[tools] add script to simplify backporting patch to Node.js

tools/release/backport_node.py

Index: tools/release/backport_node.py
diff --git a/tools/release/backport_node.py b/tools/release/backport_node.py
new file mode 100755
index 0000000000000000000000000000000000000000..61a931aa03452e18f07c55b63f0c7cf309ad648b
--- /dev/null
+++ b/tools/release/backport_node.py
@@ -0,0 +1,96 @@
+#!/usr/bin/env python
+# Copyright 2017 the V8 project authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""
+Use this script to cherry-pick a V8 commit to backport to a Node.js checkout.
+
+Requirements:
+  - Node.js checkout to backport to.
+  - V8 checkout that contains the commit to cherry-pick.
+
+Usage:
+  $ backport_node.py <path_to_v8> <path_to_node> <commit-hash>
+
+  This will apply the commit to <path_to_node>/deps/v8 and create a commit in
+  the Node.js checkout and copy over the original commit message.
+
+Optional flags:
+  --no-review  Run `gclient sync` on the V8 checkout before updating.
+"""
+
+import argparse
+import os
+import subprocess
+import sys
+
+TARGET_SUBDIR = os.path.join("deps", "v8")
+
+def CherryPick(options):
+  print ">> Apply patch."
+  patch = subprocess.Popen(["git", "diff-tree", "-p", options.commit],
+                           stdout=subprocess.PIPE, cwd=options.v8_path)
+  patch.wait()
+  try:
+    subprocess.check_output(["git", "apply", "-3", "--directory=%s" % TARGET_SUBDIR],
+                            stdin=patch.stdout, cwd=options.node_path)
+  except:
+    print ">> In another shell, please resolve patch conflicts"
+    print ">> and `git add` affected files."
+    print ">> Finally continue by entering RESOLVED."
+    while raw_input("[RESOLVED]") != "RESOLVED":
+      print ">> You need to type RESOLVED"
+
+def CreateCommit(options):
+  print ">> Creating commit."
+  # Find short hash from source.
+  shorthash = subprocess.check_output(
+      ["git", "rev-parse", "--short", options.commit],
+      cwd=options.v8_path).strip()
+
+  # Commit message
+  title = "deps: backport %s from upstream V8"  % shorthash
+  body = subprocess.check_output(
+      ["git", "log", options.commit, "-1", "--format=%B"],
+      cwd=options.v8_path).strip()
+  body = '\n'.join("    " + line for line in body.splitlines())
+
+  message = title + "\n\nOriginal commit message:\n\n" + body
+
+  # Create commit at target.
+  review_message = "" if options.no_review else "-e"
+  git_commands = [
+    ["git", "checkout", "-b", "backport_%s" % shorthash],  # new branch
+    ["git", "add", TARGET_SUBDIR],                         # add files
+    ["git", "commit", "-m", message, review_message]       # new commit
+  ]
+  for command in git_commands:
+    subprocess.check_call(command, cwd=options.node_path)
+
+def ParseOptions(args):
+  parser = argparse.ArgumentParser(description="Backport V8 commit to Node.js")
+  parser.add_argument("v8_path", help="Path to V8 checkout")
+  parser.add_argument("node_path", help="Path to Node.js checkout")
+  parser.add_argument("commit", help="Commit to backport")
+  parser.add_argument("--no-review", action="store_true",
+                      help="Skip editing commit message")
+  options = parser.parse_args(args)
+  options.v8_path = os.path.abspath(options.v8_path)
+  assert os.path.isdir(options.v8_path)
+  options.node_path = os.path.abspath(options.node_path)
+  assert os.path.isdir(options.node_path)
+  return options
+
+def Main(args):
+  options = ParseOptions(args)
+  try:
+    CherryPick(options)
+    CreateCommit(options)
+  except:
+    print ">> Failed. Resetting."
+    subprocess.check_output(["git", "reset", "--hard"], cwd=options.node_path)
+    raise
+
+if __name__ == "__main__":
+  Main(sys.argv[1:])