fix: Windows ARM cross-compile

src/scikit_build_core/builder/builder.py

@@ -14,7 +14,7 @@
 from ..resources import find_python
 from ..settings.skbuild_model import ScikitBuildSettings
 from .generator import set_environment_for_gen
-from .sysconfig import get_python_include_dir, get_python_library
+from .sysconfig import get_platform, get_python_include_dir, get_python_library
 
 __all__: list[str] = ["Builder"]
 
@@ -45,6 +45,9 @@ def get_archs(self) -> list[str]:
         if sys.platform.startswith("darwin"):
             archs = re.findall(r"-arch (\S+)", self.config.env.get("ARCHFLAGS", ""))
             return archs
+        if sys.platform.startswith("win"):
+            if get_platform(self.config.env) == "win-arm64":
+                return ["win_arm64"]
 
         return []
 
@@ -94,9 +97,13 @@ def configure(
         if version is not None:
             cache_config["SKBUILD_PROJECT_VERSION"] = str(version)
 
-        # Classic Find Python
-        python_library = get_python_library()
+        if limited_abi is None:
+            limited_abi = self.settings.wheel.py_api.startswith("cp3")
+
+        python_library = get_python_library(self.config.env, abi3=limited_abi)
         python_include_dir = get_python_include_dir()
+
+        # Classic Find Python
         cache_config["PYTHON_EXECUTABLE"] = sys.executable
         cache_config["PYTHON_INCLUDE_DIR"] = python_include_dir
         if python_library:
@@ -109,9 +116,6 @@ def configure(
             cache_config[f"{prefix}_INCLUDE_DIR"] = python_include_dir
             cache_config[f"{prefix}_FIND_REGISTRY"] = "NEVER"
 
-        if limited_abi is None:
-            limited_abi = self.settings.wheel.py_api.startswith("cp3")
-
         if limited_abi:
             cache_config["SKBUILD_SOABI"] = (
                 "" if sys.platform.startswith("win") else "abi3"

src/scikit_build_core/builder/sysconfig.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import configparser
 import os
 import sys
 import sysconfig
@@ -30,7 +31,18 @@ def __dir__() -> list[str]:
     return __all__
 
 
-def get_python_library() -> Path | None:
+def get_python_library(env: Mapping[str, str], *, abi3: bool = False) -> Path | None:
+    # When cross-compiling, check DIST_EXTRA_CONFIG first
+    config_file = env.get("DIST_EXTRA_CONFIG", None)
+    if config_file and Path(config_file).is_file():
+        cp = configparser.ConfigParser()
+        cp.read(config_file)
+        result = cp.get("build_ext", "library_dirs", fallback="")
+        if result:
+            logger.info("Reading DIST_EXTRA_CONFIG:build_ext.library_dirs={}", result)
+            minor = "" if abi3 else sys.version_info[1]
+            return Path(result) / f"python3{minor}.lib"
+
     libdirstr = sysconfig.get_config_var("LIBDIR")
     ldlibrarystr = sysconfig.get_config_var("LDLIBRARY")
     libdir: Path | None = libdirstr and Path(libdirstr)
@@ -96,8 +108,11 @@ def get_platform(env: Mapping[str, str] | None = None) -> str:
     """
     if env is None:
         env = os.environ
-    if os.name == "nt" and "VSCMD_ARG_TGT_ARCH" in env:
-        return TARGET_TO_PLAT.get(env["VSCMD_ARG_TGT_ARCH"]) or get_host_platform()
+    if sys.platform.startswith("win"):
+        if "VSCMD_ARG_TGT_ARCH" in env:
+            return TARGET_TO_PLAT.get(env["VSCMD_ARG_TGT_ARCH"]) or get_host_platform()
+        if "arm64" in env.get("SETUPTOOLS_EXT_SUFFIX", "").lower():
+            return "win-arm64"
     return get_host_platform()
 
 

tests/test_builder.py

@@ -4,6 +4,7 @@
 import sys
 import sysconfig
 import typing
+from pathlib import Path
 from types import SimpleNamespace
 
 import pytest
@@ -54,14 +55,34 @@ def test_get_python_include_dir():
 def test_get_python_library():
     pprint.pprint(sysconfig.get_config_vars())
 
-    lib = get_python_library()
+    lib = get_python_library({})
     if sys.platform.startswith("win"):
         assert lib is None
     else:
         assert lib
         assert lib.is_file()
 
 
+@pytest.mark.skipif(not sys.platform.startswith("win"), reason="Windows only")
+def test_get_python_library_xcompile(tmp_path):
+    config_path = tmp_path / "tmp.cfg"
+    config_path.write_text(
+        """\
+[build_ext]
+library_dirs=C:\\Python\\libs
+    """
+    )
+    env = {"DIST_EXTRA_CONFIG": str(config_path)}
+    lib = get_python_library(env)
+    assert lib
+    assert lib.parent == Path("C:\\Python\\libs")
+    assert lib.parent != Path("C:\\Python\\libs\\python3.lib")
+
+    lib2 = get_python_library(env, abi3=True)
+    assert lib2
+    assert lib2 == Path("C:\\Python\\libs\\python3.lib")
+
+
 @pytest.mark.parametrize("archs", (["x86_64"], ["arm64", "universal2"]))
 def test_builder_macos_arch(monkeypatch, archs):
     archflags = " ".join(f"-arch {arch}" for arch in archs)