Improve namespace lookup using .debug_names parent chain

lldb/source/Plugins/SymbolFile/DWARF/DWARFIndex.cpp

@@ -151,3 +151,19 @@ bool DWARFIndex::ProcessTypeDieMatchQuery(
     return true;
   return callback(die);
 }
+
+void DWARFIndex::GetNamespacesWithParents(
+    ConstString name, const CompilerDeclContext &parent_decl_ctx,
+    llvm::function_ref<bool(DWARFDIE die)> callback) {
+  GetNamespaces(name, [&](DWARFDIE die) {
+    return ProcessNamespaceDieMatchParents(parent_decl_ctx, die, callback);
+  });
+}
+
+bool DWARFIndex::ProcessNamespaceDieMatchParents(
+    const CompilerDeclContext &parent_decl_ctx, DWARFDIE die,
+    llvm::function_ref<bool(DWARFDIE die)> callback) {
+  if (!SymbolFileDWARF::DIEInDeclContext(parent_decl_ctx, die))
+    return true;
+  return callback(die);
+}

lldb/source/Plugins/SymbolFile/DWARF/DWARFIndex.h

@@ -71,6 +71,14 @@ class DWARFIndex {
   virtual void
   GetTypesWithQuery(TypeQuery &query,
                     llvm::function_ref<bool(DWARFDIE die)> callback);
+  /// Get namespace DIEs whose base name match \param name with \param
+  /// parent_decl_ctx in its decl parent chain.  A base implementation
+  /// is provided. Specializations should override this if they are able to
+  /// provide a faster implementation.
+  virtual void
+  GetNamespacesWithParents(ConstString name,
+                           const CompilerDeclContext &parent_decl_ctx,
+                           llvm::function_ref<bool(DWARFDIE die)> callback);
   virtual void
   GetFunctions(const Module::LookupInfo &lookup_info, SymbolFileDWARF &dwarf,
                const CompilerDeclContext &parent_decl_ctx,
@@ -127,6 +135,9 @@ class DWARFIndex {
   bool
   ProcessTypeDieMatchQuery(TypeQuery &query, DWARFDIE die,
                            llvm::function_ref<bool(DWARFDIE die)> callback);
+  bool ProcessNamespaceDieMatchParents(
+      const CompilerDeclContext &parent_decl_ctx, DWARFDIE die,
+      llvm::function_ref<bool(DWARFDIE die)> callback);
 };
 } // namespace dwarf
 } // namespace lldb_private::plugin

lldb/source/Plugins/SymbolFile/DWARF/DebugNamesDWARFIndex.cpp

@@ -565,6 +565,48 @@ void DebugNamesDWARFIndex::GetTypesWithQuery(
   m_fallback.GetTypesWithQuery(query, callback);
 }
 
+void DebugNamesDWARFIndex::GetNamespacesWithParents(
+    ConstString name, const CompilerDeclContext &parent_decl_ctx,
+    llvm::function_ref<bool(DWARFDIE die)> callback) {
+  std::vector<lldb_private::CompilerContext> parent_contexts =
+      parent_decl_ctx.GetCompilerContext();
+  if (parent_contexts.empty())
+    return GetNamespaces(name, callback);
+
+  llvm::SmallVector<CompilerContext> parent_named_contexts;
+  std::copy_if(parent_contexts.rbegin(), parent_contexts.rend(),
+               std::back_inserter(parent_named_contexts),
+               [](const CompilerContext &ctx) { return !ctx.name.IsEmpty(); });
+  for (const DebugNames::Entry &entry :
+       m_debug_names_up->equal_range(name.GetStringRef())) {
+    lldb_private::dwarf::Tag entry_tag = entry.tag();
+    if (entry_tag == DW_TAG_namespace ||
+        entry_tag == DW_TAG_imported_declaration) {
+      std::optional<llvm::SmallVector<Entry, 4>> parent_chain =
+          getParentChain(entry);
+      if (!parent_chain) {
+        // Fallback: use the base class implementation.
+        if (!ProcessEntry(entry, [&](DWARFDIE die) {
+              return ProcessNamespaceDieMatchParents(parent_decl_ctx, die,
+                                                     callback);
+            }))
+          return;
+        continue;
+      }
+
+      if (WithinParentChain(parent_named_contexts, *parent_chain) &&
+          !ProcessEntry(entry, [&](DWARFDIE die) {
+            // After .debug_names filtering still sending to base class for
+            // further filtering before calling the callback.
+            return ProcessNamespaceDieMatchParents(parent_decl_ctx, die,
+                                                   callback);
+          }))
+        return;
+    }
+  }
+  m_fallback.GetNamespacesWithParents(name, parent_decl_ctx, callback);
+}
+
 void DebugNamesDWARFIndex::GetFunctions(
     const Module::LookupInfo &lookup_info, SymbolFileDWARF &dwarf,
     const CompilerDeclContext &parent_decl_ctx,

lldb/source/Plugins/SymbolFile/DWARF/DebugNamesDWARFIndex.h

@@ -55,7 +55,9 @@ class DebugNamesDWARFIndex : public DWARFIndex {
   void
   GetTypesWithQuery(TypeQuery &query,
                     llvm::function_ref<bool(DWARFDIE die)> callback) override;
-
+  void GetNamespacesWithParents(
+      ConstString name, const CompilerDeclContext &parent_decl_ctx,
+      llvm::function_ref<bool(DWARFDIE die)> callback) override;
   void GetFunctions(const Module::LookupInfo &lookup_info,
                     SymbolFileDWARF &dwarf,
                     const CompilerDeclContext &parent_decl_ctx,

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

@@ -2899,7 +2899,7 @@ SymbolFileDWARF::FindNamespace(ConstString name,
   if (!DeclContextMatchesThisSymbolFile(parent_decl_ctx))
     return namespace_decl_ctx;
 
-  m_index->GetNamespaces(name, [&](DWARFDIE die) {
+  m_index->GetNamespacesWithParents(name, parent_decl_ctx, [&](DWARFDIE die) {
     if (!DIEInDeclContext(parent_decl_ctx, die, only_root_namespaces))
       return true; // The containing decl contexts don't match