Question: how to implement a basic object schema? about fluent-json-schema

[aboutlo]

Still, a bug in fluent because of the spec

given

const schema = S.object().additionalProperties(true).title('title string coerce')

expect:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "additionalProperties": true,
  "title": "title string coerce"
}

rather than:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "additionalProperties": {},
  "title": "title string coerce"
}

However, additionalProperties: {} is valid it means don't strip
I found somewhere else where they are discussing the same topic: OAI/OpenAPI-Specification#668 (comment)

[jsumners]

Thank you.

[aboutlo]

I don't know how it works fastJson in details but I have the feeling the issue could be there

to me

{
    title: 'check string coerce',
    type: 'object',
    properties: {},
    additionalProperties: true
  }

become

const schema = S.object().additionalProperties(true).title('title string coerce')
console.log(JSON.stringify(schema.valueOf(),undefined,2))

which will generate

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "additionalProperties": {},
  "title": "title string coerce"
}

I wonder about additionalProperties: true it isn't required to be set as true because by default a schema accepts an object with extra props. additionalProperties: true will be translated as additionalProperties: {}

So either you set to false or you pass a schema to specify which kind of extra props you want.

[jsumners]

Without additionalProperties:true fast-json-stringify will strip properties that are not explicitly stated in the schema.

[aboutlo]

So looking to the reference:
https://json-schema.org/latest/json-schema-validation.html#rfc.section.6.5.6

The value of "additionalProperties" MUST be a valid JSON Schema.

So the bug is here: https://github.com/fastify/fluent-schema/blob/73adbf43075104d5ac05a874313fd7dbbda72474/src/ObjectSchema.js#L52-L52

we should need something like this:

additionalProperties: value => {
      if (typeof value !== 'boolean' && !isFluentSchema(value))
        throw new Error("'additionalProperties' must be a boolean or a FluentSchema object")
      const attribute =
        typeof value === 'boolean'
          ? value.valueOf()
          : omit(value.valueOf(), ['$schema'])
      return setAttribute({ schema, ...options }, [
        'additionalProperties',
        attribute,
        'array',
      ])
    }

[jsumners]

FYI: re-reading this issue this morning I noticed that I left out a "not" in my last reply. Please re-read it to make sure it still makes sense.

[aboutlo]

PR merged