Allow additionalItems keyword into schema

[rjlohan]

We originally converted items to disallow mixed tuple validation of lists, and rather expected an array to allow only a single consistent type.

However, we also omitted the additionalItems keyword which can be used in certain validation cases to allow an array to validate a single type with a fixed set of allowed values. An example of this is the AWS::CloudFront::Distribution.DistributionConfig.CacheBehavior.AllowedMethods field which uses a set of array values as a wonky enum validation.

SEE: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-cloudfront-distribution-cachebehavior.html#cfn-cloudfront-distribution-cachebehavior-allowedmethods

This needs to be put into the schema;

"additionalItems": { 
    "type": "boolean"
}

[rjlohan]

Also to demonstrate the schema I want (which is valid and functional JSON Schema) but I cannot have because of htis missing keyword;

{
  "AllowedMethods": {
    "oneOf": [
      {
        "additionalItems": false,
        "items": {
          "enum": [
            "GET",
            "HEAD"
          ],
          "type": "string"
        },
        "minItems": 2,
        "uniqueItems": true
      },
      {
        "additionalItems": false,
        "items": {
          "enum": [
            "GET",
            "HEAD",
            "OPTIONS"
          ],
          "type": "string"
        },
        "minItems": 3,
        "uniqueItems": true
      },
      {
        "additionalItems": false,
        "items": {
          "enum": [
            "GET",
            "HEAD",
            "PUT",
            "POST",
            "PATCH",
            "DELETE"
          ],
          "type": "string"
        },
        "minItems": 6,
        "uniqueItems": true
      }
    ],
    "type": "array"
  }
}

[aygold92]

I don't understand how this relates to additionalItems? additionalItems is false in each section above. Taking away the additionalItems=false, this schema accomplishes what you are trying to do and is valid in our current schema

[rjlohan]

The intent of this schema is to require that one of those 3 lists-of-strings is specified. There are no alternatives allowed.

Valid inputs against this schema are one of these (with items in any order); "AllowedMethods": [ "GET", "HEAD" ] "AllowedMethods": [ "GET", "HEAD", "OPTIONS" ] "AllowedMethods": [ "GET", "HEAD", "PUT", "POST", "PATCH", "DELETE" ]

With "additionalItems": true (or absent) the following invalid items become allowed;

"AllowedMethods": [ "GET", "GET", "GET", "GET" ] "AllowedMethods": [ "HEAD", "GET", "GET", "HEAD" ]

[aygold92]

That's not what I gathered from the docs https://json-schema.org/understanding-json-schema/reference/array.html#list-validation

In each oneOf block, you use items as a single schema, and there are multiple notes about this

Note

When items is a single schema, the additionalItems keyword is meaningless, and it should not be used.

Note

additionalItems doesn’t make sense if you’re doing “list validation” (items is an object), and is ignored in the case.

By your schema above, removing additionalItems: false. "AllowedMethods": [ "GET", "GET", "GET", "GET" ] fails each schema because of the "uniqueItems: true" constraint

[rjlohan]

The various tools I've used to validate are not compliant with the docs here, perhaps because of the oneOf block around the different items schemas. uniqueItems is also not validating correctly the way I want, though the additionalItems statement does work.

Besides the point of 'this should be irrelevant' is there any reason to block this schema enhancement if it seems supported by tools?

[rjlohan]

Closing this, as the suggestion from @aygold92 about uniqueItems did actually work when I fiddled a bit.