macOS: Prevent leaking font data when creating QRawFont from QByteArrays

CTFontCreateWithGraphicsFont has a bug causing it to never release the
graphics font, which cascades down to the data provider never being
released and releaseFontData never being called.

Instead of relying on a callback to release the byte array font data,
we attach the font data to the engine's lifetime. Note that we are
still leaking the CoreFoundation types.

Change-Id: I6eda4212638ccc9439b90e004222272d204c707a
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm

@@ -419,37 +419,16 @@ QFontEngine *QCoreTextFontDatabaseEngineFactory<QFontEngineFT>::fontEngine(const
 }
 #endif
 
-template <>
+template <class T>
-QFontEngine *QCoreTextFontDatabaseEngineFactory<QCoreTextFontEngine>::fontEngine(const QByteArray &fontData, qreal pixelSize, QFont::HintingPreference hintingPreference)
+QFontEngine *QCoreTextFontDatabaseEngineFactory<T>::fontEngine(const QByteArray &fontData, qreal pixelSize, QFont::HintingPreference hintingPreference)
 {
-    Q_UNUSED(hintingPreference);
+    return T::create(fontData, pixelSize, hintingPreference);
-
-    QByteArray* fontDataCopy = new QByteArray(fontData);
-    QCFType<CGDataProviderRef> dataProvider = CGDataProviderCreateWithData(fontDataCopy,
-            fontDataCopy->constData(), fontDataCopy->size(), releaseFontData);
-
-    CGFontRef cgFont = CGFontCreateWithDataProvider(dataProvider);
-
-    QFontEngine *fontEngine = NULL;
-    if (cgFont == NULL) {
-        qWarning("QCoreTextFontDatabase::fontEngine: CGFontCreateWithDataProvider failed");
-    } else {
-        QFontDef def;
-        def.pixelSize = pixelSize;
-        def.pointSize = pixelSize * 72.0 / qt_defaultDpi();
-        fontEngine = new QCoreTextFontEngine(cgFont, def);
-        CFRelease(cgFont);
-    }
-
-    return fontEngine;
 }
 
+// Explicitly instantiate so that we don't need the plugin to involve FreeType
+template class QCoreTextFontDatabaseEngineFactory<QCoreTextFontEngine>;
 #ifndef QT_NO_FREETYPE
-template <>
+template class QCoreTextFontDatabaseEngineFactory<QFontEngineFT>;
-QFontEngine *QCoreTextFontDatabaseEngineFactory<QFontEngineFT>::fontEngine(const QByteArray &fontData, qreal pixelSize, QFont::HintingPreference hintingPreference)
-{
-    return QFontEngineFT::create(fontData, pixelSize, hintingPreference);
-}
 #endif
 
 QFont::StyleHint styleHintFromNSString(NSString *style)

src/platformsupport/fontdatabases/mac/qfontengine_coretext.mm

@@ -177,6 +177,43 @@ CGAffineTransform qt_transform_from_fontdef(const QFontDef &fontDef)
     return transform;
 }
 
+// Keeps font data alive until engine is disposed
+class QCoreTextRawFontEngine : public QCoreTextFontEngine
+{
+public:
+    QCoreTextRawFontEngine(CGFontRef font, const QFontDef &def, const QByteArray &fontData)
+        : QCoreTextFontEngine(font, def)
+        , m_fontData(fontData)
+    {}
+    QByteArray m_fontData;
+};
+
+QCoreTextFontEngine *QCoreTextFontEngine::create(const QByteArray &fontData, qreal pixelSize, QFont::HintingPreference hintingPreference)
+{
+    Q_UNUSED(hintingPreference);
+
+    QCFType<CFDataRef> fontDataReference = fontData.toRawCFData();
+    QCFType<CGDataProviderRef> dataProvider = CGDataProviderCreateWithCFData(fontDataReference);
+
+    // Note: CTFontCreateWithGraphicsFont (which we call from the  QCoreTextFontEngine
+    // constructor) has a bug causing it to retain the CGFontRef but never release it.
+    // The result is that we are leaking the CGFont, CGDataProvider, and CGData, but
+    // as the CGData is created from the raw QByteArray data, which we deref in the
+    // subclass above during destruction, we're at least not leaking the font data,
+    // (unless CoreText copies it internally). http://stackoverflow.com/questions/40805382/
+    QCFType<CGFontRef> cgFont = CGFontCreateWithDataProvider(dataProvider);
+
+    if (!cgFont) {
+        qWarning("QCoreTextFontEngine::create: CGFontCreateWithDataProvider failed");
+        return nullptr;
+    }
+
+    QFontDef def;
+    def.pixelSize = pixelSize;
+    def.pointSize = pixelSize * 72.0 / qt_defaultDpi();
+    return new QCoreTextRawFontEngine(cgFont, def, fontData);
+}
+
 QCoreTextFontEngine::QCoreTextFontEngine(CTFontRef font, const QFontDef &def)
     : QFontEngine(Mac)
 {

src/platformsupport/fontdatabases/mac/qfontengine_coretext_p.h

@@ -123,6 +123,8 @@ public:
 
     static int antialiasingThreshold;
     static QFontEngine::GlyphFormat defaultGlyphFormat;
+
+    static QCoreTextFontEngine *create(const QByteArray &fontData, qreal pixelSize, QFont::HintingPreference hintingPreference);
 private:
     void init();
     QImage imageForGlyph(glyph_t glyph, QFixed subPixelPosition, bool colorful, const QTransform &m);