minProperties is not respected

[romansavchenko]

minProperties is usually used to not allow empty objects.
I'm seeing this behavior fail.

 'use strict'

const test = require('tap').test
const build = require('..')

test('minProperties', (t) => {
  t.plan(1)

  const stringify = build({
    title: 'object with missing values',
    type: 'object',
    minProperties: 1,
    properties: {
      shouldNotBeReturned: {
        type: 'object',
        properties: {
          str: {
            type: 'string'
          }
        }
      }
    }
  })

  t.equal('{}', stringify({ shouldNotBeReturned: {} }))
})

It returns { "shouldNotBeReturned": {} } instead of the expected {}
{ "shouldNotBeReturned": {} } is invalid per the schema

[mcollina]

I'm kind of lost on why you expect this type of output. Can you please articulate more?

[romansavchenko]

As far as I understand currently anything that fails json schema validation is not returned right?
Like if I had "additionalProperties"=false, anything not in the schema would not be returned.

const stringify = build({
    type: 'object',
    additionalProperties: false,
    properties: {
      a: {
        type: 'string'
      }
    }
  })

  t.equal('{}', stringify({ 'c': 'b' }))

or is additionalProperties a special case and other schema validations don't do this?
Did a quick test with enum and it looks like additionalProperties might indeed be a special case.

[mcollina]

Considering our code, I think the best approach would be to throw if minProperties is not respected. I don't think there is any other way that would be performant. Would you like to send a PR?

[romansavchenko]

I kind of feel like we should leave it as is, and say additionalProperties is a special case.

If we throw for minProperties we should probably throw for all schema failures like (enum, minLength, maxLength, etc.)
Throwing for everthing however, seems less useful since our goal is to stringily fast not necessarily validate the schema.

[mcollina]

would you like to send a PR to amend the docs mentioning additionalProperties is a special case?

[romansavchenko]

Sure.

I'm curious how throwing would impact the Fastify server. Would things not matching the schema just be unhandled errors?

[mcollina]

yes

[romansavchenko]

Updated docs #135