Issue #17098: Be more stringent of setting __loader__ on early imported

modules. Also made test more rigorous.

Lib/importlib/_bootstrap.py

@@ -1704,10 +1704,13 @@ def _setup(sys_module, _imp_module):
         BYTECODE_SUFFIXES = DEBUG_BYTECODE_SUFFIXES
 
     module_type = type(sys)
-    for module in sys.modules.values():
+    for name, module in sys.modules.items():
         if isinstance(module, module_type):
             if not hasattr(module, '__loader__'):
-                module.__loader__ = BuiltinImporter
+                if name in sys.builtin_module_names:
+                    module.__loader__ = BuiltinImporter
+                elif _imp.is_frozen(name):
+                    module.__loader__ = FrozenImporter
 
     self_module = sys.modules[__name__]
     for builtin_name in ('_io', '_warnings', 'builtins', 'marshal'):

Lib/test/test_importlib/test_api.py

@@ -184,6 +184,12 @@ class StartupTests(unittest.TestCase):
             if isinstance(module, types.ModuleType):
                 self.assertTrue(hasattr(module, '__loader__'),
                         '{!r} lacks a __loader__ attribute'.format(name))
+                if name in sys.builtin_module_names:
+                    self.assertEqual(importlib.machinery.BuiltinImporter,
+                                     module.__loader__)
+                elif imp.is_frozen(name):
+                    self.assertEqual(importlib.machinery.FrozenImporter,
+                                     module.__loader__)
 
 def test_main():
     from test.support import run_unittest