Index: clang-tidy/tool/run-clang-tidy.py
===================================================================
--- clang-tidy/tool/run-clang-tidy.py
+++ clang-tidy/tool/run-clang-tidy.py
@@ -75,8 +75,8 @@
 
 
 def get_tidy_invocation(f, clang_tidy_binary, checks, tmpdir, build_path,
-                        header_filter, extra_arg, extra_arg_before, quiet,
-                        config):
+                        vfsoverlay, header_filter, extra_arg, extra_arg_before,
+                        quiet, config):
   """Gets a command line for clang-tidy."""
   start = [clang_tidy_binary]
   if header_filter is not None:
@@ -98,6 +98,8 @@
   for arg in extra_arg_before:
       start.append('-extra-arg-before=%s' % arg)
   start.append('-p=' + build_path)
+  if vfsoverlay is not None:
+    start.append('-vfsoverlay=' + vfsoverlay)
   if quiet:
       start.append('-quiet')
   if config:
@@ -158,9 +160,10 @@
   while True:
     name = queue.get()
     invocation = get_tidy_invocation(name, args.clang_tidy_binary, args.checks,
-                                     tmpdir, build_path, args.header_filter,
-                                     args.extra_arg, args.extra_arg_before,
-                                     args.quiet, args.config)
+                                     tmpdir, build_path, args.vfsoverlay,
+                                     args.header_filter, args.extra_arg,
+                                     args.extra_arg_before, args.quiet,
+                                     args.config)
     sys.stdout.write(' '.join(invocation) + '\n')
     return_code = subprocess.call(invocation)
     if return_code != 0:
@@ -209,6 +212,9 @@
                       'code after applying fixes')
   parser.add_argument('-p', dest='build_path',
                       help='Path used to read a compile command database.')
+  parser.add_argument('-vfsoverlay', dest='vfsoverlay',
+                      help='Overlay the virtual filesystem described by file '
+                      'over the real file system.')
   parser.add_argument('-extra-arg', dest='extra_arg',
                       action='append', default=[],
                       help='Additional argument to append to the compiler '