bug#21480: 25.0.50; Frame width gets set to 16 pixels wider than the provided width in the args

[Kaushal Modi <kaushal.modi@gmail.com>]

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Hi,

I have been using a hack to deal with this bug for over a year now. I
believe I am seeing this problem ever since I starting understanding more
and more of elisp, around emacs 24.3.

Problem:
- I save the frame width using `frame-pixel-width' to a defvar.
- I then set the frame size using `set-frame-size' with that defvar as one
of the args
- I notice that the frame had got wider! When I do a readback using
`frame-pixel-width', it is exactly 16 pixels wider than expected.

I have seen this problem on emacsen built earlier on RHEL 5 and now on RHEL
6 too.

Evaluate the below code in the scratch buffer in an emacs -Q session. Then
when you keep on hitting F2, you will see that the frame keeps on getting
wider.

Now if you uncomment the line with the "<-- HACK" comment, reeval the code
and then keep on hitting F2, the frame width will stay the same (which was
the end goal of the below code).



(defvar bkp--frame-height-px nil)
(defvar bkp--frame-width-px nil)

(defun modi/toggle-menu-bar ()
  "Toggle the menu bar.
Also restore the original frame size when disabling the menu bar."
  (interactive)
  (let ((frame-resize-pixelwise t))
    ;; If the menu bar is hidden currently, take a backup of the frame
height.
    (when (null menu-bar-mode)
      (setq bkp--frame-height-px (frame-pixel-height))
      (setq bkp--frame-width-px  (frame-pixel-width))

      ;; ;; `frame-pixel-width' is returning a value higher by 16 pixels
compared
      ;; ;; to that set using `set-frame-size'. So the below adjustment has
to be made.
      ;; (setq bkp--frame-width-px  (- (frame-pixel-width) 16))) ; <-- HACK

    (menu-bar-mode 'toggle)
    ;; Restore frame size if menu bar is hidden after toggle
    (when (null menu-bar-mode)
      (set-frame-size nil bkp--frame-width-px bkp--frame-height-px
:pixelwise))))

(global-set-key (kbd "<f2>") #'modi/toggle-menu-bar)



-----------------------------------------------------------------------------------------------------


In GNU Emacs 25.0.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.23)
 of 2015-09-14
Repository revision: 1ee47d477ddb9c567eaf63154f78fad5d5826b78
Windowing system distributor 'The X.Org Foundation', version 11.0.60900000
System Description: Red Hat Enterprise Linux Workstation release 6.6
(Santiago)

Configured using:
 'configure --prefix=/home/kmodi/usr_local/apps/6/emacs/master
 'CPPFLAGS=-fgnu89-inline -I/home/kmodi/usr_local/6/include
 -I/usr/include/freetype2 -I/usr/include'
 'LDFLAGS=-L/home/kmodi/usr_local/6/lib
 -L/home/kmodi/usr_local/6/lib64''

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NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE LIBOTF XFT ZLIB
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Major mode: Lisp Interaction

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Recent messages:
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Memory information:
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--
Kaushal Modi

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