Separate __post_init__

Author: abravalheri

distutils/extension.py

@@ -31,9 +31,10 @@ class _Extension:
 
     # The use of a parent class as a "trick":
     # - We need to modify __init__ so to achieve backwards compatibility
+    #   and keep allowing arbitrary keywords to be ignored
     # - But we don't want to throw away the dataclass-generated __init__
-    # - We also want to fool the typechecker to consider the same type
-    #   signature as the dataclass-generated __init__
+    #   specially because we don't want to have to redefine all the typing
+    #   for the function arguments
 
     name: str
     """
@@ -139,42 +140,42 @@ class _Extension:
 _safe = tuple(f.name for f in fields(_Extension))
 
 
-if TYPE_CHECKING:
-
-    @dataclass
-    class Extension(_Extension):
-        pass
-
-else:
-
-    @dataclass(init=False)
-    class Extension(_Extension):
-        def __init__(self, name, sources, *args, **kwargs):
-            if not isinstance(name, str):
-                raise TypeError("'name' must be a string")
-
-            # handle the string case first; since strings are iterable, disallow them
-            if isinstance(sources, str):
-                raise TypeError(
-                    "'sources' must be an iterable of strings or PathLike objects, not a string"
-                )
-
-            # now we check if it's iterable and contains valid types
-            try:
-                sources = list(map(os.fspath, sources))
-            except TypeError:
-                raise TypeError(
-                    "'sources' must be an iterable of strings or PathLike objects"
-                )
+@dataclass(init=True if TYPE_CHECKING else False)  # type: ignore[literal-required]
+class Extension(_Extension):
+    if not TYPE_CHECKING:
 
+        def __init__(self, *args, **kwargs):
             extra = {repr(k): kwargs.pop(k) for k in tuple(kwargs) if k not in _safe}
             if extra:
-                warnings.warn(f"Unknown Extension options: {','.join(extra)}")
+                msg = f"""
+                Please remove unknown `Extension` options: {','.join(extra)}
+                this kind of usage is deprecated and may cause errors in the future.
+                """
+                warnings.warn(msg)
 
             # Ensure default values (e.g. []) are used instead of None:
-            positional = {k: v for k, v in zip(_safe[2:], args) if v is not None}
+            positional = {k: v for k, v in zip(_safe, args) if v is not None}
             keywords = {k: v for k, v in kwargs.items() if v is not None}
-            super().__init__(name, sources, **positional, **keywords)
+            super().__init__(**positional, **keywords)
+            self.__post_init__()  # does not seem to be called when customizing __init__
+
+    def __post_init__(self):
+        if not isinstance(self.name, str):
+            raise TypeError("'name' must be a string")
+
+        # handle the string case first; since strings are iterable, disallow them
+        if isinstance(self.sources, str):
+            raise TypeError(
+                "'sources' must be an iterable of strings or PathLike objects, not a string"
+            )
+
+        # now we check if it's iterable and contains valid types
+        try:
+            self.sources = list(map(os.fspath, self.sources))
+        except TypeError:
+            raise TypeError(
+                "'sources' must be an iterable of strings or PathLike objects"
+            )
 
 
 def read_setup_file(filename):  # noqa: C901

distutils/tests/test_extension.py

@@ -2,11 +2,13 @@
 
 import os
 import pathlib
+import re
 import warnings
+from dataclasses import dataclass, field
 from distutils.extension import Extension, read_setup_file
+from typing import TYPE_CHECKING
 
 import pytest
-from test.support.warnings_helper import check_warnings
 
 
 class TestExtension:
@@ -109,9 +111,46 @@ def test_extension_init(self):
         assert ext.optional is False
 
         # if there are unknown keyword options, warn about them
-        with check_warnings() as w:
+        msg = re.escape("unknown `Extension` options: 'chic'")
+        with pytest.warns(UserWarning, match=msg) as w:
             warnings.simplefilter('always')
             ext = Extension('name', ['file1', 'file2'], chic=True)
 
-        assert len(w.warnings) == 1
-        assert str(w.warnings[0].message) == "Unknown Extension options: 'chic'"
+        assert len(w) == 1
+
+
+def test_can_be_extended_by_setuptools() -> None:
+    # Emulate how it could be extended in setuptools
+
+    @dataclass(init=True if TYPE_CHECKING else False)  # type: ignore[literal-required]
+    class setuptools_Extension(Extension):
+        py_limited_api: bool = False
+        _full_name: str = field(init=False, repr=False)
+
+        if not TYPE_CHECKING:
+            # Custom __init__ is only needed for backwards compatibility
+            # (to ignore arbitrary keywords)
+
+            def __init__(self, *args, py_limited_api=False, **kwargs):
+                self.py_limited_api = py_limited_api
+                super().__init__(*args, **kwargs)
+
+    ext1 = setuptools_Extension("name", ["hello.c"], py_limited_api=True)
+    assert ext1.py_limited_api is True
+    assert ext1.define_macros == []
+
+    msg = re.escape("unknown `Extension` options: 'world'")
+    with pytest.warns(UserWarning, match=msg):
+        ext2 = setuptools_Extension("name", ["hello.c"], world=True)  # type: ignore[call-arg]
+
+    assert "world" not in ext2.__dict__
+    assert ext2.py_limited_api is False
+
+    # Without __init__ customization the following warning would be an error:
+    msg = re.escape("unknown `Extension` options: '_full_name'")
+    with pytest.warns(UserWarning, match=msg):
+        ext3 = setuptools_Extension("name", ["hello.c"], _full_name="hello")  # type: ignore[call-arg]
+
+    assert "_full_name" not in ext3.__dict__
+    ext3._full_name = "hello world"  # can still be set in build_ext
+    assert ext3._full_name == "hello world"