Fixed build_ext assumption that cross-compilation on Windows always uses MSVCCompiler by Avasam · Pull Request #399 · pypa/distutils

Avasam · 2026-02-20T00:26:13Z

Fixes the following error if providing --plat-name when using msys2-mingw on Windows:

Traceback (most recent call last):
  File "D:/a/_temp/msys64/mingw64/lib/python3.12/site-packages/pyproject_hooks/_in_process/_in_process.py", line 389, in <module>
    main()
  File "D:/a/_temp/msys64/mingw64/lib/python3.12/site-packages/pyproject_hooks/_in_process/_in_process.py", line 373, in main
    json_out["return_val"] = hook(**hook_input["kwargs"])
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:/a/_temp/msys64/mingw64/lib/python3.12/site-packages/pyproject_hooks/_in_process/_in_process.py", line 280, in build_wheel
    return _build_backend().build_wheel(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/build_meta.py", line 438, in build_wheel
    return _build(['bdist_wheel'])
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/build_meta.py", line 429, in _build
    return self._build_with_temp_dir(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/build_meta.py", line 410, in _build_with_temp_dir
    self.run_setup()
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/build_meta.py", line 317, in run_setup
    exec(code, locals())
  File "<string>", line 1963, in <module>
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/__init__.py", line 117, in setup
    return distutils.core.setup(**attrs)  # type: ignore[return-value]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/_distutils/core.py", line 186, in setup
    return run_commands(dist)
           ^^^^^^^^^^^^^^^^^^
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/_distutils/core.py", line 202, in run_commands
    dist.run_commands()
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/_distutils/dist.py", line 1000, in run_commands
    self.run_command(cmd)
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/dist.py", line 1107, in run_command
    super().run_command(command)
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/_distutils/dist.py", line 1019, in run_command
    cmd_obj.run()
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/command/bdist_wheel.py", line 370, in run
    self.run_command("build")
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/_distutils/cmd.py", line 341, in run_command
    self.distribution.run_command(command)
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/dist.py", line 1107, in run_command
    super().run_command(command)
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/_distutils/dist.py", line 1019, in run_command
    cmd_obj.run()
  File "<string>", line 354, in run
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/_distutils/command/build.py", line 135, in run
    self.run_command(cmd_name)
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/_distutils/cmd.py", line 341, in run_command
    self.distribution.run_command(command)
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/dist.py", line 1107, in run_command
    super().run_command(command)
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/_distutils/dist.py", line 1019, in run_command
    cmd_obj.run()
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/command/build_ext.py", line 97, in run
    _build_ext.run(self)
  File "D:/a/_temp/msys64/tmp/build-env-g6pjoax9/lib/python3.12/site-packages/setuptools/_distutils/command/build_ext.py", line 336, in run
    self.compiler.initialize(self.plat_name)
    ^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'MinGW32Compiler' object has no attribute 'initialize'

This could've been caught with static type checking, but attr-defined is currently disabled in mypy

Avasam · 2026-02-26T02:20:49Z

+            # late initialization of compiler even if they shouldn't...)
+            self.plat_name != get_platform()
+            # Initialization is a MSVCCompiler specific concept
+            and hasattr(self.compiler, "initialize")


I would've done

Suggested change

and hasattr(self.compiler, "initialize")

and isinstance(MSVCCompiler, self.compiler)

But who knows if someone downstream added a custom non-MSVCCompiler with .initialize that relies on being called.

Or it could be considered so internal that it's fine to do the more "proper" check that also helps static checkers.

I wonder if we shouldn't instead just have the base Compiler provide a degenerate initialize() method, allowing any Compiler to potentially implement it.

But what's really annoying is this other factor "people may rely on late initialization of compiler even if they shouldn't". That really deserves a better explanation. Looks like it was made 18 years ago (Avasam@f39783d#diff-08754ed5a9d7fff430bd6aa04a88d70fd4ef8972aecab7b07373c86271a7c07c) or maybe even earlier, as that's a bundle that seems to trace back to issue 2513 aka python/cpython#46765.

I'm not fully convinced I'd add a dummy def initialize to base Compiler. Unless there's a demand for it. As it would also subtly affect downstream hasattr(self.compiler, "initialize") checks.
I think it's fine for the concept to be MSVC specific.

Sidenote: Funny how this comes full circle, mhammond being the author of that issue you linked, and I'm opening this PR for MinGW support in his pywin32 package

I guess we don't need to deal with the 'cross-compiling' concern here. Let's implement the degenerate method to eliminate the one conditional.

As it would also subtly affect downstream hasattr(self.compiler, "initialize") checks

I checked and Setuptools doesn't rely on this interface. And if there are checks further downstream, they shouldn't be relying on the presence of class attributes for such behavior.

Fine by me ! 👍

…ses MSVCCompiler

…or non-MSVC compilers build_ext.run() unconditionally called compiler.initialize() when cross-compiling on Windows, assuming an MSVCCompiler. With any other compiler (e.g. MinGW/msys2) this raised AttributeError. Rather than guard the call with hasattr(), give the base Compiler a no-op initialize() that non-MSVC compilers inherit; MSVCCompiler continues to override it. This also makes the method visible to static type checkers. The redundant os.name == 'nt' guard is dropped since initialize() is now safe on every compiler. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Avasam mentioned this pull request Feb 20, 2026

build_msys2_mingw Avasam/pywin32#24

Open

Avasam commented Feb 26, 2026

View reviewed changes

Avasam mentioned this pull request May 1, 2026

Fix mingw compiler detection with cross-compilation mhammond/pywin32#2743

Merged

Fixed build_ext assumption that cross-compilation on Windows always u…

04db78d

…ses MSVCCompiler

Avasam force-pushed the patch-1 branch from 99831e1 to 04db78d Compare July 4, 2026 19:08

jaraco mentioned this pull request Jul 5, 2026

Remove cross-compiler conditional initialization #410

Open

jaraco force-pushed the patch-1 branch from f85b9c6 to e4eab56 Compare July 5, 2026 19:19

jaraco force-pushed the patch-1 branch from e4eab56 to 85fc968 Compare July 5, 2026 19:32

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Fixed build_ext assumption that cross-compilation on Windows always uses MSVCCompiler#399

Fixed build_ext assumption that cross-compilation on Windows always uses MSVCCompiler#399
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	and hasattr(self.compiler, "initialize")
	and isinstance(MSVCCompiler, self.compiler)

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Avasam commented Feb 20, 2026 •

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