To satisfy both Windows (https://github.com/docker-library/golang/pull/92) building and "non-AUFS" (https://github.com/docker-library/official-images/pull/1612, https://github.com/docker-library/official-images/pull/1537) building ("build machine" constraints, if you will), an update to the manifest file format is necessary.
To this end, we're introducing a new format which uses RFC 2822, allowing much more expressivity (especially for additional metadata like `Constraints`) and readability. The new tool also includes backwards compatibility for the older line-based manifest file format, but its usage is discouraged (and we will be slowly converting at least the `docker-library` repos to use the new format in their `generate-stackbrew-library.sh` scripts).
One of the tangential benefits of this conversion is a massive increase in the speed of the tool (`bashbrew list --all` on a very fast system with an SSD and a flaming hot cache used to take ~5s and now takes ~0.012s).
Tianon Gravi