bug fix: add sandcastle_alias in file access events

Reviewed By: jdelliot

Differential Revision: D68737319

fbshipit-source-id: 6b01849ca0465dfbefcd93fc0424460ba09d1c2b

eden/fs/telemetry/LogEvent.h

@@ -750,6 +750,12 @@ struct FileAccessEvent : public EdenFSFileAccessEvent {
     event.addString("filename", filename);
     event.addString("source", source);
     event.addString("source_detail", source_detail);
+
+    if (auto alias = std::getenv("SANDCASTLE_ALIAS")) {
+      // Log the Sandcastle job alias if set. If we decide to use predictive
+      // prefetch profiles on sandcastle, we will want the sandcastle alias.
+      event.addString("sandcastle_alias", alias);
+    }
   }
 };