[REQ] Spec: allow including partial specs

[cpuguy83]

What kind of request is this?

New feature

What is your request or suggestion?

Sometimes there's a lot of shared things between specs, especially if multiple versions of a package need to be supported.
This can end up with a lot of duplication and is potentially prone to errors due to out-of-sync specs.

I think it could be possible at every object to allow something like an @include field to pull in a spec using any source type, which would be pulled in, unmarshalled, and merged into the main spec. The included type must match the type where its being included in.
e.g.

dependencies:
  @include:
     - context: {}
        path: path/to/deps.partial.yml

Multiple @includes can be used here and merged together with the base.

Are you willing to submit PRs to contribute to this feature request?

• Yes, I am willing to implement it.

[adamperlin]

A few questions here.

1. Can included spec fragments reference other includes themselves? Or I guess to be very specific, are recursive includes allowed? I don't necessarily see a problem with this, but it might complicate the feature a bit. We may have to consider things like circular includes for example.

2. How to handle conflicting spec fields? When merging in fields from other partial specs, it is possible that multiple different partial specs will specify a value for the same field (which will need to be unique in its section of the spec). Is that case simply an error?

[cpuguy83]

1. I would not start with recursive includes
2. Agree, error on merge conflict is best.