Make optional parameters omittable

src/Nirum/Targets/Python.hs

@@ -370,6 +370,11 @@ mpcBehindName :: MethodParameterCode -> T.Text
 mpcBehindName MethodParameterCode { mpcParam = Parameter pName _ _ } =
     toBehindSnakeCaseText pName
 
+mpcOptional :: MethodParameterCode -> Bool
+mpcOptional mpc = case mpcType mpc of
+    OptionModifier _ -> True
+    _ -> False
+
 mpcType :: MethodParameterCode -> TypeExpression
 mpcType MethodParameterCode { mpcParam = Parameter _ typeExpr _ } = typeExpr
 
@@ -1313,7 +1318,11 @@ class #{className}(service_type):
             try:
                 field_value = value['#{mpcBehindName mpc}']
             except KeyError:
+%{ if mpcOptional mpc }
+                result['#{mpcAttributeName mpc}'] = None
+%{ else }
                 on_error('.#{mpcBehindName mpc}', 'Expected to exist.')
+%{ endif }
             else:
                 result['#{mpcAttributeName mpc}'] = \
                     table['#{mpcBehindName mpc}'](

test/nirum_fixture/fixture/foo.nrm

@@ -125,6 +125,7 @@ union animal = cat
 service sample-service (
     sample-method (animal a, product b/bb, gender c, way d/dd,
                    uuid e, binary f/ff, bigint g, text h/hh),
+    sample-method-with-optional-param(uuid a, animal? b),
     animal sample-method-that-returns(),
 );
 

test/python/service_test.py

@@ -144,6 +144,28 @@ def test_service_deserialize_arguments(fx_method_args):
     assert errors == {('', 'Expected an object.')}
 
 
+def test_service_deserialize_arguments_with_omitted_keys(fx_dog):
+    m = SampleService.sample_method_with_optional_param
+    f = m.__nirum_deserialize_arguments__
+    payload = {
+        'a': 'f7db93e3-731e-48ef-80a2-cac81e02f1ae',
+        'b': fx_dog[1],
+    }
+    expected = {
+        'a': uuid.UUID('F7DB93E3-731E-48EF-80A2-CAC81E02F1AE'),
+        'b': fx_dog[0],
+    }
+    assert f(payload) == expected
+    assert f(dict(payload, b=None)) == dict(expected, b=None)
+    assert f({'a': payload['a']}) == dict(expected, b=None)
+    with raises(ValueError) as e:
+        f({'b': fx_dog[1]})
+    assert str(e.value) == '.a: Expected to exist.'
+    with raises(ValueError) as e:
+        f(dict(payload, b=dict(fx_dog[1], name=None)))
+    assert str(e.value) == '.b.name: Expected a string.'
+
+
 def test_service_argument_serializers(fx_method_args):
     args, expected = fx_method_args
     table = SampleService.sample_method.__nirum_argument_serializers__