chore[layout]: empty pack round trip scan (#3868)

Signed-off-by: Joe Isaacs <[email protected]>

Author: joseph-isaacs

vortex-file/src/tests.rs

@@ -16,12 +16,13 @@ use vortex_array::arrays::{
 };
 use vortex_array::stream::ArrayStreamExt;
 use vortex_array::validity::Validity;
-use vortex_array::{Array, IntoArray, ToCanonical};
+use vortex_array::{Array, ArrayRef, IntoArray, ToCanonical};
 use vortex_buffer::{Buffer, ByteBufferMut, buffer};
 use vortex_dtype::PType::I32;
 use vortex_dtype::{DType, DecimalDType, Nullability, PType, StructFields};
 use vortex_error::VortexResult;
-use vortex_expr::{and, eq, get_item, gt, gt_eq, lit, lt, lt_eq, or, root, select};
+use vortex_expr::{PackExpr, and, eq, get_item, gt, gt_eq, lit, lt, lt_eq, or, root, select};
+use vortex_layout::scan::ScanBuilder;
 use vortex_scalar::Scalar;
 
 use crate::{V1_FOOTER_FBS_SIZE, VERSION, VortexFile, VortexOpenOptions, VortexWriteOptions};
@@ -1149,6 +1150,26 @@ async fn write_nullable_top_level_struct() {
         .unwrap();
 }
 
+async fn round_trip(
+    array: &dyn Array,
+    f: impl Fn(ScanBuilder<ArrayRef>) -> VortexResult<ScanBuilder<ArrayRef>>,
+) -> VortexResult<ArrayRef> {
+    let buffer: Bytes = VortexWriteOptions::default()
+        .write(vec![], array.to_array_stream())
+        .await?
+        .into();
+
+    let vxf = VortexOpenOptions::in_memory()
+        .with_dtype(array.dtype().clone())
+        .open(buffer)
+        .await?;
+
+    assert_eq!(vxf.dtype(), array.dtype());
+    assert_eq!(vxf.row_count(), array.len() as u64);
+
+    f(vxf.scan()?)?.into_array_stream()?.read_all().await
+}
+
 #[tokio::test]
 async fn write_nullable_nested_struct() -> VortexResult<()> {
     let nested_dtype = DType::struct_(
@@ -1169,25 +1190,7 @@ async fn write_nullable_nested_struct() -> VortexResult<()> {
     )?
     .into_array();
 
-    let buffer: Bytes = VortexWriteOptions::default()
-        .write(vec![], array.to_array_stream())
-        .await?
-        .into();
-
-    let vxf = VortexOpenOptions::in_memory()
-        .with_dtype(array.dtype().clone())
-        .open(buffer)
-        .await?;
-
-    assert_eq!(vxf.dtype(), array.dtype());
-    assert_eq!(vxf.row_count(), 3);
-
-    let result = vxf
-        .scan()?
-        .into_array_stream()?
-        .read_all()
-        .await?
-        .to_struct()?;
+    let result = round_trip(&array, Ok).await?.to_struct()?;
 
     assert_eq!(result.len(), 3);
     assert_eq!(result.fields().len(), 1);
@@ -1200,3 +1203,21 @@ async fn write_nullable_nested_struct() -> VortexResult<()> {
 
     Ok(())
 }
+
+#[tokio::test]
+async fn scan_empty_fields() -> VortexResult<()> {
+    let array = (0..10000).collect::<PrimitiveArray>();
+
+    let result = round_trip(array.as_ref(), |scan| {
+        Ok(scan.with_projection(PackExpr::try_new_expr(
+            Default::default(),
+            vec![],
+            Nullability::Nullable,
+        )?))
+    })
+    .await?;
+
+    assert_eq!(result.len(), array.len());
+
+    Ok(())
+}