bug#55412: 28.1; In Emacs 28.1, using ':eval' in 'frame-title-format' doesn't work properly

[martin rudalics]

> ;;; In Emacs 28.1, using ':eval' in 'frame-title-format' doesn't work like it
> ;;; used to in Emacs 27 and earlier. In fact, it is completely broken, if one
> ;;; uses a frame-parameter in ':eval'.
> ;;;
> ;;; The following elisp snippet demonstrates the problem in an Emacs 28.1
> ;;; instance started with 'emacs -Q'
>
> (defun title-suffix ()
>    (cdr (assoc 'title-suffix (frame-parameters (selected-frame)))))
>
> (defvar title-prefix "Test")
> (setq frame-title-format (list title-prefix '(:eval (title-suffix)) " %b"))
>
> ;;; The original frame should show a frame title of 'Test *scratch*'
> (set-frame-parameter (selected-frame) 'title-suffix "")
>
> ;;; The next frame created should show a frame title of 'Test-xxx *scratch*'
> (make-frame-command)
> (set-frame-parameter (selected-frame) 'title-suffix "-xxx")
>
> ;;; The third frame created should show a frame title of 'Test-yyy *scratch*'
> (make-frame-command)
> (set-frame-parameter (selected-frame) 'title-suffix "-yyy")
>
> ;;; In Emacs 27 and earlier, that is exactly what happens. Selecting a
> ;;; different frame doesn't change the titles of all other frames.
>
> ;;; In Emacs 28.1, all frames show the same frame title, with the last one
> ;;; selected determining which one is shown for the bunch of them. Changing to
> ;;; a different frame changes the titles of all frames to the title of the
> ;;; newly selected one.

Could you try the attached patch?  Its purpose is to solve a more
general problem in this area and I had to scrape it out from my sources
so there are most likely dragons around.  But AFAICT it does not exhibit
the problem you see, tested with a GNUstep build on old stable Debian.

Thanks, martin

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