Move validation into _pattern_stack

Lib/pathlib/__init__.py

@@ -472,17 +472,21 @@ def _pattern_stack(self):
         """Stack of path components, to be used with patterns in glob()."""
         parts = self._tail.copy()
         pattern = self._raw_path
-        if pattern.endswith('**'):
+        if self.anchor:
+            raise NotImplementedError("Non-relative patterns are unsupported")
+        elif not parts:
+            raise ValueError("Unacceptable pattern: {!r}".format(pattern))
+        elif pattern[-1] in (self.pathmod.sep, self.pathmod.altsep):
+            # GH-65238: pathlib doesn't preserve trailing slash. Add it back.
+            parts.append('')
+        elif parts[-1] == '**':
             # GH-70303: '**' only matches directories. Add trailing slash.
             warnings.warn(
                 "Pattern ending '**' will match files and directories in a "
                 "future Python release. Add a trailing slash to match only "
                 "directories and remove this warning.",
                 FutureWarning, 4)
             parts.append('')
-        elif pattern[-1] in (self.pathmod.sep, self.pathmod.altsep):
-            # GH-65238: pathlib doesn't preserve trailing slash. Add it back.
-            parts.append('')
         parts.reverse()
         return parts
 

Lib/pathlib/_abc.py

@@ -430,7 +430,10 @@ def is_absolute(self):
     @property
     def _pattern_stack(self):
         """Stack of path components, to be used with patterns in glob()."""
-        return self._stack[1]
+        anchor, parts = self._stack
+        if anchor:
+            raise NotImplementedError("Non-relative patterns are unsupported")
+        return parts
 
     def match(self, path_pattern, *, case_sensitive=None):
         """
@@ -733,11 +736,6 @@ def glob(self, pattern, *, case_sensitive=None, follow_symlinks=None):
         """
         if not isinstance(pattern, PurePathBase):
             pattern = self.with_segments(pattern)
-        if pattern.anchor:
-            raise NotImplementedError("Non-relative patterns are unsupported")
-        elif not pattern.parts:
-            raise ValueError("Unacceptable pattern: {!r}".format(pattern))
-
         if case_sensitive is None:
             # TODO: evaluate case-sensitivity of each directory in _select_children().
             case_sensitive = _is_case_sensitive(self.pathmod)