api: make custom coeff less forceful on spacing

devito/finite_differences/tools.py

@@ -339,5 +339,8 @@ def process_weights(weights, expr, dim):
         return shape[weights.dimensions.index(wdim)], wdim, False
     else:
         # Adimensional weight from custom coeffs need to be multiplied by h^order
-        scale = not all(sympify(w).has(dim.spacing) for w in weights if w != 0)
+        if all(sympify(w).is_Number for w in weights):
+            scale = True
+        else:
+            scale = False
         return len(list(weights)), None, scale

tests/test_symbolic_coefficients.py

@@ -372,3 +372,31 @@ def test_backward_compat_mixed(self):
         assert '7.0*f(x + 3*h_x)' in str(eqe.rhs)
         assert '0.5*g(x + h_x)' in str(eqe.rhs)
         assert 'g(x + 2*h_x)' not in str(eqe.rhs)
+
+    def test_backward_compat_array_of_func(self):
+        grid = Grid(shape=(11, 11, 11))
+        x, _, _ = grid.dimensions
+        hx = x.spacing
+
+        f = Function(name='f', grid=grid, space_order=16, coefficients='symbolic')
+
+        # Define stencil coefficients.
+        weights = Function(name="w", space_order=0, shape=(9,), dimensions=(x,))
+        wdx = [weights[0]]
+        for iq in range(1, weights.shape[0]):
+            wdx.append(weights[iq])
+            wdx.insert(0, weights[iq])
+
+        # Plain numbers for comparison
+        wdxn = np.random.rand(17)
+
+        # Number with spacing
+        wdxns = wdxn / hx
+
+        dexev = f.dx(weights=wdx).evaluate
+        dexevn = f.dx(weights=wdxn).evaluate
+        dexevns = f.dx(weights=wdxns).evaluate
+
+        assert all(a.as_coefficient(1/hx) for a in dexevn.args)
+        assert all(a.as_coefficient(1/hx) for a in dexevns.args)
+        assert all(not a.as_coefficient(1/hx) for a in dexev.args)