Can default values form cycles? about graphql-core HOT 2 OPEN

@Cito Thanks for your reply! I created an issue and used your examples, but please add more context if you think that something is missing

from graphql-core.

Thanks for the feedback @mat-sop.

Let's first simplify the problematic SDL a bit to get to the core of it:

"""Example 1"""
type Query { field(recursiveInput: RecursiveInput): String }

input RecursiveInput {
  self: RecursiveInput = {value: "foo"}
  value: String 
}

The spec actually says something about such recursions here. Though it does not explicitly mention your example, the spirit of the spec is that recursive definitions are in principle allowed, but only if it is possible to construct valid values from them. This can be possible by breaking the chain with a null value if the definition allows that.

The problem I see in this example is the default value of {value: "foo"}. Since this is lacking the self field, the default value for self is looked up, which leads to a recursion. If you leave out the default value or change it to be = null, everything is fine:

"""Example 2"""
type Query { field(recursiveInput: RecursiveInput): String }

input RecursiveInput {
  self: RecursiveInput
  value: String 
}

However, the following also looks fine to me but still breaks:

"""Example 3"""
type Query { field(recursiveInput: RecursiveInput): String }

input RecursiveInput {
  self: RecursiveInput = {value: "foo", self: null}
  value: String 
}

On the other hand, the following actually invalid example does not give an error:

"""Example 4"""
type Query { field(recursiveInput: RecursiveInput): String }

input RecursiveInput {
  self: RecursiveInput!
  value: String 
}

I found that the same problems exists in graphql-js. which also throws a "Maximum call stack size exceeded" error in the cases where Python raises a RecursionError. Since the goal of graphql-core is to replicate graphql-js, I do not consider it a bug in graphql-core, but something that might need to be fixed in grapqhl-js.

I currently see three things that could be improved here:

• Example 1 should produce a proper error instead of creating a stack overflow
• Example 3 should not produce an error
• Example 4 should produce an error showing that this is an invalid definition

But this should be discussed in the issue tracker of GraphQL.js.

I would be glad if you could create an issue there. Otherwise I will do it when I find some more time.

from graphql-core.