avoid eager struct canonicalizing

Signed-off-by: Andrew Duffy <[email protected]>

Author: a10y

encodings/fsst/src/array.rs

@@ -21,7 +21,6 @@ use vortex_array::DeserializeMetadata;
 use vortex_array::Precision;
 use vortex_array::ProstMetadata;
 use vortex_array::SerializeMetadata;
-use vortex_array::ToCanonical;
 use vortex_array::arrays::VarBinArray;
 use vortex_array::arrays::VarBinVTable;
 use vortex_array::serde::ArrayChildren;

vortex-layout/src/layouts/struct_/reader.rs

@@ -2,7 +2,6 @@
 // SPDX-FileCopyrightText: Copyright the Vortex contributors
 
 use std::collections::BTreeSet;
-use std::ops::Not;
 use std::ops::Range;
 use std::sync::Arc;
 
@@ -11,9 +10,8 @@ use itertools::Itertools;
 use vortex_array::ArrayRef;
 use vortex_array::IntoArray;
 use vortex_array::MaskFuture;
-use vortex_array::ToCanonical;
-use vortex_array::arrays::MaskedArray;
-use vortex_array::arrays::StructArray;
+use vortex_array::arrays::ScalarFnArray;
+use vortex_array::arrays::ScalarFnVTable;
 use vortex_array::builtins::ArrayBuiltins;
 use vortex_array::expr::ExactExpr;
 use vortex_array::expr::Expression;
@@ -26,8 +24,6 @@ use vortex_array::expr::transform::PartitionedExpr;
 use vortex_array::expr::transform::partition;
 use vortex_array::expr::transform::replace;
 use vortex_array::expr::transform::replace_root_fields;
-use vortex_array::validity::Validity;
-use vortex_array::vtable::ValidityHelper;
 use vortex_dtype::DType;
 use vortex_dtype::FieldMask;
 use vortex_dtype::FieldName;
@@ -349,18 +345,17 @@ impl LayoutReader for StructReader {
 
                 // If root expression was a pack, then we apply the validity to each child field
                 if is_pack_merge {
-                    let struct_array = array.to_struct();
-                    let masked_fields: Vec<ArrayRef> = struct_array
-                        .fields()
-                        .iter()
+                    let array = array.as_::<ScalarFnVTable>();
+                    let masked_children: Vec<ArrayRef> = array
+                        .children()
+                        .into_iter()
                         .map(|a| a.mask(&validity))
                         .try_collect()?;
 
-                    Ok(StructArray::try_new(
-                        struct_array.names().clone(),
-                        masked_fields,
-                        struct_array.len(),
-                        struct_array.validity().clone(),
+                    Ok(ScalarFnArray::try_new(
+                        array.scalar_fn().clone(),
+                        masked_children,
+                        array.len(),
                     )?
                     .into_array())
                 } else {