[LLDB] Add formatters for MSVC STL std::atomic

[Nerixyz]

Adds synthetic children and a summary provider for std::atomic on MSVC's STL. This currently only supports DWARF because it relies on the template argument. Once there are PDB tests, this will probably use the return type of some method like value() because template types aren't available there.

Towards #24834.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: nerix (Nerixyz)

Changes

Adds synthetic children and a summary provider for std::atomic on MSVC's STL. This currently only supports DWARF because it relies on the template argument. Once there are PDB tests, this will probably use the return type of some method like value() because template types aren't available there.

Towards #24834.

---

Full diff: https://github.com/llvm/llvm-project/pull/149801.diff

5 Files Affected:

• (modified) lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt (+1)
• (modified) lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp (+14)
• (modified) lldb/source/Plugins/Language/CPlusPlus/MsvcStl.h (+7)
• (added) lldb/source/Plugins/Language/CPlusPlus/MsvcStlAtomic.cpp (+102)
• (modified) lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/atomic/TestDataFormatterStdAtomic.py (+6)

diff --git a/lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt b/lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt
index 5905d9b9a6d03..ce4e2d6f0f5af 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt
+++ b/lldb/source/Plugins/Language/CPlusPlus/CMakeLists.txt
@@ -34,6 +34,7 @@ add_lldb_library(lldbPluginCPlusPlusLanguage PLUGIN
   LibStdcppTuple.cpp
   LibStdcppUniquePointer.cpp
   MsvcStl.cpp
+  MsvcStlAtomic.cpp
   MsvcStlSmartPointer.cpp
   MsvcStlTuple.cpp
   MsvcStlVector.cpp
diff --git a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
index a0d5e1dfe3227..16b4d55d2db73 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
@@ -1763,6 +1763,9 @@ static void LoadMsvcStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
       .SetDontShowValue(false)
       .SetShowMembersOneLiner(false)
       .SetHideItemNames(false);
+  SyntheticChildren::Flags stl_synth_flags;
+  stl_synth_flags.SetCascades(true).SetSkipPointers(false).SetSkipReferences(
+      false);
 
   using StringElementType = StringPrinter::StringElementType;
 
@@ -1784,6 +1787,17 @@ static void LoadMsvcStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
           stl_summary_flags,
           MsvcStlStringSummaryProvider<StringElementType::UTF32>,
           "MSVC STL std::u32string summary provider"));
+
+  stl_summary_flags.SetDontShowChildren(false);
+  stl_summary_flags.SetSkipPointers(false);
+
+  AddCXXSynthetic(cpp_category_sp, MsvcStlAtomicSyntheticFrontEndCreator,
+                  "MSVC STL std::atomic synthetic children",
+                  "^std::atomic<.+>$", stl_synth_flags, true);
+
+  AddCXXSummary(cpp_category_sp, MsvcStlAtomicSummaryProvider,
+                "MSVC STL std::atomic summary provider", "^std::atomic<.+>$",
+                stl_summary_flags, true);
 }
 
 static void LoadSystemFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
diff --git a/lldb/source/Plugins/Language/CPlusPlus/MsvcStl.h b/lldb/source/Plugins/Language/CPlusPlus/MsvcStl.h
index c08eecfdecee7..3ac12c17a96e1 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/MsvcStl.h
+++ b/lldb/source/Plugins/Language/CPlusPlus/MsvcStl.h
@@ -71,6 +71,13 @@ SyntheticChildrenFrontEnd *
 MsvcStlOptionalSyntheticFrontEndCreator(CXXSyntheticChildren *,
                                         lldb::ValueObjectSP valobj_sp);
 
+// MSVC STL std::atomic<>
+bool MsvcStlAtomicSummaryProvider(ValueObject &valobj, Stream &stream,
+                                  const TypeSummaryOptions &options);
+SyntheticChildrenFrontEnd *
+MsvcStlAtomicSyntheticFrontEndCreator(CXXSyntheticChildren *,
+                                      lldb::ValueObjectSP valobj_sp);
+
 } // namespace formatters
 } // namespace lldb_private
 
diff --git a/lldb/source/Plugins/Language/CPlusPlus/MsvcStlAtomic.cpp b/lldb/source/Plugins/Language/CPlusPlus/MsvcStlAtomic.cpp
new file mode 100644
index 0000000000000..3ec324577ac76
--- /dev/null
+++ b/lldb/source/Plugins/Language/CPlusPlus/MsvcStlAtomic.cpp
@@ -0,0 +1,102 @@
+//===-- MsvcStlAtomic.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/TypeSynthetic.h"
+
+using namespace lldb;
+
+namespace lldb_private {
+namespace formatters {
+
+class MsvcStlAtomicSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
+public:
+  MsvcStlAtomicSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp);
+
+  llvm::Expected<uint32_t> CalculateNumChildren() override;
+
+  lldb::ValueObjectSP GetChildAtIndex(uint32_t idx) override;
+
+  lldb::ChildCacheState Update() override;
+
+  llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) override;
+
+private:
+  ValueObject *m_storage = nullptr;
+  CompilerType m_element_type;
+};
+
+} // namespace formatters
+} // namespace lldb_private
+
+lldb_private::formatters::MsvcStlAtomicSyntheticFrontEnd::
+    MsvcStlAtomicSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp)
+    : SyntheticChildrenFrontEnd(*valobj_sp), m_element_type() {
+  if (valobj_sp)
+    Update();
+}
+
+llvm::Expected<uint32_t> lldb_private::formatters::
+    MsvcStlAtomicSyntheticFrontEnd::CalculateNumChildren() {
+  return m_storage ? 1 : 0;
+}
+
+lldb::ValueObjectSP
+lldb_private::formatters::MsvcStlAtomicSyntheticFrontEnd::GetChildAtIndex(
+    uint32_t idx) {
+  if (idx == 0)
+    return m_storage->Cast(m_element_type)->Clone(ConstString("Value"));
+  return nullptr;
+}
+
+lldb::ChildCacheState
+lldb_private::formatters::MsvcStlAtomicSyntheticFrontEnd::Update() {
+  m_storage = nullptr;
+  m_element_type.Clear();
+
+  ValueObjectSP storage_sp = m_backend.GetChildMemberWithName("_Storage");
+  if (!storage_sp)
+    return lldb::ChildCacheState::eRefetch;
+
+  m_element_type = m_backend.GetCompilerType().GetTypeTemplateArgument(0);
+  if (!m_element_type)
+    return lldb::ChildCacheState::eRefetch;
+
+  m_storage = storage_sp.get();
+  return lldb::ChildCacheState::eRefetch;
+}
+
+llvm::Expected<size_t> lldb_private::formatters::
+    MsvcStlAtomicSyntheticFrontEnd::GetIndexOfChildWithName(ConstString name) {
+  if (name == "Value")
+    return 0;
+  return llvm::createStringError("Type has no child named '%s'",
+                                 name.AsCString());
+}
+
+lldb_private::SyntheticChildrenFrontEnd *
+lldb_private::formatters::MsvcStlAtomicSyntheticFrontEndCreator(
+    CXXSyntheticChildren *, lldb::ValueObjectSP valobj_sp) {
+  return new MsvcStlAtomicSyntheticFrontEnd(valobj_sp);
+}
+
+bool lldb_private::formatters::MsvcStlAtomicSummaryProvider(
+    ValueObject &valobj, Stream &stream, const TypeSummaryOptions &options) {
+  auto synth_sp = valobj.GetSyntheticValue();
+  if (!synth_sp)
+    return false;
+
+  auto value_sp = synth_sp->GetChildAtIndex(0);
+  std::string summary;
+  if (value_sp->GetSummaryAsCString(summary, options) && !summary.empty()) {
+    stream << summary;
+    return true;
+  }
+  return false;
+}
diff --git a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/atomic/TestDataFormatterStdAtomic.py b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/atomic/TestDataFormatterStdAtomic.py
index 8186e1d66985b..bdf12ca3b86db 100644
--- a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/atomic/TestDataFormatterStdAtomic.py
+++ b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/atomic/TestDataFormatterStdAtomic.py
@@ -67,3 +67,9 @@ def do_test(self):
     def test_libcxx(self):
         self.build(dictionary={"USE_LIBCPP": 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()

[Michael137]

Suggested change

stl_summary_flags.SetSkipPointers(false);

We already set this above

[Michael137]

What happens if you don't set this? I think we probably do want this to be true? Would that make std::atomic look like:

(std::atomic<int>) val = 5

?

(i.e., just not print the synthetic child?)

I know that's not what libc++/libstdc++ does, but we probably should?

[Michael137]

Can be done separately since that's what libc++ and libstdc++ already do

[Nerixyz]

Would that make std::atomic look like:

(std::atomic<int>) val = 5

?

Yes. I don't think that's always desired. Atomics can store structs as well (not sure why) and users might want to inspect these. This is also done in the tests here.

[Michael137]

Yea, I wondered if for summaries that can't be formatted without children this would then fall back to showing the children. But yea maybe not. Either way, not something you have to deal with here