Type mismatch causes a compiler error

[Stas Boukarev]

(defun foo (a b)
  (loop for x across (cons a b)
        sum x))
=>
The value NIL is not of type (AND ATOM (NOT NULL)).

[Stas Boukarev (stassats)]

Reduced:

(defun foo ()
  (macrolet ((x (&rest args)
               (declare (ignore args))
               a))
    (let (a)
      (declare (type vector a))
      (x #.#'list))))

[Stas Boukarev (stassats)]

In fbea35e879891723259dfa55589b498228390bb9