Hi all,

With the introduction of native records ert lost the ability to peek inside structures when comparing unequal values:

(require 'ert)
(cl-defstruct xyz a b c)
(defvar xyz123 (make-xyz :a 1 :b 2 :c 3))
(defvar xyz143 (make-xyz :a 1 :b 4 :c 3))
(should (equal xyz123 xyz143))

Emacs 25 said this:

Test failed: ((should (equal xyz123 xyz143)) 
  :form (equal [cl-struct-xyz 1 2 3 nil] [cl-struct-xyz 1 4 3 nil]) 
  :value nil
  :explanation (array-elt 2 (different-atoms (2 "#x2" "?") (4 "#x4" "?"))))

Emacs 26 says this:

Test failed: ((should (equal xyz123 xyz143))
  :form (equal #s(xyz 1 2 3) #s(xyz 1 4 3))
  :value nil 
  :explanation (different-atoms #s(xyz 1 2 3) #s(xyz 1 4 3)))

The first attached patch fixes this for all records.  The second patch adds special support for cl-structs, to get this:

Test failed: ((should (equal xyz123 xyz143)) 
  :form (equal #s(xyz 1 2 3) #s(xyz 1 4 3))
  :value nil
  :explanation (struct-field c (different-atoms (2 "#x2" "?") (4 "#x4" "?"))))

Clément.