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

Michael137 · 2025-07-07T16:20:56Z

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.

…hared_ptr formatters

Michael137 · 2025-07-07T16:49:05Z

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

 lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::
    GetIndexOfChildWithName(ConstString name) {
-  if (name == "__ptr_" || name == "pointer")
+  if (name == "pointer")


The __ptr_ here feels redundant. Happy to do this in a separate PR though.

llvmbot · 2025-07-07T16:49:43Z

@llvm/pr-subscribers-lldb

Author: Michael Buch (Michael137)

Changes

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&lt;int&gt;) 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&lt;int&gt;::element_type *) p.pointer = 0x000000010016c6a0
(lldb) v *p.pointer
(std::shared_ptr&lt;int&gt;::element_type) *p.pointer = 10

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

Full diff: https://github.com/llvm/llvm-project/pull/147340.diff

5 Files Affected:

(modified) lldb/include/lldb/DataFormatters/FormattersHelpers.h (+5)
(modified) lldb/source/DataFormatters/FormattersHelpers.cpp (+13)
(modified) lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp (+7-7)
(modified) lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp (+6-6)
(modified) lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/shared_ptr/TestDataFormatterStdSharedPtr.py (+4)

diff --git a/lldb/include/lldb/DataFormatters/FormattersHelpers.h b/lldb/include/lldb/DataFormatters/FormattersHelpers.h
index 6a47cf37eac64..c7ce199452e1d 100644
--- a/lldb/include/lldb/DataFormatters/FormattersHelpers.h
+++ b/lldb/include/lldb/DataFormatters/FormattersHelpers.h
@@ -63,6 +63,11 @@ void DumpCxxSmartPtrPointerSummary(Stream &stream, ValueObject &ptr,
 bool ContainerSizeSummaryProvider(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 GetCxxSmartPtrElementPointerType(ValueObject &ptr,
+                                                     ValueObject &container);
+
 Address GetArrayAddressOrPointerValue(ValueObject &valobj);
 
 time_t GetOSXEpoch();
diff --git a/lldb/source/DataFormatters/FormattersHelpers.cpp b/lldb/source/DataFormatters/FormattersHelpers.cpp
index 028fc5da73dc0..104c2ce6f1c0a 100644
--- a/lldb/source/DataFormatters/FormattersHelpers.cpp
+++ b/lldb/source/DataFormatters/FormattersHelpers.cpp
@@ -151,3 +151,16 @@ bool lldb_private::formatters::ContainerSizeSummaryProvider(
   return FormatEntity::FormatStringRef("size=${svar%#}", stream, nullptr,
                                        nullptr, nullptr, &valobj, false, false);
 }
+
+ValueObjectSP lldb_private::formatters::GetCxxSmartPtrElementPointerType(
+    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());
+}
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp
index 3079de4936a85..f73a77836034f 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp
@@ -264,11 +264,7 @@ 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 +289,11 @@ 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 = GetCxxSmartPtrElementPointerType(*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 +305,7 @@ 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 == "$$dereference$$")
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
index 84442273aebd4..d66b8339809be 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
@@ -273,11 +273,7 @@ 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 +293,11 @@ 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 = GetCxxSmartPtrElementPointerType(*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;
 }
diff --git a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/shared_ptr/TestDataFormatterStdSharedPtr.py b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/shared_ptr/TestDataFormatterStdSharedPtr.py
index 8b641c9643958..3d8569da0332e 100644
--- a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/shared_ptr/TestDataFormatterStdSharedPtr.py
+++ b/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")

labath · 2025-07-08T06:53:14Z

I'm not entirely comfortable with putting the (obviously c++ specific) helper function into the DataFormatters) library. There's no reason to call this from outside the c++ language plugin, right? What would you say to putting this into some header inside the plugin (or creating a new one if we have nothing suitable)?

Michael137 · 2025-07-08T07:23:35Z

I'm not entirely comfortable with putting the (obviously c++ specific) helper function into the DataFormatters) library. There's no reason to call this from outside the c++ language plugin, right? What would you say to putting this into some header inside the plugin (or creating a new one if we have nothing suitable)?

Yup that makes sense!

Michael137 · 2025-07-08T08:13:59Z

I'm not entirely comfortable with putting the (obviously c++ specific) helper function into the DataFormatters) library. There's no reason to call this from outside the c++ language plugin, right? What would you say to putting this into some header inside the plugin (or creating a new one if we have nothing suitable)?

Put it into Generic.{h,cpp} in the language plugin. Let me know if there's a more suitable place

labath

I find Generic.h a bit... generic, but it's there, so ship it.

labath · 2025-07-08T13:09:19Z

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


+/// Return the ValueObjectSP of the underlying pointer member whose type
+/// is a desugared 'std::shared_ptr::element_type *'.
+lldb::ValueObjectSP GetCxxSmartPtrElementPointerType(ValueObject &ptr,


GetDesugaredSmartPointerValue ?

…hared_ptr formatters (llvm#147340) Follow-up to llvm#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. (cherry picked from commit f999918)

[lldb][Formatters] Consistently unwrap pointer element_type in std::s…

dba291d

…hared_ptr formatters

Michael137 requested a review from labath July 7, 2025 16:47

Michael137 commented Jul 7, 2025

View reviewed changes

Michael137 marked this pull request as ready for review July 7, 2025 16:49

Michael137 requested a review from JDevlieghere as a code owner July 7, 2025 16:49

llvmbot added the lldb label Jul 7, 2025

fixup! move helper into CPlusPlus plugin

8abf398

labath approved these changes Jul 8, 2025

View reviewed changes

fixup! GetCxxSmartPtrElementPointerType -> GetDesugaredSmartPointerValue

5f0b003

Michael137 merged commit f999918 into llvm:main Jul 8, 2025
9 checks passed

Michael137 deleted the lldb/shared_ptr-consistent-deref-format branch July 8, 2025 13:45

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