Use json-pointer instead of dot-joined paths for the field property of errors

[mike-marcacci]

Right now the an error message looks something like this:

[
    { field: 'data.y', message: 'is required'},
    { field: 'data.x', message: 'is the wrong type'}
]

This makes it easy to work with until one of the field names contains a period. Using json-pointer would solve this. It's extremely fast to build and parse, is a well known standard, and is already part of json-schema.

// the object
{
    'domains': {
        'www.google.com': {
            'company_name': 22
        }
    }
}

// the error
[
    { field: 'domains.www.google.com.company_name', message: 'is the wrong type'}
]


// using json-pointer
[
    { field: '/domains/www.google.com/company_name', message: 'is the wrong type'}
]

[watson]

A forward slash is also a valid key in JSON unfortunately - in fact any valid string can be used as a key. So for this to work simply switching the delimiter will not do the trick :(

I haven't really thought through the implications of fixing this issue - so I'm purely speaking from a technical perspective here - but I think apart from moving to a nested structure in the error messages as well, we'd have to resort to escaping to non-delimiters... at least that's the only thing I can think of right now.

[mike-marcacci]

Ah yes, the json-pointer spec already handles escaping by using ~1 to replace a slash, and ~0 to replace a tilda. This makes for really performant single-pass encoding/decoding.

Honestly, I suggest using this mostly because it is a well accepted standard; IMHO the best way to specify a path is an array of segments, which is more useful and used language constructs instead of convention to ensure fidelity.

[LinusU]

I would love to have this implemented, since currently a root-object called data is appended to the fields. This means that your first error in the second example actually is this:

[
    { field: 'data.domains.www.google.com.company_name', message: 'is the wrong type'}
]

Notice the data. part. This confused me big time as documented in #109.

I think that it would be immensely useful for it to print / for the root instead of data..

@mafintosh If you give the go-ahead, I would be happy to implement this for you :)