Fix weight when reading old serialized QFonts

The QFont::fromString() needs to differ between strings
produced before and after Qt 6.0 when interpreting the
weight value, since in older strings this will be the legacy
scale.

Luckily the number of tokens in the string can be used for this
purpose, since many tokens were added in Qt 6.0.

This broke KDE, where font settings are stored in QSettings
and serialized using QFont::toString() from Qt 5.

Fixes: QTBUG-88589
Change-Id: I199737fed61917f8b9d8f86176ead29a89eb8e0c
Reviewed-by: Andy Shaw <andy.shaw@qt.io>
(cherry picked from commit 1d14067680f02f47b2f8ff375c44eb64633eec02)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

3 files changed, 8 insertions, 5 deletions

diff --git a/src/gui/text/qfont.cpp b/src/gui/text/qfont.cpp
index 53344418a0..63b13df38b 100644
--- a/src/gui/text/qfont.cpp
+++ b/src/gui/text/qfont.cpp
@@ -2150,7 +2150,10 @@ bool QFont::fromString(const QString &descrip)
         if (l[2].toInt() > 0)
             setPixelSize(l[2].toInt());
         setStyleHint((StyleHint) l[3].toInt());
-        setWeight(QFont::Weight(l[4].toInt()));
+        if (count >= 16)
+            setWeight(QFont::Weight(l[4].toInt()));
+        else
+            setWeight(QFont::Weight(qt_legacyToOpenTypeWeight(l[4].toInt())));
         setStyle((QFont::Style)l[5].toInt());
         setUnderline(l[6].toInt());
         setStrikeOut(l[7].toInt());
diff --git a/tests/auto/gui/kernel/qguivariant/test/tst_qguivariant.cpp b/tests/auto/gui/kernel/qguivariant/test/tst_qguivariant.cpp
index 5a01263d80..9ef5ce75bf 100644
--- a/tests/auto/gui/kernel/qguivariant/test/tst_qguivariant.cpp
+++ b/tests/auto/gui/kernel/qguivariant/test/tst_qguivariant.cpp
@@ -334,7 +334,7 @@ void tst_QGuiVariant::toFont_data()
     QTest::addColumn<QFont>("result");
 
     QFont f("times",12,-1,false);
-    QTest::newRow( "string" ) << QVariant( QString( "times,12,-1,5,400,0,0,0,0,0" ) ) << f;
+    QTest::newRow( "string" ) << QVariant( QString( "times,12,-1,5,50,0,0,0,0,0" ) ) << f;
 }
 
 void tst_QGuiVariant::toFont()
diff --git a/tests/auto/gui/text/qfont/tst_qfont.cpp b/tests/auto/gui/text/qfont/tst_qfont.cpp
index 4cc5a81329..28959a61bf 100644
--- a/tests/auto/gui/text/qfont/tst_qfont.cpp
+++ b/tests/auto/gui/text/qfont/tst_qfont.cpp
@@ -601,7 +601,7 @@ void tst_QFont::toAndFromString()
 
     // Since Qt 6.0 it was changed to include more information in the description, so
     // this checks for compatibility
-    const QString fontStringFrom515(QLatin1String("Times New Roman,18,-1,5,700,1,0,0,1,0,Regular"));
+    const QString fontStringFrom515(QLatin1String("Times New Roman,18,-1,5,75,1,0,0,1,0,Regular"));
     QFont fontFrom515("Times New Roman", 18);
     fontFrom515.setBold(true);
     fontFrom515.setItalic(true);
@@ -628,7 +628,7 @@ void tst_QFont::toAndFromString()
 void tst_QFont::fromStringWithoutStyleName()
 {
     QFont font1;
-    font1.fromString("Noto Sans,12,-1,5,400,0,0,0,0,0,Regular");
+    font1.fromString("Noto Sans,12,-1,5,50,0,0,0,0,0,Regular");
 
     QFont font2 = font1;
     const QString str = "Times,16,-1,5,400,0,0,0,0,0,0,0,0,0,0,1";
@@ -639,7 +639,7 @@ void tst_QFont::fromStringWithoutStyleName()
     const QString fontStringFrom60(
             QLatin1String("Times New Roman,18,-1,5,700,1,0,0,1,0,1,0,150.5,2.5,50,2"));
     QFont font3;
-    font3.fromString("Noto Sans,12,-1,5,400,0,0,0,0,0,Regular");
+    font3.fromString("Noto Sans,12,-1,5,50,0,0,0,0,0,Regular");
     QFont font4 = font3;
     font4.fromString(fontStringFrom60);
     QCOMPARE(font4.toString(), fontStringFrom60);