Automatically set compiler flags to target PEP 384 Python limited API

docs/using.rst

@@ -65,3 +65,31 @@ the following configuration to the ``pyproject.toml`` file::
 .. note::
   For backwards compatibility, the setting of ``use_extension_helpers`` in
   ``setup.cfg`` will override any setting of it in ``pyproject.toml``.
+
+Python limited API
+------------------
+
+Your package may opt in to the :pep:`384` Python Limited API so that a single
+binary wheel works with many different versions of Python on the same platform.
+For this to work, any C extensions you write needs to make use only of
+`certain C functions <https://docs.python.org/3/c-api/stable.html#limited-api-list>`__.
+
+To opt in to the Python Limited API, add the following standard setuptools
+option to your project's ``setup.cfg`` file::
+
+    [bdist_wheel]
+    py_limited_api = cp311
+
+Here, ``311`` denotes API compatibility with Python >= 3.11. Replace with the
+lowest major and minor version number that you wish to support.
+
+You can also set this option in ``pyproject.toml``, using::
+
+    [tool.distutils.bdist_wheel]
+    py-limited-api = "cp312"
+
+although note that this option is not formally documented/supported by the Python
+packaging infrastructure and may change in future.
+
+The ``get_extensions()`` functions will automatically detect this option and
+add the necessary compiler flags to build your extension modules.

extension_helpers/_setup_helpers.py

@@ -14,7 +14,12 @@
 from setuptools import Extension, find_packages
 from setuptools.command.build_ext import new_compiler
 
-from ._utils import import_file, walk_skip_hidden
+from ._utils import (
+    abi_to_versions,
+    get_limited_api_option,
+    import_file,
+    walk_skip_hidden,
+)
 
 __all__ = ["get_compiler", "get_extensions", "pkg_config"]
 
@@ -135,6 +140,21 @@ def get_extensions(srcdir="."):
 
         extension.sources = sources
 
+    abi = get_limited_api_option(srcdir=srcdir)
+    if abi:
+        version_info, version_hex = abi_to_versions(abi)
+
+        if version_info is None:
+            raise ValueError(f"Unrecognized abi version for limited API: {abi}")
+
+        log.info(
+            f"Targeting PEP 384 limited API supporting Python >= {version_info[0], version_info[1]}"
+        )
+
+        for ext in ext_modules:
+            ext.py_limited_api = True
+            ext.define_macros.append(("Py_LIMITED_API", version_hex))
+
     return ext_modules
 
 

extension_helpers/_utils.py

@@ -1,12 +1,20 @@
 # Licensed under a 3-clause BSD style license - see LICENSE.rst
 
 import os
+import re
 import sys
+from configparser import ConfigParser
 from importlib import machinery as import_machinery
 from importlib.util import module_from_spec, spec_from_file_location
 from pathlib import Path
 
-__all__ = ["write_if_different", "import_file"]
+if sys.version_info >= (3, 11):
+    import tomllib
+else:
+    import tomli as tomllib
+
+
+__all__ = ["write_if_different", "import_file", "get_limited_api_option", "abi_to_versions"]
 
 
 if sys.platform == "win32":
@@ -138,3 +146,53 @@ def import_file(filename, name=None):
     loader.exec_module(mod)
 
     return mod
+
+
+def get_limited_api_option(srcdir):
+    """
+    Checks setup.cfg and pyproject.toml files in the current directory
+    for the py_limited_api setting
+    """
+
+    srcdir = Path(srcdir)
+
+    setup_cfg = srcdir / "setup.cfg"
+
+    if setup_cfg.exists():
+        cfg = ConfigParser()
+        cfg.read(setup_cfg)
+        if cfg.has_option("bdist_wheel", "py_limited_api"):
+            return cfg.get("bdist_wheel", "py_limited_api")
+
+    pyproject = srcdir / "pyproject.toml"
+    if pyproject.exists():
+        with pyproject.open("rb") as f:
+            pyproject_cfg = tomllib.load(f)
+            if (
+                "tool" in pyproject_cfg
+                and "distutils" in pyproject_cfg["tool"]
+                and "bdist_wheel" in pyproject_cfg["tool"]["distutils"]
+                and "py-limited-api" in pyproject_cfg["tool"]["distutils"]["bdist_wheel"]
+            ):
+                return pyproject_cfg["tool"]["distutils"]["bdist_wheel"]["py-limited-api"]
+
+
+def _abi_to_version_info(abi):
+    match = re.fullmatch(r"^cp(\d)(\d+)$", abi)
+    if match is None:
+        return None
+    else:
+        return int(match[1]), int(match[2])
+
+
+def _version_info_to_version_hex(major=0, minor=0):
+    """Returns a PY_VERSION_HEX for {major}.{minor).0"""
+    return f"0x{major:02X}{minor:02X}0000"
+
+
+def abi_to_versions(abi):
+    version_info = _abi_to_version_info(abi)
+    if version_info is None:
+        return None, None
+    else:
+        return version_info, _version_info_to_version_hex(*version_info)

extension_helpers/tests/test_setup_helpers.py

@@ -35,7 +35,13 @@ def test_get_compiler():
     assert get_compiler() in POSSIBLE_COMPILERS
 
 
-def _extension_test_package(tmp_path, request, extension_type="c", include_numpy=False):
+def _extension_test_package(
+    tmp_path,
+    request=None,
+    extension_type="c",
+    include_numpy=False,
+    include_setup_py=True,
+):
     """Creates a simple test package with an extension module."""
 
     test_pkg = tmp_path / "test_pkg"
@@ -106,24 +112,25 @@ def get_extensions():
         )
     )
 
-    (test_pkg / "setup.py").write_text(
-        dedent(
-            f"""\
-        import sys
-        from os.path import join
-        from setuptools import setup, find_packages
-        sys.path.insert(0, r'{extension_helpers_PATH}')
-        from extension_helpers import get_extensions
-
-        setup(
-            name='helpers_test_package',
-            version='0.1',
-            packages=find_packages(),
-            ext_modules=get_extensions()
-        )
-    """
+    if include_setup_py:
+        (test_pkg / "setup.py").write_text(
+            dedent(
+                f"""\
+            import sys
+            from os.path import join
+            from setuptools import setup, find_packages
+            sys.path.insert(0, r'{extension_helpers_PATH}')
+            from extension_helpers import get_extensions
+
+            setup(
+                name='helpers_test_package',
+                version='0.1',
+                packages=find_packages(),
+                ext_modules=get_extensions()
+            )
+        """
+            )
         )
-    )
 
     if "" in sys.path:
         sys.path.remove("")
@@ -133,7 +140,8 @@ def get_extensions():
     def finalize():
         cleanup_import("helpers_test_package")
 
-    request.addfinalizer(finalize)
+    if request:
+        request.addfinalizer(finalize)
 
     return test_pkg
 
@@ -455,3 +463,133 @@ def test():
                 pass
             else:
                 raise AssertionError(package_name + ".compiler_version should not exist")
+
+
+# Tests to make sure that limited API support works correctly
+
+
+@pytest.mark.parametrize("config", ("setup.cfg", "pyproject.toml"))
+@pytest.mark.parametrize("limited_api", (None, "cp310"))
+@pytest.mark.parametrize("extension_type", ("c", "pyx", "both"))
+def test_limited_api(tmp_path, config, limited_api, extension_type):
+
+    package = _extension_test_package(
+        tmp_path, extension_type=extension_type, include_numpy=True, include_setup_py=False
+    )
+
+    if config == "setup.cfg":
+
+        setup_cfg = dedent(
+            """\
+            [metadata]
+            name = helpers_test_package
+            version = 0.1
+
+            [options]
+            packages = find:
+
+            [extension-helpers]
+            use_extension_helpers = true
+        """
+        )
+
+        if limited_api:
+            setup_cfg += f"\n[bdist_wheel]\npy_limited_api={limited_api}"
+
+        (package / "setup.cfg").write_text(setup_cfg)
+
+        # Still require a minimal pyproject.toml file if no setup.py file
+
+        (package / "pyproject.toml").write_text(
+            dedent(
+                """
+            [build-system]
+            requires = ["setuptools>=43.0.0",
+                        "wheel"]
+            build-backend = 'setuptools.build_meta'
+
+            [tool.extension-helpers]
+            use_extension_helpers = true
+        """
+            )
+        )
+
+    elif config == "pyproject.toml":
+
+        pyproject_toml = dedent(
+            """\
+            [build-system]
+            requires = ["setuptools>=43.0.0",
+                        "wheel"]
+            build-backend = 'setuptools.build_meta'
+
+            [project]
+            name = "hehlpers_test_package"
+            version = "0.1"
+
+            [tool.setuptools.packages]
+            find = {namespaces = false}
+
+            [tool.extension-helpers]
+            use_extension_helpers = true
+            """
+        )
+
+        if limited_api:
+            pyproject_toml += f'\n[tool.distutils.bdist_wheel]\npy-limited-api = "{limited_api}"'
+
+        (package / "pyproject.toml").write_text(pyproject_toml)
+
+    with chdir(package):
+        subprocess.run([sys.executable, "-m", "build", "--wheel", "--no-isolation"], check=True)
+
+    wheels = os.listdir(package / "dist")
+
+    assert len(wheels) == 1
+    assert ("abi3" in wheels[0]) == (limited_api is not None)
+
+
+def test_limited_api_invalid_abi(tmp_path, capsys):
+
+    package = _extension_test_package(
+        tmp_path, extension_type="c", include_numpy=True, include_setup_py=False
+    )
+
+    (package / "setup.cfg").write_text(
+        dedent(
+            """\
+        [metadata]
+        name = helpers_test_package
+        version = 0.1
+
+        [options]
+        packages = find:
+
+        [extension-helpers]
+        use_extension_helpers = true
+
+        [bdist_wheel]
+        py_limited_api=invalid
+    """
+        )
+    )
+
+    (package / "pyproject.toml").write_text(
+        dedent(
+            """
+    [build-system]
+    requires = ["setuptools>=43.0.0",
+                "wheel"]
+    build-backend = 'setuptools.build_meta'
+    """
+        )
+    )
+
+    with chdir(package):
+        result = subprocess.run(
+            [sys.executable, "-m", "build", "--wheel", "--no-isolation"], stderr=subprocess.PIPE
+        )
+
+    assert result.stderr.strip().endswith(
+        b"ValueError: Unrecognized abi version for limited API: invalid"
+    )