Extract "identity_func" function to be used instead of lambda x: x

In theory should result in slightly smaller memory footprint and faster
execution. In practice, it simplifies testing of scalar's default behavior.

Replicates graphql/graphql-js@3d06795

Author: Cito

README.md

@@ -13,7 +13,7 @@ a query language for APIs created by Facebook.
 [![Code Style](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/ambv/black)
 
 The current version 1.0.5 of GraphQL-core-next is up-to-date with GraphQL.js version
-14.3.1. All parts of the API are covered by an extensive test suite of currently 1784
+14.3.1. All parts of the API are covered by an extensive test suite of currently 1786
 unit tests.
 
 

docs/modules/pyutils.rst

@@ -12,6 +12,7 @@ PyUtils
 .. autofunction:: did_you_mean
 .. autoclass:: EventEmitter
 .. autoclass:: EventEmitterAsyncIterator
+.. autofunction:: identity_func
 .. autofunction:: inspect
 .. autofunction:: is_finite
 .. autofunction:: is_integer

graphql/pyutils/__init__.py

@@ -13,6 +13,7 @@
 from .dedent import dedent
 from .did_you_mean import did_you_mean
 from .event_emitter import EventEmitter, EventEmitterAsyncIterator
+from .identity_func import identity_func
 from .inspect import inspect
 from .is_finite import is_finite
 from .is_integer import is_integer
@@ -32,6 +33,7 @@
     "did_you_mean",
     "EventEmitter",
     "EventEmitterAsyncIterator",
+    "identity_func",
     "inspect",
     "is_finite",
     "is_integer",

graphql/pyutils/identity_func.py

@@ -0,0 +1,13 @@
+from typing import cast, Any, TypeVar
+
+from ..error import INVALID
+
+__all__ = ["identity_func"]
+
+
+T = TypeVar("T")
+
+
+def identity_func(x: T = cast(Any, INVALID), *_args: Any) -> T:
+    """Return the first received argument."""
+    return x

graphql/type/definition.py

@@ -42,7 +42,7 @@
     UnionTypeExtensionNode,
     ValueNode,
 )
-from ..pyutils import AwaitableOrValue, cached_property, inspect
+from ..pyutils import AwaitableOrValue, cached_property, identity_func, inspect
 from ..utilities.value_from_ast_untyped import value_from_ast_untyped
 
 if TYPE_CHECKING:  # pragma: no cover
@@ -278,10 +278,6 @@ def resolve_thunk(thunk: Any) -> Any:
     return thunk() if callable(thunk) else thunk
 
 
-def default_value_parser(value: Any) -> Any:
-    return value
-
-
 # Unfortunately these types cannot be specified any better in Python:
 GraphQLScalarSerializer = Callable
 GraphQLScalarValueParser = Callable
@@ -357,7 +353,7 @@ def __init__(
                 f"{name} extension AST nodes must be ScalarTypeExtensionNode."
             )
         self.serialize = serialize  # type: ignore
-        self.parse_value = parse_value or default_value_parser
+        self.parse_value = parse_value or identity_func
         self.parse_literal = parse_literal or value_from_ast_untyped
 
     def __repr__(self):

graphql/utilities/build_ast_schema.py

@@ -24,7 +24,7 @@
     parse,
     Node,
 )
-from ..pyutils import inspect
+from ..pyutils import identity_func, inspect
 from ..type import (
     GraphQLArgument,
     GraphQLDeprecatedDirective,
@@ -385,7 +385,7 @@ def _make_scalar_def(ast_node: ScalarTypeDefinitionNode) -> GraphQLScalarType:
             name=ast_node.name.value,
             description=ast_node.description.value if ast_node.description else None,
             ast_node=ast_node,
-            serialize=lambda value: value,
+            serialize=identity_func,
         )
 
     def _make_input_object_def(

graphql/utilities/build_client_schema.py

@@ -3,7 +3,7 @@
 
 from ..error import INVALID
 from ..language import DirectiveLocation, parse_value
-from ..pyutils import inspect
+from ..pyutils import identity_func, inspect
 from ..type import (
     GraphQLArgument,
     GraphQLDirective,
@@ -126,7 +126,7 @@ def build_scalar_def(scalar_introspection: Dict) -> GraphQLScalarType:
         return GraphQLScalarType(
             name=scalar_introspection["name"],
             description=scalar_introspection.get("description"),
-            serialize=lambda value: value,
+            serialize=identity_func,
         )
 
     def build_object_def(object_introspection: Dict) -> GraphQLObjectType:

graphql/validation/rules/values_of_correct_type.py

@@ -125,11 +125,14 @@ def enter_enum_value(self, node: EnumValueNode, *_args):
         if not is_enum_type(type_):
             self.is_valid_scalar(node)
         elif node.value not in type_.values:
-            type_ = cast(GraphQLEnumType, type_)
             self.report_error(
                 GraphQLError(
                     bad_enum_value_message(
-                        type_.name, print_ast(node), enum_type_suggestion(type_, node)
+                        type_.name,
+                        print_ast(node),
+                        enum_type_suggestion(
+                            cast(GraphQLEnumType, type_), cast(EnumValueNode, node)
+                        ),
                     ),
                     node,
                 )
@@ -165,7 +168,9 @@ def is_valid_scalar(self, node: ValueNode) -> None:
                 bad_enum_value_message(
                     location_type,
                     print_ast(node),
-                    enum_type_suggestion(cast(GraphQLEnumType, type_), node),
+                    enum_type_suggestion(
+                        cast(GraphQLEnumType, type_), cast(EnumValueNode, node)
+                    ),
                 )
                 if is_enum_type(type_)
                 else bad_value_message(location_type, print_ast(node))
@@ -197,5 +202,4 @@ def is_valid_scalar(self, node: ValueNode) -> None:
 
 
 def enum_type_suggestion(type_: GraphQLEnumType, node: EnumValueNode) -> List[str]:
-    all_names = list(type_.values)
-    return suggestion_list(print_ast(node), all_names)
+    return suggestion_list(print_ast(node), list(type_.values))

tests/pyutils/test_identity_func.py

@@ -0,0 +1,18 @@
+from graphql.error import INVALID
+from graphql.pyutils import identity_func
+
+
+def describe_identity_func():
+    def returns_the_first_argument_it_receives():
+        assert identity_func() is INVALID
+        assert identity_func(INVALID) is INVALID
+        assert identity_func(None) is None
+        obj = object()
+        assert identity_func(obj) is obj
+
+        assert identity_func(INVALID, None) is INVALID
+        assert identity_func(None, INVALID) is None
+
+        assert identity_func(None, INVALID, obj) is None
+        assert identity_func(INVALID, None, obj) is INVALID
+        assert identity_func(obj, None, INVALID) is obj

tests/type/test_definition.py

@@ -3,6 +3,7 @@
 from pytest import mark, raises
 
 from graphql.error import INVALID
+from graphql.pyutils import identity_func
 from graphql.type import (
     GraphQLArgument,
     GraphQLEnumValue,
@@ -19,6 +20,7 @@
     GraphQLString,
     GraphQLUnionType,
 )
+from graphql.utilities import value_from_ast_untyped
 
 ScalarType = GraphQLScalarType("Scalar", serialize=lambda: None)
 ObjectType = GraphQLObjectType("Object", {})
@@ -45,6 +47,12 @@ def accepts_a_scalar_type_defining_parse_value_and_parse_literal():
             parse_literal=lambda: None,
         )
 
+    def provides_default_methods_if_omitted():
+        scalar = GraphQLScalarType("Foo", lambda: None)
+
+        assert scalar.parse_value is identity_func
+        assert scalar.parse_literal is value_from_ast_untyped
+
     def rejects_a_scalar_type_not_defining_serialize():
         with raises(
             TypeError, match="missing 1 required positional argument: 'serialize'"