Stop obsolete folder counts during directory traversal

src/foldermodel.cpp

@@ -431,11 +431,22 @@ void FolderModel::summarize(Entry &entry, bool showHidden) {
     }
 }
 
-int FolderModel::itemCount(const QString &folder, bool showHidden) {
+int FolderModel::itemCount(const QString &folder, bool showHidden, const std::function<bool()> &stop) {
+    if (stop && stop())
+        return -1;
     int count = 0;
-    for (QDirIterator it(folder, entryFilters(showHidden)); it.hasNext(); it.next())
-        ++count;
-    return count;
+    // Let hidden entries through too: filtering a long run inside Qt would
+    // give this loop no chance to notice cancellation. On Linux a dot name
+    // is hidden, as in listRecent(). The iterator still excludes . and ...
+    QDirIterator it(folder, entryFilters(true));
+    while (it.hasNext()) {
+        if (stop && stop())
+            return -1;
+        it.next();
+        if (showHidden || !it.fileName().startsWith('.'))
+            ++count;
+    }
+    return stop && stop() ? -1 : count;
 }
 
 void FolderModel::reload() {
@@ -527,10 +538,11 @@ void FolderModel::countFolders(quint64 generation) {
     watcher->setFuture(QtConcurrent::run([folders, showHidden, latest, generation]() mutable {
         // Overtaken (another folder, or a re-read), the counts would be
         // thrown away, so it stops instead of listing every subfolder.
+        const auto overtaken = [&] { return *latest != generation; };
         for (auto &folder : folders) {
-            if (*latest != generation)
+            if (overtaken())
                 break;
-            folder.second.itemCount = itemCount(folder.second.path, showHidden);
+            folder.second.itemCount = itemCount(folder.second.path, showHidden, overtaken);
         }
         return folders;
     }));

src/foldermodel.h

@@ -120,7 +120,8 @@ class FolderModel : public QAbstractListModel {
     static void summarize(Entry &entry, bool showHidden);
     // Only how many items a folder holds, for the folder counts, which have
     // no use for its pictures or their order.
-    static int itemCount(const QString &folder, bool showHidden);
+    // Returns -1 (unknown) if stopped, never a partially counted folder.
+    static int itemCount(const QString &folder, bool showHidden, const std::function<bool()> &stop = {});
     static QStringList sortModes();
     static void sortEntries(QVector<Entry> &entries, const QString &sort, const QLocale &locale = QLocale());
     // The Recents view: a path that isn't a folder, listing recently used files.

tests/folio_tests.cpp

@@ -561,6 +561,35 @@ private slots:
         QCOMPARE(FolderModel::itemCount(dir.path(), true), 5);
     }
 
+    void folderCountStopsInsideTheFolderAndCanBeRetried()
+    {
+        QTemporaryDir dir;
+        for (int i = 0; i < 64; ++i)
+            write(dir.filePath(QString::number(i) + ".txt"), "x");
+        int checks = 0;
+        // Cancellation arrives during one folder, rather than between folders.
+        const int count = FolderModel::itemCount(dir.path(), false, [&] { return ++checks >= 4; });
+        QCOMPARE(count, -1); // Unknown, never a partial count.
+        QVERIFY(checks >= 4);
+        QVERIFY(checks < 64);
+        QCOMPARE(FolderModel::itemCount(dir.path(), false), 64);
+
+        // An empty or not-yet-started folder is unknown too once cancelled.
+        QTemporaryDir empty;
+        QCOMPARE(FolderModel::itemCount(empty.path(), false, [] { return true; }), -1);
+        QCOMPARE(FolderModel::itemCount(dir.path(), true, [] { return true; }), -1);
+        QCOMPARE(FolderModel::itemCount(empty.path(), false), 0);
+
+        // Hidden entries still take work to enumerate, even when not counted.
+        QTemporaryDir hidden;
+        for (int i = 0; i < 64; ++i)
+            write(hidden.filePath("." + QString::number(i) + ".txt"), "x");
+        checks = 0;
+        QCOMPARE(FolderModel::itemCount(hidden.path(), false, [&] { return ++checks >= 4; }), -1);
+        QCOMPARE(FolderModel::itemCount(hidden.path(), false), 0);
+        QCOMPARE(FolderModel::itemCount(hidden.path(), true), 64);
+    }
+
     void folderModelLoadsInTheBackground()
     {
         QTemporaryDir dir;