pathlib ABCs: remove caching of path parser case sensitivity (#130194)

Remove the caching `_is_case_sensitive()` function. 

The cache used to speed up `PurePath.[full_]match()` and `Path.[r]glob()`,
but that's no longer the case - these methods use
`self.parser is posixpath` to determine case sensitivity.

This makes the `pathlib._abc` module a little easier to backport to Python
3.8, where `functools.cache()` is unavailable.

Author: barneygale

Lib/pathlib/_abc.py

@@ -11,18 +11,12 @@
 WritablePath.
 """
 
-import functools
 from abc import ABC, abstractmethod
 from glob import _PathGlobber, _no_recurse_symlinks
 from pathlib import PurePath, Path
 from pathlib._os import magic_open, CopyReader, CopyWriter
 
 
-@functools.cache
-def _is_case_sensitive(parser):
-    return parser.normcase('Aa') == 'Aa'
-
-
 def _explode_path(path):
     """
     Split the path into a 2-tuple (anchor, parts), where *anchor* is the
@@ -201,7 +195,7 @@ def full_match(self, pattern, *, case_sensitive=None):
         if not isinstance(pattern, JoinablePath):
             pattern = self.with_segments(pattern)
         if case_sensitive is None:
-            case_sensitive = _is_case_sensitive(self.parser)
+            case_sensitive = self.parser.normcase('Aa') == 'Aa'
         globber = _PathGlobber(pattern.parser.sep, case_sensitive, recursive=True)
         match = globber.compile(str(pattern))
         return match(str(self)) is not None
@@ -297,13 +291,12 @@ def glob(self, pattern, *, case_sensitive=None, recurse_symlinks=True):
         anchor, parts = _explode_path(pattern)
         if anchor:
             raise NotImplementedError("Non-relative patterns are unsupported")
+        case_sensitive_default = self.parser.normcase('Aa') == 'Aa'
         if case_sensitive is None:
-            case_sensitive = _is_case_sensitive(self.parser)
-            case_pedantic = False
-        elif case_sensitive == _is_case_sensitive(self.parser):
+            case_sensitive = case_sensitive_default
             case_pedantic = False
         else:
-            case_pedantic = True
+            case_pedantic = case_sensitive_default != case_sensitive
         recursive = True if recurse_symlinks else _no_recurse_symlinks
         globber = _PathGlobber(self.parser.sep, case_sensitive, case_pedantic, recursive)
         select = globber.selector(parts)