Stop re-wrapping an inherited set_password once per MRO class

keyring/backend.py

@@ -53,12 +53,17 @@ def _validate_username_in_set_password(cls):
         Wrap ``set_password`` such to validate the passed username.
         """
         orig = cls.set_password
+        if getattr(orig, '_validates_username', False):
+            # inherited from a base class that was already wrapped; wrapping
+            # again would validate (and warn) once per class in the MRO.
+            return
 
         @functools.wraps(orig)
         def wrapper(self, system, username, *args, **kwargs):
             self._validate_username(username)
             return orig(self, system, username, *args, **kwargs)
 
+        wrapper._validates_username = True
         cls.set_password = wrapper
 
 

newsfragments/+set-password-wrap.bugfix.rst

@@ -0,0 +1 @@
+Fixed ``KeyringBackendMeta`` re-wrapping ``set_password`` once per class in the MRO, which made the empty-username deprecation warning fire more than once per call and misattribute its source location.

tests/test_backend_meta.py

@@ -0,0 +1,61 @@
+"""Tests for keyring.backend.KeyringBackendMeta."""
+
+import warnings
+
+import pytest
+
+from keyring import backend
+
+
+class BaseKeyring(backend.KeyringBackend):
+    """A backend defining ``set_password``, so the metaclass wraps it once."""
+
+    priority = 1
+
+    def get_password(self, service, username):
+        return None
+
+    def set_password(self, service, username, password):
+        self.saved = (service, username, password)
+
+
+class DerivedKeyring(BaseKeyring):
+    """A subclass inheriting ``set_password``, so it must not be re-wrapped."""
+
+
+class TestValidateUsernameInSetPassword:
+    def test_validates_username_once(self):
+        """
+        The metaclass wraps ``set_password`` on every class it creates, but a
+        subclass that merely inherits ``set_password`` already has the
+        wrapped version. Re-wrapping makes the username validation (and its
+        deprecation warning) run once per class in the MRO.
+        """
+        keyring = DerivedKeyring()
+        with pytest.deprecated_call() as record:
+            keyring.set_password('svc', '', 'pw')
+        assert len(record) == 1
+        assert keyring.saved == ('svc', '', 'pw')
+
+    def test_overridden_set_password_is_still_wrapped(self):
+        """
+        A subclass that supplies its own ``set_password`` is not yet
+        wrapped, so it must be.
+        """
+
+        class OverridingKeyring(BaseKeyring):
+            def set_password(self, service, username, password):
+                self.saved = (service, username, password)
+
+        keyring = OverridingKeyring()
+        with pytest.deprecated_call() as record:
+            keyring.set_password('svc', '', 'pw')
+        assert len(record) == 1
+        assert keyring.saved == ('svc', '', 'pw')
+
+    def test_no_warning_for_nonempty_username(self):
+        keyring = DerivedKeyring()
+        with warnings.catch_warnings(record=True) as record:
+            warnings.simplefilter('always')
+            keyring.set_password('svc', 'user', 'pw')
+        assert [w for w in record if w.category is DeprecationWarning] == []