Make marked merge base invalid when the upstream changes.

git_common.py

 # Copyright 2014 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.
 
 # Monkeypatch IMapIterator so that Ctrl-C can kill everything properly.
 # Derived from https://gist.github.com/aljungberg/626518
 import multiprocessing.pool
 from multiprocessing.pool import IMapIterator
 def wrapper(func):
   def wrap(self, timeout=None):
@@ skipping 334 matching lines @@
 
   return skipped, branch_tree
 
 
 def get_or_create_merge_base(branch, parent=None):
   """Finds the configured merge base for branch.
 
   If parent is supplied, it's used instead of calling upstream(branch).
   """
   base = branch_config(branch, 'base')
+  base_upstream = branch_config(branch, 'base-upstream')
   parent = parent or upstream(branch)
+  if not parent:
+    return None
   actual_merge_base = run('merge-base', parent, branch)
 
+  if base_upstream != parent:
+    base = None
+    base_upstream = None
+
   def is_ancestor(a, b):
     return run_with_retcode('merge-base', '--is-ancestor', a, b) == 0
 
   if base:
     if not is_ancestor(base, branch):
       logging.debug('Found WRONG pre-set merge-base for %s: %s', branch, base)
       base = None
     elif is_ancestor(base, actual_merge_base):
       logging.debug('Found OLD pre-set merge-base for %s: %s', branch, base)
       base = None
     else:
       logging.debug('Found pre-set merge-base for %s: %s', branch, base)
 
   if not base:
     base = actual_merge_base
-    manual_merge_base(branch, base)
+    manual_merge_base(branch, base, parent)
 
   return base
 
 
 def hash_multi(*reflike):
   return run('rev-parse', *reflike).splitlines()
 
 
 def hash_one(reflike):
   return run('rev-parse', reflike)
@@ skipping 18 matching lines @@
   ret = run('hash-object', '-t', kind, '-w', '--stdin', stdin=f)
   f.close()
   return ret
 
 
 def is_dormant(branch):
   # TODO(iannucci): Do an oldness check?
   return branch_config(branch, 'dormant', 'false') != 'false'
 
 
-def manual_merge_base(branch, base):
+def manual_merge_base(branch, base, parent):
   set_branch_config(branch, 'base', base)
+  set_branch_config(branch, 'base-upstream', parent)
 
 
 def mktree(treedict):
   """Makes a git tree object and returns its hash.
 
   See |tree()| for the values of mode, type, and ref.
 
   Args:
     treedict - { name: (mode, type, ref) }
   """
@@ skipping 44 matching lines @@
     run('rebase', *args)
     return RebaseRet(True, '')
   except subprocess2.CalledProcessError as cpe:
     if abort:
       run('rebase', '--abort')
     return RebaseRet(False, cpe.stdout)
 
 
 def remove_merge_base(branch):
   del_branch_config(branch, 'base')
+  del_branch_config(branch, 'base-upstream')
 
 
 def root():
   return config('depot-tools.upstream', 'origin/master')
 
 
 def run(*cmd, **kwargs):
   """The same as run_with_stderr, except it only returns stdout."""
   return run_with_stderr(*cmd, **kwargs)[0]
 
@@ skipping 162 matching lines @@
     return None
   return ret
 
 
 def upstream(branch):
   try:
     return run('rev-parse', '--abbrev-ref', '--symbolic-full-name',
                branch+'@{upstream}')
   except subprocess2.CalledProcessError:
     return None