From fee692189f655900d85b5e3538be9499b422c08b Mon Sep 17 00:00:00 2001
From: Jonah Gao <jonahgao@msn.com>
Date: Mon, 15 Apr 2024 19:59:49 +0800
Subject: [PATCH] fix: panic when casting `ListArray` to `FixedSizeList`
 (#5643)

---
 arrow-cast/src/cast/list.rs |  6 ++++--
 arrow-cast/src/cast/mod.rs  | 21 +++++++++++++++++++++
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/arrow-cast/src/cast/list.rs b/arrow-cast/src/cast/list.rs
index 33faacdccb92..2ceab1d0c8c2 100644
--- a/arrow-cast/src/cast/list.rs
+++ b/arrow-cast/src/cast/list.rs
@@ -63,7 +63,9 @@ where
 {
     let cap = array.len() * size as usize;
 
-    let mut nulls = (cast_options.safe || array.null_count() != 0).then(|| {
+    // Whether the resulting array may contain null lists
+    let nullable = cast_options.safe || array.null_count() != 0;
+    let mut nulls = nullable.then(|| {
         let mut buffer = BooleanBufferBuilder::new(array.len());
         match array.nulls() {
             Some(n) => buffer.append_buffer(n.inner()),
@@ -74,7 +76,7 @@ where
 
     // Nulls in FixedSizeListArray take up space and so we must pad the values
     let values = array.values().to_data();
-    let mut mutable = MutableArrayData::new(vec![&values], cast_options.safe, cap);
+    let mut mutable = MutableArrayData::new(vec![&values], nullable, cap);
     // The end position in values of the last incorrectly-sized list slice
     let mut last_pos = 0;
     for (idx, w) in array.offsets().windows(2).enumerate() {
diff --git a/arrow-cast/src/cast/mod.rs b/arrow-cast/src/cast/mod.rs
index d559715911bb..8b7579c4cfc0 100644
--- a/arrow-cast/src/cast/mod.rs
+++ b/arrow-cast/src/cast/mod.rs
@@ -6806,6 +6806,27 @@ mod tests {
             3,
         )) as ArrayRef;
         assert_eq!(expected.as_ref(), res.as_ref());
+
+        // The safe option is false and the source array contains a null list.
+        // issue: https://github.com/apache/arrow-rs/issues/5642
+        let array = Arc::new(ListArray::from_iter_primitive::<Int32Type, _, _>(vec![
+            Some(vec![Some(1), Some(2), Some(3)]),
+            None,
+        ])) as ArrayRef;
+        let res = cast_with_options(
+            array.as_ref(),
+            &DataType::FixedSizeList(Arc::new(Field::new("item", DataType::Int32, true)), 3),
+            &CastOptions {
+                safe: false,
+                ..Default::default()
+            },
+        )
+        .unwrap();
+        let expected = Arc::new(FixedSizeListArray::from_iter_primitive::<Int32Type, _, _>(
+            vec![Some(vec![Some(1), Some(2), Some(3)]), None],
+            3,
+        )) as ArrayRef;
+        assert_eq!(expected.as_ref(), res.as_ref());
     }
 
     #[test]