Re: [BuildStream] How to synchronize nested junctions

[Tristan Van Berkom <tristan vanberkom codethink co uk>]

On Wed, 2019-04-10 at 12:05 +0100, Chandan Singh wrote:
> Hi,
>
> tl;dr: nested junctions are hard, and we need a way to make
> experiences
> involving them nicer.

Hi Chandan,

This was considered in Jürg's initial implementation of junctions.

See:

    https://docs.buildstream.build/elements/junction.html#nested-junctions

Specifically:

    "BuildStream uses the junction element name as key to determine
     which junctions to merge. It is recommended that the name of a
     junction is set to the same as the name of the linked project."

I realize that this is really not an obvious thing to realize in
practice, maybe we need better messaging around this (and maybe there
are still edge cases around this which don't work perfectly and
conveniently ?).

Maybe even some enhancements are possible around here, I am skeptical
about having recursive junction lookups; when the end project wants to
address sub-sub project elements, there is already the option of
including a matching junction to the sub-sub project in the calling
project, using a matching junction element name.

Before considering further enhancements, I just wanted to point out the
current, existing solution for this.

Cheers,
    -Tristan