Better cast errors (#4436)

Without this PR it just shows: `Error: Vortex error: Cannot cast array
with invalid values to non-nullable type.` - super hard to understand
what columns are involved

---------

Signed-off-by: blaginin <[email protected]>

Author: blaginin

vortex-expr/src/exprs/cast.rs

@@ -81,7 +81,13 @@ impl VTable for CastVTable {
 
     fn evaluate(expr: &Self::Expr, scope: &Scope) -> VortexResult<ArrayRef> {
         let array = expr.child.evaluate(scope)?;
-        compute_cast(&array, &expr.target)
+        compute_cast(&array, &expr.target).map_err(|e| {
+            e.with_context(format!(
+                "Failed to cast array of dtype {} to {}",
+                array.dtype(),
+                expr.target
+            ))
+        })
     }
 
     fn return_dtype(expr: &Self::Expr, _scope: &DType) -> VortexResult<DType> {

vortex-expr/src/exprs/pack.rs

@@ -107,7 +107,12 @@ impl VTable for PackVTable {
         let value_arrays = expr
             .values
             .iter()
-            .map(|value_expr| value_expr.unchecked_evaluate(scope))
+            .zip_eq(expr.names.iter())
+            .map(|(value_expr, name)| {
+                value_expr
+                    .unchecked_evaluate(scope)
+                    .map_err(|e| e.with_context(format!("Can't evaluate '{name}'")))
+            })
             .process_results(|it| it.collect::<Vec<_>>())?;
         let validity = match expr.nullability {
             Nullability::NonNullable => Validity::NonNullable,