fix build w/ flatten (#195)

mlx/ops.cpp

@@ -283,21 +283,36 @@ array flatten(
     int end_axis /* = -1 */,
     StreamOrDevice s /* = {} */) {
   auto ndim = static_cast<int>(a.ndim());
-  start_axis += (start_axis < 0 ? ndim : 0);
-  end_axis += (end_axis < 0 ? ndim + 1 : 0);
-  start_axis = std::max(0, start_axis);
-  end_axis = std::min(ndim, end_axis);
-  if (end_axis < start_axis) {
+  auto start_ax = start_axis + (start_axis < 0 ? ndim : 0);
+  auto end_ax = end_axis + (end_axis < 0 ? ndim : 0);
+  start_ax = std::max(0, start_ax);
+  end_ax = std::min(ndim - 1, end_ax);
+  if (a.ndim() == 0) {
+    return reshape(a, {1}, s);
+  }
+  if (end_ax < start_ax) {
     throw std::invalid_argument(
         "[flatten] start_axis must be less than or equal to end_axis");
   }
-  if (start_axis == end_axis and a.ndim() != 0) {
+  if (start_ax >= ndim) {
+    std::ostringstream msg;
+    msg << "[flatten] Invalid start_axis " << start_axis << " for array with "
+        << ndim << " dimensions.";
+    throw std::invalid_argument(msg.str());
+  }
+  if (end_ax < 0) {
+    std::ostringstream msg;
+    msg << "[flatten] Invalid end_axis " << end_axis << " for array with "
+        << ndim << " dimensions.";
+    throw std::invalid_argument(msg.str());
+  }
+  if (start_ax == end_ax) {
     return a;
   }
-  std::vector<int> new_shape(a.shape().begin(), a.shape().begin() + start_axis);
+  std::vector<int> new_shape(a.shape().begin(), a.shape().begin() + start_ax);
   new_shape.push_back(-1);
   new_shape.insert(
-      new_shape.end(), a.shape().begin() + end_axis + 1, a.shape().end());
+      new_shape.end(), a.shape().begin() + end_ax + 1, a.shape().end());
   return reshape(a, new_shape, s);
 }
 

python/tests/test_array.py

@@ -906,7 +906,7 @@ class TestArray(mlx_tests.MLXTestCase):
         # Check slice assign with negative indices works
         a = mx.zeros((5, 5), mx.int32)
         a[2:-2, 2:-2] = 4
-        self.assertEquals(a[2, 2].item(), 4)
+        self.assertEqual(a[2, 2].item(), 4)
 
     def test_slice_negative_step(self):
         a_np = np.arange(20)

tests/ops_tests.cpp

@@ -73,6 +73,12 @@ TEST_CASE("test flatten") {
   // Check start > end throws
   CHECK_THROWS(flatten(x, 2, 1));
 
+  // Check start >= ndim throws
+  CHECK_THROWS(flatten(x, 5, 6));
+
+  // Check end < 0 throws
+  CHECK_THROWS(flatten(x, -5, -4));
+
   // Check scalar flattens to 1D
   x = array(1);
   CHECK_EQ(flatten(x, -3, -1).shape(), std::vector<int>({1}));