Index: clang-tools-extra/trunk/clang-tidy/tool/run-clang-tidy.py
===================================================================
--- clang-tools-extra/trunk/clang-tidy/tool/run-clang-tidy.py
+++ clang-tools-extra/trunk/clang-tidy/tool/run-clang-tidy.py
@@ -36,6 +36,7 @@
 
 from __future__ import print_function
 import argparse
+import glob
 import json
 import multiprocessing
 import os
@@ -47,6 +48,7 @@
 import tempfile
 import threading
 import traceback
+import yaml
 
 
 def find_compilation_database(path):
@@ -89,6 +91,31 @@
   return start
 
 
+def merge_replacement_files(tmpdir, mergefile):
+  """Merge all replacement files in a directory into a single file"""
+  # The fixes suggested by clang-tidy >= 4.0.0 are given under
+  # the top level key 'Diagnostics' in the output yaml files
+  mergekey="Diagnostics"
+  merged=[]
+  for replacefile in glob.iglob(os.path.join(tmpdir, '*.yaml')):
+    content = yaml.safe_load(open(replacefile, 'r'))
+    if not content:
+      continue # Skip empty files.
+    merged.extend(content.get(mergekey, []))
+
+  if merged:
+    # MainSourceFile: The key is required by the definition inside
+    # include/clang/Tooling/ReplacementsYaml.h, but the value
+    # is actually never used inside clang-apply-replacements,
+    # so we set it to '' here.
+    output = { 'MainSourceFile': '', mergekey: merged }
+    with open(mergefile, 'w') as out:
+      yaml.safe_dump(output, out)
+  else:
+    # Empty the file:
+    open(mergefile, 'w').close()
+
+
 def check_clang_apply_replacements_binary(args):
   """Checks if invoking supplied clang-apply-replacements binary works."""
   try:
@@ -101,7 +128,7 @@
 
 
 def apply_fixes(args, tmpdir):
-  """Calls clang-apply-fixes on a given directory. Deletes the dir when done."""
+  """Calls clang-apply-fixes on a given directory."""
   invocation = [args.clang_apply_replacements_binary]
   if args.format:
     invocation.append('-format')
@@ -143,6 +170,9 @@
                       'headers to output diagnostics from. Diagnostics from '
                       'the main file of each translation unit are always '
                       'displayed.')
+  parser.add_argument('-export-fixes', metavar='filename', dest='export_fixes',
+                      help='Create a yaml file to store suggested fixes in, '
+                      'which can be applied with clang-apply-replacements.')
   parser.add_argument('-j', type=int, default=0,
                       help='number of tidy instances to be run in parallel.')
   parser.add_argument('files', nargs='*', default=['.*'],
@@ -194,7 +224,7 @@
     max_task = multiprocessing.cpu_count()
 
   tmpdir = None
-  if args.fix:
+  if args.fix or args.export_fixes:
     check_clang_apply_replacements_binary(args)
     tmpdir = tempfile.mkdtemp()
 
@@ -222,24 +252,32 @@
     # This is a sad hack. Unfortunately subprocess goes
     # bonkers with ctrl-c and we start forking merrily.
     print('\nCtrl-C detected, goodbye.')
-    if args.fix:
+    if tmpdir:
       shutil.rmtree(tmpdir)
     os.kill(0, 9)
 
+  return_code = 0
+  if args.export_fixes:
+    print('Writing fixes to ' + args.export_fixes + ' ...')
+    try:
+      merge_replacement_files(tmpdir, args.export_fixes)
+    except:
+      print('Error exporting fixes.\n', file=sys.stderr)
+      traceback.print_exc()
+      return_code=1
+
   if args.fix:
     print('Applying fixes ...')
-    successfully_applied = False
-
     try:
       apply_fixes(args, tmpdir)
-      successfully_applied = True
     except:
       print('Error applying fixes.\n', file=sys.stderr)
       traceback.print_exc()
+      return_code=1
 
+  if tmpdir:
     shutil.rmtree(tmpdir)
-    if not successfully_applied:
-      sys.exit(1)
+  sys.exit(return_code)
 
 if __name__ == '__main__':
   main()