plumbing: commitgraph, fix types and handle commit-graph-chains

Unfortunately the original variant makes some incorrect typing
assumptions about commit-graphs which make handling graph chains
difficult to do correctly. This creates a new subpackage and deprecates
the old one. It then adds support commit graph chains.

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

1 files changed, 40 insertions, 0 deletions

diff --git a/plumbing/format/commitgraph/v2/commitgraph.go b/plumbing/format/commitgraph/v2/commitgraph.go
new file mode 100644
index 0000000..7c67b63
--- /dev/null
+++ b/plumbing/format/commitgraph/v2/commitgraph.go
@@ -0,0 +1,40 @@
+package v2
+
+import (
+	"io"
+	"time"
+
+	"github.com/go-git/go-git/v5/plumbing"
+)
+
+// CommitData is a reduced representation of Commit as presented in the commit graph
+// file. It is merely useful as an optimization for walking the commit graphs.
+type CommitData struct {
+	// TreeHash is the hash of the root tree of the commit.
+	TreeHash plumbing.Hash
+	// ParentIndexes are the indexes of the parent commits of the commit.
+	ParentIndexes []uint32
+	// ParentHashes are the hashes of the parent commits of the commit.
+	ParentHashes []plumbing.Hash
+	// Generation number is the pre-computed generation in the commit graph
+	// or zero if not available.
+	Generation uint64
+	// When is the timestamp of the commit.
+	When time.Time
+}
+
+// Index represents a representation of commit graph that allows indexed
+// access to the nodes using commit object hash
+type Index interface {
+	// GetIndexByHash gets the index in the commit graph from commit hash, if available
+	GetIndexByHash(h plumbing.Hash) (uint32, error)
+	// GetHashByIndex gets the hash given an index in the commit graph
+	GetHashByIndex(i uint32) (plumbing.Hash, error)
+	// GetNodeByIndex gets the commit node from the commit graph using index
+	// obtained from child node, if available
+	GetCommitDataByIndex(i uint32) (*CommitData, error)
+	// Hashes returns all the hashes that are available in the index
+	Hashes() []plumbing.Hash
+
+	io.Closer
+}