fix: Raise errors instead of panicking when sink_csv fails

crates/polars-pipe/src/executors/sinks/output/file_sink.rs

@@ -22,8 +22,8 @@ pub(super) fn init_writer_thread(
     // all chunks per push should be collected to determine in which order they should
     // be written
     morsels_per_sink: usize,
-) -> JoinHandle<()> {
-    std::thread::spawn(move || {
+) -> JoinHandle<PolarsResult<()>> {
+    std::thread::spawn(move || -> PolarsResult<()> {
         // keep chunks around until all chunks per sink are written
         // then we write them all at once.
         let mut chunks = Vec::with_capacity(morsels_per_sink);
@@ -51,7 +51,7 @@ pub(super) fn init_writer_thread(
                         if df.n_chunks() > 1 {
                             df.as_single_chunk();
                         }
-                        writer._write_batch(&df).unwrap();
+                        writer._write_batch(&df)?;
                     }
                 }
                 // all chunks are written remove them
@@ -62,21 +62,22 @@ pub(super) fn init_writer_thread(
                         if df.n_chunks() > 1 {
                             df.as_single_chunk();
                         }
-                        writer._write_batch(&df).unwrap();
+                        writer._write_batch(&df)?;
                     }
-                    writer._finish().unwrap();
-                    return;
+                    writer._finish()?;
+                    return Ok(());
                 }
             }
         }
+        Ok(())
     })
 }
 
 // Ensure the data is return in the order it was streamed
 #[derive(Clone)]
 pub struct FilesSink {
     pub(crate) sender: Sender<Option<DataChunk>>,
-    pub(crate) io_thread_handle: Arc<Option<JoinHandle<()>>>,
+    pub(crate) io_thread_handle: Arc<Option<JoinHandle<PolarsResult<()>>>>,
 }
 
 impl Sink for FilesSink {
@@ -106,7 +107,7 @@ impl Sink for FilesSink {
             .take()
             .unwrap()
             .join()
-            .unwrap();
+            .unwrap()?;
 
         // return a dummy dataframe;
         Ok(FinalizedSink::Finished(Default::default()))

crates/polars-pipe/src/pipeline/dispatcher/mod.rs

@@ -304,7 +304,9 @@ impl PipeLine {
     ) -> PolarsResult<Option<FinalizedSink>> {
         let (sink_shared_count, mut reduced_sink) = self.run_pipeline_no_finalize(ec, pipelines)?;
         assert_eq!(sink_shared_count, 0);
-        Ok(reduced_sink.finalize(ec).ok())
+
+        let finalized_reduced_sink = reduced_sink.finalize(ec)?;
+        Ok(Some(finalized_reduced_sink))
     }
 }
 

py-polars/tests/unit/streaming/test_streaming_io.py

@@ -194,6 +194,14 @@ def test_sink_csv_batch_size_zero() -> None:
         lf.sink_csv("test.csv", batch_size=0)
 
 
+def test_sink_csv_nested_data() -> None:
+    lf = pl.LazyFrame({"list": [[1, 2, 3, 4, 5]]})
+    with pytest.raises(
+        pl.exceptions.ComputeError, match="CSV format does not support nested data"
+    ):
+        lf.sink_csv("path")
+
+
 def test_scan_csv_only_header_10792(io_files_path: Path) -> None:
     foods_file_path = io_files_path / "only_header.csv"
     df = pl.scan_csv(foods_file_path).collect(streaming=True)