480     if repo._activebookmark:

   480     return subset & baseset([destutil.destmerge(repo)])

   481         bmheads = repo.bookmarkheads(repo._activebookmark)

   482         curhead = repo[repo._activebookmark].node()

   483         if len(bmheads) == 2:

   484             if curhead == bmheads[0]:

   485                 node = bmheads[1]

   486             else:

   487                 node = bmheads[0]

   488         elif len(bmheads) > 2:

   489             raise error.Abort(_("multiple matching bookmarks to merge - "

   490                 "please merge with an explicit rev or bookmark"),

   491                 hint=_("run 'hg heads' to see all heads"))

   492         elif len(bmheads) <= 1:

   493             raise error.Abort(_("no matching bookmark to merge - "

   494                 "please merge with an explicit rev or bookmark"),

   495                 hint=_("run 'hg heads' to see all heads"))

   496     else:

   497         branch = repo[None].branch()

   498         bheads = repo.branchheads(branch)

   499         nbhs = [bh for bh in bheads if not repo[bh].bookmarks()]

   500 

   501         if len(nbhs) > 2:

   502             raise error.Abort(_("branch '%s' has %d heads - "

   503                                "please merge with an explicit rev")

   504                              % (branch, len(bheads)),

   505                              hint=_("run 'hg heads .' to see heads"))

   506 

   507         parent = repo.dirstate.p1()

   508         if len(nbhs) <= 1:

   509             if len(bheads) > 1:

   510                 raise error.Abort(_("heads are bookmarked - "

   511                                    "please merge with an explicit rev"),

   512                                  hint=_("run 'hg heads' to see all heads"))

   513             if len(repo.heads()) > 1:

   514                 raise error.Abort(_("branch '%s' has one head - "

   515                                    "please merge with an explicit rev")

   516                                  % branch,

   517                                  hint=_("run 'hg heads' to see all heads"))

   518             msg, hint = _('nothing to merge'), None

   519             if parent != repo.lookup(branch):

   520                 hint = _("use 'hg update' instead")

   521             raise error.Abort(msg, hint=hint)

   522 

   523         if parent not in bheads:

   524             raise error.Abort(_('working directory not at a head revision'),

   525                              hint=_("use 'hg update' or merge with an "

   526                                     "explicit revision"))

   527         if parent == nbhs[0]:

   528             node = nbhs[-1]

   529         else:

   530             node = nbhs[0]

   531     return subset & baseset([repo[node].rev()])