Fix BaseForm.__add__ simplification of Zero

Author: nbouziani

test/test_duals.py

@@ -101,6 +101,9 @@ def test_addition():
     V = FunctionSpace(domain_2d, f_2d)
     V_dual = V.dual()
 
+    fvector_2d = FiniteElement("Lagrange", triangle, 1, (2, ), identity_pullback, H1)
+    W = FunctionSpace(domain_2d, fvector_2d)
+
     u = TrialFunction(V)
     v = TestFunction(V)
 
@@ -132,6 +135,11 @@ def test_addition():
     res -= ZeroBaseForm((v,))
     assert res == L
 
+    # Simplification with respect to ufl.Zero
+    a_W = Matrix(W, W)
+    res = a_W + Zero(W.ufl_element().value_shape)
+    assert res == a_W
+
 
 def test_scalar_mult():
     domain_2d = Mesh(FiniteElement("Lagrange", triangle, 1, (2, ), identity_pullback, H1))

ufl/form.py

@@ -137,7 +137,7 @@ def __add__(self, other):
         if isinstance(other, (int, float)) and other == 0:
             # Allow adding 0 or 0.0 as a no-op, needed for sum([a,b])
             return self
-        elif isinstance(other, Zero) and not (other.ufl_shape or other.ufl_free_indices):
+        elif isinstance(other, Zero):
             # Allow adding ufl Zero as a no-op, needed for sum([a,b])
             return self