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Fix "git rebase-update" when multiple branch are stale.

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Fix a bug that left branches tracking a dead branch if both their parent
and grand-parent were left with no changes after a "rebase-update" step.

Given the following initial state:
  $ git map-branches -v
  origin/master
    a
      b
        c *        [ ahead 1 ]

without this patch, a "git rebase-update" on this tree state would
leave the branch "c" as tracking a non-existing branch "a":

  $ git recursive-rebase
  a up-to-date
  b up-to-date
  c up-to-date
  Reparented c to track a (was tracking b)
  Deleted branch b (was 448d1da).
  Deleted branch a (was 448d1da).
  $ git map-branches -v
  {a:GONE}
    c *

with the patch, we record that the branch "c" is tracking must be
updated twice and we end up in a state were "c" is correctly tracking
"origin/master":

  $ git recursive-rebase
  a up-to-date
  b up-to-date
  c up-to-date
  Reparented c to track origin/master (was tracking b)
  Deleted branch b (was 448d1da).
  Deleted branch a (was 448d1da).
  $ git map-branches -v
  origin/master
    c *            [ ahead 1 ]

BUG=456806

Review URL: https://codereview.chromium.org/1482753002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@297792 0039d316-1c4b-4281-b951-d872f2087c98
This commit is contained in:
sdefresne@chromium.org
2015-12-02 18:13:54 +00:00
parent 6df90f329b
commit d421f6a477
2 changed files with 54 additions and 16 deletions
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44
git_rebase_update.py
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@@ -87,32 +87,54 @@ def remove_empty_branches(branch_tree):
tag_set = git.tags()
ensure_root_checkout = git.once(lambda: git.run('checkout', git.root()))
deletions = set()
deletions = {}
reparents = {}
downstreams = collections.defaultdict(list)
for branch, parent in git.topo_iter(branch_tree, top_down=False):
downstreams[parent].append(branch)
# If branch and parent have the same state, then branch has to be marked
# for deletion and its children and grand-children reparented to parent.
if git.hash_one(branch) == git.hash_one(parent):
ensure_root_checkout()
logging.debug('branch %s merged to %s', branch, parent)
# Mark branch for deletion while remembering the ordering, then add all
# its children as grand-children of its parent and record reparenting
# information if necessary.
deletions[branch] = len(deletions)
for down in downstreams[branch]:
if down in deletions:
continue
if parent in tag_set:
git.set_branch_config(down, 'remote', '.')
git.set_branch_config(down, 'merge', 'refs/tags/%s' % parent)
print ('Reparented %s to track %s [tag] (was tracking %s)'
% (down, parent, branch))
# Record the new and old parent for down, or update such a record
# if it already exists. Keep track of the ordering so that reparenting
# happen in topological order.
downstreams[parent].append(down)
if down not in reparents:
reparents[down] = (len(reparents), parent, branch)
else:
git.run('branch', '--set-upstream-to', parent, down)
print ('Reparented %s to track %s (was tracking %s)'
% (down, parent, branch))
order, _, old_parent = reparents[down]
reparents[down] = (order, parent, old_parent)
deletions.add(branch)
print git.run('branch', '-d', branch)
# Apply all reparenting recorded, in order.
for branch, value in sorted(reparents.iteritems(), key=lambda x:x[1][0]):
_, parent, old_parent = value
if parent in tag_set:
git.set_branch_config(branch, 'remote', '.')
git.set_branch_config(branch, 'merge', 'refs/tags/%s' % parent)
print ('Reparented %s to track %s [tag] (was tracking %s)'
% (branch, parent, old_parent))
else:
git.run('branch', '--set-upstream-to', parent, branch)
print ('Reparented %s to track %s (was tracking %s)'
% (branch, parent, old_parent))
# Apply all deletions recorded, in order.
for branch, _ in sorted(deletions.iteritems(), key=lambda x: x[1]):
print git.run('branch', '-d', branch)
def rebase_branch(branch, parent, start_hash):