Index.map followups

[jreback]

xref #15081, a couple of issues

• IntervalIndex.map is xfailed
• parametrize indexex/common.py/test_map similar to how indexex/datetimelike.py/test_map is done (IOW on dict / Series) (COMPAT: map infers all-nan / empty correctly #18491)
• resolve datetimelike with empty map [2] should be all NaT for the datetimelikes. (COMPAT: map infers all-nan / empty correctly #18491)

In [2]: pd.date_range('20130101', periods=3).map({})
Out[2]: Float64Index([nan, nan, nan], dtype='float64')

In [3]: pd.Index([1,2,3]).map({})
Out[3]: Float64Index([nan, nan, nan], dtype='float64')

[jreback]

cc @jorisvandenbossche (point 3)
cc @jschendel (point 1)

[jschendel]

Regarding point 1: To be clear, the underlying issue referenced here is #16410, right? test_map xpasses locally for me, and that was the closest thing I could find based on the xfail message. The problem described in #16410 is still occurring, but I haven't immediately been able to produce any errors with map using a similar setup.

[jschendel]

Side note: should mapping an empty dictionary against an IntervalIndex return an IntervalIndex? Currently returns a Float64Index, which seems kind of strange:

In [2]: pd.interval_range(0, 4).map({})
Out[2]: Float64Index([nan, nan, nan, nan], dtype='float64')

[jreback]

@jschendel I just noticed that test_interval.py/test_map is xfailed. It might have been disabled during this re-factoring. if that is the case, then just need to re-eable.

#18491 fixes all of the Indexes to return correctly there own type if {} is passed. I think II should do the same (but again still xfailed).

[jorisvandenbossche]

@jreback Is there a specific reason you pinged me for point 3 ? (apart from general attention)

[jreback]

@jorisvandenbossche no, you had raised the point in the original issue (note this is all now resolved by #18491)