fix: preserve default-config key order in Configuration.dump

confuse/core.py

@@ -676,6 +676,24 @@ def dump(self, full: bool = True, redact: bool = False) -> str:
             temp_root.redactions = self.redactions
             out_dict = temp_root.flatten(redact=redact)
 
+        # `keys()` enumerates the sources in priority order, so keys that
+        # only appear in a lower-priority source (such as the defaults) are
+        # listed after every key of the highest-priority source. Restore the
+        # documented ordering by putting the keys of the default source
+        # first, in the order they appear there.
+        default_keys = [
+            key for source in self.sources if source.default for key in source.keys()
+        ]
+        if default_keys:
+            ordered = OrderedDict()
+            for key in default_keys:
+                if key in out_dict:
+                    ordered[key] = out_dict[key]
+            for key, value in out_dict.items():
+                if key not in ordered:
+                    ordered[key] = value
+            out_dict = ordered
+
         yaml_out = yaml.dump(
             out_dict,
             Dumper=yaml_util.Dumper,

test/test_dump.py

@@ -63,6 +63,17 @@ def test_dump_sans_defaults(self):
         yaml = config.dump(full=False).strip()
         assert yaml == "baz: qux"
 
+    def test_dump_follows_default_key_order(self):
+        config = confuse.Configuration("myapp", read=False)
+        config.add({"foo": "bar", "baz": "qux"})
+        config.sources[0].default = True
+        # A higher-priority source that lists the keys in a different order
+        # and only overrides the second one.
+        config.set({"baz": "override"})
+
+        yaml = config.dump().strip()
+        assert yaml == "foo: bar\nbaz: override"
+
 
 class RedactTest(unittest.TestCase):
     def test_no_redaction(self):