[Lldb-commits] [lldb] 401b5cc - [LLDB] Add formatters for MSVC STL std::variant (#148554)
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Mon Jul 21 04:46:38 PDT 2025
Author: nerix
Date: 2025-07-21T12:46:34+01:00
New Revision: 401b5ccf6b507ed36e959e7ae2f4b5e052647196
URL: https://github.com/llvm/llvm-project/commit/401b5ccf6b507ed36e959e7ae2f4b5e052647196
DIFF: https://github.com/llvm/llvm-project/commit/401b5ccf6b507ed36e959e7ae2f4b5e052647196.diff
LOG: [LLDB] Add formatters for MSVC STL std::variant (#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).
Towards #24834.
Added:
lldb/source/Plugins/Language/CPlusPlus/MsvcStlVariant.cpp
Modified:
lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt
lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.h
lldb/source/Plugins/Language/CPlusPlus/MsvcStl.h
lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/variant/TestDataFormatterStdVariant.py
Removed:
################################################################################
diff --git a/lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt b/lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt
index 5905d9b9a6d03..e1dd5bf84d7eb 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt
+++ b/lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt
@@ -36,6 +36,7 @@ add_lldb_library(lldbPluginCPlusPlusLanguage PLUGIN
MsvcStl.cpp
MsvcStlSmartPointer.cpp
MsvcStlTuple.cpp
+ MsvcStlVariant.cpp
MsvcStlVector.cpp
MSVCUndecoratedNameParser.cpp
diff --git a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
index a0d5e1dfe3227..481fe6106849c 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
@@ -1449,11 +1449,6 @@ 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<.+>$", eFormatterMatchRegex,
- SyntheticChildrenSP(new ScriptedSyntheticChildren(
- stl_synth_flags,
- "lldb.formatters.cpp.gnu_libstdcpp.VariantSynthProvider")));
stl_summary_flags.SetDontShowChildren(false);
stl_summary_flags.SetSkipPointers(false);
@@ -1509,9 +1504,6 @@ static void LoadLibStdcppFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
TypeSummaryImplSP(new ScriptSummaryFormat(
stl_summary_flags,
"lldb.formatters.cpp.gnu_libstdcpp.ForwardListSummaryProvider")));
- AddCXXSummary(cpp_category_sp, LibStdcppVariantSummaryProvider,
- "libstdc++ std::variant summary provider", "^std::variant<.+>$",
- stl_summary_flags, true);
AddCXXSynthetic(
cpp_category_sp,
@@ -1649,6 +1641,25 @@ GenericOptionalSyntheticFrontEndCreator(CXXSyntheticChildren *children,
return LibStdcppOptionalSyntheticFrontEndCreator(children, valobj_sp);
}
+static 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)
@@ -1713,6 +1724,9 @@ static void LoadCommonStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
AddCXXSynthetic(cpp_category_sp, GenericForwardListSyntheticFrontEndCreator,
"std::forward_list synthetic children",
"^std::forward_list<.+>(( )?&)?$", stl_synth_flags, true);
+ AddCXXSynthetic(cpp_category_sp, GenericVariantSyntheticFrontEndCreator,
+ "std::variant synthetic children", "^std::variant<.*>$",
+ stl_synth_flags, true);
SyntheticChildren::Flags stl_deref_flags = stl_synth_flags;
stl_deref_flags.SetFrontEndWantsDereference();
@@ -1749,6 +1763,9 @@ static void LoadCommonStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
AddCXXSummary(cpp_category_sp, GenericOptionalSummaryProvider,
"MSVC STL/libstd++ std::optional summary provider",
"^std::optional<.+>(( )?&)?$", stl_summary_flags, true);
+ AddCXXSummary(cpp_category_sp, GenericVariantSummaryProvider,
+ "MSVC STL/libstdc++ std::variant summary provider",
+ "^std::variant<.*>$", stl_summary_flags, true);
}
static void LoadMsvcStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.h b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.h
index 8d2025e940ead..429142f63a4bd 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.h
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.h
@@ -61,6 +61,9 @@ 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 c08eecfdecee7..9058d2e579adb 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/MsvcStl.h
+++ b/lldb/source/Plugins/Language/CPlusPlus/MsvcStl.h
@@ -71,6 +71,14 @@ SyntheticChildrenFrontEnd *
MsvcStlOptionalSyntheticFrontEndCreator(CXXSyntheticChildren *,
lldb::ValueObjectSP valobj_sp);
+// MSVC STL std::variant<>
+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..52a3d98d2af4b
--- /dev/null
+++ b/lldb/source/Plugins/Language/CPlusPlus/MsvcStlVariant.cpp
@@ -0,0 +1,188 @@
+//===-- 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'
+// }
+// }
+
+ValueObjectSP GetStorageMember(ValueObject &valobj, llvm::StringRef name) {
+ // Find the union
+ ValueObjectSP union_sp = valobj.GetChildAtIndex(0);
+ if (!union_sp)
+ return nullptr;
+ return union_sp->GetChildMemberWithName(name);
+}
+
+ValueObjectSP GetHead(ValueObject &valobj) {
+ return GetStorageMember(valobj, "_Head");
+}
+ValueObjectSP GetTail(ValueObject &valobj) {
+ return GetStorageMember(valobj, "_Tail");
+}
+
+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) {
+ // We need to find the std::_Variant_storage base class.
+
+ // -> std::_SMF_control (typedef to std::_Variant_base)
+ ValueObjectSP container_sp = outer.GetSP()->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;
+ // Resolve the typedef
+ if (storage_type.IsTypedefType())
+ storage_type = storage_type.GetTypedefedType();
+
+ CompilerType active_type = storage_type.GetTypeTemplateArgument(1, true);
+ 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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