Subject: 28.0.50; :box attribute in header-line truncates header-line-format text

From: Andrey Orst <[email-masked]>
Date: Thu, 9 Apr 2020 14:50:17 +0300

Some days ago I've noticed that my custom header-line for
Treemacs lacks one character for some reason:

I've checked some of my older screenshots and there was nothing
like that, "Treemacs" was fully visible. After a bit of digging I've
figured out that that's the :box attribute causing this.

Minimal recipe:

    emacs -q --eval "(progn (setq header-line-format \"1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16\") (face-remap-add-relative 'header-line :box
'(:line-width 20)))"

Emacs should appear with pretty huge header-line at the top. Try to
resize the frame. Notice that amount of dots changes. Without the :box
dots are being truncated by the edge of the window as those should.
With :box it happens somewhere at the middle of the window.

Screenshots:

Without :box all numbers can be seen up to window edge:

In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.13,
cairo version 1.16.0)
 of 2020-04-01 built on toolbox
Repository revision: 953b5b4a6d2b47bd762df4edfc4764b3d518dda9
Repository branch: master
Windowing system distributor 'Fedora Project', version 11.0.12006000
System Description: Fedora 31 (Workstation Edition)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
funcall-interactively: End of buffer [13 times]

Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND DBUS GSETTINGS GLIB NOTIFY
INOTIFY LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS JSON PDUMPER LCMS2
GMP

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search seq
byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils time-date subr-x
cl-loaddefs cl-lib face-remap tooltip eldoc electric uniquify ediff-hook
vc-hooks lisp-float-type mwheel term/x-win x-win term/common-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list replace
newcomment text-mode elisp-mode lisp-mode prog-mode register page
tab-bar menu-bar rfn-eshadow isearch timer select scroll-bar mouse
jit-lock font-lock syntax facemenu font-core term/tty-colors frame
minibuffer cl-generic cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
composite charscript charprop case-table epa-hook jka-cmpr-hook help
simple abbrev obarray cl-preloaded nadvice loaddefs button faces
cus-face macroexp files text-properties overlay sha1 md5 base64 format
env code-pages mule custom widget hashtable-print-readable backquote
threads dbusbind inotify lcms2 dynamic-setting system-font-setting
font-render-setting cairo move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 44584 10639)
 (symbols 48 6025 1)
 (strings 32 15561 1892)
 (string-bytes 1 511454)
 (vectors 16 9348)
 (vector-slots 8 126328 9916)
 (floats 8 21 38)
 (intervals 56 186 7)
 (buffers 992 10))

-- 
Best regards,
Andrey Orst