[lldb-dap] Fix segfault in JSONUtils.cpp when GetUUIDString() returns nullptr (#169844)

When creating a stack frame in JSONUtils.cpp CreateStackFrame() the code
constructs a std::string from module.GetUUIDString(), which can return
nullptr in some cases (as documented in the implementation of
SBModule::GetUUIDString()). This causes a segmentation fault when passed
to the std::string constructor.

This fix adds a null check before constructing the UUID string, falling
back to an empty string if nullptr is returned. The existing empty check
ensures the moduleId field is omitted from the JSON when no UUID exists.

rdar://163811812

---------

Co-authored-by: Ebuka Ezike <yerimyah1@gmail.com>

Author: aahrun

lldb/tools/lldb-dap/Handler/CompileUnitsRequestHandler.cpp

@@ -60,12 +60,12 @@ void CompileUnitsRequestHandler::operator()(
   llvm::json::Object body;
   llvm::json::Array units;
   const auto *arguments = request.getObject("arguments");
-  const std::string module_id =
-      GetString(arguments, "moduleId").value_or("").str();
+  const llvm::StringRef module_id =
+      GetString(arguments, "moduleId").value_or("");
   int num_modules = dap.target.GetNumModules();
   for (int i = 0; i < num_modules; i++) {
     auto curr_module = dap.target.GetModuleAtIndex(i);
-    if (module_id == curr_module.GetUUIDString()) {
+    if (module_id == llvm::StringRef(curr_module.GetUUIDString())) {
       int num_units = curr_module.GetNumCompileUnits();
       for (int j = 0; j < num_units; j++) {
         auto curr_unit = curr_module.GetCompileUnitAtIndex(j);

lldb/tools/lldb-dap/JSONUtils.cpp

@@ -554,9 +554,8 @@ llvm::json::Value CreateStackFrame(DAP &dap, lldb::SBFrame &frame,
 
   lldb::SBModule module = frame.GetModule();
   if (module.IsValid()) {
-    std::string uuid = module.GetUUIDString();
-    if (!uuid.empty())
-      object.try_emplace("moduleId", uuid);
+    if (const llvm::StringRef uuid = module.GetUUIDString(); !uuid.empty())
+      object.try_emplace("moduleId", uuid.str());
   }
 
   return llvm::json::Value(std::move(object));