Memoize coerced default values on the input value

src/graphql/type/definition.py

@@ -1254,16 +1254,16 @@ class GraphQLDefaultInput:  # noqa: PLW1641
     literal: ConstValueNode | None
     """GraphQL literal default value, or None if a runtime value is provided instead."""
 
-    __slots__ = "_memoized_coercion", "literal", "value"
+    __slots__ = "_memoized_coerced_value", "literal", "value"
 
     def __init__(
         self, value: Any = Undefined, literal: ConstValueNode | None = None
     ) -> None:
         self.value = value
         self.literal = literal
-        # Used to memoize the result of coercing the default value, together with
-        # the type it was coerced to (see coerce_default_value() in the utilities).
-        self._memoized_coercion: tuple[GraphQLInputType | None, Any] = None, Undefined
+        # Used to memoize the result of coercing the default value of a variable
+        # signature (see coerce_default_value() in the utilities).
+        self._memoized_coerced_value: Any = Undefined
 
     def __eq__(self, other: object) -> bool:
         return self is other or (
@@ -1352,6 +1352,10 @@ class GraphQLArgument:  # noqa: PLW1641
     ast_node: InputValueDefinitionNode | None
     """AST node from which this schema element was built, if available."""
 
+    # Used to memoize the result of coercing the default value
+    # (see coerce_default_value() in the utilities).
+    _memoized_coerced_value: Any = Undefined
+
     def __init__(
         self,
         type_: GraphQLInputType,
@@ -3326,6 +3330,10 @@ class GraphQLInputField:  # noqa: PLW1641
     ast_node: InputValueDefinitionNode | None
     """AST node from which this schema element was built, if available."""
 
+    # Used to memoize the result of coercing the default value
+    # (see coerce_default_value() in the utilities).
+    _memoized_coerced_value: Any = Undefined
+
     def __init__(
         self,
         type_: GraphQLInputType,

src/graphql/utilities/coerce_input_value.py

@@ -18,6 +18,8 @@
     is_iterable,
 )
 from ..type import (
+    GraphQLArgument,
+    GraphQLInputField,
     GraphQLInputType,
     assert_leaf_type,
     is_input_object_type,
@@ -31,7 +33,7 @@
     from ..execution.get_variable_signature import GraphQLVariableSignature
     from ..execution.values import FragmentVariableValues, VariableValues
     from ..language import ConstValueNode
-    from ..type import GraphQLArgument, GraphQLInputField
+    from ..type import GraphQLDefaultInput
 
 __all__ = ["coerce_default_value", "coerce_input_literal", "coerce_input_value"]
 
@@ -351,16 +353,20 @@ def coerce_default_value(
 
     :meta private:
     """
-    # The external default value is coerced; the result is memoized in a hidden
-    # field on the GraphQLDefaultInput object. (Contrary to GraphQL.js, which
-    # memoizes on the input value itself, this also works for the immutable
-    # variable signatures that reuse this function for fragment arguments.)
-    # It is only reused for the same type, as a default can be used with
-    # different types, e.g. after extend_schema() replaced the type.
+    # The external default value is coerced; like in GraphQL.js, the result is
+    # memoized in a hidden field on the input value itself, since the same default
+    # can be used with different types, e.g. after extend_schema() replaced the
+    # type. The immutable variable signatures that reuse this function for fragment
+    # arguments memoize it on their default instead, which is not shared.
     default_input = input_value.default
     if default_input is not None:
-        coerced_type, coerced_value = default_input._memoized_coercion  # noqa: SLF001
-        if coerced_type is not input_value.type:
+        memo: GraphQLArgument | GraphQLInputField | GraphQLDefaultInput = (
+            input_value
+            if isinstance(input_value, (GraphQLArgument, GraphQLInputField))
+            else default_input
+        )
+        coerced_value = memo._memoized_coerced_value  # noqa: SLF001
+        if coerced_value is Undefined:
             coerced_value = (
                 coerce_input_literal(default_input.literal, input_value.type)
                 if default_input.literal is not None
@@ -377,7 +383,7 @@ def coerce_default_value(
                     f" to be valid, found: {found}."
                 )
                 raise TypeError(msg)
-            default_input._memoized_coercion = input_value.type, coerced_value  # noqa: SLF001
+            memo._memoized_coerced_value = coerced_value  # noqa: SLF001
         return coerced_value
 
     # The deprecated internal default value is used as is.

tests/utilities/test_coerce_input_value.py

@@ -717,7 +717,7 @@ def coerce_input_value(value):
         assert coerce_default_value(input_value) == "hello"
         assert coerce_input_value_calls == ["hello"]
 
-    def memoizes_coercion_per_type():
+    def coerces_shared_default_per_type():
         color_enum = GraphQLEnumType("Color", {"RED": 0, "BLUE": 1})
         shared_default = GraphQLDefaultInput("RED")
 
@@ -727,3 +727,30 @@ def memoizes_coercion_per_type():
         assert coerce_default_value(color_value) == 0
         assert coerce_default_value(string_value) == "RED"
         assert coerce_default_value(color_value) == 0
+
+    def memoizes_coercion_of_shared_default_per_input_value():
+        coerce_input_value_calls: list[Any] = []
+
+        def coerce_input_value(value):
+            coerce_input_value_calls.append(value)
+            return value
+
+        spy_scalar = GraphQLScalarType(
+            "SpyScalar", coerce_input_value=coerce_input_value
+        )
+        other_spy_scalar = GraphQLScalarType(
+            "SpyScalar", coerce_input_value=coerce_input_value
+        )
+
+        shared_default = GraphQLDefaultInput(literal=StringValueNode(value="hello"))
+
+        input_value = GraphQLInputField(spy_scalar, default=shared_default)
+        other_input_value = GraphQLInputField(other_spy_scalar, default=shared_default)
+
+        assert coerce_default_value(input_value) == "hello"
+        assert coerce_default_value(other_input_value) == "hello"
+
+        # Call a second time
+        assert coerce_default_value(input_value) == "hello"
+        assert coerce_default_value(other_input_value) == "hello"
+        assert coerce_input_value_calls == ["hello", "hello"]