Build wheels for PyPy on macOS (#33)

* Try older setuptools to build macOS PyPy wheels
* Updated classifiers and added comment explaining setuptools version
* Use cibuildwheel GHA instead of specifying command
* Explicitly request PyPy wheels
  * cibuildwheel will disable them by default in the future

.github/workflows/package.yml

@@ -10,12 +10,11 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v4
-    - run: pipx install cibuildwheel==2.21.3
-    - run: cibuildwheel --output-dir wheelhouse
+    - uses: pypa/cibuildwheel@v2.22.0
+      with:
+        output-dir: wheelhouse
       env:
-        # The Apple linker does not recognise one of the flags passed to it
-        # while building for PyPy. Skip it.
-        CIBW_SKIP: pp*-macosx*
+        CIBW_BUILD: cp* pp*
         CIBW_TEST_COMMAND: python -m unittest discover -s {package}/tests -t {package}
     - uses: actions/upload-artifact@v4
       with:

pyproject.toml

@@ -1,5 +1,8 @@
 [build-system]
-requires = ["setuptools>=61.0"]
+# The Apple linker does not recognise `-Bsymbolic-functions`, one of the
+# arguments passed to it on macOS when building wheels for PyPy. Using an older
+# version of setuptools fixes this problem.
+requires = ["setuptools==70.0.0"]
 build-backend = "setuptools.build_meta"
 
 [project]
@@ -19,6 +22,8 @@ classifiers = [
     "Operating System :: Microsoft :: Windows",
     "Operating System :: POSIX",
     "Operating System :: Unix",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3 :: Only",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",