diff --git a/src/libfetchers/tree-info.cc b/src/libfetchers/tree-info.cc
new file mode 100644
index 000000000..50795e162
--- /dev/null
+++ b/src/libfetchers/tree-info.cc
@@ -0,0 +1,26 @@
+#include "tree-info.hh"
+#include "store-api.hh"
+
+#include <nlohmann/json.hpp>
+
+namespace nix::fetchers {
+
+StorePath TreeInfo::computeStorePath(Store & store) const
+{
+    assert(narHash);
+    return store.makeFixedOutputPath(true, narHash, "source");
+}
+
+nlohmann::json TreeInfo::toJson() const
+{
+    nlohmann::json json;
+    assert(narHash);
+    json["narHash"] = narHash.to_string(SRI);
+    if (revCount)
+        json["revCount"] = *revCount;
+    if (lastModified)
+        json["lastModified"] = *lastModified;
+    return json;
+}
+
+}