There are a few goals with this refactor:
1. Remove external access to fields that no longer make sense and/or
won't make sense soon due to other potential changes. For example,
there can now be multiple blobs associated with a ref (for different
compression types), so the fact that you could access the "Blob"
field from the Info method on Ref incorrectly implied there was just
a single blob for the ref. This is on top of the fact that there is
no need for external access to blob digests.
2. Centralize use of cache metadata inside the cache package.
Previously, many parts of the code outside the cache package could
obtain the bolt storage item for any ref and read/write it directly.
This made it hard to understand what fields are used and when. Now,
the Metadata method has been removed from the Ref interface and
replaced with getters+setters for metadata fields we want to expose
outside the package, which makes it much easier to track and
understand. Similar changes have been made to the metadata search
interface.
3. Use a consistent getter+setter interface for metadata, replacing
the mix of interfaces like Metadata(), Size(), Info() and other
inconsistencies.
Signed-off-by: Erik Sipsma <erik@sipsma.dev>
Refactor the interface to avoid such issues in the future.
BuildKit own mounts are stateless and not affected but
a different mountable implementation could get confused.
Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
