What to do with future Ambiguity Error about overlapping names when sorting?

[TomAugspurger]

xref #17361

In [24]: df = pd.DataFrame({"a": [1, 2], "b": [3, 4]}, index=pd.Index([1, 2], name='a'))

In [25]: df.sort_values(['a', 'b'])
/Users/taugspurger/.virtualenvs/pandas-dev/bin/ipython:1: FutureWarning: 'a' is both an index level and a column label.
Defaulting to column, but this will raise an ambiguity error in a future version
  #!/Users/taugspurger/Envs/pandas-dev/bin/python3
Out[25]:
   a  b
a
1  1  3
2  2  4

What should the user do in this situation? Should we provide a keyword to disambiguate? A literal like pd.ColumnLabel('a') or pd.IndexName('a')? Or do we require that they rename an index or column? Right now, they're essentially stuck with the last one. If we want to discourage that, then I suppose that's OK. But it's somewhat common to end up with overlapping names, from e.g. a groupby.

cc @jmmease

[jorisvandenbossche]

This is exactly the same as #21080 ?

[jorisvandenbossche]

I updated #21080 with the additional text you had here