Extract _is_typing() to module level

Author: AA-Turner

sphinx/domains/python/__init__.py

@@ -52,6 +52,8 @@
     py_sig_re,
 )
 
+_TYPING_ALL = frozenset(typing.__all__)
+
 logger = logging.getLogger(__name__)
 
 pairindextypes = {
@@ -1076,13 +1078,6 @@ def builtin_resolver(
     app: Sphinx, env: BuildEnvironment, node: pending_xref, contnode: Element
 ) -> Element | None:
     """Do not emit nitpicky warnings for built-in types."""
-
-    def istyping(s: str) -> bool:
-        if s.startswith('typing.'):
-            s = s.split('.', 1)[1]
-
-        return s in typing.__all__
-
     if node.get('refdomain') != 'py':
         return None
     elif node.get('reftype') in {'class', 'obj'} and node.get('reftarget') == 'None':
@@ -1092,13 +1087,17 @@ def istyping(s: str) -> bool:
         if inspect.isclass(getattr(builtins, reftarget, None)):
             # built-in class
             return contnode
-        if istyping(reftarget):
+        if _is_typing(reftarget):
             # typing class
             return contnode
 
     return None
 
 
+def _is_typing(s: str, /) -> bool:
+    return s.removeprefix('typing.') in _TYPING_ALL
+
+
 def setup(app: Sphinx) -> ExtensionMetadata:
     app.setup_extension('sphinx.directives')