1 files changed, 273 insertions, 0 deletions
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibCxxVariant.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibCxxVariant.cpp
new file mode 100644
index 00000000000..a7da282f778
--- /dev/null
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibCxxVariant.cpp
@@ -0,0 +1,273 @@
+//===-- LibCxxVariant.cpp --------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "LibCxxVariant.h"
+#include "lldb/DataFormatters/FormattersHelpers.h"
+
+#include "llvm/ADT/Optional.h"
+#include "llvm/ADT/ScopeExit.h"
+
+using namespace lldb;
+using namespace lldb_private;
+
+// libc++ variant implementation contains two members that we care about both
+// are contained in the __impl member.
+// - __index which tells us which of the variadic template types is the active
+//   type for the variant
+// - __data is a variadic union which recursively contains itself as member
+//   which refers to the tailing variadic types.
+//   - __head which refers to the leading non pack type
+//     - __value refers to the actual value contained
+//   - __tail which refers to the remaining pack types
+//
+// e.g. given std::variant<int,double,char> v1
+//
+// (lldb) frame var -R v1.__impl.__data
+//(... __union<... 0, int, double, char>) v1.__impl.__data = {
+// ...
+//  __head = {
+//    __value = ...
+//  }
+//  __tail = {
+//  ...
+//    __head = {
+//      __value = ...
+//    }
+//    __tail = {
+//    ...
+//      __head = {
+//        __value = ...
+//  ...
+//
+// So given
+// - __index equal to 0 the active value is contained in
+//
+//     __data.__head.__value
+//
+// - __index equal to 1 the active value is contained in
+//
+//     __data.__tail.__head.__value
+//
+// - __index equal to 2 the active value is contained in
+//
+//      __data.__tail.__tail.__head.__value
+//
+
+namespace {
+// libc++ std::variant index could have one of three states
+// 1) VALID, we can obtain it and its not variant_npos
+// 2) INVALID, we can't obtain it or it is not a type we expect
+// 3) NPOS, its value is variant_npos which means the variant has no value
+enum class LibcxxVariantIndexValidity { VALID, INVALID, NPOS };
+
+LibcxxVariantIndexValidity
+LibcxxVariantGetIndexValidity(ValueObjectSP &impl_sp) {
+  ValueObjectSP index_sp(
+      impl_sp->GetChildMemberWithName(ConstString("__index"), true));
+
+  if (!index_sp)
+    return LibcxxVariantIndexValidity::INVALID;
+
+  int64_t index_value = index_sp->GetValueAsSigned(0);
+
+  CompilerType index_compiler_type = index_sp->GetCompilerType();
+
+  // We are expecting two layers of typedefs before we obtain the basic type
+  // The next two checks verify this.
+  if (!index_compiler_type.IsTypedefType())
+    return LibcxxVariantIndexValidity::INVALID;
+
+  if (!index_compiler_type.GetTypedefedType().IsTypedefType())
+    return LibcxxVariantIndexValidity::INVALID;
+
+  lldb::BasicType index_basic_type = index_compiler_type.GetTypedefedType()
+                                         .GetTypedefedType()
+                                         .GetBasicTypeEnumeration();
+
+  if (index_basic_type == eBasicTypeInvalid)
+    return LibcxxVariantIndexValidity::INVALID;
+
+  if (index_value == -1)
+    return LibcxxVariantIndexValidity::NPOS;
+
+  return LibcxxVariantIndexValidity::VALID;
+}
+
+llvm::Optional<uint64_t> LibcxxVariantIndexValue(ValueObjectSP &impl_sp) {
+  ValueObjectSP index_sp(
+      impl_sp->GetChildMemberWithName(ConstString("__index"), true));
+
+  if (!index_sp)
+    return {};
+
+  return {index_sp->GetValueAsUnsigned(0)};
+}
+
+ValueObjectSP LibcxxVariantGetNthHead(ValueObjectSP &impl_sp, uint64_t index) {
+  ValueObjectSP data_sp(
+      impl_sp->GetChildMemberWithName(ConstString("__data"), true));
+
+  if (!data_sp)
+    return ValueObjectSP{};
+
+  ValueObjectSP current_level = data_sp;
+  for (uint64_t n = index; n != 0; --n) {
+    ValueObjectSP tail_sp(
+        current_level->GetChildMemberWithName(ConstString("__tail"), true));
+
+    if (!tail_sp)
+      return ValueObjectSP{};
+
+    current_level = tail_sp;
+  }
+
+  return current_level->GetChildMemberWithName(ConstString("__head"), true);
+};
+} // namespace
+
+namespace lldb_private {
+namespace formatters {
+bool LibcxxVariantSummaryProvider(ValueObject &valobj, Stream &stream,
+                                  const TypeSummaryOptions &options) {
+  ValueObjectSP valobj_sp(valobj.GetNonSyntheticValue());
+  if (!valobj_sp)
+    return false;
+
+  ValueObjectSP impl_sp(
+      valobj_sp->GetChildMemberWithName(ConstString("__impl"), true));
+
+  if (!impl_sp)
+    return false;
+
+  LibcxxVariantIndexValidity validity = LibcxxVariantGetIndexValidity(impl_sp);
+
+  if (validity == LibcxxVariantIndexValidity::INVALID)
+    return false;
+
+  if (validity == LibcxxVariantIndexValidity::NPOS) {
+    stream.Printf(" No Value");
+    return true;
+  }
+
+  auto optional_index_value = LibcxxVariantIndexValue(impl_sp);
+
+  if (!optional_index_value)
+    return false;
+
+  uint64_t index_value = *optional_index_value;
+
+  ValueObjectSP nth_head = LibcxxVariantGetNthHead(impl_sp, index_value);
+
+  if (!nth_head)
+    return false;
+
+  CompilerType head_type = nth_head->GetCompilerType();
+
+  if (!head_type)
+    return false;
+
+  CompilerType template_type = head_type.GetTypeTemplateArgument(1);
+
+  if (!template_type)
+    return false;
+
+  stream.Printf(" Active Type = %s ", template_type.GetTypeName().GetCString());
+
+  return true;
+}
+} // namespace formatters
+} // namespace lldb_private
+
+namespace {
+class VariantFrontEnd : public SyntheticChildrenFrontEnd {
+public:
+  VariantFrontEnd(ValueObject &valobj) : SyntheticChildrenFrontEnd(valobj) {
+    Update();
+  }
+
+  size_t GetIndexOfChildWithName(const ConstString &name) override {
+    return formatters::ExtractIndexFromString(name.GetCString());
+  }
+
+  bool MightHaveChildren() override { return true; }
+  bool Update() override;
+  size_t CalculateNumChildren() override { return m_size; }
+  ValueObjectSP GetChildAtIndex(size_t idx) override;
+
+private:
+  size_t m_size = 0;
+  ValueObjectSP m_base_sp;
+};
+} // namespace
+
+bool VariantFrontEnd::Update() {
+  m_size = 0;
+  ValueObjectSP impl_sp(
+      m_backend.GetChildMemberWithName(ConstString("__impl"), true));
+  if (!impl_sp)
+    return false;
+
+  LibcxxVariantIndexValidity validity = LibcxxVariantGetIndexValidity(impl_sp);
+
+  if (validity == LibcxxVariantIndexValidity::INVALID)
+    return false;
+
+  if (validity == LibcxxVariantIndexValidity::NPOS)
+    return true;
+
+  m_size = 1;
+
+  return false;
+}
+
+ValueObjectSP VariantFrontEnd::GetChildAtIndex(size_t idx) {
+  if (idx >= m_size)
+    return ValueObjectSP();
+
+  ValueObjectSP impl_sp(
+      m_backend.GetChildMemberWithName(ConstString("__impl"), true));
+
+  auto optional_index_value = LibcxxVariantIndexValue(impl_sp);
+
+  if (!optional_index_value)
+    return ValueObjectSP();
+
+  uint64_t index_value = *optional_index_value;
+
+  ValueObjectSP nth_head = LibcxxVariantGetNthHead(impl_sp, index_value);
+
+  if (!nth_head)
+    return ValueObjectSP();
+
+  CompilerType head_type = nth_head->GetCompilerType();
+
+  if (!head_type)
+    return ValueObjectSP();
+
+  CompilerType template_type = head_type.GetTypeTemplateArgument(1);
+
+  if (!template_type)
+    return ValueObjectSP();
+
+  ValueObjectSP head_value(
+      nth_head->GetChildMemberWithName(ConstString("__value"), true));
+
+  if (!head_value)
+    return ValueObjectSP();
+
+  return head_value->Clone(ConstString(ConstString("Value").AsCString()));
+}
+
+SyntheticChildrenFrontEnd *
+formatters::LibcxxVariantFrontEndCreator(CXXSyntheticChildren *,
+                                         lldb::ValueObjectSP valobj_sp) {
+  if (valobj_sp)
+    return new VariantFrontEnd(*valobj_sp);
+  return nullptr;
+}