Use "monospace" as fallback system FixedFont in KDE theme; logging

Also de-duplicate the "monospace" string in qgenericunixthemes.cpp,
and add tst_QFontDatabase::systemFixedFont() to verify that
QFontDatabase::systemFont(QFontDatabase::FixedFont) really returns
a monospace font across platforms.  Replace commented-out qDebug()s
with qt.text.font.match and qt.text.font.db logging categories to
troubleshoot when the test fails (among other uses).  Add qt.qpa.fonts
logging category to unix themes to show default system and fixed fonts
(font engines on other platforms are already using this category).

Fixes: QTBUG-54623
Change-Id: I2aa62b8c783d9ddb591a5e06e8df85c4af5bcb0c
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 9 insertions, 3 deletions

diff --git a/src/platformsupport/themes/genericunix/qgenericunixthemes.cpp b/src/platformsupport/themes/genericunix/qgenericunixthemes.cpp
index 1003812767..6db25a90da 100644
--- a/src/platformsupport/themes/genericunix/qgenericunixthemes.cpp
+++ b/src/platformsupport/themes/genericunix/qgenericunixthemes.cpp
@@ -76,6 +76,7 @@
 QT_BEGIN_NAMESPACE
 
 Q_DECLARE_LOGGING_CATEGORY(qLcTray)
+Q_LOGGING_CATEGORY(lcQpaFonts, "qt.qpa.fonts")
 
 ResourceHelper::ResourceHelper()
 {
@@ -96,6 +97,7 @@ const char *QGenericUnixTheme::name = "generic";
 // Default system font, corresponding to the value returned by 4.8 for
 // XRender/FontConfig which we can now assume as default.
 static const char defaultSystemFontNameC[] = "Sans Serif";
+static const char defaultFixedFontNameC[] = "monospace";
 enum { defaultSystemFontSize = 9 };
 
 #if !defined(QT_NO_DBUS) && !defined(QT_NO_SYSTEMTRAYICON)
@@ -136,9 +138,10 @@ public:
     QGenericUnixThemePrivate()
         : QPlatformThemePrivate()
         , systemFont(QLatin1String(defaultSystemFontNameC), defaultSystemFontSize)
-        , fixedFont(QStringLiteral("monospace"), systemFont.pointSize())
+        , fixedFont(QLatin1String(defaultFixedFontNameC), systemFont.pointSize())
     {
         fixedFont.setStyleHint(QFont::TypeWriter);
+        qCDebug(lcQpaFonts) << "default fonts: system" << systemFont << "fixed" << fixedFont;
     }
 
     const QFont systemFont;
@@ -390,7 +393,7 @@ void QKdeThemePrivate::refresh()
     if (QFont *fixedFont = kdeFont(readKdeSetting(QStringLiteral("fixed"), kdeDirs, kdeVersion, kdeSettings))) {
         resources.fonts[QPlatformTheme::FixedFont] = fixedFont;
     } else {
-        fixedFont = new QFont(QLatin1String(defaultSystemFontNameC), defaultSystemFontSize);
+        fixedFont = new QFont(QLatin1String(defaultFixedFontNameC), defaultSystemFontSize);
         fixedFont->setStyleHint(QFont::TypeWriter);
         resources.fonts[QPlatformTheme::FixedFont] = fixedFont;
     }
@@ -403,6 +406,8 @@ void QKdeThemePrivate::refresh()
     if (QFont *toolBarFont = kdeFont(readKdeSetting(QStringLiteral("toolBarFont"), kdeDirs, kdeVersion, kdeSettings)))
         resources.fonts[QPlatformTheme::ToolButtonFont] = toolBarFont;
 
+    qCDebug(lcQpaFonts) << "default fonts: system" << resources.fonts[QPlatformTheme::SystemFont]
+                        << "fixed" << resources.fonts[QPlatformTheme::FixedFont];
     qDeleteAll(kdeSettings);
 }
 
@@ -716,8 +721,9 @@ public:
         QString fontName = gtkFontName.left(split);
 
         systemFont = new QFont(fontName, size);
-        fixedFont = new QFont(QLatin1String("monospace"), systemFont->pointSize());
+        fixedFont = new QFont(QLatin1String(defaultFixedFontNameC), systemFont->pointSize());
         fixedFont->setStyleHint(QFont::TypeWriter);
+        qCDebug(lcQpaFonts) << "default fonts: system" << systemFont << "fixed" << fixedFont;
     }
 
     mutable QFont *systemFont;