Update target branch before backporting PR

tools/backport_pr.py

@@ -1,93 +1,94 b''
 #!/usr/bin/env python
 """
 Backport pull requests to a particular branch.
 
 Usage: backport_pr.py branch PR
 
 e.g.:
 
     backport_pr.py 0.13.1 123
 
 to backport PR #123 onto branch 0.13.1
 
 """
 
 from __future__ import print_function
 
 import os
 import sys
 from subprocess import Popen, PIPE, check_call, check_output
 from urllib import urlopen
 
 from gh_api import get_pull_request, get_pull_request_files
 
 def find_rejects(root='.'):
     for dirname, dirs, files in os.walk(root):
         for fname in files:
             if fname.endswith('.rej'):
                 yield os.path.join(dirname, fname)
 
 def get_current_branch():
     branches = check_output(['git', 'branch'])
     for branch in branches.splitlines():
         if branch.startswith('*'):
             return branch[1:].strip()
 
 def backport_pr(branch, num, project='ipython/ipython'):
     current_branch = get_current_branch()
     if branch != current_branch:
         check_call(['git', 'checkout', branch])
+    check_call(['git', 'pull'])
     pr = get_pull_request(project, num, auth=True)
     files = get_pull_request_files(project, num, auth=True)
     patch_url = pr['patch_url']
     title = pr['title']
     description = pr['body']
     fname = "PR%i.patch" % num
     if os.path.exists(fname):
         print("using patch from {fname}".format(**locals()))
         with open(fname) as f:
             patch = f.read()
     else:
         req = urlopen(patch_url)
         patch = req.read()
     
     msg = "Backport PR #%i: %s" % (num, title) + '\n\n' + description
     check = Popen(['git', 'apply', '--check', '--verbose'], stdin=PIPE)
     a,b = check.communicate(patch)
     
     if check.returncode:
         print("patch did not apply, saving to {fname}".format(**locals()))
         print("edit {fname} until `cat {fname} | git apply --check` succeeds".format(**locals()))
         print("then run tools/backport_pr.py {num} again".format(**locals()))
         if not os.path.exists(fname):
             with open(fname, 'wb') as f:
                 f.write(patch)
         return 1
     
     p = Popen(['git', 'apply'], stdin=PIPE)
     a,b = p.communicate(patch)
     
     filenames = [ f['filename'] for f in files ]
 
     commit = Popen(['git', 'commit', '-m', msg] + filenames)
     commit.wait()
     if commit.returncode:
         print("commit failed!")
         return 1
     else:
         print("PR #%i applied, with msg:" % num)
         print()
         print(msg)
         print()
     
     if branch != current_branch:
         check_call(['git', 'checkout', current_branch])
     
     return 0
 
 if __name__ == '__main__':
     if len(sys.argv) < 3:
         print(__doc__)
         sys.exit(1)
     
     sys.exit(backport_pr(sys.argv[1], int(sys.argv[2])))