Improve grouping by name for non-ASCII file names

This commit prevents that all non-ASCII letters which are not umlauts
are grouped in a single group "Others", and that the joint group of
an ASCII letter and the associated umlaut in some locales is called
"Others" if there is only the umlaut in the group.

BUG: 315569
REVIEW: 109457
FIXED-IN: 4.10.2

1 files changed, 28 insertions, 21 deletions

diff --git a/src/kitemviews/kfileitemmodel.cpp b/src/kitemviews/kfileitemmodel.cpp
index 26521a6b6..7ba78a436 100644
--- a/src/kitemviews/kfileitemmodel.cpp
+++ b/src/kitemviews/kfileitemmodel.cpp
@@ -33,6 +33,9 @@
 #include <QTimer>
 #include <QWidget>
 
+#include <algorithm>
+#include <vector>
+
 // #define KFILEITEMMODEL_DEBUG
 
 KFileItemModel::KFileItemModel(QObject* parent) :
@@ -1612,6 +1615,11 @@ bool KFileItemModel::useMaximumUpdateInterval() const
     return !m_dirLister->url().isLocalFile();
 }
 
+static bool localeAwareLessThan(const QChar& c1, const QChar& c2)
+{
+    return QString::localeAwareCompare(c1, c2) < 0;
+}
+
 QList<QPair<int, QVariant> > KFileItemModel::nameRoleGroups() const
 {
     Q_ASSERT(!m_itemData.isEmpty());
@@ -1621,7 +1629,6 @@ QList<QPair<int, QVariant> > KFileItemModel::nameRoleGroups() const
 
     QString groupValue;
     QChar firstChar;
-    bool isLetter = false;
     for (int i = 0; i <= maxIndex; ++i) {
         if (isChildItem(i)) {
             continue;
@@ -1637,31 +1644,31 @@ QList<QPair<int, QVariant> > KFileItemModel::nameRoleGroups() const
 
         if (firstChar != newFirstChar) {
             QString newGroupValue;
-            if (newFirstChar >= QLatin1Char('A') && newFirstChar <= QLatin1Char('Z')) {
-                // Apply group 'A' - 'Z'
-                newGroupValue = newFirstChar;
-                isLetter = true;
+            if (newFirstChar.isLetter()) {
+                // Try to find a matching group in the range 'A' to 'Z'.
+                static std::vector<QChar> lettersAtoZ;
+                if (lettersAtoZ.empty()) {
+                    for (char c = 'A'; c <= 'Z'; ++c) {
+                        lettersAtoZ.push_back(QLatin1Char(c));
+                    }
+                }
+
+                std::vector<QChar>::iterator it = std::lower_bound(lettersAtoZ.begin(), lettersAtoZ.end(), newFirstChar, localeAwareLessThan);
+                if (it != lettersAtoZ.end()) {
+                    if (localeAwareLessThan(newFirstChar, *it) && it != lettersAtoZ.begin()) {
+                        // newFirstChar belongs to the group preceding *it.
+                        // Example: for an umlaut 'A' in the German locale, *it would be 'B' now.
+                        --it;
+                    }
+                    newGroupValue = *it;
+                } else {
+                    newGroupValue = newFirstChar;
+                }
             } else if (newFirstChar >= QLatin1Char('0') && newFirstChar <= QLatin1Char('9')) {
                 // Apply group '0 - 9' for any name that starts with a digit
                 newGroupValue = i18nc("@title:group Groups that start with a digit", "0 - 9");
-                isLetter = false;
             } else {
-                if (isLetter) {
-                    // If the current group is 'A' - 'Z' check whether a locale character
-                    // fits into the existing group.
-                    // TODO: This does not work in the case if e.g. the group 'O' starts with
-                    // an umlaut 'O' -> provide unit-test to document this known issue
-                    const QChar prevChar(firstChar.unicode() - ushort(1));
-                    const QChar nextChar(firstChar.unicode() + ushort(1));
-                    const QString currChar(newFirstChar);
-                    const bool partOfCurrentGroup = currChar.localeAwareCompare(prevChar) > 0 &&
-                                                    currChar.localeAwareCompare(nextChar) < 0;
-                    if (partOfCurrentGroup) {
-                        continue;
-                    }
-                }
                 newGroupValue = i18nc("@title:group", "Others");
-                isLetter = false;
             }
 
             if (newGroupValue != groupValue) {