Removed an internal assertion for the optional stable value and inste… (

pytorch#117414)

…ad defaulted to the standard (=false).

Fixes pytorch#117255.
Pull Request resolved: pytorch#117414
Approved by: https://github.com/ezyang

aten/src/ATen/native/Sorting.cpp

@@ -72,9 +72,6 @@ TORCH_META_FUNC(topk)
 
 TORCH_META_FUNC2(sort, stable)
 (const Tensor& self, c10::optional<bool> stable, int64_t dim, bool descending) {
-  TORCH_INTERNAL_ASSERT(
-      stable.has_value(),
-      "sort(): c10::optional<bool> for stable has to have value.");
   maybe_wrap_dim(dim, self.dim());
 
   // See issue: https://github.com/pytorch/pytorch/issues/65863
@@ -953,7 +950,7 @@ TORCH_IMPL_FUNC(sort_stable_out)
     indices.zero_();
   } else {
     dim = maybe_wrap_dim(dim, self.dim());
-    sort_stub(self.device().type(), self, values, indices, dim, descending, stable.value());
+    sort_stub(self.device().type(), self, values, indices, dim, descending, stable.value_or(false));
   }
 }
 

test/test_sort_and_select.py

@@ -137,6 +137,13 @@ def test_sort(self, device):
             self.assertIsOrdered('descending', x, res2val, res2ind,
                                  'random with NaNs')
 
+    def test_sort_stable_none(self):
+        # Called sort with stable=None used to trigger an assertion
+        # See https://github.com/pytorch/pytorch/issues/117255
+        x = torch.ones(10)
+        y = x.sort(stable=None).values
+        self.assertTrue(torch.all(y == torch.ones(10)).item())
+
     @onlyCUDA
     def test_sort_large_slice(self, device):
         # tests direct cub path