fix(rewrite): Handle sum of empty make vector

Author: aseyboldt

pytensor/tensor/rewriting/basic.py

@@ -980,7 +980,14 @@ def local_sum_make_vector(fgraph, node):
     elements = array.owner.inputs
     acc_dtype = node.op.acc_dtype
     out_dtype = node.op.dtype
-    element_sum = cast(add(*[cast(value, acc_dtype) for value in elements]), out_dtype)
+    if len(elements) == 0:
+        element_sum = zeros(dtype=out_dtype, shape=())
+    elif len(elements) == 1:
+        element_sum = cast(elements[0], out_dtype)
+    else:
+        element_sum = cast(
+            add(*[cast(value, acc_dtype) for value in elements]), out_dtype
+        )
 
     return [element_sum]
 

tests/tensor/rewriting/test_basic.py

@@ -1321,6 +1321,23 @@ def test_local_sum_make_vector():
     for var in between:
         assert (var.owner is None) or (not isinstance(var.owner.op, Sum))
 
+    # Check empty MakeVector
+    mv = MakeVector(config.floatX)
+    output = mv().sum()
+
+    output = rewrite_graph(output)
+    between = vars_between([a, b, c], [output])
+    for var in between:
+        assert (var.owner is None) or (not isinstance(var.owner.op, Sum))
+
+    mv = MakeVector(config.floatX)
+    output = mv(a).sum()
+
+    output = rewrite_graph(output)
+    between = vars_between([a, b, c], [output])
+    for var in between:
+        assert (var.owner is None) or (not isinstance(var.owner.op, Sum))
+
 
 @pytest.mark.parametrize(
     "dtype",