Segfault when parsing template specializations involving nested type access

[anarthal]

MrDocs version: develop (2024-10-24).

The following:

#include <type_traits>

template <class T, class = void>
struct S
{
    void store(const void*) {}
};

template <class T>
struct S<T, std::void_t<typename T::a::b>>
{
    void store(const void*) {}
};

int main() {}

Segfaults with the default config options:

-- The C compiler identification is GNU 11.4.0
-- The CXX compiler identification is GNU 11.4.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/ruben/workspace/mrdocs-repro/doc/reference-output/.temp/build

mrdocs: /__w/mrdocs/third-party/llvm-project/install/include/clang/AST/Type.h:957: const clang::ExtQualsTypeCommonBase* clang::QualType::getCommonPtr() const: Assertion `!isNull() && "Cannot retrieve a NULL type pointer"' failed.
PLEASE submit a bug report to https://github.com/cppalliance/mrdocs/issues/ and include the crash backtrace.
Stack dump:
0.      <eof> parser at end of file
 #0 0x0000000003245bb0 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x3245bb0)
 #1 0x0000000003242b3b SignalHandler(int) Signals.cpp:0:0
 #2 0x0000000003384670 __restore_rt libc_sigaction.o:0:0
 #3 0x00000000033a821c __pthread_kill (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x33a821c)
 #4 0x00000000033845ee raise (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x33845ee)
 #5 0x000000000043aed9 abort (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x43aed9)
 #6 0x000000000043adf5 _nl_load_domain.cold loadmsgcat.o:0:0
 #7 0x000000000337cac7 (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x337cac7)
 #8 0x000000000055d24d clang::mrdocs::(anonymous namespace)::ASTVisitor::getSFINAETemplate(clang::QualType, bool) (.isra.0) ASTVisitor.cpp:0:0
 #9 0x000000000056251d clang::mrdocs::(anonymous namespace)::ASTVisitor::isSFINAEType(clang::QualType) ASTVisitor.cpp:0:0
#10 0x0000000000565eca clang::mrdocs::(anonymous namespace)::TerminalTypeVisitor<clang::mrdocs::(anonymous namespace)::TypeInfoBuilder>::Visit(clang::QualType) (.isra.0) ASTVisitor.cpp:0:0
#11 0x00000000005667e1 clang::mrdocs::(anonymous namespace)::ASTVisitor::buildTypeInfo(clang::QualType, clang::mrdocs::(anonymous namespace)::ASTVisitor::ExtractMode) ASTVisitor.cpp:0:0
#12 0x000000000056783f clang::mrdocs::(anonymous namespace)::ASTVisitor::buildTemplateArg(clang::TemplateArgument const&) ASTVisitor.cpp:0:0
#13 0x0000000000567cf0 void clang::mrdocs::(anonymous namespace)::ASTVisitor::buildTemplateArgs<std::ranges::transform_view<std::ranges::owning_view<llvm::ArrayRef<clang::TemplateArgumentLoc>>, clang::mrdocs::(anonymous namespace)::ASTVisitor::buildTemplateArgs(std::vector<std::unique_ptr<clang::mrdocs::TArg, std::default_delete<clang::mrdocs::TArg>>, std::allocator<std::unique_ptr<clang::mrdocs::TArg, std::default_delete<clang::mrdocs::TArg>>>>&, clang::ASTTemplateArgumentListInfo const*)::'lambda'(auto&)>>(std::vector<std::unique_ptr<clang::mrdocs::TArg, std::default_delete<clang::mrdocs::TArg>>, std::allocator<std::unique_ptr<clang::mrdocs::TArg, std::default_delete<clang::mrdocs::TArg>>>>&, auto&&) ASTVisitor.cpp:0:0
#14 0x0000000000577a01 void clang::mrdocs::(anonymous namespace)::ASTVisitor::traverse<clang::ClassTemplatePartialSpecializationDecl>(clang::ClassTemplatePartialSpecializationDecl*, clang::ClassTemplateDecl*) ASTVisitor.cpp:0:0
#15 0x0000000000576ffa clang::mrdocs::(anonymous namespace)::ASTVisitor::traverseContext(clang::DeclContext*) ASTVisitor.cpp:0:0
#16 0x0000000000576969 void clang::mrdocs::(anonymous namespace)::ASTVisitor::traverseDecl<>(clang::Decl*) ASTVisitor.cpp:0:0
#17 0x0000000000579998 clang::mrdocs::(anonymous namespace)::ASTVisitorConsumer::HandleTranslationUnit(clang::ASTContext&) ASTVisitor.cpp:0:0
#18 0x00000000008692cc clang::ParseAST(clang::Sema&, bool, bool) (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x8692cc)
#19 0x00000000007a6799 clang::FrontendAction::Execute() (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x7a6799)
#20 0x00000000007264be clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x7264be)
#21 0x00000000006e00d2 clang::tooling::FrontendActionFactory::runInvocation(std::shared_ptr<clang::CompilerInvocation>, clang::FileManager*, std::shared_ptr<clang::PCHContainerOperations>, clang::DiagnosticConsumer*) (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x6e00d2)
#22 0x00000000006d7111 clang::tooling::ToolInvocation::runInvocation(char const*, clang::driver::Compilation*, std::shared_ptr<clang::CompilerInvocation>, std::shared_ptr<clang::PCHContainerOperations>) (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x6d7111)
#23 0x00000000006db0b8 clang::tooling::ToolInvocation::run() (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x6db0b8)
#24 0x00000000006dd414 clang::tooling::ClangTool::run(clang::tooling::ToolAction*) (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x6dd414)
#25 0x00000000004ce0b6 clang::mrdocs::CorpusImpl::build(std::shared_ptr<clang::mrdocs::ConfigImpl const> const&, clang::tooling::CompilationDatabase const&)::'lambda'(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>)::operator()(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>) const CorpusImpl.cpp:0:0
#26 0x00000000004cfd0e clang::mrdocs::CorpusImpl::build(std::shared_ptr<clang::mrdocs::ConfigImpl const> const&, clang::tooling::CompilationDatabase const&) (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x4cfd0e)
#27 0x000000000048fafb clang::mrdocs::DoGenerateAction(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>> const&, clang::mrdocs::ReferenceDirectories const&, char const**) (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x48fafb)
#28 0x00000000004981ef clang::mrdocs::mrdocs_main(int, char const**) (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x4981ef)
#29 0x000000000043b7cd main (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x43b7cd)
#30 0x000000000336b678 __libc_start_call_main libc-start.o:0:0
#31 0x000000000336d840 __libc_start_main (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x336d840)
#32 0x0000000000487ca5 _start (/opt/mrdocs-develop-2024-10-24/bin/mrdocs+0x487ca5)
Aborted (core dumped)

Compilation database:

[
{
  "directory": "[redacted]/mrdocs-repro/doc/build",
  "command": "/usr/bin/c++    -o CMakeFiles/main.dir/main.cpp.o -c [redacted]/mrdocs-repro/main.cpp",
  "file": "[redacted]/mrdocs-repro/main.cpp"
}
]

[anarthal]

This issue blocks the generation of Boost.MySQL docs, since connection.hpp uses a similar pattern.