Resolvers: `default` option breaks codegen for big numbers

[matthew-salerno]

Description

First mention in #3132. Given the following valibot resolver:

{
  name: 'valibot',
  '~resolvers': {
    number(ctx) {
      const { $, plugin, symbols, schema } = ctx;
      const { v } = symbols;
      const big = plugin.symbolOnce('Big', {
        external: 'big.js',
        importKind: 'named',
      });
      return $(v).attr('instance').call(big);
    },
  },
},

There is no way to handle the behavior of default numbers, leading to improper codegen like this:

I am unsure if Zod has the same issue.

Reproducible example or configuration

https://stackblitz.com/edit/ttamttam-hey-api-default-resolvers

OpenAPI specification (optional)

No response

System information (optional)

No response

[bolt-new-by-stackblitz]

Start a new pull request in StackBlitz Codeflow.

• ttamttam-hey-api-default-resolvers (Open reproduction)

[dosubot]

Hi @matthew-salerno! I'm Dosu and I’m helping the openapi-ts team.

There’s no official documentation or examples for handling default values with custom number resolvers (like Big.js) in either the Valibot or Zod plugins for openapi-ts. Both plugins support number types in generated schemas, but they don’t address how the default option interacts with custom number parsing or resolvers, nor do they provide workarounds for this scenario. This likely means codegen applies the default value (e.g., 0) without transforming it to your custom type, resulting in type mismatches or improper code output.

If you need this behavior, you may need to experiment with alternative resolver patterns or review the codegen logic for extension points. Right now, this use case appears undocumented and unsupported in both Valibot and Zod plugins, so monitoring for future updates or community solutions is recommended.
Valibot plugin docs | Zod plugin docs

To reply, just mention @dosu.

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