fix: name fragment variables as such in execution errors

Replicates graphql/graphql-js@6ce253d

Author: Cito

src/graphql/execution/values.py

@@ -270,7 +270,8 @@ def coerce_argument(
             # before execution. This is a runtime check to ensure execution does
             # not continue with an invalid argument value.
             msg = (
-                f"Argument '{arg_name}' of required type '{arg_type}' was not provided."
+                f"{print_argument_or_fragment_variable(arg_def, arg_name, node)}"
+                f" of required type '{arg_type}' was not provided."
             )
             raise GraphQLError(msg, node)
         coerced_default_value = coerce_default_value(arg_def)
@@ -312,11 +313,10 @@ def coerce_argument(
         def on_argument_value_error(
             error: GraphQLError,
             path: list[str | int],
-            arg_name: str = arg_name,
         ) -> None:
             error.message = (
-                f"Argument '{arg_name}' has invalid value"
-                f"{print_path_list(path)}: {error.message}"
+                f"{print_argument_or_fragment_variable(arg_def, arg_name, node)}"
+                f" has invalid value{print_path_list(path)}: {error.message}"
             )
             raise error
 
@@ -334,6 +334,19 @@ def on_argument_value_error(
     coerced_values[out_name] = coerced_value
 
 
+# TODO: clean up the naming of is_required_argument() and arg_def
+# if/when experimental fragment variables are merged
+def print_argument_or_fragment_variable(
+    arg_def: GraphQLArgument | GraphQLVariableSignature,
+    arg_name: str,
+    node: FieldNode | DirectiveNode | FragmentSpreadNode,
+) -> str:
+    """Describe an argument or fragment variable for use in error messages."""
+    if isinstance(arg_def, GraphQLVariableSignature):
+        return f"Variable '${arg_def.name}' defined by fragment '{node.name.value}'"
+    return f"Argument '{arg_name}'"
+
+
 NodeWithDirective: TypeAlias = (
     EnumValueDefinitionNode
     | ExecutableDefinitionNode

tests/execution/test_variables.py

@@ -1189,10 +1189,15 @@ def when_a_value_is_required_and_not_provided():
                 }
                 """
             )
-            assert result.errors is not None
-            assert len(result.errors) == 1
-            assert result.errors[0].message.startswith(
-                "Argument 'value' of required type 'String!'"
+            assert result == (
+                None,
+                [
+                    {
+                        "message": "Variable '$value' defined by fragment 'a'"
+                        " of required type 'String!' was not provided.",
+                        "locations": [(3, 19)],
+                    }
+                ],
             )
 
         def when_the_definition_has_a_default_and_is_provided():
@@ -1257,11 +1262,16 @@ def when_the_definition_has_a_non_nullable_default_and_is_provided_null():
                 }
                 """
             )
-            assert result.errors is not None
-            assert len(result.errors) == 1
-            assert result.errors[0].message.startswith(
-                "Argument 'value' has invalid value:"
-                " Expected value of non-null type 'String!' not to be None."
+            assert result == (
+                None,
+                [
+                    {
+                        "message": "Variable '$value' defined by fragment 'a'"
+                        " has invalid value: Expected value of non-null type"
+                        " 'String!' not to be None.",
+                        "locations": [(3, 31)],
+                    }
+                ],
             )
 
         def when_the_definition_has_no_default_and_is_not_provided():