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#!/usr/bin/env python
# vim:ts=4:sw=4:softtabstop=4:smarttab:expandtab
# Copyright (c) 2020 Kevin B. Hendricks, Stratford Ontario Canada
#
# Dulwich is dual-licensed under the Apache License, Version 2.0 and the GNU
# General Public License as public by the Free Software Foundation; version 2.0
# or (at your option) any later version. You can redistribute it and/or
# modify it under the terms of either of these two licenses.
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# You should have received a copy of the licenses; if not, see
# <http://www.gnu.org/licenses/> for a copy of the GNU General Public License
# and <http://www.apache.org/licenses/LICENSE-2.0> for a copy of the Apache
# License, Version 2.0.
"""Implementation of merge-base following the approach of git."""
from collections import deque
from typing import Deque
def _find_lcas(lookup_parents, c1, c2s):
cands = []
cstates = {}
# Flags to Record State
_ANC_OF_1 = 1 # ancestor of commit 1
_ANC_OF_2 = 2 # ancestor of commit 2
_DNC = 4 # Do Not Consider
_LCA = 8 # potential LCA (Lowest Common Ancestor)
def _has_candidates(wlst, cstates):
for cmt in wlst:
if cmt in cstates:
if not ((cstates[cmt] & _DNC) == _DNC):
return True
return False
# initialize the working list states with ancestry info
# note possibility of c1 being one of c2s should be handled
wlst: Deque[bytes] = deque()
cstates[c1] = _ANC_OF_1
wlst.append(c1)
for c2 in c2s:
cflags = cstates.get(c2, 0)
cstates[c2] = cflags | _ANC_OF_2
wlst.append(c2)
# loop while at least one working list commit is still viable (not marked as _DNC)
# adding any parents to the list in a breadth first manner
while _has_candidates(wlst, cstates):
cmt = wlst.popleft()
# Look only at ANCESTRY and _DNC flags so that already
# found _LCAs can still be marked _DNC by lower _LCAS
cflags = cstates[cmt] & (_ANC_OF_1 | _ANC_OF_2 | _DNC)
if cflags == (_ANC_OF_1 | _ANC_OF_2):
# potential common ancestor if not already in candidates add it
if not (cstates[cmt] & _LCA) == _LCA:
cstates[cmt] = cstates[cmt] | _LCA
cands.append(cmt)
# mark any parents of this node _DNC as all parents
# would be one generation further removed common ancestors
cflags = cflags | _DNC
parents = lookup_parents(cmt)
if parents:
for pcmt in parents:
pflags = cstates.get(pcmt, 0)
# if this parent was already visited with no new ancestry/flag information
# do not add it to the working list again
if ((pflags & cflags) == cflags):
continue
cstates[pcmt] = pflags | cflags
wlst.append(pcmt)
# walk final candidates removing any superseded by _DNC by later lower _LCAs
results = []
for cmt in cands:
if not ((cstates[cmt] & _DNC) == _DNC):
results.append(cmt)
return results
def find_merge_base(repo, commit_ids):
"""Find lowest common ancestors of commit_ids[0] and *any* of commits_ids[1:].
Args:
repo: Repository object
commit_ids: list of commit ids
Returns:
list of lowest common ancestor commit_ids
"""
if not commit_ids:
return []
c1 = commit_ids[0]
if not len(commit_ids) > 1:
return [c1]
c2s = commit_ids[1:]
if c1 in c2s:
return [c1]
parents_provider = repo.parents_provider()
return _find_lcas(parents_provider.get_parents, c1, c2s)
def find_octopus_base(repo, commit_ids):
"""Find lowest common ancestors of *all* provided commit_ids.
Args:
repo: Repository
commit_ids: list of commit ids
Returns:
list of lowest common ancestor commit_ids
"""
if not commit_ids:
return []
if len(commit_ids) <= 2:
return find_merge_base(repo, commit_ids)
parents_provider = repo.parents_provider()
lcas = [commit_ids[0]]
others = commit_ids[1:]
for cmt in others:
next_lcas = []
for ca in lcas:
res = _find_lcas(parents_provider.get_parents, cmt, [ca])
next_lcas.extend(res)
lcas = next_lcas[:]
return lcas
def can_fast_forward(repo, c1, c2):
"""Is it possible to fast-forward from c1 to c2?
Args:
repo: Repository to retrieve objects from
c1: Commit id for first commit
c2: Commit id for second commit
"""
if c1 == c2:
return True
# Algorithm: Find the common ancestor
parents_provider = repo.parents_provider()
lcas = _find_lcas(parents_provider.get_parents, c1, [c2])
return lcas == [c1]