Reraise sensible errors from auto_chmod

Author: Avasam

newsfragments/4593.feature.rst

@@ -0,0 +1 @@
+Reraise sensible errors from ``setuptools.command.easy_install.auto_chmod`` instead of nonsensical ``TypeError: 'Exception' object is not subscriptable`` -- by :user:`Avasam`

setuptools/command/easy_install.py

@@ -34,7 +34,7 @@
 from collections.abc import Iterable
 from glob import glob
 from sysconfig import get_path
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Callable, TypeVar
 
 from jaraco.text import yield_lines
 
@@ -89,6 +89,8 @@
     'get_exe_prefixes',
 ]
 
+_T = TypeVar("_T")
+
 
 def is_64bit():
     return struct.calcsize("P") == 8
@@ -1786,13 +1788,18 @@ def _first_line_re():
     return re.compile(first_line_re.pattern.decode())
 
 
-def auto_chmod(func, arg, exc):
-    if func in [os.unlink, os.remove] and os.name == 'nt':
-        chmod(arg, stat.S_IWRITE)
-        return func(arg)
-    et, ev, _ = sys.exc_info()
-    # TODO: This code doesn't make sense. What is it trying to do?
-    raise (ev[0], ev[1] + (" %s %s" % (func, arg)))
+# Must match shutil._OnExcCallback
+def auto_chmod(func: Callable[..., _T], arg: str, exc: BaseException) -> _T:
+    """shutils onexc callback to automatically call chmod for certain functions."""
+    if os.name != 'nt':
+        raise OSError(f"Can't call auto_chmod on non-nt os {os.name!r}") from exc
+    supported_methods = {os.unlink, os.remove}
+    if func not in supported_methods:
+        raise ValueError(
+            f"Argument func is not one of {[method.__name__ for method in supported_methods]} (got: {func.__name__!r})"
+        ) from exc
+    chmod(arg, stat.S_IWRITE)
+    return func(arg)
 
 
 def update_dist_caches(dist_path, fix_zipimporter_caches):