build: introduce sd-bus-provider option

Based on https://github.com/emersion/mako/commit/67f2ed1862a9

include/xdpw.h

@@ -2,9 +2,9 @@
 #define XDPW_H
 
 #include <wayland-client.h>
-#ifdef HAVE_SYSTEMD
+#ifdef HAVE_LIBSYSTEMD
 #include <systemd/sd-bus.h>
-#elif HAVE_ELOGIND
+#elif HAVE_LIBELOGIND
 #include <elogind/sd-bus.h>
 #endif
 

meson.build

@@ -3,7 +3,7 @@ project(
 	'c',
 	version: '0.1.0',
 	license: 'MIT',
-	meson_version: '>=0.47.0',
+	meson_version: '>=0.50.0',
 	default_options: [
 		'c_std=c11',
 		'warning_level=2',
@@ -27,13 +27,24 @@ pipewire = dependency('libpipewire-0.3', version: '>= 0.3.2')
 wayland_client = dependency('wayland-client')
 wayland_protos = dependency('wayland-protocols', version: '>=1.14')
 
-logind = dependency('libsystemd', required: false)
-if logind.found()
-	add_project_arguments('-DHAVE_SYSTEMD=1', language: 'c')
-else
-	logind = dependency('libelogind')
-	add_project_arguments('-DHAVE_ELOGIND=1', language: 'c')
+if get_option('sd-bus-provider') == 'auto'
+	assert(get_option('auto_features').auto(), 'sd-bus-provider must not be set to auto since auto_features != auto')
+	sdbus = dependency('libsystemd',
+		required: false,
+		not_found_message: 'libsystemd not found, trying libelogind',
+	)
+	if not sdbus.found()
+		sdbus = dependency('libelogind',
+			required: false,
+		)
 	endif
+	if not sdbus.found()
+		error('Neither libsystemd, nor libelogind was found')
+	endif
+else
+	sdbus = dependency(get_option('sd-bus-provider'))
+endif
+add_project_arguments('-DHAVE_' + sdbus.name().to_upper() + '=1', language: 'c')
 
 subdir('protocols')
 
@@ -53,7 +64,7 @@ executable(
 	dependencies: [
 		wayland_client,
 		wlr_protos,
-		logind,
+		sdbus,
 		pipewire,
 		rt,
 	],

meson_options.txt

@@ -1 +1,2 @@
+option('sd-bus-provider', type: 'combo', choices: ['auto', 'libsystemd', 'libelogind'], value: 'auto', description: 'Provider of the sd-bus library')
 option('systemd', type: 'feature', value: 'auto', description: 'Install systemd user service unit')