Index: test/clang-tidy/check_clang_tidy.py
===================================================================
--- test/clang-tidy/check_clang_tidy.py
+++ test/clang-tidy/check_clang_tidy.py
@@ -25,6 +25,7 @@
 """
 
 import argparse
+import os
 import re
 import subprocess
 import sys
@@ -35,9 +36,90 @@
     f.write(text)
     f.truncate()
 
+
+# Remove the contents of the CHECK lines to avoid CHECKs matching on
+# themselves.  We need to keep the comments to preserve line numbers while
+# avoiding empty lines which could potentially trigger formatting-related
+# checks.
+def clean_text(input_text):
+  return re.sub('// *CHECK-[A-Z-]*:[^\r\n]*', '//', input_text)
+
+
+def write_cleaned_header(input_file_path, temp_file_name, header_file_name):
+  src_path = os.path.join(os.path.dirname(input_file_path), header_file_name)
+  fixed_path = os.path.join(os.path.dirname(temp_file_name), header_file_name)
+  with open(src_path, 'r') as input_file:
+    cleaned_text = clean_text(input_file.read())
+  cleaned_path = fixed_path + '.orig'
+  write_file(cleaned_path, cleaned_text)
+  write_file(fixed_path, cleaned_text)
+  return cleaned_path, fixed_path, src_path
+
+
+def separate_output(clang_tidy_output, header_file_name, input_file_name):
+  input_file_name = os.path.basename(input_file_name)
+  input_file_output = ''
+  header_file_output = ''
+  input_messages = True
+  for line in clang_tidy_output.splitlines(True):
+    if input_messages:
+      if header_file_name in line:
+        input_messages = False
+        header_file_output += line
+      else:
+        input_file_output += line
+    else:
+      if input_file_name in line:
+        input_messages = True
+        input_file_output += line
+      else:
+        header_file_output += line
+  return header_file_output, input_file_output
+
+
+def try_run(args):
+  try:
+    process_output = \
+      subprocess.check_output(args, stderr=subprocess.STDOUT).decode()
+  except subprocess.CalledProcessError as e:
+    print('%s failed:\n%s' % (' '.join(args), e.output.decode()))
+    raise
+  return process_output
+
+
+def check_output_for_messages(messages_file, input_file_name):
+  try_run(
+    ['FileCheck', '-input-file=' + messages_file, input_file_name,
+       '-check-prefix=CHECK-MESSAGES',
+       '-implicit-check-not={{warning|error}}:'])
+
+
+def check_output_for_fixes(temp_file_name, input_file_name):
+  try_run(
+      ['FileCheck', '-input-file=' + temp_file_name, input_file_name,
+       '-check-prefix=CHECK-FIXES', '-strict-whitespace'])
+
+
+def has_checks(input_text):
+  has_check_fixes = input_text.find('CHECK-FIXES') >= 0
+  has_check_messages = input_text.find('CHECK-MESSAGES') >= 0
+  return has_check_fixes, has_check_messages
+
+
+def diff_source_files(original_file_name, temp_file_name):
+  try:
+    diff_output = subprocess.check_output(
+      ['diff', '-u', original_file_name, temp_file_name],
+      stderr=subprocess.STDOUT)
+  except subprocess.CalledProcessError as e:
+    diff_output = e.output
+  return diff_output
+
+
 def main():
   parser = argparse.ArgumentParser()
   parser.add_argument('-resource-dir')
+  parser.add_argument('--header-filter')
   parser.add_argument('input_file_name')
   parser.add_argument('check_name')
   parser.add_argument('temp_file_name')
@@ -45,6 +127,7 @@
   args, extra_args = parser.parse_known_args()
 
   resource_dir = args.resource_dir
+  header_filter = args.header_filter
   input_file_name = args.input_file_name
   check_name = args.check_name
   temp_file_name = args.temp_file_name
@@ -66,70 +149,64 @@
   with open(input_file_name, 'r') as input_file:
     input_text = input_file.read()
 
-  has_check_fixes = input_text.find('CHECK-FIXES') >= 0
-  has_check_messages = input_text.find('CHECK-MESSAGES') >= 0
+  has_check_fixes, has_check_messages = has_checks(input_text)
 
   if not has_check_fixes and not has_check_messages:
     sys.exit('Neither CHECK-FIXES nor CHECK-MESSAGES found in the input')
 
-  # Remove the contents of the CHECK lines to avoid CHECKs matching on
-  # themselves.  We need to keep the comments to preserve line numbers while
-  # avoiding empty lines which could potentially trigger formatting-related
-  # checks.
-  cleaned_test = re.sub('// *CHECK-[A-Z-]*:[^\r\n]*', '//', input_text)
-
+  cleaned_test = clean_text(input_text)
   write_file(temp_file_name, cleaned_test)
-
   original_file_name = temp_file_name + ".orig"
   write_file(original_file_name, cleaned_test)
 
-  args = ['clang-tidy', temp_file_name, '-fix', '--checks=-*,' + check_name] + \
-        clang_tidy_extra_args
+  cleaned_header_path = ''
+  fixed_header_path = ''
+  source_header_path = ''
+  if header_filter is not None:
+    cleaned_header_path, fixed_header_path, source_header_path = \
+      write_cleaned_header(input_file_name, temp_file_name, header_filter)
+    args = ['clang-tidy', '-header-filter=%s' % header_filter,
+            temp_file_name, '-fix', '--checks=-*,' + check_name] + \
+        clang_tidy_extra_args + [ '-I', '.' ]
+  else:
+    args = ['clang-tidy', temp_file_name, '-fix', '--checks=-*,' + check_name] + \
+          clang_tidy_extra_args
+
   print('Running ' + repr(args) + '...')
-  try:
-    clang_tidy_output = \
-        subprocess.check_output(args, stderr=subprocess.STDOUT).decode()
-  except subprocess.CalledProcessError as e:
-    print('clang-tidy failed:\n' + e.output.decode())
-    raise
+  clang_tidy_output = try_run(args)
 
   print('------------------------ clang-tidy output -----------------------\n' +
         clang_tidy_output +
         '\n------------------------------------------------------------------')
 
-  try:
-    diff_output = subprocess.check_output(
-        ['diff', '-u', original_file_name, temp_file_name],
-        stderr=subprocess.STDOUT)
-  except subprocess.CalledProcessError as e:
-    diff_output = e.output
+  diff_output = diff_source_files(original_file_name, temp_file_name)
+  if header_filter is not None:
+    diff_output += diff_source_files(cleaned_header_path, fixed_header_path)
 
   print('------------------------------ Fixes -----------------------------\n' +
         diff_output.decode() +
         '\n------------------------------------------------------------------')
 
   if has_check_fixes:
-    try:
-      subprocess.check_output(
-          ['FileCheck', '-input-file=' + temp_file_name, input_file_name,
-           '-check-prefix=CHECK-FIXES', '-strict-whitespace'],
-          stderr=subprocess.STDOUT)
-    except subprocess.CalledProcessError as e:
-      print('FileCheck failed:\n' + e.output.decode())
-      raise
+    if header_filter is not None:
+      check_output_for_fixes(fixed_header_path, source_header_path)
+    check_output_for_fixes(temp_file_name, input_file_name)
 
   if has_check_messages:
     messages_file = temp_file_name + '.msg'
-    write_file(messages_file, clang_tidy_output)
-    try:
-      subprocess.check_output(
-          ['FileCheck', '-input-file=' + messages_file, input_file_name,
-           '-check-prefix=CHECK-MESSAGES',
-           '-implicit-check-not={{warning|error}}:'],
-          stderr=subprocess.STDOUT)
-    except subprocess.CalledProcessError as e:
-      print('FileCheck failed:\n' + e.output.decode())
-      raise
+    if header_filter is not None:
+      header_messages_file = messages_file + '.h'
+      header_output, input_file_output = \
+        separate_output(clang_tidy_output, header_filter, input_file_name)
+      write_file(header_messages_file, header_output)
+      write_file(messages_file, input_file_output)
+
+      check_output_for_messages(messages_file, input_file_name)
+      check_output_for_messages(header_messages_file, source_header_path)
+    else:
+      write_file(messages_file, clang_tidy_output)
+      check_output_for_messages(messages_file, input_file_name)
+
 
 if __name__ == '__main__':
   main()
Index: test/clang-tidy/modernize-redundant-void-arg.h
===================================================================
--- /dev/null
+++ test/clang-tidy/modernize-redundant-void-arg.h
@@ -0,0 +1,8 @@
+#ifndef LLVM_CLANG_TOOLS_EXTRA_TEST_CLANG_TIDY_MODERNIZE_REDUNDANT_VOID_ARG_H
+#define LLVM_CLANG_TOOLS_EXTRA_TEST_CLANG_TIDY_MODERNIZE_REDUNDANT_VOID_ARG_H
+
+extern int foo(void);
+// CHECK-MESSAGES: :[[@LINE-1]]:16: warning: redundant void argument list in function declaration [modernize-redundant-void-arg]
+// CHECK-FIXES: {{^}}extern int foo();{{$}}
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_TEST_CLANG_TIDY_MODERNIZE_REDUNDANT_VOID_ARG_H
Index: test/clang-tidy/modernize-redundant-void-arg.cpp
===================================================================
--- test/clang-tidy/modernize-redundant-void-arg.cpp
+++ test/clang-tidy/modernize-redundant-void-arg.cpp
@@ -1,4 +1,6 @@
-// RUN: %check_clang_tidy %s modernize-redundant-void-arg %t
+// RUN: %check_clang_tidy --header-filter=modernize-redundant-void-arg.h %s modernize-redundant-void-arg %t
+
+#include "modernize-redundant-void-arg.h"
 
 #define NULL 0