Applying numba.typed.List to a nested Python list doesn't result in a nested typed-list

[rht]

Reporting a bug

Instead, it turns into a reflected list.

• I have tried using the latest released version of Numba (most recent is
  visible in the change log (https://github.com/numba/numba/blob/master/CHANGE_LOG).
• I have included below a minimal working reproducer (if you are unsure how
  to write one see http://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports).

I'm copy-pasting the example reported by @esc in #6090 (comment):

In [4]: List([[1, 2, 3], [4, 5, 6]])
Out[4]: ListType[reflected list(int64)<iv=None>]([[4892186944], [<IPython.lib.pretty.Group object at 0x124ad7040>, <IPython.lib.pretty.Group object at 0x124934cd0>]])

Additionally, there is a segmentation fault when the reflected list is assigned to a Python variable.

In [6]: l = List([[1, 2, 3], [4, 5, 6]])
/Users/vhaenel/git/numba/numba/typed/typedlist.py:66: NumbaPendingDeprecationWarning:
Encountered the use of a type that is scheduled for deprecation: type 'reflected list' found for argument 'item' of function 'impl_append.<locals>.impl'.

For more information visit https://numba.pydata.org/numba-doc/latest/reference/deprecation.html#deprecation-of-reflection-for-list-and-set-types

File "numba/typed/listobject.py", line 596:

    def impl(l, item):
    ^

  l.append(item)
/Users/vhaenel/git/numba/numba/core/ir_utils.py:2031: NumbaPendingDeprecationWarning:
Encountered the use of a type that is scheduled for deprecation: type 'reflected list' found for argument 'item' of function '_append'.

For more information visit https://numba.pydata.org/numba-doc/latest/reference/deprecation.html#deprecation-of-reflection-for-list-and-set-types

File "numba/typed/typedlist.py", line 65:
@njit
def _append(l, item):
^

  warnings.warn(NumbaPendingDeprecationWarning(msg, loc=loc))

In [7]: l
Out[7]: [1]    46853 segmentation fault (core dumped)  ipython

[stuartarchibald]

Thanks for the report. Given the typed list ctor implementation I don't think this is unexpected, but clearly shouldn't happen.

[rht]

Reminder to update the documentation to be along the line of #6090 once fixed.

[esc]

@rht thanks for reporting, much appreciated.