[lldb][Formatters] Consistently unwrap pointer element_type in std::shared_ptr formatters (#147340)

Follow-up to
#147165 (review)

Currently when we explicitly dereference a std::shared_ptr, both the
libstdc++ and libc++ formatters will cast the type of the synthetic
pointer child to whatever the `std::shared_ptr::element_type` is aliased
to. E.g.,
```
(lldb) v p
(std::shared_ptr<int>) p = 10 strong=1 weak=0 {
  pointer = 0x000000010016c6a0
}
(lldb) v *p
(int) *p = 10
```

However, when we print (or dereference) `p.pointer`, the type devolves
to something less user-friendly:
```
(lldb) v p.pointer
(std::shared_ptr<int>::element_type *) p.pointer = 0x000000010016c6a0
(lldb) v *p.pointer
(std::shared_ptr<int>::element_type) *p.pointer = 10
```

This patch changes both formatters to store the casted type. Then
`GetChildAtIndex` will consistently use the unwrapped type.

Author: Michael137

lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt

@@ -12,6 +12,7 @@ add_lldb_library(lldbPluginCPlusPlusLanguage PLUGIN
   CPlusPlusLanguage.cpp
   CPlusPlusNameParser.cpp
   CxxStringTypes.cpp
+  Generic.cpp
   GenericBitset.cpp
   GenericOptional.cpp
   LibCxx.cpp

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

@@ -0,0 +1,22 @@
+//===-- Generic.cpp ------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===---------------------------------------------------------------------===//
+
+#include "Generic.h"
+
+lldb::ValueObjectSP lldb_private::formatters::GetDesugaredSmartPointerValue(
+    ValueObject &ptr, ValueObject &container) {
+  auto container_type = container.GetCompilerType().GetNonReferenceType();
+  if (!container_type)
+    return nullptr;
+
+  auto arg = container_type.GetTypeTemplateArgument(0);
+  if (!arg)
+    return nullptr;
+
+  return ptr.Cast(arg.GetPointerType());
+}

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

@@ -19,6 +19,11 @@ namespace formatters {
 bool GenericOptionalSummaryProvider(ValueObject &valobj, Stream &stream,
                                     const TypeSummaryOptions &options);
 
+/// Return the ValueObjectSP of the underlying pointer member whose type
+/// is a desugared 'std::shared_ptr::element_type *'.
+lldb::ValueObjectSP GetDesugaredSmartPointerValue(ValueObject &ptr,
+                                                  ValueObject &container);
+
 } // namespace formatters
 } // namespace lldb_private
 

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

@@ -25,6 +25,7 @@
 #include "lldb/ValueObject/ValueObjectConstResult.h"
 
 #include "Plugins/Language/CPlusPlus/CxxStringTypes.h"
+#include "Plugins/Language/CPlusPlus/Generic.h"
 #include "Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.h"
 #include "Plugins/TypeSystem/Clang/TypeSystemClang.h"
 #include "lldb/lldb-enumerations.h"
@@ -264,11 +265,7 @@ lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::GetChildAtIndex(
 
   if (idx == 1) {
     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);
+    ValueObjectSP value_sp = m_ptr_obj->Dereference(status);
     if (status.Success())
       return value_sp;
   }
@@ -293,7 +290,11 @@ lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::Update() {
   if (!ptr_obj_sp)
     return lldb::ChildCacheState::eRefetch;
 
-  m_ptr_obj = ptr_obj_sp->Clone(ConstString("pointer")).get();
+  auto cast_ptr_sp = GetDesugaredSmartPointerValue(*ptr_obj_sp, *valobj_sp);
+  if (!cast_ptr_sp)
+    return lldb::ChildCacheState::eRefetch;
+
+  m_ptr_obj = cast_ptr_sp->Clone(ConstString("pointer")).get();
 
   lldb::ValueObjectSP cntrl_sp(valobj_sp->GetChildMemberWithName("__cntrl_"));
 
@@ -305,7 +306,7 @@ lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::Update() {
 llvm::Expected<size_t>
 lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::
     GetIndexOfChildWithName(ConstString name) {
-  if (name == "__ptr_" || name == "pointer")
+  if (name == "pointer")
     return 0;
 
   if (name == "object" || name == "$$dereference$$")

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

@@ -9,6 +9,7 @@
 #include "LibStdcpp.h"
 #include "LibCxx.h"
 
+#include "Plugins/Language/CPlusPlus/Generic.h"
 #include "Plugins/TypeSystem/Clang/TypeSystemClang.h"
 #include "lldb/DataFormatters/FormattersHelpers.h"
 #include "lldb/DataFormatters/StringPrinter.h"
@@ -273,11 +274,7 @@ LibStdcppSharedPtrSyntheticFrontEnd::GetChildAtIndex(uint32_t idx) {
       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);
+    ValueObjectSP value_sp = m_ptr_obj->Dereference(status);
     if (status.Success())
       return value_sp;
   }
@@ -297,7 +294,11 @@ lldb::ChildCacheState LibStdcppSharedPtrSyntheticFrontEnd::Update() {
   if (!ptr_obj_sp)
     return lldb::ChildCacheState::eRefetch;
 
-  m_ptr_obj = ptr_obj_sp->Clone(ConstString("pointer")).get();
+  auto cast_ptr_sp = GetDesugaredSmartPointerValue(*ptr_obj_sp, *valobj_sp);
+  if (!cast_ptr_sp)
+    return lldb::ChildCacheState::eRefetch;
+
+  m_ptr_obj = cast_ptr_sp->Clone(ConstString("pointer")).get();
 
   return lldb::ChildCacheState::eRefetch;
 }

lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/shared_ptr/TestDataFormatterStdSharedPtr.py

@@ -99,6 +99,10 @@ def do_test(self):
             "wie", type="std::weak_ptr<int>", summary="nullptr strong=2 weak=2"
         )
 
+        self.expect_var_path("si.pointer", type="int *")
+        self.expect_var_path("*si.pointer", type="int", value="47")
+        self.expect_var_path("si.object", type="int", value="47")
+
         self.runCmd("settings set target.experimental.use-DIL true")
         self.expect_var_path("ptr_node->value", value="1")
         self.expect_var_path("ptr_node->next->value", value="2")