Improve static output shape of AdvancedSubtensor1

pytensor/tensor/subtensor.py

@@ -1992,8 +1992,7 @@ class AdvancedSubtensor1(COp):
             raise TypeError("index must be vector")
         if x_.type.ndim == 0:
             raise TypeError("cannot index into a scalar")
-        out_shape = (ilist_.type.shape[0],) + x_.type.shape[1:]
-        out_shape = tuple(1 if s == 1 else None for s in out_shape)
+        out_shape = (ilist_.type.shape[0], *x_.type.shape[1:])
         return Apply(self, [x_, ilist_], [TensorType(dtype=x.dtype, shape=out_shape)()])
 
     def perform(self, node, inp, out_):

tests/tensor/test_subtensor.py

@@ -34,6 +34,7 @@ from pytensor.tensor.subtensor import (
     advanced_inc_subtensor1,
     advanced_set_subtensor,
     advanced_set_subtensor1,
+    advanced_subtensor1,
     as_index_literal,
     basic_shape,
     get_canonical_form_slice,
@@ -2707,12 +2708,26 @@ def test_index_vars_to_types():
         [(7, 13), (slice(None, None, 2), slice(-1, 1, -1)), (4, 11)],
     ],
 )
-def test_static_shapes(x_shape, indices, expected):
+def test_subtensor_static_shapes(x_shape, indices, expected):
     x = ptb.tensor(dtype="float64", shape=x_shape)
     y = x[indices]
     assert y.type.shape == expected
 
 
+@pytest.mark.parametrize(
+    "x_shape, indices, expected",
+    [
+        [(None, 5, None, 3), vector(shape=(1,)), (1, 5, None, 3)],
+        [(None, 5, None, 3), vector(shape=(2,)), (2, 5, None, 3)],
+        [(None, 5, None, 3), vector(shape=(None,)), (None, 5, None, 3)],
+    ],
+)
+def test_advanced_subtensor1_static_shapes(x_shape, indices, expected):
+    x = ptb.tensor(dtype="float64", shape=x_shape)
+    y = advanced_subtensor1(x, indices.astype(int))
+    assert y.type.shape == expected
+
+
 def test_vectorize_subtensor_without_batch_indices():
     signature = "(t1,t2,t3),()->(t1,t3)"