ench: add warn for saving non-existent paths

src/main.rs

@@ -42,6 +42,13 @@ fn main() -> Result<()> {
         archive.mode(HeaderMode::Complete);
         archive.follow_symlinks(false);
         for path in path {
+            if !path.exists() {
+                println!(
+                    "warn: path {} does not exist, and will not be cached",
+                    path.display()
+                );
+                continue;
+            }
             if path.is_dir() {
                 // we actually want to write out all the directory contents
                 archive.append_dir_all("", path).unwrap();