feat[vortex-expr]: better debug print (#5374)

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

Author: joseph-isaacs

vortex-array/src/expr/expression.rs

@@ -3,7 +3,7 @@
 
 use std::any::Any;
 use std::fmt;
-use std::fmt::{Display, Formatter};
+use std::fmt::{Debug, Display, Formatter};
 use std::hash::{Hash, Hasher};
 use std::sync::Arc;
 
@@ -18,7 +18,7 @@ use crate::expr::{ChildName, ExprId, ExprVTable, ExpressionView, StatsCatalog, V
 ///
 /// Expressions represent scalar computations that can be performed on data. Each
 /// expression consists of an encoding (vtable), heap-allocated metadata, and child expressions.
-#[derive(Clone, Debug)]
+#[derive(Clone)]
 pub struct Expression {
     /// The vtable for this expression.
     vtable: ExprVTable,
@@ -270,6 +270,33 @@ impl Display for Expression {
     }
 }
 
+struct FormatExpressionData<'a> {
+    vtable: &'a ExprVTable,
+    data: &'a Arc<dyn Any + Send + Sync>,
+}
+
+impl<'a> Debug for FormatExpressionData<'a> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        self.vtable.as_dyn().fmt_data(self.data.as_ref(), f)
+    }
+}
+
+impl Debug for Expression {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Expression")
+            .field("vtable", &self.vtable)
+            .field(
+                "data",
+                &FormatExpressionData {
+                    vtable: &self.vtable,
+                    data: &self.data,
+                },
+            )
+            .field("children", &self.children)
+            .finish()
+    }
+}
+
 impl PartialEq for Expression {
     fn eq(&self, other: &Self) -> bool {
         self.vtable.as_dyn().id() == other.vtable.as_dyn().id()

vortex-array/src/expr/exprs/binary.rs

@@ -587,4 +587,19 @@ mod tests {
             DType::Bool(Nullability::Nullable)
         );
     }
+
+    #[test]
+    fn test_debug_print() {
+        let expr = gt(lit(1), lit(2));
+        assert_eq!(
+            format!("{expr:?}"),
+            "Expression { vtable: vortex.binary, data: >, children: [Expression { vtable: vortex.literal, data: 1i32, children: [] }, Expression { vtable: vortex.literal, data: 2i32, children: [] }] }"
+        );
+    }
+
+    #[test]
+    fn test_display_print() {
+        let expr = gt(lit(1), lit(2));
+        assert_eq!(format!("{expr}"), "(1i32 > 2i32)");
+    }
 }