Subject: 29.0.92; A :box with negative vertical width does not avoid any increase in the line height

From: Sebastian Miele <[email-masked]>
Date: Mon, 19 Jun 2023 14:46:17 +0200

In ‘src/emacs -Q’ create a buffer in fundamental mode and add the
following contents:

  text
  text
  text

At the end of the second line, evaluate (‘eval-expression’):

  (insert (propertize "text" 'face '(:box '(:line-width (-1 . -1)))))

The height of the line clearly changes.  But that is contrary to what
the manual says about the ‘:box’ face attribute:

  "A negative horizontal or vertical width −N means to draw a line of
  width N that occupies the space of the underlying text, thus avoiding
  any increase in the character height or width."

Apart from that:

(1) Using ‘:line-width (-1 . -1)’ seems to yield the exact same result
as ‘:line-width (1 . 1)’ does, both in width and in height.

(2) Using even larger negative values has no effect.
‘:line-width (-10 . -10)’ also seems to yield the exact same result as
‘:line-width (1 . 1)’ does.

Apparantly, all negative values are treates as positive 1, contrary to
what the manual states.

In GNU Emacs 29.0.92 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.38, cairo version 1.17.8) of 2023-06-18 built on huette
Repository revision: a24e9e3fee59435422af0473b7ec585de2c13b4e
Repository branch: emacs-29
Windowing system distributor 'The X.Org Foundation', version 11.0.12101008
System Description: Arch Linux

Configured using:
 'configure --with-x-toolkit=gtk --with-native-compilation=yes
 --with-tree-sitter --with-json --with-mailutils --with-imagemagick'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ
IMAGEMAGICK JPEG JSON LCMS2 LIBOTF LIBSYSTEMD LIBXML2 M17N_FLT MODULES
NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3
THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XDBE XIM XINPUT2
XPM GTK3 ZLIB

Important settings:
  value of $LC_COLLATE: C
  value of $LANG: C.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-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
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils comp comp-cstr
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composite emoji-zwj charscript charprop case-table epa-hook
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theme-loaddefs faces cus-face macroexp files window text-properties
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native-compile emacs)

Memory information:
((conses 16 65864 6640)
 (symbols 48 7137 0)
 (strings 32 19744 3785)
 (string-bytes 1 595129)
 (vectors 16 15226)
 (vector-slots 8 279775 8789)
 (floats 8 28 24)
 (intervals 56 241 0)
 (buffers 984 13))