Regression "oneOf with Date results to null"

[mashpie]

💥 Regression Report

#325 "oneOf with Date results to null" seams to persist in 2.7.2 and up

Last working version

Worked up to version: 2.7.1

Stopped working in version: 2.7.2

To Reproduce

Steps to reproduce the behavior:

'use strict'

const fastJson = require('fast-json-stringify')
const S = require('fluent-json-schema')

/**
 * @todo works up to fast-json-stringify@2.7.1
 * but broken in fast-json-stringify@2.7.2
 */ 
const isoDateOrEmptyString = S.anyOf([
  S.string().format('date'),
  S.string().maxLength(0).default('')
])

const exampleSchema = S.object()
  .additionalProperties(false)
  .id('exampleSchema')
  .prop('dateIso', isoDateOrEmptyString)
  .prop('dateEmpty', isoDateOrEmptyString)
  .prop('dateNull', isoDateOrEmptyString)
  .valueOf()

const stringify = fastJson(exampleSchema)

console.log(stringify({
  dateIso: '2020-01-01',
  dateEmpty: '',
  dateNull: null,
}))

/**
 * expected
 * @example {"dateIso":"2020-01-01","dateEmpty":"","dateNull":null}
 */

/**
 * reported
 * @example {"dateIso":null,"dateEmpty":"","dateNull":null}
 */

Expected behavior

the snippet should report:

{"dateIso":"2020-01-01","dateEmpty":"","dateNull":null}

Your Environment

• node version: 14
• fastify version: 3.15.1 but reproducable without any fastify
• os: Mac, Linux

Background

I encountered that regression today while upgrading a bunch of services deployed as fastify (v3.7.x - v3.15.1) apps. The JSON returned null for all valid iso formatted dates we had while still handling empty strings correctly. Fortunately we were able to monkey patch dependencies by:

  "resolutions": {
    "fast-json-stringify": "2.7.1"
  }

The same behavior is reproducible without fastify and just plain json-schema. Accordingly, the snippet above fails with a package.json like so:

{
  "name": "tmp-fast-json-stringify",
  "version": "0.0.0",
  "main": "index.js",
  "license": "MIT",
  "dependencies": {
    "fast-json-stringify": "^2.7.3",
    "fluent-json-schema": "^3.0.0"
  }
}

but works with

{
  "name": "tmp-fast-json-stringify",
  "version": "0.0.0",
  "main": "index.js",
  "license": "MIT",
  "dependencies": {
    "fast-json-stringify": "2.7.1",
    "fluent-json-schema": "^3.0.0"
  }
}

Hope this helps to track down that issue :)

[zekth]

Thanks for reporting it. The test assertions were only on date-time not date. I'll take a look