fix: Raise if list.concat is called on a non list column

crates/polars-expr/src/dispatch/mod.rs

@@ -371,6 +371,7 @@ pub fn function_expr_to_udf(func: IRFunctionExpr) -> SpecialEq<Arc<dyn ColumnsUd
         #[cfg(feature = "fused")]
         F::Fused(op) => map_as_slice!(misc::fused, op),
         F::ConcatExpr { rechunk } => map_as_slice!(misc::concat_expr, rechunk),
+        F::ConcatList => wrap!(list::concat),
         #[cfg(feature = "cov")]
         F::Correlation { method } => map_as_slice!(misc::corr, method),
         #[cfg(feature = "peaks")]

crates/polars-plan/dsl-schema-hashes.json

@@ -66,7 +66,7 @@
   "FileSinkOptions": "edebcf5e3965add5e4fd1be14ca6bdddc55fa22e6e829dca04beb321de0c992c",
   "FileWriteFormat": "1a685aba7dd5d6c0aefc99a9060d1b57f166ea44ef57ad0d0d0c565dbabda811",
   "FillNullStrategy": "459a9a9702415f9ca9e5218bb573609a60291e73162c38fbc046c97feb1b7500",
-  "FunctionExpr": "1b723aff4de79571f7263b470de2d4bfb9f1204ae91c7e5e09b37f66bc27875c",
+  "FunctionExpr": "04d59b9375612be6a620c3d3b8e9f7eeb4c4f8896e098e3abedb9336ff8694bf",
   "FunctionFlags": "54fd84a1b628c426b8d0f5e9bca174093e07da8992a9a9bb4c191d07133e0046",
   "FunctionOptions": "0784524479a30a7d91b890b03feac9eca6c46d04f0a7c3f4a9a2d827c3e34b5e",
   "GroupbyOptions": "0cda61fc19eb9866157ae4afeed3dc018294aaea5f02692b085885de771bfcdb",

crates/polars-plan/src/dsl/function_expr/mod.rs

@@ -265,6 +265,7 @@ pub enum FunctionExpr {
     UpperBound,
     LowerBound,
     ConcatExpr(bool),
+    ConcatList,
     #[cfg(feature = "cov")]
     Correlation {
         method: correlation::CorrelationMethod,
@@ -596,6 +597,7 @@ impl Hash for FunctionExpr {
             UpperBound => {},
             LowerBound => {},
             ConcatExpr(rechunk) => rechunk.hash(state),
+            ConcatList => {},
             #[cfg(feature = "peaks")]
             PeakMin => {},
             #[cfg(feature = "peaks")]
@@ -834,6 +836,7 @@ impl Display for FunctionExpr {
             UpperBound => "upper_bound",
             LowerBound => "lower_bound",
             ConcatExpr(..) => "concat_expr",
+            ConcatList => "concat_list",
             #[cfg(feature = "cov")]
             Correlation { method, .. } => return Display::fmt(method, f),
             #[cfg(feature = "peaks")]

crates/polars-plan/src/dsl/functions/concat.rs

@@ -112,7 +112,7 @@ pub fn concat_list<E: AsRef<[IE]>, IE: Into<Expr> + Clone>(s: E) -> PolarsResult
 
     Ok(Expr::Function {
         input: s,
-        function: FunctionExpr::ListExpr(ListFunction::Concat),
+        function: FunctionExpr::ConcatList,
     })
 }
 

crates/polars-plan/src/dsl/functions/mod.rs

@@ -52,7 +52,6 @@ pub use temporal::*;
 
 #[cfg(feature = "arg_where")]
 use crate::dsl::function_expr::FunctionExpr;
-use crate::dsl::function_expr::ListFunction;
 #[cfg(all(feature = "concat_str", feature = "strings"))]
 use crate::dsl::function_expr::StringFunction;
 use crate::dsl::*;

crates/polars-plan/src/dsl/list.rs

@@ -296,6 +296,17 @@ impl ListNameSpace {
         }
     }
 
+    /// Concatenate the list with another list.
+    pub fn concat<E: AsRef<[IE]>, IE: Into<Expr> + Clone>(self, other: E) -> Expr {
+        let mut input: Vec<_> = other.as_ref().iter().map(|e| e.clone().into()).collect();
+        input.insert(0, self.0);
+
+        Expr::Function {
+            input,
+            function: FunctionExpr::ListExpr(ListFunction::Concat),
+        }
+    }
+
     pub fn agg<E: Into<Expr>>(self, other: E) -> Expr {
         Expr::Eval {
             expr: Arc::new(self.0),

crates/polars-plan/src/plans/aexpr/function_expr/list.rs

@@ -73,7 +73,7 @@ impl IRListFunction {
     pub(super) fn get_field(&self, mapper: FieldsMapper) -> PolarsResult<Field> {
         use IRListFunction::*;
         match self {
-            Concat => mapper.map_to_list_supertype(),
+            Concat => mapper.ensure_is_list()?.map_to_list_supertype(),
             #[cfg(feature = "is_in")]
             Contains { nulls_equal: _ } => mapper.ensure_is_list()?.with_dtype(DataType::Boolean),
             #[cfg(feature = "list_drop_nulls")]

crates/polars-plan/src/plans/aexpr/function_expr/mod.rs

@@ -277,6 +277,7 @@ pub enum IRFunctionExpr {
     ConcatExpr {
         rechunk: bool,
     },
+    ConcatList,
     #[cfg(feature = "cov")]
     Correlation {
         method: correlation::IRCorrelationMethod,
@@ -613,6 +614,7 @@ impl Hash for IRFunctionExpr {
             #[cfg(feature = "round_series")]
             Ceil => {},
             ConcatExpr { rechunk } => rechunk.hash(state),
+            ConcatList => {},
             #[cfg(feature = "peaks")]
             PeakMin => {},
             #[cfg(feature = "peaks")]
@@ -853,6 +855,7 @@ impl Display for IRFunctionExpr {
             #[cfg(feature = "fused")]
             Fused(fused) => return Display::fmt(fused, f),
             ConcatExpr { .. } => "concat_expr",
+            ConcatList => "concat_list",
             #[cfg(feature = "cov")]
             Correlation { method, .. } => return Display::fmt(method, f),
             #[cfg(feature = "peaks")]
@@ -1172,6 +1175,8 @@ impl IRFunctionExpr {
             F::ConcatExpr { .. } => FunctionOptions::groupwise()
                 .with_flags(|f| f | FunctionFlags::INPUT_WILDCARD_EXPANSION)
                 .with_supertyping(Default::default()),
+            F::ConcatList => FunctionOptions::elementwise()
+                .with_flags(|f| f | FunctionFlags::INPUT_WILDCARD_EXPANSION),
             #[cfg(feature = "cov")]
             F::Correlation { .. } => {
                 FunctionOptions::aggregation().with_supertyping(Default::default())

crates/polars-plan/src/plans/aexpr/function_expr/schema.rs

@@ -285,6 +285,7 @@ impl IRFunctionExpr {
             #[cfg(feature = "fused")]
             Fused(_) => mapper.map_to_supertype(),
             ConcatExpr { .. } => mapper.map_to_supertype(),
+            ConcatList => mapper.map_to_list_supertype(),
             #[cfg(feature = "cov")]
             Correlation { .. } => mapper.map_to_float_dtype(),
             #[cfg(feature = "peaks")]

crates/polars-plan/src/plans/conversion/dsl_to_ir/expr_expansion.rs

@@ -82,6 +82,7 @@ fn function_input_wildcard_expansion(function: &FunctionExpr) -> FunctionExpansi
             | F::Coalesce
             | F::ListExpr(ListFunction::Concat)
             | F::ConcatExpr(..)
+            | F::ConcatList
             | F::MinHorizontal
             | F::MaxHorizontal
             | F::FoldHorizontal { .. }

crates/polars-plan/src/plans/conversion/dsl_to_ir/functions.rs

@@ -914,6 +914,7 @@ pub(super) fn convert_functions(
             ));
         },
         F::ConcatExpr(rechunk) => I::ConcatExpr { rechunk },
+        F::ConcatList => I::ConcatList,
         #[cfg(feature = "cov")]
         F::Correlation { method } => {
             use CorrelationMethod as C;

crates/polars-plan/src/plans/conversion/ir_to_dsl.rs

@@ -1024,6 +1024,7 @@ pub fn ir_function_to_dsl(input: Vec<Expr>, function: IRFunctionExpr) -> Expr {
             };
         },
         IF::ConcatExpr { rechunk } => F::ConcatExpr(rechunk),
+        IF::ConcatList => F::ConcatList,
         #[cfg(feature = "cov")]
         IF::Correlation { method } => {
             use CorrelationMethod as C;

crates/polars-python/src/expr/list.rs

@@ -39,6 +39,11 @@ impl PyExpr {
         self.inner.clone().list().eval(expr.inner).into()
     }
 
+    fn list_concat(&self, other: Vec<PyExpr>) -> Self {
+        let other: Vec<_> = other.into_iter().map(|e| e.inner).collect();
+        self.inner.clone().list().concat(&other).into()
+    }
+
     fn list_agg(&self, expr: PyExpr) -> Self {
         self.inner.clone().list().agg(expr.inner).into()
     }

crates/polars-python/src/lazyframe/visitor/expr_nodes.rs

@@ -1352,6 +1352,9 @@ pub(crate) fn into_py(py: Python<'_>, expr: &AExpr) -> PyResult<Py<PyAny>> {
                 IRFunctionExpr::ConcatExpr { .. } => {
                     return Err(PyNotImplementedError::new_err("concat expr"));
                 },
+                IRFunctionExpr::ConcatList => {
+                    return Err(PyNotImplementedError::new_err("concat list"));
+                },
                 IRFunctionExpr::Correlation { .. } => {
                     return Err(PyNotImplementedError::new_err("corr"));
                 },

py-polars/src/polars/_plr.pyi

@@ -1592,6 +1592,7 @@ class PyExpr:
     def list_count_matches(self, expr: PyExpr) -> PyExpr: ...
     def list_diff(self, n: int, null_behavior: NullBehavior) -> PyExpr: ...
     def list_eval(self, expr: PyExpr, _parallel: bool) -> PyExpr: ...
+    def list_concat(self, other: list[PyExpr]) -> PyExpr: ...
     def list_agg(self, expr: PyExpr) -> PyExpr: ...
     def list_filter(self, predicate: PyExpr) -> PyExpr: ...
     def list_get(self, index: PyExpr, null_on_oob: bool) -> PyExpr: ...

py-polars/src/polars/expr/list.py

@@ -530,8 +530,8 @@ def concat(self, other: list[Expr | str] | Expr | str | Series | list[Any]) -> E
         other_list: list[Expr | str | Series]
         other_list = [other] if not isinstance(other, list) else copy.copy(other)  # type: ignore[arg-type]
 
-        other_list.insert(0, wrap_expr(self._pyexpr))
-        return F.concat_list(other_list)
+        other_exprs = [parse_into_expression(e) for e in other_list]
+        return wrap_expr(self._pyexpr.list_concat(other_exprs))
 
     def get(
         self,

py-polars/tests/unit/datatypes/test_temporal.py

@@ -1088,12 +1088,6 @@ def test_from_dict_tu_consistency() -> None:
 def test_date_arr_concat() -> None:
     expected = {"d": [[date(2000, 1, 1), date(2000, 1, 1)]]}
 
-    # type date
-    df = pl.DataFrame({"d": [date(2000, 1, 1)]})
-    assert (
-        df.select(pl.col("d").list.concat(pl.col("d"))).to_dict(as_series=False)
-        == expected
-    )
     # type list[date]
     df = pl.DataFrame({"d": [[date(2000, 1, 1)]]})
     assert (

py-polars/tests/unit/operations/namespaces/list/test_list.py

@@ -1362,3 +1362,14 @@ def test_list_sample_fraction_boundary_values_22024() -> None:
     s.list.sample(fraction=0.0)
     s.list.sample(fraction=1.0)
     s.list.sample(fraction=pl.Series([0.0, 1.0]))
+
+
+def test_list_concat_on_non_list_raises_25649() -> None:
+    """Test that list.concat on a non-list column raises during schema collection."""
+    lf = pl.LazyFrame({"a": ["a", "b", "c"], "b": [1, 2, 3]})
+
+    with pytest.raises(
+        InvalidOperationError,
+        match="expected List data type for list operation",
+    ):
+        lf.select(pl.col("a").list.concat(["a", "b"])).collect_schema()