Add some validation to input arguments

graphene/experimental/decorators/mutation.py

@@ -1,9 +1,33 @@
+from typing import List
+
 from graphene.types.field import Field
+from graphene.types.inputobjecttype import InputObjectType
+from graphene.types.scalars import Scalar
 from graphene.utils.str_converters import to_camel_case
 
 
+class MutationInvalidArgumentsError(Exception):
+    def __init__(self, mutation_name: str, invalid_arguments: List[str]):
+        invalid_arguments = sorted(invalid_arguments)
+
+        if len(invalid_arguments) == 1:
+            message = (
+                f"Argument `{invalid_arguments[0]}` is not a valid type "
+                f"in mutation `{mutation_name}`. "
+            )
+        else:
+            head = ", ".join(invalid_arguments[:-1])
+            message = (
+                f"Arguments `{head}` and `{invalid_arguments[-1]}` are not valid types "
+                f"in mutation `{mutation_name}`. "
+            )
+
+        message += "Arguments to a mutation need to be either a Scalar type or an InputObjectType."
+
+        super().__init__(message)
+
+
 def mutation(return_type, arguments=None, **kwargs):
-    # TODO: validate input arguments
     if arguments is None:
         arguments = {}
 
@@ -11,13 +35,23 @@ def mutation(return_type, arguments=None, **kwargs):
         name = kwargs.pop("name", None) or resolver_function.__name__
         description = kwargs.pop("description", None) or resolver_function.__doc__
 
+        invalid_arguments = []
+        for argument_name, argument in arguments.items():
+            if not (
+                isinstance(argument, Scalar) or isinstance(argument, InputObjectType)
+            ):
+                invalid_arguments.append(argument_name)
+
+        if len(invalid_arguments) > 0:
+            raise MutationInvalidArgumentsError(name, invalid_arguments)
+
         return Field(
             return_type,
             args=arguments,
             name=to_camel_case(name),
             resolver=resolver_function,
             description=description,
-            **kwargs
+            **kwargs,
         )
 
     return decorate

graphene/experimental/decorators/tests/test_mutation.py

@@ -1,8 +1,10 @@
 from textwrap import dedent
 
-from graphene import String, ObjectType, Schema, Union, Field
+import pytest
 
-from ..mutation import mutation
+from graphene import Boolean, Field, InputObjectType, ObjectType, Schema, String, Union
+
+from ..mutation import mutation, MutationInvalidArgumentsError
 
 
 def test_mutation_basic():
@@ -160,3 +162,122 @@ def test_mutation_complex_return():
         }
     """
     )
+
+
+def test_mutation_complex_input():
+    class User(ObjectType):
+        name = String(required=True)
+        email = String(required=True)
+
+    class CreateUserSuccess(ObjectType):
+        user = Field(User, required=True)
+
+    class CreateUserError(ObjectType):
+        error_message = String(required=True)
+
+    class CreateUserOutput(Union):
+        class Meta:
+            types = [
+                CreateUserSuccess,
+                CreateUserError,
+            ]
+
+    class CreateUserInput(InputObjectType):
+        name = String(required=True)
+        email = String(required=True)
+
+    @mutation(
+        CreateUserOutput,
+        required=True,
+        arguments={"user": CreateUserInput(required=True)},
+    )
+    def create_user(root, info, user):
+        return CreateUserSuccess(user=User(**user))
+
+    class Query(ObjectType):
+        a = String()
+
+    schema = Schema(query=Query, mutations=[create_user])
+    result = schema.execute(
+        """
+        mutation CreateUserMutation {
+            createUser(user: { name: "Kate", email: "kate@example.com" }) {
+                __typename
+                ... on CreateUserSuccess {
+                    user {
+                        name
+                    }
+                }
+            }
+        }
+    """
+    )
+
+    assert not result.errors
+    assert result.data == {
+        "createUser": {"__typename": "CreateUserSuccess", "user": {"name": "Kate"}}
+    }
+
+    assert str(schema) == dedent(
+        """\
+        type Query {
+          a: String
+        }
+
+        type Mutation {
+          createUser(user: CreateUserInput!): CreateUserOutput!
+        }
+
+        union CreateUserOutput = CreateUserSuccess | CreateUserError
+
+        type CreateUserSuccess {
+          user: User!
+        }
+
+        type User {
+          name: String!
+          email: String!
+        }
+
+        type CreateUserError {
+          errorMessage: String!
+        }
+
+        input CreateUserInput {
+          name: String!
+          email: String!
+        }
+    """
+    )
+
+
+def test_raises_error_invalid_input():
+    class User(ObjectType):
+        name = String(required=True)
+        email = String(required=True)
+
+    with pytest.raises(MutationInvalidArgumentsError) as validation_error:
+
+        @mutation(
+            Boolean, required=True, arguments={"user": User},
+        )
+        def create_user(root, info, user):
+            return True
+
+    assert str(validation_error.value) == (
+        "Argument `user` is not a valid type in mutation `create_user`. "
+        "Arguments to a mutation need to be either a Scalar type or an InputObjectType."
+    )
+
+    with pytest.raises(MutationInvalidArgumentsError) as validation_error:
+
+        @mutation(
+            Boolean, required=True, arguments={"user": User, "user2": User},
+        )
+        def create_user2(root, info, user):
+            return True
+
+    assert str(validation_error.value) == (
+        "Arguments `user` and `user2` are not valid types in mutation `create_user2`. "
+        "Arguments to a mutation need to be either a Scalar type or an InputObjectType."
+    )