This means slightly more typing in "zero-value" cases (`nil` vs `dockerfile.Metadata{}`), but the tradeoff is that it's simpler to use and reason about (and all the struct members are pointer-type map/slice values anyhow, so copying the struct is still pretty cheap).
This also swaps the scanner error handling to return the partially parsed Metadata object alongside the scanner error -- the error already tells us the object isn't fully complete data, so it's fair/fine to return and will likely just be ignored by the caller instead. This also allows us to get to 100% code coverage. 👀
This also updates our "treat `oci-import` just like `FROM scratch`" code to *actually* parse `FROM scratch` so we can't accidentally cause "missing data" bugs there in the future, and I implemented that using `sync.OnceValues` which requires upgrading to Go 1.21, but IMO that's a worthwhile tradeoff (because `sync.OnceValues` makes that code so clean/simple).
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).
This allows us to manipulate/use the repo lists from bashbrew directly in fun ways.
For example, `bashbrew list --namespaces='_' --all | xargs -n1 docker pull`.
Tianon Gravi