[GitHub] [arrow-datafusion] alamb commented on a diff in pull request #4437: feat: `DataFusionError::find_root`

[GitBox <gi...@apache.org>]

alamb commented on code in PR #4437:
URL: https://github.com/apache/arrow-datafusion/pull/4437#discussion_r1036108112


##########
datafusion/common/src/error.rs:
##########
@@ -333,8 +334,101 @@ impl From<DataFusionError> for io::Error {
     }
 }
 
+/// Helper for [`DataFusionError::find_root`].
+enum OtherErr<'a> {
+    Arrow(&'a ArrowError),
+    Dyn(&'a (dyn std::error::Error + Send + Sync + 'static)),
+}
+
+impl DataFusionError {
+    /// Get underlying error.

Review Comment:
   ```suggestion
       /// Get deepest underlying [`DataFusionError`]
       ///
       /// [`DatafusionError`]s sometimes form a chain, such as `DatafusionError::ArrowError()` in order to conform
       /// to the correct error signature. Thus sometimes there is a chain several layers deep that can obscure the
       /// original error. This function finds the lowest level DataFusionError possible.
       ///
       /// For example,  `find_root` will return`DataFusionError::ResourceExhausted` given the input
       /// ```text
       /// DataFusionError::ArrowError
       ///   ArrowError::External
       ///    Box(DataFusionError::Context)
       ///      DataFusionError::ResourceExhausted
       /// ```
   ```



##########
datafusion/common/src/error.rs:
##########
@@ -353,6 +447,61 @@ mod test {
         assert_eq!(res.to_string(), "Arrow error: Schema error: bar");
     }
 
+    #[test]
+    fn test_find_root_error() {

Review Comment:
   👍 



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