Infer the dimension name and 1d coordinate variable (if appropriate)
    for concatenating along the new dimension.

def _calc_concat_dim_coord(dim):
    """
    Infer the dimension name and 1d coordinate variable (if appropriate)
    for concatenating along the new dimension.
    """
    from .dataarray import DataArray

    if isinstance(dim, str):
        coord = None
    elif not isinstance(dim, (DataArray, Variable)):
        dim_name = getattr(dim, 'name', None)
        if dim_name is None:
            dim_name = 'concat_dim'
        coord = IndexVariable(dim_name, dim)
        dim = dim_name
    elif not isinstance(dim, DataArray):
        coord = as_variable(dim).to_index_variable()
        dim, = coord.dims
    else:
        coord = dim
        dim, = coord.dims
    return dim, coord