 clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) (/opt/llvm15/bin/clang-15+0x5c684e4)
#28 0x0000556d093014ae clang::Sema::RequireCompleteTypeImpl(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser*) (/opt/llvm15/bin/clang-15+0x65804ae)
#29 0x0000556d093017a9 clang::Sema::RequireCompleteType(clang::SourceLocation, clang::QualType, clang::Sema::CompleteTypeKind, clang::Sema::TypeDiagnoser&) (/opt/llvm15/bin/clang-15+0x65807a9)
#30 0x0000556d08a2e6f7 clang::Sema::RequireCompleteDeclContext(clang::CXXScopeSpec&, clang::DeclContext*) (/opt/llvm15/bin/clang-15+0x5cad6f7)
#31 0x0000556d091267ed clang::Sema::CheckTypenameType(clang::ElaboratedTypeKeyword, clang::SourceLocation, clang::NestedNameSpecifierLoc, clang::IdentifierInfo const&, clang::SourceLocation, bool) (/opt/llvm15/bin/clang-15+0x63a57ed)
#32 0x0000556d0922f2c9 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::RebuildDependentNameType(clang::ElaboratedTypeKeyword, clang::SourceLocation, clang::NestedNameSpecifierLoc, clang::IdentifierInfo const*, clang::SourceLocation, bool) SemaTemplateInstantiate.cpp:0:0
#33 0x0000556d0925820a clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformDependentNameType(clang::TypeLocBuilder&, clang::DependentNameTypeLoc, bool) SemaTemplateInstantiate.cpp:0:0
#34 0x0000556d0924b413 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformType(clang::TypeSourceInfo*) SemaTemplateInstantiate.cpp:0:0
#35 0x0000556d0924e813 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformRequiresExpr(clang::RequiresExpr*) SemaTemplateInstantiate.cpp:0:0
#36 0x0000556d0925102a (anonymous namespace)::TemplateInstantiator::TransformRequiresExpr(clang::RequiresExpr*) SemaTemplateInstantiate.cpp:0:0
#37 0x0000556d0924599c clang::Sema::SubstExpr(clang::Expr*, clang::MultiLevelTemplateArgumentList const&) (/opt/llvm15/bin/clang-15+0x64c499c)
#38 0x0000556d08b1950b calculateConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceLocation, clang::MultiLevelTemplateArgumentList&, clang::Expr const*, clang::ConstraintSatisfaction&)::'lambda'(clang::Expr const*)::operator()(clang::Expr const*) const SemaConcept.cpp:0:0
#39 0x0000556d08b1a783 bool calculateConstraintSatisfaction<calculateConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceLocation, clang::MultiLevelTemplateArgumentList&, clang::Expr const*, clang::ConstraintSatisfaction&)::'lambda'(clang::Expr const*)>(clang::Sema&, clang::Expr const*, clang::ConstraintSatisfaction&, calculateConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceLocation, clang::MultiLevelTemplateArgumentList&, clang::Expr const*, clang::ConstraintSatisfaction&)::'lambda'(clang::Expr const*)&&) SemaConcept.cpp:0:0
#40 0x0000556d08b1abbc CheckConstraintSatisfaction(clang::Sema&, clang::NamedDecl const*, llvm::ArrayRef<clang::Expr const*>, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceRange, clang::ConstraintSatisfaction&) SemaConcept.cpp:0:0
#41 0x0000556d08b1ad90 clang::Sema::CheckConstraintSatisfaction(clang::NamedDecl const*, llvm::ArrayRef<clang::Expr const*>, llvm::ArrayRef<clang::TemplateArgument>, clang::SourceRange, clang::ConstraintSatisfaction&) (/opt/llvm15/bin/clang-15+0x5d99d90)
#42 0x0000556d0913a236 clang::Sema::CheckConceptTemplateId(clang::CXXScopeSpec const&, clang::SourceLocation, clang::DeclarationNameInfo const&, clang::NamedDecl*, clang::ConceptDecl*, clang::TemplateArgumentListInfo const*) (/opt/llvm15/bin/clang-15+0x63b9236)
#43 0x0000556d0913c246 clang::Sema::BuildTemplateIdExpr(clang::CXXScopeSpec const&, clang::SourceLocation, clang::LookupResult&, bool, clang::TemplateArgumentListInfo const*) (/opt/llvm15/bin/clang-15+0x63bb246)
#44 0x0000556d08d65169 clang::Sema::ActOnIdExpression(clang::Scope*, clang::CXXScopeSpec&, clang::SourceLocation, clang::UnqualifiedId&, bool, bool, clang::CorrectionCandidateCallback*, bool, clang::Token*) (/opt/llvm15/bin/clang-15+0x5fe4169)
#45 0x0000556d0894085c clang::Parser::tryParseCXXIdExpression(clang::CXXScopeSpec&, bool, clang::Token&) (/opt/llvm15/bin/clang-15+0x5bbf85c)
#46 0x0000556d08940b4a clang::Parser::ParseCXXIdExpression(bool) (/opt/llvm15/bin/clang-15+0x5bbfb4a)
#47 0x0000556d08926275 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/llvm15/bin/clang-15+0x5ba5275)
#48 0x0000556d08925bce clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/llvm15/bin/clang-15+0x5ba4bce)
#49 0x0000556d0893269b clang::Parser::ParseConstantExpressionInExprEvalContext(clang::Parser::TypeCastState) (/opt/llvm15/bin/clang-15+0x5bb169b)
#50 0x0000556d0890ef3f clang::Parser::ParseStaticAssertDeclaration(clang::SourceLocation&) (/opt/llvm15/bin/clang-15+0x5b8df3f)
#51 0x0000556d088ffff7 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/llvm15/bin/clang-15+0x5b7eff7)
#52 0x0000556d088d6d9a clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/llvm15/bin/clang-15+0x5b55d9a)
#53 0x0000556d088d815d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/llvm15/bin/clang-15+0x5b5715d)
#54 0x0000556d088c9f7b clang::ParseAST(clang::Sema&, bool, bool) (/opt/llvm15/bin/clang-15+0x5b48f7b)
#55 0x0000556d07297079 clang::FrontendAction::Execute() (/opt/llvm15/bin/clang-15+0x4516079)
#56 0x0000556d07234ec6 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/llvm15/bin/clang-15+0x44b3ec6)
#57 0x0000556d0734fe84 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/llvm15/bin/clang-15+0x45cee84)
#58 0x0000556d040fc71c cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/llvm15/bin/clang-15+0x137b71c)
#59 0x0000556d040f5ba2 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&) driver.cpp:0:0
#60 0x0000556d070bf409 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#61 0x0000556d0676458e llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/llvm15/bin/clang-15+0x39e358e)
#62 0x0000556d070bfe70 clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (.part.0) Job.cpp:0:0
#63 0x0000556d0708c714 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/llvm15/bin/clang-15+0x430b714)
#64 0x0000556d0708cf26 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/llvm15/bin/clang-15+0x430bf26)
#65 0x0000556d070976ed clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/llvm15/bin/clang-15+0x43166ed)
#66 0x0000556d040fa9d2 clang_main(int, char**) (/opt/llvm15/bin/clang-15+0x13799d2)
#67 0x00007f076f954790 (/usr/lib/libc.so.6+0x23790)
#68 0x00007f076f95484a __libc_start_main (/usr/lib/libc.so.6+0x2384a)
#69 0x0000556d040f4ec5 _start (/opt/llvm15/bin/clang-15+0x1373ec5)
clang-15: error: clang frontend command failed with exit code 134 (use -v to see invocation)
clang version 15.0.7
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/llvm15/bin

Clang 15 associated run script

# Crash reproducer for clang version 15.0.7
# Driver args: "-std=c++20" "-c" "test.cc"
# Original command:  "/opt/llvm15/bin/clang-15" "-cc1" "-triple" "x86_64-unknown-linux-gnu" "-emit-obj" "-mrelax-all" "--mrelax-relocations" "-disable-free" "-clear-ast-before-backend" "-main-file-name" "test.cc" "-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=/tmp" "-resource-dir" "/opt/llvm15/lib/clang/15.0.7" "-internal-isystem" "/usr/lib64/gcc/x86_64-pc-linux-gnu/12.2.1/../../../../include/c++/12.2.1" "-internal-isystem" "/usr/lib64/gcc/x86_64-pc-linux-gnu/12.2.1/../../../../include/c++/12.2.1/x86_64-pc-linux-gnu" "-internal-isystem" "/usr/lib64/gcc/x86_64-pc-linux-gnu/12.2.1/../../../../include/c++/12.2.1/backward" "-internal-isystem" "/opt/llvm15/lib/clang/15.0.7/include" "-internal-isystem" "/usr/local/include" "-internal-isystem" "/usr/lib64/gcc/x86_64-pc-linux-gnu/12.2.1/../../../../x86_64-pc-linux-gnu/include" "-internal-externc-isystem" "/include" "-internal-externc-isystem" "/usr/include" "-std=c++20" "-fdeprecated-macro" "-fdebug-compilation-dir=/tmp" "-ferror-limit" "19" "-fgnuc-version=4.2.1" "-fno-implicit-modules" "-fcxx-exceptions" "-fexceptions" "-fcolor-diagnostics" "-faddrsig" "-D__GCC_HAVE_DWARF2_CFI_ASM=1" "-o" "test.o" "-x" "c++" "test.cc"
 "/opt/llvm15/bin/clang-15" "-cc1" "-triple" "x86_64-unknown-linux-gnu" "-emit-obj" "-mrelax-all" "--mrelax-relocations" "-disable-free" "-clear-ast-before-backend" "-main-file-name" "test.cc" "-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=/tmp" "-std=c++20" "-fdeprecated-macro" "-fdebug-compilation-dir=/tmp" "-ferror-limit" "19" "-fgnuc-version=4.2.1" "-fno-implicit-modules" "-fcxx-exceptions" "-fexceptions" "-fcolor-diagnostics" "-faddrsig" "-D__GCC_HAVE_DWARF2_CFI_ASM=1" "-x" "c++" "test-ecfebd.cpp"

[llvmbot]

@llvm/issue-subscribers-c-20

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[shafik]

I believe this is: #58534

CC @erichkeane @usx95

[zyn0217]

Fixed by #83997.
All the examples are now successfully compiled and don't cause crashes on the assertion trunk build. Closing.

https://godbolt.org/z/vezb5Kdxo