fix(expr-ir): Reject Selectors that do more than select

narwhals/_plan/_guards.py

@@ -94,11 +94,8 @@ def is_into_expr_column(obj: Any) -> TypeIs[IntoExprColumn]:
     return isinstance(obj, (str, _expr().Expr, _series().Series))
 
 
-def is_column_name_or_selector(
-    obj: Any, *, allow_expr: bool = False
-) -> TypeIs[ColumnNameOrSelector]:
-    tps = (str, _selectors().Selector) if not allow_expr else (str, _expr().Expr)
-    return isinstance(obj, tps)
+def is_column_name_or_selector(obj: Any) -> TypeIs[ColumnNameOrSelector]:
+    return isinstance(obj, (str, _selectors().Selector))
 
 
 def is_compliant_series(

narwhals/_plan/_parse.py

@@ -15,7 +15,6 @@
     is_expr,
     is_into_expr_column,
     is_iterable_reject,
-    is_selector,
 )
 from narwhals._plan.common import flatten_hash_safe
 from narwhals._plan.exceptions import (
@@ -147,14 +146,12 @@ def parse_into_selector_ir(
 def _parse_into_selector(
     input: ColumnNameOrSelector | Expr, /, *, require_all: bool = True
 ) -> Selector:
-    if is_selector(input):
-        selector = input
+    if is_expr(input):
+        selector = input.meta.as_selector()
     elif isinstance(input, str):
         import narwhals._plan.selectors as cs
 
         selector = cs.by_name(input, require_all=require_all)
-    elif is_expr(input):
-        selector = input.meta.as_selector()
     else:
         msg = f"cannot turn {qualified_type_name(input)!r} into a selector"
         raise TypeError(msg)
@@ -257,14 +254,14 @@ def _parse_into_iter_selector_ir(
 
     if not _is_empty_sequence(first_input):
         if _is_iterable(first_input) and not isinstance(first_input, str):
-            if more_inputs:  # pragma: no cover
+            if more_inputs:
                 raise invalid_into_expr_error(first_input, more_inputs, {})
             else:
                 for into in first_input:  # type: ignore[var-annotated]
                     yield parse_into_selector_ir(into)
         else:
             yield parse_into_selector_ir(first_input)
-    for into in more_inputs:  # pragma: no cover
+    for into in more_inputs:
         yield parse_into_selector_ir(into)
 
 

tests/plan/compliant_test.py

@@ -7,7 +7,11 @@
 import pytest
 
 from narwhals._plan import selectors as ncs
-from narwhals.exceptions import ColumnNotFoundError, InvalidOperationError
+from narwhals.exceptions import (
+    ColumnNotFoundError,
+    InvalidIntoExprError,
+    InvalidOperationError,
+)
 
 pytest.importorskip("pyarrow")
 pytest.importorskip("numpy")
@@ -22,6 +26,7 @@
     dataframe,
     first,
     last,
+    re_compile,
     series,
 )
 
@@ -549,6 +554,12 @@ def test_drop_strict() -> None:
     assert df.drop(ncs.last(), "z", strict=False).collect_schema().names() == ["a"]
 
 
+def test_drop_invalid(data_small_dh: Data) -> None:
+    df = dataframe(data_small_dh)
+    with pytest.raises(InvalidOperationError):
+        df.drop(ncs.first().first())
+
+
 def test_drop_nulls(data_small_dh: Data) -> None:
     df = dataframe(data_small_dh)
     expected: Data = {"d": [], "e": [], "f": [], "g": [], "h": []}
@@ -575,6 +586,36 @@ def test_drop_nulls_invalid(data_small_dh: Data) -> None:
         df.drop_nulls(ncs.by_index(-999))
 
 
+def test_sort() -> None:
+    data_sort = {
+        "a": [8, 8, 1, None, 1, 1],
+        "b": [None, 0.9, 3.0, 0.9, None, None],
+        "c": [1, 1, 1, 2, 1, 2],
+        "idx": [0, 1, 2, 3, 4, 5],
+    }
+    result = dataframe(data_sort).sort(
+        ncs.first(), "c", ncs.float(), descending=[True, False, False], nulls_last=True
+    )
+    expected = {
+        "a": [8, 8, 1, 1, 1, None],
+        "b": [0.9, None, 3.0, None, None, 0.9],
+        "c": [1, 1, 1, 1, 2, 2],
+        "idx": [1, 0, 2, 4, 5, 3],
+    }
+    assert_equal_data(result, expected)
+
+
+def test_sort_invalid(data_small_dh: Data) -> None:
+    df = dataframe(data_small_dh)
+    with pytest.raises(ColumnNotFoundError):
+        df.sort(())
+    with pytest.raises(
+        InvalidIntoExprError,
+        match=re_compile(r"passing both iterable and positional inputs is not supported"),
+    ):
+        df.sort(["d"], ["e", "f"])  # type: ignore[arg-type]
+
+
 DROP_ROW_1: Data = {
     "d": [7, 8],
     "e": [9, 7],

tests/plan/frame_unique_test.py

@@ -39,16 +39,7 @@ def test_unique_invalid_keep(data: Data) -> None:
         (nwp.nth(5).meta.as_selector(), ColumnNotFoundError),
         (["a", "b", "A"], ColumnNotFoundError),
         (nwp.col("a").first(), InvalidOperationError),
-        pytest.param(
-            ncs.first().last(),
-            InvalidOperationError,
-            # TODO @dangotbanned: Fix this in another PR
-            # Need to be stricter on the Selector check
-            marks=pytest.mark.xfail(
-                reason="narwhals/_plan/_expansion.py:160: 'Last' object has no attribute 'iter_expand_names'",
-                raises=AttributeError,
-            ),
-        ),
+        (ncs.first().last(), InvalidOperationError),
     ],
 )
 def test_unique_invalid_subset(data: Data, subset: Any, err: type[Exception]) -> None: