compiler: Properly expand dimensions for array([]) with ndarray elements

This matches host NumPy behaviour (and, in either case, was
previously broken, as it still continued past the array element
type).

artiq/compiler/transforms/inferencer.py

@@ -892,7 +892,10 @@ class Inferencer(algorithm.Visitor):
                         return  # undetermined yet
                     if not builtins.is_iterable(elt) or builtins.is_str(elt):
                         break
-                    num_dims += 1
+                    if builtins.is_array(elt):
+                        num_dims += elt.find()["num_dims"].value
+                    else:
+                        num_dims += 1
                     elt = builtins.get_iterable_elt(elt)
 
                 if explicit_dtype is not None:

artiq/test/lit/integration/array.py

@@ -42,6 +42,9 @@ assert matrix[1, 0] == 4.0
 assert matrix[1, 1] == 8.0
 assert matrix[1, 2] == 6.0
 
+array_of_matrices = array([matrix, matrix])
+assert array_of_matrices.shape == (2, 2, 3)
+
 three_tensor = array([[[1.0, 2.0, 3.0], [4.0, 5.0, 6.0]]])
 assert len(three_tensor) == 1
 assert three_tensor.shape == (1, 2, 3)