natural sort: exclude extension when comparing filenames

Currently natural sort compares the entire filenames
(basename.extension) when sorting. This causes eg.
"a 2.txt" to appear before "a.txt" when sorted by ascending.
This is unintuitive since people prioritize basenames more
than file extensions.

Instead, change natural sort to compare by basename only and
fallback to comparing extensions if basenames were equal.
This change causes "a.txt" to appear before "a 2.txt" and
matches how other platforms such as GNOME and Windows behave.

BUG: 416025
BUG: 470538
BUG: 421869
BUG: 312027

2 files changed, 26 insertions, 3 deletions

diff --git a/src/kitemviews/kfileitemmodel.cpp b/src/kitemviews/kfileitemmodel.cpp
index fb5851c36..f8c30b9e4 100644
--- a/src/kitemviews/kfileitemmodel.cpp
+++ b/src/kitemviews/kfileitemmodel.cpp
@@ -2249,7 +2249,24 @@ int KFileItemModel::stringCompare(const QString &a, const QString &b, const QCol
     QMutexLocker collatorLock(s_collatorMutex());
 
     if (m_naturalSorting) {
-        return collator.compare(a, b);
+        // Split extension, taking into account it can be empty
+        constexpr QString::SectionFlags flags = QString::SectionSkipEmpty | QString::SectionIncludeLeadingSep;
+
+        // Sort by baseName first
+        const QString aBaseName = a.section('.', 0, 0, flags);
+        const QString bBaseName = b.section('.', 0, 0, flags);
+
+        const int res = collator.compare(aBaseName, bBaseName);
+        if (res != 0 || (aBaseName.length() == a.length() && bBaseName.length() == b.length())) {
+            return res;
+        }
+
+        // sliced() has undefined behavior when pos < 0 or pos > size().
+        Q_ASSERT(aBaseName.length() <= a.length() && aBaseName.length() >= 0);
+        Q_ASSERT(bBaseName.length() <= b.length() && bBaseName.length() >= 0);
+
+        // baseNames were equal, sort by extension
+        return collator.compare(a.sliced(aBaseName.length()), b.sliced(bBaseName.length()));
     }
 
     const int result = QString::compare(a, b, collator.caseSensitivity());
diff --git a/src/kitemviews/kfileitemmodel.h b/src/kitemviews/kfileitemmodel.h
index 5662d4fa8..10be27128 100644
--- a/src/kitemviews/kfileitemmodel.h
+++ b/src/kitemviews/kfileitemmodel.h
@@ -365,7 +365,11 @@ private:
         ItemData *parent;
     };
 
-    enum RemoveItemsBehavior { KeepItemData, DeleteItemData, DeleteItemDataIfUnfiltered };
+    enum RemoveItemsBehavior {
+        KeepItemData,
+        DeleteItemData,
+        DeleteItemDataIfUnfiltered
+    };
 
     void insertItems(QList<ItemData *> &items);
     void removeItems(const KItemRangeList &itemRanges, RemoveItemsBehavior behavior);
@@ -588,7 +592,9 @@ inline bool KFileItemModel::isRoleValueNatural(RoleType roleType)
 
 inline bool KFileItemModel::nameLessThan(const ItemData *a, const ItemData *b)
 {
-    return a->item.text() < b->item.text();
+    // Split extension, taking into account it can be empty
+    constexpr QString::SectionFlags flags = QString::SectionSkipEmpty | QString::SectionIncludeLeadingSep;
+    return a->item.text().section('.', 0, 0, flags) < b->item.text().section('.', 0, 0, flags);
 }
 
 inline bool KFileItemModel::isChildItem(int index) const