This provides a way to mark artifacts as latest. In LilyBuildConfig.add_repo, there is a new argument artifact_latest_branch_map, which is a mapping from branch name to a ref name. <STORAGE_DIR>/repos/<REPO_ID>/latest{,-good}/<REF_NAME> will point to the build dir of the latest or latest good build.

Type: add

Configure a repo with such a mapping {'servant': 'serv'}. Run a pipeline on servant that passes. Verify both latest and latest-good link are updated. Run a pipeline on servant that fails. Verify only latest link is updated. Run a pipeline on another branch. Verify no link is updated.