Reload QLibraryInfo's settings when QCoreApplication becomes available

Some of the paths may only be resolvable if the application path is
known. On some platforms we can only figure out the application path
if argv[0] is known. Thus, if the paths have been queried before the
QCoreApplication is created, the cached settings may be wrong. We have
to reload them after creating the QCoreApplication.

Task-number: QTBUG-38598
Change-Id: Idf5822be87aa0872b099480040acd7b49939a22c
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

src/corelib/global/qlibraryinfo.cpp

@@ -63,12 +63,16 @@ extern void qDumpCPUFeatures(); // in qsimd.cpp
 struct QLibrarySettings
 {
     QLibrarySettings();
+    void load();
+
     QScopedPointer<QSettings> settings;
 #ifdef QT_BUILD_QMAKE
     bool haveDevicePaths;
     bool haveEffectiveSourcePaths;
     bool haveEffectivePaths;
     bool havePaths;
+#else
+    bool reloadOnQAppAvailable;
 #endif
 };
 Q_GLOBAL_STATIC(QLibrarySettings, qt_library_settings)
@@ -93,16 +97,31 @@ public:
     static QSettings *configuration()
     {
         QLibrarySettings *ls = qt_library_settings();
-        return ls ? ls->settings.data() : 0;
+        if (ls) {
+#ifndef QT_BUILD_QMAKE
+            if (ls->reloadOnQAppAvailable && QCoreApplication::instance() != 0)
+                ls->load();
+#endif
+            return ls->settings.data();
+        } else {
+            return 0;
+        }
     }
 };
 
 static const char platformsSection[] = "Platforms";
 
 QLibrarySettings::QLibrarySettings()
-    : settings(QLibraryInfoPrivate::findConfiguration())
 {
+    load();
+}
+
+void QLibrarySettings::load()
+{
+    // If we get any settings here, those won't change when the application shows up.
+    settings.reset(QLibraryInfoPrivate::findConfiguration());
 #ifndef QT_BUILD_QMAKE
+    reloadOnQAppAvailable = (settings.data() == 0 && QCoreApplication::instance() == 0);
     bool haveDevicePaths;
     bool haveEffectivePaths;
     bool havePaths;