obsutil: maintain a homogenous list when computing successors

In practice, this wasn't a problem because of an internal check for an empty
list, but it avoids the following pytype error:

    File "/mnt/c/Users/Matt/hg/mercurial/obsutil.py", line 823, in successorsandmarkers: No attribute 'markers' on List[nothing] [attribute-error]
      In Union[Any, List[nothing], _succs]

Differential Revision: https://phab.mercurial-scm.org/D10213

mercurial/obsutil.py

@@ -1,1049 +1,1049 b''
 # obsutil.py - utility functions for obsolescence
 #
 # Copyright 2017 Boris Feld <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
 import re
 
 from .i18n import _
 from .node import (
     hex,
     short,
 )
 from . import (
     diffutil,
     encoding,
     error,
     phases,
     pycompat,
     util,
 )
 from .utils import dateutil
 
 ### obsolescence marker flag
 
 ## bumpedfix flag
 #
 # When a changeset A' succeed to a changeset A which became public, we call A'
 # "bumped" because it's a successors of a public changesets
 #
 # o    A' (bumped)
 # |`:
 # | o  A
 # |/
 # o    Z
 #
 # The way to solve this situation is to create a new changeset Ad as children
 # of A. This changeset have the same content than A'. So the diff from A to A'
 # is the same than the diff from A to Ad. Ad is marked as a successors of A'
 #
 # o   Ad
 # |`:
 # | x A'
 # |'|
 # o | A
 # |/
 # o Z
 #
 # But by transitivity Ad is also a successors of A. To avoid having Ad marked
 # as bumped too, we add the `bumpedfix` flag to the marker. <A', (Ad,)>.
 # This flag mean that the successors express the changes between the public and
 # bumped version and fix the situation, breaking the transitivity of
 # "bumped" here.
 bumpedfix = 1
 usingsha256 = 2
 
 
 class marker(object):
     """Wrap obsolete marker raw data"""
 
     def __init__(self, repo, data):
         # the repo argument will be used to create changectx in later version
         self._repo = repo
         self._data = data
         self._decodedmeta = None
 
     def __hash__(self):
         return hash(self._data)
 
     def __eq__(self, other):
         if type(other) != type(self):
             return False
         return self._data == other._data
 
     def prednode(self):
         """Predecessor changeset node identifier"""
         return self._data[0]
 
     def succnodes(self):
         """List of successor changesets node identifiers"""
         return self._data[1]
 
     def parentnodes(self):
         """Parents of the predecessors (None if not recorded)"""
         return self._data[5]
 
     def metadata(self):
         """Decoded metadata dictionary"""
         return dict(self._data[3])
 
     def date(self):
         """Creation date as (unixtime, offset)"""
         return self._data[4]
 
     def flags(self):
         """The flags field of the marker"""
         return self._data[2]
 
 
 def getmarkers(repo, nodes=None, exclusive=False):
     """returns markers known in a repository
 
     If <nodes> is specified, only markers "relevant" to those nodes are are
     returned"""
     if nodes is None:
         rawmarkers = repo.obsstore
     elif exclusive:
         rawmarkers = exclusivemarkers(repo, nodes)
     else:
         rawmarkers = repo.obsstore.relevantmarkers(nodes)
 
     for markerdata in rawmarkers:
         yield marker(repo, markerdata)
 
 
 def sortedmarkers(markers):
     # last item of marker tuple ('parents') may be None or a tuple
     return sorted(markers, key=lambda m: m[:-1] + (m[-1] or (),))
 
 
 def closestpredecessors(repo, nodeid):
     """yield the list of next predecessors pointing on visible changectx nodes
 
     This function respect the repoview filtering, filtered revision will be
     considered missing.
     """
 
     precursors = repo.obsstore.predecessors
     stack = [nodeid]
     seen = set(stack)
 
     while stack:
         current = stack.pop()
         currentpreccs = precursors.get(current, ())
 
         for prec in currentpreccs:
             precnodeid = prec[0]
 
             # Basic cycle protection
             if precnodeid in seen:
                 continue
             seen.add(precnodeid)
 
             if precnodeid in repo:
                 yield precnodeid
             else:
                 stack.append(precnodeid)
 
 
 def allpredecessors(obsstore, nodes, ignoreflags=0):
     """Yield node for every precursors of <nodes>.
 
     Some precursors may be unknown locally.
 
     This is a linear yield unsuited to detecting folded changesets. It includes
     initial nodes too."""
 
     remaining = set(nodes)
     seen = set(remaining)
     prec = obsstore.predecessors.get
     while remaining:
         current = remaining.pop()
         yield current
         for mark in prec(current, ()):
             # ignore marker flagged with specified flag
             if mark[2] & ignoreflags:
                 continue
             suc = mark[0]
             if suc not in seen:
                 seen.add(suc)
                 remaining.add(suc)
 
 
 def allsuccessors(obsstore, nodes, ignoreflags=0):
     """Yield node for every successor of <nodes>.
 
     Some successors may be unknown locally.
 
     This is a linear yield unsuited to detecting split changesets. It includes
     initial nodes too."""
     remaining = set(nodes)
     seen = set(remaining)
     while remaining:
         current = remaining.pop()
         yield current
         for mark in obsstore.successors.get(current, ()):
             # ignore marker flagged with specified flag
             if mark[2] & ignoreflags:
                 continue
             for suc in mark[1]:
                 if suc not in seen:
                     seen.add(suc)
                     remaining.add(suc)
 
 
 def _filterprunes(markers):
     """return a set with no prune markers"""
     return {m for m in markers if m[1]}
 
 
 def exclusivemarkers(repo, nodes):
     """set of markers relevant to "nodes" but no other locally-known nodes
 
     This function compute the set of markers "exclusive" to a locally-known
     node. This means we walk the markers starting from <nodes> until we reach a
     locally-known precursors outside of <nodes>. Element of <nodes> with
     locally-known successors outside of <nodes> are ignored (since their
     precursors markers are also relevant to these successors).
 
     For example:
 
         # (A0 rewritten as A1)
         #
         # A0 <-1- A1 # Marker "1" is exclusive to A1
 
         or
 
         # (A0 rewritten as AX; AX rewritten as A1; AX is unkown locally)
         #
         # <-1- A0 <-2- AX <-3- A1 # Marker "2,3" are exclusive to A1
 
         or
 
         # (A0 has unknown precursors, A0 rewritten as A1 and A2 (divergence))
         #
         #          <-2- A1 # Marker "2" is exclusive to A0,A1
         #        /
         # <-1- A0
         #        \
         #         <-3- A2 # Marker "3" is exclusive to A0,A2
         #
         # in addition:
         #
         #  Markers "2,3" are exclusive to A1,A2
         #  Markers "1,2,3" are exclusive to A0,A1,A2
 
         See test/test-obsolete-bundle-strip.t for more examples.
 
     An example usage is strip. When stripping a changeset, we also want to
     strip the markers exclusive to this changeset. Otherwise we would have
     "dangling"" obsolescence markers from its precursors: Obsolescence markers
     marking a node as obsolete without any successors available locally.
 
     As for relevant markers, the prune markers for children will be followed.
     Of course, they will only be followed if the pruned children is
     locally-known. Since the prune markers are relevant to the pruned node.
     However, while prune markers are considered relevant to the parent of the
     pruned changesets, prune markers for locally-known changeset (with no
     successors) are considered exclusive to the pruned nodes. This allows
     to strip the prune markers (with the rest of the exclusive chain) alongside
     the pruned changesets.
     """
     # running on a filtered repository would be dangerous as markers could be
     # reported as exclusive when they are relevant for other filtered nodes.
     unfi = repo.unfiltered()
 
     # shortcut to various useful item
     has_node = unfi.changelog.index.has_node
     precursorsmarkers = unfi.obsstore.predecessors
     successormarkers = unfi.obsstore.successors
     childrenmarkers = unfi.obsstore.children
 
     # exclusive markers (return of the function)
     exclmarkers = set()
     # we need fast membership testing
     nodes = set(nodes)
     # looking for head in the obshistory
     #
     # XXX we are ignoring all issues in regard with cycle for now.
     stack = [n for n in nodes if not _filterprunes(successormarkers.get(n, ()))]
     stack.sort()
     # nodes already stacked
     seennodes = set(stack)
     while stack:
         current = stack.pop()
         # fetch precursors markers
         markers = list(precursorsmarkers.get(current, ()))
         # extend the list with prune markers
         for mark in successormarkers.get(current, ()):
             if not mark[1]:
                 markers.append(mark)
         # and markers from children (looking for prune)
         for mark in childrenmarkers.get(current, ()):
             if not mark[1]:
                 markers.append(mark)
         # traverse the markers
         for mark in markers:
             if mark in exclmarkers:
                 # markers already selected
                 continue
 
             # If the markers is about the current node, select it
             #
             # (this delay the addition of markers from children)
             if mark[1] or mark[0] == current:
                 exclmarkers.add(mark)
 
             # should we keep traversing through the precursors?
             prec = mark[0]
 
             # nodes in the stack or already processed
             if prec in seennodes:
                 continue
 
             # is this a locally known node ?
             known = has_node(prec)
             # if locally-known and not in the <nodes> set the traversal
             # stop here.
             if known and prec not in nodes:
                 continue
 
             # do not keep going if there are unselected markers pointing to this
             # nodes. If we end up traversing these unselected markers later the
             # node will be taken care of at that point.
             precmarkers = _filterprunes(successormarkers.get(prec))
             if precmarkers.issubset(exclmarkers):
                 seennodes.add(prec)
                 stack.append(prec)
 
     return exclmarkers
 
 
 def foreground(repo, nodes):
     """return all nodes in the "foreground" of other node
 
     The foreground of a revision is anything reachable using parent -> children
     or precursor -> successor relation. It is very similar to "descendant" but
     augmented with obsolescence information.
 
     Beware that possible obsolescence cycle may result if complex situation.
     """
     repo = repo.unfiltered()
     foreground = set(repo.set(b'%ln::', nodes))
     if repo.obsstore:
         # We only need this complicated logic if there is obsolescence
         # XXX will probably deserve an optimised revset.
         has_node = repo.changelog.index.has_node
         plen = -1
         # compute the whole set of successors or descendants
         while len(foreground) != plen:
             plen = len(foreground)
             succs = {c.node() for c in foreground}
             mutable = [c.node() for c in foreground if c.mutable()]
             succs.update(allsuccessors(repo.obsstore, mutable))
             known = (n for n in succs if has_node(n))
             foreground = set(repo.set(b'%ln::', known))
     return {c.node() for c in foreground}
 
 
 # effectflag field
 #
 # Effect-flag is a 1-byte bit field used to store what changed between a
 # changeset and its successor(s).
 #
 # The effect flag is stored in obs-markers metadata while we iterate on the
 # information design. That's why we have the EFFECTFLAGFIELD. If we come up
 # with an incompatible design for effect flag, we can store a new design under
 # another field name so we don't break readers. We plan to extend the existing
 # obsmarkers bit-field when the effect flag design will be stabilized.
 #
 # The effect-flag is placed behind an experimental flag
 # `effect-flags` set to off by default.
 #
 
 EFFECTFLAGFIELD = b"ef1"
 
 DESCCHANGED = 1 << 0  # action changed the description
 METACHANGED = 1 << 1  # action change the meta
 DIFFCHANGED = 1 << 3  # action change diff introduced by the changeset
 PARENTCHANGED = 1 << 2  # action change the parent
 USERCHANGED = 1 << 4  # the user changed
 DATECHANGED = 1 << 5  # the date changed
 BRANCHCHANGED = 1 << 6  # the branch changed
 
 METABLACKLIST = [
     re.compile(b'^branch$'),
     re.compile(b'^.*-source$'),
     re.compile(b'^.*_source$'),
     re.compile(b'^source$'),
 ]
 
 
 def metanotblacklisted(metaitem):
     """Check that the key of a meta item (extrakey, extravalue) does not
     match at least one of the blacklist pattern
     """
     metakey = metaitem[0]
 
     return not any(pattern.match(metakey) for pattern in METABLACKLIST)
 
 
 def _prepare_hunk(hunk):
     """Drop all information but the username and patch"""
     cleanhunk = []
     for line in hunk.splitlines():
         if line.startswith(b'# User') or not line.startswith(b'#'):
             if line.startswith(b'@@'):
                 line = b'@@\n'
             cleanhunk.append(line)
     return cleanhunk
 
 
 def _getdifflines(iterdiff):
     """return a cleaned up lines"""
     lines = next(iterdiff, None)
 
     if lines is None:
         return lines
 
     return _prepare_hunk(lines)
 
 
 def _cmpdiff(leftctx, rightctx):
     """return True if both ctx introduce the "same diff"
 
     This is a first and basic implementation, with many shortcoming.
     """
     diffopts = diffutil.diffallopts(leftctx.repo().ui, {b'git': True})
 
     # Leftctx or right ctx might be filtered, so we need to use the contexts
     # with an unfiltered repository to safely compute the diff
 
     # leftctx and rightctx can be from different repository views in case of
     # hgsubversion, do don't try to access them from same repository
     # rightctx.repo() and leftctx.repo() are not always the same
     leftunfi = leftctx._repo.unfiltered()[leftctx.rev()]
     leftdiff = leftunfi.diff(opts=diffopts)
     rightunfi = rightctx._repo.unfiltered()[rightctx.rev()]
     rightdiff = rightunfi.diff(opts=diffopts)
 
     left, right = (0, 0)
     while None not in (left, right):
         left = _getdifflines(leftdiff)
         right = _getdifflines(rightdiff)
 
         if left != right:
             return False
     return True
 
 
 def geteffectflag(source, successors):
     """From an obs-marker relation, compute what changed between the
     predecessor and the successor.
     """
     effects = 0
 
     for changectx in successors:
         # Check if description has changed
         if changectx.description() != source.description():
             effects |= DESCCHANGED
 
         # Check if user has changed
         if changectx.user() != source.user():
             effects |= USERCHANGED
 
         # Check if date has changed
         if changectx.date() != source.date():
             effects |= DATECHANGED
 
         # Check if branch has changed
         if changectx.branch() != source.branch():
             effects |= BRANCHCHANGED
 
         # Check if at least one of the parent has changed
         if changectx.parents() != source.parents():
             effects |= PARENTCHANGED
 
         # Check if other meta has changed
         changeextra = changectx.extra().items()
         ctxmeta = list(filter(metanotblacklisted, changeextra))
 
         sourceextra = source.extra().items()
         srcmeta = list(filter(metanotblacklisted, sourceextra))
 
         if ctxmeta != srcmeta:
             effects |= METACHANGED
 
         # Check if the diff has changed
         if not _cmpdiff(source, changectx):
             effects |= DIFFCHANGED
 
     return effects
 
 
 def getobsoleted(repo, tr=None, changes=None):
     """return the set of pre-existing revisions obsoleted by a transaction
 
     Either the transaction or changes item of the transaction (for hooks)
     must be provided, but not both.
     """
     if (tr is None) == (changes is None):
         e = b"exactly one of tr and changes must be provided"
         raise error.ProgrammingError(e)
     torev = repo.unfiltered().changelog.index.get_rev
     phase = repo._phasecache.phase
     succsmarkers = repo.obsstore.successors.get
     public = phases.public
     if changes is None:
         changes = tr.changes
     addedmarkers = changes[b'obsmarkers']
     origrepolen = changes[b'origrepolen']
     seenrevs = set()
     obsoleted = set()
     for mark in addedmarkers:
         node = mark[0]
         rev = torev(node)
         if rev is None or rev in seenrevs or rev >= origrepolen:
             continue
         seenrevs.add(rev)
         if phase(repo, rev) == public:
             continue
         if set(succsmarkers(node) or []).issubset(addedmarkers):
             obsoleted.add(rev)
     return obsoleted
 
 
 class _succs(list):
     """small class to represent a successors with some metadata about it"""
 
     def __init__(self, *args, **kwargs):
         super(_succs, self).__init__(*args, **kwargs)
         self.markers = set()
 
     def copy(self):
         new = _succs(self)
         new.markers = self.markers.copy()
         return new
 
     @util.propertycache
     def _set(self):
         # immutable
         return set(self)
 
     def canmerge(self, other):
         return self._set.issubset(other._set)
 
 
 def successorssets(repo, initialnode, closest=False, cache=None):
     """Return set of all latest successors of initial nodes
 
     The successors set of a changeset A are the group of revisions that succeed
     A. It succeeds A as a consistent whole, each revision being only a partial
     replacement. By default, the successors set contains non-obsolete
     changesets only, walking the obsolescence graph until reaching a leaf. If
     'closest' is set to True, closest successors-sets are return (the
     obsolescence walk stops on known changesets).
 
     This function returns the full list of successor sets which is why it
     returns a list of tuples and not just a single tuple. Each tuple is a valid
     successors set. Note that (A,) may be a valid successors set for changeset A
     (see below).
 
     In most cases, a changeset A will have a single element (e.g. the changeset
     A is replaced by A') in its successors set. Though, it is also common for a
     changeset A to have no elements in its successor set (e.g. the changeset
     has been pruned). Therefore, the returned list of successors sets will be
     [(A',)] or [], respectively.
 
     When a changeset A is split into A' and B', however, it will result in a
     successors set containing more than a single element, i.e. [(A',B')].
     Divergent changesets will result in multiple successors sets, i.e. [(A',),
     (A'')].
 
     If a changeset A is not obsolete, then it will conceptually have no
     successors set. To distinguish this from a pruned changeset, the successor
     set will contain itself only, i.e. [(A,)].
 
     Finally, final successors unknown locally are considered to be pruned
     (pruned: obsoleted without any successors). (Final: successors not affected
     by markers).
 
     The 'closest' mode respect the repoview filtering. For example, without
     filter it will stop at the first locally known changeset, with 'visible'
     filter it will stop on visible changesets).
 
     The optional `cache` parameter is a dictionary that may contains
     precomputed successors sets. It is meant to reuse the computation of a
     previous call to `successorssets` when multiple calls are made at the same
     time. The cache dictionary is updated in place. The caller is responsible
     for its life span. Code that makes multiple calls to `successorssets`
     *should* use this cache mechanism or risk a performance hit.
 
     Since results are different depending of the 'closest' most, the same cache
     cannot be reused for both mode.
     """
 
     succmarkers = repo.obsstore.successors
 
     # Stack of nodes we search successors sets for
     toproceed = [initialnode]
     # set version of above list for fast loop detection
     # element added to "toproceed" must be added here
     stackedset = set(toproceed)
     if cache is None:
         cache = {}
 
     # This while loop is the flattened version of a recursive search for
     # successors sets
     #
     # def successorssets(x):
     #    successors = directsuccessors(x)
     #    ss = [[]]
     #    for succ in directsuccessors(x):
     #        # product as in itertools cartesian product
     #        ss = product(ss, successorssets(succ))
     #    return ss
     #
     # But we can not use plain recursive calls here:
     # - that would blow the python call stack
     # - obsolescence markers may have cycles, we need to handle them.
     #
     # The `toproceed` list act as our call stack. Every node we search
     # successors set for are stacked there.
     #
     # The `stackedset` is set version of this stack used to check if a node is
     # already stacked. This check is used to detect cycles and prevent infinite
     # loop.
     #
     # successors set of all nodes are stored in the `cache` dictionary.
     #
     # After this while loop ends we use the cache to return the successors sets
     # for the node requested by the caller.
     while toproceed:
         # Every iteration tries to compute the successors sets of the topmost
         # node of the stack: CURRENT.
         #
         # There are four possible outcomes:
         #
         # 1) We already know the successors sets of CURRENT:
         #    -> mission accomplished, pop it from the stack.
         # 2) Stop the walk:
         #    default case: Node is not obsolete
         #    closest case: Node is known at this repo filter level
         #      -> the node is its own successors sets. Add it to the cache.
         # 3) We do not know successors set of direct successors of CURRENT:
         #    -> We add those successors to the stack.
         # 4) We know successors sets of all direct successors of CURRENT:
         #    -> We can compute CURRENT successors set and add it to the
         #       cache.
         #
         current = toproceed[-1]
 
         # case 2 condition is a bit hairy because of closest,
         # we compute it on its own
         case2condition = (current not in succmarkers) or (
             closest and current != initialnode and current in repo
         )
 
         if current in cache:
             # case (1): We already know the successors sets
             stackedset.remove(toproceed.pop())
         elif case2condition:
             # case (2): end of walk.
             if current in repo:
                 # We have a valid successors.
                 cache[current] = [_succs((current,))]
             else:
                 # Final obsolete version is unknown locally.
                 # Do not count that as a valid successors
                 cache[current] = []
         else:
             # cases (3) and (4)
             #
             # We proceed in two phases. Phase 1 aims to distinguish case (3)
             # from case (4):
             #
             #     For each direct successors of CURRENT, we check whether its
             #     successors sets are known. If they are not, we stack the
             #     unknown node and proceed to the next iteration of the while
             #     loop. (case 3)
             #
             #     During this step, we may detect obsolescence cycles: a node
             #     with unknown successors sets but already in the call stack.
             #     In such a situation, we arbitrary set the successors sets of
             #     the node to nothing (node pruned) to break the cycle.
             #
             #     If no break was encountered we proceed to phase 2.
             #
             # Phase 2 computes successors sets of CURRENT (case 4); see details
             # in phase 2 itself.
             #
             # Note the two levels of iteration in each phase.
             # - The first one handles obsolescence markers using CURRENT as
             #   precursor (successors markers of CURRENT).
             #
             #   Having multiple entry here means divergence.
             #
             # - The second one handles successors defined in each marker.
             #
             #   Having none means pruned node, multiple successors means split,
             #   single successors are standard replacement.
             #
             for mark in sortedmarkers(succmarkers[current]):
                 for suc in mark[1]:
                     if suc not in cache:
                         if suc in stackedset:
                             # cycle breaking
                             cache[suc] = []
                         else:
                             # case (3) If we have not computed successors sets
                             # of one of those successors we add it to the
                             # `toproceed` stack and stop all work for this
                             # iteration.
                             toproceed.append(suc)
                             stackedset.add(suc)
                             break
                 else:
                     continue
                 break
             else:
                 # case (4): we know all successors sets of all direct
                 # successors
                 #
                 # Successors set contributed by each marker depends on the
                 # successors sets of all its "successors" node.
                 #
                 # Each different marker is a divergence in the obsolescence
                 # history. It contributes successors sets distinct from other
                 # markers.
                 #
                 # Within a marker, a successor may have divergent successors
                 # sets. In such a case, the marker will contribute multiple
                 # divergent successors sets. If multiple successors have
                 # divergent successors sets, a Cartesian product is used.
                 #
                 # At the end we post-process successors sets to remove
                 # duplicated entry and successors set that are strict subset of
                 # another one.
                 succssets = []
                 for mark in sortedmarkers(succmarkers[current]):
                     # successors sets contributed by this marker
                     base = _succs()
                     base.markers.add(mark)
                     markss = [base]
                     for suc in mark[1]:
                         # cardinal product with previous successors
                         productresult = []
                         for prefix in markss:
                             for suffix in cache[suc]:
                                 newss = prefix.copy()
                                 newss.markers.update(suffix.markers)
                                 for part in suffix:
                                     # do not duplicated entry in successors set
                                     # first entry wins.
                                     if part not in newss:
                                         newss.append(part)
                                 productresult.append(newss)
                         if productresult:
                             markss = productresult
                     succssets.extend(markss)
                 # remove duplicated and subset
                 seen = []
                 final = []
                 candidates = sorted(
                     (s for s in succssets if s), key=len, reverse=True
                 )
                 for cand in candidates:
                     for seensuccs in seen:
                         if cand.canmerge(seensuccs):
                             seensuccs.markers.update(cand.markers)
                             break
                     else:
                         final.append(cand)
                         seen.append(cand)
                 final.reverse()  # put small successors set first
                 cache[current] = final
     return cache[initialnode]
 
 
 def successorsandmarkers(repo, ctx):
     """compute the raw data needed for computing obsfate
     Returns a list of dict, one dict per successors set
     """
     if not ctx.obsolete():
         return None
 
     ssets = successorssets(repo, ctx.node(), closest=True)
 
     # closestsuccessors returns an empty list for pruned revisions, remap it
     # into a list containing an empty list for future processing
     if ssets == []:
-        ssets = [[]]
+        ssets = [_succs()]
 
     # Try to recover pruned markers
     succsmap = repo.obsstore.successors
     fullsuccessorsets = []  # successor set + markers
     for sset in ssets:
         if sset:
             fullsuccessorsets.append(sset)
         else:
             # successorsset return an empty set() when ctx or one of its
             # successors is pruned.
             # In this case, walk the obs-markers tree again starting with ctx
             # and find the relevant pruning obs-makers, the ones without
             # successors.
             # Having these markers allow us to compute some information about
             # its fate, like who pruned this changeset and when.
 
             # XXX we do not catch all prune markers (eg rewritten then pruned)
             # (fix me later)
             foundany = False
             for mark in succsmap.get(ctx.node(), ()):
                 if not mark[1]:
                     foundany = True
                     sset = _succs()
                     sset.markers.add(mark)
                     fullsuccessorsets.append(sset)
             if not foundany:
                 fullsuccessorsets.append(_succs())
 
     values = []
     for sset in fullsuccessorsets:
         values.append({b'successors': sset, b'markers': sset.markers})
 
     return values
 
 
 def _getobsfate(successorssets):
     """Compute a changeset obsolescence fate based on its successorssets.
     Successors can be the tipmost ones or the immediate ones. This function
     return values are not meant to be shown directly to users, it is meant to
     be used by internal functions only.
     Returns one fate from the following values:
     - pruned
     - diverged
     - superseded
     - superseded_split
     """
 
     if len(successorssets) == 0:
         # The commit has been pruned
         return b'pruned'
     elif len(successorssets) > 1:
         return b'diverged'
     else:
         # No divergence, only one set of successors
         successors = successorssets[0]
 
         if len(successors) == 1:
             return b'superseded'
         else:
             return b'superseded_split'
 
 
 def obsfateverb(successorset, markers):
     """Return the verb summarizing the successorset and potentially using
     information from the markers
     """
     if not successorset:
         verb = b'pruned'
     elif len(successorset) == 1:
         verb = b'rewritten'
     else:
         verb = b'split'
     return verb
 
 
 def markersdates(markers):
     """returns the list of dates for a list of markers"""
     return [m[4] for m in markers]
 
 
 def markersusers(markers):
     """Returns a sorted list of markers users without duplicates"""
     markersmeta = [dict(m[3]) for m in markers]
     users = {
         encoding.tolocal(meta[b'user'])
         for meta in markersmeta
         if meta.get(b'user')
     }
 
     return sorted(users)
 
 
 def markersoperations(markers):
     """Returns a sorted list of markers operations without duplicates"""
     markersmeta = [dict(m[3]) for m in markers]
     operations = {
         meta.get(b'operation') for meta in markersmeta if meta.get(b'operation')
     }
 
     return sorted(operations)
 
 
 def obsfateprinter(ui, repo, successors, markers, formatctx):
     """Build a obsfate string for a single successorset using all obsfate
     related function defined in obsutil
     """
     quiet = ui.quiet
     verbose = ui.verbose
     normal = not verbose and not quiet
 
     line = []
 
     # Verb
     line.append(obsfateverb(successors, markers))
 
     # Operations
     operations = markersoperations(markers)
     if operations:
         line.append(b" using %s" % b", ".join(operations))
 
     # Successors
     if successors:
         fmtsuccessors = [formatctx(repo[succ]) for succ in successors]
         line.append(b" as %s" % b", ".join(fmtsuccessors))
 
     # Users
     users = markersusers(markers)
     # Filter out current user in not verbose mode to reduce amount of
     # information
     if not verbose:
         currentuser = ui.username(acceptempty=True)
         if len(users) == 1 and currentuser in users:
             users = None
 
     if (verbose or normal) and users:
         line.append(b" by %s" % b", ".join(users))
 
     # Date
     dates = markersdates(markers)
 
     if dates and verbose:
         min_date = min(dates)
         max_date = max(dates)
 
         if min_date == max_date:
             fmtmin_date = dateutil.datestr(min_date, b'%Y-%m-%d %H:%M %1%2')
             line.append(b" (at %s)" % fmtmin_date)
         else:
             fmtmin_date = dateutil.datestr(min_date, b'%Y-%m-%d %H:%M %1%2')
             fmtmax_date = dateutil.datestr(max_date, b'%Y-%m-%d %H:%M %1%2')
             line.append(b" (between %s and %s)" % (fmtmin_date, fmtmax_date))
 
     return b"".join(line)
 
 
 filteredmsgtable = {
     b"pruned": _(b"hidden revision '%s' is pruned"),
     b"diverged": _(b"hidden revision '%s' has diverged"),
     b"superseded": _(b"hidden revision '%s' was rewritten as: %s"),
     b"superseded_split": _(b"hidden revision '%s' was split as: %s"),
     b"superseded_split_several": _(
         b"hidden revision '%s' was split as: %s and %d more"
     ),
 }
 
 
 def _getfilteredreason(repo, changeid, ctx):
     """return a human-friendly string on why a obsolete changeset is hidden"""
     successors = successorssets(repo, ctx.node())
     fate = _getobsfate(successors)
 
     # Be more precise in case the revision is superseded
     if fate == b'pruned':
         return filteredmsgtable[b'pruned'] % changeid
     elif fate == b'diverged':
         return filteredmsgtable[b'diverged'] % changeid
     elif fate == b'superseded':
         single_successor = short(successors[0][0])
         return filteredmsgtable[b'superseded'] % (changeid, single_successor)
     elif fate == b'superseded_split':
 
         succs = []
         for node_id in successors[0]:
             succs.append(short(node_id))
 
         if len(succs) <= 2:
             fmtsuccs = b', '.join(succs)
             return filteredmsgtable[b'superseded_split'] % (changeid, fmtsuccs)
         else:
             firstsuccessors = b', '.join(succs[:2])
             remainingnumber = len(succs) - 2
 
             args = (changeid, firstsuccessors, remainingnumber)
             return filteredmsgtable[b'superseded_split_several'] % args
 
 
 def divergentsets(repo, ctx):
     """Compute sets of commits divergent with a given one"""
     cache = {}
     base = {}
     for n in allpredecessors(repo.obsstore, [ctx.node()]):
         if n == ctx.node():
             # a node can't be a base for divergence with itself
             continue
         nsuccsets = successorssets(repo, n, cache)
         for nsuccset in nsuccsets:
             if ctx.node() in nsuccset:
                 # we are only interested in *other* successor sets
                 continue
             if tuple(nsuccset) in base:
                 # we already know the latest base for this divergency
                 continue
             base[tuple(nsuccset)] = n
     return [
         {b'divergentnodes': divset, b'commonpredecessor': b}
         for divset, b in pycompat.iteritems(base)
     ]
 
 
 def whyunstable(repo, ctx):
     result = []
     if ctx.orphan():
         for parent in ctx.parents():
             kind = None
             if parent.orphan():
                 kind = b'orphan'
             elif parent.obsolete():
                 kind = b'obsolete'
             if kind is not None:
                 result.append(
                     {
                         b'instability': b'orphan',
                         b'reason': b'%s parent' % kind,
                         b'node': parent.hex(),
                     }
                 )
     if ctx.phasedivergent():
         predecessors = allpredecessors(
             repo.obsstore, [ctx.node()], ignoreflags=bumpedfix
         )
         immutable = [
             repo[p] for p in predecessors if p in repo and not repo[p].mutable()
         ]
         for predecessor in immutable:
             result.append(
                 {
                     b'instability': b'phase-divergent',
                     b'reason': b'immutable predecessor',
                     b'node': predecessor.hex(),
                 }
             )
     if ctx.contentdivergent():
         dsets = divergentsets(repo, ctx)
         for dset in dsets:
             divnodes = [repo[n] for n in dset[b'divergentnodes']]
             result.append(
                 {
                     b'instability': b'content-divergent',
                     b'divergentnodes': divnodes,
                     b'reason': b'predecessor',
                     b'node': hex(dset[b'commonpredecessor']),
                 }
             )
     return result