fix: allow assigning provider-enabled instances to FastifyInstance

[driimus]

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added - as guide in fix(type-providers): assignability of instance with enabled type provider fastify#4371
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

Fix for fastify/fastify#4342 specific to this type provider.

[sinclairzx81]

@RafaelGSS Hi, just noticed this PR was still pending.

I think it should be ok to merge this one through as the type specs were updated on fastify/fastify#4371 in preparation for this. The original PR provided adequate testing when infering unknown for unresolvable types (currently the providers infer as never). So this PR would be the subsequent downstream update inline with the main project specs (see here)

There's also a similar PR ready to go through for fastify/fastify-type-provider-json-schema-to-ts#21 package which implements the same update as this provider.

So just as a quick reminder on this. This update relates specifically to enabling contravariance of the FastifyInstance when configured with a Type Provider. This should help greatly improve type composability and assignment of FastifyInstance (as it makes the configured provider instance assignable to non configured instances, which is awesome)

I don't anticipate this change causing any problems in existing codebases currently using this or the json-schema provider. But may want to use a minor revision just in case.

Would be a great to see this PR merged through!

[RafaelGSS]

@driimus can you rebase?

[driimus]

@RafaelGSS the PR is already up-to-date with main. Happy to rebase onto another ref if you have one in mind.

If it's about the failing CI for node14/windows, that shouldn't be related to the changes in this PR.

It sounds more like tapjs/tapjs#843. The project doesn't have a lockfile so the version of tap that gets installed is newer than the one in package.json:

fastify-type-provider-typebox/package.json

Line 46 in cbd027e

"tap": "^16.3.0",

I've created a clone of the repo to run the CI workflow on main: https://github.com/driimus/ff-type-provier-private/actions/runs/3473691689
Potential fixes:

• setting the npm cli to >=7, <9: https://github.com/driimus/ff-type-provier-private/actions/runs/3473716044
• pinning tap to 16.3.0: https://github.com/driimus/ff-type-provier-private/actions/runs/3473928980

Unless the tap issue (or npm/cli#5856) is resolved quickly, there might be a need to coordinate the fix across repos in the fastify org.

[RafaelGSS]

LGTM.

[RafaelGSS]

I think the most appropriate is to release the minor when the tap issue is resolved.