Store build information in metadata.

Build.hx

package ;

import haxe.rtti.Meta;

typedef BuildInfo = {
  date: Date,
}
class Build {
  static public var info(get, null):BuildInfo;
  static function get_info() {
    if (info == null) {
      var meta = Meta.getType(Build);
      info = {
        date: Date.fromTime(meta.date[0])
      }
    }
    return info;
  }
  #if macro
  static public function storeInfo() {
    switch haxe.macro.Context.getType('Build') {
      case TInst(cl, _):
        var cl = cl.get();
        var m = cl.meta;
        if (m.has('info'))
          m.remove('info');
        m.add('date', [macro $v{Date.now().getTime()}], cl.pos);
      default: throw 'assert';
    }
  }
  #end
}