https://github.com/Nerixyz created
https://github.com/llvm/llvm-project/pull/148554
Adds a summary and synthetic children for MSVC STL's `std::variant`.
This one is a bit complicated because of DWARF vs PDB differences. I put the
representations in comments. Being able to `GetChildMemberWithName` a member in
an anonymous union would make this a lot simpler (`std::optional` will have
something similar iirc).
Draft, because I'll split up the libstdc++ and Makefile changes.
>From ccd7869f4602fb514e8dacaf17370f972d13351d Mon Sep 17 00:00:00 2001
From: Nerixyz <nerix...@outlook.de>
Date: Mon, 14 Jul 2025 00:30:48 +0200
Subject: [PATCH] [LLDB] Add formatters for MSVC STL std::variant
---
lldb/examples/synthetic/gnu_libstdcpp.py | 32 ---
.../Python/lldbsuite/test/make/Makefile.rules | 4 -
.../Plugins/Language/CPlusPlus/CMakeLists.txt | 1 +
.../Language/CPlusPlus/CPlusPlusLanguage.cpp | 38 ++-
.../Plugins/Language/CPlusPlus/LibStdcpp.cpp | 46 ++++
.../Plugins/Language/CPlusPlus/LibStdcpp.h | 3 +
.../Plugins/Language/CPlusPlus/MsvcStl.h | 7 +
.../Language/CPlusPlus/MsvcStlVariant.cpp | 221 ++++++++++++++++++
.../variant/TestDataFormatterStdVariant.py | 6 +
9 files changed, 312 insertions(+), 46 deletions(-)
create mode 100644 lldb/source/Plugins/Language/CPlusPlus/MsvcStlVariant.cpp
diff --git a/lldb/examples/synthetic/gnu_libstdcpp.py
b/lldb/examples/synthetic/gnu_libstdcpp.py
index 20b9488af5597..f42a009c21f48 100644
--- a/lldb/examples/synthetic/gnu_libstdcpp.py
+++ b/lldb/examples/synthetic/gnu_libstdcpp.py
@@ -882,38 +882,6 @@ def update(self):
return False
-def VariantSummaryProvider(valobj, dict):
- raw_obj = valobj.GetNonSyntheticValue()
- index_obj = raw_obj.GetChildMemberWithName("_M_index")
- data_obj = raw_obj.GetChildMemberWithName("_M_u")
- if not (index_obj and index_obj.IsValid() and data_obj and
data_obj.IsValid()):
- return "<Can't find _M_index or _M_u>"
-
- def get_variant_npos_value(index_byte_size):
- if index_byte_size == 1:
- return 0xFF
- elif index_byte_size == 2:
- return 0xFFFF
- else:
- return 0xFFFFFFFF
-
- npos_value = get_variant_npos_value(index_obj.GetByteSize())
- index = index_obj.GetValueAsUnsigned(0)
- if index == npos_value:
- return " No Value"
-
- # Strip references and typedefs.
- variant_type = raw_obj.GetType().GetCanonicalType().GetDereferencedType()
- template_arg_count = variant_type.GetNumberOfTemplateArguments()
-
- # Invalid index can happen when the variant is not initialized yet.
- if index >= template_arg_count:
- return " <Invalid>"
-
- active_type = variant_type.GetTemplateArgumentType(index)
- return f" Active Type = {active_type.GetDisplayTypeName()} "
-
-
class VariantSynthProvider:
def __init__(self, valobj, dict):
self.raw_obj = valobj.GetNonSyntheticValue()
diff --git a/lldb/packages/Python/lldbsuite/test/make/Makefile.rules
b/lldb/packages/Python/lldbsuite/test/make/Makefile.rules
index 58833e1b0cc78..8521ca508a479 100644
--- a/lldb/packages/Python/lldbsuite/test/make/Makefile.rules
+++ b/lldb/packages/Python/lldbsuite/test/make/Makefile.rules
@@ -344,10 +344,6 @@ endif
#----------------------------------------------------------------------
ifeq "$(OS)" "Windows_NT"
ifeq ($(CC_TYPE), clang)
- # Clang for Windows doesn't support C++ Exceptions
- CXXFLAGS += -fno-exceptions
- CXXFLAGS += -D_HAS_EXCEPTIONS=0
-
# MSVC 2015 or higher is required, which depends on c++14, so
# append these values unconditionally.
CXXFLAGS += -fms-compatibility-version=19.0
diff --git a/lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt
b/lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt
index 296159ea28407..462c40ec93a0b 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt
+++ b/lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt
@@ -35,6 +35,7 @@ add_lldb_library(lldbPluginCPlusPlusLanguage PLUGIN
LibStdcppUniquePointer.cpp
MsvcStl.cpp
MsvcStlSmartPointer.cpp
+ MsvcStlVariant.cpp
MSVCUndecoratedNameParser.cpp
LINK_COMPONENTS
diff --git a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
index 2db3e6f0ca315..3feee55f487dc 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
@@ -1451,11 +1451,6 @@ static void
LoadLibStdcppFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
SyntheticChildrenSP(new ScriptedSyntheticChildren(
stl_synth_flags,
"lldb.formatters.cpp.gnu_libstdcpp.StdForwardListSynthProvider")));
- cpp_category_sp->AddTypeSynthetic(
- "^std::variant<.+>$", eFormatterMatchRegex,
- SyntheticChildrenSP(new ScriptedSyntheticChildren(
- stl_synth_flags,
- "lldb.formatters.cpp.gnu_libstdcpp.VariantSynthProvider")));
stl_summary_flags.SetDontShowChildren(false);
stl_summary_flags.SetSkipPointers(false);
@@ -1517,11 +1512,6 @@ static void
LoadLibStdcppFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
TypeSummaryImplSP(new ScriptSummaryFormat(
stl_summary_flags,
"lldb.formatters.cpp.gnu_libstdcpp.ForwardListSummaryProvider")));
- cpp_category_sp->AddTypeSummary(
- "^std::variant<.+>$", eFormatterMatchRegex,
- TypeSummaryImplSP(new ScriptSummaryFormat(
- stl_summary_flags,
- "lldb.formatters.cpp.gnu_libstdcpp.VariantSummaryProvider")));
AddCXXSynthetic(
cpp_category_sp,
@@ -1599,6 +1589,25 @@ GenericSmartPointerSummaryProvider(ValueObject &valobj,
Stream &stream,
return LibStdcppSmartPointerSummaryProvider(valobj, stream, options);
}
+static lldb_private::SyntheticChildrenFrontEnd *
+GenericVariantSyntheticFrontEndCreator(CXXSyntheticChildren *children,
+ lldb::ValueObjectSP valobj_sp) {
+ if (!valobj_sp)
+ return nullptr;
+
+ if (IsMsvcStlVariant(*valobj_sp))
+ return MsvcStlVariantSyntheticFrontEndCreator(children, valobj_sp);
+ return new ScriptedSyntheticChildren::FrontEnd(
+ "lldb.formatters.cpp.gnu_libstdcpp.VariantSynthProvider", *valobj_sp);
+}
+
+static bool GenericVariantSummaryProvider(ValueObject &valobj, Stream &stream,
+ const TypeSummaryOptions &options) {
+ if (IsMsvcStlVariant(valobj))
+ return MsvcStlVariantSummaryProvider(valobj, stream, options);
+ return LibStdcppVariantSummaryProvider(valobj, stream, options);
+}
+
/// Load formatters that are formatting types from more than one STL
static void LoadCommonStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
if (!cpp_category_sp)
@@ -1648,6 +1657,12 @@ static void
LoadCommonStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
AddCXXSynthetic(cpp_category_sp, GenericSmartPointerSyntheticFrontEndCreator,
"std::weak_ptr synthetic children",
"^std::weak_ptr<.+>(( )?&)?$", stl_synth_flags, true);
+ AddCXXSynthetic(cpp_category_sp, GenericVariantSyntheticFrontEndCreator,
+ "std::variant synthetic children", "^std::variant<.*>$",
+ stl_synth_flags, true);
+
+ stl_summary_flags.SetDontShowChildren(false);
+ stl_summary_flags.SetSkipPointers(false);
AddCXXSummary(cpp_category_sp, GenericSmartPointerSummaryProvider,
"MSVC STL/libstdc++ std::shared_ptr summary provider",
@@ -1655,6 +1670,9 @@ static void
LoadCommonStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
AddCXXSummary(cpp_category_sp, GenericSmartPointerSummaryProvider,
"MSVC STL/libstdc++ std::weak_ptr summary provider",
"^std::weak_ptr<.+>(( )?&)?$", stl_summary_flags, true);
+ AddCXXSummary(cpp_category_sp, GenericVariantSummaryProvider,
+ "MSVC STL/libstdc++ std::variant summary provider",
+ "^std::variant<.*>$", stl_summary_flags, true);
}
static void LoadMsvcStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
index c80a52d0f9ed6..595e835b37df9 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
@@ -366,3 +366,49 @@ bool
lldb_private::formatters::LibStdcppSmartPointerSummaryProvider(
return true;
}
+
+static uint64_t LibStdcppVariantNposValue(size_t index_byte_size) {
+ switch (index_byte_size) {
+ case 1:
+ return 0xff;
+ case 2:
+ return 0xffff;
+ default:
+ return 0xffff'ffff;
+ }
+}
+
+bool formatters::LibStdcppVariantSummaryProvider(
+ ValueObject &valobj, Stream &stream, const TypeSummaryOptions &options) {
+ ValueObjectSP valobj_sp = valobj.GetNonSyntheticValue();
+ if (!valobj_sp)
+ return false;
+
+ ValueObjectSP index_obj = valobj_sp->GetChildMemberWithName("_M_index");
+ ValueObjectSP data_obj = valobj_sp->GetChildMemberWithName("_M_u");
+ if (!index_obj || !data_obj)
+ return false;
+
+ auto index_bytes = index_obj->GetByteSize();
+ if (!index_bytes)
+ return false;
+ auto npos_value = LibStdcppVariantNposValue(*index_bytes);
+ auto index = index_obj->GetValueAsUnsigned(0);
+ if (index == npos_value) {
+ stream.Printf(" No Value");
+ return true;
+ }
+
+ auto variant_type =
+ valobj_sp->GetCompilerType().GetCanonicalType().GetNonReferenceType();
+ if (!variant_type)
+ return false;
+ if (index >= variant_type.GetNumTemplateArguments(true)) {
+ stream.Printf(" <Invalid>");
+ return true;
+ }
+
+ auto active_type = variant_type.GetTypeTemplateArgument(index, true);
+ stream << " Active Type = " << active_type.GetDisplayTypeName() << " ";
+ return true;
+}
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.h
b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.h
index 8d4d777edee88..707f255954727 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.h
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.h
@@ -57,6 +57,9 @@ SyntheticChildrenFrontEnd *
LibStdcppUniquePtrSyntheticFrontEndCreator(CXXSyntheticChildren *,
lldb::ValueObjectSP);
+bool LibStdcppVariantSummaryProvider(ValueObject &valobj, Stream &stream,
+ const TypeSummaryOptions &options);
+
} // namespace formatters
} // namespace lldb_private
diff --git a/lldb/source/Plugins/Language/CPlusPlus/MsvcStl.h
b/lldb/source/Plugins/Language/CPlusPlus/MsvcStl.h
index edf3f4e8a5387..26bf01d9866bd 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/MsvcStl.h
+++ b/lldb/source/Plugins/Language/CPlusPlus/MsvcStl.h
@@ -37,6 +37,13 @@ bool MsvcStlSmartPointerSummaryProvider(ValueObject &valobj,
Stream &stream,
lldb_private::SyntheticChildrenFrontEnd *
MsvcStlSmartPointerSyntheticFrontEndCreator(lldb::ValueObjectSP valobj_sp);
+bool IsMsvcStlVariant(ValueObject &valobj);
+bool MsvcStlVariantSummaryProvider(ValueObject &valobj, Stream &stream,
+ const TypeSummaryOptions &options);
+SyntheticChildrenFrontEnd *
+MsvcStlVariantSyntheticFrontEndCreator(CXXSyntheticChildren *,
+ lldb::ValueObjectSP valobj_sp);
+
} // namespace formatters
} // namespace lldb_private
diff --git a/lldb/source/Plugins/Language/CPlusPlus/MsvcStlVariant.cpp
b/lldb/source/Plugins/Language/CPlusPlus/MsvcStlVariant.cpp
new file mode 100644
index 0000000000000..e8a6b0e930c2c
--- /dev/null
+++ b/lldb/source/Plugins/Language/CPlusPlus/MsvcStlVariant.cpp
@@ -0,0 +1,221 @@
+//===--
MsvcStlVariant.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 "MsvcStl.h"
+#include "lldb/DataFormatters/FormattersHelpers.h"
+#include "lldb/Symbol/CompilerType.h"
+#include <optional>
+
+using namespace lldb;
+using namespace lldb_private;
+
+namespace {
+
+// A variant when using DWARF looks as follows:
+// (lldb) fr v -R v1
+// (std::variant<int, double, char>) v1 = {
+// std::_SMF_control<std::_Variant_base<int, double, char>, int, double,
char>
+// = {
+// std::_Variant_storage<int, double, char> = {
+// = {
+// _Head = 0
+// _Tail = {
+// = {
+// _Head = 2
+// _Tail = {
+// = {
+// _Head = '\0'
+// _Tail = {}
+// }
+// }
+// }
+// }
+// }
+// }
+// _Which = '\x01'
+// }
+// }
+//
+// ... when using PDB, it looks like this:
+// (lldb) fr v -R v1
+// (std::variant<int,double,char>) v1 = {
+// std::_Variant_base<int,double,char> = {
+// std::_Variant_storage_<1,int,double,char> = {
+// _Head = 0
+// _Tail = {
+// _Head = 2
+// _Tail = {
+// _Head = '\0'
+// _Tail = {}
+// }
+// }
+// }
+// _Which = '\x01'
+// }
+// }
+
+ValueObjectSP GetStorageAtIndex(ValueObject &valobj, size_t index) {
+ // PDB flattens the members on unions to the parent
+ if (valobj.GetCompilerType().GetNumFields() == 2)
+ return valobj.GetChildAtIndex(index);
+
+ // DWARF keeps the union
+ ValueObjectSP union_sp = valobj.GetChildAtIndex(0);
+ if (!union_sp)
+ return nullptr;
+ return union_sp->GetChildAtIndex(index);
+}
+
+ValueObjectSP GetHead(ValueObject &valobj) {
+ return GetStorageAtIndex(valobj, 0);
+}
+ValueObjectSP GetTail(ValueObject &valobj) {
+ return GetStorageAtIndex(valobj, 1);
+}
+
+std::optional<int64_t> GetIndexValue(ValueObject &valobj) {
+ ValueObjectSP index_sp = valobj.GetChildMemberWithName("_Which");
+ if (!index_sp)
+ return std::nullopt;
+
+ return {index_sp->GetValueAsSigned(-1)};
+}
+
+ValueObjectSP GetNthStorage(ValueObject &outer, int64_t index) {
+ ValueObjectSP container_sp = outer.GetSP();
+
+ // When using DWARF, we need to find the std::_Variant_storage base class.
+ // There, the top level type doesn't have any fields.
+ if (container_sp->GetCompilerType().GetNumFields() == 0) {
+ // -> std::_SMF_control (typedef to std::_Variant_base)
+ container_sp = container_sp->GetChildAtIndex(0);
+ if (!container_sp)
+ return nullptr;
+ // -> std::_Variant_storage
+ container_sp = container_sp->GetChildAtIndex(0);
+ if (!container_sp)
+ return nullptr;
+ }
+
+ for (int64_t i = 0; i < index; i++) {
+ container_sp = GetTail(*container_sp);
+ if (!container_sp)
+ return nullptr;
+ }
+ return container_sp;
+}
+
+} // namespace
+
+bool formatters::IsMsvcStlVariant(ValueObject &valobj) {
+ if (auto valobj_sp = valobj.GetNonSyntheticValue()) {
+ return valobj_sp->GetChildMemberWithName("_Which") != nullptr;
+ }
+ return false;
+}
+
+bool formatters::MsvcStlVariantSummaryProvider(
+ ValueObject &valobj, Stream &stream, const TypeSummaryOptions &options) {
+ ValueObjectSP valobj_sp(valobj.GetNonSyntheticValue());
+ if (!valobj_sp)
+ return false;
+
+ auto index = GetIndexValue(*valobj_sp);
+ if (!index)
+ return false;
+
+ if (*index < 0) {
+ stream.Printf(" No Value");
+ return true;
+ }
+
+ ValueObjectSP storage = GetNthStorage(*valobj_sp, *index);
+ if (!storage)
+ return false;
+ CompilerType storage_type = storage->GetCompilerType();
+ if (!storage_type)
+ return false;
+ // With DWARF, it's a typedef, with PDB, it's not
+ if (storage_type.IsTypedefType())
+ storage_type = storage_type.GetTypedefedType();
+
+ CompilerType active_type = storage_type.GetTypeTemplateArgument(1, true);
+ if (!active_type) {
+ // not enough debug info, try the type of _Head
+ ValueObjectSP head_sp = GetHead(*storage);
+ if (!head_sp)
+ return false;
+ active_type = head_sp->GetCompilerType();
+ if (!active_type)
+ return false;
+ }
+
+ stream << " Active Type = " << active_type.GetDisplayTypeName() << " ";
+ return true;
+}
+
+namespace {
+class VariantFrontEnd : public SyntheticChildrenFrontEnd {
+public:
+ VariantFrontEnd(ValueObject &valobj) : SyntheticChildrenFrontEnd(valobj) {
+ Update();
+ }
+
+ llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) override {
+ auto optional_idx = formatters::ExtractIndexFromString(name.GetCString());
+ if (!optional_idx) {
+ return llvm::createStringError("Type has no child named '%s'",
+ name.AsCString());
+ }
+ return *optional_idx;
+ }
+
+ lldb::ChildCacheState Update() override;
+ llvm::Expected<uint32_t> CalculateNumChildren() override { return m_size; }
+ ValueObjectSP GetChildAtIndex(uint32_t idx) override;
+
+private:
+ size_t m_size = 0;
+};
+} // namespace
+
+lldb::ChildCacheState VariantFrontEnd::Update() {
+ m_size = 0;
+
+ auto index = GetIndexValue(m_backend);
+ if (index && *index >= 0)
+ m_size = 1;
+
+ return lldb::ChildCacheState::eRefetch;
+}
+
+ValueObjectSP VariantFrontEnd::GetChildAtIndex(uint32_t idx) {
+ if (idx >= m_size)
+ return nullptr;
+
+ auto index = GetIndexValue(m_backend);
+ if (!index)
+ return nullptr;
+
+ ValueObjectSP storage_sp = GetNthStorage(m_backend, *index);
+ if (!storage_sp)
+ return nullptr;
+
+ ValueObjectSP head_sp = GetHead(*storage_sp);
+ if (!head_sp)
+ return nullptr;
+
+ return head_sp->Clone(ConstString("Value"));
+}
+
+SyntheticChildrenFrontEnd *formatters::MsvcStlVariantSyntheticFrontEndCreator(
+ CXXSyntheticChildren *, lldb::ValueObjectSP valobj_sp) {
+ if (valobj_sp)
+ return new VariantFrontEnd(*valobj_sp);
+ return nullptr;
+}
diff --git
a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/variant/TestDataFormatterStdVariant.py
b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/variant/TestDataFormatterStdVariant.py
index 9365cfc96783e..9f32ad97c1f0a 100644
---
a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/variant/TestDataFormatterStdVariant.py
+++
b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/variant/TestDataFormatterStdVariant.py
@@ -83,3 +83,9 @@ def test_libcxx(self):
def test_libstdcxx(self):
self.build(dictionary={"USE_LIBSTDCPP": 1})
self.do_test()
+
+ @add_test_categories(["msvcstl"])
+ def test_msvcstl(self):
+ # No flags, because the "msvcstl" category checks that the MSVC STL is
used by default.
+ self.build()
+ self.do_test()
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