Root $id not overrided by S.extend

[aboutlo]

Unfortunately S.extend doesn't work as expected. I have been too optimistic.

The problem is here: https://github.com/fastify/fluent-schema/blob/master/src/utils.js#L140-L150

Basically, fluent-schema adds attributes to the last prop declared. However with S.extend(base).id('extend') the id will be added to the last prop from the base rather than the root document.

I have the feeling we need to change the syntax to:

S.object()
  .id('extend')
  .prop('bar').extend(S.object()id('base').prop('foo'))

I need to dig into more

For now, this PR contains only the tests to expose the issue

[Eomm]

Could you use symbols to ignore prop that has been imported/extented in the main S.object?

[aboutlo]

Not sure if I get what you mean.
Are you referring to S.extend(Base).id('extended') case?
the issue is in how we add an attribute.

const setAttribute = ({ schema, ...options }, attribute) => {
  const [key, value] = attribute
  const currentProp = last(schema.properties)
  if (currentProp) {
    const { name, ...props } = currentProp
    return options.factory({ schema, ...options }).prop(name, {
      [key]: value,
      ...props,
    })
  }
  return options.factory({ schema: { ...schema, [key]: value }, ...options })

currentProp is the last prop added so the id will be added to the last prop added in the base not at the root level as the syntax let you imagine.

In order to fix that I had to change the order:

const base = S.object().id('base')
S.object().id('extended').extend(base)

With this approach extend can merge the extended and base schemas in the right order

 const extended = merge(state, schema)

https://github.com/fastify/fluent-schema/pull/54/files#diff-6882624535de7cb6b7bae3a1912c1b18R258

[aboutlo]

notice: this is breaking change. The previous API is broken and I can't figure out a way to support the original approach S.extend(S.object().id('base').prop('foo')).id('extended').prop('bar')

[mcollina]

lgtm, +1 to bump the major.