Refine toJSONSchema unrepresentables

[Mihailoff]

https://zod.dev/json-schema#unrepresentable

By default, Zod will throw an error if any of these are encountered.

You can change this behavior by setting the unrepresentable option to "any". This will convert any unrepresentable types to {} (the equivalent of unknown in JSON Schema).

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The chosen default to {} is overly conservative in my opinion. Some types can be represented as { type: "string", format: "date" } quite nicely.

JSON Schema supports the format property. It's used to provide semantic validation for strings and is defined in the JSON Schema specification.

The format property allows you to specify that a string should conform to a particular format. Common formats include:

• Date and time formats: date-time, date, time, duration
• Email formats: email, idn-email
• Hostnames: hostname, idn-hostname
• IP addresses: ipv4, ipv6
• URIs: uri, uri-reference, iri, iri-reference
• UUIDs: uuid
• Regular expressions: regex
• JSON pointers: json-pointer, relative-json-pointer

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This could be a way forward

z.toJSONSchema(z.bigint(), { format: [z.date, z.bigint] })

{
  "type": "string",
  "format": "bigint"
}

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But to be honest I'd even go with some sensible defaults:

• z.function is true unrepresentable
• z.date is better with format

[Mihailoff]

Some more examples:

// Standard JSON Schema formats
z.toJSONSchema(z.string().email())     // { "type": "string", "format": "email" }
z.toJSONSchema(z.string().url())       // { "type": "string", "format": "uri" }
z.toJSONSchema(z.string().uuid())      // { "type": "string", "format": "uuid" }
z.toJSONSchema(z.string().datetime())  // { "type": "string", "format": "date-time" }
z.toJSONSchema(z.string().ip())        // { "type": "string", "format": "ipv4" }

// Can use format for semantic meaning
z.toJSONSchema(z.date())              // { "type": "string", "format": "date" }
z.toJSONSchema(z.bigint())            // { "type": "string", "format": "bigint" }
z.toJSONSchema(z.int64())             // { "type": "integer", "format": "int64" }

[Mihailoff]

If you carefully read the documentation, there is an override option https://zod.dev/json-schema#override

// support z.date() as ISO datetime strings
const result = z.toJSONSchema(z.date(), {
  unrepresentable: "any",
  override: (ctx) => {
    const def = ctx.zodSchema._zod.def;
    if(def.type ==="date"){
      ctx.jsonSchema.type = "string";
      ctx.jsonSchema.format = "date-time";
    }
  },
});