Introduce a new signal "groupsChanged"

Sometimes when items are renamed, the order of the items in the
directory is not affected, but the groups still change (simple example:
with files a, b, c, e, rename "c" to "d"). At the moment, we always emit
the itemsMoved signal in such a case to make sure that the view is
updated. However, it would be preferable if this signal was not emitted
because it can trigger some quite expensive operations which are not
needed at all.

This commit introduces a new signal groupsChanged and modifies
KFileItemModel and KItemListView such that these classes make use of it.
Some unit tests for the new functionality are included as well.

Thanks to Emmanuel Pescosta for finding a latent bug in the code which
was triggered by this change and fixed in
998954db6d53999dfa75d380cbb4ca3111589f66.

REVIEW: 111808

1 files changed, 37 insertions, 13 deletions

diff --git a/src/kitemviews/kfileitemmodel.cpp b/src/kitemviews/kfileitemmodel.cpp
index 1b4911dec..c7e1c8600 100644
--- a/src/kitemviews/kfileitemmodel.cpp
+++ b/src/kitemviews/kfileitemmodel.cpp
@@ -689,7 +689,6 @@ void KFileItemModel::resortAllItems()
         oldUrls.append(itemData->item.url());
     }
 
-    m_groups.clear();
     m_items.clear();
 
     // Resort the items
@@ -698,20 +697,45 @@ void KFileItemModel::resortAllItems()
         m_items.insert(m_itemData.at(i)->item.url(), i);
     }
 
-    // Determine the indexes that have been moved
-    QList<int> movedToIndexes;
-    movedToIndexes.reserve(itemCount);
-    for (int i = 0; i < itemCount; i++) {
-        const int newIndex = m_items.value(oldUrls.at(i));
-        movedToIndexes.append(newIndex);
+    // Determine the first index that has been moved.
+    int firstMovedIndex = 0;
+    while (firstMovedIndex < itemCount
+           && firstMovedIndex == m_items.value(oldUrls.at(firstMovedIndex))) {
+        ++firstMovedIndex;
     }
 
-    // Don't check whether items have really been moved and always emit a
-    // itemsMoved() signal after resorting: In case of grouped items
-    // the groups might change even if the items themselves don't change their
-    // position. Let the receiver of the signal decide whether a check for moved
-    // items makes sense.
-    emit itemsMoved(KItemRange(0, itemCount), movedToIndexes);
+    const bool itemsHaveMoved = firstMovedIndex < itemCount;
+    if (itemsHaveMoved) {
+        m_groups.clear();
+
+        int lastMovedIndex = itemCount - 1;
+        while (lastMovedIndex > firstMovedIndex
+               && lastMovedIndex == m_items.value(oldUrls.at(lastMovedIndex))) {
+            --lastMovedIndex;
+        }
+
+        Q_ASSERT(firstMovedIndex <= lastMovedIndex);
+
+        // Create a list movedToIndexes, which has the property that
+        // movedToIndexes[i] is the new index of the item with the old index
+        // firstMovedIndex + i.
+        const int movedItemsCount = lastMovedIndex - firstMovedIndex + 1;
+        QList<int> movedToIndexes;
+        movedToIndexes.reserve(movedItemsCount);
+        for (int i = firstMovedIndex; i <= lastMovedIndex; ++i) {
+            const int newIndex = m_items.value(oldUrls.at(i));
+            movedToIndexes.append(newIndex);
+        }
+
+        emit itemsMoved(KItemRange(firstMovedIndex, movedItemsCount), movedToIndexes);
+    } else if (groupedSorting()) {
+        // The groups might have changed even if the order of the items has not.
+        const QList<QPair<int, QVariant> > oldGroups = m_groups;
+        m_groups.clear();
+        if (groups() != oldGroups) {
+            emit groupsChanged();
+        }
+    }
 
 #ifdef KFILEITEMMODEL_DEBUG
     kDebug() << "[TIME] Resorting of" << itemCount << "items:" << timer.elapsed();