📦 Move packaging to PEP 517 in-tree backend

This essentially allows the cythonization opt-out be controlled by the
`pure-python` PEP 517 config setting that can be passed to
the corresponding build frontends via their respective CLIs.

.github/workflows/reusable-build-wheel.yml

@@ -0,0 +1,79 @@
+---
+
+name: Build wheel
+
+on:
+  workflow_call:
+    inputs:
+      dists-artifact-name:
+        description: Workflow artifact name containing dists
+        required: true
+        type: string
+      cython-tracing:
+        description: Whether to build Cython modules with line tracing
+        default: '0'
+        required: false
+        type: string
+      os:
+        description: VM OS to use, without version suffix
+        default: ubuntu
+        required: false
+        type: string
+      qemu:
+        description: Emulated QEMU architecture
+        default: ''
+        required: false
+        type: string
+      source-tarball-name:
+        description: Sdist filename wildcard
+        required: true
+        type: string
+
+env:
+  FORCE_COLOR: "1"  # Make tools pretty.
+  PIP_DISABLE_PIP_VERSION_CHECK: "1"
+  PIP_NO_PYTHON_VERSION_WARNING: "1"
+
+jobs:
+
+  build-wheel:
+    name: Build wheels on ${{ inputs.os }} ${{ inputs.qemu }}
+    runs-on: ${{ inputs.os }}-latest
+    # Ref: https://github.com/python-jsonschema/check-jsonschema/issues/354
+    timeout-minutes: 60  # FIXME: ${{ inputs.qemu && '60' || '20' }}
+    steps:
+    - name: Retrieve the project source from an sdist inside the GHA artifact
+      uses: re-actors/checkout-python-sdist@release/v1
+      with:
+        source-tarball-name: ${{ inputs.source-tarball-name }}
+        workflow-artifact-name: ${{ inputs.dists-artifact-name }}
+
+    - name: Set up QEMU
+      if: inputs.qemu
+      uses: docker/setup-qemu-action@v3
+      with:
+        platforms: all
+      id: qemu
+    - name: Prepare emulation
+      if: inputs.qemu
+      run: |
+        # Build emulated architectures only if QEMU is set,
+        # use default "auto" otherwise
+        echo "CIBW_ARCHS_LINUX=${{ inputs.qemu }}" >> "${GITHUB_ENV}"
+      shell: bash
+
+    - name: Build wheels
+      uses: pypa/[email protected]
+      env:
+        CIBW_ARCHS_MACOS: x86_64 arm64 universal2
+        CIBW_CONFIG_SETTINGS: >-  # Cython line tracing for coverage collection
+          pure-python=false
+          with-cython-tracing=${{ inputs.cython-tracing }}
+
+    - name: Upload built artifacts for testing and publishing
+      uses: actions/upload-artifact@v3
+      with:
+        name: ${{ inputs.dists-artifact-name }}
+        path: ./wheelhouse/*.whl
+
+...

MANIFEST.in

@@ -1,17 +1,22 @@
+include pyproject.toml
+include pytest.ini
+include pytest.ci.ini
 include LICENSE
 include CHANGES.rst
 include README.rst
 include CONTRIBUTORS.txt
 graft frozenlist
+graft packaging
 graft docs
+graft requirements
 graft tests
-include frozenlist/*.c
 global-exclude *.pyc
 global-exclude *.pyd
 global-exclude *.so
 global-exclude *.lib
 global-exclude *.dll
 global-exclude *.a
 global-exclude *.obj
+exclude frozenlist/*.c
 exclude frozenlist/*.html
 prune docs/_build

packaging/README.md

@@ -0,0 +1,11 @@
+# `pep517_backend` in-tree build backend
+
+The `pep517_backend.hooks` importable exposes callables declared by PEP 517
+and PEP 660 and is integrated into `pyproject.toml`'s
+`[build-system].build-backend` through `[build-system].backend-path`.
+
+# Design considerations
+
+`__init__.py` is to remain empty, leaving `hooks.py` the only entrypoint
+exposing the callables. The logic is contained in private modules. This is
+to prevent import-time side effects.

packaging/pep517_backend/__init__.py

@@ -0,0 +1 @@
+"""PEP 517 build backend for optionally pre-building Cython."""

packaging/pep517_backend/__main__.py

@@ -0,0 +1,6 @@
+import sys
+
+from . import cli
+
+if __name__ == "__main__":
+    sys.exit(cli.run_main_program(argv=sys.argv))