Enable opening of .world files

If a .world file is being opened, load the world and try to open its
first map. Also make sure .world files are shown in the Project view.

Thanks to SpiderDave for this suggestion!

src/libtiled/worldmanager.cpp

@@ -549,6 +549,27 @@ QVector<World::MapEntry> World::contextMaps(const QString &fileName) const
     return allMaps();
 }
 
+QString World::firstMap() const
+{
+    if (!maps.isEmpty())
+        return maps.first().fileName;
+
+    if (!patterns.isEmpty()) {
+        const QDir dir(QFileInfo(fileName).dir());
+        const QStringList entries = dir.entryList(QDir::Files | QDir::Readable);
+
+        for (const World::Pattern &pattern : patterns) {
+            for (const QString &fileName : entries) {
+                QRegularExpressionMatch match = pattern.regexp.match(fileName);
+                if (match.hasMatch())
+                    return dir.filePath(fileName);
+            }
+        }
+    }
+
+    return QString();
+}
+
 void World::error(const QString &message) const
 {
     ERROR(message, [fileName = this->fileName] { QDesktopServices::openUrl(QUrl::fromLocalFile(fileName)); }, this);

src/libtiled/worldmanager.h

@@ -76,6 +76,7 @@ struct TILEDSHARED_EXPORT World
     QVector<MapEntry> allMaps() const;
     QVector<MapEntry> mapsInRect(const QRect &rect) const;
     QVector<MapEntry> contextMaps(const QString &fileName) const;
+    QString firstMap() const;
 
     void error(const QString &message) const;
     void warning(const QString &message) const;

src/tiled/mainwindow.cpp

@@ -995,6 +995,20 @@ bool MainWindow::openFile(const QString &fileName, FileFormat *fileFormat)
     if (mDocumentManager->switchToDocument(fileName))
         return true;
 
+    // HACK: World files can't open as document, but we can instead open the
+    // first map in the world.
+    if (fileName.endsWith(QLatin1String(".world"))) {
+        QString errorString;
+        World *world = WorldManager::instance().loadWorld(fileName, &errorString);
+        if (!world) {
+            QMessageBox::critical(this, tr("Error Loading World"), errorString);
+            return false;
+        } else {
+            mLoadedWorlds = WorldManager::instance().worlds().keys();
+            return openFile(world->firstMap());
+        }
+    }
+
     QString error;
     DocumentPtr document = mDocumentManager->loadDocument(fileName, fileFormat, &error);
 

src/tiled/projectmodel.cpp

@@ -366,6 +366,10 @@ void ProjectModel::updateNameFilters()
         nameFilters.append(Utils::cleanFilterList(filter));
     }
 
+    // HACK: Needed to display world files in the project, since they do not
+    // have a registered FileFormat.
+    nameFilters.append(QLatin1String("*.world"));
+
     nameFilters.removeDuplicates();
 
     if (mNameFilters != nameFilters) {