backport: Implement OneOf Input Objects via @OneOf directive

Replicates graphql/graphql-js@29144f7

Author: Cito

.mypy.ini

@@ -1,5 +1,5 @@
 [mypy]
-python_version = 3.7
+python_version = 3.9
 check_untyped_defs = True
 no_implicit_optional = True
 strict_optional = True

src/graphql/__init__.py

@@ -256,6 +256,7 @@
     GraphQLSkipDirective,
     GraphQLDeprecatedDirective,
     GraphQLSpecifiedByDirective,
+    GraphQLOneOfDirective,
     # "Enum" of Type Kinds
     TypeKind,
     # Constant Deprecation Reason
@@ -488,6 +489,7 @@
     "GraphQLSkipDirective",
     "GraphQLDeprecatedDirective",
     "GraphQLSpecifiedByDirective",
+    "GraphQLOneOfDirective",
     "TypeKind",
     "DEFAULT_DEPRECATION_REASON",
     "introspection_types",

src/graphql/execution/values.py

@@ -122,7 +122,11 @@ def coerce_variable_values(
             continue
 
         def on_input_value_error(
-            path: List[Union[str, int]], invalid_value: Any, error: GraphQLError
+            path: List[Union[str, int]],
+            invalid_value: Any,
+            error: GraphQLError,
+            var_name: str = var_name,
+            var_def_node: VariableDefinitionNode = var_def_node,
         ) -> None:
             invalid_str = inspect(invalid_value)
             prefix = f"Variable '${var_name}' got invalid value {invalid_str}"
@@ -196,7 +200,8 @@ def get_argument_values(
                         value_node,
                     )
                 continue  # pragma: no cover
-            is_null = variable_values[variable_name] is None
+            variable_value = variable_values[variable_name]
+            is_null = variable_value is None or variable_value is Undefined
 
         if is_null and is_non_null_type(arg_type):
             raise GraphQLError(

src/graphql/type/__init__.py

@@ -132,6 +132,7 @@
     GraphQLSkipDirective,
     GraphQLDeprecatedDirective,
     GraphQLSpecifiedByDirective,
+    GraphQLOneOfDirective,
     # Keyword Args
     GraphQLDirectiveKwargs,
     # Constant Deprecation Reason
@@ -276,6 +277,7 @@
     "GraphQLSkipDirective",
     "GraphQLDeprecatedDirective",
     "GraphQLSpecifiedByDirective",
+    "GraphQLOneOfDirective",
     "GraphQLDirectiveKwargs",
     "DEFAULT_DEPRECATION_REASON",
     "is_specified_scalar_type",

src/graphql/type/definition.py

@@ -1373,6 +1373,7 @@ def __copy__(self) -> "GraphQLEnumValue":  # pragma: no cover
 class GraphQLInputObjectTypeKwargs(GraphQLNamedTypeKwargs, total=False):
     fields: GraphQLInputFieldMap
     out_type: Optional[GraphQLInputFieldOutType]
+    is_one_of: bool
 
 
 class GraphQLInputObjectType(GraphQLNamedType):
@@ -1402,6 +1403,7 @@ class GeoPoint(GraphQLInputObjectType):
 
     ast_node: Optional[InputObjectTypeDefinitionNode]
     extension_ast_nodes: Tuple[InputObjectTypeExtensionNode, ...]
+    is_one_of: bool
 
     def __init__(
         self,
@@ -1412,6 +1414,7 @@ def __init__(
         extensions: Optional[Dict[str, Any]] = None,
         ast_node: Optional[InputObjectTypeDefinitionNode] = None,
         extension_ast_nodes: Optional[Collection[InputObjectTypeExtensionNode]] = None,
+        is_one_of: bool = False,
     ) -> None:
         super().__init__(
             name=name,
@@ -1437,6 +1440,7 @@ def __init__(
         self._fields = fields
         if out_type is not None:
             self.out_type = out_type  # type: ignore
+        self.is_one_of = is_one_of
 
     @staticmethod
     def out_type(value: Dict[str, Any]) -> Any:
@@ -1456,6 +1460,7 @@ def to_kwargs(self) -> GraphQLInputObjectTypeKwargs:
                 if self.out_type is GraphQLInputObjectType.out_type
                 else self.out_type
             ),
+            is_one_of=self.is_one_of,
         )
 
     def __copy__(self) -> "GraphQLInputObjectType":  # pragma: no cover

src/graphql/type/directives.py

@@ -22,6 +22,7 @@
     "GraphQLSkipDirective",
     "GraphQLDeprecatedDirective",
     "GraphQLSpecifiedByDirective",
+    "GraphQLOneOfDirective",
     "DirectiveLocation",
     "DEFAULT_DEPRECATION_REASON",
 ]
@@ -237,12 +238,21 @@ def assert_directive(directive: Any) -> GraphQLDirective:
     description="Exposes a URL that specifies the behavior of this scalar.",
 )
 
+# Used to declare an Input Object as a OneOf Input Objects.
+GraphQLOneOfDirective = GraphQLDirective(
+    name="oneOf",
+    locations=[DirectiveLocation.INPUT_OBJECT],
+    args={},
+    description="Indicates an Input Object is a OneOf Input Object.",
+)
+
 
 specified_directives: Tuple[GraphQLDirective, ...] = (
     GraphQLIncludeDirective,
     GraphQLSkipDirective,
     GraphQLDeprecatedDirective,
     GraphQLSpecifiedByDirective,
+    GraphQLOneOfDirective,
 )
 """A tuple with all directives from the GraphQL specification"""
 

src/graphql/type/introspection.py

@@ -282,6 +282,7 @@ def args(directive, _info, includeDeprecated=False):
             resolve=TypeResolvers.input_fields,
         ),
         "ofType": GraphQLField(__Type, resolve=TypeResolvers.of_type),
+        "isOneOf": GraphQLField(GraphQLBoolean, resolve=TypeResolvers.is_one_of),
     },
 )
 
@@ -368,6 +369,10 @@ def input_fields(type_, _info, includeDeprecated=False):
     def of_type(type_, _info):
         return getattr(type_, "of_type", None)
 
+    @staticmethod
+    def is_one_of(type_, _info):
+        return type_.is_one_of if is_input_object_type(type_) else None
+
 
 __Field: GraphQLObjectType = GraphQLObjectType(
     name="__Field",

src/graphql/type/validate.py

@@ -12,7 +12,7 @@
 )
 
 from ..error import GraphQLError
-from ..pyutils import inspect
+from ..pyutils import Undefined, inspect
 from ..language import (
     DirectiveNode,
     InputValueDefinitionNode,
@@ -493,6 +493,28 @@ def validate_input_fields(self, input_obj: GraphQLInputObjectType) -> None:
                     ],
                 )
 
+            if input_obj.is_one_of:
+                self.validate_one_of_input_object_field(input_obj, field_name, field)
+
+    def validate_one_of_input_object_field(
+        self,
+        type_: GraphQLInputObjectType,
+        field_name: str,
+        field: GraphQLInputField,
+    ) -> None:
+        if is_non_null_type(field.type):
+            self.report_error(
+                f"OneOf input field {type_.name}.{field_name} must be nullable.",
+                field.ast_node and field.ast_node.type,
+            )
+
+        if field.default_value is not Undefined:
+            self.report_error(
+                f"OneOf input field {type_.name}.{field_name}"
+                " cannot have a default value.",
+                field.ast_node,
+            )
+
 
 def get_operation_type_node(
     schema: GraphQLSchema, operation: OperationType

src/graphql/utilities/coerce_input_value.py

@@ -127,6 +127,30 @@ def coerce_input_value(
                         + did_you_mean(suggestions)
                     ),
                 )
+
+        if type_.is_one_of:
+            keys = list(coerced_dict)
+            if len(keys) != 1:
+                on_error(
+                    path.as_list() if path else [],
+                    input_value,
+                    GraphQLError(
+                        "Exactly one key must be specified"
+                        f" for OneOf type '{type_.name}'.",
+                    ),
+                )
+            else:
+                key = keys[0]
+                value = coerced_dict[key]
+                if value is None:
+                    on_error(
+                        (path.as_list() if path else []) + [key],
+                        value,
+                        GraphQLError(
+                            f"Field '{key}' must be non-null.",
+                        ),
+                    )
+
         return type_.out_type(coerced_dict)
 
     if is_leaf_type(type_):

src/graphql/utilities/extend_schema.py

@@ -67,6 +67,7 @@
     GraphQLSchema,
     GraphQLSchemaKwargs,
     GraphQLSpecifiedByDirective,
+    GraphQLOneOfDirective,
     GraphQLType,
     GraphQLUnionType,
     assert_schema,
@@ -605,6 +606,7 @@ def build_input_object_type(
             fields=lambda: build_input_field_map(all_nodes),
             ast_node=ast_node,
             extension_ast_nodes=extension_nodes,
+            is_one_of=is_one_of(ast_node),
         )
 
     build_type_for_kind = cast(
@@ -698,3 +700,10 @@ def get_specified_by_url(
 
     specified_by_url = get_directive_values(GraphQLSpecifiedByDirective, node)
     return specified_by_url["url"] if specified_by_url else None
+
+
+def is_one_of(node: InputObjectTypeDefinitionNode) -> bool:
+    """Given an input object node, returns if the node should be OneOf."""
+    from ..execution import get_directive_values
+
+    return get_directive_values(GraphQLOneOfDirective, node) is not None