iOS: Fix showing emoji characters

In d5abda313dab0f83873d34b7c4ddbe8d8a06dacf, we started populating
meta-fallback-fonts in the font database because some that are
returned as fallbacks are not in the main list of fonts on the
system, so we would exclude them, thinking they were non-existent.

But populating these fonts by name does not always work, as
the system explicitly forbids requesting meta-fonts by name
for some cases. One of these was the emoji font, which would
resolve to a incompatible font descriptor and support for
emojis would be broken.

The fix is to retain the font descriptors we get from the
system instead, since these are guaranteed to be refer to the
correct font. This also saves us an unnecessary round-trip.

Task-number: QTBUG-78821
Task-number: QTBUG-77467
Change-Id: Icb17ccc75811eebf03919437828ba71f3ef08938
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 6 insertions, 10 deletions

diff --git a/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm b/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm
index e8ea194897..e78fb4e8e4 100644
--- a/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm
+++ b/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm
@@ -481,7 +481,12 @@ QStringList QCoreTextFontDatabase::fallbacksForFamily(const QString &family, QFo
                     for (int i = 0; i < numCascades; ++i) {
                         CTFontDescriptorRef fontFallback = (CTFontDescriptorRef) CFArrayGetValueAtIndex(cascadeList, i);
                         QCFString fallbackFamilyName = (CFStringRef) CTFontDescriptorCopyAttribute(fontFallback, kCTFontFamilyNameAttribute);
-                        fallbackList.append(QString::fromCFString(fallbackFamilyName));
+
+                        QString fallbackName = QString::fromCFString(fallbackFamilyName);
+                        fallbackList.append(fallbackName);
+
+                        if (!qt_isFontFamilyPopulated(fallbackName))
+                            const_cast<QCoreTextFontDatabase *>(this)->populateFromDescriptor(fontFallback, fallbackName);
                     }
 
                     // .Apple Symbols Fallback will be at the beginning of the list and we will
@@ -494,15 +499,6 @@ QStringList QCoreTextFontDatabase::fallbacksForFamily(const QString &family, QFo
 
                     addExtraFallbacks(&fallbackList);
 
-                    // Since iOS 13, the cascade list may contain meta-fonts which have not been
-                    // populated to the database, such as ".AppleJapaneseFont". It is important that we
-                    // include this in the fallback list, in order to get fallback support for all
-                    // languages
-                    for (const QString &fallback : fallbackList) {
-                        if (!qt_isFontFamilyPopulated(fallback))
-                            const_cast<QCoreTextFontDatabase *>(this)->populateFamily(fallback);
-                    }
-
                     extern QStringList qt_sort_families_by_writing_system(QChar::Script, const QStringList &);
                     fallbackList = qt_sort_families_by_writing_system(script, fallbackList);