classic: Install the session for Wayland and ship override sessions

The regular GNOME session ships with three options:

* GNOME
* GNOME on Wayland (available when GDM starts in X11)
* GNOME on Xorg (available when GDM starts in Wayland)

The main GNOME session is set up so it works to match how GDM starts,
so GNOME is on Wayland if GDM is (or GNOME is on X11 if GDM is).

For GNOME Classic, we are missing this setup, so port this behavior
over from the GNOME session setup.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/195>

data/gnome-classic-wayland.desktop.in

@@ -0,0 +1,8 @@
+[Desktop Entry]
+Name=GNOME Classic on Wayland
+Comment=This session logs you into GNOME Classic
+Exec=env GNOME_SHELL_SESSION_MODE=classic gnome-session
+TryExec=gnome-session
+Type=Application
+DesktopNames=GNOME-Classic;GNOME;
+X-GDM-SessionRegisters=true

data/gnome-classic-xorg.desktop.in

@@ -0,0 +1,8 @@
+[Desktop Entry]
+Name=GNOME Classic on Xorg
+Comment=This session logs you into GNOME Classic
+Exec=env GNOME_SHELL_SESSION_MODE=classic gnome-session
+TryExec=gnome-session
+Type=Application
+DesktopNames=GNOME-Classic;GNOME;
+X-GDM-SessionRegisters=true

data/meson.build

@@ -1,12 +1,34 @@
-session_desktop = 'gnome-classic.desktop'
-i18n.merge_file('',
-  input:  session_desktop + '.in',
-  output: session_desktop,
-  po_dir: '../po',
-  install: true,
-  install_dir: xsessiondir,
-  type: 'desktop'
-)
+session_desktop_base = 'gnome-classic'
+
+session_desktops = [
+  session_desktop_base,
+  session_desktop_base + '-xorg',
+  session_desktop_base + '-wayland',
+]
+
+foreach name: session_desktops
+    session_desktop = name + '.desktop'
+    if name.endswith('-xorg')
+        session_instdir = xsessiondir
+    elif name.endswith('-wayland')
+        session_instdir = wlsessiondir
+    else
+        # FIXME: The same target can not be copied into two directories.
+        #        There is a workaround in meson/session-post-install.py until proper
+        #        solution arises:
+        #        https://github.com/mesonbuild/meson/issues/2416
+        session_instdir = xsessiondir
+        #session_instdir = [ xesssiondir, wlsessiondir ]
+    endif
+    i18n.merge_file('',
+      input:  session_desktop + '.in',
+      output: session_desktop,
+      po_dir: '../po',
+      install: true,
+      install_dir: session_instdir,
+      type: 'desktop'
+    )
+endforeach
 
 classic_uuids = []
 foreach e : classic_extensions

meson.build

@@ -20,6 +20,7 @@ themedir = join_paths(shelldir, 'theme')
 schemadir = join_paths(datadir, 'glib-2.0', 'schemas')
 sessiondir = join_paths(datadir, 'gnome-session', 'sessions')
 xsessiondir = join_paths(datadir, 'xsessions')
+wlsessiondir = join_paths(datadir, 'wayland-sessions')
 
 ver_arr = meson.project_version().split('.')
 shell_version = ver_arr[0]
@@ -83,6 +84,10 @@ endforeach
 
 if classic_mode_enabled
   subdir('data')
+  meson.add_install_script(
+    'meson/session-post-install.py',
+    join_paths(get_option('prefix'), datadir)
+  )
 endif
 
 subdir('extensions')

meson/session-post-install.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python3
+
+import os
+import shutil
+import sys
+
+if os.environ.get('DESTDIR'):
+  install_root = os.environ.get('DESTDIR') + os.path.abspath(sys.argv[1])
+else:
+  install_root = sys.argv[1]
+
+# FIXME: Meson is unable to copy a generated target file:
+#        https://groups.google.com/forum/#!topic/mesonbuild/3iIoYPrN4P0
+dst_dir = os.path.join(install_root, 'wayland-sessions')
+if not os.path.exists(dst_dir):
+  os.makedirs(dst_dir)
+
+src = os.path.join(install_root, 'xsessions', 'gnome-classic.desktop')
+dst = os.path.join(dst_dir, 'gnome-classic.desktop')
+shutil.copyfile(src, dst)