Remove calls to typing.cast with better type narrowing

mypy.ini

@@ -4,6 +4,7 @@
 python_version = 3.8
 strict = False
 warn_unused_ignores = True
+warn_redundant_casts = True
 # required to support namespace packages: https://github.com/python/mypy/issues/14057
 explicit_package_bases = True
 exclude = (?x)(

setuptools/command/editable_wheel.py

@@ -519,7 +519,7 @@ def template_vars(self) -> Tuple[str, str, Dict[str, str], Dict[str, List[str]]]
         )
 
         legacy_namespaces = {
-            cast(str, pkg): find_package_path(pkg, roots, self.dist.src_root or "")
+            pkg: find_package_path(pkg, roots, self.dist.src_root or "")
             for pkg in self.dist.namespace_packages or []
         }
 

setuptools/config/_apply_pyprojecttoml.py

@@ -10,7 +10,6 @@
 
 import logging
 import os
-from collections.abc import Mapping
 from email.headerregistry import Address
 from functools import partial, reduce
 from inspect import cleandoc
@@ -22,6 +21,7 @@
     Callable,
     Dict,
     List,
+    Mapping,
     Optional,
     Set,
     Tuple,
@@ -39,7 +39,7 @@
     from setuptools.dist import Distribution  # noqa
 
 EMPTY: Mapping = MappingProxyType({})  # Immutable dict-like
-_DictOrStr = Union[dict, str]
+_LongDescriptionValue = Union[str, Mapping[str, str]]
 _CorrespFn = Callable[["Distribution", Any, StrPath], None]
 _Correspondence = Union[str, _CorrespFn]
 
@@ -153,15 +153,17 @@ def _guess_content_type(file: str) -> Optional[str]:
     raise ValueError(f"Undefined content type for {file}, {msg}")
 
 
-def _long_description(dist: "Distribution", val: _DictOrStr, root_dir: StrPath):
+def _long_description(
+    dist: "Distribution", val: _LongDescriptionValue, root_dir: StrPath
+):
     from setuptools.config import expand
 
     if isinstance(val, str):
-        file: Union[str, list] = val
+        file: Union[str, tuple[()]] = val
         text = expand.read_files(file, root_dir)
         ctype = _guess_content_type(val)
     else:
-        file = val.get("file") or []
+        file = val.get("file") or ()
         text = val.get("text") or expand.read_files(file, root_dir)
         ctype = val["content-type"]
 
@@ -171,6 +173,10 @@ def _long_description(dist: "Distribution", val: _DictOrStr, root_dir: StrPath):
         _set_config(dist, "long_description_content_type", ctype)
 
     if file:
+        # Due to bad type narrowing, mypy sees file as `str | tuple[Any, ...]`
+        # and flipping the condition mypy sees val as `str | None`.
+        # Pyright gets both w/o issue. Can't use `tuple[()]()` until Python 3.9. So casting instead.
+        # https://github.com/python/mypy/issues/17273
         dist._referenced_files.add(cast(str, file))
 
 

setuptools/config/expand.py

@@ -39,7 +39,6 @@
     Tuple,
     TypeVar,
     Union,
-    cast,
 )
 from pathlib import Path
 from types import ModuleType
@@ -119,7 +118,7 @@ def glob_relative(
     return expanded_values
 
 
-def read_files(filepaths: Union[str, bytes, Iterable[StrPath]], root_dir=None) -> str:
+def read_files(filepaths: Union[StrPath, Iterable[StrPath]], root_dir=None) -> str:
     """Return the content of the files concatenated using ``\n`` as str
 
     This function is sandboxed and won't reach anything outside ``root_dir``
@@ -339,18 +338,13 @@ def version(value: Union[Callable, Iterable[Union[str, int]], str]) -> str:
     """When getting the version directly from an attribute,
     it should be normalised to string.
     """
-    if callable(value):
-        value = value()
+    _value = value() if callable(value) else value
 
-    value = cast(Iterable[Union[str, int]], value)
-
-    if not isinstance(value, str):
-        if hasattr(value, '__iter__'):
-            value = '.'.join(map(str, value))
-        else:
-            value = '%s' % value
-
-    return value
+    if isinstance(_value, str):
+        return _value
+    if hasattr(_value, '__iter__'):
+        return '.'.join(map(str, _value))
+    return '%s' % _value
 
 
 def canonic_package_data(package_data: dict) -> dict:

setuptools/dist.py

@@ -272,6 +272,7 @@ class Distribution(_Distribution):
     }
 
     _patched_dist = None
+    namespace_packages: List[str]
 
     def patch_missing_pkg_info(self, attrs):
         # Fake up a replacement for the data that would normally come from