Idea: `.meta(...)` method on ZodType

[mmkal]

I've considered asking this for a bit, for the sake of trpc-cli. That takes advantage of .describe('...') to allow adding CLI docs for zod input parameters, but it would be nice to add richer metadata.

How I think it could work:

1. Define a new ZodMeta interface (maybe make it generic with the same typeargs as ZodType)
2. Only add a description property to it
3. Add a metadata: ZodMeta prop to ZodType
4. Have .describe('foo') update the metadata to { description: 'foo' } (maybe shallow-merging the old value?)
5. Update the description property of ZodType to get description() { return this.metadata.description } for backwards-compatibility

The fun part would be: end users could then use module augmentation to add to ZodMeta however they like, e.g. I in trpc-cli could do:

import {z} from 'zod'

declare module 'zod' {
  export interface ZodMeta {
    alias: string
  }
}

const router = t.router({
  test: t.input(
    z.object({
      glob: z.string().meta({
        description: 'Glob pattern for test files',
        alias: 'g',
      })
    })
  ).mutation(...)
)

Looking at the issues, I think this would cover a few requests zod has got:

https://github.com/colinhacks/zod/issues/3734 https://github.com/colinhacks/zod/issues/3732 https://github.com/colinhacks/zod/issues/3736 (maybe) https://github.com/colinhacks/zod/issues/3673 https://github.com/colinhacks/zod/issues/1439

Possible more but I didn't go that far back in the issues. In general, with trpc and OpenAI adopting zod, there will be more cases where people use zod as a user-facing part of their libraries and applications, so there might be more and more requests for the ability to attach metadat to types

Alternatively, these fields could somehow be dumped onto ZodDef, which is where description lives now but that doesn't feel quite right to me.

[klh]

i like the idea of removing all the non entity related stuff to a meta field, it would make it more consistent across types