plumbing: commitgraph, Add generation v2 support

This PR adds in support for generation v2 support and a couple of new
walkers to match --date-order etc options on log. This PR also fixes a
bug in the chain code and adds more tests.

Signed-off-by: Andrew Thornton <art27@cantab.net>

1 files changed, 7 insertions, 0 deletions

diff --git a/plumbing/object/commitgraph/commitnode_object.go b/plumbing/object/commitgraph/commitnode_object.go
index 1bd37e3..7256bed 100644
--- a/plumbing/object/commitgraph/commitnode_object.go
+++ b/plumbing/object/commitgraph/commitnode_object.go
@@ -85,6 +85,13 @@ func (c *objectCommitNode) Generation() uint64 {
 	return math.MaxUint64
 }
 
+func (c *objectCommitNode) GenerationV2() uint64 {
+	// Commit nodes representing objects outside of the commit graph can never
+	// be reached by objects from the commit-graph thus we return the highest
+	// possible value.
+	return math.MaxUint64
+}
+
 func (c *objectCommitNode) Commit() (*object.Commit, error) {
 	return c.commit, nil
 }