bug#55149: 29.0.50; Commit f30625943e broke magit/with-editor

[Tassilo Horn <thorn@fastmail.fm>]

Juri Linkov <juri@linkov.net> writes:

> I have the same problem, and distilled it to the shortest test case:
>
> ```
> (defun testa ()
>   1)
>
> (advice-add 'testa :after
>             (lambda (&rest _) 2))
>
> (defun testb ()
>   (interactive)
>   (message "! %S" (testa)))
> ```
>
> In 28 it returns 1.
> In 29 it returns 2.
>
> The regression is that the return value of :after now overrides
> the return value of the original function.

Oh, indeed.  But isn't that exactly as documented for add-function?

 :after (lambda (&rest r) (apply OLDFUN r) (apply FUNCTION r))

Of course, we'd rather want

 :after (lambda (&rest r) (prog1 (apply OLDFUN r) (apply FUNCTION r)))

Bye,
Tassilo