From 25930202dee5651ebf70170dbeca791239fdc0fe Mon Sep 17 00:00:00 2001
From: Liam Bao <liam.zw.bao@gmail.com>
Date: Fri, 24 Apr 2026 19:32:00 -0400
Subject: [PATCH] Fix JSON reader panic for non-nullable zero-size
 FixedSizeList

---
 arrow-json/src/reader/list_array.rs |  8 +++++++-
 arrow-json/src/reader/mod.rs        | 26 ++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/arrow-json/src/reader/list_array.rs b/arrow-json/src/reader/list_array.rs
index ac574fab1615..713447540876 100644
--- a/arrow-json/src/reader/list_array.rs
+++ b/arrow-json/src/reader/list_array.rs
@@ -215,7 +215,13 @@ impl ArrayDecoder for FixedSizeListArrayDecoder {
         let values = self.decoder.decode(tape, &child_pos)?;
         let nulls = nulls.as_mut().map(|x| NullBuffer::new(x.finish()));
 
-        let array = FixedSizeListArray::try_new(self.field.clone(), self.size, values, nulls)?;
+        let array = FixedSizeListArray::try_new_with_length(
+            self.field.clone(),
+            self.size,
+            values,
+            nulls,
+            pos.len(),
+        )?;
         Ok(Arc::new(array))
     }
 }
diff --git a/arrow-json/src/reader/mod.rs b/arrow-json/src/reader/mod.rs
index 04fe207c27ec..b25a3d3a4832 100644
--- a/arrow-json/src/reader/mod.rs
+++ b/arrow-json/src/reader/mod.rs
@@ -2368,6 +2368,32 @@ mod tests {
         assert!(values.is_null(5));
     }
 
+    #[test]
+    fn test_fixed_size_list_zero_size_non_nullable() {
+        let buf = r#"
+        {"a": []}
+        {"a": []}
+        {"a": []}
+        "#;
+
+        let field = Field::new_list_field(DataType::Int32, true);
+        let schema = Arc::new(Schema::new(vec![Field::new(
+            "a",
+            DataType::FixedSizeList(Arc::new(field), 0),
+            false,
+        )]));
+
+        let batches = do_read(buf, 1024, false, false, schema);
+        assert_eq!(batches.len(), 1);
+
+        let col = batches[0].column(0).as_fixed_size_list();
+        assert_eq!(col.len(), 3);
+        assert_eq!(col.value_length(), 0);
+
+        let values = col.values().as_primitive::<Int32Type>();
+        assert!(values.values().is_empty());
+    }
+
     #[test]
     fn test_fixed_size_list_wrong_size() {
         let buf = r#"{"a": [1, 2, 3]}"#;