macOS: Fix regression with some characters in non-bundle apps

.Noto Sans Univeral is a system-generated font, but for some
undiscovered reason, it has different content when the app
has a valid Info.plist versus when it does not.

When there is no valid Info.plist, the font will act as a
last-resort font and return a question mark glyph (index 4)
for all characters it does not support. This was discovered
with emojis, but I also verified that the font returns index
4 for a random character in the Cherokee range, in order to
check if this was specific for emojis or not.

This causes the font to take precedence over anything that
follows it in the fallback list in apps that do not have
a valid Info.plist, so it has to be at the end of the list.

Note that in these apps, it will act as a last-resort font,
so the glyphs returned for missing characters will be
different from in a regular app bundle. But this seems
safer than to exclude the font entirely, given that
Noto Sans cover a large range of characters and might be
needed.

This font also refactors the look up of fonts to push to
the end to avoid doing lots of unnecessary looping over
the list.

Fixes: QTBUG-78833
Change-Id: I38bec5d5941681c4b4586072f7811d31561e1051
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 18 insertions, 2 deletions

diff --git a/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm b/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm
index e78fb4e8e4..c450e91d49 100644
--- a/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm
+++ b/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm
@@ -478,6 +478,9 @@ QStringList QCoreTextFontDatabase::fallbacksForFamily(const QString &family, QFo
                 if (cascadeList) {
                     QStringList fallbackList;
                     const int numCascades = CFArrayGetCount(cascadeList);
+
+                    int symbolIndex = -1;
+                    int notoSansUniversalIndex = -1;
                     for (int i = 0; i < numCascades; ++i) {
                         CTFontDescriptorRef fontFallback = (CTFontDescriptorRef) CFArrayGetValueAtIndex(cascadeList, i);
                         QCFString fallbackFamilyName = (CFStringRef) CTFontDescriptorCopyAttribute(fontFallback, kCTFontFamilyNameAttribute);
@@ -487,15 +490,28 @@ QStringList QCoreTextFontDatabase::fallbacksForFamily(const QString &family, QFo
 
                         if (!qt_isFontFamilyPopulated(fallbackName))
                             const_cast<QCoreTextFontDatabase *>(this)->populateFromDescriptor(fontFallback, fallbackName);
+
+                        if (fallbackName == QLatin1String(".Apple Symbols Fallback"))
+                            symbolIndex = fallbackList.size() - 1;
+                        else if (fallbackName == QLatin1String(".Noto Sans Universal"))
+                            notoSansUniversalIndex = fallbackList.size() - 1;
                     }
 
                     // .Apple Symbols Fallback will be at the beginning of the list and we will
                     // detect that this has glyphs for Arabic and other writing systems.
                     // Since it is a symbol font, it should be the last resort, so that
                     // the proper fonts for these writing systems are preferred.
-                    int symbolIndex = fallbackList.indexOf(QLatin1String(".Apple Symbols Fallback"));
-                    if (symbolIndex >= 0)
+                    if (symbolIndex >= 0) {
                         fallbackList.move(symbolIndex, fallbackList.size() - 1);
+                        if (notoSansUniversalIndex > symbolIndex)
+                            --notoSansUniversalIndex;
+                    }
+
+                    // .Noto Sans Universal appears to have a bug when the application
+                    // does not have a valid Info.plist, which causes it to return glyph #4
+                    // (a question mark) for any character.
+                    if (notoSansUniversalIndex >= 0)
+                        fallbackList.move(notoSansUniversalIndex, fallbackList.size() - 1);
 
                     addExtraFallbacks(&fallbackList);