Can default values form cycles?

从 graphql/utilities/build_ast_schema.py 以及经过 graphql/utilities/value_from_ast.py、graphql/type/definition.py 和 graphql/type/schema.py 的 traceback 路径开始。使用报告中所述的 Python 和 graphql-core 版本重现递归的 InputA/InputB schema，然后将其行为与 GraphQL 规范进行比较。完成标准是：根据规范对 issue 进行分类，并使递归默认值获得经过明确设计和测试的结果，而不是无界的 RecursionError。

Hi, I’ve been working with input fields' default values, and I encountered this question - can default values form cycles? I looked into the spec but I haven’t found answer. I tried to create a schema with such values:


from graphql import build_schema

schema_str = """
schema { query: Query }
type Query { _skip: String! }

input InputA {
  id: ID!
  fieldB: InputB = {id: "1"}
}

input InputB {
  id: ID!
  fieldA: InputA = {id: "1"}
}
"""
build_schema(schema_str)

I used graphql-core==3.2.3 and python-3.11.1, as a result, I got this exception:

Traceback (most recent call last):
  File ".../lib/python3.11/site-packages/graphql/type/definition.py", line 1456, in fields
    fields = resolve_thunk(self._fields)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/type/definition.py", line 300, in resolve_thunk
    return thunk() if callable(thunk) else thunk
           ^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/utilities/extend_schema.py", line 605, in <lambda>
    fields=lambda: build_input_field_map(all_nodes),
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
RecursionError: maximum recursion depth exceeded

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File ".../lib/python3.11/site-packages/graphql/type/definition.py", line 1456, in fields
    fields = resolve_thunk(self._fields)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/type/definition.py", line 300, in resolve_thunk
    return thunk() if callable(thunk) else thunk
           ^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/utilities/extend_schema.py", line 605, in <lambda>
    fields=lambda: build_input_field_map(all_nodes),
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/utilities/extend_schema.py", line 471, in build_input_field_map
    default_value=value_from_ast(field.default_value, type_),
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/utilities/value_from_ast.py", line 107, in value_from_ast
    fields = type_.fields
             ^^^^^^^^^^^^
  File "".../lib/python3.11/functools.py", line 1001, in __get__
    val = self.func(instance)
          ^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/type/definition.py", line 1459, in fields
    raise cls(f"{self.name} fields cannot be resolved. {error}") from error
TypeError: InputB fields cannot be resolved. maximum recursion depth exceeded

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File ".../lib/python3.11/site-packages/graphql/type/definition.py", line 1456, in fields
    fields = resolve_thunk(self._fields)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/type/definition.py", line 300, in resolve_thunk
    return thunk() if callable(thunk) else thunk
           ^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/utilities/extend_schema.py", line 605, in <lambda>
    fields=lambda: build_input_field_map(all_nodes),
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/utilities/extend_schema.py", line 471, in build_input_field_map
    default_value=value_from_ast(field.default_value, type_),
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/utilities/value_from_ast.py", line 107, in value_from_ast
    fields = type_.fields
             ^^^^^^^^^^^^
  File "".../lib/python3.11/functools.py", line 1001, in __get__
    val = self.func(instance)
          ^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/type/definition.py", line 1459, in fields
    raise cls(f"{self.name} fields cannot be resolved. {error}") from error
TypeError: InputA fields cannot be resolved. InputB fields cannot be resolved. maximum recursion depth exceeded

The above exception was the direct cause of the following exception:

...
# 4k lines of the same error, each with extra `InputB fields cannot be resolved.`
...

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "scheam_test.py", line 17, in <module>
    build_schema(schema_str)
  File ".../lib/python3.11/site-packages/graphql/utilities/build_ast_schema.py", line 95, in build_schema
    return build_ast_schema(
           ^^^^^^^^^^^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/utilities/build_ast_schema.py", line 84, in build_ast_schema
    return GraphQLSchema(**schema_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/type/schema.py", line 218, in __init__
    collect_referenced_types(type_)
  File ".../lib/python3.11/site-packages/graphql/type/schema.py", line 438, in collect_referenced_types
    for field in named_type.fields.values():
                 ^^^^^^^^^^^^^^^^^
  File "".../lib/python3.11/functools.py", line 1001, in __get__
    val = self.func(instance)
          ^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.11/site-packages/graphql/type/definition.py", line 1459, in fields
    raise cls(f"{self.name} fields cannot be resolved. {error}") from error
TypeError: InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. InputA fields cannot be resolved. InputB fields cannot be resolved. maximum recursion depth exceeded

I wonder if this is not allowed but not mentioned in the specification or is it a bug in graphql-core?