[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 llvm/llvm-project#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).

Author: Nerixyz

lldb/source/Plugins/Language/CPlusPlus/GenericOptional.cpp

@@ -74,9 +74,10 @@ lldb::ChildCacheState GenericOptionalFrontend::Update() {
 
   if (m_stdlib == StdLib::LibCxx)
     engaged_sp = m_backend.GetChildMemberWithName("__engaged_");
-  else if (m_stdlib == StdLib::LibStdcpp)
-    engaged_sp = m_backend.GetChildMemberWithName("_M_payload")
-                     ->GetChildMemberWithName("_M_engaged");
+  else if (m_stdlib == StdLib::LibStdcpp) {
+    if (ValueObjectSP payload = m_backend.GetChildMemberWithName("_M_payload"))
+      engaged_sp = payload->GetChildMemberWithName("_M_engaged");
+  }
 
   if (!engaged_sp)
     return lldb::ChildCacheState::eRefetch;

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) {

lldb/test/Shell/Process/Windows/msstl_smoke.cpp

@@ -0,0 +1,56 @@
+// This smoke test ensures that LLDB doesn't crash when formatting types from MSVC's STL.
+// FIXME: LLDB currently has no built-in formatters for MSVC's STL (#24834)
+
+// REQUIRES: target-windows
+// RUN: %build --compiler=clang-cl -o %t.exe --std c++20 -- %s
+// RUN: env LLDB_USE_NATIVE_PDB_READER=1 %lldb -f %t.exe -o "b main" -o "run" -o "fr v" -o c | FileCheck %s
+
+#include <bitset>
+#include <coroutine>
+#include <deque>
+#include <forward_list>
+#include <list>
+#include <map>
+#include <memory>
+#include <optional>
+#include <set>
+#include <string>
+#include <tuple>
+#include <unordered_map>
+#include <unordered_set>
+#include <variant>
+#include <vector>
+
+int main() {
+  std::shared_ptr<int> foo;
+  std::weak_ptr<int> weak = foo;
+  std::unique_ptr<int> unique(new int(42));
+  std::optional<int> opt;
+  std::string str = "str";
+  std::string longStr = "string that is long enough such that no SSO can happen";
+  std::wstring wStr = L"wstr";
+  std::wstring longWStr = L"string that is long enough such that no SSO can happen";
+  std::tuple<int, bool, float> tuple{1, false, 4.2};
+  std::coroutine_handle<> coroHandle;
+  std::bitset<16> bitset(123);
+
+  std::map<int, int> map{{1, 2}, {2, 4}, {3, 6}, {4, 8}, {5, 10}};
+  auto mapIt = map.find(3);
+  auto mapItEnd = map.find(9);
+  std::set<int> set{1, 2, 3};
+  std::multimap<int, int> mMap{{1, 2}, {1, 1}, {2, 4}};
+  std::multiset<int> mSet{1, 2, 3};
+
+  std::variant<int, float, std::string, std::monostate> variant;
+  std::list<int> list{1, 2, 3};
+  std::forward_list<int> fwList{1, 2, 3};
+
+  std::unordered_map<int, int> uMap{{1, 2}, {2, 4}, {3, 6}};
+  std::unordered_set<int> uSet{1, 2, 4};
+  std::unordered_multimap<int, int> uMMap{{1, 2}, {1, 1}, {2, 4}};
+  std::unordered_multiset<int> uMSet{1, 1, 2};
+  std::deque<int> deque{1, 2, 3};
+  std::vector<int> vec{1, 2, 3};
+}
+
+// CHECK: Process {{.*}} exited with status = 0 (0x00000000)