address PR comments

- remove unneeded test
- pre-compute allowed keys

src/cattr/gen.py

@@ -184,9 +184,10 @@ def make_dict_structure_fn(
             )
     lines.append("    }")
     if _cattrs_forbid_extra_keys:
-        post_lines.append(f"  allowed_fields = {set(a.name for a in attrs)}")
+        allowed_fields = {a.name for a in attrs}
+        globs["__c_a"] = allowed_fields
         post_lines += [
-            "  unknown_fields = set(o.keys()) - allowed_fields",
+            "  unknown_fields = set(o.keys()) - __c_a",
             "  if unknown_fields:",
             "    raise Exception(",
             f"      'Extra fields in constructor for {cl_name}: ' + ', '.join(unknown_fields)"

tests/metadata/test_genconverter.py

@@ -72,23 +72,6 @@ def test_simple_roundtrip_with_extra_keys_forbidden(cls_and_vals, strat):
     assert inst == converter.structure(unstructured, cl)
 
 
-@given(simple_typed_attrs(defaults=True), unstructure_strats)
-def test_simple_roundtrip_defaults_with_extra_keys_forbidden(
-    attr_and_vals, strat
-):
-    """
-    Simple classes can be unstructured and restructured with forbid_extra_keys=True.
-    """
-    a, _ = attr_and_vals
-    cl = make_class("HypClass", {"a": a})
-    converter = Converter(unstruct_strat=strat, forbid_extra_keys=True)
-    inst = cl()
-    assert converter.unstructure(
-        converter.structure({}, cl)
-    ) == converter.unstructure(inst)
-    assert inst == converter.structure(converter.unstructure(inst), cl)
-
-
 @given(simple_typed_classes() | simple_typed_dataclasses())
 def test_forbid_extra_keys(cls_and_vals):
     """