[lldb][DataFormatters] Support newer _LIBCPP_COMPRESSED_PAIR layout (#155153)

Starting with https://github.com/llvm/llvm-project/pull/154686 the
compressed_pair children are now wrapped in an anonymous structure.

This patch adjusts the LLDB data-formatters to support that.

Outstanding questions:
1. Should GetChildMemberWithName look through anonymous structures? That
will break users most likely. But maybe introducing a new API is worth
it? Then we wouldnt have to do this awkward passing around of
`anon_struct_index`
2. Do we support the layout without the anonymous structure? It's not
too much added complexity. And we did release that version of libc++, so
there is code out there compiled against it. But there is no great way
of testing it (some of our macOS matrix bots do test it i suppose, but
not in a targeted way). We have the layout "simulator" tests for some of
the STL types which I will adjust.

1 files changed, 13 insertions, 16 deletions

diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp
index 41441df..8576696 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp
@@ -200,7 +200,8 @@ public:
   llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) override;
 
 private:
-  llvm::Expected<uint32_t> CalculateNumChildrenForOldCompressedPairLayout();
+  llvm::Expected<uint32_t>
+  CalculateNumChildrenForOldCompressedPairLayout(ValueObject &pair);
 
   /// Returns the ValueObject for the __tree_node type that
   /// holds the key/value pair of the node at index \ref idx.
@@ -254,16 +255,8 @@ lldb_private::formatters::LibcxxStdMapSyntheticFrontEnd::
 
 llvm::Expected<uint32_t>
 lldb_private::formatters::LibcxxStdMapSyntheticFrontEnd::
-    CalculateNumChildrenForOldCompressedPairLayout() {
-  ValueObjectSP node_sp(m_tree->GetChildMemberWithName("__pair3_"));
-  if (!node_sp)
-    return 0;
-
-  if (!isOldCompressedPairLayout(*node_sp))
-    return llvm::createStringError("Unexpected std::map layout: expected "
-                                   "old __compressed_pair layout.");
-
-  node_sp = GetFirstValueOfLibCXXCompressedPair(*node_sp);
+    CalculateNumChildrenForOldCompressedPairLayout(ValueObject &pair) {
+  auto node_sp = GetFirstValueOfLibCXXCompressedPair(pair);
 
   if (!node_sp)
     return 0;
@@ -281,12 +274,16 @@ llvm::Expected<uint32_t> lldb_private::formatters::
   if (m_tree == nullptr)
     return 0;
 
-  if (auto node_sp = m_tree->GetChildMemberWithName("__size_")) {
-    m_count = node_sp->GetValueAsUnsigned(0);
-    return m_count;
-  }
+  auto [size_sp, is_compressed_pair] = GetValueOrOldCompressedPair(
+      *m_tree, /*anon_struct_idx=*/2, "__size_", "__pair3_");
+  if (!size_sp)
+    return llvm::createStringError("Unexpected std::map layout");
 
-  return CalculateNumChildrenForOldCompressedPairLayout();
+  if (is_compressed_pair)
+    return CalculateNumChildrenForOldCompressedPairLayout(*size_sp);
+
+  m_count = size_sp->GetValueAsUnsigned(0);
+  return m_count;
 }
 
 ValueObjectSP