Ask user for confirmation before closing a non-favorite playlist, as it will be deleted. Don't ask if middle-clicked

src/playlist/playlistmanager.cpp

@@ -15,7 +15,6 @@
    along with Clementine.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include "playlist.h"
 #include "playlistbackend.h"
 #include "playlistcontainer.h"
 #include "playlistmanager.h"
@@ -34,6 +33,7 @@
 #include <QFileInfo>
 #include <QFuture>
 #include <QFutureWatcher>
+#include <QMessageBox>
 #include <QtDebug>
 
 using smart_playlists::GeneratorPtr;
@@ -293,7 +293,6 @@ bool PlaylistManager::Close(int id) {
   emit PlaylistClosed(id);
 
   if (!data.p->is_favorite()) {
-    // TODO: should we warn the user this action cannot be undone?
     playlist_backend_->RemovePlaylist(id);
     emit PlaylistDeleted(id);
   }

src/playlist/playlistmanager.h

@@ -25,11 +25,11 @@
 #include <QSettings>
 
 #include "core/song.h"
+#include "playlist.h"
 #include "smartplaylists/generator_fwd.h"
 
 class Application;
 class LibraryBackend;
-class Playlist;
 class PlaylistBackend;
 class PlaylistContainer;
 class PlaylistParser;
@@ -162,6 +162,7 @@ public:
   QItemSelection active_selection() const { return selection(active_id()); }
 
   QString GetPlaylistName(int index) const { return playlists_[index].name; }
+  bool IsPlaylistFavorite(int index) const { return playlists_[index].p->is_favorite(); }
 
   void Init(LibraryBackend* library_backend, PlaylistBackend* playlist_backend,
             PlaylistSequence* sequence, PlaylistContainer* playlist_container);

src/playlist/playlisttabbar.cpp

@@ -94,7 +94,7 @@ void PlaylistTabBar::mouseReleaseEvent(QMouseEvent* e) {
   if (e->button() == Qt::MidButton) {
     // Update menu index
     menu_index_ = tabAt(e->pos());
-    Close();
+    Close(false);
   }
 
   QTabBar::mouseReleaseEvent(e);
@@ -151,13 +151,26 @@ void PlaylistTabBar::HideEditor() {
   manager_->SetCurrentPlaylist(manager_->current()->id());
 }
 
-void PlaylistTabBar::Close() {
+void PlaylistTabBar::Close(bool ask_for_delete) {
   if (menu_index_ == -1)
     return;
 
+  const int playlist_id = tabData(menu_index_).toInt();
+
+  if (ask_for_delete && !manager_->IsPlaylistFavorite(playlist_id)) {
+    if (QMessageBox::question(this,
+          tr("Remove playlist"),
+          tr("You are about to remove a playlist which is not part of your favorite playlists: "
+             "the playlist will be deleted (this action cannot be undone). \n"
+             "Are you sure you want to continue?"),
+          QMessageBox::Yes, QMessageBox::Cancel) != QMessageBox::Yes) {
+        return;
+      }
+  }
+
   // Just hide the tab from the UI - don't delete it completely (it can still
   // be resurrected from the Playlists tab).
-  emit Close(tabData(menu_index_).toInt());
+  emit Close(playlist_id);
 
   // Select the nearest tab.
   if (menu_index_ > 1) {

src/playlist/playlisttabbar.h

@@ -76,7 +76,7 @@ private slots:
   void Rename();
   void RenameInline();
   void HideEditor();
-  void Close();
+  void Close(bool ask_for_delete = true);
   void CloseFromTabIndex(int index);
   // Used when playlist's favorite flag isn't changed from the favorite widget
   // (e.g. from the playlistlistcontainer): will update the favorite widget