Urgh I made some wrong amends and I'm too tired to separate the commits out this time

ancestor: Split out of reachability
mergebase: Add merge base routines
internal/commitquery: Add commit query context engine thingy
internal/peel: Shared tag peeling
errors: Shared object query errors
internal/testgit: Add rooted repo helpers; remove raw path access
objectstore/memory: Add in-memory object store
objectid: Add Compare helper

1 files changed, 43 insertions, 0 deletions

diff --git a/mergebase/base.go b/mergebase/base.go
new file mode 100644
index 00000000..ee0473b3
--- /dev/null
+++ b/mergebase/base.go
@@ -0,0 +1,43 @@
+package mergebase
+
+import (
+	commitgraphread "codeberg.org/lindenii/furgit/format/commitgraph/read"
+	"codeberg.org/lindenii/furgit/objectid"
+	"codeberg.org/lindenii/furgit/objectstore"
+)
+
+// Base reports one merge base between left and right, if any.
+//
+// Both inputs are peeled through annotated tags before commit traversal.
+func Base(
+	store objectstore.Store,
+	graph *commitgraphread.Reader,
+	left objectid.ObjectID,
+	right objectid.ObjectID,
+) (objectid.ObjectID, bool, error) {
+	query := Query(store, graph, left, right)
+	seq := query.Seq()
+
+	var (
+		first objectid.ObjectID
+		ok    bool
+	)
+
+	seq(func(id objectid.ObjectID) bool {
+		first = id
+		ok = true
+
+		return false
+	})
+
+	err := query.Err()
+	if err != nil {
+		return objectid.ObjectID{}, false, err
+	}
+
+	if !ok {
+		return objectid.ObjectID{}, false, nil
+	}
+
+	return first, true, nil
+}