meson: Add optional libsystemd dependency

To utilize the API provided by libsystemd it would be better to
create a separate HAVE_LIBSYSTEMD configuration option instead of
having to rely on HAVE_NATIVE_BACKEND.

For now this will be utilized for getting the control group of a
MetaWindow.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1960>

config.h.meson

@@ -34,6 +34,9 @@
 /* Building with libwacom for advanced tablet management */
 #mesondefine HAVE_LIBWACOM
 
+/* Building with libsystemd */
+#mesondefine HAVE_LIBSYSTEMD
+
 /* Define if you want to enable the native (KMS) backend based on systemd */
 #mesondefine HAVE_NATIVE_BACKEND
 

meson.build

@@ -191,13 +191,15 @@ if have_libgudev
   endif
 endif
 
+have_libsystemd = get_option('systemd')
+libsystemd_dep = dependency('libsystemd', required: have_libsystemd)
+
 have_native_backend = get_option('native_backend')
 if have_native_backend
   libdrm_dep = dependency('libdrm')
   libgbm_dep = dependency('gbm', version: gbm_req)
   libinput_dep = dependency('libinput', version: libinput_req)
 
-  libsystemd_dep = dependency('libsystemd', required: false)
   if libsystemd_dep.found()
     logind_provider_dep = libsystemd_dep
   else
@@ -389,6 +391,7 @@ cdata.set_quoted('PACKAGE_VERSION', meson.project_version())
 
 cdata.set('HAVE_EGL', have_egl)
 cdata.set('HAVE_WAYLAND', have_wayland)
+cdata.set('HAVE_LIBSYSTEMD', have_libsystemd)
 cdata.set('HAVE_NATIVE_BACKEND', have_native_backend)
 cdata.set('HAVE_REMOTE_DESKTOP', have_remote_desktop)
 cdata.set('HAVE_EGL_DEVICE', have_egl_device)

meson_options.txt

@@ -39,6 +39,12 @@ option('wayland',
   description: 'Enable Wayland support'
 )
 
+option('systemd',
+  type: 'boolean',
+  value: true,
+  description: 'Enable systemd support'
+)
+
 option('native_backend',
   type: 'boolean',
   value: true,

src/meson.build

@@ -118,6 +118,12 @@ if have_wayland
   ]
 endif
 
+if have_libsystemd
+  mutter_pkg_private_deps += [
+    libsystemd_dep,
+  ]
+endif
+
 if have_native_backend
   mutter_pkg_private_deps += [
     libdrm_dep,