fix: IPC don't write variadic_buffer_counts in blocks, but only dictionaries

crates/polars-arrow/src/io/ipc/write/common.rs

@@ -254,13 +254,9 @@ fn set_variadic_buffer_counts(counts: &mut Vec<i64>, array: &dyn Array) {
             let array = array.as_any().downcast_ref::<FixedSizeListArray>().unwrap();
             set_variadic_buffer_counts(counts, array.values().as_ref())
         },
-        ArrowDataType::Dictionary(_, _, _) => {
-            let array = array
-                .as_any()
-                .downcast_ref::<DictionaryArray<u32>>()
-                .unwrap();
-            set_variadic_buffer_counts(counts, array.values().as_ref())
-        },
+        // Don't traverse dictionary values as those are set when the `Dictionary` IPC struct
+        // is read.
+        ArrowDataType::Dictionary(_, _, _) => (),
         _ => (),
     }
 }

crates/polars-plan/src/plans/ir/scan_sources.rs

@@ -1,3 +1,4 @@
+use std::fmt::{Debug, Formatter};
 use std::fs::File;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
@@ -14,10 +15,10 @@ use super::FileScanOptions;
 
 /// Set of sources to scan from
 ///
-/// This is can either be a list of paths to files, opened files or in-memory buffers. Mixing of
+/// This can either be a list of paths to files, opened files or in-memory buffers. Mixing of
 /// buffers is not currently possible.
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
-#[derive(Debug, Clone)]
+#[derive(Clone)]
 pub enum ScanSources {
     Paths(Arc<[PathBuf]>),
 
@@ -27,6 +28,16 @@ pub enum ScanSources {
     Buffers(Arc<[bytes::Bytes]>),
 }
 
+impl Debug for ScanSources {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Paths(p) => write!(f, "paths: {:?}", p.as_ref()),
+            Self::Files(p) => write!(f, "files: {} files", p.len()),
+            Self::Buffers(b) => write!(f, "buffers: {} in-memory-buffers", b.len()),
+        }
+    }
+}
+
 /// A reference to a single item in [`ScanSources`]
 #[derive(Debug, Clone, Copy)]
 pub enum ScanSourceRef<'a> {

py-polars/tests/unit/io/test_ipc.py

@@ -340,3 +340,17 @@ def test_ipc_decimal_15920(
         path = f"{tmp_path}/data"
         df.write_ipc(path)
         assert_frame_equal(pl.read_ipc(path), df)
+
+
+def test_ipc_variadic_buffers_categorical_binview_18636() -> None:
+    df = pl.DataFrame(
+        {
+            "Test": pl.Series(["Value012"], dtype=pl.Categorical),
+            "Test2": pl.Series(["Value Two 20032"], dtype=pl.String),
+        }
+    )
+
+    b = io.BytesIO()
+    df.write_ipc(b)
+    b.seek(0)
+    assert_frame_equal(pl.read_ipc(b), df)