[Lldb-commits] [lldb] [lldb][DWARFIndex] Use IDX_parent to implement GetFullyQualifiedType query (PR #79932)

[Adrian Prantl via lldb-commits]

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@@ -218,6 +219,104 @@ void DebugNamesDWARFIndex::GetCompleteObjCClass(
   m_fallback.GetCompleteObjCClass(class_name, must_be_implementation, callback);
 }
 
+namespace {
+using Entry = llvm::DWARFDebugNames::Entry;
+
+/// If `entry` and all of its parents have an `IDX_parent`, use that information
+/// to build and return a list of at most `max_parents` parent Entries.
+/// `entry` itself is not included in the list.
+/// If any parent does not have an `IDX_parent`, or the Entry data is corrupted,
+/// nullopt is returned.
+static std::optional<llvm::SmallVector<Entry, 4>>
+getParentChain(Entry entry, uint32_t max_parents) {
+  llvm::SmallVector<Entry, 4> parent_entries;
+
+  do {
+    if (!entry.hasParentInformation())
+      return std::nullopt;
+
+    llvm::Expected<std::optional<Entry>> parent = entry.getParentDIEEntry();
+    if (!parent) { // Bad data.
+      consumeError(parent.takeError());
+      return std::nullopt;
+    }
+
+    // Last parent in the chain
+    if (!parent->has_value())
+      break;
+
+    parent_entries.push_back(**parent);
+    entry = **parent;
+  } while (parent_entries.size() < max_parents);
+
+  return parent_entries;
+}
+} // namespace
+
+void DebugNamesDWARFIndex::GetFullyQualifiedType(
+    const DWARFDeclContext &context,
+    llvm::function_ref<bool(DWARFDIE die)> callback) {
+  if (context.GetSize() == 0)
+    return;
+
+  // Fallback: use the base class implementation.
+  auto fallback_impl = [&](const DebugNames::Entry &entry) {
+    return ProcessEntry(entry, [&](DWARFDIE die) {
+      return GetFullyQualifiedTypeImpl(context, die, callback);
+    });
+  };
+
+  llvm::StringRef leaf_name = context[0].name;
+  llvm::SmallVector<llvm::StringRef> parent_names;
+  for (auto idx : llvm::seq<int>(1, context.GetSize()))
+    parent_names.emplace_back(context[idx].name);
+
+  for (const DebugNames::Entry &entry :
+       m_debug_names_up->equal_range(leaf_name)) {
+    if (!isType(entry.tag()))
+      continue;
+
+    // Grab at most one extra parent, subsequent parents are not necessary to
+    // test equality.
+    auto parent_chain = getParentChain(entry, parent_names.size() + 1);
+
+    if (!parent_chain) {
+      if (!fallback_impl(entry))
+        return;
+      continue;
+    }
+
+    if (SameParentChain(parent_names, *parent_chain) &&
----------------
adrian-prantl wrote:

This might benefit fro a few high-level comments about what's happening in this loop?

https://github.com/llvm/llvm-project/pull/79932