fix custom signal handling, which was broken after #166

[tornaria]

There was a typo in #181: when the pari sigint handling was converted
to a general mechanism, the line

	PARI_SIGINT_pending = 0;

got translated into

	custom_signal_unblock();

instead of the correct

	custom_set_pending_signal(0);

This error didn't take effect until #166 removed the pari sigint
handling.

This causes some doctest failures in sagemath:

src/sage/coding/linear_code.py
src/sage/geometry/integral_points.pxi
src/sage/rings/integer.pyx
src/sage/rings/polynomial/polynomial_element.pyx

related to mishandling of AlarmInterrupt.

See: https://github.com/sagemath/cysignals/pull/181/files#r1904885037

Here's one way to trigger the bug without sagemath:

Python 3.13.1 (main, Dec 14 2024, 12:44:03) [GCC 13.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import cypari2
>>> from cysignals.alarm import alarm
>>> try:
...     alarm(0.5)
...     while True: pass
... except:
...     pass
...
>>> cypari2.Pari()
Traceback (most recent call last):
  File "<python-input-3>", line 1, in <module>
	cypari2.Pari()
	~~~~~~~~~~~~^^
  File "cypari2/pari_instance.pyx", line 471, in cypari2.pari_instance.Pari.__cinit__
  File "cypari2/closure.pyx", line 138, in cypari2.closure._pari_init_closure
cysignals.signals.AlarmInterrupt

I added a test in tests/test_custom_signals.py that checks the bug is fixed.

[tornaria]

@dimpase @tobiasdiez: do you know why the cygwin test is failing? It stops with

ModuleNotFoundError: No module named 'mesonpy'

but earlier

Successfully installed Cython-3.0.11 Pygments-2.19.1 Sphinx-7.4.7 alabaster-0.7.16 babel-2.16.0 build-1.2.2.post1 charset-normalizer-3.4.1 docutils-0.21.2 exceptiongroup-1.2.2 flake8-7.1.1 importlib-metadata-8.5.0 mccabe-0.7.0 meson-1.6.1 meson-python-0.17.1 pluggy-1.5.0 pycodestyle-2.12.1 pyflakes-3.2.0 pyproject-metadata-0.9.0 pyproject_hooks-1.2.0 pytest-8.3.4 sphinxcontrib-applehelp-2.0.0 sphinxcontrib-devhelp-2.0.0 sphinxcontrib-htmlhelp-2.1.0 sphinxcontrib-jsmath-1.0.1 sphinxcontrib-qthelp-2.0.0 sphinxcontrib-serializinghtml-2.0.0 tomli-2.2.1 zipp-3.21.0

says meson-python-0.17.1 is installed.

[dimpase]

I'm having a look, but cygwin is more dead than alive, IMHO. We should not worry too much about it. meson-python isn't even listed as a package here: https://cygwin.com/cgit/cygwin-infra/pkg-maint/plain/cygwin-pkg-maint

[tornaria]

I'm having a look, but cygwin is more dead than alive, IMHO. We should not worry too much about it. meson-python isn't even listed as a package here: https://cygwin.com/cgit/cygwin-infra/pkg-maint/plain/cygwin-pkg-maint

Sure, but if it's broken then maybe it should be dropped from CI.

Note it was working not so long ago:
https://github.com/sagemath/cysignals/actions/runs/12239853593/job/34569737654
https://github.com/sagemath/cysignals/actions/runs/12200523630/job/34469785701

[dimpase]

tested this on the current Gentoo (applied https://github.com/sagemath/cysignals/pull/216.patch), all good. @orlitzky

[dimpase]

I'm having a look, but cygwin is more dead than alive, IMHO. We should not worry too much about it. meson-python isn't even listed as a package here: https://cygwin.com/cgit/cygwin-infra/pkg-maint/plain/cygwin-pkg-maint

Sure, but if it's broken then maybe it should be dropped from CI.

Note it was working not so long ago: https://github.com/sagemath/cysignals/actions/runs/12239853593/job/34569737654 https://github.com/sagemath/cysignals/actions/runs/12200523630/job/34469785701

That's from the pre-meson era.
Has it ever worked with meson? I suspect something is off with, like two different pythons at play, one a non-cygwin, the other cygwin.

[dimpase]

I created #218 to try to fix cygwin CI, basically by pip-installing the requirements.txt in the same place as building the package. It goes a bit further, but still fails quickly with a cryptic error in ninja, see
https://github.com/sagemath/cysignals/actions/runs/12773544430/job/35605683764