fix: custom cross compiling environment

docs/api/scikit_build_core.builder.rst

@@ -17,6 +17,14 @@ scikit\_build\_core.builder.builder module
    :undoc-members:
    :show-inheritance:
 
+scikit\_build\_core.builder.cross\_compile module
+-------------------------------------------------
+
+.. automodule:: scikit_build_core.builder.cross_compile
+   :members:
+   :undoc-members:
+   :show-inheritance:
+
 scikit\_build\_core.builder.generator module
 --------------------------------------------
 

src/scikit_build_core/builder/builder.py

@@ -15,6 +15,7 @@
 from ..cmake import CMaker
 from ..resources import find_python
 from ..settings.skbuild_model import ScikitBuildSettings
+from .cross_compile import auto_cross_compile_env
 from .generator import set_environment_for_gen
 from .sysconfig import (
     get_platform,
@@ -183,10 +184,11 @@ def configure(
         # Add the pre-defined or passed CMake defines
         cmake_defines.update(self.settings.cmake.define)
 
-        self.config.configure(
-            defines=cmake_defines,
-            cmake_args=[*self.get_cmake_args(), *configure_args],
-        )
+        with auto_cross_compile_env(self.config.env):
+            self.config.configure(
+                defines=cmake_defines,
+                cmake_args=[*self.get_cmake_args(), *configure_args],
+            )
 
     def build(self, build_args: list[str]) -> None:
         self.config.build(build_args=build_args, verbose=self.settings.cmake.verbose)

src/scikit_build_core/builder/cross_compile.py

@@ -0,0 +1,79 @@
+from __future__ import annotations
+
+import contextlib
+import os
+import sysconfig
+import tempfile
+from collections.abc import Generator, MutableMapping
+from pathlib import Path
+
+from .._logging import logger
+
+__all__ = ["set_cross_compile_env", "auto_cross_compile_env"]
+
+
+def __dir__() -> list[str]:
+    return __all__
+
+
+@contextlib.contextmanager
+def auto_cross_compile_env(
+    env: MutableMapping[str, str]
+) -> Generator[None, None, None]:
+    if "SETUPTOOLS_EXT_SUFFIX" not in env:
+        yield
+        return
+
+    with set_cross_compile_env(env["SETUPTOOLS_EXT_SUFFIX"], env):
+        yield
+
+
+@contextlib.contextmanager
+def set_cross_compile_env(
+    ext_suffix: str,
+    env: MutableMapping[str, str],
+) -> Generator[None, None, None]:
+    """
+    Generate python file and set environment variables to cross-compile Python
+    extensions. Do not call if _PYTHON_SYSCONFIGDATA_NAME is already set.
+    """
+
+    if "_PYTHON_SYSCONFIGDATA_NAME" in env:
+        logger.debug(
+            "Not setting up cross compiling explicitly due to _PYTHON_SYSCONFIGDATA_NAME already set."
+        )
+        yield
+        return
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        tmp_dir = Path(tmpdir).resolve()
+        cross_compile_file = (
+            tmp_dir / f"_cross_compile_{ext_suffix.replace('.', '_')}.py"
+        )
+        build_time_vars = sysconfig.get_config_vars()
+        build_time_vars["EXT_SUFFIX"] = ext_suffix
+        build_time_vars["SOABI"] = ext_suffix.rsplit(maxsplit=1)[0]
+        output_text = f"build_time_vars = {build_time_vars!r}\n"
+        cross_compile_file.write_text(output_text)
+        current_path = env.get("PYTHONPATH", "")
+        env["PYTHONPATH"] = (
+            os.pathsep.join([current_path, str(tmp_dir)])
+            if current_path
+            else str(tmp_dir)
+        )
+        env["_PYTHON_SYSCONFIGDATA_NAME"] = cross_compile_file.stem
+        logger.info("Cross-compiling is enabled to {!r}.", ext_suffix)
+        logger.debug(
+            "Setting _PYTHON_SYSCONFIGDATA_NAME to {!r}.",
+            env["_PYTHON_SYSCONFIGDATA_NAME"],
+        )
+        logger.debug("Setting PYTHONPATH to {!r}.", env["PYTHONPATH"])
+        logger.debug("Cross compile output file contents: {}", output_text)
+        try:
+            yield
+        finally:
+            del env["_PYTHON_SYSCONFIGDATA_NAME"]
+            if current_path:
+                env["PYTHONPATH"] = current_path
+            else:
+                del env["PYTHONPATH"]

tests/test_cross_compile.py

@@ -0,0 +1,39 @@
+from __future__ import annotations
+
+import os
+import subprocess
+import sys
+import sysconfig
+
+import pytest
+
+from scikit_build_core.builder.cross_compile import set_cross_compile_env
+
+ext_suffix = sysconfig.get_config_var("EXT_SUFFIX")
+
+
+@pytest.mark.skipif(
+    ext_suffix != ".cp311-win_amd64.pyd",
+    reason=f"Only tests '.cp311-win_amd64.pyd', got {ext_suffix!r}",
+)
+def test_environment():
+    env = os.environ.copy()
+    cmd = [
+        sys.executable,
+        "-c",
+        "import sysconfig; print(sysconfig.get_config_var('SOABI'), sysconfig.get_config_var('EXT_SUFFIX'))",
+    ]
+
+    with set_cross_compile_env(".cp311-win_arm64.pyd", env):
+        result = subprocess.run(
+            cmd, check=True, capture_output=True, text=True, env=env
+        )
+        soabi, ext_suffix = result.stdout.strip().split()
+        print(soabi, ext_suffix)
+        assert soabi == "cp311-win_arm64"
+        assert ext_suffix == ".cp311-win_arm64.pyd"
+
+    result = subprocess.run(cmd, check=True, capture_output=True, text=True, env=env)
+    soabi, ext_suffix = result.stdout.strip().split()
+    assert soabi == "cp311-win_amd64"
+    assert ext_suffix == ".cp311-win_amd64.pyd"

tests/test_module_dir.py

@@ -29,7 +29,11 @@ def on_all_modules(
 
 def test_all_modules_filter_all():
     all_modules = on_all_modules("scikit_build_core", pkg=False)
-    all_modules = (n for n in all_modules if not n.split(".")[-1].startswith("__"))
+    all_modules = (
+        n
+        for n in all_modules
+        if not n.split(".")[-1].startswith("__") and "resources" not in n
+    )
     for name in all_modules:
         module = importlib.import_module(name)
 
@@ -45,7 +49,11 @@ def test_all_modules_filter_all():
 
 def test_all_modules_has_all():
     all_modules = on_all_modules("scikit_build_core", pkg=True)
-    all_modules = (n for n in all_modules if not n.split(".")[-1].startswith("_"))
+    all_modules = (
+        n
+        for n in all_modules
+        if not n.split(".")[-1].startswith("_") and "resources" not in n
+    )
     for name in all_modules:
         module = importlib.import_module(name)