- Move to commit.CommitDescendsFrom
- When searching for an ancestor in the commit history, prune
whenever the commit.Height() < ancestor.Height()
- Add new test TestCommitDescendsFrom to verify correctness and pruning.
The Dataset.Commit() code pathway still enforces fast-forward-only
behavior, but a new SetHead() method allows the HEAD of a Dataset to
be forced to any other Commit.
noms sync detects the case where the source Commit is not a descendent
of the provided sink Dataset's HEAD and uses the new API to force the
sink to the desired new Commit, printing out the now-abandoned old
HEAD.
Fixes#2240
This changes so that all commit struct types have a meta field
(which might be an empty struct).
Increment the serialization version since the old data does not
necessarily have the meta field.
Fixes ##2112
We now compute the commit type based on the type of the value and
the type of the parents.
For the first commit we get:
```
struct Commit {
parents: Set<Ref<Cycle<0>>>,
value: T,
}
```
As long as we continue to commit values with type T that type stays
the same.
When we later commits a value of type U we get:
```
struct Commit {
parents: Set<Ref<struct Commit {
parents: Set<Ref<Cycle<0>>>,
value: T | U
}>>,
value: U,
}
```
The new type gets combined as a union type for the value of the inner
commit struct.
Fixes#1495
Change Dataset.Pull to use a single algorithm to pull data from a
source to a sink, regardless of which (if any) is local. The basic
algorithm is described in the first section of pulling.md. This
implementation is equivalent but phrased a bit differently. The
algorithm actually used is described in the second section of
pulling.md
The main changes:
- datas.Pull(), which implements the new pulling algorithm
- RefHeap, a priority queue that sorts types.Ref by ref-height and
then by ref.TargetHash()
- Add has() to both Database implementations. Cache has() checks.
- Switch Dataset to use new datas.Pull(). Currently not concurrent.
Toward #1568
Mostly, prune reachableChunks
