Index: clang-tidy/ClangTidy.h
===================================================================
--- clang-tidy/ClangTidy.h
+++ clang-tidy/ClangTidy.h
@@ -16,6 +16,7 @@
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Tooling/Refactoring.h"
+#include "clang/Tooling/Tooling.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/raw_ostream.h"
 #include <memory>
@@ -225,9 +226,7 @@
 /// \param Profile if provided, it enables check profile collection in
 /// MatchFinder, and will contain the result of the profile.
 void runClangTidy(clang::tidy::ClangTidyContext &Context,
-                  const tooling::CompilationDatabase &Compilations,
-                  ArrayRef<std::string> InputFiles,
-                  llvm::IntrusiveRefCntPtr<vfs::FileSystem> BaseFS,
+                  clang::tooling::ClangTool &Tool,
                   ProfileData *Profile = nullptr);
 
 // FIXME: This interface will need to be significantly extended to be useful.
@@ -238,7 +237,7 @@
 /// clang-format configuration file is found, the given \P FormatStyle is used.
 void handleErrors(ClangTidyContext &Context, bool Fix,
                   unsigned &WarningsAsErrorsCount,
-                  llvm::IntrusiveRefCntPtr<vfs::FileSystem> BaseFS);
+                  clang::tooling::ClangTool &Tool);
 
 /// \brief Serializes replacements into YAML and writes them to the specified
 /// output stream.
Index: clang-tidy/ClangTidy.cpp
===================================================================
--- clang-tidy/ClangTidy.cpp
+++ clang-tidy/ClangTidy.cpp
@@ -38,7 +38,6 @@
 #include "clang/Tooling/DiagnosticsYaml.h"
 #include "clang/Tooling/Refactoring.h"
 #include "clang/Tooling/ReplacementsYaml.h"
-#include "clang/Tooling/Tooling.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Signals.h"
 #include <algorithm>
@@ -89,9 +88,9 @@
 
 class ErrorReporter {
 public:
-  ErrorReporter(ClangTidyContext &Context, bool ApplyFixes,
-                llvm::IntrusiveRefCntPtr<vfs::FileSystem> BaseFS)
-      : Files(FileSystemOptions(), BaseFS), DiagOpts(new DiagnosticOptions()),
+  ErrorReporter(ClangTidyContext &Context, bool ApplyFixes, ClangTool &Tool)
+      : Files(FileSystemOptions(), Tool.getFiles().getVirtualFileSystem()),
+        DiagOpts(new DiagnosticOptions()),
         DiagPrinter(new TextDiagnosticPrinter(llvm::outs(), &*DiagOpts)),
         Diags(IntrusiveRefCntPtr<DiagnosticIDs>(new DiagnosticIDs), &*DiagOpts,
               DiagPrinter),
@@ -474,13 +473,8 @@
 }
 
 void runClangTidy(clang::tidy::ClangTidyContext &Context,
-                  const CompilationDatabase &Compilations,
-                  ArrayRef<std::string> InputFiles,
-                  llvm::IntrusiveRefCntPtr<vfs::FileSystem> BaseFS,
+                  ClangTool &Tool,
                   ProfileData *Profile) {
-  ClangTool Tool(Compilations, InputFiles,
-                 std::make_shared<PCHContainerOperations>(), BaseFS);
-
   // Add extra arguments passed by the clang-tidy command-line.
   ArgumentsAdjuster PerFileExtraArgumentsInserter =
       [&Context](const CommandLineArguments &Args, StringRef Filename) {
@@ -551,8 +545,8 @@
 
 void handleErrors(ClangTidyContext &Context, bool Fix,
                   unsigned &WarningsAsErrorsCount,
-                  llvm::IntrusiveRefCntPtr<vfs::FileSystem> BaseFS) {
-  ErrorReporter Reporter(Context, Fix, BaseFS);
+                  ClangTool &Tool) {
+  ErrorReporter Reporter(Context, Fix, Tool);
   vfs::FileSystem &FileSystem =
       *Reporter.getSourceManager().getFileManager().getVirtualFileSystem();
   auto InitialWorkingDir = FileSystem.getCurrentWorkingDirectory();
Index: clang-tidy/tool/CMakeLists.txt
===================================================================
--- clang-tidy/tool/CMakeLists.txt
+++ clang-tidy/tool/CMakeLists.txt
@@ -16,6 +16,7 @@
   clangAST
   clangASTMatchers
   clangBasic
+  clangFrontend
   clangTidy
   clangTidyAndroidModule
   clangTidyAbseilModule
Index: clang-tidy/tool/ClangTidyMain.cpp
===================================================================
--- clang-tidy/tool/ClangTidyMain.cpp
+++ clang-tidy/tool/ClangTidyMain.cpp
@@ -339,10 +339,8 @@
 
 llvm::IntrusiveRefCntPtr<vfs::FileSystem>
 getVfsOverlayFromFile(const std::string &OverlayFile) {
-  llvm::IntrusiveRefCntPtr<vfs::OverlayFileSystem> OverlayFS(
-      new vfs::OverlayFileSystem(vfs::getRealFileSystem()));
   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> Buffer =
-      OverlayFS->getBufferForFile(OverlayFile);
+      vfs::getRealFileSystem()->getBufferForFile(OverlayFile);
   if (!Buffer) {
     llvm::errs() << "Can't load virtual filesystem overlay file '"
                  << OverlayFile << "': " << Buffer.getError().message()
@@ -357,8 +355,7 @@
                  << OverlayFile << "'.\n";
     return nullptr;
   }
-  OverlayFS->pushOverlay(FS);
-  return OverlayFS;
+  return FS;
 }
 
 static int clangTidyMain(int argc, const char **argv) {
@@ -432,10 +429,10 @@
     llvm::cl::PrintHelpMessage(/*Hidden=*/false, /*Categorized=*/true);
     return 1;
   }
-  llvm::IntrusiveRefCntPtr<vfs::FileSystem> BaseFS(
-      VfsOverlay.empty() ? vfs::getRealFileSystem()
+  llvm::IntrusiveRefCntPtr<vfs::FileSystem> VirtualFileSystem(
+      VfsOverlay.empty() ? nullptr
                          : getVfsOverlayFromFile(VfsOverlay));
-  if (!BaseFS)
+  if (!VfsOverlay.empty() && !VirtualFileSystem)
     return 1;
 
   ProfileData Profile;
@@ -445,8 +442,10 @@
   llvm::InitializeAllAsmParsers();
 
   ClangTidyContext Context(std::move(OwningOptionsProvider));
-  runClangTidy(Context, OptionsParser.getCompilations(), PathList, BaseFS,
-               EnableCheckProfile ? &Profile : nullptr);
+  ClangTool Tool(OptionsParser.getCompilations(), PathList,
+                 std::make_shared<PCHContainerOperations>(),
+                 VirtualFileSystem, true);
+  runClangTidy(Context, Tool, EnableCheckProfile ? &Profile : nullptr);
   ArrayRef<ClangTidyError> Errors = Context.getErrors();
   bool FoundErrors =
       std::find_if(Errors.begin(), Errors.end(), [](const ClangTidyError &E) {
@@ -459,7 +458,7 @@
 
   // -fix-errors implies -fix.
   handleErrors(Context, (FixErrors || Fix) && !DisableFixes, WErrorCount,
-               BaseFS);
+               Tool);
 
   if (!ExportFixes.empty() && !Errors.empty()) {
     std::error_code EC;