bug#62164: 29.0.60; ediff behaves poorly by default on tiling window managers

[Spencer Baugh <sbaugh@janestreet.com>]

ediff defaults to a multiframe UI on graphical displays.  If the user is
running a tiling window manager on X, the control panel frame gets tiled
and the whole thing becomes either very ugly or unusable.

This is a very long-standing bug, but it should be fixed.  Most tiling
window manager users work around this with:

(setq ediff-window-setup-function 'ediff-setup-windows-plain)

But I would rather the multiframe UI just work correctly by default.

On X, perhaps we should set _NET_WM_WINDOW_TYPE to
_NET_WM_WINDOW_TYPE_UTILITY for the ediff control panel frame, so that
tiling window managers float the control panel frame frame by default.
This would probably need to be a new frame parameter specific to X.  I
can try to make that change if that seems reasonable.  (This would also
be useful for allowing other packages to have multiframe UI modes.)

I'm not sure what we'd do for other windowing systems.  Probably the
only other platform where tiling window managers are at all common is
Wayland; perhaps there's some way to set this hint through PGTK?


In GNU Emacs 29.0.60 (build 3, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.15.12, Xaw scroll bars) of 2023-03-13 built on
 igm-qws-u22796a
Repository revision: e759905d2e0828eac4c8164b09113b40f6899656
Repository branch: emacs-29
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: CentOS Linux 7 (Core)

Configured using:
 'configure --with-x-toolkit=lucid --with-modules
 --with-gif=ifavailable'

Configured features:
CAIRO DBUS FREETYPE GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON
LIBSELINUX LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND
SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE XIM XINPUT2 XPM LUCID
ZLIB

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

Major mode: ELisp/d

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  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 mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils ediff ediff-merg ediff-mult ediff-wind
ediff-diff ediff-help ediff-init ediff-util pp apropos thai-util
thai-word mule-util lao-util enriched disp-table facemenu view savehist
misearch multi-isearch ibuffer ibuffer-loaddefs display-line-numbers
hippie-exp comint ansi-osc ansi-color ring dabbrev saveplace completion
time-date subr-x cl-extra vc-git diff-mode easy-mmode vc-dispatcher
bug-reference find-func shortdoc text-property-search cl-print byte-opt
gv bytecomp byte-compile thingatpt help-fns radix-tree help-mode
cl-loaddefs cl-lib rmc iso-transl tooltip cconv eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode 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 lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch easymenu
timer select scroll-bar mouse jit-lock font-lock syntax font-core
term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine 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 emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind inotify
dynamic-setting system-font-setting font-render-setting cairo x-toolkit
xinput2 x multi-tty make-network-process emacs)

Memory information:
((conses 16 185840 15713)
 (symbols 48 11378 0)
 (strings 32 34965 1522)
 (string-bytes 1 1003016)
 (vectors 16 20776)
 (vector-slots 8 523892 22186)
 (floats 8 131 236)
 (intervals 56 2030 18)
 (buffers 976 20)
 (heap 1024 26111 1190))