Yanking does not use top entry in the kill ring

Question

I want to delete regions without adding them to the kill ring following this thread:

(defun backward-kill-word-no-kill-ring ()
  "Delete the previous word and remove it from the kill ring."
  (interactive)
  (backward-kill-word 1)
  (setq kill-ring (cdr kill-ring))
  )

(global-set-key (kbd "M-DEL") 'backward-kill-word-no-kill-ring)

It fails and I don't understand why. If I type abcd, copy it with Cmd-C, and yank it with C-y, Emacs inserts abcd and the kill ring, viewed with C-h v kill-ring RET, is:

(Value:
(#("abcd" 0 4
    (fontified t))
...

If I type 123, delete it with M-DEL, which calls my function, and then yank with C-y, Emacs inserts https://www.fablabs.io/labs, which I had copied 30 minutes ago and is no longer an entry in the kill ring, and the kill ring is:

Value:
(#("123" 0 3
   (fontified t))
  #("abcd" 0 4
    (fontified t))
...

Then I cut text with C-w (kill-region), yank in another buffer, and it's the same link that comes first and my cut text that comes second (after M-y).

Where does yank grab its text if not from the kill ring?

Update

Following Tobias's comment, I had save-interprogram-paste-before-kill at t, and have the same behavior when I set it to nil and start Emacs with emacs -Q. When I follow the steps above, after M-DEL of 123, Emacs inserts the last entry from the kill ring, abcd. (When I first asked the question, I may have missed that the inserted text was the last entry of the kill ring, even after searching for the string in the kill-ring information buffer.)

Further udpate

A similar question asks how to delete text without adding to the kill ring. The solution there, as the answer by Tobias here, is more elegant than my first attempt. I edited the question to understand why Emacs is using the last entry in the kill ring instead of the top entry.

Further update (10 March)

I follow the steps above with emacs -Q, copy abcd to the clipboard and yank it, copy the function and keybinding and execute it, and after M-DEL of 123, Emacs inserts the last entry from the kill ring, abcd.

The kill ring after that insertion is:

Value:
("(defun backward-kill-word-no-kill-ring ()
  \"Delete the previous word and remove it from the kill ring.\"
  (interactive)
  (backward-kill-word 1)
  (setq kill-ring (cdr kill-ring))
  )

(global-set-key (kbd \"M-DEL\") 'backward-kill-word-no-kill-ring)"
 #("abcd" 0 4
   (fontified t)))

The Emacs version is:

GNU Emacs 26.3 (build 1, x86_64-apple-darwin18.2.0, NS appkit-1671.20 Version 10.14.3 (Build 18D109)) of 2019-09-02

The values of interprogram-paste-function and interprogram-cut-function are the default ones, gui-selection-value and gui-select-text. The behavior is the same if I use M-w instead of Cmd-C to copy the first piece, abcd, to the kill ring.

Answer 1

I don't know why your kill-ring gets messed up. It might be that it is some inter-program action that modifies the kill-ring.

But the right way to implement deleting instead of killing is:

(defun delete-word (arg)
  "Delete characters forward until encountering the end of a word.
With argument ARG, do this that many times."
  (interactive "p")
  (delete-region (point) (progn (forward-word arg) (point))))

(defun backward-delete-word (arg)
  "Delete characters backward until encountering the beginning of a word.
With argument ARG, do this that many times."
  (interactive "p")
  (delete-word (- arg)))

Note, that I just copied the stuff from simple.el and replaced kill with delete.