in doctest, arrow() does not understand it must call arrow3d()

[Dima Pasechnik]

This is with the latest 9.3.beta5 on a Gentoo machine:

./sage -t --random-seed=0 src/sage/plot/arrow.py
too many failed tests, not using stored timings
Running doctests with ID 2021-01-01-09-55-29-e04bf10a.
Git branch: HEAD
Using --optional=build,dochtml,gentoo,memlimit,pip,sage,sage_spkg
Doctesting 1 file.
*** Warning: not enough memory, new PARI stack 432537600
sage -t --random-seed=0 src/sage/plot/arrow.py
**********************************************************************

File "src/sage/plot/arrow.py", line 455, in sage.plot.arrow.arrow
Failed example:
arrow((0,0,1), (1,1,1))
Exception raised:
Traceback (most recent call last):
File "/mnt/opt/Sage/sage-dev/local/lib/python3.9/site-packages/sage/plot/arrow.py",
line 464, in arrow
return arrow2d(tailpoint, headpoint, **kwds)
File "/mnt/opt/Sage/sage-dev/local/lib/python3.9/site-packages/sage/misc/decorators.py",
line 651, in wrapper
return func(*args, **kwds)
File "/mnt/opt/Sage/sage-dev/local/lib/python3.9/site-packages/sage/misc/decorators.py",
line 491, in wrapper
return func(*args, **options)
File "/mnt/opt/Sage/sage-dev/local/lib/python3.9/site-packages/sage/plot/arrow.py",
line 627, in arrow2d
xtail, ytail = tailpoint
ValueError: too many values to unpack (expected 2)
...


In a terminal session this command works as expected, launching a web
page in a browser.

So this is something to do with the context manager or whatever this
is called in doctesting framework
(on this machine a lot of doctests fail in weird ways).

What is going on?

[Dima Pasechnik]

OK, the real problem is as follows: arrow() correctly tries to import
and start arrow3d(), but....

ImportError:
/mnt/opt/Sage/sage-dev/local/lib/python3.9/site-packages/sage/modules/vector_double_dense.cpython-39-x86_64-linux-gnu.so:
failed to map segment from shared object

(and this only happens in a doctest, running in terminal works)