Clang frontend C++ crash on invalid code in template-parameter-list

[brutalsavage]

To quickly reproduce: https://gcc.godbolt.org/z/1jqzhEdTE

template <class... T // invalid instantiation (note adding an "," removes the crash)
          T... Args> 
struct tuple;

template<auto... Vs,
    T... Vs3>
auto foo() { 
    tuple a;
    return a;
}

Compiling the above invalid code crashes clang clang++ -x c++, crashes locally using clang-17.0 (a10019a), also on trunk (see godbolt link)

Note: changing the first template to

template <class... T, // add comma 
          T... Args> 
struct tuple;

removes the crash

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[brutalsavage]

assertion-trunk godbolt: https://gcc.godbolt.org/z/E8Yz7fEYq

Assertion:

clang++: /root/llvm-project/clang/lib/AST/RecordLayoutBuilder.cpp:3295: 
const clang::ASTRecordLayout& clang::ASTContext::getASTRecordLayout(const clang::RecordDecl*) const: 
Assertion `D && "Cannot get layout of forward declarations!"' failed.

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 -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics <source>
1.	<source>:9:13: current parser token ';'
2.	<source>:7:12: parsing function body 'foo'
3.	<source>:7:12: in compound statement ('{}')
 #0 0x000055e6a899824f llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3c2824f)
 #1 0x000055e6a8995fbc llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3c25fbc)
 #2 0x000055e6a88df3b8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007f05b0b54420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00007f05b062100b raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b)
 #5 0x00007f05b0600859 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22859)
 #6 0x00007f05b0600729 (/lib/x86_64-linux-gnu/libc.so.6+0x22729)
 #7 0x00007f05b0611fd6 (/lib/x86_64-linux-gnu/libc.so.6+0x33fd6)
 #8 0x000055e6ac44cb98 clang::ASTContext::getASTRecordLayout(clang::RecordDecl const*) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x76dcb98)
 #9 0x000055e6abff4c21 clang::ASTContext::getTypeInfoImpl(clang::Type const*) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7284c21)
#10 0x000055e6abff3d2f clang::ASTContext::getTypeInfo(clang::Type const*) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7283d2f)
#11 0x000055e6abff3f9f clang::ASTContext::getTypeInfoImpl(clang::Type const*) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7283f9f)
#12 0x000055e6abff3d2f clang::ASTContext::getTypeInfo(clang::Type const*) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7283d2f)
#13 0x000055e6abff3f9f clang::ASTContext::getTypeInfoImpl(clang::Type const*) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7283f9f)
#14 0x000055e6abff3d2f clang::ASTContext::getTypeInfo(clang::Type const*) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7283d2f)
#15 0x000055e6ac0061db clang::ASTContext::getTypeAlignInChars(clang::QualType) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x72961db)
#16 0x000055e6aba37b4d clang::Sema::getNamedReturnInfo(clang::VarDecl const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6cc7b4d)
#17 0x000055e6aba37ca8 clang::Sema::getNamedReturnInfo(clang::Expr*&, clang::Sema::SimplerImplicitMoveMode) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6cc7ca8)
#18 0x000055e6aba6b8d4 clang::Sema::BuildReturnStmt(clang::SourceLocation, clang::Expr*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6cfb8d4)
#19 0x000055e6aba6dbff clang::Sema::ActOnReturnStmt(clang::SourceLocation, clang::Expr*, clang::Scope*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6cfdbff)
#20 0x000055e6ab1ca08f clang::Parser::ParseReturnStatement() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x645a08f)
#21 0x000055e6ab1cd280 clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x645d280)
#22 0x000055e6ab1ce9b1 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x645e9b1)
#23 0x000055e6ab1cf9a9 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x645f9a9)
#24 0x000055e6ab1d135a clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x646135a)
#25 0x000055e6ab0fbe81 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x638be81)
#26 0x000055e6ab1eb08a clang::Parser::ParseSingleDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo const&, clang::ParsingDeclRAIIObject&, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x647b08a)
#27 0x000055e6ab1f0cb6 clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#28 0x000055e6ab1f0f33 clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6480f33)
#29 0x000055e6ab12b19e clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x63bb19e)
#30 0x000055e6ab0f63b4 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x63863b4)
#31 0x000055e6ab0f72f6 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x63872f6)
#32 0x000055e6ab0eb0ba clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x637b0ba)
#33 0x000055e6a9beb598 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4e7b598)
#34 0x000055e6a943bc79 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x46cbc79)
#35 0x000055e6a93c0316 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4650316)
#36 0x000055e6a951e0b6 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47ae0b6)
#37 0x000055e6a5e4116d cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x10d116d)
#38 0x000055e6a5e3ce6a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#39 0x000055e6a9228c1d 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
#40 0x000055e6a88df8c0 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b6f8c0)
#41 0x000055e6a922923f 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
#42 0x000055e6a91f0a1c clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4480a1c)
#43 0x000055e6a91f14ad 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+++0x44814ad)
#44 0x000055e6a91f958d clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x448958d)
#45 0x000055e6a5e3f3ca clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x10cf3ca)
#46 0x000055e6a5d462b5 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xfd62b5)
#47 0x00007f05b0602083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#48 0x000055e6a5e37c4e _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x10c7c4e)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
ASM generation compiler returned: 134

[shafik]

Confirmed

[shafik]

The case in: #79745 might be slightly simpler

[AMS21]

Looked a bit around and adding this patch prevents this crash and passes check-clang. Although I'm not sure if that would be the correct way to fix this since I'm not very familiar with the clang code base.

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index f7c9e4521b5f..d335df53679d 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -2284,6 +2284,9 @@ TypeInfo ASTContext::getTypeInfoImpl(const Type *T) const {
 
     const auto *RT = cast<RecordType>(TT);
     const RecordDecl *RD = RT->getDecl();
+    if (!RD->getDefinition())
+      break;
+
     const ASTRecordLayout &Layout = getASTRecordLayout(RD);
     Width = toBits(Layout.getSize());
     Align = toBits(Layout.getAlignment());

[shafik]

@AMS21 we assume we have a complete type at that point, so that is not a proper fix.

I had a fix earlier and just posted it: #79788