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

[Felipe de Azevedo Piovezan via lldb-commits]

================
@@ -218,6 +219,106 @@ 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.
+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;
+
+  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 each entry, grab its parent chain and check if we have a match.
+  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.
+    std::optional<llvm::SmallVector<Entry, 4>> parent_chain =
+        getParentChain(entry, parent_names.size() + 1);
----------------
felipepiovezan wrote:

> Since we are only fetching the same number of items

Actually, rereading this portion of your comment, this is the faulty assumption. We are not fetching the same number of items, we are fetching +1 items.

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