Decouple within-build (structured attrs) and unstable CLI path info JSON

See code comment for details.

src/libstore/parsed-derivations.cc

@@ -135,18 +135,37 @@ static std::regex shVarName("[A-Za-z_][A-Za-z0-9_]*");
 /**
  * Write a JSON representation of store object metadata, such as the
  * hash and the references.
+ *
+ * @note Do *not* use `ValidPathInfo::toJSON` because this function is
+ * subject to stronger stability requirements since it is used to
+ * prepare build environments. Perhaps someday we'll have a versionining
+ * mechanism to allow this to evolve again and get back in sync, but for
+ * now we don't have one.
  */
 static nlohmann::json pathInfoToJSON(
     Store & store,
     const StorePathSet & storePaths)
 {
-    nlohmann::json::array_t jsonList = nlohmann::json::array();
+    using nlohmann::json;
+
+    nlohmann::json::array_t jsonList = json::array();
 
     for (auto & storePath : storePaths) {
         auto info = store.queryPathInfo(storePath);
 
-        auto & jsonPath = jsonList.emplace_back(
-            info->toJSON(store, false, HashFormat::Nix32));
+        auto & jsonPath = jsonList.emplace_back(json::object());
+
+        jsonPath["narHash"] = info->narHash.to_string(HashFormat::Nix32, true);
+        jsonPath["narSize"] = info->narSize;
+
+        {
+            auto & jsonRefs = jsonPath["references"] = json::array();
+            for (auto & ref : info->references)
+                jsonRefs.emplace_back(store.printStorePath(ref));
+        }
+
+        if (info->ca)
+            jsonPath["ca"] = renderContentAddress(info->ca);
 
         // Add the path to the object whose metadata we are including.
         jsonPath["path"] = store.printStorePath(storePath);