CI, BUILD: SciPy build failure with Cython 3.0.3 (bisected)

[tylerjereddy]

This appears to be slightly different from the pandas issue at cython-5747, and I bisected the failure to build SciPy main on Cython commits:

401e880a336576b765e5d6bb1a9718947243d92b is the first bad commit
commit 401e880a336576b765e5d6bb1a9718947243d92b
Author: da-woods <dw-git@d-woods.co.uk>
Date:   Fri Sep 29 11:11:22 2023 +0100

    Show performance hints for nogil functions requiring exception checks (GH-5673)
    
    Performance hints come out similar to warnings but do not make `-Werror` fail.

 Cython/Compiler/Errors.py       | 14 +++++++++
 Cython/Compiler/ExprNodes.py    |  7 +++--
 Cython/Compiler/Nodes.py        |  3 +-
 Cython/Compiler/Options.py      |  4 +++
 Cython/Compiler/PyrexTypes.py   | 13 ++++++++-
 Cython/Compiler/Scanning.py     |  1 +
 Cython/Compiler/Symtab.py       | 12 ++++++++
 Cython/Compiler/TreeFragment.py |  8 +++++-
 Cython/Compiler/UtilityCode.py  |  3 +-
 runtests.py                     | 64 +++++++++++++++++++++++++----------------
 tests/run/nogil.pxd             |  1 +
 tests/run/nogil.pyx             | 39 ++++++++++++++++++++++++-
 tests/run/nogil_other.pxd       |  2 ++
 13 files changed, 138 insertions(+), 33 deletions(-)
 create mode 100644 tests/run/nogil.pxd
 create mode 100644 tests/run/nogil_other.pxd

[tylerjereddy]

Sample failure log here: https://github.com/scipy/scipy/actions/runs/6422201150/job/17438217924?pr=19350

[tylerjereddy]

I actually meant to open upstream, but keeping this ticket open perhaps makes sense until resolved since the CI fails may be confusing otherwise. Here's the upstream ticket: cython/cython#5748

[tylerjereddy]

The upstream folks have both a one-line patch/fix and a small reproducer/regression test, so things are going well on resolving this soon it seems.

[rgommers]

I was going to propose yanking Cython 3.0.3, but there's quite a few bug fixes in there that other projects may need - so yanking isn't necessarily a helpful thing to do. Now that it's fixed upstream, we can avoid this release. I'll open a PR.