Fix tuple getter in std unique pointer pretty-printer

Summary: Check case when _M_t child member is not present.

Reviewers: labath, tberghammer

Reviewed By: labath, tberghammer

Differential Revision: https://reviews.llvm.org/D47932
Patch by Aleksandr Urakov <aleksandr.urakov@jetbrains.com>.

llvm-svn: 334411

lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libstdcpp/unique_ptr/invalid/TestDataFormatterInvalidStdUniquePtr.py

@@ -0,0 +1,5 @@
+import lldbsuite.test.lldbinline as lldbinline
+from lldbsuite.test.decorators import *
+
+lldbinline.MakeInlineTest(__file__, globals(), [no_debug_info_test])
+

lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libstdcpp/unique_ptr/invalid/main.cpp

@@ -0,0 +1,11 @@
+// Test that we don't crash when trying to pretty-print structures that don't
+// have the layout our data formatters expect.
+namespace std {
+template<typename T, typename Deleter = void>
+class unique_ptr {};
+}
+
+int main() {
+  std::unique_ptr<int> U;
+  return 0; //% self.expect("frame variable U", substrs=["unique_ptr", "{}"])
+}

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

@@ -67,6 +67,8 @@ ValueObjectSP LibStdcppUniquePtrSyntheticFrontEnd::GetTuple() {
 
   ValueObjectSP obj_child_sp =
       valobj_sp->GetChildMemberWithName(ConstString("_M_t"), true);
+  if (!obj_child_sp)
+      return nullptr;
 
   ValueObjectSP obj_subchild_sp =
       obj_child_sp->GetChildMemberWithName(ConstString("_M_t"), true);