fix: binary operations in aggregation context on literals (pola-rs#12430

)

crates/polars-lazy/src/physical_plan/expressions/binary.rs

@@ -114,9 +114,13 @@ impl BinaryExpr {
         let left_s = ac_l.series().rechunk();
         let right_s = ac_r.series().rechunk();
         let res_s = apply_operator(&left_s, &right_s, self.op)?;
-        let ca = ListChunked::full(&name, &res_s, ac_l.groups.len());
         ac_l.with_update_groups(UpdateGroups::WithSeriesLen);
-        ac_l.with_series(ca.into_series(), true, Some(&self.expr))?;
+        let res_s = if res_s.len() == 1 {
+            res_s.new_from_index(0, ac_l.groups.len())
+        } else {
+            ListChunked::full(&name, &res_s, ac_l.groups.len()).into_series()
+        };
+        ac_l.with_series(res_s, true, Some(&self.expr))?;
         Ok(ac_l)
     }
 

py-polars/tests/unit/operations/test_aggregations.py

@@ -315,3 +315,16 @@ def test_first_last_unit_length_12363() -> None:
         "a_last": [2],
         "b_last": [None],
     }
+
+
+def test_binary_op_agg_context_no_simplify_expr_12423() -> None:
+    expect = pl.DataFrame({"x": [1], "y": [1]}, schema={"x": pl.Int64, "y": pl.Int32})
+
+    for simplify_expression in (True, False):
+        assert_frame_equal(
+            expect,
+            pl.LazyFrame({"x": [1]})
+            .group_by("x")
+            .agg(y=pl.lit(1) * pl.lit(1))
+            .collect(simplify_expression=simplify_expression),
+        )