Re: [BuildStream] Specifying default dependencies for element kinds

[Jürg Billeter <j bitron ch>]

On Thu, 2019-06-13 at 00:13 +0100, Chandan Singh wrote:
> If we just add composition support for dependencies, that would
> already solve most of our issues. It would make me extra happy if we
> can make the default composition behavior configurable, but that can
> be a separate discussion. (The use-case there being that, at least in
> case of dependencies, I expect that we'd want to extend the list
> majority of the time rather than overwriting it.)

Using composition support for default dependencies sounds sensible to
me. If we were to implement default dependency support with a different
mechanism, we'd still have to provide a way to override default
dependencies. So I think it's much better to use the existing mechanism
and not cause confusion reinventing the wheel.

I agree that the default composition behavior for lists is not ideal in
this case. Whatever we come up with to improve this situation will
likely also help includes with dependencies, which are still
interesting, in my opinion, as they provide more flexibility (you can
support multiple sets of default dependencies for a single plugin).

> Unless I have missed some detail I don't see why such composition
> couldn't support this behavior, as other fields already support this.
> So, we should be coverted here.

It might not be trivial as dependencies are already needed in the
loader, before plugins are even instantiated. However, we can hopefully
find a reasonable way to implement this.

Cheers,
Jürg