Conditional property is not allowed when using additionalProperties(false)

[JorisCodePeople]

Prerequisites

• [X] I have written a descriptive issue title
• [X] I have searched existing issues to ensure the bug has not already been reported

Fastify version

?

Plugin version

3.1.0

Node.js version

16.17.1

Operating system

Windows

Operating system version (i.e. 20.04, 11.3, 10)

10

Description

When I declare a conditional property on an object that has additionalProperties(false), that property is not allowed in a JSON file using the resulting schema.

Steps to Reproduce

Fluent schema:

const S = require('fluent-json-schema')

const testSchema = S.object()
  .additionalProperties(false)
  .prop('$schema', S.string().required())
  .prop('type', S.string().required())
  .allOf([S.ifThen(S.object().prop('type', S.const('type1')), S.object().prop('value', S.string().required()))])

resulting schema:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "additionalProperties": false,
  "allOf": [
    {
      "if": {
        "properties": {
          "type": {
            "const": "type1"
          }
        }
      },
      "then": {
        "properties": {
          "value": {
            "type": "string"
          }
        },
        "required": [
          "value"
        ]
      }
    }
  ],
  "properties": {
    "$schema": {
      "type": "string"
    },
    "type": {
      "type": "string"
    }
  },
  "required": [
    "$schema",
    "type"
  ]
}

JSON using the schema:

{
  "$schema": "../schemas/test.schema.json",
  "type": "type1",
  "value": "something"
}

Expected Behavior

When type === "type1", i'd expect value to be an allowed (even required) property. It is not. However, when starting to write the property name, it is suggested by VSCode as an attribute.