Add ListVector::get_entry (#640)

Fixes #635

Author: mlafeldt

crates/duckdb/src/core/vector.rs

@@ -231,6 +231,12 @@ impl ListVector {
         self.entries.as_mut_slice::<duckdb_list_entry>()[idx].length = length as u64;
     }
 
+    /// Get offset and length for the entry at index.
+    pub fn get_entry(&self, idx: usize) -> (usize, usize) {
+        let entry = self.entries.as_slice::<duckdb_list_entry>()[idx];
+        (entry.offset as usize, entry.length as usize)
+    }
+
     /// Set row as null
     pub fn set_null(&mut self, row: usize) {
         unsafe {
@@ -368,7 +374,7 @@ impl StructVector {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::core::{DataChunkHandle, LogicalTypeId};
+    use crate::core::{DataChunkHandle, LogicalTypeHandle, LogicalTypeId};
     use std::ffi::CString;
 
     #[test]
@@ -395,4 +401,21 @@ mod tests {
             &vec![0x68, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64],
         );
     }
+
+    #[test]
+    fn test_list_vector_get_entry() {
+        let list_type = LogicalTypeHandle::list(&LogicalTypeId::Integer.into());
+        let chunk = DataChunkHandle::new(&[list_type]);
+        chunk.set_len(3);
+
+        let mut list_vector = chunk.list_vector(0);
+
+        list_vector.set_entry(0, 0, 2);
+        list_vector.set_entry(1, 2, 1);
+        list_vector.set_entry(2, 3, 2);
+
+        assert_eq!(list_vector.get_entry(0), (0, 2));
+        assert_eq!(list_vector.get_entry(1), (2, 1));
+        assert_eq!(list_vector.get_entry(2), (3, 2));
+    }
 }