Backport PEP420 namespace package support from Cython 3

[mkoeppe]

After #33011, downstream packages that use Cython and cimport Sage modules need to activate PEP 420 namespace package support in Cython using with cython_namespace_package_support (as is done in https://github.com/sagemath/sage-prod/blob/develop/src/setup.py#L106 for sagelib).

This feature is standard in the upcoming Cython 3 (#29863). Until downstream packages are updated, we can patch our Cython.

Upstream backport PR:

• Backport to 0.29.x: Add PEP420 namespace support cython/cython#4918

Depends on #34237

CC: @culler @tscrim @videlec @jhpalmieri

Component: packages: standard

Author: Matthias Koeppe

Branch/Commit: 48a9ba2

Reviewer: Marc Culler, John Palmieri

Issue created by migration from https://trac.sagemath.org/ticket/34221

[mkoeppe]

Branch: u/mkoeppe/backport_pep420_namespace_package_support_from_cython_3

[mkoeppe]

New commits:

7e72b2a

build/pkgs/cython/patches/4918.patch: New

[mkoeppe]

Commit: 7e72b2a

[mkoeppe]

Description changed:

--- 
+++ 
@@ -1,6 +1,6 @@
 After #33011, downstream packages that use Cython and `cimport` Sage modules need to activate PEP 420 namespace package support in Cython using `with cython_namespace_package_support` (as is done in https://github.com/sagemath/sage-prod/blob/develop/src/setup.py#L106 for sagelib).
 
-This feature is standard in the upcoming Cython 3. Until downstream packages are updated, we can patch our Cython.
+This feature is standard in the upcoming Cython 3 (#29863). Until downstream packages are updated, we can patch our Cython.
 
 Upstream backport PR:
 - https://github.com/cython/cython/pull/4918

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

176531a

build/pkgs/cython/package-version.txt: Add patchlevel

[sagetrac-git]

Changed commit from 7e72b2a to 176531a

[culler]

comment:5

This solved all of the problems that I ran into with the p_group_cohomology and sage_numerical_backends_coin packages. The problems were caused by cython not finding the .pxd files that were needed for cimport statements. With this patch the cimports worked and I got a successful build of 9.7.beta6 on an arm64 mac with a minimal environment.

[mkoeppe]

comment:6

Thanks for testing!

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

a2f7980	24237: upgrade; Cython 0.29.32
48a9ba2	Merge #34237

[sagetrac-git]

Changed commit from 176531a to 48a9ba2

[mkoeppe]

Dependencies: #34237

[jhpalmieri]

comment:11

This works for me and also fixes the problems with sage_numerical_backends_coin. p_group_cohomology still fails for me ("ld: library not found for -lmodres"), for what that's worth.

[jhpalmieri]

Reviewer: Marc Culler, John Palmieri