Re: [BuildStream] Proposal: Allowing download-only sources to work on local files

[tristan maat codethink co uk (Tristan Daniël Maat)]

Hi,

> Being picky, I would personally try to avoid having two
> mutually-exclusive keys for the same thing; perhaps the proposed single
> 'url' key could be named something less confusing (I'd choose
> 'location' but that's already taken; 'from' ?) and there could be a
> 'local:' scheme for use with local files. That might be an uglier
> change, however.
>
>   - kind: zip
>     from: local:files/some-archive.zip

My main problem with this is that it will cause a fair bit of churn on
the project end; I realize we're definitely not backwards compatible,
and hence this is less important of a point, but I don't think we'd need
to change the key. Sticking with `url` is probably fine, it's still a
resource locator.

My second point is that this is a non-standard extension of URI. I
wanted to deliberately avoid that, because it's not a particularly nice
thing to do; especially because URIs are by definition expected to point
to an absolute location.

If we do use this proposal, I'd prefer a `bst-project:` scheme - but I'd
be happier with my own proposal from whenever ago [1], which is to
introduce a %{project} variable that would allow users to use:

    - kind: zip
      url: file://%{project}/files/some-archive.zip

This is a little less succinct, but it doesn't bend URI standards and
feels a bit less magic.

Regards,

Tristan

[1]: https://gitlab.com/BuildStream/buildstream/issues/388