fix: resolve lint failure and validate variant slots

Signed-off-by: Joe Isaacs <joe.isaacs@live.co.uk>

Author: joseph-isaacs

vortex-array/src/arrays/chunked/vtable/mod.rs

@@ -20,7 +20,6 @@ use crate::IntoArray;
 use crate::Precision;
 use crate::ToCanonical;
 use crate::arrays::ChunkedArray;
-use crate::arrays::Primitive;
 use crate::arrays::PrimitiveArray;
 use crate::arrays::chunked::compute::kernel::PARENT_KERNELS;
 use crate::arrays::chunked::compute::rules::PARENT_RULES;
@@ -226,9 +225,11 @@ impl VTable for Chunked {
 
         #[cfg(debug_assertions)]
         {
-            let chunk_offsets = chunk_offsets.as_opt::<Primitive>().unwrap_or_else(|| {
-                vortex_panic!("Chunked array chunk_offsets slot must be primitive")
-            });
+            let chunk_offsets = chunk_offsets
+                .as_opt::<crate::arrays::Primitive>()
+                .unwrap_or_else(|| {
+                    vortex_panic!("Chunked array chunk_offsets slot must be primitive")
+                });
             let chunk_offsets_buf = chunk_offsets.to_buffer::<u64>();
             debug_assert_eq!(
                 chunk_offsets_buf.len(),

vortex-array/src/arrays/variant/vtable/mod.rs

@@ -9,6 +9,7 @@ use std::hash::Hasher;
 use vortex_error::VortexExpect;
 use vortex_error::VortexResult;
 use vortex_error::vortex_ensure;
+use vortex_error::vortex_err;
 use vortex_error::vortex_panic;
 
 use crate::ArrayEq;
@@ -142,7 +143,12 @@ impl VTable for Variant {
             NUM_SLOTS,
             slots.len()
         );
-        array.slots = [slots.into_iter().next().vortex_expect("must exist")];
+        let child = slots
+            .into_iter()
+            .next()
+            .vortex_expect("VariantArray slot vector length was validated")
+            .ok_or_else(|| vortex_err!("VariantArray child slot must be present"))?;
+        array.slots = [Some(child)];
         Ok(())
     }
 
@@ -151,3 +157,22 @@ impl VTable for Variant {
         Ok(ExecutionStep::done(array.clone().into_array()))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::arrays::PrimitiveArray;
+    use crate::dtype::Nullability;
+
+    #[test]
+    fn with_slots_rejects_missing_child() {
+        let mut array = VariantArray::new(
+            PrimitiveArray::from_iter([1u8, 2, 3]).into_array(),
+            Nullability::NonNullable,
+        );
+
+        let err = <Variant as VTable>::with_slots(&mut array, vec![None]).unwrap_err();
+
+        assert!(err.to_string().contains("child slot must be present"));
+    }
+}