fix: Field nullability mismatch when converting struct arrays to arrow (

#2174)

seems to be part of issues I ran into as part of #2155.

vortex-array/src/array/bool/compute/to_arrow.rs

@@ -12,7 +12,6 @@ impl ToArrowFn<BoolArray> for BoolEncoding {
         if data_type != &DataType::Boolean {
             vortex_bail!("Unsupported data type: {data_type}");
         }
-
         Ok(Some(Arc::new(ArrowBoolArray::new(
             array.boolean_buffer(),
             array.logical_validity()?.to_null_buffer(),

vortex-array/src/array/struct_/compute/to_arrow.rs

@@ -6,7 +6,7 @@ use itertools::Itertools;
 use vortex_error::{vortex_bail, VortexResult};
 
 use crate::array::{StructArray, StructEncoding};
-use crate::compute::{to_arrow, ToArrowFn};
+use crate::compute::{to_arrow, try_cast, ToArrowFn};
 use crate::variants::StructArrayTrait;
 
 impl ToArrowFn<StructArray> for StructEncoding {
@@ -24,6 +24,14 @@ impl ToArrowFn<StructArray> for StructEncoding {
             .iter()
             .zip_eq(array.children())
             .map(|(field, arr)| {
+                // We check that the Vortex array nullability is compatible with the field
+                // nullability. In other words, make sure we don't return any nulls for a
+                // non-nullable field.
+                let _ = try_cast(
+                    &arr,
+                    &arr.dtype().with_nullability(field.is_nullable().into()),
+                )?;
+
                 to_arrow(arr, field.data_type()).map_err(|err| {
                     err.with_context(format!("Failed to canonicalize field {}", field))
                 })
@@ -42,12 +50,12 @@ impl ToArrowFn<StructArray> for StructEncoding {
                 .names()
                 .iter()
                 .zip(field_arrays.iter())
-                .zip(array.dtypes().iter())
-                .map(|((name, arrow_field), vortex_field)| {
+                .zip(target_fields.iter())
+                .map(|((name, field_array), target_field)| {
                     Field::new(
                         &**name,
-                        arrow_field.data_type().clone(),
-                        vortex_field.is_nullable(),
+                        field_array.data_type().clone(),
+                        target_field.is_nullable(),
                     )
                 })
                 .map(Arc::new)
@@ -61,3 +69,52 @@ impl ToArrowFn<StructArray> for StructEncoding {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use vortex_buffer::buffer;
+    use vortex_dtype::FieldNames;
+
+    use super::*;
+    use crate::array::PrimitiveArray;
+    use crate::arrow::IntoArrowArray;
+    use crate::validity::Validity;
+    use crate::IntoArray as _;
+
+    #[test]
+    fn nullable_non_null_to_arrow() {
+        let xs = PrimitiveArray::new(buffer![0i64, 1, 2, 3, 4], Validity::AllValid);
+
+        let struct_a = StructArray::try_new(
+            FieldNames::from(["xs".into()]),
+            vec![xs.into_array()],
+            5,
+            Validity::AllValid,
+        )
+        .unwrap();
+
+        let fields = vec![Field::new("xs", DataType::Int64, false)];
+        let arrow_dt = DataType::Struct(fields.into());
+
+        struct_a.into_array().into_arrow(&arrow_dt).unwrap();
+    }
+
+    #[test]
+    fn nullable_with_nulls_to_arrow() {
+        let xs =
+            PrimitiveArray::from_option_iter(vec![Some(0_i64), Some(1), Some(2), None, Some(3)]);
+
+        let struct_a = StructArray::try_new(
+            FieldNames::from(["xs".into()]),
+            vec![xs.into_array()],
+            5,
+            Validity::AllValid,
+        )
+        .unwrap();
+
+        let fields = vec![Field::new("xs", DataType::Int64, false)];
+        let arrow_dt = DataType::Struct(fields.into());
+
+        assert!(struct_a.into_array().into_arrow(&arrow_dt).is_err());
+    }
+}

vortex-datafusion/src/persistent/opener.rs

@@ -6,9 +6,8 @@ use datafusion_physical_expr::{split_conjunction, PhysicalExpr};
 use futures::{FutureExt as _, StreamExt, TryStreamExt};
 use object_store::ObjectStore;
 use tokio::runtime::Handle;
-use vortex_array::array::StructArray;
 use vortex_array::arrow::FromArrowType;
-use vortex_array::ContextRef;
+use vortex_array::{ContextRef, IntoArrayVariant};
 use vortex_dtype::{DType, FieldNames};
 use vortex_error::VortexResult;
 use vortex_expr::datafusion::convert_expr_to_vortex;
@@ -98,7 +97,7 @@ impl FileOpener for VortexFileOpener {
             Ok(vxf
                 .scan(Scan::new(this.projection.clone()).with_some_filter(this.filter.clone()))?
                 .map_ok(move |array| {
-                    let st = StructArray::try_from(array)?;
+                    let st = array.into_struct()?;
                     st.into_record_batch_with_schema(projected_arrow_schema.as_ref())
                 })
                 .map(|r| r.and_then(|inner| inner))