Faker Plugin: Fixing Max Call Stack With Self-Referencing Types

by Dimemap Team 64 views

Hey guys! Today, we're diving deep into a quirky issue with the kubb framework and its plugin-faker. Specifically, we're tackling the dreaded "Max call stack size exceeded" error that pops up when using self-referencing types. So, buckle up, and let's get started!

The Problem: Infinite Loops with Self-Referencing Types

When working with self-referencing types, the plugin-faker in kubb can sometimes go into overdrive, leading to an infinite loop. Imagine a scenario where you have a Node type that can contain children of the same Node type. The generated mock output might look something like this:

export function createNode(data?: Partial<Node>): Node {
  return {
    ...{ id: faker.string.alpha(), children: faker.helpers.multiple(() => createNode()) },
    ...data || {}
  }
}

See the problem? The createNode function is calling itself recursively via the children property, without any condition to stop it. This will inevitably lead to the "Max call stack size exceeded" error, crashing your application. This issue occurs every single time you generate mocks for such self-referencing types.

Why does this happen? Well, the faker.helpers.multiple(() => createNode()) part is the culprit. It keeps generating new nodes indefinitely, creating an infinite tree structure. This is a common pitfall when dealing with recursive data structures, and it's crucial to handle it correctly in your mock generation logic.

To illustrate further, consider a family tree. Each person can have parents, who in turn can have parents, and so on. If the mock generator doesn't have a stopping condition, it will keep creating ancestors infinitely, eventually exhausting the call stack. This is precisely what happens with the Node type and its children property.

The core challenge here is to find a way to break this infinite recursion. We need to introduce a mechanism that either limits the depth of the generated tree or provides a way to override the recursive behavior when necessary. Without such a mechanism, the plugin-faker becomes unusable for self-referencing types, which are quite common in many real-world applications.

Proposed Solutions

Okay, so how do we fix this? I've got a couple of ideas that might just do the trick. Let's explore them and see what you guys think.

Solution 1: Exclude Optional Fields

One potential solution involves adding a flag or variable that allows you to exclude optional fields during mock generation. Many self-referencing types have optional properties that trigger the infinite loop. By skipping these optional fields, we can prevent the recursion from happening in the first place.

Here's how it might look in code:

export function createNode(data?: Partial<Node>, options?: { excludeOptional: boolean }): Node {
  return {
    ...excludeOptional ? { id: faker.string.alpha() } : { id: faker.string.alpha(), children: faker.helpers.multiple(() => createNode()) },
    ...data || {}
  }
}

In this example, if excludeOptional is set to true, the children property (which is often optional in self-referencing types) will not be generated. This effectively breaks the recursion and prevents the "Max call stack size exceeded" error.

This approach has the added benefit of reducing the complexity of the generated mocks. Often, you don't need all the optional fields to be populated, especially when dealing with complex data structures. Excluding them can make the mocks easier to work with and understand.

However, there are also potential drawbacks to this approach. In some cases, the optional fields might be essential for testing or development. Excluding them might lead to incomplete or inaccurate mocks. Therefore, it's important to provide a way to selectively exclude optional fields, rather than applying this rule globally.

Solution 2: Prioritize Passed Data

Another approach is to prioritize the data object passed to the createNode function. Instead of blindly generating all fields, the function should first check if a value for a particular field is already provided in the data object. If so, it should use that value instead of generating a new one.

This can be particularly useful for overriding fields that cause infinite loops. For example, if you know that the children property is causing the issue, you can simply pass an empty array in the data object:

createNode({ children: [] })

This will prevent the plugin-faker from generating new children recursively, effectively breaking the infinite loop. Here's how the code might look:

export function createNode(data?: Partial<Node>): Node {
  const baseNode = { id: faker.string.alpha() };
  const children = data?.children || faker.helpers.multiple(() => createNode());

  return {
    ...baseNode,
    children,
    ...data || {},
  };
}

This way, even if there's a field that could cause an infinite loop, we can override it to prevent this. This approach provides more flexibility and control over the mock generation process.

The advantage of this solution is that it allows you to selectively override specific fields, while still benefiting from the automatic generation of other fields. This can be particularly useful when you need to create mocks with specific characteristics or constraints.

However, this approach also requires more manual intervention. You need to identify the fields that are causing the infinite loops and explicitly override them. This can be time-consuming and error-prone, especially when dealing with complex data structures.

Additional Information and Context

For those curious about the specifics, this issue was reported while running kubb version 4.1.2 on MacOS. The kubb.config.ts file uses the plugin-faker, and the Swagger/OpenAPI file contains self-referencing types. The issue occurs every time the mock generator is run for these types.

The versions of external packages like @tanstack-query, MSW, React, and Vue are not directly relevant to this issue, as it is primarily related to the mock generation logic within the plugin-faker.

Conclusion

So, there you have it, guys! The "Max call stack size exceeded" error with self-referencing types in kubb's plugin-faker can be a real headache. But with a few clever solutions, like excluding optional fields or prioritizing passed data, we can tame those infinite loops and generate mocks without crashing. What do you think about these solutions? Any better ideas? Let's keep the discussion going!