Fix rust test for logical plan optimizer for categoricals pola-rs#9828

crates/polars-plan/src/logical_plan/optimizer/type_coercion/mod.rs

@@ -519,28 +519,56 @@ fn early_escape(type_self: &DataType, type_other: &DataType) -> Option<()> {
     }
 }
 
-// TODO: Fix this test and re-enable it (currently does not compile)
-// #[cfg(test)]
+#[cfg(test)]
 // #[cfg(feature = "dtype-categorical")]
-// mod test {
-//     use polars_core::prelude::*;
-
-//     use super::*;
-//     use crate::prelude::*;
-
-//     #[test]
-//     fn test_categorical_utf8() {
-//         let mut rules: Vec<Box<dyn OptimizationRule>> = vec![Box::new(TypeCoercionRule {})];
-//         let schema = Schema::from_iter([Field::new("fruits", DataType::Categorical(None))]);
-
-//         let expr = col("fruits").eq(lit("somestr"));
-//         let out = optimize_expr(expr.clone(), schema.clone(), &mut rules);
-//         // we test that the fruits column is not casted to utf8 for the comparison
-//         assert_eq!(out, expr);
-
-//         let expr = col("fruits") + (lit("somestr"));
-//         let out = optimize_expr(expr, schema, &mut rules);
-//         let expected = col("fruits").cast(DataType::Utf8) + lit("somestr");
-//         assert_eq!(out, expected);
-//     }
-// }
+mod test {
+    use polars_core::prelude::*;
+
+    use super::*;
+
+    #[test]
+    fn test_categorical_utf8() {
+        let mut expr_arena = Arena::new();
+        let mut lp_arena = Arena::new();
+        let optimizer = StackOptimizer {};
+        let rules: &mut [Box<dyn OptimizationRule>] = &mut [Box::new(TypeCoercionRule {})];
+
+        let df = DataFrame::new(Vec::from([Series::new_empty(
+            "fruits",
+            &DataType::Categorical(None),
+        )]))
+        .unwrap();
+
+        let expr_in = vec![col("fruits").eq(lit("somestr"))];
+        let lp = LogicalPlanBuilder::from_existing_df(df.clone())
+            .project(expr_in.clone(), Default::default())
+            .build();
+
+        let mut lp_top = to_alp(lp, &mut expr_arena, &mut lp_arena).unwrap();
+        lp_top = optimizer
+            .optimize_loop(rules, &mut expr_arena, &mut lp_arena, lp_top)
+            .unwrap();
+        let lp = node_to_lp(lp_top, &expr_arena, &mut lp_arena);
+
+        // we test that the fruits column is not casted to utf8 for the comparison
+        if let LogicalPlan::Projection { expr, .. } = lp {
+            assert_eq!(expr, expr_in);
+        };
+
+        let expr_in = vec![col("fruits") + (lit("somestr"))];
+        let lp = LogicalPlanBuilder::from_existing_df(df)
+            .project(expr_in, Default::default())
+            .build();
+        let mut lp_top = to_alp(lp, &mut expr_arena, &mut lp_arena).unwrap();
+        lp_top = optimizer
+            .optimize_loop(rules, &mut expr_arena, &mut lp_arena, lp_top)
+            .unwrap();
+        let lp = node_to_lp(lp_top, &expr_arena, &mut lp_arena);
+
+        // we test that the fruits column is casted to utf8 for the addition
+        let expected = vec![col("fruits").cast(DataType::Utf8) + lit("somestr")];
+        if let LogicalPlan::Projection { expr, .. } = lp {
+            assert_eq!(expr, expected);
+        };
+    }
+}