Fix cross-platform compilation using distutils._msvccompiler.MSVCCompiler

distutils/_msvccompiler.py

@@ -284,7 +284,7 @@ def initialize(self, plat_name=None):
                 f"--plat-name must be one of {tuple(_vcvars_names)}"
             )
 
-        plat_spec = _get_vcvars_spec(get_host_platform(), get_platform())
+        plat_spec = _get_vcvars_spec(get_host_platform(), plat_name)
 
         vc_env = _get_vc_env(plat_spec)
         if not vc_env:

distutils/tests/test_msvccompiler.py

@@ -2,11 +2,13 @@
 
 import os
 import sys
+import sysconfig
 import threading
 import unittest.mock as mock
 from distutils import _msvccompiler
 from distutils.errors import DistutilsPlatformError
 from distutils.tests import support
+from distutils.util import get_platform
 
 import pytest
 
@@ -28,6 +30,30 @@ def _find_vcvarsall(plat_spec):
                 'wont find this version',
             )
 
+    @pytest.mark.skipif(
+        not sysconfig.get_platform().startswith("win"),
+        reason="Only run test for non-mingw Windows platforms",
+    )
+    @pytest.mark.parametrize(
+        "plat_name, expected",
+        [
+            ("win-arm64", "win-arm64"),
+            ("win-amd64", "win-amd64"),
+            (None, get_platform()),
+        ],
+    )
+    def test_cross_platform_compilation_paths(self, monkeypatch, plat_name, expected):
+        """
+        Ensure a specified target platform is passed to _get_vcvars_spec.
+        """
+        compiler = _msvccompiler.MSVCCompiler()
+
+        def _get_vcvars_spec(host_platform, platform):
+            assert platform == expected
+
+        monkeypatch.setattr(_msvccompiler, '_get_vcvars_spec', _get_vcvars_spec)
+        compiler.initialize(plat_name)
+
     @needs_winreg
     def test_get_vc_env_unicode(self):
         test_var = 'ṰḖṤṪ┅ṼẨṜ'

newsfragments/298.bugfix.rst

@@ -0,0 +1 @@
+Fix cross-platform compilation using ``distutils._msvccompiler.MSVCCompiler`` -- by :user:`saschanaz` and :user:`Avasam`