test_importlib: restore builtins after import

Lib/test/test_importlib/test_util.py

@@ -33,6 +33,32 @@
     _interpreters = None
 
 
+class ImportImportlibTests(unittest.TestCase):
+
+    def test_restores_missing_builtin_import_metadata(self):
+        missing = object()
+        attrs = {
+            attr: getattr(util.builtins, attr, missing)
+            for attr in ('__loader__', '__spec__')
+        }
+        try:
+            for attr in attrs:
+                if hasattr(util.builtins, attr):
+                    delattr(util.builtins, attr)
+
+            util.import_importlib('importlib')
+
+            for attr in attrs:
+                self.assertFalse(hasattr(util.builtins, attr))
+        finally:
+            for attr, value in attrs.items():
+                if value is missing:
+                    if hasattr(util.builtins, attr):
+                        delattr(util.builtins, attr)
+                else:
+                    setattr(util.builtins, attr, value)
+
+
 class DecodeSourceBytesTests:
 
     source = "string ='ü'"

Lib/test/test_importlib/util.py

@@ -68,8 +68,24 @@ def import_importlib(module_name):
     """Import a module from importlib both w/ and w/o _frozen_importlib."""
     fresh = ('importlib',) if '.' in module_name else ()
     frozen = import_helper.import_fresh_module(module_name)
-    source = import_helper.import_fresh_module(module_name, fresh=fresh,
-                                         blocked=('_frozen_importlib', '_frozen_importlib_external'))
+    missing = object()
+    builtin_attrs = {
+        attr: getattr(builtins, attr, missing)
+        for attr in ('__loader__', '__spec__')
+    }
+    try:
+        source = import_helper.import_fresh_module(
+            module_name,
+            fresh=fresh,
+            blocked=('_frozen_importlib', '_frozen_importlib_external'),
+        )
+    finally:
+        for attr, value in builtin_attrs.items():
+            if value is missing:
+                if hasattr(builtins, attr):
+                    delattr(builtins, attr)
+            else:
+                setattr(builtins, attr, value)
     return {'Frozen': frozen, 'Source': source}