[gnome-session] Revert "meson: Do not use a post_install workaround to install wayland-session"

[Marco Trevisan <marcotrevi src gnome org>]

commit 97c40a947cea7dd6aa95de74e1f3b89d58ab1e3c
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Wed Feb 10 17:56:33 2021 +0100

    Revert "meson: Do not use a post_install workaround to install wayland-session"
    
    Looks like that using a file-to-be-generated doesn't work as expected,
    so reverting previous patch.
    
    Sorry for the troubles.
    
    This reverts commit 1da09ac5bb5099e9a43cad9b8e98022f27c533c3.

 data/meson.build      | 18 ++++++++++--------
 meson_post_install.py |  9 +++++++++
 2 files changed, 19 insertions(+), 8 deletions(-)
---
diff --git a/data/meson.build b/data/meson.build
index d3d00fc1..e02b80d3 100644
--- a/data/meson.build
+++ b/data/meson.build
@@ -47,6 +47,16 @@ foreach name: desktops
   )
 
   install_dir = join_paths(session_datadir, 'xsessions')
+  # FIXME: The same target can not be copied into two directories.
+  #        There is a workaround in meson_post_install.py until proper solution arises:
+  #        https://groups.google.com/forum/#!topic/mesonbuild/3iIoYPrN4P0
+  if name == desktop_plain
+    #install_dir: [
+    #  join_paths(session_datadir, 'xsessions'),
+    #  join_paths(session_datadir, 'wayland-sessions')
+    #]
+  endif
+
   desktop_target = i18n.merge_file(
     desktop,
     type: 'desktop',
@@ -56,14 +66,6 @@ foreach name: desktops
     install: true,
     install_dir: install_dir
   )
-
-  if name == desktop_plain
-    # We can't install the same target in two locations, however at install
-    # phase we've already generated the file (happening during configuration)
-    # so we can be confident in installing the built file directly.
-    install_data(files(meson.current_build_dir() / desktop),
-      install_dir: session_datadir / 'wayland-sessions')
-  endif
 endforeach
 
 sessions = [
diff --git a/meson_post_install.py b/meson_post_install.py
index 912ebfaa..e2e352cc 100644
--- a/meson_post_install.py
+++ b/meson_post_install.py
@@ -15,3 +15,12 @@ if not os.environ.get('DESTDIR'):
   print('Compile gsettings schemas...')
   subprocess.call(['glib-compile-schemas', schemadir])
 
+# FIXME: this is due to 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.desktop')
+dst = os.path.join(dst_dir, 'gnome.desktop')
+shutil.copyfile(src, dst)