fix[file]: read the one-row pruning result in can_prune instead of re… (#8369)

## Summary

Closes: #8366

`VortexFile::can_prune` stopped pruning for every `and`/`or` and `eq`
predicate after #7575 removed bottom-up constant-folding. 

This change makes `can_prune` mirror that
read-out (execute to `Canonical`, take the row-0 scalar) and adds an
end-to-end regression test covering bare, `and`/`or`, and `eq`
predicates with non-falsifiable controls.


---------

Signed-off-by: Thomas Santerre <thomas@santerre.xyz>

Author: tomsanbear

vortex-file/src/file.rs

@@ -247,7 +247,13 @@ impl VortexFile {
         let mut ctx = self.session.create_execution_ctx();
         Ok(match applied.execute::<Columnar>(&mut ctx)? {
             Columnar::Constant(s) => s.scalar().as_bool().value() == Some(true),
-            Columnar::Canonical(_) => false,
+            Columnar::Canonical(c) => {
+                c.into_array()
+                    .execute_scalar(0, &mut ctx)?
+                    .as_bool()
+                    .value()
+                    == Some(true)
+            }
         })
     }
 

vortex-file/src/tests.rs

@@ -35,6 +35,7 @@ use vortex_array::dtype::PType::I32;
 use vortex_array::dtype::StructFields;
 use vortex_array::expr::and;
 use vortex_array::expr::cast;
+use vortex_array::expr::col;
 use vortex_array::expr::eq;
 use vortex_array::expr::get_item;
 use vortex_array::expr::gt;
@@ -1953,3 +1954,39 @@ async fn test_segment_ordering_zonemaps_after_data() -> VortexResult<()> {
 
     Ok(())
 }
+
+#[tokio::test]
+#[cfg_attr(miri, ignore)]
+async fn test_can_prune_composite_predicates() -> VortexResult<()> {
+    // Regression test for `can_prune` after `ScalarFnConstantRule` was removed
+    // (#7575): composite falsification trees no longer constant-fold during
+    // execution, so `can_prune` must read the one-row evaluated result instead
+    // of requiring a `Columnar::Constant`. `Eq` is affected too: its
+    // falsification is internally `or(min > lit, lit > max)`.
+    let st = StructArray::from_fields(&[
+        ("age", buffer![15i32, 18, 22, 25].into_array()),
+        ("price", buffer![120i32, 130, 140, 150].into_array()),
+    ])?;
+    let mut buf = ByteBufferMut::empty();
+    SESSION
+        .write_options()
+        .write(&mut buf, st.into_array().to_array_stream())
+        .await?;
+    let file = SESSION.open_options().open_buffer(buf)?;
+
+    // Bare comparisons: falsified directly by min/max stats.
+    assert!(file.can_prune(&gt(col("age"), lit(30)))?);
+    assert!(file.can_prune(&lt(col("price"), lit(100)))?);
+
+    // Composite predicates whose falsifications are boolean trees.
+    assert!(file.can_prune(&and(gt(col("age"), lit(30)), lt(col("price"), lit(100))))?);
+    assert!(file.can_prune(&or(gt(col("age"), lit(30)), lt(col("age"), lit(10))))?);
+    assert!(file.can_prune(&eq(col("age"), lit(5)))?);
+
+    // Non-falsifiable controls: rows may match, so pruning must refuse.
+    assert!(!file.can_prune(&gt(col("age"), lit(20)))?);
+    assert!(!file.can_prune(&eq(col("age"), lit(18)))?);
+    assert!(!file.can_prune(&and(gt(col("age"), lit(20)), gt(col("price"), lit(100))))?);
+
+    Ok(())
+}