Normalize Unicode compatibility characters as well

This expands a number of ligatures.

autotests/stringutiltest.cpp

@@ -26,6 +26,8 @@ private Q_SLOTS:
         QTest::newRow("normalized") << _("normal") << _("normal");
         QTest::newRow("case-folding") << _("NORMAL") << _("normal");
         QTest::newRow("umlaut") << _("NöRMÄl") << _("normal");
+        QTest::newRow("ligature1") << _("finish") << _("finish");
+        QTest::newRow("ligature2") << _("off") << _("off");
     }
 
     void testNormalize()

src/lib/mergeutil.cpp

@@ -373,13 +373,16 @@ static bool isSameTouristAttraction(const TouristAttraction &lhs, const TouristA
 }
 
 // compute the "difference" between @p lhs and @p rhs
-static QString diffString(const QString &lhs, const QString &rhs)
+static QString diffString(const QString &rawLhs, const QString &rawRhs)
 {
+    const auto lhs = StringUtil::normalize(rawLhs);
+    const auto rhs = StringUtil::normalize(rawRhs);
+
     QString diff;
     // this is just a basic linear-time heuristic, this would need to be more something like
     // the Levenstein Distance algorithm
     for (int i = 0, j = 0; i < lhs.size() || j < rhs.size();) {
-        if (i < lhs.size() && j < rhs.size() && StringUtil::normalize(lhs[i]) == StringUtil::normalize(rhs[j])) {
+        if (i < lhs.size() && j < rhs.size() && lhs[i] == rhs[j]) {
             ++i;
             ++j;
             continue;

src/lib/stringutil.cpp

@@ -11,28 +11,29 @@
 
 using namespace KItinerary;
 
-QChar StringUtil::normalize(QChar c)
-{
-    // case folding
-    const auto n = c.toCaseFolded();
-
-    // if the character has a canonical decomposition use that and skip the
-    // combining diacritic markers following it
-    // see https://en.wikipedia.org/wiki/Unicode_equivalence
-    // see https://en.wikipedia.org/wiki/Combining_character
-    if (n.decompositionTag() == QChar::Canonical) {
-        return n.decomposition().at(0);
-    }
-
-    return n;
-}
-
 QString StringUtil::normalize(QStringView str)
 {
     QString out;
     out.reserve(str.size());
     for (const auto c : str) {
-        out.push_back(normalize(c));
+        // case folding
+        const auto n = c.toCaseFolded();
+
+        // if the character has a canonical decomposition use that and skip the
+        // combining diacritic markers following it
+        // see https://en.wikipedia.org/wiki/Unicode_equivalence
+        // see https://en.wikipedia.org/wiki/Combining_character
+        if (n.decompositionTag() == QChar::Canonical) {
+            out.push_back(n.decomposition().at(0));
+        }
+        // handle compatibility compositions such as ligatures
+        // see https://en.wikipedia.org/wiki/Unicode_compatibility_characters
+        else if (n.decompositionTag() == QChar::Compat && n.isLetter() && n.script() == QChar::Script_Latin) {
+            out.append(n.decomposition());
+        }
+        else {
+            out.push_back(n);
+        }
     }
     return out;
 }

src/lib/stringutil.h

@@ -17,9 +17,6 @@ namespace KItinerary {
 /** String normalization and comparison utilities. */
 namespace StringUtil
 {
-    /** Convert @p c to case-folded form and remove diacritic marks. */
-    QChar normalize(QChar c);
-
     /** Strips out diacritics and converts to case-folded form.
      *  @internal only exported for unit tests
      */