fix: handle custom formats with null values

[bahmutov]

If a custom formatted value (string) has null value and the type allows it, the validation should not fail.

Example that is failing on master and this PR is fixing

{
    type: 'object',
    properties: {
      foo: {
        type: ['string', 'null'],
        format: 'as'
      }
    }
  }, {formats: {as:/^a+$/}
// object
{foo: null}

Seems this was due to fmts vs formats usage

[LinusU]

fmts[node.format] will always be truthy since it's checked in the outer if

[bahmutov]

that's good observation, but does not affect the fix. the only difference between formats and fmts is that fmts has user supplied custom formats and built-ins.

[LinusU]

I meant that you can remove that part alltogether, since it will always be true:

if (type !== 'string') validate('if (%s) {', types.string(name))

[LinusU]

Hmm, I remember having a discussion about this at my former place of work 🤔

I think that in the end, we worked around this ourself, potentially because we thought that the current behaviour was the corect one 🤔

I guess that after this change the following will pass:

// schema
{
  type: 'object',
  properties: {
    test: { format: /^a+$/ }
  }
}

// input
{ test: 123 }

whereas before it would be invalid?

This should probably be a breaking change...

@johansteffner any comments?

[bahmutov]

I just added an assertion to make sure non-string values do not pass

t.notOk(validate({foo:123}), 'not as if number')

but your concern is the "missing string" type, which I think the format is not solving (in any way)

[LinusU]

but your concern is the "missing string" type, which I think the format is not solving (in any way)

Before this patch, only passing a format without a type would still run the format on the value coerced into a string. Thus my example would not pass before, but after this patch, it would let it through.

If that is correct this needs to be a breaking change.

[johansteffner]

@LinusU the solution we ran with was checking that typeof input === 'string' before running the format validator, returning true if the value is not a string.