WHL: build limited-api compliant wheels

Author: neutrinoceros

pyproject.toml

@@ -103,3 +103,21 @@ ignore = [
     "test",
     "test/*",
 ]
+
+[tool.cibuildwheel]
+build-verbosity = 1
+skip = [
+    "*musllinux_aarch64*",
+]
+
+# Emulated testing is slow, so trust that the Python 3.12 test is good enough on aarch64
+# (takes about 5 minutes per wheel to build, and 5 minutes to test)
+test-skip = [
+    "cp3{8,9,10,11}-*_aarch64",
+]
+test-groups = "dev"
+test-command = [
+    '''python -c "import cftime; print(f'cftime v{cftime.__version__}')"''',
+    "python -m pytest -vv {package}/test"
+]
+environment = {CFTIME_LIMITED_API="1"}

setup.py

@@ -1,5 +1,6 @@
 import os
 import sys
+import sysconfig
 import numpy
 
 from Cython.Build import cythonize
@@ -29,6 +30,21 @@
 CFTIME_DIR = os.path.join(SRCDIR, NAME)
 CYTHON_FNAME = os.path.join(CFTIME_DIR, '_{}.pyx'.format(NAME))
 
+USE_PY_LIMITED_API = (
+    # require opt-in (builds are specialized by default)
+    os.getenv('CFTIME_LIMITED_API', '0') == '1'
+    # Cython + numpy + limited API de facto requires Python >=3.11
+    and sys.version_info >= (3, 11)
+    # as of Python 3.14t, free-threaded builds don't support the limited API
+    and not sysconfig.get_config_var("Py_GIL_DISABLED")
+)
+ABI3_TARGET_VERSION = "".join(str(_) for _ in sys.version_info[:2])
+ABI3_TARGET_HEX = hex(sys.hexversion & 0xFFFF00F0)
+
+if USE_PY_LIMITED_API:
+    SETUP_OPTIONS = {"bdist_wheel": {"py_limited_api": f"cp{ABI3_TARGET_VERSION}"}}
+else:
+    SETUP_OPTIONS = {}
 
 class CleanCython(Command):
     description = 'Purge artifacts built by Cython'
@@ -60,6 +76,8 @@ def run(self):
     }
     DEFINE_MACROS += [('CYTHON_TRACE', '1'),
                      ('CYTHON_TRACE_NOGIL', '1')]
+    if USE_PY_LIMITED_API:
+        DEFINE_MACROS.append(("Py_LIMITED_API", ABI3_TARGET_HEX))
     if FLAG_COVERAGE in sys.argv:
         sys.argv.remove(FLAG_COVERAGE)
     print('enable: "linetrace" Cython compiler directive')
@@ -71,7 +89,8 @@ def run(self):
     extension = Extension('{}._{}'.format(NAME, NAME),
                           sources=[os.path.relpath(CYTHON_FNAME, BASEDIR)],
                           define_macros=DEFINE_MACROS,
-                          include_dirs=[numpy.get_include(),])
+                          include_dirs=[numpy.get_include()],
+                          py_limited_api=USE_PY_LIMITED_API)
 
     ext_modules = cythonize(
         extension,
@@ -82,4 +101,5 @@ def run(self):
 setup(
     cmdclass={'clean_cython': CleanCython},
     ext_modules=ext_modules,
+    options=SETUP_OPTIONS,
 )