Issue #15 is finished

src/libexpr/primops/flakeref.hh

@@ -153,6 +153,7 @@ struct FlakeRef
     /* Check whether this is an "immutable" flake reference, that is,
        one that contains a commit hash or content hash. */
     bool isImmutable() const;
-};
 
+    FlakeRef baseRef() const;
+};
 }