add check that index-dir exists

src/main.rs

@@ -550,6 +550,23 @@ async fn ensure_dir_exists<P: AsRef<std::path::Path>>(path: P) -> Result<(), Any
     }
 }
 
+async fn verify_dir_exists<P: AsRef<std::path::Path>>(path: P) -> Result<(), AnyError> {
+    match tokio::fs::metadata(path.as_ref()).await {
+        Ok(meta) if meta.is_dir() => Ok(()),
+
+        Ok(meta) /* if ! meta.is_dir() */ => {
+            debug_assert!( ! meta.is_dir());
+            Err(format!("path exists, but is not a directory: {:?}", path.as_ref()).into())
+        }
+
+        Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
+            Err(format!("path does not exist: {}", path.as_ref().display()).into())
+        }
+
+        Err(e) => Err(e.into()),
+    }
+}
+
 async fn ensure_file_parent_dir_exists<P: AsRef<std::path::Path>>(path: P) -> Result<(), AnyError> {
     if let Some(parent_dir) = path.as_ref().parent() {
         ensure_dir_exists(parent_dir).await
@@ -757,7 +774,10 @@ async fn run(config: Config) -> Result<(), AnyError> {
             tmp
         }
 
-        (_, Some(path)) => path,
+        (_, Some(path)) => {
+            verify_dir_exists(&path).await?;
+            path
+        }
 
         _ => unreachable!(),
     };