Clarify usage of plugin-meta and dependency check

[lependu]

Hi! I found the following issues with plugin-meta definitions and dependency check:

1. Currently the README instructions about plugin-metadata definition states that we need to pass dependencies {Object}, but fastify/fastify/lib/pluginUtils.js accepts {Array} of strings.

2. There is no mention of decorators {Object} property which we can use for the same purpose.

3. If I am not mistaken, in case of we pass dependencies {Array} property, the dependency chek only passes if the dependency plugin declares name property in its own plugin definition. Currently most of the plugins in the Ecosystem list lacks of that property, therefore they will result a false negative dependency check.

4. If the previous assumption is correct and it is the intended behaviour, than we need to update the plugin definitions of the existing plugins with the name property. Up until that point it would be safer to use the decorators {Object} plugin-meta definition.

I am sorry for the TLDR, but I am aware of that this functionality is WIP and therefore there are a lot of moving parts. I am happy to create PR(s) if it is required.

[mcollina]

Can you please make an example of what you think it's happening right now vs what it should be happening according to you?

[lependu]

@mcollina I like how it works now, but I would improve the README:

I think it should be something like this

You can also pass some metadata that will be handled by Fastify, such as the dependencies of your plugin.

const fp = require('fastify-plugin')

function plugin (fastify, opts, next) {
  // your plugin code
  next()
}

module.exports = fp(plugin, {
  fastify: '0.x',
  // You need to define only one of the [dependency|decorator] properties.
  decorators: {
    fastify: ['plugin1', 'plugin2'],
    reply: ['compress']
  },
  dependencies: ['plugin1-name, plugin2-name']
})

And I think we should update Ecosystem plugins with name property, because

dependency only works if the name property defined int the plugin's meta.
For example:

plugin.js

const fp = require('fastify-plugin')

function plugin (fastify, opts, next) {
  // your plugin code
  next()
}

module.exports = fp(plugin, {
  fastify: '0.x',
  dependencies: ['fastify-redis']
})

server.js

const Fastify = require('fastify')                                              
const redis = require('fastify-redis')                                          
const plugin = require('./plugin')   

module.exports = (options) => {                                                    
  const instance = Fastify()                                                    
  instance
   .register(redis)
   .register(plugin)
   // more code
  return instance
}

This will throw error (even if the dependency registered), simply because fastify-redis does not have name property in its plugin definition.

[delvedor]

@lependu why You need to define only one of the [dependency|decorator] properties.?
You may need both.

[lependu]

@delvedor Corrected.

One more question: May I create PRs which updates Ecosystem plugins with name property?

[delvedor]

Sure!