Set item bug fix (#879)

* set item shaping bug fix

* Add extra tests

python/src/indexing.cpp

@@ -196,6 +196,7 @@ auto mlx_expand_ellipsis(
   int non_none_indices_after = 0;
   std::vector<nb::object> r_indices;
   int i = 0;
+  bool has_ellipsis = false;
 
   // Start from dimension 0 till we hit an ellipsis
   for (; i < entries.size(); i++) {
@@ -208,6 +209,7 @@ auto mlx_expand_ellipsis(
       indices.push_back(idx);
       non_none_indices_before += !idx.is_none();
     } else {
+      has_ellipsis = true;
       break;
     }
   }
@@ -231,12 +233,14 @@ auto mlx_expand_ellipsis(
   int non_none_indices = non_none_indices_before + non_none_indices_after;
 
   // Expand ellipsis
+  if (has_ellipsis) {
     for (int axis = non_none_indices_before;
          axis < shape.size() - non_none_indices_after;
          axis++) {
       indices.push_back(nb::slice(0, shape[axis], 1));
       non_none_indices++;
     }
+  }
 
   // Insert indices collected after the ellipsis
   indices.insert(indices.end(), r_indices.rbegin(), r_indices.rend());
@@ -409,6 +413,10 @@ array mlx_get_item_nd(array src, const nb::tuple& entries) {
         out_shape.push_back(src.shape(axis++));
       }
     }
+
+    out_shape.insert(
+        out_shape.end(), src.shape().begin() + axis, src.shape().end());
+
     src = reshape(src, out_shape);
   }
 
@@ -580,6 +588,7 @@ std::tuple<std::vector<array>, array, std::vector<int>> mlx_scatter_args_nd(
   int num_slices = 0;
   int num_arrays = 0;
   int num_strided_slices = 0;
+  int num_simple_slices_post = 0;
   {
     bool have_array = false;
     bool have_non_array = false;
@@ -595,6 +604,7 @@ std::tuple<std::vector<array>, array, std::vector<int>> mlx_scatter_args_nd(
         auto slice = nb::cast<nb::slice>(idx);
         int stride = get_slice_int(nb::getattr(slice, "step"), 1);
         num_strided_slices += (stride != 1);
+        num_simple_slices_post += (stride == 1);
 
       } else if (nb::isinstance<array>(idx)) {
         have_array = true;
@@ -603,16 +613,17 @@ std::tuple<std::vector<array>, array, std::vector<int>> mlx_scatter_args_nd(
         }
         max_dim = std::max(nb::cast<array>(idx).ndim(), max_dim);
         num_arrays++;
+        num_simple_slices_post = 0;
       }
     }
   }
 
   // We have index dims for the arrays, strided slices (implemented as arrays),
   // none
-  int idx_ndim = max_dim + num_strided_slices + num_none;
+  int idx_ndim = max_dim + num_none + num_slices - num_simple_slices_post;
 
   // If we have simple non-strided slices, we also attach an index for that
-  idx_ndim += (num_slices < num_strided_slices);
+  idx_ndim = idx_ndim == 0 ? 1 : idx_ndim;
 
   // Go over each index type and translate to the needed scatter args
   std::vector<array> arr_indices;
@@ -639,22 +650,27 @@ std::tuple<std::vector<array>, array, std::vector<int>> mlx_scatter_args_nd(
       std::vector<int> idx_shape(idx_ndim, 1);
 
       // If it's a simple slice, we only need to add the start index
-      if (stride == 1) {
+      if (array_num >= num_arrays && num_strided_slices <= 0 && stride == 1) {
         auto idx = array({start}, idx_shape, uint32);
         slice_shapes.push_back(end - start);
         arr_indices.push_back(idx);
+
+        // Add the shape to the update
+        update_shape[ax - 1] = slice_shapes.back();
       }
       // Otherwise we expand the slice into indices using arange
       else {
         auto idx = arange(start, end, stride, uint32);
         auto loc = slice_num + (arrays_first ? max_dim : 0);
-        slice_num++;
         idx_shape[loc] = idx.size();
-        slice_shapes.push_back(idx.size());
         arr_indices.push_back(reshape(idx, idx_shape));
-      }
+
+        slice_num++;
+        num_strided_slices--;
+
         // Add the shape to the update
-      update_shape[ax - 1] = slice_shapes.back();
+        update_shape[ax - 1] = 1;
+      }
     } else if (nb::isinstance<nb::int_>(pyidx)) {
       // Add index to arrays
       arr_indices.push_back(get_int_index(pyidx, src.shape(ax++)));

python/tests/test_array.py

@@ -1058,6 +1058,29 @@ class TestArray(mlx_tests.MLXTestCase):
         a[2:-2, 2:-2] = 4
         self.assertEqual(a[2, 2].item(), 4)
 
+        # Check slice array slice
+        check_slices(
+            np.zeros((5, 4, 4)),
+            np.arange(4 * 2 * 3).reshape(4, 2, 3),
+            slice(0, 4),
+            np.array([1, 3]),
+            slice(None, -1),
+        )
+        check_slices(
+            np.zeros((5, 4, 4)),
+            np.arange(4 * 2 * 2).reshape(4, 2, 2),
+            slice(0, 4),
+            np.array([1, 3]),
+            slice(0, 4, 2),
+        )
+
+        check_slices(
+            np.zeros((1, 10, 4)),
+            np.arange(2 * 4).reshape(1, 2, 4),
+            slice(None, None, None),
+            np.array([1, 3]),
+        )
+
     def test_array_at(self):
         a = mx.array(1)
         a = a.at[None].add(1)