[lldb] Add libstdcpp initializer_list formatter (#167515)

Make the existing libc++ formatter generic
Add initializer_list summary provider.
Add test for `libstdcpp`

Author: da-viper

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

@@ -14,11 +14,11 @@ add_lldb_library(lldbPluginCPlusPlusLanguage PLUGIN
   CxxStringTypes.cpp
   Generic.cpp
   GenericBitset.cpp
+  GenericInitializerList.cpp
   GenericList.cpp
   GenericOptional.cpp
   LibCxx.cpp
   LibCxxAtomic.cpp
-  LibCxxInitializerList.cpp
   LibCxxMap.cpp
   LibCxxQueue.cpp
   LibCxxRangesRefView.cpp

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

@@ -899,11 +899,6 @@ static void LoadLibCxxFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
       "libc++ std::unordered containers synthetic children",
       "^std::__[[:alnum:]]+::unordered_(multi)?(map|set)<.+> >$",
       stl_synth_flags, true);
-  AddCXXSynthetic(
-      cpp_category_sp,
-      lldb_private::formatters::LibcxxInitializerListSyntheticFrontEndCreator,
-      "libc++ std::initializer_list synthetic children",
-      "^std::initializer_list<.+>$", stl_synth_flags, true);
   AddCXXSynthetic(cpp_category_sp, LibcxxQueueFrontEndCreator,
                   "libc++ std::queue synthetic children",
                   "^std::__[[:alnum:]]+::queue<.+>$", stl_synth_flags, true);
@@ -1705,6 +1700,14 @@ static void LoadCommonStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
           },
           "MSVC STL/libstdc++ std::wstring summary provider"));
 
+  // NOTE: it is loaded as a common formatter because the libc++ version is not
+  // in the `__1` namespace, hence we need to dispatch based on the class
+  // layout.
+  AddCXXSynthetic(cpp_category_sp,
+                  GenericInitializerListSyntheticFrontEndCreator,
+                  "std::initializer_list synthetic children",
+                  "^std::initializer_list<.+>$", stl_synth_flags, true);
+
   stl_summary_flags.SetDontShowChildren(false);
   stl_summary_flags.SetSkipPointers(false);
 
@@ -1748,6 +1751,9 @@ static void LoadCommonStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
                   "^std::(multi)?(map|set)<.+>(( )?&)?$", stl_synth_flags,
                   true);
 
+  AddCXXSummary(cpp_category_sp, ContainerSizeSummaryProvider,
+                "std::initializer_list summary provider",
+                "^std::initializer_list<.+>$", stl_summary_flags, true);
   AddCXXSummary(cpp_category_sp, GenericSmartPointerSummaryProvider,
                 "MSVC STL/libstdc++ std::shared_ptr summary provider",
                 "^std::shared_ptr<.+>(( )?&)?$", stl_summary_flags, true);

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

@@ -24,6 +24,9 @@ bool GenericOptionalSummaryProvider(ValueObject &valobj, Stream &stream,
 lldb::ValueObjectSP GetDesugaredSmartPointerValue(ValueObject &ptr,
                                                   ValueObject &container);
 
+SyntheticChildrenFrontEnd *
+GenericInitializerListSyntheticFrontEndCreator(CXXSyntheticChildren *,
+                                               lldb::ValueObjectSP valobj_sp);
 } // namespace formatters
 } // namespace lldb_private
 

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

@@ -0,0 +1,145 @@
+//===-- GenericInitializerList.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 "lldb/DataFormatters/FormattersHelpers.h"
+#include "lldb/Utility/ConstString.h"
+#include "lldb/ValueObject/ValueObject.h"
+#include <cstddef>
+#include <optional>
+#include <type_traits>
+
+using namespace lldb;
+using namespace lldb_private;
+
+namespace generic_check {
+template <class T>
+using size_func = decltype(T::GetSizeMember(std::declval<ValueObject &>()));
+template <class T>
+using start_func = decltype(T::GetStartMember(std::declval<ValueObject &>()));
+namespace {
+template <typename...> struct check_func : std::true_type {};
+} // namespace
+
+template <typename T>
+using has_functions = check_func<size_func<T>, start_func<T>>;
+} // namespace generic_check
+
+struct LibCxx {
+  static ValueObjectSP GetStartMember(ValueObject &backend) {
+    return backend.GetChildMemberWithName("__begin_");
+  }
+
+  static ValueObjectSP GetSizeMember(ValueObject &backend) {
+    return backend.GetChildMemberWithName("__size_");
+  }
+};
+
+struct LibStdcpp {
+  static ValueObjectSP GetStartMember(ValueObject &backend) {
+    return backend.GetChildMemberWithName("_M_array");
+  }
+
+  static ValueObjectSP GetSizeMember(ValueObject &backend) {
+    return backend.GetChildMemberWithName("_M_len");
+  }
+};
+
+namespace lldb_private::formatters {
+
+template <class StandardImpl>
+class GenericInitializerListSyntheticFrontEnd
+    : public SyntheticChildrenFrontEnd {
+public:
+  static_assert(generic_check::has_functions<StandardImpl>::value,
+                "Missing Required Functions.");
+
+  GenericInitializerListSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp)
+      : SyntheticChildrenFrontEnd(*valobj_sp), m_element_type() {
+    if (valobj_sp)
+      Update();
+  }
+
+  ~GenericInitializerListSyntheticFrontEnd() override {
+    // this needs to stay around because it's a child object who will follow its
+    // parent's life cycle
+    // delete m_start;
+  }
+
+  llvm::Expected<uint32_t> CalculateNumChildren() override {
+    m_num_elements = 0;
+
+    const ValueObjectSP size_sp(StandardImpl::GetSizeMember(m_backend));
+    if (size_sp)
+      m_num_elements = size_sp->GetValueAsUnsigned(0);
+    return m_num_elements;
+  }
+
+  lldb::ValueObjectSP GetChildAtIndex(uint32_t idx) override {
+    if (!m_start)
+      return {};
+
+    uint64_t offset = static_cast<uint64_t>(idx) * m_element_size;
+    offset = offset + m_start->GetValueAsUnsigned(0);
+    StreamString name;
+    name.Printf("[%" PRIu64 "]", (uint64_t)idx);
+    return CreateValueObjectFromAddress(name.GetString(), offset,
+                                        m_backend.GetExecutionContextRef(),
+                                        m_element_type);
+  }
+
+  lldb::ChildCacheState Update() override {
+    m_start = nullptr;
+    m_num_elements = 0;
+    m_element_type = m_backend.GetCompilerType().GetTypeTemplateArgument(0);
+    if (!m_element_type.IsValid())
+      return lldb::ChildCacheState::eRefetch;
+
+    llvm::Expected<uint64_t> size_or_err = m_element_type.GetByteSize(nullptr);
+    if (!size_or_err)
+      LLDB_LOG_ERRORV(GetLog(LLDBLog::DataFormatters), size_or_err.takeError(),
+                      "{0}");
+    else {
+      m_element_size = *size_or_err;
+      // Store raw pointers or end up with a circular dependency.
+      m_start = StandardImpl::GetStartMember(m_backend).get();
+    }
+
+    return lldb::ChildCacheState::eRefetch;
+  }
+
+  llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) override {
+    if (!m_start) {
+      return llvm::createStringError("Type has no child named '%s'",
+                                     name.AsCString());
+    }
+    auto optional_idx = formatters::ExtractIndexFromString(name.GetCString());
+    if (!optional_idx) {
+      return llvm::createStringError("Type has no child named '%s'",
+                                     name.AsCString());
+    }
+    return *optional_idx;
+  }
+
+private:
+  ValueObject *m_start = nullptr;
+  CompilerType m_element_type;
+  uint32_t m_element_size = 0;
+  size_t m_num_elements = 0;
+};
+
+SyntheticChildrenFrontEnd *GenericInitializerListSyntheticFrontEndCreator(
+    CXXSyntheticChildren * /*unused*/, lldb::ValueObjectSP valobj_sp) {
+  if (!valobj_sp)
+    return nullptr;
+
+  if (LibCxx::GetStartMember(*valobj_sp) != nullptr)
+    return new GenericInitializerListSyntheticFrontEnd<LibCxx>(valobj_sp);
+
+  return new GenericInitializerListSyntheticFrontEnd<LibStdcpp>(valobj_sp);
+}
+} // namespace lldb_private::formatters

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

@@ -194,10 +194,6 @@ SyntheticChildrenFrontEnd *
 LibCxxUnorderedMapIteratorSyntheticFrontEndCreator(CXXSyntheticChildren *,
                                                    lldb::ValueObjectSP);
 
-SyntheticChildrenFrontEnd *
-LibcxxInitializerListSyntheticFrontEndCreator(CXXSyntheticChildren *,
-                                              lldb::ValueObjectSP);
-
 SyntheticChildrenFrontEnd *LibcxxQueueFrontEndCreator(CXXSyntheticChildren *,
                                                       lldb::ValueObjectSP);
 

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

@@ -28,13 +28,25 @@ def do_test(self):
             substrs=["stopped", "stop reason = breakpoint"],
         )
 
-        self.expect("frame variable ili", substrs=["[1] = 2", "[4] = 5"])
+        self.expect(
+            "frame variable ili",
+            substrs=["ili = size=5", "[0] = 1", "[1] = 2", "[4] = 5"],
+        )
         self.expect(
             "frame variable ils",
-            substrs=['[4] = "surprise it is a long string!! yay!!"'],
+            substrs=[
+                "ils = size=5",
+                '[0] = "1"',
+                '[4] = "surprise it is a long string!! yay!!"',
+            ],
         )
 
     @add_test_categories(["libc++"])
     def test_libcxx(self):
         self.build(dictionary={"USE_LIBCPP": 1})
         self.do_test()
+
+    @add_test_categories(["libstdcxx"])
+    def test_libstdcpp(self):
+        self.build(dictionary={"USE_LIBSTDCPP": 1})
+        self.do_test()

lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/initializer_list/TestDataFormatterStdInitializerList.py

@@ -1,6 +1,5 @@
 #include <initializer_list>
 #include <string>
-#include <vector>
 
 int main() {
   std::initializer_list<int> ili{1, 2, 3, 4, 5};