Tidy the free-threaded wheel build configuration

No functional change to the default builds.

CIBW_ENABLE=cpython-freethreading was a no-op here. cibuildwheel 3.3.0 gates
only cp313t behind that group (selector.py checks fnmatch(build_id, "cp313t-*")
before consulting the enable set); cp314t is selectable by default, and this
matrix builds no cp313t. The option is also deprecated in 3.4.1 and removed in
4.0, so leaving it set would break a later cibuildwheel bump for no benefit.

The matrix excludes now say why each one is there. 3.11t and 3.12t are not
build identifiers at all, since free threading starts at 3.13, so without the
exclude cibuildwheel selects nothing and the job fails on an empty wheelhouse.
3.13t is a deliberate choice about NumPy instead: no cp313t wheels are
published from 2.5 onwards, 2.4.6 being the last, which was confirmed by
installing numpy on a free-threaded 3.13 and watching 2.5.3 build from source.

CIBW_TEST_COMMAND uses bool(...) rather than == 1 on the Py_GIL_DISABLED config
var. The var is always an int on 3.13+, on Windows too, so this is not a fix,
just the idiom the free-threading porting guide uses. It also prints the flag
so the log shows which ABI the job exercised.

cmake.version moves to >=3.30.3. CMake 3.30 is the first whose FindPython3
understands the free-threaded "t" ABI, and scikit-build-core only sends the
Python3_FIND_ABI hint when the configured specifier admits 3.30+, so at >=3.15
a 3.15-3.29 system CMake would silently skip it. 3.30.3 adds the
Python3_DEFINITIONS that a Windows free-threaded build needs, since PC/pyconfig.h
relies on Py_GIL_DISABLED being defined to auto-link python3XXt.lib.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: Transurgeon

.github/workflows/build-and-publish.yml

@@ -32,17 +32,18 @@ jobs:
       matrix:
         os: [ ubuntu-22.04, macos-14, windows-2022 ]
         python-version: [ "3.11", "3.12", "3.13", "3.14" ]
-        # "" builds the default (GIL) interpreter, "t" the free-threaded one.
-        # Only 3.14t: NumPy >= 2.5 ships no cp313t wheels on any platform, so a
-        # 3.13t build would have to compile NumPy from source.
+        # "" builds the default interpreter, "t" the free-threaded one.
         abi: [ "", "t" ]
         exclude:
-          - python-version: "3.11"
-            abi: "t"
-          - python-version: "3.12"
-            abi: "t"
-          - python-version: "3.13"
-            abi: "t"
+          # Free threading does not exist before 3.13: cp311t and cp312t are
+          # not build identifiers at all, so cibuildwheel would select nothing
+          # and the job would fail on an empty wheelhouse.
+          - { python-version: "3.11", abi: "t" }
+          - { python-version: "3.12", abi: "t" }
+          # NumPy ships no cp313t wheels from 2.5 onwards (2.4.6 is the last
+          # release with one), so a 3.13t build would compile NumPy from
+          # source: that timed out under QEMU and failed outright on macOS.
+          - { python-version: "3.13", abi: "t" }
 
     env:
       PYTHON_VERSION: ${{ matrix.python-version }}
@@ -71,10 +72,9 @@ jobs:
       - name: Build wheels
         uses: pypa/cibuildwheel@v3.3.0
         env:
+          # No CIBW_ENABLE needed: cibuildwheel 3.x gates only cp313t behind
+          # cpython-freethreading, and cp314t is selectable by default.
           CIBW_BUILD: "cp3${{ env.PYTHON_SUBVERSION }}${{ matrix.abi }}-*"
-          # Opt in to cp3XXt build identifiers; harmless for the GIL builds since
-          # CIBW_BUILD already selects a single ABI.
-          CIBW_ENABLE: "cpython-freethreading"
           CIBW_SKIP: "*-win32 *-manylinux_i686 *-musllinux*"
           CIBW_ARCHS_MACOS: "x86_64 universal2"
           CIBW_ARCHS_LINUX: "auto aarch64"
@@ -83,9 +83,9 @@ jobs:
           CIBW_ENVIRONMENT_WINDOWS: "CMAKE_TOOLCHAIN_FILE=C:/vcpkg/scripts/buildsystems/vcpkg.cmake"
           # Bundle openblas.dll into the wheel (auditwheel/delocate handle this on Linux/macOS)
           CIBW_REPAIR_WHEEL_COMMAND_WINDOWS: "delvewheel repair -w {dest_dir} {wheel} --add-path C:/vcpkg/installed/x64-windows/bin"
-          # On free-threaded builds also assert the import did not re-enable the GIL,
-          # i.e. the extension really declares Py_MOD_GIL_NOT_USED.
-          CIBW_TEST_COMMAND: python -c "import sys, sysconfig, sparsediffpy; ft = sysconfig.get_config_var('Py_GIL_DISABLED') == 1; assert not ft or not sys._is_gil_enabled(), 'GIL re-enabled on import'"
+          # On free-threaded builds also assert the import did not re-enable the
+          # GIL, i.e. the extension really declares Py_MOD_GIL_NOT_USED.
+          CIBW_TEST_COMMAND: python -c "import sys, sysconfig, sparsediffpy; ft = bool(sysconfig.get_config_var('Py_GIL_DISABLED')); assert not ft or not sys._is_gil_enabled(), 'GIL re-enabled on import'; print('freethreaded_build=', ft)"
       - name: Check wheels
         shell: bash
         run: |

pyproject.toml

@@ -15,7 +15,11 @@ file = "README.md"
 content-type = "text/markdown"
 
 [tool.scikit-build]
-cmake.version = ">=3.15"
+# CMake 3.30 is the first whose FindPython3 understands the free-threaded ("t")
+# ABI, and scikit-build-core only sends the Python3_FIND_ABI hint when this
+# specifier admits 3.30+. 3.30.3 adds the Python3_DEFINITIONS a Windows
+# free-threaded build needs to link python3XXt.lib.
+cmake.version = ">=3.30.3"
 cmake.build-type = "Release"
 wheel.packages = ["sparsediffpy"]
 # Persistent build dir: avoids scikit-build-core's TemporaryDirectory, whose cleanup