meson: Permit disabling (and forcing) installation of udev rules

In some cases (e.g. inside the flatpak), it does not make sense to
generate and install udev rules.

libfprint/meson.build

@@ -332,7 +332,7 @@ udev_hwdb_generator = custom_target('udev-hwdb',
     install: false,
 )
 
-if udev_rules
+if install_udev_rules
     udev_rules = executable('fprint-list-udev-rules',
         'fprint-list-udev-rules.c',
         dependencies: libfprint_private_dep,

meson.build

@@ -166,7 +166,8 @@ imaging_dep = dependency('', required: false)
 gudev_dep = dependency('', required: false)
 libfprint_conf.set10('HAVE_PIXMAN', false)
 
-udev_rules = false
+udev_rules = get_option('udev_rules')
+install_udev_rules = udev_rules.enabled()
 
 foreach driver: drivers
     if driver == 'uru4000'
@@ -184,7 +185,7 @@ foreach driver: drivers
         libfprint_conf.set10('HAVE_PIXMAN', true)
     endif
         if udev_drivers.contains(driver)
-            udev_rules = true
+            install_udev_rules = true
 
             gudev_dep = dependency('gudev-1.0', required: false)
             if not gudev_dep.found()
@@ -198,7 +199,11 @@ foreach driver: drivers
     endif
 endforeach
 
-if udev_rules
+if udev_rules.disabled()
+    install_udev_rules = false
+endif
+
+if install_udev_rules
     udev_rules_dir = get_option('udev_rules_dir')
     if udev_rules_dir == 'auto'
         udev_dep = dependency('udev')

meson_options.txt

@@ -6,6 +6,10 @@ option('introspection',
        description: 'Build GObject Introspection repository',
        type: 'boolean',
        value: true)
+option('udev_rules',
+       description: 'Whether to create and install udev rules (auto: turn on when needed by a driver)',
+       type: 'feature',
+       value: 'auto')
 option('udev_rules_dir',
        description: 'Installation path for udev rules',
        type: 'string',