[LLDB][NativePDB] Let native pdb use class layout in debug info.

Before, class layout in native pdb is not hooked up in [[https://github.com/llvm/llvm-project/blob/main/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp#L9375-L9380 | here]].
This changes hooked it up by refactoring SymbolFileNativePDB and PdbAstBuilder.
PdbIndex (corresponds to a single pdb file) is removed from PdbAstBuilder, so it
can only be accessed via SymbolFileNativePDB and we can construct PdbAstBuilder
with just TypeSystemClang.

Reviewed By: labath

Differential Revision: https://reviews.llvm.org/D134509

8 files changed, 432 insertions, 308 deletions

diff --git a/lldb/include/lldb/Symbol/TypeSystem.h b/lldb/include/lldb/Symbol/TypeSystem.h
index 769449a4933b..57bdfa5b626a 100644
--- a/lldb/include/lldb/Symbol/TypeSystem.h
+++ b/lldb/include/lldb/Symbol/TypeSystem.h
@@ -31,6 +31,9 @@ class DWARFASTParser;
 class PDBASTParser;
 
 namespace lldb_private {
+namespace npdb {
+  class PdbAstBuilder;
+} // namespace npdb
 
 /// A SmallBitVector that represents a set of source languages (\p
 /// lldb::LanguageType).  Each lldb::LanguageType is represented by
@@ -88,6 +91,7 @@ public:
 
   virtual DWARFASTParser *GetDWARFParser() { return nullptr; }
   virtual PDBASTParser *GetPDBParser() { return nullptr; }
+  virtual npdb::PdbAstBuilder *GetNativePDBParser() { return nullptr; }
 
   virtual SymbolFile *GetSymbolFile() const { return m_sym_file; }
 
@@ -366,7 +370,7 @@ public:
   LLVM_DUMP_METHOD virtual void
   dump(lldb::opaque_compiler_type_t type) const = 0;
 #endif
-  
+
   virtual void DumpValue(lldb::opaque_compiler_type_t type,
                          ExecutionContext *exe_ctx, Stream *s,
                          lldb::Format format, const DataExtractor &data,
diff --git a/lldb/source/Plugins/SymbolFile/NativePDB/PdbAstBuilder.cpp b/lldb/source/Plugins/SymbolFile/NativePDB/PdbAstBuilder.cpp
index ab467f20990c..2e17aa1260a8 100644
--- a/lldb/source/Plugins/SymbolFile/NativePDB/PdbAstBuilder.cpp
+++ b/lldb/source/Plugins/SymbolFile/NativePDB/PdbAstBuilder.cpp
@@ -24,6 +24,7 @@
 
 #include "PdbUtil.h"
 #include "UdtRecordCompleter.h"
+#include "SymbolFileNativePDB.h"
 
 using namespace lldb_private;
 using namespace lldb_private::npdb;
@@ -94,59 +95,6 @@ struct CreateMethodDecl : public TypeVisitorCallbacks {
 };
 } // namespace
 
-static llvm::Optional<PdbCompilandSymId> FindSymbolScope(PdbIndex &index,
-                                                         PdbCompilandSymId id) {
-  CVSymbol sym = index.ReadSymbolRecord(id);
-  if (symbolOpensScope(sym.kind())) {
-    // If this exact symbol opens a scope, we can just directly access its
-    // parent.
-    id.offset = getScopeParentOffset(sym);
-    // Global symbols have parent offset of 0.  Return llvm::None to indicate
-    // this.
-    if (id.offset == 0)
-      return llvm::None;
-    return id;
-  }
-
-  // Otherwise we need to start at the beginning and iterate forward until we
-  // reach (or pass) this particular symbol
-  CompilandIndexItem &cii = index.compilands().GetOrCreateCompiland(id.modi);
-  const CVSymbolArray &syms = cii.m_debug_stream.getSymbolArray();
-
-  auto begin = syms.begin();
-  auto end = syms.at(id.offset);
-  std::vector<PdbCompilandSymId> scope_stack;
-
-  while (begin != end) {
-    if (begin.offset() > id.offset) {
-      // We passed it.  We couldn't even find this symbol record.
-      lldbassert(false && "Invalid compiland symbol id!");
-      return llvm::None;
-    }
-
-    // We haven't found the symbol yet.  Check if we need to open or close the
-    // scope stack.
-    if (symbolOpensScope(begin->kind())) {
-      // We can use the end offset of the scope to determine whether or not
-      // we can just outright skip this entire scope.
-      uint32_t scope_end = getScopeEndOffset(*begin);
-      if (scope_end < id.offset) {
-        begin = syms.at(scope_end);
-      } else {
-        // The symbol we're looking for is somewhere in this scope.
-        scope_stack.emplace_back(id.modi, begin.offset());
-      }
-    } else if (symbolEndsScope(begin->kind())) {
-      scope_stack.pop_back();
-    }
-    ++begin;
-  }
-  if (scope_stack.empty())
-    return llvm::None;
-  // We have a match!  Return the top of the stack
-  return scope_stack.back();
-}
-
 static clang::TagTypeKind TranslateUdtKind(const TagRecord &cr) {
   switch (cr.Kind) {
   case TypeRecordKind::Class:
@@ -207,65 +155,11 @@ TranslateCallingConvention(llvm::codeview::CallingConvention conv) {
   }
 }
 
-static llvm::Optional<CVTagRecord>
-GetNestedTagDefinition(const NestedTypeRecord &Record,
-                       const CVTagRecord &parent, TpiStream &tpi) {
-  // An LF_NESTTYPE is essentially a nested typedef / using declaration, but it
-  // is also used to indicate the primary definition of a nested class.  That is
-  // to say, if you have:
-  // struct A {
-  //   struct B {};
-  //   using C = B;
-  // };
-  // Then in the debug info, this will appear as:
-  // LF_STRUCTURE `A::B` [type index = N]
-  // LF_STRUCTURE `A`
-  //   LF_NESTTYPE [name = `B`, index = N]
-  //   LF_NESTTYPE [name = `C`, index = N]
-  // In order to accurately reconstruct the decl context hierarchy, we need to
-  // know which ones are actual definitions and which ones are just aliases.
-
-  // If it's a simple type, then this is something like `using foo = int`.
-  if (Record.Type.isSimple())
-    return llvm::None;
-
-  CVType cvt = tpi.getType(Record.Type);
-
-  if (!IsTagRecord(cvt))
-    return llvm::None;
-
-  // If it's an inner definition, then treat whatever name we have here as a
-  // single component of a mangled name.  So we can inject it into the parent's
-  // mangled name to see if it matches.
-  CVTagRecord child = CVTagRecord::create(cvt);
-  std::string qname = std::string(parent.asTag().getUniqueName());
-  if (qname.size() < 4 || child.asTag().getUniqueName().size() < 4)
-    return llvm::None;
-
-  // qname[3] is the tag type identifier (struct, class, union, etc).  Since the
-  // inner tag type is not necessarily the same as the outer tag type, re-write
-  // it to match the inner tag type.
-  qname[3] = child.asTag().getUniqueName()[3];
-  std::string piece;
-  if (qname[3] == 'W')
-    piece = "4";
-  piece += Record.Name;
-  piece.push_back('@');
-  qname.insert(4, std::move(piece));
-  if (qname != child.asTag().UniqueName)
-    return llvm::None;
-
-  return std::move(child);
-}
-
 static bool IsAnonymousNamespaceName(llvm::StringRef name) {
   return name == "`anonymous namespace'" || name == "`anonymous-namespace'";
 }
 
-PdbAstBuilder::PdbAstBuilder(ObjectFile &obj, PdbIndex &index, TypeSystemClang &clang)
-    : m_index(index), m_clang(clang) {
-  BuildParentMap();
-}
+PdbAstBuilder::PdbAstBuilder(TypeSystemClang &clang) : m_clang(clang) {}
 
 lldb_private::CompilerDeclContext PdbAstBuilder::GetTranslationUnitDecl() {
   return ToCompilerDeclContext(*m_clang.GetTranslationUnitDecl());
@@ -273,6 +167,8 @@ lldb_private::CompilerDeclContext PdbAstBuilder::GetTranslationUnitDecl() {
 
 std::pair<clang::DeclContext *, std::string>
 PdbAstBuilder::CreateDeclInfoForType(const TagRecord &record, TypeIndex ti) {
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
   // FIXME: Move this to GetDeclContextContainingUID.
   if (!record.hasUniqueName())
     return CreateDeclInfoForUndecoratedName(record.Name);
@@ -297,8 +193,8 @@ PdbAstBuilder::CreateDeclInfoForType(const TagRecord &record, TypeIndex ti) {
   // If this type doesn't have a parent type in the debug info, then the best we
   // can do is to say that it's either a series of namespaces (if the scope is
   // non-empty), or the translation unit (if the scope is empty).
-  auto parent_iter = m_parent_types.find(ti);
-  if (parent_iter == m_parent_types.end()) {
+  llvm::Optional<TypeIndex> parent_index = pdb->GetParentType(ti);
+  if (!parent_index) {
     if (scopes.empty())
       return {context, uname};
 
@@ -322,7 +218,7 @@ PdbAstBuilder::CreateDeclInfoForType(const TagRecord &record, TypeIndex ti) {
   // recurse into our lazy type creation / AST reconstruction logic to get an
   // LLDB TypeSP for the parent.  This will cause the AST to automatically get
   // the right DeclContext created for any parent.
-  clang::QualType parent_qt = GetOrCreateType(parent_iter->second);
+  clang::QualType parent_qt = GetOrCreateType(*parent_index);
   if (parent_qt.isNull())
     return {nullptr, ""};
 
@@ -330,120 +226,6 @@ PdbAstBuilder::CreateDeclInfoForType(const TagRecord &record, TypeIndex ti) {
   return {context, uname};
 }
 
-void PdbAstBuilder::BuildParentMap() {
-  LazyRandomTypeCollection &types = m_index.tpi().typeCollection();
-
-  llvm::DenseMap<TypeIndex, TypeIndex> forward_to_full;
-  llvm::DenseMap<TypeIndex, TypeIndex> full_to_forward;
-
-  struct RecordIndices {
-    TypeIndex forward;
-    TypeIndex full;
-  };
-
-  llvm::StringMap<RecordIndices> record_indices;
-
-  for (auto ti = types.getFirst(); ti; ti = types.getNext(*ti)) {
-    CVType type = types.getType(*ti);
-    if (!IsTagRecord(type))
-      continue;
-
-    CVTagRecord tag = CVTagRecord::create(type);
-
-    RecordIndices &indices = record_indices[tag.asTag().getUniqueName()];
-    if (tag.asTag().isForwardRef())
-      indices.forward = *ti;
-    else
-      indices.full = *ti;
-
-    if (indices.full != TypeIndex::None() &&
-        indices.forward != TypeIndex::None()) {
-      forward_to_full[indices.forward] = indices.full;
-      full_to_forward[indices.full] = indices.forward;
-    }
-
-    // We're looking for LF_NESTTYPE records in the field list, so ignore
-    // forward references (no field list), and anything without a nested class
-    // (since there won't be any LF_NESTTYPE records).
-    if (tag.asTag().isForwardRef() || !tag.asTag().containsNestedClass())
-      continue;
-
-    struct ProcessTpiStream : public TypeVisitorCallbacks {
-      ProcessTpiStream(PdbIndex &index, TypeIndex parent,
-                       const CVTagRecord &parent_cvt,
-                       llvm::DenseMap<TypeIndex, TypeIndex> &parents)
-          : index(index), parents(parents), parent(parent),
-            parent_cvt(parent_cvt) {}
-
-      PdbIndex &index;
-      llvm::DenseMap<TypeIndex, TypeIndex> &parents;
-
-      unsigned unnamed_type_index = 1;
-      TypeIndex parent;
-      const CVTagRecord &parent_cvt;
-
-      llvm::Error visitKnownMember(CVMemberRecord &CVR,
-                                   NestedTypeRecord &Record) override {
-        std::string unnamed_type_name;
-        if (Record.Name.empty()) {
-          unnamed_type_name =
-              llvm::formatv("<unnamed-type-$S{0}>", unnamed_type_index).str();
-          Record.Name = unnamed_type_name;
-          ++unnamed_type_index;
-        }
-        llvm::Optional<CVTagRecord> tag =
-            GetNestedTagDefinition(Record, parent_cvt, index.tpi());
-        if (!tag)
-          return llvm::ErrorSuccess();
-
-        parents[Record.Type] = parent;
-        return llvm::ErrorSuccess();
-      }
-    };
-
-    CVType field_list_cvt = m_index.tpi().getType(tag.asTag().FieldList);
-    ProcessTpiStream process(m_index, *ti, tag, m_parent_types);
-    FieldListRecord field_list;
-    if (llvm::Error error = TypeDeserializer::deserializeAs<FieldListRecord>(
-            field_list_cvt, field_list))
-      llvm::consumeError(std::move(error));
-    if (llvm::Error error = visitMemberRecordStream(field_list.Data, process))
-      llvm::consumeError(std::move(error));
-  }
-
-  // Now that we know the forward -> full mapping of all type indices, we can
-  // re-write all the indices.  At the end of this process, we want a mapping
-  // consisting of fwd -> full and full -> full for all child -> parent indices.
-  // We can re-write the values in place, but for the keys, we must save them
-  // off so that we don't modify the map in place while also iterating it.
-  std::vector<TypeIndex> full_keys;
-  std::vector<TypeIndex> fwd_keys;
-  for (auto &entry : m_parent_types) {
-    TypeIndex key = entry.first;
-    TypeIndex value = entry.second;
-
-    auto iter = forward_to_full.find(value);
-    if (iter != forward_to_full.end())
-      entry.second = iter->second;
-
-    iter = forward_to_full.find(key);
-    if (iter != forward_to_full.end())
-      fwd_keys.push_back(key);
-    else
-      full_keys.push_back(key);
-  }
-  for (TypeIndex fwd : fwd_keys) {
-    TypeIndex full = forward_to_full[fwd];
-    m_parent_types[full] = m_parent_types[fwd];
-  }
-  for (TypeIndex full : full_keys) {
-    TypeIndex fwd = full_to_forward[full];
-    m_parent_types[fwd] = m_parent_types[full];
-  }
-
-  // Now that
-}
-
 static bool isLocalVariableType(SymbolKind K) {
   switch (K) {
   case S_REGISTER:
@@ -457,7 +239,10 @@ static bool isLocalVariableType(SymbolKind K) {
 }
 
 clang::Decl *PdbAstBuilder::GetOrCreateSymbolForId(PdbCompilandSymId id) {
-  CVSymbol cvs = m_index.ReadSymbolRecord(id);
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
+  CVSymbol cvs = index.ReadSymbolRecord(id);
 
   if (isLocalVariableType(cvs.kind())) {
     clang::DeclContext *scope = GetParentDeclContext(id);
@@ -534,6 +319,9 @@ clang::DeclContext *PdbAstBuilder::GetOrCreateDeclContextForUid(PdbSymUid uid) {
 
 std::pair<clang::DeclContext *, std::string>
 PdbAstBuilder::CreateDeclInfoForUndecoratedName(llvm::StringRef name) {
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
   MSVCUndecoratedNameParser parser(name);
   llvm::ArrayRef<MSVCUndecoratedNameSpecifier> specs = parser.GetSpecifiers();
 
@@ -547,7 +335,7 @@ PdbAstBuilder::CreateDeclInfoForUndecoratedName(llvm::StringRef name) {
   llvm::StringRef scope_name = specs.back().GetFullName();
 
   // It might be a class name, try that first.
-  std::vector<TypeIndex> types = m_index.tpi().findRecordsByName(scope_name);
+  std::vector<TypeIndex> types = index.tpi().findRecordsByName(scope_name);
   while (!types.empty()) {
     clang::QualType qt = GetOrCreateType(types.back());
     if (qt.isNull())
@@ -569,24 +357,27 @@ PdbAstBuilder::CreateDeclInfoForUndecoratedName(llvm::StringRef name) {
 clang::DeclContext *PdbAstBuilder::GetParentDeclContext(PdbSymUid uid) {
   // We must do this *without* calling GetOrCreate on the current uid, as
   // that would be an infinite recursion.
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex& index = pdb->GetIndex();
   switch (uid.kind()) {
   case PdbSymUidKind::CompilandSym: {
     llvm::Optional<PdbCompilandSymId> scope =
-        FindSymbolScope(m_index, uid.asCompilandSym());
+        pdb->FindSymbolScope(uid.asCompilandSym());
     if (scope)
       return GetOrCreateDeclContextForUid(*scope);
 
-    CVSymbol sym = m_index.ReadSymbolRecord(uid.asCompilandSym());
+    CVSymbol sym = index.ReadSymbolRecord(uid.asCompilandSym());
     return CreateDeclInfoForUndecoratedName(getSymbolName(sym)).first;
   }
   case PdbSymUidKind::Type: {
     // It could be a namespace, class, or global.  We don't support nested
     // functions yet.  Anyway, we just need to consult the parent type map.
     PdbTypeSymId type_id = uid.asTypeSym();
-    auto iter = m_parent_types.find(type_id.index);
-    if (iter == m_parent_types.end())
+    llvm::Optional<TypeIndex> parent_index = pdb->GetParentType(type_id.index);
+    if (!parent_index)
       return FromCompilerDeclContext(GetTranslationUnitDecl());
-    return GetOrCreateDeclContextForUid(PdbTypeSymId(iter->second));
+    return GetOrCreateDeclContextForUid(PdbTypeSymId(*parent_index));
   }
   case PdbSymUidKind::FieldListMember:
     // In this case the parent DeclContext is the one for the class that this
@@ -599,7 +390,7 @@ clang::DeclContext *PdbAstBuilder::GetParentDeclContext(PdbSymUid uid) {
     // that up in the TPI stream.  If it's found, it's a type, othewrise it's
     // a series of namespaces.
     // FIXME: do this.
-    CVSymbol global = m_index.ReadSymbolRecord(uid.asGlobalSym());
+    CVSymbol global = index.ReadSymbolRecord(uid.asGlobalSym());
     switch (global.kind()) {
     case SymbolKind::S_GDATA32:
     case SymbolKind::S_LDATA32:
@@ -651,19 +442,21 @@ bool PdbAstBuilder::CompleteTagDecl(clang::TagDecl &tag) {
     return true;
 
   PdbTypeSymId type_id = PdbSymUid(status.uid).asTypeSym();
-
-  lldbassert(IsTagRecord(type_id, m_index.tpi()));
+  PdbIndex &index = static_cast<SymbolFileNativePDB *>(
+                        m_clang.GetSymbolFile()->GetBackingSymbolFile())
+                        ->GetIndex();
+  lldbassert(IsTagRecord(type_id, index.tpi()));
 
   clang::QualType tag_qt = m_clang.getASTContext().getTypeDeclType(&tag);
   TypeSystemClang::SetHasExternalStorage(tag_qt.getAsOpaquePtr(), false);
 
   TypeIndex tag_ti = type_id.index;
-  CVType cvt = m_index.tpi().getType(tag_ti);
+  CVType cvt = index.tpi().getType(tag_ti);
   if (cvt.kind() == LF_MODIFIER)
     tag_ti = LookThroughModifierRecord(cvt);
 
-  PdbTypeSymId best_ti = GetBestPossibleDecl(tag_ti, m_index.tpi());
-  cvt = m_index.tpi().getType(best_ti.index);
+  PdbTypeSymId best_ti = GetBestPossibleDecl(tag_ti, index.tpi());
+  cvt = index.tpi().getType(best_ti.index);
   lldbassert(IsTagRecord(cvt));
 
   if (IsForwardRefUdt(cvt)) {
@@ -673,7 +466,7 @@ bool PdbAstBuilder::CompleteTagDecl(clang::TagDecl &tag) {
   }
 
   TypeIndex field_list_ti = GetFieldListIndex(cvt);
-  CVType field_list_cvt = m_index.tpi().getType(field_list_ti);
+  CVType field_list_cvt = index.tpi().getType(field_list_ti);
   if (field_list_cvt.kind() != LF_FIELDLIST)
     return false;
   FieldListRecord field_list;
@@ -684,7 +477,7 @@ bool PdbAstBuilder::CompleteTagDecl(clang::TagDecl &tag) {
   // Visit all members of this class, then perform any finalization necessary
   // to complete the class.
   CompilerType ct = ToCompilerType(tag_qt);
-  UdtRecordCompleter completer(best_ti, ct, tag, *this, m_index,
+  UdtRecordCompleter completer(best_ti, ct, tag, *this, index,
                                m_cxx_record_map);
   llvm::Error error =
       llvm::codeview::visitMemberRecordStream(field_list.Data, completer);
@@ -900,7 +693,10 @@ PdbAstBuilder::GetOrCreateVariableDecl(PdbCompilandSymId scope_id,
   if (!scope)
     return nullptr;
 
-  CVSymbol sym = m_index.ReadSymbolRecord(var_id);
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
+  CVSymbol sym = index.ReadSymbolRecord(var_id);
   return CreateVariableDecl(PdbSymUid(var_id), sym, *scope);
 }
 
@@ -908,7 +704,10 @@ clang::VarDecl *PdbAstBuilder::GetOrCreateVariableDecl(PdbGlobalSymId var_id) {
   if (clang::Decl *decl = TryGetDecl(var_id))
     return llvm::dyn_cast<clang::VarDecl>(decl);
 
-  CVSymbol sym = m_index.ReadSymbolRecord(var_id);
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
+  CVSymbol sym = index.ReadSymbolRecord(var_id);
   auto context = FromCompilerDeclContext(GetTranslationUnitDecl());
   return CreateVariableDecl(PdbSymUid(var_id), sym, *context);
 }
@@ -918,7 +717,10 @@ PdbAstBuilder::GetOrCreateTypedefDecl(PdbGlobalSymId id) {
   if (clang::Decl *decl = TryGetDecl(id))
     return llvm::dyn_cast<clang::TypedefNameDecl>(decl);
 
-  CVSymbol sym = m_index.ReadSymbolRecord(id);
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
+  CVSymbol sym = index.ReadSymbolRecord(id);
   lldbassert(sym.kind() == S_UDT);
   UDTSym udt = llvm::cantFail(SymbolDeserializer::deserializeAs<UDTSym>(sym));
 
@@ -950,7 +752,10 @@ clang::QualType PdbAstBuilder::CreateType(PdbTypeSymId type) {
   if (type.index.isSimple())
     return CreateSimpleType(type.index);
 
-  CVType cvt = m_index.tpi().getType(type.index);
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
+  CVType cvt = index.tpi().getType(type.index);
 
   if (cvt.kind() == LF_MODIFIER) {
     ModifierRecord modifier;
@@ -1006,7 +811,10 @@ clang::QualType PdbAstBuilder::GetOrCreateType(PdbTypeSymId type) {
   if (iter != m_uid_to_type.end())
     return iter->second;
 
-  PdbTypeSymId best_type = GetBestPossibleDecl(type, m_index.tpi());
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
+  PdbTypeSymId best_type = GetBestPossibleDecl(type, index.tpi());
 
   clang::QualType qt;
   if (best_type.index != type.index) {
@@ -1026,7 +834,7 @@ clang::QualType PdbAstBuilder::GetOrCreateType(PdbTypeSymId type) {
     return {};
 
   m_uid_to_type[toOpaqueUid(type)] = qt;
-  if (IsTagRecord(type, m_index.tpi())) {
+  if (IsTagRecord(type, index.tpi())) {
     clang::TagDecl *tag = qt->getAsTagDecl();
     lldbassert(m_decl_to_status.count(tag) == 0);
 
@@ -1045,6 +853,9 @@ PdbAstBuilder::CreateFunctionDecl(PdbCompilandSymId func_id,
                                   bool is_inline, clang::DeclContext *parent) {
   clang::FunctionDecl *function_decl = nullptr;
   if (parent->isRecord()) {
+    SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+        m_clang.GetSymbolFile()->GetBackingSymbolFile());
+    PdbIndex &index = pdb->GetIndex();
     clang::QualType parent_qt = llvm::cast<clang::TypeDecl>(parent)
                                     ->getTypeForDecl()
                                     ->getCanonicalTypeInternal();
@@ -1058,29 +869,29 @@ PdbAstBuilder::CreateFunctionDecl(PdbCompilandSymId func_id,
       }
     }
 
-    CVType cvt = m_index.tpi().getType(func_ti);
+    CVType cvt = index.tpi().getType(func_ti);
     MemberFunctionRecord func_record(static_cast<TypeRecordKind>(cvt.kind()));
     llvm::cantFail(TypeDeserializer::deserializeAs<MemberFunctionRecord>(
         cvt, func_record));
     TypeIndex class_index = func_record.getClassType();
 
-    CVType parent_cvt = m_index.tpi().getType(class_index);
+    CVType parent_cvt = index.tpi().getType(class_index);
     TagRecord tag_record = CVTagRecord::create(parent_cvt).asTag();
     // If it's a forward reference, try to get the real TypeIndex.
     if (tag_record.isForwardRef()) {
       llvm::Expected<TypeIndex> eti =
-          m_index.tpi().findFullDeclForForwardRef(class_index);
+          index.tpi().findFullDeclForForwardRef(class_index);
       if (eti) {
-        tag_record = CVTagRecord::create(m_index.tpi().getType(*eti)).asTag();
+        tag_record = CVTagRecord::create(index.tpi().getType(*eti)).asTag();
       }
     }
     if (!tag_record.FieldList.isSimple()) {
-      CVType field_list_cvt = m_index.tpi().getType(tag_record.FieldList);
+      CVType field_list_cvt = index.tpi().getType(tag_record.FieldList);
       FieldListRecord field_list;
       if (llvm::Error error = TypeDeserializer::deserializeAs<FieldListRecord>(
               field_list_cvt, field_list))
         llvm::consumeError(std::move(error));
-      CreateMethodDecl process(m_index, m_clang, func_ti, function_decl,
+      CreateMethodDecl process(index, m_clang, func_ti, function_decl,
                                parent_opaque_ty, func_name, func_ct);
       if (llvm::Error err = visitMemberRecordStream(field_list.Data, process))
         llvm::consumeError(std::move(err));
@@ -1107,8 +918,11 @@ PdbAstBuilder::CreateFunctionDecl(PdbCompilandSymId func_id,
 
 clang::FunctionDecl *
 PdbAstBuilder::GetOrCreateInlinedFunctionDecl(PdbCompilandSymId inlinesite_id) {
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
   CompilandIndexItem *cii =
-      m_index.compilands().GetCompiland(inlinesite_id.modi);
+      index.compilands().GetCompiland(inlinesite_id.modi);
   CVSymbol sym = cii->m_debug_stream.readSymbolAtOffset(inlinesite_id.offset);
   InlineSiteSym inline_site(static_cast<SymbolRecordKind>(sym.kind()));
   cantFail(SymbolDeserializer::deserializeAs<InlineSiteSym>(sym, inline_site));
@@ -1145,7 +959,10 @@ clang::FunctionDecl *
 PdbAstBuilder::CreateFunctionDeclFromId(PdbTypeSymId func_tid,
                                         PdbCompilandSymId func_sid) {
   lldbassert(func_tid.is_ipi);
-  CVType func_cvt = m_index.ipi().getType(func_tid.index);
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
+  CVType func_cvt = index.ipi().getType(func_tid.index);
   llvm::StringRef func_name;
   TypeIndex func_ti;
   clang::DeclContext *parent = nullptr;
@@ -1167,7 +984,7 @@ PdbAstBuilder::CreateFunctionDeclFromId(PdbTypeSymId func_tid,
     func_ti = fir.getFunctionType();
     parent = FromCompilerDeclContext(GetTranslationUnitDecl());
     if (!fir.ParentScope.isNoneType()) {
-      CVType parent_cvt = m_index.ipi().getType(fir.ParentScope);
+      CVType parent_cvt = index.ipi().getType(fir.ParentScope);
       if (parent_cvt.kind() == LF_STRING_ID) {
         StringIdRecord sir;
         cantFail(
@@ -1205,7 +1022,10 @@ PdbAstBuilder::GetOrCreateFunctionDecl(PdbCompilandSymId func_id) {
     context_name = tag->getQualifiedNameAsString();
   }
 
-  CVSymbol cvs = m_index.ReadSymbolRecord(func_id);
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
+  CVSymbol cvs = index.ReadSymbolRecord(func_id);
   ProcSym proc(static_cast<SymbolRecordKind>(cvs.kind()));
   llvm::cantFail(SymbolDeserializer::deserializeAs<ProcSym>(cvs, proc));
 
@@ -1245,7 +1065,10 @@ PdbAstBuilder::GetOrCreateFunctionDecl(PdbCompilandSymId func_id) {
 void PdbAstBuilder::CreateFunctionParameters(PdbCompilandSymId func_id,
                                              clang::FunctionDecl &function_decl,
                                              uint32_t param_count) {
-  CompilandIndexItem *cii = m_index.compilands().GetCompiland(func_id.modi);
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
+  CompilandIndexItem *cii = index.compilands().GetCompiland(func_id.modi);
   CVSymbolArray scope =
       cii->m_debug_stream.getSymbolArrayForScope(func_id.offset);
 
@@ -1340,7 +1163,10 @@ clang::QualType PdbAstBuilder::CreateEnumType(PdbTypeSymId id,
 clang::QualType PdbAstBuilder::CreateArrayType(const ArrayRecord &ar) {
   clang::QualType element_type = GetOrCreateType(ar.ElementType);
 
-  uint64_t element_size = GetSizeOfType({ar.ElementType}, m_index.tpi());
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
+  uint64_t element_size = GetSizeOfType({ar.ElementType}, index.tpi());
   if (element_type.isNull() || element_size == 0)
     return {};
   uint64_t element_count = ar.Size / element_size;
@@ -1353,7 +1179,10 @@ clang::QualType PdbAstBuilder::CreateArrayType(const ArrayRecord &ar) {
 clang::QualType PdbAstBuilder::CreateFunctionType(
     TypeIndex args_type_idx, TypeIndex return_type_idx,
     llvm::codeview::CallingConvention calling_convention) {
-  TpiStream &stream = m_index.tpi();
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
+  TpiStream &stream = index.tpi();
   CVType args_cvt = stream.getType(args_type_idx);
   ArgListRecord args;
   llvm::cantFail(
@@ -1405,8 +1234,11 @@ static bool isBlockDecl(clang::DeclContext &context) {
 
 void PdbAstBuilder::ParseAllNamespacesPlusChildrenOf(
     llvm::Optional<llvm::StringRef> parent) {
-  TypeIndex ti{m_index.tpi().TypeIndexBegin()};
-  for (const CVType &cvt : m_index.tpi().typeArray()) {
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
+  TypeIndex ti{index.tpi().TypeIndexBegin()};
+  for (const CVType &cvt : index.tpi().typeArray()) {
     PdbTypeSymId tid{ti};
     ++ti;
 
@@ -1439,9 +1271,9 @@ void PdbAstBuilder::ParseAllNamespacesPlusChildrenOf(
     }
   }
 
-  uint32_t module_count = m_index.dbi().modules().getModuleCount();
+  uint32_t module_count = index.dbi().modules().getModuleCount();
   for (uint16_t modi = 0; modi < module_count; ++modi) {
-    CompilandIndexItem &cii = m_index.compilands().GetOrCreateCompiland(modi);
+    CompilandIndexItem &cii = index.compilands().GetOrCreateCompiland(modi);
     const CVSymbolArray &symbols = cii.m_debug_stream.getSymbolArray();
     auto iter = symbols.begin();
     while (iter != symbols.end()) {
@@ -1495,11 +1327,14 @@ static CVSymbolArray skipFunctionParameters(clang::Decl &decl,
 }
 
 void PdbAstBuilder::ParseBlockChildren(PdbCompilandSymId block_id) {
-  CVSymbol sym = m_index.ReadSymbolRecord(block_id);
+  SymbolFileNativePDB *pdb = static_cast<SymbolFileNativePDB *>(
+      m_clang.GetSymbolFile()->GetBackingSymbolFile());
+  PdbIndex &index = pdb->GetIndex();
+  CVSymbol sym = index.ReadSymbolRecord(block_id);
   lldbassert(sym.kind() == S_GPROC32 || sym.kind() == S_LPROC32 ||
              sym.kind() == S_BLOCK32 || sym.kind() == S_INLINESITE);
   CompilandIndexItem &cii =
-      m_index.compilands().GetOrCreateCompiland(block_id.modi);
+      index.compilands().GetOrCreateCompiland(block_id.modi);
   CVSymbolArray symbols =
       cii.m_debug_stream.getSymbolArrayForScope(block_id.offset);
 
diff --git a/lldb/source/Plugins/SymbolFile/NativePDB/PdbAstBuilder.h b/lldb/source/Plugins/SymbolFile/NativePDB/PdbAstBuilder.h
index e4d9c6e6e0bb..b94176e815e0 100644
--- a/lldb/source/Plugins/SymbolFile/NativePDB/PdbAstBuilder.h
+++ b/lldb/source/Plugins/SymbolFile/NativePDB/PdbAstBuilder.h
@@ -51,7 +51,7 @@ struct DeclStatus {
 class PdbAstBuilder {
 public:
   // Constructors and Destructors
-  PdbAstBuilder(ObjectFile &obj, PdbIndex &index, TypeSystemClang &clang);
+  PdbAstBuilder(TypeSystemClang &clang);
 
   lldb_private::CompilerDeclContext GetTranslationUnitDecl();
 
@@ -83,7 +83,7 @@ public:
   clang::DeclContext *FromCompilerDeclContext(CompilerDeclContext context);
 
   TypeSystemClang &clang() { return m_clang; }
-  ClangASTImporter &importer() { return m_importer; }
+  ClangASTImporter &GetClangASTImporter() { return m_importer; }
 
   void Dump(Stream &stream);
 
@@ -126,19 +126,16 @@ private:
   void ParseDeclsForSimpleContext(clang::DeclContext &context);
   void ParseBlockChildren(PdbCompilandSymId block_id);
 
-  void BuildParentMap();
   std::pair<clang::DeclContext *, std::string>
   CreateDeclInfoForType(const llvm::codeview::TagRecord &record, TypeIndex ti);
   std::pair<clang::DeclContext *, std::string>
   CreateDeclInfoForUndecoratedName(llvm::StringRef uname);
   clang::QualType CreateSimpleType(TypeIndex ti);
 
-  PdbIndex &m_index;
   TypeSystemClang &m_clang;
 
   ClangASTImporter m_importer;
 
-  llvm::DenseMap<TypeIndex, TypeIndex> m_parent_types;
   llvm::DenseMap<clang::Decl *, DeclStatus> m_decl_to_status;
   llvm::DenseMap<lldb::user_id_t, clang::Decl *> m_uid_to_decl;
   llvm::DenseMap<lldb::user_id_t, clang::QualType> m_uid_to_type;
diff --git a/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp b/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
index 304b64904352..a34ce045e675 100644
--- a/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
+++ b/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
@@ -8,12 +8,6 @@
 
 #include "SymbolFileNativePDB.h"
 
-#include "clang/AST/Attr.h"
-#include "clang/AST/CharUnits.h"
-#include "clang/AST/Decl.h"
-#include "clang/AST/DeclCXX.h"
-#include "clang/AST/Type.h"
-
 #include "Plugins/ExpressionParser/Clang/ClangUtil.h"
 #include "Plugins/Language/CPlusPlus/MSVCUndecoratedNameParser.h"
 #include "Plugins/ObjectFile/PDB/ObjectFilePDB.h"
@@ -59,7 +53,6 @@
 #include "llvm/Support/MemoryBuffer.h"
 
 #include "DWARFLocationExpression.h"
-#include "PdbAstBuilder.h"
 #include "PdbSymUid.h"
 #include "PdbUtil.h"
 #include "UdtRecordCompleter.h"
@@ -233,6 +226,57 @@ static bool IsClassRecord(TypeLeafKind kind) {
   }
 }
 
+static llvm::Optional<CVTagRecord>
+GetNestedTagDefinition(const NestedTypeRecord &Record,
+                       const CVTagRecord &parent, TpiStream &tpi) {
+  // An LF_NESTTYPE is essentially a nested typedef / using declaration, but it
+  // is also used to indicate the primary definition of a nested class.  That is
+  // to say, if you have:
+  // struct A {
+  //   struct B {};
+  //   using C = B;
+  // };
+  // Then in the debug info, this will appear as:
+  // LF_STRUCTURE `A::B` [type index = N]
+  // LF_STRUCTURE `A`
+  //   LF_NESTTYPE [name = `B`, index = N]
+  //   LF_NESTTYPE [name = `C`, index = N]
+  // In order to accurately reconstruct the decl context hierarchy, we need to
+  // know which ones are actual definitions and which ones are just aliases.
+
+  // If it's a simple type, then this is something like `using foo = int`.
+  if (Record.Type.isSimple())
+    return llvm::None;
+
+  CVType cvt = tpi.getType(Record.Type);
+
+  if (!IsTagRecord(cvt))
+    return llvm::None;
+
+  // If it's an inner definition, then treat whatever name we have here as a
+  // single component of a mangled name.  So we can inject it into the parent's
+  // mangled name to see if it matches.
+  CVTagRecord child = CVTagRecord::create(cvt);
+  std::string qname = std::string(parent.asTag().getUniqueName());
+  if (qname.size() < 4 || child.asTag().getUniqueName().size() < 4)
+    return llvm::None;
+
+  // qname[3] is the tag type identifier (struct, class, union, etc).  Since the
+  // inner tag type is not necessarily the same as the outer tag type, re-write
+  // it to match the inner tag type.
+  qname[3] = child.asTag().getUniqueName()[3];
+  std::string piece;
+  if (qname[3] == 'W')
+    piece = "4";
+  piece += Record.Name;
+  piece.push_back('@');
+  qname.insert(4, std::move(piece));
+  if (qname != child.asTag().UniqueName)
+    return llvm::None;
+
+  return std::move(child);
+}
+
 void SymbolFileNativePDB::Initialize() {
   PluginManager::RegisterPlugin(GetPluginNameStatic(),
                                 GetPluginDescriptionStatic(), CreateInstance,
@@ -311,9 +355,7 @@ void SymbolFileNativePDB::InitializeObject() {
                    "Failed to initialize");
   } else {
     ts_or_err->SetSymbolFile(this);
-    auto *clang = llvm::cast_or_null<TypeSystemClang>(&ts_or_err.get());
-    lldbassert(clang);
-    m_ast = std::make_unique<PdbAstBuilder>(*m_objfile_sp, *m_index, *clang);
+    BuildParentMap();
   }
 }
 
@@ -338,6 +380,10 @@ Block &SymbolFileNativePDB::CreateBlock(PdbCompilandSymId block_id) {
   CompUnitSP comp_unit = GetOrCreateCompileUnit(*cii);
   lldb::user_id_t opaque_block_uid = toOpaqueUid(block_id);
   BlockSP child_block = std::make_shared<Block>(opaque_block_uid);
+  auto ts_or_err = GetTypeSystemForLanguage(comp_unit->GetLanguage());
+  if (auto err = ts_or_err.takeError())
+    return *child_block;
+  PdbAstBuilder* ast_builder = ts_or_err->GetNativePDBParser();
 
   switch (sym.kind()) {
   case S_GPROC32:
@@ -381,7 +427,7 @@ Block &SymbolFileNativePDB::CreateBlock(PdbCompilandSymId block_id) {
           block_base + block.CodeSize, func_base);
     }
     parent_block.AddChild(child_block);
-    m_ast->GetOrCreateBlockDecl(block_id);
+    ast_builder->GetOrCreateBlockDecl(block_id);
     m_blocks.insert({opaque_block_uid, child_block});
     break;
   }
@@ -392,7 +438,7 @@ Block &SymbolFileNativePDB::CreateBlock(PdbCompilandSymId block_id) {
     std::shared_ptr<InlineSite> inline_site = m_inline_sites[opaque_block_uid];
     Block &parent_block = GetOrCreateBlock(inline_site->parent_id);
     parent_block.AddChild(child_block);
-    m_ast->GetOrCreateInlinedFunctionDecl(block_id);
+    ast_builder->GetOrCreateInlinedFunctionDecl(block_id);
     // Copy ranges from InlineSite to Block.
     for (size_t i = 0; i < inline_site->ranges.GetSize(); ++i) {
       auto *entry = inline_site->ranges.GetEntryAtIndex(i);
@@ -453,7 +499,10 @@ lldb::FunctionSP SymbolFileNativePDB::CreateFunction(PdbCompilandSymId func_id,
 
   comp_unit.AddFunction(func_sp);
 
-  m_ast->GetOrCreateFunctionDecl(func_id);
+  auto ts_or_err = GetTypeSystemForLanguage(comp_unit.GetLanguage());
+  if (auto err = ts_or_err.takeError())
+    return func_sp;
+  ts_or_err->GetNativePDBParser()->GetOrCreateFunctionDecl(func_id);
 
   return func_sp;
 }
@@ -746,12 +795,15 @@ TypeSP SymbolFileNativePDB::CreateAndCacheType(PdbTypeSymId type_id) {
   }
 
   PdbTypeSymId best_decl_id = full_decl_uid ? *full_decl_uid : type_id;
-
-  clang::QualType qt = m_ast->GetOrCreateType(best_decl_id);
+  auto ts_or_err = GetTypeSystemForLanguage(lldb::eLanguageTypeC_plus_plus);
+  if (auto err = ts_or_err.takeError())
+    return nullptr;
+  PdbAstBuilder* ast_builder = ts_or_err->GetNativePDBParser();
+  clang::QualType qt = ast_builder->GetOrCreateType(best_decl_id);
   if (qt.isNull())
     return nullptr;
 
-  TypeSP result = CreateType(best_decl_id, m_ast->ToCompilerType(qt));
+  TypeSP result = CreateType(best_decl_id, ast_builder->ToCompilerType(qt));
   if (!result)
     return nullptr;
 
@@ -840,8 +892,10 @@ VariableSP SymbolFileNativePDB::CreateGlobalVariable(PdbGlobalSymId var_id) {
   SymbolFileTypeSP type_sp =
       std::make_shared<SymbolFileType>(*this, toOpaqueUid(tid));
   Variable::RangeList ranges;
-
-  m_ast->GetOrCreateVariableDecl(var_id);
+  auto ts_or_err = GetTypeSystemForLanguage(comp_unit->GetLanguage());
+  if (auto err = ts_or_err.takeError())
+    return nullptr;
+  ts_or_err->GetNativePDBParser()->GetOrCreateVariableDecl(var_id);
 
   ModuleSP module_sp = GetObjectFile()->GetModule();
   DWARFExpressionList location(
@@ -941,10 +995,14 @@ Block &SymbolFileNativePDB::GetOrCreateBlock(PdbCompilandSymId block_id) {
 
 void SymbolFileNativePDB::ParseDeclsForContext(
     lldb_private::CompilerDeclContext decl_ctx) {
-  clang::DeclContext *context = m_ast->FromCompilerDeclContext(decl_ctx);
+  TypeSystem* ts_or_err = decl_ctx.GetTypeSystem();
+  if (!ts_or_err)
+    return;
+  PdbAstBuilder* ast_builder = ts_or_err->GetNativePDBParser();
+  clang::DeclContext *context = ast_builder->FromCompilerDeclContext(decl_ctx);
   if (!context)
     return;
-  m_ast->ParseDeclsForContext(*context);
+  ast_builder->ParseDeclsForContext(*context);
 }
 
 lldb::CompUnitSP SymbolFileNativePDB::ParseCompileUnitAtIndex(uint32_t index) {
@@ -1563,7 +1621,16 @@ size_t SymbolFileNativePDB::ParseSymbolArrayInScope(
   return count;
 }
 
-void SymbolFileNativePDB::DumpClangAST(Stream &s) { m_ast->Dump(s); }
+void SymbolFileNativePDB::DumpClangAST(Stream &s) {
+  auto ts_or_err = GetTypeSystemForLanguage(eLanguageTypeC_plus_plus);
+  if (!ts_or_err)
+    return;
+  TypeSystemClang *clang =
+      llvm::dyn_cast_or_null<TypeSystemClang>(&ts_or_err.get());
+  if (!clang)
+    return;
+  clang->GetNativePDBParser()->Dump(s);
+}
 
 void SymbolFileNativePDB::FindGlobalVariables(
     ConstString name, const CompilerDeclContext &parent_decl_ctx,
@@ -1767,8 +1834,12 @@ VariableSP SymbolFileNativePDB::CreateLocalVariable(PdbCompilandSymId scope_id,
       toOpaqueUid(var_id), name.c_str(), name.c_str(), sftype, var_scope,
       &block, scope_ranges, &decl, var_info.location, external, artificial,
       location_is_constant_data, static_member);
-  if (!is_param)
-    m_ast->GetOrCreateVariableDecl(scope_id, var_id);
+  if (!is_param) {
+    auto ts_or_err = GetTypeSystemForLanguage(comp_unit_sp->GetLanguage());
+    if (auto err = ts_or_err.takeError())
+      return nullptr;
+    ts_or_err->GetNativePDBParser()->GetOrCreateVariableDecl(scope_id, var_id);
+  }
   m_local_variables[toOpaqueUid(var_id)] = var_sp;
   return var_sp;
 }
@@ -1790,7 +1861,10 @@ TypeSP SymbolFileNativePDB::CreateTypedef(PdbGlobalSymId id) {
 
   TypeSP target_type = GetOrCreateType(udt.Type);
 
-  (void)m_ast->GetOrCreateTypedefDecl(id);
+  auto ts_or_err = GetTypeSystemForLanguage(lldb::eLanguageTypeC_plus_plus);
+  if (auto err = ts_or_err.takeError())
+    return nullptr;
+  ts_or_err->GetNativePDBParser()->GetOrCreateTypedefDecl(id);
 
   Declaration decl;
   return std::make_shared<lldb_private::Type>(
@@ -1924,28 +1998,38 @@ size_t SymbolFileNativePDB::ParseVariablesForContext(const SymbolContext &sc) {
 }
 
 CompilerDecl SymbolFileNativePDB::GetDeclForUID(lldb::user_id_t uid) {
-  if (auto decl = m_ast->GetOrCreateDeclForUid(uid))
-    return *decl;
-  else
+  auto ts_or_err = GetTypeSystemForLanguage(lldb::eLanguageTypeC_plus_plus);
+  if (auto err = ts_or_err.takeError())
     return CompilerDecl();
+  if (auto decl = ts_or_err->GetNativePDBParser()->GetOrCreateDeclForUid(uid))
+    return *decl;
+  return CompilerDecl();
 }
 
 CompilerDeclContext
 SymbolFileNativePDB::GetDeclContextForUID(lldb::user_id_t uid) {
+  auto ts_or_err = GetTypeSystemForLanguage(lldb::eLanguageTypeC_plus_plus);
+  if (auto err = ts_or_err.takeError())
+    return {};
+  PdbAstBuilder *ast_builder = ts_or_err->GetNativePDBParser();
   clang::DeclContext *context =
-      m_ast->GetOrCreateDeclContextForUid(PdbSymUid(uid));
+      ast_builder->GetOrCreateDeclContextForUid(PdbSymUid(uid));
   if (!context)
     return {};
 
-  return m_ast->ToCompilerDeclContext(*context);
+  return ast_builder->ToCompilerDeclContext(*context);
 }
 
 CompilerDeclContext
 SymbolFileNativePDB::GetDeclContextContainingUID(lldb::user_id_t uid) {
-  clang::DeclContext *context = m_ast->GetParentDeclContext(PdbSymUid(uid));
+  auto ts_or_err = GetTypeSystemForLanguage(lldb::eLanguageTypeC_plus_plus);
+  if (auto err = ts_or_err.takeError())
+    return CompilerDeclContext();
+  PdbAstBuilder *ast_builder = ts_or_err->GetNativePDBParser();
+  clang::DeclContext *context = ast_builder->GetParentDeclContext(PdbSymUid(uid));
   if (!context)
     return CompilerDeclContext();
-  return m_ast->ToCompilerDeclContext(*context);
+  return ast_builder->ToCompilerDeclContext(*context);
 }
 
 Type *SymbolFileNativePDB::ResolveTypeUID(lldb::user_id_t type_uid) {
@@ -1977,12 +2061,23 @@ SymbolFileNativePDB::GetDynamicArrayInfoForUID(
   return llvm::None;
 }
 
-
 bool SymbolFileNativePDB::CompleteType(CompilerType &compiler_type) {
+  std::lock_guard<std::recursive_mutex> guard(GetModuleMutex());
+
+  TypeSystemClang *clang_type_system =
+      llvm::dyn_cast_or_null<TypeSystemClang>(compiler_type.GetTypeSystem());
+  if (!clang_type_system)
+    return false;
+
+  PdbAstBuilder *ast_builder =
+      static_cast<PdbAstBuilder *>(clang_type_system->GetNativePDBParser());
+  if (ast_builder &&
+      ast_builder->GetClangASTImporter().CanImport(compiler_type))
+    return ast_builder->GetClangASTImporter().CompleteType(compiler_type);
   clang::QualType qt =
       clang::QualType::getFromOpaquePtr(compiler_type.GetOpaqueQualType());
 
-  return m_ast->CompleteType(qt);
+  return ast_builder->CompleteType(qt);
 }
 
 void SymbolFileNativePDB::GetTypes(lldb_private::SymbolContextScope *sc_scope,
@@ -2009,3 +2104,176 @@ uint64_t SymbolFileNativePDB::GetDebugInfoSize() {
   // PDB files are a separate file that contains all debug info.
   return m_index->pdb().getFileSize();
 }
+
+void SymbolFileNativePDB::BuildParentMap() {
+  LazyRandomTypeCollection &types = m_index->tpi().typeCollection();
+
+  llvm::DenseMap<TypeIndex, TypeIndex> forward_to_full;
+  llvm::DenseMap<TypeIndex, TypeIndex> full_to_forward;
+
+  struct RecordIndices {
+    TypeIndex forward;
+    TypeIndex full;
+  };
+
+  llvm::StringMap<RecordIndices> record_indices;
+
+  for (auto ti = types.getFirst(); ti; ti = types.getNext(*ti)) {
+    CVType type = types.getType(*ti);
+    if (!IsTagRecord(type))
+      continue;
+
+    CVTagRecord tag = CVTagRecord::create(type);
+
+    RecordIndices &indices = record_indices[tag.asTag().getUniqueName()];
+    if (tag.asTag().isForwardRef())
+      indices.forward = *ti;
+    else
+      indices.full = *ti;
+
+    if (indices.full != TypeIndex::None() &&
+        indices.forward != TypeIndex::None()) {
+      forward_to_full[indices.forward] = indices.full;
+      full_to_forward[indices.full] = indices.forward;
+    }
+
+    // We're looking for LF_NESTTYPE records in the field list, so ignore
+    // forward references (no field list), and anything without a nested class
+    // (since there won't be any LF_NESTTYPE records).
+    if (tag.asTag().isForwardRef() || !tag.asTag().containsNestedClass())
+      continue;
+
+    struct ProcessTpiStream : public TypeVisitorCallbacks {
+      ProcessTpiStream(PdbIndex &index, TypeIndex parent,
+                       const CVTagRecord &parent_cvt,
+                       llvm::DenseMap<TypeIndex, TypeIndex> &parents)
+          : index(index), parents(parents), parent(parent),
+            parent_cvt(parent_cvt) {}
+
+      PdbIndex &index;
+      llvm::DenseMap<TypeIndex, TypeIndex> &parents;
+
+      unsigned unnamed_type_index = 1;
+      TypeIndex parent;
+      const CVTagRecord &parent_cvt;
+
+      llvm::Error visitKnownMember(CVMemberRecord &CVR,
+                                   NestedTypeRecord &Record) override {
+        std::string unnamed_type_name;
+        if (Record.Name.empty()) {
+          unnamed_type_name =
+              llvm::formatv("<unnamed-type-$S{0}>", unnamed_type_index).str();
+          Record.Name = unnamed_type_name;
+          ++unnamed_type_index;
+        }
+        llvm::Optional<CVTagRecord> tag =
+            GetNestedTagDefinition(Record, parent_cvt, index.tpi());
+        if (!tag)
+          return llvm::ErrorSuccess();
+
+        parents[Record.Type] = parent;
+        return llvm::ErrorSuccess();
+      }
+    };
+
+    CVType field_list_cvt = m_index->tpi().getType(tag.asTag().FieldList);
+    ProcessTpiStream process(*m_index, *ti, tag, m_parent_types);
+    FieldListRecord field_list;
+    if (llvm::Error error = TypeDeserializer::deserializeAs<FieldListRecord>(
+            field_list_cvt, field_list))
+      llvm::consumeError(std::move(error));
+    if (llvm::Error error = visitMemberRecordStream(field_list.Data, process))
+      llvm::consumeError(std::move(error));
+  }
+
+  // Now that we know the forward -> full mapping of all type indices, we can
+  // re-write all the indices.  At the end of this process, we want a mapping
+  // consisting of fwd -> full and full -> full for all child -> parent indices.
+  // We can re-write the values in place, but for the keys, we must save them
+  // off so that we don't modify the map in place while also iterating it.
+  std::vector<TypeIndex> full_keys;
+  std::vector<TypeIndex> fwd_keys;
+  for (auto &entry : m_parent_types) {
+    TypeIndex key = entry.first;
+    TypeIndex value = entry.second;
+
+    auto iter = forward_to_full.find(value);
+    if (iter != forward_to_full.end())
+      entry.second = iter->second;
+
+    iter = forward_to_full.find(key);
+    if (iter != forward_to_full.end())
+      fwd_keys.push_back(key);
+    else
+      full_keys.push_back(key);
+  }
+  for (TypeIndex fwd : fwd_keys) {
+    TypeIndex full = forward_to_full[fwd];
+    m_parent_types[full] = m_parent_types[fwd];
+  }
+  for (TypeIndex full : full_keys) {
+    TypeIndex fwd = full_to_forward[full];
+    m_parent_types[fwd] = m_parent_types[full];
+  }
+}
+
+llvm::Optional<PdbCompilandSymId>
+SymbolFileNativePDB::FindSymbolScope(PdbCompilandSymId id) {
+  CVSymbol sym = m_index->ReadSymbolRecord(id);
+  if (symbolOpensScope(sym.kind())) {
+    // If this exact symbol opens a scope, we can just directly access its
+    // parent.
+    id.offset = getScopeParentOffset(sym);
+    // Global symbols have parent offset of 0.  Return llvm::None to indicate
+    // this.
+    if (id.offset == 0)
+      return llvm::None;
+    return id;
+  }
+
+  // Otherwise we need to start at the beginning and iterate forward until we
+  // reach (or pass) this particular symbol
+  CompilandIndexItem &cii = m_index->compilands().GetOrCreateCompiland(id.modi);
+  const CVSymbolArray &syms = cii.m_debug_stream.getSymbolArray();
+
+  auto begin = syms.begin();
+  auto end = syms.at(id.offset);
+  std::vector<PdbCompilandSymId> scope_stack;
+
+  while (begin != end) {
+    if (begin.offset() > id.offset) {
+      // We passed it.  We couldn't even find this symbol record.
+      lldbassert(false && "Invalid compiland symbol id!");
+      return llvm::None;
+    }
+
+    // We haven't found the symbol yet.  Check if we need to open or close the
+    // scope stack.
+    if (symbolOpensScope(begin->kind())) {
+      // We can use the end offset of the scope to determine whether or not
+      // we can just outright skip this entire scope.
+      uint32_t scope_end = getScopeEndOffset(*begin);
+      if (scope_end < id.offset) {
+        begin = syms.at(scope_end);
+      } else {
+        // The symbol we're looking for is somewhere in this scope.
+        scope_stack.emplace_back(id.modi, begin.offset());
+      }
+    } else if (symbolEndsScope(begin->kind())) {
+      scope_stack.pop_back();
+    }
+    ++begin;
+  }
+  if (scope_stack.empty())
+    return llvm::None;
+  // We have a match!  Return the top of the stack
+  return scope_stack.back();
+}
+
+llvm::Optional<llvm::codeview::TypeIndex>
+SymbolFileNativePDB::GetParentType(llvm::codeview::TypeIndex ti) {
+  auto parent_iter = m_parent_types.find(ti);
+  if (parent_iter == m_parent_types.end())
+    return llvm::None;
+  return parent_iter->second;
+}
diff --git a/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.h b/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.h
index 4bb37d9e7675..51ed1212d53b 100644
--- a/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.h
+++ b/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.h
@@ -19,6 +19,7 @@
 
 #include "CompileUnitIndex.h"
 #include "PdbIndex.h"
+#include "PdbAstBuilder.h"
 
 namespace clang {
 class TagDecl;
@@ -37,7 +38,6 @@ struct UnionRecord;
 namespace lldb_private {
 
 namespace npdb {
-class PdbAstBuilder;
 
 class SymbolFileNativePDB : public SymbolFileCommon {
   friend class UdtRecordCompleter;
@@ -137,6 +137,8 @@ public:
   void FindFunctions(const RegularExpression &regex, bool include_inlines,
                      SymbolContextList &sc_list) override;
 
+  llvm::Optional<PdbCompilandSymId> FindSymbolScope(PdbCompilandSymId id);
+
   void FindTypes(ConstString name, const CompilerDeclContext &parent_decl_ctx,
                  uint32_t max_matches,
                  llvm::DenseSet<SymbolFile *> &searched_symbol_files,
@@ -158,8 +160,13 @@ public:
   llvm::pdb::PDBFile &GetPDBFile() { return m_index->pdb(); }
   const llvm::pdb::PDBFile &GetPDBFile() const { return m_index->pdb(); }
 
+  PdbIndex &GetIndex() { return *m_index; };
+
   void DumpClangAST(Stream &s) override;
 
+  llvm::Optional<llvm::codeview::TypeIndex>
+  GetParentType(llvm::codeview::TypeIndex ti);
+
 private:
   struct LineTableEntryComparator {
     bool operator()(const lldb_private::LineTable::Entry &lhs,
@@ -180,6 +187,8 @@ private:
     InlineSite(PdbCompilandSymId parent_id) : parent_id(parent_id){};
   };
 
+  void BuildParentMap();
+
   uint32_t CalculateNumCompileUnits() override;
 
   lldb::CompUnitSP ParseCompileUnitAtIndex(uint32_t index) override;
@@ -262,8 +271,6 @@ private:
   std::unique_ptr<llvm::pdb::PDBFile> m_file_up;
   std::unique_ptr<PdbIndex> m_index;
 
-  std::unique_ptr<PdbAstBuilder> m_ast;
-
   llvm::DenseMap<lldb::user_id_t, lldb::VariableSP> m_global_vars;
   llvm::DenseMap<lldb::user_id_t, lldb::VariableSP> m_local_variables;
   llvm::DenseMap<lldb::user_id_t, lldb::BlockSP> m_blocks;
@@ -271,6 +278,8 @@ private:
   llvm::DenseMap<lldb::user_id_t, lldb::CompUnitSP> m_compilands;
   llvm::DenseMap<lldb::user_id_t, lldb::TypeSP> m_types;
   llvm::DenseMap<lldb::user_id_t, std::shared_ptr<InlineSite>> m_inline_sites;
+  llvm::DenseMap<llvm::codeview::TypeIndex, llvm::codeview::TypeIndex>
+      m_parent_types;
 };
 
 } // namespace npdb
diff --git a/lldb/source/Plugins/SymbolFile/NativePDB/UdtRecordCompleter.cpp b/lldb/source/Plugins/SymbolFile/NativePDB/UdtRecordCompleter.cpp
index c0308196c760..16e9990ff3f0 100644
--- a/lldb/source/Plugins/SymbolFile/NativePDB/UdtRecordCompleter.cpp
+++ b/lldb/source/Plugins/SymbolFile/NativePDB/UdtRecordCompleter.cpp
@@ -312,6 +312,6 @@ void UdtRecordCompleter::complete() {
   TypeSystemClang::CompleteTagDeclarationDefinition(m_derived_ct);
 
   if (auto *record_decl = llvm::dyn_cast<clang::CXXRecordDecl>(&m_tag_decl)) {
-    m_ast_builder.importer().SetRecordLayout(record_decl, m_layout);
+    m_ast_builder.GetClangASTImporter().SetRecordLayout(record_decl, m_layout);
   }
 }
diff --git a/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp b/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp
index 7e0a19c6b8bf..4adf653b6c50 100644
--- a/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp
+++ b/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp
@@ -73,6 +73,7 @@
 #include "Plugins/LanguageRuntime/ObjC/ObjCLanguageRuntime.h"
 #include "Plugins/SymbolFile/DWARF/DWARFASTParserClang.h"
 #include "Plugins/SymbolFile/PDB/PDBASTParser.h"
+#include "Plugins/SymbolFile/NativePDB/PdbAstBuilder.h"
 
 #include <cstdio>
 
@@ -9364,6 +9365,12 @@ PDBASTParser *TypeSystemClang::GetPDBParser() {
   return m_pdb_ast_parser_up.get();
 }
 
+npdb::PdbAstBuilder *TypeSystemClang::GetNativePDBParser() {
+  if (!m_native_pdb_ast_parser_up)
+    m_native_pdb_ast_parser_up = std::make_unique<npdb::PdbAstBuilder>(*this);
+  return m_native_pdb_ast_parser_up.get();
+}
+
 bool TypeSystemClang::LayoutRecordType(
     const clang::RecordDecl *record_decl, uint64_t &bit_size,
     uint64_t &alignment,
@@ -9377,6 +9384,8 @@ bool TypeSystemClang::LayoutRecordType(
     importer = &m_dwarf_ast_parser_up->GetClangASTImporter();
   if (!importer && m_pdb_ast_parser_up)
     importer = &m_pdb_ast_parser_up->GetClangASTImporter();
+  if (!importer && m_native_pdb_ast_parser_up)
+    importer = &m_native_pdb_ast_parser_up->GetClangASTImporter();
   if (!importer)
     return false;
 
diff --git a/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.h b/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.h
index ff8e12e821d1..7c045fdf088c 100644
--- a/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.h
+++ b/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.h
@@ -443,6 +443,7 @@ public:
   // TypeSystem methods
   DWARFASTParser *GetDWARFParser() override;
   PDBASTParser *GetPDBParser() override;
+  npdb::PdbAstBuilder *GetNativePDBParser() override;
 
   // TypeSystemClang callbacks for external source lookups.
   void CompleteTagDecl(clang::TagDecl *);
@@ -1071,6 +1072,7 @@ private:
   std::unique_ptr<clang::ModuleMap> m_module_map_up;
   std::unique_ptr<DWARFASTParserClang> m_dwarf_ast_parser_up;
   std::unique_ptr<PDBASTParser> m_pdb_ast_parser_up;
+  std::unique_ptr<npdb::PdbAstBuilder> m_native_pdb_ast_parser_up;
   std::unique_ptr<clang::MangleContext> m_mangle_ctx_up;
   uint32_t m_pointer_byte_size = 0;
   bool m_ast_owned = false;