Remove stale keys when reloading YAML sources

confuse/sources.py

@@ -98,9 +98,12 @@ def load(self) -> None:
         elif self.filename is None:
             raise TypeError("filename is required for YamlSource")
         else:
-            value = yaml_util.load_yaml(self.filename, loader=self.loader) or {}
+            value = yaml_util.load_yaml(self.filename, loader=self.loader)
+            if value is None:
+                value = {}
 
         if isinstance(value, dict):
+            self.clear()
             self.update(value)
         else:
             # We enforce that the loaded YAML is a mapping (dict)

docs/changelog.rst

@@ -13,9 +13,11 @@ Unreleased
     New features
     ~~~~~~~~~~~~
 
-..
-    Bug fixes
-    ~~~~~~~~~
+Bug fixes
+~~~~~~~~~
+
+- Remove stale keys when reloading YAML sources, allowing deleted overrides to
+  fall back to lower-priority sources.
 
 ..
     For plugin developers

test/test_yaml.py

@@ -114,3 +114,100 @@ def test_list_unchanged(self):
     def test_invalid_yaml_string_unchanged(self):
         v = confuse.yaml_util.parse_as_scalar("!", confuse.Loader)
         assert v == "!"
+
+
+class TestYamlReload:
+    def test_removed_keys_reveal_defaults(self, tmp_path):
+        path = tmp_path / "config.yaml"
+        path.write_text("foo: override\nremoved: old\nkept: before\n")
+        config = confuse.Configuration("test", read=False)
+        config.add({"foo": "default"})
+        config.set_file(str(path))
+        config.set({"memory": "preserved"})
+        foo = config["foo"]
+        assert foo.get() == "override"
+
+        path.write_text("kept: after\nadded: new\n")
+        config.reload()
+
+        assert foo.get() == "default"
+        assert not config["removed"].exists()
+        assert config["kept"].get() == "after"
+        assert config["added"].get() == "new"
+        assert config["memory"].get() == "preserved"
+
+    @pytest.mark.parametrize(
+        "contents", ["", "{}", "# Empty configuration\n", "null", "~"]
+    )
+    def test_empty_file_clears_source(self, tmp_path, contents):
+        path = tmp_path / "config.yaml"
+        path.write_text("foo: bar\n")
+        source = confuse.YamlSource(str(path))
+
+        path.write_text(contents)
+        source.load()
+
+        assert source == {}
+
+    def test_missing_optional_file_clears_source(self, tmp_path):
+        path = tmp_path / "config.yaml"
+        path.write_text("foo: bar\n")
+        source = confuse.YamlSource(str(path), optional=True)
+
+        path.unlink()
+        source.load()
+
+        assert source == {}
+        path.write_text("new: value\n")
+        source.load()
+        assert source == {"new": "value"}
+
+    @pytest.mark.parametrize(
+        "contents, error",
+        [
+            ("foo: [", confuse.ConfigReadError),
+            ("- item", TypeError),
+            ("[]", TypeError),
+            ("false", TypeError),
+            ("0", TypeError),
+            ("0.0", TypeError),
+            ('""', TypeError),
+        ],
+    )
+    def test_failed_reload_preserves_source(self, tmp_path, contents, error):
+        path = tmp_path / "config.yaml"
+        path.write_text("foo: bar\n")
+        source = confuse.YamlSource(str(path))
+
+        path.write_text(contents)
+        with pytest.raises(error):
+            source.load()
+
+        assert source == {"foo": "bar"}
+
+    def test_missing_required_file_preserves_source(self, tmp_path):
+        path = tmp_path / "config.yaml"
+        path.write_text("foo: bar\n")
+        source = confuse.YamlSource(str(path))
+
+        path.unlink()
+        with pytest.raises(confuse.ConfigReadError):
+            source.load()
+
+        assert source == {"foo": "bar"}
+
+    def test_reload_preserves_source_metadata_and_order(self, tmp_path):
+        path = tmp_path / "config.yaml"
+        path.write_text("first: before\nsecond: before\n")
+        source = confuse.YamlSource(str(path), default=True, base_for_paths=True)
+        config = confuse.Configuration("test", read=False)
+        config.add(source)
+
+        path.write_text("second: after\nfirst: after\n")
+        config.reload()
+
+        assert config.sources[0] is source
+        assert list(source) == ["second", "first"]
+        assert source.filename == str(path)
+        assert source.default is True
+        assert source.base_for_paths is True