Serialize with maximum precision when converting float to FloatValue (#…

…164)

We make use of the float representation algorithm provided by the
Python str method, which guarantees maximum precision while keeping
the representation as short as possible, additionally removing the
superfluous `.0` suffix for integers (same as in GraphQL.js).

src/graphql/utilities/ast_from_value.py

@@ -115,9 +115,12 @@ 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}")
+            return IntValueNode(value=str(serialized))
         if isinstance(serialized, float) and isfinite(serialized):
-            return FloatValueNode(value=f"{serialized:g}")
+            value = str(serialized)
+            if value.endswith('.0'):
+                value = value[:-2]
+            return FloatValueNode(value=value)
 
         if isinstance(serialized, str):
             # Enum types use Enum literals.

tests/utilities/test_ast_from_value.py

@@ -86,6 +86,12 @@ def converts_float_values_to_float_asts():
 
         assert ast_from_value(1e40, GraphQLFloat) == FloatValueNode(value="1e+40")
 
+        assert ast_from_value(123456789.01234567, GraphQLFloat) == FloatValueNode(
+            value="123456789.01234567"
+        )
+
+        assert ast_from_value(1.1, GraphQLFloat) == FloatValueNode(value="1.1")
+
     def converts_string_values_to_string_asts():
         assert ast_from_value("hello", GraphQLString) == StringValueNode(value="hello")