2162 def back_out(ctx, parent=None, wc=None):

  2163     if parent is None:

  2164         if ctx.p2() is not None:

  2165             raise error.ProgrammingError(

  2166                 b"must specify parent of merge commit to back out"

  2167             )

  2168         parent = ctx.p1()

  2169     return update(

  2170         ctx.repo(),

  2171         parent,

  2172         branchmerge=True,

  2173         force=True,

  2174         ancestor=ctx.node(),

  2175         mergeancestor=False,

  2176     )

  2177 

  2178