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..d20744d631470c0fb7c9165828591c9bc115c917
--- /dev/null
+++ b/tools/clang_format_merge_driver/install_git_hook.py
@@ -0,0 +1,45 @@
+#!/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 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(
+        ['git', 'config', 'merge.clang-format.version'])
+    try:
+      if int(current_version) >= _VERSION:
+        print 'Skipping...'

[Nico, 2016/09/22 13:22:37]

this is probably fast enough that we could just unconditionally call `git
config` on every runhooks, then we don't need this versioning stuff.

Is it possible to write an absolute path for the driver path? Then the driver
could be in src/ too and we could write an absolute path to it. (And if we
config'd every runhooks, we'd even survive local repo moves as long as they're
followed by another runhook)

[dcheng, 2016/09/22 17:08:53]

Oops, I meant to remove this print anyway.

+        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(
+      ['git', 'config', 'merge.clang-format.name', 'clang-format merge driver'])

[Nico, 2016/09/22 13:22:37]

Is the cwd for running hooks guaranteed? Does this do the right thing if you're
not in src/ when running runhooks?

[dcheng, 2016/09/22 17:08:53]

That's why there's an os.chdir on line 16 =)

+  subprocess.check_call(['git', 'config', 'merge.clang-format.driver',
+                         'clang_format_merge_driver %O %A %B %P'])
+  subprocess.check_call(
+      ['git', 'config', 'merge.clang-format.recursive', 'binary'])
+  subprocess.check_call(
+      ['git', 'config', 'merge.clang-format.version', str(_VERSION)])
+
+
+if __name__ == '__main__':
+  sys.exit(main())