Use proper type hints for serializers

Author: Cito

src/graphql/type/definition.py

@@ -293,10 +293,9 @@ def resolve_thunk(thunk: Any) -> Any:
     return thunk() if callable(thunk) else thunk
 
 
-# Unfortunately these types cannot be specified any better in Python:
-GraphQLScalarSerializer = Callable
-GraphQLScalarValueParser = Callable
-GraphQLScalarLiteralParser = Callable
+GraphQLScalarSerializer = Callable[[Any], Any]
+GraphQLScalarValueParser = Callable[[Any], Any]
+GraphQLScalarLiteralParser = Callable[[ValueNode, Optional[Dict[str, Any]]], Any]
 
 
 class GraphQLScalarType(GraphQLNamedType):

tests/execution/test_variables.py

@@ -2,7 +2,7 @@
 
 from graphql.execution import execute
 from graphql.execution.values import get_variable_values
-from graphql.language import parse, OperationDefinitionNode
+from graphql.language import parse, OperationDefinitionNode, StringValueNode, ValueNode
 from graphql.pyutils import Undefined
 from graphql.type import (
     GraphQLArgument,
@@ -26,10 +26,15 @@ def parse_serialized_value(value: str) -> str:
     return "DeserializedValue"
 
 
+def parse_literal_value(ast: ValueNode, _variables=None) -> str:
+    assert isinstance(ast, StringValueNode)
+    return parse_serialized_value(ast.value)
+
+
 TestComplexScalar = GraphQLScalarType(
     name="ComplexScalar",
-    parse_value=lambda value: parse_serialized_value(value),
-    parse_literal=lambda ast, _variables=None: parse_serialized_value(ast.value),
+    parse_value=parse_serialized_value,
+    parse_literal=parse_literal_value,
 )
 
 

tests/type/test_definition.py

@@ -22,6 +22,7 @@
     StringValueNode,
     TypeDefinitionNode,
     TypeExtensionNode,
+    ValueNode,
     UnionTypeDefinitionNode,
     UnionTypeExtensionNode,
 )
@@ -185,10 +186,11 @@ def rejects_a_scalar_type_defining_serialize_with_incorrect_type():
         )
 
     def rejects_a_scalar_type_defining_parse_literal_but_not_parse_value():
+        def parse_literal(_node: ValueNode, _vars=None):
+            return Undefined  # pragma: no cover
+
         with raises(TypeError) as exc_info:
-            GraphQLScalarType(
-                "SomeScalar", parse_literal=lambda: None  # pragma: no cover
-            )
+            GraphQLScalarType("SomeScalar", parse_literal=parse_literal)
         assert str(exc_info.value) == (
             "SomeScalar must provide both"
             " 'parse_value' and 'parse_literal' as functions."

tests/utilities/test_value_from_ast.py

@@ -1,6 +1,6 @@
 from math import isnan, nan
 
-from graphql.language import parse_value
+from graphql.language import parse_value, ValueNode
 from graphql.pyutils import Undefined
 from graphql.type import (
     GraphQLBoolean,
@@ -60,7 +60,7 @@ def pass_through_parse_literal(node, _vars=None):
 
         assert _value_from('"value"', pass_through_scalar) == "value"
 
-        def throw_parse_literal(_node, _vars=None):
+        def throw_parse_literal(_node: ValueNode, _vars=None):
             raise RuntimeError("Test")
 
         throw_scalar = GraphQLScalarType(
@@ -71,9 +71,12 @@ def throw_parse_literal(_node, _vars=None):
 
         assert _value_from("value", throw_scalar) is Undefined
 
+        def undefined_parse_literal(_node: ValueNode, _vars=None):
+            return Undefined
+
         return_undefined_scalar = GraphQLScalarType(
             "ReturnUndefinedScalar",
-            parse_literal=lambda _node, _vars=None: Undefined,
+            parse_literal=undefined_parse_literal,
             parse_value=lambda value: value,  # pragma: no cover
         )