bug#39074: 27.0.60; [PATCH] Horizontal line messes with variable value display in Custom buffers

[Kévin Le Gouguec]

Hi,

Unless I'm mistaken, commit 84a3793b19 introduced a bug when the user
pushes the button to show the value of the last variable in a Custom
buffer.  From emacs -Q:

- M-x customize-group RET visual-line RET
- move point to the "Show Value" button for "Visual Line Fringe
  Indicators" (shown with the etc/images/custom/right icon on a GUI)
- hit RET
- the variable's description has moved *after* the horizontal line
  (cf. screenshot)

custom-horizontal-line.png
Description: PNG image

AFAICT, this is because the function that was introduced to de-duplicate
the horizontal line code does

(let ((p (point)))
  (insert "\n")
  …)

whereas the code to draw the last line did:

(let ((p (1+ (point))))
  (insert "\n\n")
  …)

If I'm not mistaken, this can be fixed simply by adding (insert "\n")
before the final call to custom-group--draw-horizontal-line, as done in
this patch:

0001-Fix-glitch-with-horizontal-lines-in-Custom-buffers.patch
Description: Text Data

I'm not entirely sure why this extra newline is necessary; I haven't
done much digging other than looking at the commit that introduced this
issue.  Maybe the rest of custom-group-value-create does something fishy
and this patch only works around that…

WDYT?


Thank you for your time.


In GNU Emacs 28.0.50 (build 4, i686-pc-linux-gnu, GTK+ Version 3.24.5, cairo 
version 1.16.0)
 of 2020-01-08 built on little-buster
Repository revision: 724af7671590cd91df37f64df6be73f6dca0144d
Repository branch: master
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