This patch adds an optional MergePolicy field to CommitOptions. It's a
callback. If the caller sets it, then the commit code will look for a
common ancestor between the Dataset HEAD and the provided Commit. If
the caller-provided Commit descends from HEAD, then Commit proceeds as
normal.
If it does not, but there is a common ancestor, the code runs
merge.ThreeWay() on the values of the provided Commit, HEAD, and the
common ancestor, invoking the MergePolicy callback to resolve
conflicts. If merge succeeds, a merge Commit is created that descends
from both HEAD and the caller-provided Commit. This becomes the new
HEAD of the Dataset.
Fixes#2534
Noms SDK users frequently shoot themselves in the foot because they're
holding onto an "old" Database object. That is, they have a Database
tucked away in some internal state, they call Commit() on it, and
don't replace the object in their internal state with the new Database
returned from Commit.
This PR changes the Database and Dataset Go API to be in line with the
proposal in Issue #2589. JS follows in a separate patch.
Once we integrate noms-merge into the `noms commit` command, this
function will allow us to stop requiring users to pass in the common
ancestor to be used when merging. The code can just find it and merge
away.
Toward #2535
- 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.
For compound types (List, Set, Map, Ref) the concrete type may be a
union. If that is the case all the types in the union must be a
subtype of the concrete type's element type.
`C<T | V>` is a subtype of `C<S>` iff T is a subtype of S and V is a
subtype of S.
fix misspellings; fix code that was not gofmt'd - plus take advantage of gofmt -s too; couple of unreachable golint reported fixes; reference go report card results and tests
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
