[LLDB] Avoid crashes when inspecting MSVC STL types (#140761)

When inspecting/printing types from MSVC's STL, LLDB would crash because
it assumes these types were from libstdc++. Specifically,
`std::shared_ptr` and `std::optional` would crash because of a null
pointer dereference. I added a minimal test that tests the types with
C++ helpers for libstdc++ (only tests for crashes).

- Fixes #115216 
- Fixes #120310 

This still has one unresolved discussion: What about MS STL types? This
is https://github.com/llvm/llvm-project/issues/24834, but there was a
bit of discussion in #120310 as well. The main issue is that MSVC's STL
uses the same type names as libstdc++ (i.e. neither uses an inline
namespace like libc++ for some types).

1 files changed, 3 insertions, 0 deletions

diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
index 02113ba..08cfcd4 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
@@ -379,6 +379,9 @@ LibStdcppSharedPtrSyntheticFrontEnd::CalculateNumChildren() {
 
 lldb::ValueObjectSP
 LibStdcppSharedPtrSyntheticFrontEnd::GetChildAtIndex(uint32_t idx) {
+  if (!m_ptr_obj)
+    return nullptr;
+
   if (idx == 0)
     return m_ptr_obj->GetSP();
   if (idx == 1) {