Fix broken code on canonicalising slices

Author: Dhruvanshu-Joshi

pytensor/tensor/rewriting/subtensor.py

@@ -398,7 +398,7 @@ def local_replace_slice(fgraph, node):
     x = node.inputs[0]
 
     if not idxs:
-        return [x]
+        return
 
     new_idxs = list(idxs)
     idx_flag = False
@@ -433,7 +433,12 @@ def local_replace_slice(fgraph, node):
             raise AssertionError(
                 f"The type of the returned variable {x[tuple(new_idxs)].type} did not match with the type of the original variable {node.outputs[0].type}"
             )
-        return [x[tuple(new_idxs)]]
+
+        out = x[tuple(new_idxs)]
+        # Copy over previous output stacktrace
+        copy_stack_trace(node.outputs, out)
+
+        return [out]
 
 
 # fast_compile to allow opt subtensor(cast{float32}(make_vector))