py3: typing should not be installed in Python 3

[videlec]

typing is a standard Sage package but it is also included in Python 3.7 standard library. This module is not compatible with Python > 3.5. For example it breaks pytest

  File "/opt/sage/local/lib/python3.7/site-packages/_pytest/assertion/__init__.py", line 6, in <module>
    from _pytest.assertion import rewrite
  File "/opt/sage/local/lib/python3.7/site-packages/_pytest/assertion/rewrite.py", line 15, in <module>
    from typing import Dict
  File "/opt/sage/local/lib/python3.7/site-packages/typing.py", line 1356, in <module>
    class Callable(extra=collections_abc.Callable, metaclass=CallableMeta):
  File "/opt/sage/local/lib/python3.7/site-packages/typing.py", line 1004, in __new__
    self._abc_registry = extra._abc_registry
AttributeError: type object 'Callable' has no attribute '_abc_registry'
FAIL eantic_sage.py (exit status: 1)

We should disable the installation of typing when Sage is built with Python 3.

CC: @antonio-rojas @embray @kiwifb @timokau @infinity0 @isuruf @saraedum @slel @SnarkBoojum @tobihan

Component: packages: standard

Author: Vincent Delecroix

Branch/Commit: 68e941e

Reviewer: Julian Rüth

Issue created by migration from https://trac.sagemath.org/ticket/28499

[videlec]

Author: Vincent Delecroix

[videlec]

Branch: u/vdelecroix/28499

[videlec]

New commits:

68e941e

28499: do not install typing with Python 3

[videlec]

Commit: 68e941e

[saraedum]

comment:3

Not a very elegant fix but I think that's just the limitations of SPKGs. So, this looks good to me. I cannot test it because I have no Python 3 SageMath installed. If you're confident that this works, feel free to set this to positive review.

[saraedum]

Reviewer: Julian Rüth

[saraedum]

comment:4

CCing a usual suspect for testing Python 3 stuff :)

[saraedum]

comment:5

Or wait for #28041 and GitLab CI will test it automatically.

[videlec]

comment:6

Works for me on Python 3.

[slel]

comment:8

cc-ing packagers for various distros

[embray]

comment:9

There is another way. With an spkg-configure.m4, in I believe the third argument to [https://github.com/sagemath/sagetrac-mirror/blob/develop/m4/sage_spkg_configure.m4 SAGE_SPKG_CONFIGURE` you can pass a check for whether the package is even required.

It's not well documented how to do this, but if you set sage_require_typing=no in this check then it won't require installation of the package (it will just be treated as a dummy package).

[fchapoton]

comment:10

moving milestone to 9.0 (after release of 8.9)

[vbraun]

Changed branch from u/vdelecroix/28499 to 68e941e