The logic for computing canonical references conflated the semantics of
annotated and lighweight tags, yielding confusing/wrong results. The
main culprit was the call to `peel_to_commit` in
`impl ReadRepository for Repository`, peeling tag objects away.
To resolve this, we separate out quroum computation per object type: one
implementation for commits, and one for tags.
Also move move canonical error types and methods into their own
module to have a cleaner file structure for the main logic.
Capture the `BTreeMap<Oid, u8>` type into a `Votes` struct, with its own API.
We were getting the objects from the repository twice – once in `Canonical::new`
and once again in `ensure_commit_or_tag` – so the latter was removed.
Use an `enum CanonicalObject` to specify which object types the canonical
process supports.
During `converges`, separate commits and tags, and ensure that we are only
looking at objects of one type. Note, that Fintan think this is actually the
*wrong* place to do it because we already filter the objects – so we should
keep track of that information higher up the callstack.
Co-authored-by: Fintan Halpenny <fintan.halpenny@gmail.com>
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