Simplify code as cattrs depends on modern attrs

This modern version of `attrs` provides the `alias` attribute on
fields that contains the name we should use here.

Also add a test to verify that structuring and unstructuring aliased
attributes (which can be triggered by prefixing an attribute with an
underscore) works as expected.

HISTORY.md

@@ -34,6 +34,8 @@
   ([#408](https://github.com/python-attrs/cattrs/pull/408))
 - Fix structuring `Final` lists.
   ([#412](https://github.com/python-attrs/cattrs/issues/412))
+- Remove some unused lines in the unstructuring code.
+  ([#416](https://github.com/python-attrs/cattrs/pull/416))
 
 
 ## 23.1.2 (2023-06-02)

src/cattrs/converters.py

@@ -511,16 +511,12 @@ def structure_attrs_fromdict(self, obj: Mapping[str, Any], cl: Type[T]) -> T:
 
         conv_obj = {}  # Start with a fresh dict, to ignore extra keys.
         for a in fields(cl):
-            name = a.name
-
             try:
-                val = obj[name]
+                val = obj[a.name]
             except KeyError:
                 continue
 
-            if name[0] == "_":
-                name = name[1:]
-
+            # try .alias and .name because this code also supports dataclasses!
             conv_obj[getattr(a, "alias", a.name)] = self._structure_attribute(a, val)
 
         return cl(**conv_obj)

tests/test_converter.py

@@ -381,6 +381,23 @@ class C:
     assert inst == converter.structure(unstructured, C)
 
 
+def test_dict_roundtrip_with_alias():
+    """
+    A class with an aliased attribute can be unstructured and structured.
+    """
+
+    converter = Converter()
+
+    @define
+    class C:
+        _a: int
+
+    inst = C(a=0)
+    unstructured = converter.unstructure(inst)
+    assert unstructured == {"_a": 0}
+    assert converter.structure(unstructured, C) == inst
+
+
 @given(simple_typed_classes(defaults=True))
 def test_type_overrides(cl_and_vals):
     """