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

[Spencer Baugh]

Here's a patch which supports making the control frame into a utility
window with a user option.

>From f23dc72acd370ace6fd934f46e1d6f9a72f943bf Mon Sep 17 00:00:00 2001
From: Spencer Baugh <sbaugh@janestreet.com>
Date: Tue, 9 May 2023 14:22:29 -0400
Subject: [PATCH] Allow setting the ediff control frame as a utility window
 under X

This is a step in the direction of making ediff behave better by
default under tiling window managers and fixing bug#62164.

* lisp/vc/ediff-wind.el (ediff-x-utility-control-frame): Add
defcustom.
(ediff-frame-make-utility, ediff-setup-control-frame): Allow setting
the control frame up as a utility window under X. (bug#62164)
---
 lisp/vc/ediff-wind.el | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/lisp/vc/ediff-wind.el b/lisp/vc/ediff-wind.el
index eb903f093f9..9eaed48f16c 100644
--- a/lisp/vc/ediff-wind.el
+++ b/lisp/vc/ediff-wind.el
@@ -69,6 +69,16 @@ ediff-window-setup-function
                 (function :tag "Other function"))
   :version "24.3")
 
+(defcustom ediff-x-utility-control-frame nil
+  "If non-nil, the control frame is a utility window under X.
+
+This is useful in tiling window managers, where this will cause
+the control frame to be floating rather than tiled.  It should be
+harmless on other well-behaved window managers."
+  :type '(choice (const :tag "Control frame is utility window" t)
+                 (const :tag "Control frame is normal window" nil))
+  :version "30.1")
+
 (ediff-defvar-local ediff-multiframe nil
   "Indicates if we are in a multiframe setup.")
 
@@ -873,6 +883,16 @@ ediff-window-ok-for-display
     (not (ediff-frame-has-dedicated-windows (window-frame wind)))
     )))
 
+(defun ediff-frame-make-utility (frame)
+  (let ((x-fast-protocol-requests t))
+    (x-change-window-property
+     "_NET_WM_WINDOW_TYPE" '("_NET_WM_WINDOW_TYPE_UTILITY")
+     frame "ATOM" 32 t)
+    (x-change-window-property
+     "WM_TRANSIENT_FOR"
+     (list (string-to-number (frame-parameter nil 'window-id)))
+     frame "WINDOW" 32 t)))
+
 ;; Prepare or refresh control frame
 (defun ediff-setup-control-frame (ctl-buffer designated-minibuffer-frame)
   (let ((window-min-height 1)
@@ -948,6 +968,8 @@ ediff-setup-control-frame
     (goto-char (point-min))
 
     (modify-frame-parameters ctl-frame adjusted-parameters)
+    (when (and ediff-x-utility-control-frame (eq window-system 'x))
+      (ediff-frame-make-utility ctl-frame))
     (make-frame-visible ctl-frame)
 
     ;; This works around a bug in 19.25 and earlier.  There, if frame gets
-- 
2.30.2