bug#25778: 25.1; [PATCH] Drastically simplify xdg-open check

[Vasilij Schneidermann <v.schneidermann@gmail.com>]

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A user on #emacs brought it to my attention that the xdg-open detection
for browse-url is more complex than it should be and fails detecting
their Linux desktop.  Looking at the definition of
`browse-url-can-use-xdg-open' reveals that it replicates the desktop
environment check as done by `xdg-open` (which is done to detect the
DE-specific default browser setting, not to prevent people not using a
popular desktop environment from using xdg-open).  As enumerating all
possible kinds of Linux desktop is a futile endeavor, I've completely
eliminated this check from it so that the only ones left are whether
we're in a graphical session (by checking $DISPLAY) and whether
`xdg-open` has been found on $PATH.

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From 6c99e7ace3110b73a5b212203acc728165be092b Mon Sep 17 00:00:00 2001
From: Vasilij Schneidermann <v.schneidermann@gmail.com>
Date: Fri, 17 Feb 2017 19:08:54 +0100
Subject: [PATCH] Drastically simplify check for xdg-open

* browse-url.el (browse-url-can-use-xdg-open): Simplify xdg-open check
---
 lisp/net/browse-url.el | 34 +++-------------------------------
 1 file changed, 3 insertions(+), 31 deletions(-)

diff --git a/lisp/net/browse-url.el b/lisp/net/browse-url.el
index a7c879cbfb..bf7561306c 100644
--- a/lisp/net/browse-url.el
+++ b/lisp/net/browse-url.el
@@ -45,7 +45,7 @@
 ;; browse-url-generic                 arbitrary
 ;; browse-url-default-windows-browser MS-Windows browser
 ;; browse-url-default-macosx-browser  macOS browser
-;; browse-url-xdg-open                Free Desktop xdg-open on Gnome, KDE, Xfce4, LXDE
+;; browse-url-xdg-open                Free Desktop xdg-open
 ;; browse-url-kde                     KDE konqueror (kfm)
 ;; browse-url-elinks                  Elinks      Don't know (tried with 0.12.GIT)
 
@@ -944,36 +944,8 @@ instead of `browse-url-new-window-flag'."
 
 (defun browse-url-can-use-xdg-open ()
   "Return non-nil if the \"xdg-open\" program can be used.
-xdg-open is a desktop utility that calls your preferred web browser.
-This requires you to be running either Gnome, KDE, Xfce4 or LXDE."
-  (and (getenv "DISPLAY")
-       (executable-find "xdg-open")
-       ;; xdg-open may call gnome-open and that does not wait for its child
-       ;; to finish.  This child may then be killed when the parent dies.
-       ;; Use nohup to work around.  See bug#7166, bug#8917, bug#9779 and
-       ;; http://lists.gnu.org/archive/html/emacs-devel/2009-07/msg00279.html
-       (executable-find "nohup")
-       (or (getenv "GNOME_DESKTOP_SESSION_ID")
-	   ;; GNOME_DESKTOP_SESSION_ID is deprecated, check on Dbus also.
-	   (condition-case nil
-	       (eq 0 (call-process
-		      "dbus-send" nil nil nil
-				  "--dest=org.gnome.SessionManager"
-				  "--print-reply"
-				  "/org/gnome/SessionManager"
-				  "org.gnome.SessionManager.CanShutdown"))
-	     (error nil))
-	   (equal (getenv "KDE_FULL_SESSION") "true")
-	   (condition-case nil
-	       (eq 0 (call-process
-		      "/bin/sh" nil nil nil
-		      "-c"
-		      ;; FIXME use string-match rather than grep.
-		      "xprop -root _DT_SAVE_MODE|grep xfce4"))
-	     (error nil))
-	   (member (getenv "DESKTOP_SESSION") '("LXDE" "Lubuntu"))
-	   (equal (getenv "XDG_CURRENT_DESKTOP") "LXDE"))))
-
+xdg-open is a desktop utility that calls your preferred web browser."
+  (and (getenv "DISPLAY") (executable-find "xdg-open")))
 
 ;;;###autoload
 (defun browse-url-xdg-open (url &optional ignored)
-- 
2.11.0