breaking: JSON Schema draft-2020-12

[Eomm]

Evaluate if the next major version should set the JSON schema draft-2020-12 as default

Ref: fastify/fastify#4549
AJV docs: https://ajv.js.org/guide/schema-language.html#draft-2019-09-and-draft-2020-12

[jsumners]

The AJV docs recommend sticking with 07 if you don't need the two new properties as all schemas will be affected by the reduced performance required to support them.

[Eomm]

I'm not too much into it tbh - I think we can provide:

1. an option to let the user switch the json version
2. release a npm tagged version that is equal to main but loads the other json schema standard
3. other ideas...

[gurgunday]

The AJV docs recommend sticking with 07 if you don't need the two new properties as all schemas will be affected by the reduced performance required to support them.

Wow, I just discovered this:

Draft-2019-09 features performance cost (even when not used)

+1 for keeping 07 the default and letting the user choose

[bcomnes]

Somewhat related, is there a way to opt into the 2019 or 2020 version without having to re-implement a ValidatorCompiler? (Like opt into the defaults, but with a few more of the keywords).

If you register 2019, and add the 07 spec, can you pick which one you use with the $schema field?