commit cb94fd9523b01c1b26c29b6408cb5262da0fbe7c
author Vadim Shtayura <vadimsh@chromium.org> Tue Jan 08 19:29:22 2019
committer Commit Bot <commit-bot@chromium.org> Tue Jan 08 19:29:22 2019
tree 2640fd25293bb40c96fe2273db4c5fd3afeb30c0
parent 608ee0461bb9138d2a8e31f1ff60332cd64cf0fb

[lucicfg] Add empty core.gitiles_poller, define 'triggers/triggered_by' rels.

It's a first instance of polymorphism in lucicfg: 'triggered_by' can refer to
either a builder or a gitiles_poller. As additional complication, we allow to
refer to builders via either their full names ("<bucket>/<name>") or short names
("<name>"), if the latter is non-ambiguous. Same for gitiles_poller names.

This is resolved by introduction of a new internal 'triggerer' node: it is an
entity that can be referred to in 'triggered_by' relation. Both 'builder' and
'gitiles_poller' (each) have two 'triggerer' nodes as children: a bucket-scoped
one and a global one.

This is very similar to 'builder_ref', except the direction of the relation is
reversed: a 'builder_ref' has associated builders as children, but 'triggerer'
has them as parents. This allows to catch cycles in triggering graphs.

For example, a builder that triggers itself produces the following cycle:
  core.builder_ref('b') ->
  core.builder('ci/b') ->
  core.triggerer('ci/b') ->
  core.builder_ref('b')

While such cycle doesn't necessarily mean an invalid configuration, it does
have a potential to introduce a positive feedback loop in runtime that can blow
everything up, so we forbid them.

R=tandrii@chromium.org, nodir@chromium.org
BUG=833946

Change-Id: I25b21a51fc2b355a8688182ccf55820c768ee46b
Reviewed-on: https://chromium-review.googlesource.com/c/1394188
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>
Reviewed-by: Nodir Turakulov <nodir@chromium.org>