Re: [BuildStream] plugin as elements

[Jürg Billeter <j bitron ch>]

Hi Ben,

On Fri, 2020-04-24 at 14:48 +0000, Benjamin Schubert wrote:
> An example would be:
>
> project.conf:
>
> plugins:
>   - origin: bst
>     path: my_junction:plugins.bst
>     sources:
>       git: 0
>   - origin: bst
>     path: internal_plugins.bst
>     elements:
>       cmake: 0

I'm wondering whether we should define a new dict key instead of
reusing the `path` key to specify an element as plugin source. If so,
we could even implicitly infer `origin: bst` from the use of the new
key, unless we think that makes the format overall more confusing.

> kind: plugin
> sources:
> - kind: tar
>   url: gitlab:bst-plugins-experimental/tree/master.tar.gz

As far as I can tell, `kind: plugin` elements won't contain anything
specific to plugin loading in their definitions. Could it make sense to
use the existing `kind: import` instead? This doesn't mean that we have
to support arbitrary element kinds as plugin sources (as other elements
would have to be built), however, it would mean that users don't have
to learn about another special element kind.

> Any comments, suggestions, problems?
> Does anyone foresee any problems that this would bring with regard to
> remote execution?

Element plugins are always handled locally, so I don't expect this to
cause any problems with remote execution.

Cheers,
Jürg