services: gdm: Add Wayland support.

* gnu/packages/patches/gdm-wayland-session-wrapper-from-env.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/gnome.scm (gdm): Use it.
* gnu/services/xorg.scm (<gdm-configuration>)[wayland-session]: New field.
(gdm-wayland-session-wrapper): New procedure.
(gdm-configuration-file): Point to this new procedure.
* doc/guix.texi (X Window): Update it.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

doc/guix.texi

@@ -18309,6 +18309,10 @@ The GDM package to use.
 
 @item @code{wayland?} (default: @code{#f})
 When true, enables Wayland in GDM, necessary to use Wayland sessions.
+
+@item @code{wayland-session} (default: @code{gdm-wayland-session-wrapper})
+The Wayland session wrapper to use, needed to setup the
+environment.
 @end table
 @end deftp
 

gnu/local.mk

@@ -1102,6 +1102,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/gdm-default-session.patch		\
   %D%/packages/patches/gdm-elogind-support.patch		\
   %D%/packages/patches/gdm-remove-hardcoded-xwayland-path.patch	\
+  %D%/packages/patches/gdm-wayland-session-wrapper-from-env.patch	\
   %D%/packages/patches/geary-CVE-2020-24661.patch		\
   %D%/packages/patches/genimage-signedness.patch		\
   %D%/packages/patches/geoclue-config.patch			\

gnu/packages/gnome.scm

@@ -8150,7 +8150,8 @@ (define-public gdm
                (search-patches
                 "gdm-default-session.patch"
                 "gdm-elogind-support.patch"
-                "gdm-remove-hardcoded-xwayland-path.patch"))))
+                "gdm-remove-hardcoded-xwayland-path.patch"
+                "gdm-wayland-session-wrapper-from-env.patch"))))
     (build-system meson-build-system)
     (arguments
      `(#:glib-or-gtk? #t

gnu/packages/patches/gdm-wayland-session-wrapper-from-env.patch

@@ -0,0 +1,35 @@
+Get wayland-session wrapper from environment.
+
+---
+ daemon/gdm-session.c | 6 ++++--
+ 1 file changed, 4 insertions(+), 2 deletions(-)
+
+diff --git a/daemon/gdm-session.c b/daemon/gdm-session.c
+index 4e303e70..1deca4e9 100644
+--- a/daemon/gdm-session.c
++++ b/daemon/gdm-session.c
+@@ -2888,8 +2888,9 @@ gdm_session_start_session (GdmSession *self,
+                                                            allow_remote_connections? "--allow-remote-connections " : "",
+                                                            command);
+                         } else {
+-                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session %s\"%s\"",
++                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session %s\"%s %s\"",
+                                                            register_session ? "--register-session " : "",
++                                                           g_getenv ("GDM_WAYLAND_SESSION"),
+                                                            command);
+                         }
+                 } else if (run_xsession_script) {
+@@ -2906,8 +2907,9 @@ gdm_session_start_session (GdmSession *self,
+                                                            register_session ? "--register-session " : "",
+                                                            self->selected_program);
+                         } else {
+-                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session %s\"%s\"",
++                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session %s\"%s %s\"",
+                                                            register_session ? "--register-session " : "",
++                                                           g_getenv ("GDM_WAYLAND_SESSION"),
+                                                            self->selected_program);
+                         }
+                 } else {
+--
+2.33.0
+

gnu/services/xorg.scm

@@ -870,6 +870,24 @@ (define profiles
        (apply execl (string-append #$dbus "/bin/dbus-daemon")
               (program-arguments)))))
 
+;; Wrapper script for Wayland sessions, similar to Xsession.
+;;
+;; See `xinitrc`.  By default, it launches the specified session through a
+;; login shell.  With the default Guix configuration, this should source
+;; /etc/profile, setting up the Guix profile environment variables.  However,
+;; gdm launches its own graphical session through the same method, so we need
+;; to ignore this case, since `gdm` doesn't have a login shell.
+(define gdm-wayland-session-wrapper
+  (program-file
+   "gdm-wayland-session-wrapper"
+   #~((let* ((user (getpw (getuid)))
+	    (name (passwd:name user))
+	    (shell (passwd:shell user))
+	    (args (cdr (command-line))))
+        (if (string=? name "gdm")
+	    (apply execl (cons (car args) args))
+	    (execl shell shell "--login" "-c" (string-join args)))))))
+
 (define-record-type* <gdm-configuration>
   gdm-configuration make-gdm-configuration
   gdm-configuration?
@@ -885,7 +903,9 @@ (define-record-type* <gdm-configuration>
                       (default (xorg-configuration)))
   (x-session gdm-configuration-x-session
              (default (xinitrc)))
-  (wayland? gdm-configuration-wayland? (default #f)))
+  (wayland? gdm-configuration-wayland? (default #f))
+  (wayland-session gdm-configuration-wayland-session
+                   (default gdm-wayland-session-wrapper)))
 
 (define (gdm-configuration-file config)
   (mixed-text-file "gdm-custom.conf"
@@ -983,7 +1003,10 @@ (define (gdm-shepherd-service config)
                            ;; Add XCURSOR_PATH so that mutter can find its
                            ;; cursors.  gdm doesn't login so doesn't source
                            ;; the corresponding line in /etc/profile.
-                           "XCURSOR_PATH=/run/current-system/profile/share/icons"))))
+                           "XCURSOR_PATH=/run/current-system/profile/share/icons"
+                           (string-append
+                            "GDM_WAYLAND_SESSION="
+                            #$(gdm-configuration-wayland-session config))))))
          (stop #~(make-kill-destructor))
          (respawn? #t))))