bug#16028: 24.3.50; Latest build completely breaks my thumnail frames code

[Drew Adams]

> Perhaps the real-life thumbnail-mode does something to restore the
> frame dimensions, thus countermanding the effect of making the font
> smaller?

This is the core code, for thumbifying & dethumbifying:

(defcustom thumfr-frame-parameters
  '((menu-bar-lines . 0) (tool-bar-lines . 0) (scroll-bar-width . 6))
  "*Frame parameters for thumbnail frames.
Use this to show or hide things like the menu bar, tool bar, tab bar,
and scroll bars for thumbnail frames."
  :type '(repeat (cons symbol sexp))
  :group 'Thumbnail-Frames
  :set (lambda (sym defs)
         (custom-set-default sym defs)
         (dolist (frm  (frame-list))
           (when (and (frame-live-p frm)
                      (frame-parameter frm 'thumfr-thumbnail-frame))
             (modify-frame-parameters frm thumfr-frame-parameters)))))

(defun thumfr-thumbify-frame (&optional frame)
  "Create a thumbnail version of FRAME (default: selected frame).
Variable `thumfr-frame-parameters' is used to determine
which frame parameters (such as `menu-bar-lines') to remove."
  (interactive)
  (setq frame  (or frame (selected-frame)))
  (let* ((tf-params      (frame-parameter frame 'thumfr-non-thumbnail-frame))
         (non-tf-params  (thumfr-remove-if #'thumfr-thumfr-parameter-p
                                           (frame-parameters frame))))
    (when thumfr-rename-when-thumbify-flag (rename-non-minibuffer-frame))
    (unless (frame-parameter frame 'thumfr-thumbnail-frame)
      (set-frame-parameter frame 'thumfr-thumbnail-frame non-tf-params)
      (set-frame-parameter frame 'thumfr-non-thumbnail-frame nil)
      (condition-case thumfr-thumbify-frame
          (progn
            (enlarge-font (- thumfr-font-difference) frame)
            (when tf-params (modify-frame-parameters frame tf-params))
            (when thumfr-next-stack-xoffset
              (set-frame-position frame thumfr-next-stack-xoffset
                                  thumfr-next-stack-yoffset)
              (setq thumfr-next-stack-xoffset  nil
                    thumfr-next-stack-yoffset  nil))
            (modify-frame-parameters frame thumfr-frame-parameters))
        (font-too-small                 ; Try again, with a larger font.
         (set-frame-parameter frame 'thumfr-non-thumbnail-frame tf-params)
         (set-frame-parameter frame 'thumfr-thumbnail-frame nil)
         (unless (> thumfr-font-difference 0)
           (error (error-message-string thumfr-thumbify-frame)))
         (let ((thumfr-font-difference  (1- thumfr-font-difference)))
           (thumfr-thumbify-frame frame)))
        (error
         (set-frame-parameter frame 'thumfr-non-thumbnail-frame tf-params)
         (set-frame-parameter frame 'thumfr-thumbnail-frame nil)
         (error (error-message-string thumfr-thumbify-frame)))))))

(defun thumfr-dethumbify-frame (&optional frame)
  "Restore thumbnail FRAME to original size (default: selected frame)."
  (interactive)
  (setq frame  (or frame (selected-frame)))
  (let* ((non-tf-params  (frame-parameter frame 'thumfr-thumbnail-frame))
         (tf-params      (thumfr-remove-if #'thumfr-thumfr-parameter-p
                                           (frame-parameters frame))))
    (when non-tf-params                 ; No-op if not a thumbnail.
      (set-frame-parameter frame 'thumfr-non-thumbnail-frame tf-params)
      (set-frame-parameter frame 'thumfr-thumbnail-frame nil)
      (condition-case thumfr-dethumbify-frame
          (progn
            (enlarge-font thumfr-font-difference frame)
            (modify-frame-parameters frame non-tf-params))
        (error
         (set-frame-parameter frame 'thumfr-thumbnail-frame non-tf-params)
         (set-frame-parameter frame 'thumfr-non-thumbnail-frame nil)
         (error (error-message-string thumfr-dethumbify-frame))))
      (select-frame-set-input-focus frame)
      (thumfr-only-raise-frame frame))))

(defun thumfr-thumfr-parameter-p (parameter+value)
  "Return non-nil if PARAMETER+VALUE is a `thumb-frm.el' frame parameter.
PARAMETER+VALUE is a frame-parameter cons: (PARAMETER . VALUE).
This means that PARAMETER is either `thumbfr-thumbnail-frame' or
`thumbfr-non-thumbnail-frame'."
  (memq (car parameter+value)
        '(thumfr-thumbnail-frame thumfr-non-thumbnail-frame)))

To be clear (I was not, before; sorry), the problem is not with shrinking
and enlarging the font and having the frame size follow.  For instance, my
commands `zoom-frm-out' and `zoom-frm-in' work fine in this respect.

The problem is with thumbifying (`thumfr-thumbify-frame').

Running it through the debugger, I see that the frame _is_ shrunk
correctly, along with the font, at this point in the code:

(enlarge-font (- thumfr-font-difference) frame)
...
(modify-frame-parameters frame thumfr-frame-parameters)

But if I don't go through the debugger, it does not work.  And if I just
hit `c' in the debugger, instead of `d' throughout, it also does not work.

This is 100% reproducible.  Dunno why stepping through the debugger would
work, and even hitting `c' for the `enlarge-font' call works, but hitting
`c' for the `condition-case' does not.

HTH.