Scrollbar width not respected in restored frames

[PierGianLuca]

Hi everyone,

I'm on Ubuntu 20.04, KDE Plasma X11. Emacs 29.1 from tarball.

I consistently see a discrepancy between the vertical-scrollbar width of the 
initial frames, restored from a previous session, and of subsequent frames 
called with make-frame-command (C-x52).

Here is an example, I'd like to know whether others see this behaviour too:

1. Make sure Desktop-save-mode is on

2. Select any geometry you like in default-frame-alist and specify scroll-bar-width with 
some value (in my case it's "21")

3. Create a new frame with "C-x 5 2".

4. Check that the vertical scrollbar respects the width specified in default-frame-alist. 
If you like, check the window geometry with some tool like "xwininfo".

5. Close all other frames, make sure the one you created in step 3. is the only 
one left.

6. Quit the Emacs session

7. Start Emacs. You should see the frame from the previous session.

8. Check the width of the vertical scrollbar in this frame. You should see it's different 
from the one right before you quit Emacs. This should be confirmed by 
"xwininfo" or similar tool.

9. Create a new frame with "C-x 5 2". You should see that the new frame respects the 
scrollbar width of "default-frame-alist" (and it's different from the one of the first, 
initially restored frame).


May this be a bug in desktop-save-mode?

Here are some additional details:

• If the frame width is changed *manually* (for instance first enlarge then 
bring to original size) then the correct width is restored upon restarting Emacs


• The erroneous scrollbar width that Emacs presents when restoring windows 
seems to be the default one


• Specifying the width in "early-init.el" with

(add-to-list 'default-frame-alist '(scroll-bar-width . 21))

has no effect. Same if initial-frame-alist is used instead/in addition


• Specifying

(setq frame-resize-pixelwise t)

either in init.el or early-init.el doesn't solve this.


• I see this behaviour both when configuring Emacs with "--with-x-toolkit=lucid" and with 
"--with-x-toolkit=gtk", and both with or without "--without-toolkit-scroll-bars".


•  My windows manager (KWin) has an explicit rule to respect any geometry that 
Emacs asks. I made sure of this: I can resize the Emacs windows as I please, 
and their geometries are respected upon restarting.


Cheers,
Luca