fix(polars): ensure t.select(col=scalar) results in len(t) rows (#…

…8665)

ibis/backends/polars/compiler.py

@@ -192,18 +192,30 @@ def project(op, **kw):
 
     selections = []
     unnests = []
+    scalars = []
     for name, arg in op.values.items():
         if isinstance(arg, ops.Unnest):
+            translated = translate(arg.arg, **kw).alias(name)
             unnests.append(name)
-            translated = translate(arg.arg, **kw)
+            selections.append(translated)
         elif isinstance(arg, ops.Value):
-            translated = translate(arg, **kw)
+            translated = translate(arg, **kw).alias(name)
+            if arg.shape.is_scalar():
+                scalars.append(translated)
+                selections.append(pl.col(name))
+            else:
+                selections.append(translated)
         else:
             raise com.TranslationError(
                 "Polars backend is unable to compile selection with "
                 f"operation type of {type(arg)}"
             )
-        selections.append(translated.alias(name))
+
+    if scalars:
+        # Scalars need to first be projected to columns with `with_columns`,
+        # otherwise if a downstream select only selects out the scalar-backed
+        # columns they'll return with only a single row.
+        lf = lf.with_columns(scalars)
 
     if selections:
         lf = lf.select(selections)

ibis/backends/tests/test_generic.py

@@ -1863,6 +1863,12 @@ def test_select_mutate_with_dict(backend):
     backend.assert_frame_equal(result, expected)
 
 
+def test_select_scalar(alltypes):
+    res = alltypes.select(y=ibis.literal(1)).limit(3).execute()
+    assert len(res.y) == 3
+    assert (res.y == 1).all()
+
+
 @pytest.mark.broken(["mssql", "oracle"], reason="incorrect syntax")
 def test_isnull_equality(con, backend, monkeypatch):
     monkeypatch.setattr(ibis.options, "default_backend", con)

ibis/backends/tests/test_temporal.py

@@ -1562,7 +1562,6 @@ def test_now(con):
     assert isinstance(result, datetime.datetime)
 
 
-@pytest.mark.notimpl(["polars"], reason="assert 1 == 5", raises=AssertionError)
 @pytest.mark.notimpl(["datafusion"], raises=com.OperationNotDefinedError)
 def test_now_from_projection(alltypes):
     n = 2
@@ -1579,9 +1578,6 @@ def test_today(con):
     assert isinstance(result, datetime.date)
 
 
-@pytest.mark.notimpl(
-    ["polars"], reason="polars fails to project literal", raises=AssertionError
-)
 def test_today_from_projection(alltypes):
     expr = alltypes.select(today=ibis.today()).limit(2).today
     ts = expr.execute()