fix: custom cross compiling environment

Signed-off-by: Henry Schreiner <[email protected]>

Author: henryiii

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, get_python_include_dir, get_python_library
 
@@ -194,10 +195,11 @@ 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 +1,80 @@
+from __future__ import annotations
+
+import contextlib
+import os
+import string
+import sysconfig
+import tempfile
+from collections.abc import Generator, MutableMapping
+from pathlib import Path
+
+from .._logging import logger
+from ..resources import resources
+
+__all__ = ["set_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
+
+    if getattr(sysconfig, "_get_sysconfigdata_name", ""):
+        logger.warning(
+            "Cross-compiling is not supported due to sysconfig._get_sysconfigdata_name missing."
+        )
+        yield
+        return
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        tmp_dir = Path(tmpdir).resolve()
+        cross_compile_file = tmp_dir / f"_cross_compile_{ext_suffix}.py"
+        input_txt = resources.read_text("_cross_compile.py")
+        output_text = string.Template(input_txt).substitute(
+            host_name=sysconfig._get_sysconfigdata_name(),  # type: ignore[attr-defined]
+            SOABI=ext_suffix.rsplit(maxsplit=1)[0],
+            EXT_SUFFIX=ext_suffix,
+        )
+        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"] = f"_cross_compile_{ext_suffix}.py"
+        try:
+            yield
+        finally:
+            del env["_PYTHON_SYSCONFIGDATA_NAME"]
+            if current_path:
+                env["PYTHONPATH"] = current_path
+            else:
+                del env["PYTHONPATH"]

src/scikit_build_core/resources/_cross_compile.py

@@ -0,0 +1,7 @@
+# Cross compiling activation template
+
+host_name = "${host_name}"
+
+build_time_vars = __import__("${host_name}").build_time_vars.copy()
+build_time_vars["SOABI"] = "${SOABI}"
+build_time_vars["EXT_SUFFIX"] = "${EXT_SUFFIX}"