Generate a JSON schema for me

[bowlofeggs]

Greetings!

I've been working on writing JSON schemas for Bodhi's messages the past few days. It's pretty rad, but I had the thought that it might be a nice convenience if fedora-messaging had the ability to generate these for me based on Python classes. I don't know exactly how I would recommend making it work, but I think it could be cool if we require Python 3 for this feature so we can use some cool Python 3 things to help out:

0. Type annotations! This way we can know the types of the items to fill in the schema in a "Pythonic" way.
1. We could use typing.NamedTuple - this is like a really fancy Enum that supports storing data with type annotations and behaviors.

Anyways, I'm quite fuzzy on the details, but I imagine some code that can introspect a class and spit out a JSON schema, and all fedora-messaging API users have to do is write nice Python classes and not worry about how JSON schema works.

Note: We would need some way to differentiate between required fields and non-required fields to fill out the required section on objects in the JSON schema. Perhaps just a _required = ['a', 'b', 'c'] on the class could do that for us?

[bowlofeggs]

To solve the problem of Python 3 being used, it may be possible to have the requested feature live in its own module and have the Python 2 version avoid packaging it.

[bowlofeggs]

import typing


class CoolThingIWant(typing.NamedTuple):
    <secret code goes here>


class User(CoolThingIWant):
    name: str
    email: str
    _required: ['name', 'email']


class Comment(CoolThingIWant):
    text: str
    user: User
    _required: ['text', 'user']
    _schema_description: str = 'A comment'


<<< print Comment._json_schema
{
        'id': f'<generate_this_somehow_maybe_using_class_name_or_some_more_metadata#',
        '$schema': 'http://json-schema.org/draft-04/schema#',
        'description': 'A comment',
        'type': 'object',
        'properties': {
            'text': {
                'type': 'string'
                'description': 'Not sure how we would generate this. Need to find a way.'
            },
            'user': {
                'type': 'object',
                <blah blah blah>
            }
        }
        <blah blah blah>
}

[bowlofeggs]

Or maybe I could do this in the https://python-jsonschema.readthedocs.io/en/latest/ project? Not sure if I would want to be able to mix with fedora-messaging features or not. I guess there are always mixin classes?