latest release + state in git both fail to compile with latest Vala (0.55.1+)

[decathorpe]

There are seven new errors with the latest version of vala:

../src/Resources.vala:41.30-41.36: error: value is less accessible than constant `Resources.PREFIX'
   41 | public const string PREFIX = _PREFIX;
      |                              ^~~~~~~ 
../src/util/system.vala:35.42-35.57: error: Invalid type for argument 1
   35 |     File prefix_dir = File.new_for_path (Resources.PREFIX);
      |                                          ^~~~~~~~~~~~~~~~  

../src/Resources.vala:26.35-26.42: error: value is less accessible than constant `Resources.APP_VERSION'
   26 | public const string APP_VERSION = _VERSION;
      |                                   ^~~~~~~~ 
../src/Photo.vala:3648.61-3648.81: error: Invalid type for argument 2
 3648 |             metadata.set_software (_ (Resources.APP_TITLE), Resources.APP_VERSION);
      |                                                             ^~~~~~~~~~~~~~~~~~~~~  

../src/main.vala:276.46-283.5: error: value is less accessible than constant `CommandlineOptions.APP_OPTIONS'
  276 |     public const OptionEntry[] APP_OPTIONS = {
      |                                              ^
  277 |         { "datadir", 'd', 0, OptionArg.FILENAME, out data_dir, N_("Path to Photos' private data"), N_("DIRECTORY")},
      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  278 |         { "no-runtime-monitoring", 0, 0, OptionArg.NONE, out no_runtime_monitoring, N_("Do not monitor library directory at runtime for changes"), null},
      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  279 |         { "no-startup-progress", 0, 0, OptionArg.NONE, out no_startup_progress, N_("Don't display startup progress meter"), null},
      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  280 |         { "version", 'v', 0, OptionArg.NONE, out show_version, N_("Show the application's version"), null},
      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  281 |         { "debug", 'D', 0, OptionArg.NONE, out debug_enabled, N_("Show extra debugging output"), null},
      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  282 |         { null }
      | ~~~~~~~~~~~~~~~~
  283 |     };
      | ~~~~~ 
../src/Resources.vala:34.43-34.57: error: value is less accessible than constant `Resources.APP_GETTEXT_PACKAGE'
   34 | public const string APP_GETTEXT_PACKAGE = GETTEXT_PACKAGE;
      |                                           ^~~~~~~~~~~~~~~ 
../src/main.vala:308.29-308.57: error: Invalid type for argument 4
  308 |                             Resources.APP_GETTEXT_PACKAGE);
      |                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~  

There's also 277 deprecation warnings, about things like Gtk.UIManager, GExiv2.Metadata.FOO, Gtk.Action, Gtk.ActionEntry, Gtk.RadioAction, Gtk.RadioActionEntry, and Gtk.ToggleAction, which have all been deprecated since GTK 3.10 (first released in 2013), so those are probably good places to start if you want to port this app to GTK4 😉