Fixed a bug with reactivating users with the admin API (#8362)

Fixes: #8359 

Trying to reactivate a user with the admin API (`PUT /_synapse/admin/v2/users/<user_name>`) causes an internal server error.

Seems to be a regression in #8033.

changelog.d/8362.bugfix

@@ -0,0 +1 @@
+Fixed a regression in v1.19.0 with reactivating users through the admin API.

synapse/storage/databases/main/user_erasure_store.py

@@ -100,7 +100,7 @@ class UserErasureStore(UserErasureWorkerStore):
                 return
 
             # They are there, delete them.
-            self.simple_delete_one_txn(
+            self.db_pool.simple_delete_one_txn(
                 txn, "erased_users", keyvalues={"user_id": user_id}
             )
 

tests/rest/admin/test_user.py

@@ -874,6 +874,10 @@ class UserRestTestCase(unittest.HomeserverTestCase):
         )
         self.render(request)
         self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
+        self._is_erased("@user:test", False)
+        d = self.store.mark_user_erased("@user:test")
+        self.assertIsNone(self.get_success(d))
+        self._is_erased("@user:test", True)
 
         # Attempt to reactivate the user (without a password).
         request, channel = self.make_request(
@@ -906,6 +910,7 @@ class UserRestTestCase(unittest.HomeserverTestCase):
         self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
         self.assertEqual("@user:test", channel.json_body["name"])
         self.assertEqual(False, channel.json_body["deactivated"])
+        self._is_erased("@user:test", False)
 
     def test_set_user_as_admin(self):
         """
@@ -996,6 +1001,15 @@ class UserRestTestCase(unittest.HomeserverTestCase):
         # Ensure they're still alive
         self.assertEqual(0, channel.json_body["deactivated"])
 
+    def _is_erased(self, user_id, expect):
+        """Assert that the user is erased or not
+        """
+        d = self.store.is_user_erased(user_id)
+        if expect:
+            self.assertTrue(self.get_success(d))
+        else:
+            self.assertFalse(self.get_success(d))
+
 
 class UserMembershipRestTestCase(unittest.HomeserverTestCase):