[lldb][Formatters] Make libc++ and libstdc++ std::shared_ptr formatters consistent with each other (#147165)

This patch adjusts the libcxx and libstdcxx std::shared_ptr formatters
to look the same.

Changes to libcxx:
* Now creates a synthetic child called `pointer` (like we already do for
`std::unique_ptr`)

Changes to libstdcxx:
* When asked to dereference the pointer, cast the type of the result
ValueObject to the element type (which we get from the template argument
to std::shared_ptr).
Before:
```
(std::__shared_ptr<int, __gnu_cxx::_S_atomic>::element_type) *foo = 123
```
After:
```
(int) *foo = 123
```

Tested in #147141

Author: Michael137

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

@@ -238,7 +238,8 @@ lldb_private::formatters::LibCxxVectorIteratorSyntheticFrontEndCreator(
 
 lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::
     LibcxxSharedPtrSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp)
-    : SyntheticChildrenFrontEnd(*valobj_sp), m_cntrl(nullptr) {
+    : SyntheticChildrenFrontEnd(*valobj_sp), m_cntrl(nullptr),
+      m_ptr_obj(nullptr) {
   if (valobj_sp)
     Update();
 }
@@ -251,28 +252,25 @@ llvm::Expected<uint32_t> lldb_private::formatters::
 lldb::ValueObjectSP
 lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::GetChildAtIndex(
     uint32_t idx) {
-  if (!m_cntrl)
+  if (!m_cntrl || !m_ptr_obj)
     return lldb::ValueObjectSP();
 
   ValueObjectSP valobj_sp = m_backend.GetSP();
   if (!valobj_sp)
     return lldb::ValueObjectSP();
 
   if (idx == 0)
-    return valobj_sp->GetChildMemberWithName("__ptr_");
+    return m_ptr_obj->GetSP();
 
   if (idx == 1) {
-    if (auto ptr_sp = valobj_sp->GetChildMemberWithName("__ptr_")) {
-      Status status;
-      auto value_type_sp =
-            valobj_sp->GetCompilerType()
-              .GetTypeTemplateArgument(0).GetPointerType();
-      ValueObjectSP cast_ptr_sp = ptr_sp->Cast(value_type_sp);
-      ValueObjectSP value_sp = cast_ptr_sp->Dereference(status);
-      if (status.Success()) {
-        return value_sp;
-      }
-    }
+    Status status;
+    auto value_type_sp = valobj_sp->GetCompilerType()
+                             .GetTypeTemplateArgument(0)
+                             .GetPointerType();
+    ValueObjectSP cast_ptr_sp = m_ptr_obj->Cast(value_type_sp);
+    ValueObjectSP value_sp = cast_ptr_sp->Dereference(status);
+    if (status.Success())
+      return value_sp;
   }
 
   return lldb::ValueObjectSP();
@@ -281,6 +279,7 @@ lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::GetChildAtIndex(
 lldb::ChildCacheState
 lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::Update() {
   m_cntrl = nullptr;
+  m_ptr_obj = nullptr;
 
   ValueObjectSP valobj_sp = m_backend.GetSP();
   if (!valobj_sp)
@@ -290,6 +289,12 @@ lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::Update() {
   if (!target_sp)
     return lldb::ChildCacheState::eRefetch;
 
+  auto ptr_obj_sp = valobj_sp->GetChildMemberWithName("__ptr_");
+  if (!ptr_obj_sp)
+    return lldb::ChildCacheState::eRefetch;
+
+  m_ptr_obj = ptr_obj_sp->Clone(ConstString("pointer")).get();
+
   lldb::ValueObjectSP cntrl_sp(valobj_sp->GetChildMemberWithName("__cntrl_"));
 
   m_cntrl = cntrl_sp.get(); // need to store the raw pointer to avoid a circular
@@ -300,10 +305,12 @@ lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::Update() {
 llvm::Expected<size_t>
 lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::
     GetIndexOfChildWithName(ConstString name) {
-  if (name == "__ptr_")
+  if (name == "__ptr_" || name == "pointer")
     return 0;
-  if (name == "$$dereference$$")
+
+  if (name == "object" || name == "$$dereference$$")
     return 1;
+
   return llvm::createStringError("Type has no child named '%s'",
                                  name.AsCString());
 }

lldb/source/Plugins/Language/CPlusPlus/LibCxx.h

@@ -105,6 +105,7 @@ class LibcxxSharedPtrSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
 
 private:
   ValueObject *m_cntrl;
+  ValueObject *m_ptr_obj;
 };
 
 class LibcxxUniquePtrSyntheticFrontEnd : public SyntheticChildrenFrontEnd {

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

@@ -77,8 +77,7 @@ class LibStdcppSharedPtrSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
   // objects are only destroyed when every shared pointer to any of them
   // is destroyed, so we must not store a shared pointer to any ValueObject
   // derived from our backend ValueObject (since we're in the same cluster).
-  ValueObject* m_ptr_obj = nullptr; // Underlying pointer (held, not owned)
-  ValueObject* m_obj_obj = nullptr; // Underlying object (held, not owned)
+  ValueObject *m_ptr_obj = nullptr; // Underlying pointer (held, not owned)
 };
 
 } // end of anonymous namespace
@@ -266,15 +265,20 @@ LibStdcppSharedPtrSyntheticFrontEnd::GetChildAtIndex(uint32_t idx) {
 
   if (idx == 0)
     return m_ptr_obj->GetSP();
+
   if (idx == 1) {
-    if (m_ptr_obj && !m_obj_obj) {
-      Status error;
-      ValueObjectSP obj_obj = m_ptr_obj->Dereference(error);
-      if (error.Success())
-        m_obj_obj = obj_obj->Clone(ConstString("object")).get();
-    }
-    if (m_obj_obj)
-      return m_obj_obj->GetSP();
+    ValueObjectSP valobj_sp = m_backend.GetSP();
+    if (!valobj_sp)
+      return nullptr;
+
+    Status status;
+    auto value_type_sp = valobj_sp->GetCompilerType()
+                             .GetTypeTemplateArgument(0)
+                             .GetPointerType();
+    ValueObjectSP cast_ptr_sp = m_ptr_obj->Cast(value_type_sp);
+    ValueObjectSP value_sp = cast_ptr_sp->Dereference(status);
+    if (status.Success())
+      return value_sp;
   }
   return lldb::ValueObjectSP();
 }
@@ -293,7 +297,6 @@ lldb::ChildCacheState LibStdcppSharedPtrSyntheticFrontEnd::Update() {
     return lldb::ChildCacheState::eRefetch;
 
   m_ptr_obj = ptr_obj_sp->Clone(ConstString("pointer")).get();
-  m_obj_obj = nullptr;
 
   return lldb::ChildCacheState::eRefetch;
 }
@@ -302,8 +305,10 @@ llvm::Expected<size_t>
 LibStdcppSharedPtrSyntheticFrontEnd::GetIndexOfChildWithName(ConstString name) {
   if (name == "pointer")
     return 0;
+
   if (name == "object" || name == "$$dereference$$")
     return 1;
+
   return llvm::createStringError("Type has no child named '%s'",
                                  name.AsCString());
 }

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/shared_ptr/TestDataFormatterLibcxxSharedPtr.py

@@ -22,7 +22,7 @@ def test_shared_ptr_variables(self):
             "sp_empty",
             type="std::shared_ptr<int>",
             summary="nullptr",
-            children=[ValueCheck(name="__ptr_")],
+            children=[ValueCheck(name="pointer")],
         )
         self.assertEqual(
             valobj.child[0].GetValueAsUnsigned(lldb.LLDB_INVALID_ADDRESS), 0
@@ -35,23 +35,23 @@ def test_shared_ptr_variables(self):
         valobj = self.expect_var_path(
             "sp_int",
             type="std::shared_ptr<int>",
-            children=[ValueCheck(name="__ptr_")],
+            children=[ValueCheck(name="pointer")],
         )
         self.assertRegex(valobj.summary, r"^10( strong=1)? weak=0$")
         self.assertNotEqual(valobj.child[0].unsigned, 0)
 
         valobj = self.expect_var_path(
             "sp_int_ref",
             type="std::shared_ptr<int> &",
-            children=[ValueCheck(name="__ptr_")],
+            children=[ValueCheck(name="pointer")],
         )
         self.assertRegex(valobj.summary, r"^10( strong=1)? weak=0$")
         self.assertNotEqual(valobj.child[0].unsigned, 0)
 
         valobj = self.expect_var_path(
             "sp_int_ref_ref",
             type="std::shared_ptr<int> &&",
-            children=[ValueCheck(name="__ptr_")],
+            children=[ValueCheck(name="pointer")],
         )
         self.assertRegex(valobj.summary, r"^10( strong=1)? weak=0$")
         self.assertNotEqual(valobj.child[0].unsigned, 0)
@@ -66,7 +66,7 @@ def test_shared_ptr_variables(self):
         valobj = self.expect_var_path(
             "sp_str",
             type="std::shared_ptr<" + string_type + ">",
-            children=[ValueCheck(name="__ptr_", summary='"hello"')],
+            children=[ValueCheck(name="pointer", summary='"hello"')],
         )
         self.assertRegex(valobj.summary, r'^"hello"( strong=1)? weak=0$')
 
@@ -85,7 +85,7 @@ def test_shared_ptr_variables(self):
                 ValueCheck(name="name", summary='"steph"'),
             ],
         )
-        self.assertEqual(str(valobj), '(User) *__ptr_ = (id = 30, name = "steph")')
+        self.assertEqual(str(valobj), '(User) *pointer = (id = 30, name = "steph")')
 
         self.expect_var_path("sp_user->id", type="int", value="30")
         self.expect_var_path("sp_user->name", type="std::string", summary='"steph"')