Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
You ran a project, and the engine could not find its source directory. Here is the convention. When a folder contains a manifest dot rush, it is a project root. And in a project root, all of the source lives under a folder called src. The entry file, and every module it loads, sit in there. If there is no src folder, there is simply nothing to run. This refusal is a teaching message: it names src as the missing piece, so you do not have to hunt for it. A common cause is putting your code files right next to the manifest, instead of inside src. Another is a typo in the folder name, or running from the wrong directory. The message gives you the root that was examined. The fix: create a src folder in the project root, and move your files into it, including the main file. Then run again. One rule, always the same, and every rush project looks familiar the moment you open it.
Text from the Rush engine's error catalogue.