Only turn optional into a Converter if needed

src/attr/converters.py

@@ -40,13 +40,19 @@ def optional_converter(val, inst, field):
                 return None
             return converter(val, inst, field)
 
+        result = Converter(
+            optional_converter, takes_self=True, takes_field=True
+        )
+
     else:
 
-        def optional_converter(val, inst, field):
+        def optional_converter(val):
             if val is None:
                 return None
             return converter(val)
 
+        result = optional_converter
+
     xtr = _AnnotationExtractor(converter)
 
     t = xtr.get_first_param_type()
@@ -57,7 +63,7 @@ def optional_converter(val, inst, field):
     if rt:
         optional_converter.__annotations__["return"] = typing.Optional[rt]
 
-    return Converter(optional_converter, takes_self=True, takes_field=True)
+    return result
 
 
 def default_if_none(default=NOTHING, factory=None):

tests/test_annotations.py

@@ -351,26 +351,22 @@ def strify(x) -> str:
         def identity(x):
             return x
 
-        assert attr.converters.optional(int2str).converter.__annotations__ == {
+        assert attr.converters.optional(int2str).__annotations__ == {
             "val": typing.Optional[int],
             "return": typing.Optional[str],
         }
-        assert attr.converters.optional(
-            int_identity
-        ).converter.__annotations__ == {"val": typing.Optional[int]}
-        assert attr.converters.optional(strify).converter.__annotations__ == {
+        assert attr.converters.optional(int_identity).__annotations__ == {
+            "val": typing.Optional[int]
+        }
+        assert attr.converters.optional(strify).__annotations__ == {
             "return": typing.Optional[str]
         }
-        assert (
-            attr.converters.optional(identity).converter.__annotations__ == {}
-        )
+        assert attr.converters.optional(identity).__annotations__ == {}
 
         def int2str_(x: int, y: int = 0) -> str:
             return str(x)
 
-        assert attr.converters.optional(
-            int2str_
-        ).converter.__annotations__ == {
+        assert attr.converters.optional(int2str_).__annotations__ == {
             "val": typing.Optional[int],
             "return": typing.Optional[str],
         }
@@ -381,7 +377,7 @@ def test_optional_non_introspectable(self):
         converter.
         """
 
-        assert attr.converters.optional(print).converter.__annotations__ == {}
+        assert attr.converters.optional(print).__annotations__ == {}
 
     def test_optional_nullary(self):
         """
@@ -391,7 +387,7 @@ def test_optional_nullary(self):
         def noop():
             pass
 
-        assert attr.converters.optional(noop).converter.__annotations__ == {}
+        assert attr.converters.optional(noop).__annotations__ == {}
 
     @pytest.mark.skipif(
         sys.version_info[:2] < (3, 11),

tests/test_converters.py

@@ -124,15 +124,15 @@ def test_success_with_type(self):
         """
         c = optional(int)
 
-        assert c("42", None, None) == 42
+        assert c("42") == 42
 
     def test_success_with_none(self):
         """
         Nothing happens if None.
         """
         c = optional(int)
 
-        assert c(None, None, None) is None
+        assert c(None) is None
 
     def test_fail(self):
         """
@@ -141,7 +141,15 @@ def test_fail(self):
         c = optional(int)
 
         with pytest.raises(ValueError):
-            c("not_an_int", None, None)
+            c("not_an_int")
+
+    def test_converter_instance(self):
+        """
+        Works when passed a Converter instance as argument.
+        """
+        c = optional(Converter(to_bool))
+
+        assert True is c("yes", None, None)
 
 
 class TestDefaultIfNone: