remove setup.py from cffi example (#617)

Author: davidhewitt

.gitignore

@@ -11,3 +11,4 @@ target
 *.egg-info
 pyo3
 docs/_build
+examples/rust_with_cffi/cffi_module.c

examples/rust_with_cffi/MANIFEST.in

@@ -1,4 +1,5 @@
 include Cargo.toml
+include build_backend.py
 include cffi_module.py
 recursive-include rust *
 recursive-include python *

examples/rust_with_cffi/build_backend.py

@@ -0,0 +1,63 @@
+import subprocess
+import sys
+from pathlib import Path
+
+from setuptools import build_meta as _setuptools_build_meta
+
+_ROOT = Path(__file__).parent
+
+
+def _generate_cffi_source():
+    """Generate the CFFI source file from the Python module.
+
+    `cffi` provides a command line tool `gen_src` that can be used to
+    generate the C source file from a Python module that defines the
+    CFFI interface.
+
+    By implementing an in-tree build backend, we can invoke this before
+    forwarding to regular setuptools build backend functions.
+    """
+
+    # cffi documents `gen_src` as a command line tool
+    subprocess.check_call(
+        [
+            sys.executable,
+            "-m",
+            "cffi.gen_src",
+            "exec-python",
+            "--ffi-var=ffi",
+            "cffi_module.py",
+            "cffi_module.c",
+        ],
+        cwd=_ROOT,
+    )
+
+
+def build_wheel(wheel_directory, config_settings=None, metadata_directory=None):
+    _generate_cffi_source()
+    return _setuptools_build_meta.build_wheel(
+        wheel_directory, config_settings, metadata_directory
+    )
+
+
+def build_sdist(sdist_directory, config_settings=None):
+    _generate_cffi_source()
+    return _setuptools_build_meta.build_sdist(sdist_directory, config_settings)
+
+
+def build_editable(wheel_directory, config_settings=None, metadata_directory=None):
+    _generate_cffi_source()
+    return _setuptools_build_meta.build_editable(
+        wheel_directory, config_settings, metadata_directory
+    )
+
+
+get_requires_for_build_wheel = _setuptools_build_meta.get_requires_for_build_wheel
+get_requires_for_build_sdist = _setuptools_build_meta.get_requires_for_build_sdist
+get_requires_for_build_editable = _setuptools_build_meta.get_requires_for_build_editable
+prepare_metadata_for_build_wheel = (
+    _setuptools_build_meta.prepare_metadata_for_build_wheel
+)
+prepare_metadata_for_build_editable = (
+    _setuptools_build_meta.prepare_metadata_for_build_editable
+)

examples/rust_with_cffi/noxfile.py

@@ -10,7 +10,7 @@ def test(session: nox.Session):
     session.install(SETUPTOOLS_RUST, "pytest")
 
     try:
-        session.install("cffi", "--only-binary=cffi")
+        session.install("cffi>=2.1", "--only-binary=cffi")
     except nox.command.CommandFailed:
         session.skip("cffi not available on this platform")
 

examples/rust_with_cffi/pyproject.toml

@@ -1,3 +1,34 @@
 [build-system]
-requires = ["setuptools", "setuptools-rust", "cffi"]
-build-backend = "setuptools.build_meta"
+requires = ["setuptools>=74.1", "setuptools-rust", "cffi>=2.1"]
+build-backend = "build_backend"
+backend-path = ["."]
+
+[project]
+name = "rust-with-cffi"
+version = "0.1.0"
+classifiers = [
+    "License :: OSI Approved :: MIT License",
+    "Development Status :: 3 - Alpha",
+    "Intended Audience :: Developers",
+    "Programming Language :: Python",
+    "Programming Language :: Rust",
+    "Operating System :: POSIX",
+    "Operating System :: MacOS :: MacOS X",
+]
+dependencies = ["cffi"]
+
+[tool.setuptools]
+package-dir = { "" = "python" }
+include-package-data = true
+zip-safe = false
+
+[tool.setuptools.packages.find]
+where = ["python"]
+
+[[tool.setuptools.ext-modules]]
+name = "rust_with_cffi.cffi"
+sources = ["cffi_module.c"]
+py-limited-api = true
+
+[[tool.setuptools-rust.ext-modules]]
+target = "rust_with_cffi.rust"