bpo-44074: let patchcheck infer the base branch name

Misc/NEWS.d/next/Tools-Demos/2021-05-08-13-57-00.bpo-44074.F09kCK.rst

@@ -0,0 +1 @@
+Make patchcheck automatically detect the correct base branch name (previously it was hardcoded to 'master')

Tools/scripts/patchcheck.py

@@ -50,7 +50,8 @@ def get_git_branch():
  try:
  return subprocess.check_output(cmd,
  stderr=subprocess.DEVNULL,
- cwd=SRCDIR)
+ cwd=SRCDIR,
+ encoding='UTF-8')
  except subprocess.CalledProcessError:
  return None
 
@@ -64,28 +65,49 @@ def get_git_upstream_remote():
  try:
  subprocess.check_output(cmd,
  stderr=subprocess.DEVNULL,
- cwd=SRCDIR)
+ cwd=SRCDIR,
+ encoding='UTF-8')
  except subprocess.CalledProcessError:
  return "origin"
  return "upstream"
 
 
+def get_git_remote_default_branch(remote_name):
+ """Get the name of the default branch for the given remote
+
+ It is typically called 'main', but may differ
+ """
+ cmd = "git remote show {}".format(remote_name).split()
+ try:
+ remote_info = subprocess.check_output(cmd,
+ stderr=subprocess.DEVNULL,
+ cwd=SRCDIR,
+ encoding='UTF-8')
+ except subprocess.CalledProcessError:
+ return None
+ for line in remote_info.splitlines():
+ if "HEAD branch:" in line:
+ base_branch = line.split(":")[1].strip()
+ return base_branch
+ return None
+
+
 @status("Getting base branch for PR",
  info=lambda x: x if x is not None else "not a PR branch")
 def get_base_branch():
  if not os.path.exists(os.path.join(SRCDIR, '.git')):
  # Not a git checkout, so there's no base branch
  return None
+ upstream_remote = get_git_upstream_remote()
  version = sys.version_info
  if version.releaselevel == 'alpha':
- base_branch = "master"
+ base_branch = get_git_remote_default_branch(upstream_remote)
  else:
  base_branch = "{0.major}.{0.minor}".format(version)
  this_branch = get_git_branch()
  if this_branch is None or this_branch == base_branch:
  # Not on a git PR branch, so there's no base branch
  return None
- upstream_remote = get_git_upstream_remote()
  return upstream_remote + "/" + base_branch