fix[rust]: fix is_in empty list (#4640)

polars/polars-lazy/src/dsl/function_expr/is_in.rs

@@ -3,6 +3,7 @@ use super::*;
 pub(super) fn is_in(s: &mut [Series]) -> Result<Series> {
     let left = &s[0];
     let other = &s[1];
+    dbg!(left, other);
 
     left.is_in(other).map(|ca| ca.into_series())
 }

polars/polars-lazy/src/dsl/mod.rs

@@ -1399,14 +1399,16 @@ impl Expr {
     pub fn is_in<E: Into<Expr>>(self, other: E) -> Self {
         let other = other.into();
         let has_literal = has_root_literal_expr(&other);
-        if has_literal {
-            if let Expr::Literal(LiteralValue::Series(s)) = &other {
-                // nothing is in an empty list return all False
-                if s.is_empty() {
-                    return Expr::Literal(LiteralValue::Boolean(false));
-                }
+        if has_literal
+            && match &other {
+                Expr::Literal(LiteralValue::Series(s)) if s.is_empty() => true,
+                Expr::Literal(LiteralValue::Null) => true,
+                _ => false,
             }
+        {
+            return Expr::Literal(LiteralValue::Boolean(false));
         }
+
         let arguments = &[other];
         // we don't have to apply on groups, so this is faster
         if has_literal {

py-polars/tests/test_lists.py

@@ -432,5 +432,18 @@ def test_list_eval_type_coercion() -> None:
     ).to_dict(False) == {"col_last": [[3]]}
 
 
-def test_is_empty_list_4559() -> None:
+def test_is_in_empty_list_4559() -> None:
     assert pl.Series(["a"]).is_in([]).to_list() == [False]
+
+
+def test_is_in_empty_list_4639() -> None:
+    df = pl.DataFrame({"a": [1, None]})
+    empty_list: list[int] = []
+
+    assert df.with_columns([pl.col("a").is_in(empty_list).alias("a_in_list")]).to_dict(
+        False
+    ) == {"a": [1, None], "a_in_list": [False, False]}
+    df = pl.DataFrame()
+    assert df.with_columns(
+        [pl.lit(None).cast(pl.Int64).is_in(empty_list).alias("in_empty_list")]
+    ).to_dict(False) == {"in_empty_list": [False]}