Add sys.lazy_modules docs and fix CI test failures

- Add ``sys.lazy_modules`` entry to Doc/library/sys.rst (frozendict
  snapshot, fresh per access, versionadded 3.15)
- Fix test_builtin.test_vars: sys.lazy_modules is served by
  sys.__getattr__ so it appears in dir() but not vars()
- Fix test_inspect.test_sys_module_has_signatures: sys.__dir__ and
  sys.__getattr__ are METH_NOARGS/METH_VARARGS builtins without
  Argument Clinic text signatures; add them to no_signature

Author: johnslavik

Doc/library/sys.rst

@@ -1483,6 +1483,27 @@ always available. Unless explicitly noted otherwise, all variables are read-only
    They hold the legacy representation of ``sys.last_exc``, as returned
    from :func:`exc_info` above.
 
+
+.. data:: lazy_modules
+
+   A read-only :class:`frozendict` snapshot of the lazy import registry for the
+   current interpreter.  Each key is a module name string; the corresponding
+   value is a :class:`frozenset` of the child attribute names that were
+   registered as lazy imports from that module.  A top-level lazy import (e.g.
+   ``lazy import json``) is represented by an empty :class:`frozenset`.
+
+   A fresh snapshot is constructed on every attribute access, so the mapping
+   reflects the state of lazy imports at the time of access.  The snapshot is
+   immutable; modifications must go through :func:`set_lazy_imports`.
+
+   The live, mutable registry is available as the private :data:`sys._lazy_modules`
+   for internal use.
+
+   See also :func:`set_lazy_imports`, :func:`get_lazy_imports`, and :pep:`810`.
+
+   .. versionadded:: 3.15
+
+
 .. data:: maxsize
 
    An integer giving the maximum value a variable of type :c:type:`Py_ssize_t` can

Lib/test/test_builtin.py

@@ -2132,7 +2132,9 @@ def getDict(self):
 
     def test_vars(self):
         self.assertEqual(set(vars()), set(dir()))
-        self.assertEqual(set(vars(sys)), set(dir(sys)))
+        # sys.lazy_modules is a virtual attribute served by sys.__getattr__,
+        # so it appears in dir() but not in vars().
+        self.assertEqual(set(vars(sys)) | {'lazy_modules'}, set(dir(sys)))
         self.assertEqual(self.get_vars_f0(), {})
         self.assertEqual(self.get_vars_f2(), {'a': 1, 'b': 2})
         self.assertRaises(TypeError, vars, 42, 42)

Lib/test/test_inspect/test_inspect.py

@@ -6179,6 +6179,9 @@ def test_sys_module_has_signatures(self):
         no_signature = {'getsizeof', 'set_asyncgen_hooks'}
         no_signature |= {name for name in ['getobjects']
                          if hasattr(sys, name)}
+        # sys.__dir__ and sys.__getattr__ are plain METH_NOARGS/METH_VARARGS
+        # builtins without Argument Clinic text signatures.
+        no_signature |= {'__dir__', '__getattr__'}
         self._test_module_has_signatures(sys, no_signature)
 
     def test_abc_module_has_signatures(self):