feat(interface): input type cannot inherit an interface type

fix #1236

Author: scratchmex

strawberry/exceptions.py

@@ -176,3 +176,13 @@ def __init__(self, field_name: str, argument_name: str, argument_type: str):
         message = f'Argument "{argument_name}" on field "{field_name}" cannot be of type\
             "{argument_type}"'
         super().__init__(message)
+
+
+class InvalidSuperclassInterface(Exception):
+    def __init__(self, input_name: str, interface_names=List[str]):
+        interface_names = ", ".join(interface_names)
+        message = (
+            f"An Input class {input_name!r} cannot inherit "
+            f"from an Interface(s) {interface_names!r}"
+        )
+        super().__init__(message)

strawberry/object_type.py

@@ -1,7 +1,7 @@
 import dataclasses
 from typing import List, Optional, Type, cast
 
-from .exceptions import MissingFieldAnnotationError, MissingReturnAnnotationError
+from .exceptions import InvalidSuperclassInterface, MissingFieldAnnotationError, MissingReturnAnnotationError
 from .field import StrawberryField, field
 from .types.type_resolver import _get_fields
 from .types.types import FederationTypeParams, TypeDefinition
@@ -99,6 +99,14 @@ def _process_type(
     interfaces = _get_interfaces(cls)
     fields = _get_fields(cls)
 
+    if is_input and interfaces:
+        interface_names = [interface.name for interface in interfaces]
+
+        raise InvalidSuperclassInterface(
+            input_name=name,
+            interface_names=interface_names
+        )
+
     cls._type_definition = TypeDefinition(
         name=name,
         is_input=is_input,

tests/schema/test_interface.py

@@ -4,6 +4,7 @@
 import pytest
 
 import strawberry
+from strawberry.exceptions import InvalidSuperclassInterface
 
 
 def test_query_interface():
@@ -161,3 +162,27 @@ def anime(self) -> Anime:
 
     assert not result.errors
     assert result.data == {"anime": {"name": "One Piece"}}
+
+
+def test_input_cannot_inherit_from_interface():
+    @strawberry.interface
+    class SomeInterface:
+        some_arg: str
+
+    with pytest.raises(InvalidSuperclassInterface):
+
+        @strawberry.input
+        class SomeInput(SomeInterface):  # this should throw an error
+            another_arg: str
+
+    @strawberry.interface
+    class SomeOtherInterface:
+        some_other_arg: str
+
+    with pytest.raises(InvalidSuperclassInterface):
+
+        @strawberry.input
+        class SomeOtherInput(
+            SomeInterface, SomeOtherInterface
+        ):  # this should throw an error
+            another_arg: str