Merge branch 'main' into bld/make-non-essential-packages-optional

apptools/preferences/preferences_helper.py

@@ -15,7 +15,7 @@
 import logging
 
 # Enthought library imports.
-from traits.api import HasTraits, Instance, Str
+from traits.api import HasTraits, Instance, Str, observe
 
 # Local imports.
 from .i_preferences import IPreferences
@@ -99,8 +99,11 @@ def _anytrait_changed(self, trait_name, old, new):
         # If the change refers to a trait defined on this class, then
         # the trait is not a preference trait and we do nothing.
 
-    def _preferences_changed(self, old, new):
-        """ Static trait change handler. """
+    @observe("preferences", post_init=True)
+    def _update_preferences_listeners(self, event):
+        """Update listeners when the preferences object changes."""
+
+        old, new = event.old, event.new
 
         # Stop listening to the old preferences node.
         if old is not None:

apptools/preferences/tests/test_preferences_helper.py

@@ -414,7 +414,9 @@ class AcmeUIPreferencesHelper(PreferencesHelper):
     def test_scoped_preferences(self):
         """ scoped preferences """
 
-        p = set_default_preferences(ScopedPreferences())
+        p = set_default_preferences(
+            ScopedPreferences(application_preferences_filename=self.tmpfile)
+        )
 
         # Set a preference value in the default scope.
         p.set("default/acme.ui.bgcolor", "blue")
@@ -605,3 +607,26 @@ class AcmeUIPreferencesHelper(PreferencesHelper):
         # attempt to create instance from invalid value
         with self.assertRaises(TraitError):
             AcmeUIPreferencesHelper(preferences_path="acme.ui")
+
+    def test_preferences_not_written_on_helper_creation(self):
+
+        class AppPreferencesHelper(PreferencesHelper):
+            #: The node that contains the preferences.
+            preferences_path = "app"
+
+            #: The user's favourite colour
+            color = Str()
+
+        default_preferences = Preferences(name="default")
+        default_preferences.set("app.color", "red")
+
+        application_preferences = Preferences(name="application")
+        preferences = ScopedPreferences(
+            scopes=[application_preferences, default_preferences]
+        )
+        self.assertIsNone(application_preferences.get("app.color"))
+
+        # Then creation of the helper should not cause the application
+        # preferences to change.
+        AppPreferencesHelper(preferences=preferences)
+        self.assertIsNone(application_preferences.get("app.color"))

apptools/preferences/tests/test_scoped_preferences.py

@@ -42,14 +42,18 @@ class ScopedPreferencesTestCase(PreferencesTestCase):
     def setUp(self):
         """ Prepares the test fixture before each test method is called. """
 
-        self.preferences = ScopedPreferences()
+        # A temporary directory that can safely be written to.
+        self.tmpdir = tempfile.mkdtemp()
+
+        self.preferences = ScopedPreferences(
+            application_preferences_filename=os.path.join(
+                self.tmpdir, "preferences.ini"
+            )
+        )
 
         # The filename of the example preferences file.
         self.example = os.fspath(files(PKG) / "example.ini")
 
-        # A temporary directory that can safely be written to.
-        self.tmpdir = tempfile.mkdtemp()
-
     def tearDown(self):
         """ Called immediately after each test method has been called. """
 

docs/releases/upcoming/343.bugfix.rst

@@ -0,0 +1 @@
+Don't write to preferences on ``PreferencesHelper`` creation. (#343)