BUG: Prevent stackoverflow on self-containing arrays

[eric-wieser]

Approaches #8306. This still errors, but it does so at a python level, without
a segfault.

This makes the following not segfault:

a = np.array([None])
a[0] = a
bool(a)

On the other hand, it still behaves incorrectly

In [8]: bool(a)
---------------------------------------------------------------------------
RecursionError                            Traceback (most recent call last)
RecursionError: maximum recursion depth exceeded while converting array to bool

During handling of the above exception, another exception occurred:

SystemError                               Traceback (most recent call last)
<ipython-input-8-7af9bc0b6a67> in <module>()
----> 1 bool(a)

SystemError: <class 'bool'> returned a result with an error set

But that's a different bug (#9078)

[juliantaylor]

can be put into the lower if scope

[juliantaylor]

needs curly braces

[eric-wieser]

Oops, was just copying cpython there

[eric-wieser]

@juliantaylor: Fixed

[juliantaylor]

needs a test, then lgtm

[eric-wieser]

Tests added - seems that we weren't testing bool(arr) at all

[juliantaylor]

should also have a python 2 comment

[juliantaylor]

thanks

[eric-wieser]

For some reason, this doesn't fix a in a - I can't work out where the recursion is happening, as Py_RichCompare is supposed to already call Py_EnterRecursiveCall

[juliantaylor]

DEPRECATE in arrayobject.c:1411 triggers another enter to the recursion checking. Once one of these errors has been thrown one must abort immediately.

[eric-wieser]

Can we remove that deprecation in 1.14? We're now at the two year mark

[juliantaylor]

probably not, as far as I recall that was one that caused enough noise to come up on the mailing list, but then I am of the opinion that deprecations are to almost never be removed, others might disagree.

[eric-wieser]

then I am of the opinion that deprecations are to almost never be removed

Well in that case, the deprecation message shouldn't have been "this will raise an error in the future" ;). But fair enough, perhaps 1.14 is too soon