1 files changed, 37 insertions, 0 deletions
diff --git a/reachability/errors.go b/reachability/errors.go
new file mode 100644
index 00000000..e52bf0a4
--- /dev/null
+++ b/reachability/errors.go
@@ -0,0 +1,37 @@
+package reachability
+
+import (
+	"fmt"
+
+	"codeberg.org/lindenii/furgit/objectid"
+	"codeberg.org/lindenii/furgit/objecttype"
+)
+
+// ErrObjectMissing indicates that a referenced object is absent from the store.
+type ErrObjectMissing struct {
+	OID objectid.ObjectID
+}
+
+func (e *ErrObjectMissing) Error() string {
+	return fmt.Sprintf("reachability: missing object %s", e.OID)
+}
+
+// ErrObjectType indicates that a referenced object has a different type than
+// what traversal expected on that edge.
+type ErrObjectType struct {
+	OID  objectid.ObjectID
+	Got  objecttype.Type
+	Want objecttype.Type
+}
+
+func (e *ErrObjectType) Error() string {
+	gotName, gotOK := objecttype.Name(e.Got)
+	if !gotOK {
+		gotName = fmt.Sprintf("type(%d)", e.Got)
+	}
+	wantName, wantOK := objecttype.Name(e.Want)
+	if !wantOK {
+		wantName = fmt.Sprintf("type(%d)", e.Want)
+	}
+	return fmt.Sprintf("reachability: object %s has type %s, want %s", e.OID, gotName, wantName)
+}