QtBase: use printf-style qWarning/qDebug where possible (II)

The printf-style version of QDebug expands to a lot less code than the
std::ostream-style version. Of course, you pay in type safety (but
compilers warn about it these days), you cannot stream complex Qt
types and streaming QStrings is awkward, but in many cases you
actually improve on readability.

But the main reason is that something that's not supposed to be
executed under normal operation has no business bloating executable
code size.

This is not an attempt at converting all qWarnings() to printf-style,
only the low-hanging fruit.

In this second part, replace
   qWarning() << "" << non-QString
with
   qWarning("..%.", non-QString).

QString (and QUrl etc) have special escaping handling when streamed
into QDebug, so leave those alone. They also seem to expand to less
code than the qPrintable() alternative, so there's no reason to
replace them.

Saves 2KiB, 3.4KiB, ~750b and ~450b in text size in QtCore, Gui,
Network and Widgets, resp., on optimized GCC 5.3 AMD64 builds.

Change-Id: Iae6823e543544347e628ca1060d6d51e3b04d3f4
Reviewed-by: Kai Koehne <kai.koehne@qt.io>

2 files changed, 6 insertions, 5 deletions

diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index 129e93db8d..1f102dcec5 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -1186,7 +1186,7 @@ static void init_plugins(const QList<QByteArray> &pluginList)
         if (plugin)
             QGuiApplicationPrivate::generic_plugin_list.append(plugin);
         else
-            qWarning() << "No such plugin for spec " << pluginSpec;
+            qWarning("No such plugin for spec \"%s\"", pluginSpec.constData());
     }
 }
 
diff --git a/src/gui/kernel/qhighdpiscaling.cpp b/src/gui/kernel/qhighdpiscaling.cpp
index 4cc9e95e81..d6e467db59 100644
--- a/src/gui/kernel/qhighdpiscaling.cpp
+++ b/src/gui/kernel/qhighdpiscaling.cpp
@@ -68,10 +68,11 @@ static inline qreal initialGlobalScaleFactor()
         }
     } else {
         if (qEnvironmentVariableIsSet(legacyDevicePixelEnvVar)) {
-            qWarning() << "Warning:" << legacyDevicePixelEnvVar << "is deprecated. Instead use:" << endl
-                       << "   " << autoScreenEnvVar << "to enable platform plugin controlled per-screen factors." << endl
-                       << "   " << screenFactorsEnvVar << "to set per-screen factors." << endl
-                       << "   " << scaleFactorEnvVar << "to set the application global scale factor.";
+            qWarning("Warning: %s is deprecated. Instead use:\n"
+                     "   %s to enable platform plugin controlled per-screen factors.\n"
+                     "   %s to set per-screen factors.\n"
+                     "   %s to set the application global scale factor.",
+                     legacyDevicePixelEnvVar, autoScreenEnvVar, screenFactorsEnvVar, scaleFactorEnvVar);
 
             int dpr = qEnvironmentVariableIntValue(legacyDevicePixelEnvVar);
             if (dpr > 0)