merge: make test for fast-forward merge stricter (issue619)

don't allow merging with an ancestor
fix != on contexts
add a test

tests/test-issue619

@@ -0,0 +1,20
+#!/bin/sh
+
+mkdir t
+cd t
+hg init
+echo a > a
+hg ci -Ama -d '1000000000 0'
+echo b > b
+hg branch b
+hg ci -Amb -d '1000000000 0'
+hg co -C 0
+
+echo fast-forward
+hg merge b
+hg ci -Ammerge -d '1000000000 0'
+
+echo bogus fast-forward should fail
+hg merge b
+
+echo done

tests/test-issue619.out

@@ -0,0 +1,10
+adding a
+marked working directory as branch b
+adding b
+0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+fast-forward
+1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+(branch merge, don't forget to commit)
+bogus fast-forward should fail
+abort: there is nothing to merge, just use 'hg update' or look at 'hg heads'
+done

mercurial/context.py

@@ -1,519 +1,525
 # context.py - changeset and file context objects for mercurial
 #
 # Copyright 2006, 2007 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms
 # of the GNU General Public License, incorporated herein by reference.
 
 from node import *
 from i18n import _
 import ancestor, bdiff, repo, revlog, util, os, errno
 
 class changectx(object):
     """A changecontext object makes access to data related to a particular
     changeset convenient."""
     def __init__(self, repo, changeid=None):
         """changeid is a revision number, node, or tag"""
         self._repo = repo
 
         if not changeid and changeid != 0:
             p1, p2 = self._repo.dirstate.parents()
             self._rev = self._repo.changelog.rev(p1)
             if self._rev == -1:
                 changeid = 'tip'
             else:
                 self._node = p1
                 return
 
         self._node = self._repo.lookup(changeid)
         self._rev = self._repo.changelog.rev(self._node)
 
     def __str__(self):
         return short(self.node())
 
     def __repr__(self):
         return "<changectx %s>" % str(self)
 
     def __eq__(self, other):
         try:
             return self._rev == other._rev
         except AttributeError:
             return False
 
+    def __ne__(self, other):
+        return not (self == other)
+
     def __nonzero__(self):
         return self._rev != nullrev
 
     def __getattr__(self, name):
         if name == '_changeset':
             self._changeset = self._repo.changelog.read(self.node())
             return self._changeset
         elif name == '_manifest':
             self._manifest = self._repo.manifest.read(self._changeset[0])
             return self._manifest
         elif name == '_manifestdelta':
             md = self._repo.manifest.readdelta(self._changeset[0])
             self._manifestdelta = md
             return self._manifestdelta
         else:
             raise AttributeError, name
 
     def changeset(self): return self._changeset
     def manifest(self): return self._manifest
 
     def rev(self): return self._rev
     def node(self): return self._node
     def user(self): return self._changeset[1]
     def date(self): return self._changeset[2]
     def files(self): return self._changeset[3]
     def description(self): return self._changeset[4]
     def branch(self): return self._changeset[5].get("branch")
     def tags(self): return self._repo.nodetags(self._node)
 
     def parents(self):
         """return contexts for each parent changeset"""
         p = self._repo.changelog.parents(self._node)
         return [changectx(self._repo, x) for x in p]
 
     def children(self):
         """return contexts for each child changeset"""
         c = self._repo.changelog.children(self._node)
         return [changectx(self._repo, x) for x in c]
 
     def filenode(self, path):
         if '_manifest' in self.__dict__:
             try:
                 return self._manifest[path]
             except KeyError:
                 raise revlog.LookupError(_("'%s' not found in manifest") % path)
         if '_manifestdelta' in self.__dict__ or path in self.files():
             if path in self._manifestdelta:
                 return self._manifestdelta[path]
         node, flag = self._repo.manifest.find(self._changeset[0], path)
         if not node:
             raise revlog.LookupError(_("'%s' not found in manifest") % path)
 
         return node
 
     def filectx(self, path, fileid=None, filelog=None):
         """get a file context from this changeset"""
         if fileid is None:
             fileid = self.filenode(path)
         return filectx(self._repo, path, fileid=fileid,
                        changectx=self, filelog=filelog)
 
     def filectxs(self):
         """generate a file context for each file in this changeset's
            manifest"""
         mf = self.manifest()
         m = mf.keys()
         m.sort()
         for f in m:
             yield self.filectx(f, fileid=mf[f])
 
     def ancestor(self, c2):
         """
         return the ancestor context of self and c2
         """
         n = self._repo.changelog.ancestor(self._node, c2._node)
         return changectx(self._repo, n)
 
 class filectx(object):
     """A filecontext object makes access to data related to a particular
        filerevision convenient."""
     def __init__(self, repo, path, changeid=None, fileid=None,
                  filelog=None, changectx=None):
         """changeid can be a changeset revision, node, or tag.
            fileid can be a file revision or node."""
         self._repo = repo
         self._path = path
 
         assert (changeid is not None
                 or fileid is not None
                 or changectx is not None)
 
         if filelog:
             self._filelog = filelog
 
         if fileid is None:
             if changectx is None:
                 self._changeid = changeid
             else:
                 self._changectx = changectx
         else:
             self._fileid = fileid
 
     def __getattr__(self, name):
         if name == '_changectx':
             self._changectx = changectx(self._repo, self._changeid)
             return self._changectx
         elif name == '_filelog':
             self._filelog = self._repo.file(self._path)
             return self._filelog
         elif name == '_changeid':
             self._changeid = self._filelog.linkrev(self._filenode)
             return self._changeid
         elif name == '_filenode':
             if '_fileid' in self.__dict__:
                 self._filenode = self._filelog.lookup(self._fileid)
             else:
                 self._filenode = self._changectx.filenode(self._path)
             return self._filenode
         elif name == '_filerev':
             self._filerev = self._filelog.rev(self._filenode)
             return self._filerev
         else:
             raise AttributeError, name
 
     def __nonzero__(self):
         try:
             n = self._filenode
             return True
         except revlog.LookupError:
             # file is missing
             return False
 
     def __str__(self):
         return "%s@%s" % (self.path(), short(self.node()))
 
     def __repr__(self):
         return "<filectx %s>" % str(self)
 
     def __eq__(self, other):
         try:
             return (self._path == other._path
                     and self._changeid == other._changeid)
         except AttributeError:
             return False
 
+    def __ne__(self, other):
+        return not (self == other)
+
     def filectx(self, fileid):
         '''opens an arbitrary revision of the file without
         opening a new filelog'''
         return filectx(self._repo, self._path, fileid=fileid,
                        filelog=self._filelog)
 
     def filerev(self): return self._filerev
     def filenode(self): return self._filenode
     def filelog(self): return self._filelog
 
     def rev(self):
         if '_changectx' in self.__dict__:
             return self._changectx.rev()
         return self._filelog.linkrev(self._filenode)
 
     def node(self): return self._changectx.node()
     def user(self): return self._changectx.user()
     def date(self): return self._changectx.date()
     def files(self): return self._changectx.files()
     def description(self): return self._changectx.description()
     def branch(self): return self._changectx.branch()
     def manifest(self): return self._changectx.manifest()
     def changectx(self): return self._changectx
 
     def data(self): return self._filelog.read(self._filenode)
     def renamed(self): return self._filelog.renamed(self._filenode)
     def path(self): return self._path
     def size(self): return self._filelog.size(self._filerev)
 
     def cmp(self, text): return self._filelog.cmp(self._filenode, text)
 
     def parents(self):
         p = self._path
         fl = self._filelog
         pl = [(p, n, fl) for n in self._filelog.parents(self._filenode)]
 
         r = self.renamed()
         if r:
             pl[0] = (r[0], r[1], None)
 
         return [filectx(self._repo, p, fileid=n, filelog=l)
                 for p,n,l in pl if n != nullid]
 
     def children(self):
         # hard for renames
         c = self._filelog.children(self._filenode)
         return [filectx(self._repo, self._path, fileid=x,
                         filelog=self._filelog) for x in c]
 
     def annotate(self, follow=False):
         '''returns a list of tuples of (ctx, line) for each line
         in the file, where ctx is the filectx of the node where
         that line was last changed'''
 
         def decorate(text, rev):
             return ([rev] * len(text.splitlines()), text)
 
         def pair(parent, child):
             for a1, a2, b1, b2 in bdiff.blocks(parent[1], child[1]):
                 child[0][b1:b2] = parent[0][a1:a2]
             return child
 
         getlog = util.cachefunc(lambda x: self._repo.file(x))
         def getctx(path, fileid):
             log = path == self._path and self._filelog or getlog(path)
             return filectx(self._repo, path, fileid=fileid, filelog=log)
         getctx = util.cachefunc(getctx)
 
         def parents(f):
             # we want to reuse filectx objects as much as possible
             p = f._path
             if f._filerev is None: # working dir
                 pl = [(n.path(), n.filerev()) for n in f.parents()]
             else:
                 pl = [(p, n) for n in f._filelog.parentrevs(f._filerev)]
 
             if follow:
                 r = f.renamed()
                 if r:
                     pl[0] = (r[0], getlog(r[0]).rev(r[1]))
 
             return [getctx(p, n) for p, n in pl if n != nullrev]
 
         # use linkrev to find the first changeset where self appeared
         if self.rev() != self._filelog.linkrev(self._filenode):
             base = self.filectx(self.filerev())
         else:
             base = self
 
         # find all ancestors
         needed = {base: 1}
         visit = [base]
         files = [base._path]
         while visit:
             f = visit.pop(0)
             for p in parents(f):
                 if p not in needed:
                     needed[p] = 1
                     visit.append(p)
                     if p._path not in files:
                         files.append(p._path)
                 else:
                     # count how many times we'll use this
                     needed[p] += 1
 
         # sort by revision (per file) which is a topological order
         visit = []
         for f in files:
             fn = [(n.rev(), n) for n in needed.keys() if n._path == f]
             visit.extend(fn)
         visit.sort()
         hist = {}
 
         for r, f in visit:
             curr = decorate(f.data(), f)
             for p in parents(f):
                 if p != nullid:
                     curr = pair(hist[p], curr)
                     # trim the history of unneeded revs
                     needed[p] -= 1
                     if not needed[p]:
                         del hist[p]
             hist[f] = curr
 
         return zip(hist[f][0], hist[f][1].splitlines(1))
 
     def ancestor(self, fc2):
         """
         find the common ancestor file context, if any, of self, and fc2
         """
 
         acache = {}
 
         # prime the ancestor cache for the working directory
         for c in (self, fc2):
             if c._filerev == None:
                 pl = [(n.path(), n.filenode()) for n in c.parents()]
                 acache[(c._path, None)] = pl
 
         flcache = {self._path:self._filelog, fc2._path:fc2._filelog}
         def parents(vertex):
             if vertex in acache:
                 return acache[vertex]
             f, n = vertex
             if f not in flcache:
                 flcache[f] = self._repo.file(f)
             fl = flcache[f]
             pl = [(f, p) for p in fl.parents(n) if p != nullid]
             re = fl.renamed(n)
             if re:
                 pl.append(re)
             acache[vertex] = pl
             return pl
 
         a, b = (self._path, self._filenode), (fc2._path, fc2._filenode)
         v = ancestor.ancestor(a, b, parents)
         if v:
             f, n = v
             return filectx(self._repo, f, fileid=n, filelog=flcache[f])
 
         return None
 
 class workingctx(changectx):
     """A workingctx object makes access to data related to
     the current working directory convenient."""
     def __init__(self, repo):
         self._repo = repo
         self._rev = None
         self._node = None
 
     def __str__(self):
         return str(self._parents[0]) + "+"
 
     def __nonzero__(self):
         return True
 
     def __getattr__(self, name):
         if name == '_parents':
             self._parents = self._repo.parents()
             return self._parents
         if name == '_status':
             self._status = self._repo.status()
             return self._status
         if name == '_manifest':
             self._buildmanifest()
             return self._manifest
         else:
             raise AttributeError, name
 
     def _buildmanifest(self):
         """generate a manifest corresponding to the working directory"""
 
         man = self._parents[0].manifest().copy()
         is_exec = util.execfunc(self._repo.root, man.execf)
         is_link = util.linkfunc(self._repo.root, man.linkf)
         copied = self._repo.dirstate.copies()
         modified, added, removed, deleted, unknown = self._status[:5]
         for i, l in (("a", added), ("m", modified), ("u", unknown)):
             for f in l:
                 man[f] = man.get(copied.get(f, f), nullid) + i
                 try:
                     man.set(f, is_exec(f), is_link(f))
                 except OSError:
                     pass
 
         for f in deleted + removed:
             if f in man:
                 del man[f]
 
         self._manifest = man
 
     def manifest(self): return self._manifest
 
     def user(self): return self._repo.ui.username()
     def date(self): return util.makedate()
     def description(self): return ""
     def files(self):
         f = self.modified() + self.added() + self.removed()
         f.sort()
         return f
 
     def modified(self): return self._status[0]
     def added(self): return self._status[1]
     def removed(self): return self._status[2]
     def deleted(self): return self._status[3]
     def unknown(self): return self._status[4]
     def clean(self): return self._status[5]
     def branch(self): return self._repo.dirstate.branch()
 
     def tags(self):
         t = []
         [t.extend(p.tags()) for p in self.parents()]
         return t
 
     def parents(self):
         """return contexts for each parent changeset"""
         return self._parents
 
     def children(self):
         return []
 
     def filectx(self, path, filelog=None):
         """get a file context from the working directory"""
         return workingfilectx(self._repo, path, workingctx=self,
                               filelog=filelog)
 
     def ancestor(self, c2):
         """return the ancestor context of self and c2"""
         return self._parents[0].ancestor(c2) # punt on two parents for now
 
 class workingfilectx(filectx):
     """A workingfilectx object makes access to data related to a particular
        file in the working directory convenient."""
     def __init__(self, repo, path, filelog=None, workingctx=None):
         """changeid can be a changeset revision, node, or tag.
            fileid can be a file revision or node."""
         self._repo = repo
         self._path = path
         self._changeid = None
         self._filerev = self._filenode = None
 
         if filelog:
             self._filelog = filelog
         if workingctx:
             self._changectx = workingctx
 
     def __getattr__(self, name):
         if name == '_changectx':
             self._changectx = workingctx(self._repo)
             return self._changectx
         elif name == '_repopath':
             self._repopath = (self._repo.dirstate.copied(self._path)
                               or self._path)
             return self._repopath
         elif name == '_filelog':
             self._filelog = self._repo.file(self._repopath)
             return self._filelog
         else:
             raise AttributeError, name
 
     def __nonzero__(self):
         return True
 
     def __str__(self):
         return "%s@%s" % (self.path(), self._changectx)
 
     def filectx(self, fileid):
         '''opens an arbitrary revision of the file without
         opening a new filelog'''
         return filectx(self._repo, self._repopath, fileid=fileid,
                        filelog=self._filelog)
 
     def rev(self):
         if '_changectx' in self.__dict__:
             return self._changectx.rev()
         return self._filelog.linkrev(self._filenode)
 
     def data(self): return self._repo.wread(self._path)
     def renamed(self):
         rp = self._repopath
         if rp == self._path:
             return None
         return rp, self._changectx._parents[0]._manifest.get(rp, nullid)
 
     def parents(self):
         '''return parent filectxs, following copies if necessary'''
         p = self._path
         rp = self._repopath
         pcl = self._changectx._parents
         fl = self._filelog
         pl = [(rp, pcl[0]._manifest.get(rp, nullid), fl)]
         if len(pcl) > 1:
             if rp != p:
                 fl = None
             pl.append((p, pcl[1]._manifest.get(p, nullid), fl))
 
         return [filectx(self._repo, p, fileid=n, filelog=l)
                 for p,n,l in pl if n != nullid]
 
     def children(self):
         return []
 
     def size(self): return os.stat(self._repo.wjoin(self._path)).st_size
     def date(self):
         t, tz = self._changectx.date()
         try:
             return (int(os.lstat(self._repo.wjoin(self._path)).st_mtime), tz)
         except OSError, err:
             if err.errno != errno.ENOENT: raise
             return (t, tz)
 
     def cmp(self, text): return self._repo.wread(self._path) == text

mercurial/merge.py

@@ -1,564 +1,564
 # merge.py - directory-level update/merge handling for Mercurial
 #
 # Copyright 2006, 2007 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms
 # of the GNU General Public License, incorporated herein by reference.
 
 from node import *
 from i18n import _
 import errno, util, os, tempfile, context
 
 def filemerge(repo, fw, fo, wctx, mctx):
     """perform a 3-way merge in the working directory
 
     fw = filename in the working directory
     fo = filename in other parent
     wctx, mctx = working and merge changecontexts
     """
 
     def temp(prefix, ctx):
         pre = "%s~%s." % (os.path.basename(ctx.path()), prefix)
         (fd, name) = tempfile.mkstemp(prefix=pre)
         data = repo.wwritedata(ctx.path(), ctx.data())
         f = os.fdopen(fd, "wb")
         f.write(data)
         f.close()
         return name
 
     fcm = wctx.filectx(fw)
     fco = mctx.filectx(fo)
 
     if not fco.cmp(fcm.data()): # files identical?
         return None
 
     fca = fcm.ancestor(fco)
     if not fca:
         fca = repo.filectx(fw, fileid=nullrev)
     a = repo.wjoin(fw)
     b = temp("base", fca)
     c = temp("other", fco)
 
     if fw != fo:
         repo.ui.status(_("merging %s and %s\n") % (fw, fo))
     else:
         repo.ui.status(_("merging %s\n") % fw)
 
     repo.ui.debug(_("my %s other %s ancestor %s\n") % (fcm, fco, fca))
 
     cmd = (os.environ.get("HGMERGE") or repo.ui.config("ui", "merge")
            or "hgmerge")
     r = util.system('%s "%s" "%s" "%s"' % (cmd, a, b, c), cwd=repo.root,
                     environ={'HG_FILE': fw,
                              'HG_MY_NODE': str(wctx.parents()[0]),
                              'HG_OTHER_NODE': str(mctx)})
     if r:
         repo.ui.warn(_("merging %s failed!\n") % fw)
 
     os.unlink(b)
     os.unlink(c)
     return r
 
 def checkunknown(wctx, mctx):
     "check for collisions between unknown files and files in mctx"
     man = mctx.manifest()
     for f in wctx.unknown():
         if f in man:
             if mctx.filectx(f).cmp(wctx.filectx(f).data()):
                 raise util.Abort(_("untracked local file '%s' differs"
                                    " from remote version") % f)
 
 def checkcollision(mctx):
     "check for case folding collisions in the destination context"
     folded = {}
     for fn in mctx.manifest():
         fold = fn.lower()
         if fold in folded:
             raise util.Abort(_("case-folding collision between %s and %s")
                              % (fn, folded[fold]))
         folded[fold] = fn
 
 def forgetremoved(wctx, mctx):
     """
     Forget removed files
 
     If we're jumping between revisions (as opposed to merging), and if
     neither the working directory nor the target rev has the file,
     then we need to remove it from the dirstate, to prevent the
     dirstate from listing the file when it is no longer in the
     manifest.
     """
 
     action = []
     man = mctx.manifest()
     for f in wctx.deleted() + wctx.removed():
         if f not in man:
             action.append((f, "f"))
 
     return action
 
 def findcopies(repo, m1, m2, ma, limit):
     """
     Find moves and copies between m1 and m2 back to limit linkrev
     """
 
     def nonoverlap(d1, d2, d3):
         "Return list of elements in d1 not in d2 or d3"
         l = [d for d in d1 if d not in d3 and d not in d2]
         l.sort()
         return l
 
     def dirname(f):
         s = f.rfind("/")
         if s == -1:
             return ""
         return f[:s]
 
     def dirs(files):
         d = {}
         for f in files:
             f = dirname(f)
             while f not in d:
                 d[f] = True
                 f = dirname(f)
         return d
 
     wctx = repo.workingctx()
 
     def makectx(f, n):
         if len(n) == 20:
             return repo.filectx(f, fileid=n)
         return wctx.filectx(f)
     ctx = util.cachefunc(makectx)
 
     def findold(fctx):
         "find files that path was copied from, back to linkrev limit"
         old = {}
         seen = {}
         orig = fctx.path()
         visit = [fctx]
         while visit:
             fc = visit.pop()
             s = str(fc)
             if s in seen:
                 continue
             seen[s] = 1
             if fc.path() != orig and fc.path() not in old:
                 old[fc.path()] = 1
             if fc.rev() < limit:
                 continue
             visit += fc.parents()
 
         old = old.keys()
         old.sort()
         return old
 
     copy = {}
     fullcopy = {}
     diverge = {}
 
     def checkcopies(c, man):
         '''check possible copies for filectx c'''
         for of in findold(c):
             fullcopy[c.path()] = of # remember for dir rename detection
             if of not in man: # original file not in other manifest?
                 if of in ma:
                     diverge.setdefault(of, []).append(c.path())
                 continue
             c2 = ctx(of, man[of])
             ca = c.ancestor(c2)
             if not ca: # unrelated?
                 continue
             # named changed on only one side?
             if ca.path() == c.path() or ca.path() == c2.path():
                 if c == ca or c2 == ca: # no merge needed, ignore copy
                     continue
                 copy[c.path()] = of
 
     if not repo.ui.configbool("merge", "followcopies", True):
         return {}, {}
 
     # avoid silly behavior for update from empty dir
     if not m1 or not m2 or not ma:
         return {}, {}
 
     u1 = nonoverlap(m1, m2, ma)
     u2 = nonoverlap(m2, m1, ma)
 
     for f in u1:
         checkcopies(ctx(f, m1[f]), m2)
 
     for f in u2:
         checkcopies(ctx(f, m2[f]), m1)
 
     d2 = {}
     for of, fl in diverge.items():
         for f in fl:
             fo = list(fl)
             fo.remove(f)
             d2[f] = (of, fo)
     #diverge = d2
 
     if not fullcopy or not repo.ui.configbool("merge", "followdirs", True):
         return copy, diverge
 
     # generate a directory move map
     d1, d2 = dirs(m1), dirs(m2)
     invalid = {}
     dirmove = {}
 
     # examine each file copy for a potential directory move, which is
     # when all the files in a directory are moved to a new directory
     for dst, src in fullcopy.items():
         dsrc, ddst = dirname(src), dirname(dst)
         if dsrc in invalid:
             # already seen to be uninteresting
             continue
         elif dsrc in d1 and ddst in d1:
             # directory wasn't entirely moved locally
             invalid[dsrc] = True
         elif dsrc in d2 and ddst in d2:
             # directory wasn't entirely moved remotely
             invalid[dsrc] = True
         elif dsrc in dirmove and dirmove[dsrc] != ddst:
             # files from the same directory moved to two different places
             invalid[dsrc] = True
         else:
             # looks good so far
             dirmove[dsrc + "/"] = ddst + "/"
 
     for i in invalid:
         if i in dirmove:
             del dirmove[i]
 
     del d1, d2, invalid
 
     if not dirmove:
         return copy, diverge
 
     # check unaccounted nonoverlapping files against directory moves
     for f in u1 + u2:
         if f not in fullcopy:
             for d in dirmove:
                 if f.startswith(d):
                     # new file added in a directory that was moved, move it
                     copy[f] = dirmove[d] + f[len(d):]
                     break
 
     return copy, diverge
 
 def manifestmerge(repo, p1, p2, pa, overwrite, partial):
     """
     Merge p1 and p2 with ancestor ma and generate merge action list
 
     overwrite = whether we clobber working files
     partial = function to filter file lists
     """
 
     repo.ui.note(_("resolving manifests\n"))
     repo.ui.debug(_(" overwrite %s partial %s\n") % (overwrite, bool(partial)))
     repo.ui.debug(_(" ancestor %s local %s remote %s\n") % (pa, p1, p2))
 
     m1 = p1.manifest()
     m2 = p2.manifest()
     ma = pa.manifest()
     backwards = (pa == p2)
     action = []
     copy = {}
     diverge = {}
 
     def fmerge(f, f2=None, fa=None):
         """merge flags"""
         if not f2:
             f2 = f
             fa = f
         a, b, c = ma.execf(fa), m1.execf(f), m2.execf(f2)
         if ((a^b) | (a^c)) ^ a:
             return 'x'
         a, b, c = ma.linkf(fa), m1.linkf(f), m2.linkf(f2)
         if ((a^b) | (a^c)) ^ a:
             return 'l'
         return ''
 
     def act(msg, m, f, *args):
         repo.ui.debug(" %s: %s -> %s\n" % (f, msg, m))
         action.append((f, m) + args)
 
     if not (backwards or overwrite):
         copy, diverge = findcopies(repo, m1, m2, ma, pa.rev())
 
     for of, fl in diverge.items():
         act("divergent renames", "dr", of, fl)
 
     copied = dict.fromkeys(copy.values())
 
     # Compare manifests
     for f, n in m1.iteritems():
         if partial and not partial(f):
             continue
         if f in m2:
             # are files different?
             if n != m2[f]:
                 a = ma.get(f, nullid)
                 # are both different from the ancestor?
                 if not overwrite and n != a and m2[f] != a:
                     act("versions differ", "m", f, f, f, fmerge(f), False)
                 # are we clobbering?
                 # is remote's version newer?
                 # or are we going back in time and clean?
                 elif overwrite or m2[f] != a or (backwards and not n[20:]):
                     act("remote is newer", "g", f, m2.flags(f))
                 # local is newer, not overwrite, check mode bits
                 elif fmerge(f) != m1.flags(f):
                     act("update permissions", "e", f, m2.flags(f))
             # contents same, check mode bits
             elif m1.flags(f) != m2.flags(f):
                 if overwrite or fmerge(f) != m1.flags(f):
                     act("update permissions", "e", f, m2.flags(f))
         elif f in copied:
             continue
         elif f in copy:
             f2 = copy[f]
             if f2 not in m2: # directory rename
                 act("remote renamed directory to " + f2, "d",
                     f, None, f2, m1.flags(f))
             elif f2 in m1: # case 2 A,B/B/B
                 act("local copied to " + f2, "m",
                     f, f2, f, fmerge(f, f2, f2), False)
             else: # case 4,21 A/B/B
                 act("local moved to " + f2, "m",
                     f, f2, f, fmerge(f, f2, f2), False)
         elif f in ma:
             if n != ma[f] and not overwrite:
                 if repo.ui.prompt(
                     (_(" local changed %s which remote deleted\n") % f) +
                     _("(k)eep or (d)elete?"), _("[kd]"), _("k")) == _("d"):
                     act("prompt delete", "r", f)
             else:
                 act("other deleted", "r", f)
         else:
             # file is created on branch or in working directory
             if (overwrite and n[20:] != "u") or (backwards and not n[20:]):
                 act("remote deleted", "r", f)
 
     for f, n in m2.iteritems():
         if partial and not partial(f):
             continue
         if f in m1:
             continue
         if f in copied:
             continue
         if f in copy:
             f2 = copy[f]
             if f2 not in m1: # directory rename
                 act("local renamed directory to " + f2, "d",
                     None, f, f2, m2.flags(f))
             elif f2 in m2: # rename case 1, A/A,B/A
                 act("remote copied to " + f, "m",
                     f2, f, f, fmerge(f2, f, f2), False)
             else: # case 3,20 A/B/A
                 act("remote moved to " + f, "m",
                     f2, f, f, fmerge(f2, f, f2), True)
         elif f in ma:
             if overwrite or backwards:
                 act("recreating", "g", f, m2.flags(f))
             elif n != ma[f]:
                 if repo.ui.prompt(
                     (_("remote changed %s which local deleted\n") % f) +
                     _("(k)eep or (d)elete?"), _("[kd]"), _("k")) == _("k"):
                     act("prompt recreating", "g", f, m2.flags(f))
         else:
             act("remote created", "g", f, m2.flags(f))
 
     return action
 
 def applyupdates(repo, action, wctx, mctx):
     "apply the merge action list to the working directory"
 
     updated, merged, removed, unresolved = 0, 0, 0, 0
     action.sort()
     for a in action:
         f, m = a[:2]
         if f and f[0] == "/":
             continue
         if m == "r": # remove
             repo.ui.note(_("removing %s\n") % f)
             util.audit_path(f)
             try:
                 util.unlink(repo.wjoin(f))
             except OSError, inst:
                 if inst.errno != errno.ENOENT:
                     repo.ui.warn(_("update failed to remove %s: %s!\n") %
                                  (f, inst.strerror))
             removed += 1
         elif m == "m": # merge
             f2, fd, flags, move = a[2:]
             r = filemerge(repo, f, f2, wctx, mctx)
             if r > 0:
                 unresolved += 1
             else:
                 if r is None:
                     updated += 1
                 else:
                     merged += 1
             if f != fd:
                 repo.ui.debug(_("copying %s to %s\n") % (f, fd))
                 repo.wwrite(fd, repo.wread(f), flags)
                 if move:
                     repo.ui.debug(_("removing %s\n") % f)
                     os.unlink(repo.wjoin(f))
             util.set_exec(repo.wjoin(fd), "x" in flags)
         elif m == "g": # get
             flags = a[2]
             repo.ui.note(_("getting %s\n") % f)
             t = mctx.filectx(f).data()
             repo.wwrite(f, t, flags)
             updated += 1
         elif m == "d": # directory rename
             f2, fd, flags = a[2:]
             if f:
                 repo.ui.note(_("moving %s to %s\n") % (f, fd))
                 t = wctx.filectx(f).data()
                 repo.wwrite(fd, t, flags)
                 util.unlink(repo.wjoin(f))
             if f2:
                 repo.ui.note(_("getting %s to %s\n") % (f2, fd))
                 t = mctx.filectx(f2).data()
                 repo.wwrite(fd, t, flags)
             updated += 1
         elif m == "dr": # divergent renames
             fl = a[2]
             repo.ui.warn("warning: detected divergent renames of %s to:\n" % f)
             for nf in fl:
                 repo.ui.warn(" %s\n" % nf)
         elif m == "e": # exec
             flags = a[2]
             util.set_exec(repo.wjoin(f), flags)
 
     return updated, merged, removed, unresolved
 
 def recordupdates(repo, action, branchmerge):
     "record merge actions to the dirstate"
 
     for a in action:
         f, m = a[:2]
         if m == "r": # remove
             if branchmerge:
                 repo.dirstate.update([f], 'r')
             else:
                 repo.dirstate.forget([f])
         elif m == "f": # forget
             repo.dirstate.forget([f])
         elif m == "g": # get
             if branchmerge:
                 repo.dirstate.update([f], 'n', st_mtime=-1)
             else:
                 repo.dirstate.update([f], 'n')
         elif m == "m": # merge
             f2, fd, flag, move = a[2:]
             if branchmerge:
                 # We've done a branch merge, mark this file as merged
                 # so that we properly record the merger later
                 repo.dirstate.update([fd], 'm')
                 if f != f2: # copy/rename
                     if move:
                         repo.dirstate.update([f], 'r')
                     if f != fd:
                         repo.dirstate.copy(f, fd)
                     else:
                         repo.dirstate.copy(f2, fd)
             else:
                 # We've update-merged a locally modified file, so
                 # we set the dirstate to emulate a normal checkout
                 # of that file some time in the past. Thus our
                 # merge will appear as a normal local file
                 # modification.
                 repo.dirstate.update([fd], 'n', st_size=-1, st_mtime=-1)
                 if move:
                     repo.dirstate.forget([f])
         elif m == "d": # directory rename
             f2, fd, flag = a[2:]
             if branchmerge:
                 repo.dirstate.update([fd], 'a')
                 if f:
                     repo.dirstate.update([f], 'r')
                     repo.dirstate.copy(f, fd)
                 if f2:
                     repo.dirstate.copy(f2, fd)
             else:
                 repo.dirstate.update([fd], 'n')
                 if f:
                     repo.dirstate.forget([f])
 
 def update(repo, node, branchmerge, force, partial, wlock):
     """
     Perform a merge between the working directory and the given node
 
     branchmerge = whether to merge between branches
     force = whether to force branch merging or file overwriting
     partial = a function to filter file lists (dirstate not updated)
     wlock = working dir lock, if already held
     """
 
     if not wlock:
         wlock = repo.wlock()
 
     wc = repo.workingctx()
     if node is None:
         # tip of current branch
         try:
             node = repo.branchtags()[wc.branch()]
         except KeyError:
             raise util.Abort(_("branch %s not found") % wc.branch())
     overwrite = force and not branchmerge
     forcemerge = force and branchmerge
     pl = wc.parents()
     p1, p2 = pl[0], repo.changectx(node)
     pa = p1.ancestor(p2)
     fp1, fp2, xp1, xp2 = p1.node(), p2.node(), str(p1), str(p2)
     fastforward = False
 
     ### check phase
     if not overwrite and len(pl) > 1:
         raise util.Abort(_("outstanding uncommitted merges"))
     if pa == p1 or pa == p2: # is there a linear path from p1 to p2?
         if branchmerge:
-            if p1.branch() != p2.branch():
+            if p1.branch() != p2.branch() and pa != p2:
                 fastforward = True
             else:
                 raise util.Abort(_("there is nothing to merge, just use "
                                    "'hg update' or look at 'hg heads'"))
     elif not (overwrite or branchmerge):
         raise util.Abort(_("update spans branches, use 'hg merge' "
                            "or 'hg update -C' to lose changes"))
     if branchmerge and not forcemerge:
         if wc.files():
             raise util.Abort(_("outstanding uncommitted changes"))
 
     ### calculate phase
     action = []
     if not force:
         checkunknown(wc, p2)
     if not util.checkfolding(repo.path):
         checkcollision(p2)
     if not branchmerge:
         action += forgetremoved(wc, p2)
     action += manifestmerge(repo, wc, p2, pa, overwrite, partial)
 
     ### apply phase
     if not branchmerge: # just jump to the new rev
         fp1, fp2, xp1, xp2 = fp2, nullid, xp2, ''
     if not partial:
         repo.hook('preupdate', throw=True, parent1=xp1, parent2=xp2)
 
     stats = applyupdates(repo, action, wc, p2)
 
     if not partial:
         recordupdates(repo, action, branchmerge)
         repo.dirstate.setparents(fp1, fp2)
         if not branchmerge and not fastforward:
             repo.dirstate.setbranch(p2.branch())
         repo.hook('update', parent1=xp1, parent2=xp2, error=stats[3])
 
     return stats