QFont: Fix possible cache misses due to misprepared cache key

Parse the requested family before we're looking/saving into the cache,
thus hitting the cached EngineData for:
* quoted family names (eg. QFont("'Arial'"))
* non-simplified family names (eg. QFont(" Arial  "))
* substituted family names (\sa QFont::insertSubstitution())
* explicit fallback list, where possible (eg. QFont("Tahoma, Arial"))

This also improves the cache hitting for the font engines in some cases.

Change-Id: I18cdc3e8d669cccec961f84e9b27329402e2b7ed
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>

src/gui/text/qfontdatabase.cpp

@@ -2732,9 +2732,16 @@ void QFontDatabase::load(const QFontPrivate *d, int script)
     if (req.stretch == 0)
         req.stretch = 100;
 
+    // respect the fallback families that might be passed through the request
+    const QStringList fallBackFamilies = familyList(req);
+
     if (!d->engineData) {
         QFontCache *fontCache = QFontCache::instance();
         // look for the requested font in the engine data cache
+        // note: fallBackFamilies are not respected in the EngineData cache key;
+        //       join them with the primary selection family to avoid cache misses
+        req.family = fallBackFamilies.join(QLatin1Char(','));
+
         d->engineData = fontCache->findEngineData(req);
         if (!d->engineData) {
             // create a new one
@@ -2748,25 +2755,18 @@ void QFontDatabase::load(const QFontPrivate *d, int script)
     if (d->engineData->engines[script])
         return;
 
-    // Until we specifically asked not to, try looking for Multi font engine
+    QFontEngine *fe = Q_NULLPTR;
-    // first, the last '1' indicates that we want Multi font engine instead
-    // of single ones
-    bool multi = !(req.styleStrategy & QFont::NoFontMerging);
-    QFontCache::Key key(req, script, multi ? 1 : 0);
 
-    QFontEngine *fe = QFontCache::instance()->findEngine(key);
+    req.fallBackFamilies = fallBackFamilies;
+    if (!req.fallBackFamilies.isEmpty())
+        req.family = req.fallBackFamilies.takeFirst();
 
     // list of families to try
     QStringList family_list;
 
     if (!req.family.isEmpty()) {
-        QStringList familiesForRequest = familyList(req);
-
         // Add primary selection
-        family_list << familiesForRequest.takeFirst();
+        family_list << req.family;
-
-        // Fallbacks requested in font request
-        req.fallBackFamilies = familiesForRequest;
 
         // add the default family
         QString defaultFamily = QGuiApplication::font().family();

tests/auto/gui/text/qfontcache/tst_qfontcache.cpp

@@ -48,6 +48,9 @@ public:
     virtual ~tst_QFontCache();
 
 private slots:
+    void engineData_data();
+    void engineData();
+
     void clear();
 };
 
@@ -69,6 +72,52 @@ tst_QFontCache::~tst_QFontCache()
 {
 }
 
+void tst_QFontCache::engineData_data()
+{
+    QTest::addColumn<QString>("family");
+    QTest::addColumn<QString>("cacheKey");
+
+    QTest::newRow("unquoted-family-name") << QString("Times New Roman") << QString("Times New Roman");
+    QTest::newRow("quoted-family-name") << QString("'Times New Roman'") << QString("Times New Roman");
+    QTest::newRow("invalid") << QString("invalid") << QString("invalid");
+    QTest::newRow("multiple") << QString("invalid, Times New Roman") << QString("invalid,Times New Roman");
+    QTest::newRow("multiple spaces") << QString("invalid,  Times New Roman ") << QString("invalid,Times New Roman");
+    QTest::newRow("multiple spaces quotes") << QString("'invalid',  Times New Roman ") << QString("invalid,Times New Roman");
+    QTest::newRow("multiple2") << QString("invalid, Times New Roman  , foobar, 'baz'") << QString("invalid,Times New Roman,foobar,baz");
+    QTest::newRow("invalid spaces") << QString("invalid spaces, Times New Roman ") << QString("invalid spaces,Times New Roman");
+    QTest::newRow("invalid spaces quotes") << QString("'invalid spaces', 'Times New Roman' ") << QString("invalid spaces,Times New Roman");
+}
+
+void tst_QFontCache::engineData()
+{
+    QFETCH(QString, family);
+    QFETCH(QString, cacheKey);
+
+    QFont f(family);
+    f.exactMatch(); // loads engine
+
+    QFontPrivate *d = QFontPrivate::get(f);
+
+    QFontDef req = d->request;
+    // copy-pasted from QFontDatabase::load(), to engineer the cache key
+    if (req.pixelSize == -1) {
+        req.pixelSize = std::floor(((req.pointSize * d->dpi) / 72) * 100 + 0.5) / 100;
+        req.pixelSize = qRound(req.pixelSize);
+    }
+    if (req.pointSize < 0)
+        req.pointSize = req.pixelSize*72.0/d->dpi;
+    if (req.weight == 0)
+        req.weight = QFont::Normal;
+    if (req.stretch == 0)
+        req.stretch = 100;
+
+    req.family = cacheKey;
+
+    QFontEngineData *engineData = QFontCache::instance()->findEngineData(req);
+
+    QCOMPARE(engineData, QFontPrivate::get(f)->engineData);
+}
+
 void tst_QFontCache::clear()
 {
 #ifdef QT_BUILD_INTERNAL