ast_from_value: reject non-finite numbers

Replicates graphql/graphql-js@4288c19

Author: Cito

src/graphql/utilities/ast_from_value.py

@@ -1,3 +1,4 @@
+from math import isfinite
 import re
 from typing import Any, Iterable, Mapping, Optional, cast
 
@@ -113,7 +114,7 @@ def ast_from_value(value: Any, type_: GraphQLInputType) -> Optional[ValueNode]:
         # Python ints and floats correspond nicely to Int and Float values.
         if isinstance(serialized, int):
             return IntValueNode(value=f"{serialized:d}")
-        if isinstance(serialized, float):
+        if isinstance(serialized, float) and isfinite(serialized):
             return FloatValueNode(value=f"{serialized:g}")
 
         if isinstance(serialized, str):

tests/utilities/test_ast_from_value.py

@@ -1,4 +1,4 @@
-from math import nan
+from math import inf, nan
 
 from pytest import raises  # type: ignore
 
@@ -134,6 +134,11 @@ def converts_using_serialize_from_a_custom_scalar_type():
             value="value"
         )
 
+        assert ast_from_value(nan, pass_through_scalar) is None
+        with raises(TypeError) as exc_info:
+            ast_from_value(inf, pass_through_scalar)
+        assert str(exc_info.value) == "Cannot convert value to AST: inf."
+
         return_null_scalar = GraphQLScalarType(
             "ReturnNullScalar", serialize=lambda value: None,
         )