A/F "friend function specialization without template args" on illegal C++

[jmorse]

Hi,

Behold this bogus template specialisation:

template <a> class b {
     template <> friend int c< b >() {}
};

Clang / GCC / MSVC all reject this with errors and diagnostics. With assertions enabled however, clang fires the following assertion failure rather than completing:

clang: /path/clang/lib/Sema/SemaDecl.cpp:10454: clang::NamedDecl *clang::Sema::ActOnFunctionDeclarator(clang::Scope *, 
    clang::Declarator &, clang::DeclContext *, clang::TypeSourceInfo *, clang::LookupResult &, clang::MultiTemplateParamsArg,
    bool &): Assertion `HasExplicitTemplateArgs && "friend function specialization without template args"' failed.

when building with the very recent 22044f0. Godbolt link of the same: https://godbolt.org/z/7jabnhEY9 . Fiddling with Godbolt, it appears the assertion failure appeared in the 14.0.0 release, and isn't present in the 13.0.0 release.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[shafik]

Confirmed.

Assertion:

clang++: /root/llvm-project/clang/lib/Sema/SemaDecl.cpp:10453:
clang::NamedDecl* clang::Sema::ActOnFunctionDeclarator(clang::Scope*, clang::Declarator&, clang::DeclContext*, clang::TypeSourceInfo*, clang::LookupResult&, clang::MultiTemplateParamsArg, bool&):
Assertion `HasExplicitTemplateArgs && "friend function specialization without template args"' 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>:2:42: current parser token '{'
2.	<source>:1:14: parsing struct/union/class body 'b'
 #0 0x00000000036b1be8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x36b1be8)
 #1 0x00000000036af8ac llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x36af8ac)
 #2 0x00000000035f91c8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007fba460a7420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00007fba45b6a00b raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b)
 #5 0x00007fba45b49859 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22859)
 #6 0x00007fba45b49729 (/lib/x86_64-linux-gnu/libc.so.6+0x22729)
 #7 0x00007fba45b5afd6 (/lib/x86_64-linux-gnu/libc.so.6+0x33fd6)
 #8 0x00000000061848b8 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+++0x61848b8)
 #9 0x000000000621e392 clang::Sema::ActOnFriendFunctionDecl(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef<clang::TemplateParameterList*>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x621e392)
#10 0x0000000005e2450e clang::Parser::ParseCXXInlineMethodDef(clang::AccessSpecifier, clang::ParsedAttributesView const&, clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::VirtSpecifiers const&, clang::SourceLocation) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e2450e)
#11 0x0000000005e65d30 clang::Parser::ParseCXXClassMemberDeclaration(clang::AccessSpecifier, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo const&, clang::ParsingDeclRAIIObject*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e65d30)
#12 0x0000000005f0837d 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+++0x5f0837d)
#13 0x0000000005f0de38 clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#14 0x0000000005e660dc clang::Parser::ParseCXXClassMemberDeclaration(clang::AccessSpecifier, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo const&, clang::ParsingDeclRAIIObject*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e660dc)
#15 0x0000000005e68225 clang::Parser::ParseCXXClassMemberDeclarationWithPragmas(clang::AccessSpecifier&, clang::ParsedAttributes&, clang::TypeSpecifierType, clang::Decl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e68225)
#16 0x0000000005e69b2a clang::Parser::ParseCXXMemberSpecification(clang::SourceLocation, clang::SourceLocation, clang::ParsedAttributes&, unsigned int, clang::Decl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e69b2a)
#17 0x0000000005e6bc00 clang::Parser::ParseClassSpecifier(clang::tok::TokenKind, clang::SourceLocation, clang::DeclSpec&, clang::Parser::ParsedTemplateInfo const&, clang::AccessSpecifier, bool, clang::Parser::DeclSpecContext, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e6bc00)
#18 0x0000000005e45380 clang::Parser::ParseDeclarationSpecifiers(clang::DeclSpec&, clang::Parser::ParsedTemplateInfo const&, clang::AccessSpecifier, clang::Parser::DeclSpecContext, clang::Parser::LateParsedAttrList*, clang::ImplicitTypenameContext) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e45380)
#19 0x0000000005f07ab2 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+++0x5f07ab2)
#20 0x0000000005f0de38 clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#21 0x0000000005f0e0f3 clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f0e0f3)
#22 0x0000000005e4bf0b clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e4bf0b)
#23 0x0000000005e16d34 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e16d34)
#24 0x0000000005e17c1d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e17c1d)
#25 0x0000000005e18050 clang::Parser::ParseFirstTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e18050)
#26 0x0000000005e0bf42 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e0bf42)
#27 0x0000000004916af8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4916af8)
#28 0x0000000004178979 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4178979)
#29 0x00000000040fb40e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x40fb40e)
#30 0x0000000004258fc6 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4258fc6)
#31 0x0000000000bd2107 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbd2107)
#32 0x0000000000bca7ba ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#33 0x0000000003f5d009 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
#34 0x00000000035f9674 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x35f9674)
#35 0x0000000003f5d5ff 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
#36 0x0000000003f25ee5 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f25ee5)
#37 0x0000000003f2694d 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+++0x3f2694d)
#38 0x0000000003f2e815 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f2e815)
#39 0x0000000000bd039c clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbd039c)
#40 0x0000000000accef1 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xaccef1)
#41 0x00007fba45b4b083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#42 0x0000000000bca29e _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbca29e)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134