DEPS hook for installing the clang-format merge driver.

tools/clang_format_merge_driver/install_git_hook.py

Index: tools/clang_format_merge_driver/install_git_hook.py
diff --git a/tools/clang_format_merge_driver/install_git_hook.py b/tools/clang_format_merge_driver/install_git_hook.py
new file mode 100755
index 0000000000000000000000000000000000000000..c4d67b584eaa0fd13ec37d0f62731d11a1583168
--- /dev/null
+++ b/tools/clang_format_merge_driver/install_git_hook.py
@@ -0,0 +1,56 @@
+#!/usr/bin/env python
+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+"""Hook to install the git config for using the clang-format merge driver."""
+
+import os
+import subprocess
+import sys
+
+_VERSION = 1
+
+
+def BuildGitCmd(*args):
+  cmd = []
+  if sys.platform == 'win32':
+    cmd.append('git.bat')

[Nico, 2016/09/23 18:05:35]

will this work on cygwin? (which seems like an argument for shell=True --
alternatively this could detect cygwin and reexec itself under cmd like
https://cs.chromium.org/chromium/tools/depot_tools/win_toolchain/get_toolchai...
but just shell=true on win is probably easier)

[dcheng, 2016/09/23 18:46:55]

sys.platform == 'cygwin' on cygwin, so it's no problem:
https://docs.python.org/2/library/sys.html

+  else:
+    cmd.append('git')
+  cmd.extend(args)
+  return cmd
+
+
+def main():
+  # Assume that the script always lives somewhere inside the git repo.
+  os.chdir(os.path.dirname(os.path.abspath(__file__)))
+
+  try:
+    current_version = subprocess.check_output(
+        BuildGitCmd('config', 'merge.clang-format.version'))
+    try:
+      if int(current_version) >= _VERSION:
+        return
+    except ValueError:
+      # Not parseable for whatever reason: reinstall the config.
+      pass
+  except subprocess.CalledProcessError:
+    # git returned a non-zero return code, the config probably doesn't exist.
+    pass
+
+  print 'Installing clang-format merge driver into .git/config...'
+
+  subprocess.check_call(
+      BuildGitCmd('config', 'merge.clang-format.name',
+                  'clang-format merge driver'))
+  subprocess.check_call(
+      BuildGitCmd('config', 'merge.clang-format.driver',
+                  'clang_format_merge_driver %O %A %B %P'))
+  subprocess.check_call(
+      BuildGitCmd('config', 'merge.clang-format.recursive', 'binary'))
+  subprocess.check_call(
+      BuildGitCmd('config', 'merge.clang-format.version', str(_VERSION)))
+
+
+if __name__ == '__main__':
+  sys.exit(main())