Do not crash when loading themed icons statically

We do not officially support static loading of icons.
In fact they still crash for simple png cases due to missing
X11 resources. But since we lazily create themed icons
we can certainly avoid the crash in this case. You will
not be able to use fallbacks here though, since we cannot
know if a fallback should be used or not in this case.

Reviewed-by: ogoffart
Task-number: QTBUG-8666

3 files changed, 28 insertions, 10 deletions

diff --git a/src/gui/image/qicon.cpp b/src/gui/image/qicon.cpp
index bf6eb8d..fad51f4 100644
--- a/src/gui/image/qicon.cpp
+++ b/src/gui/image/qicon.cpp
@@ -982,7 +982,9 @@ QIcon QIcon::fromTheme(const QString &name, const QIcon &fallback)
         icon = *cachedIcon;
     }
 
-    if (icon.availableSizes().isEmpty())
+    // Note the qapp check is to allow lazy loading of static icons
+    // Supporting fallbacks will not work for this case.
+    if (qApp && icon.availableSizes().isEmpty())
         return fallback;
 
     return icon;
diff --git a/src/gui/image/qiconloader.cpp b/src/gui/image/qiconloader.cpp
index b35e80a..72ec2e8 100644
--- a/src/gui/image/qiconloader.cpp
+++ b/src/gui/image/qiconloader.cpp
@@ -85,19 +85,30 @@ static QString fallbackTheme()
 }
 
 QIconLoader::QIconLoader() :
-        m_themeKey(1), m_supportsSvg(false)
+        m_themeKey(1), m_supportsSvg(false), m_initialized(false)
 {
-    m_systemTheme = qt_guiPlatformPlugin()->systemIconThemeName();
-    if (m_systemTheme.isEmpty())
-        m_systemTheme = fallbackTheme();
+}
+
+// We lazily initialize the loader to make static icons
+// work. Though we do not officially support this.
+void QIconLoader::ensureInitialized()
+{
+    if (!m_initialized) {
+        m_initialized = true;
+
+        Q_ASSERT(qApp);
 
+        m_systemTheme = qt_guiPlatformPlugin()->systemIconThemeName();
+        if (m_systemTheme.isEmpty())
+            m_systemTheme = fallbackTheme();
 #ifndef QT_NO_LIBRARY
-    QFactoryLoader iconFactoryLoader(QIconEngineFactoryInterfaceV2_iid,
-                                     QLatin1String("/iconengines"),
-                                     Qt::CaseInsensitive);
-    if (iconFactoryLoader.keys().contains(QLatin1String("svg")))
-        m_supportsSvg = true;
+        QFactoryLoader iconFactoryLoader(QIconEngineFactoryInterfaceV2_iid,
+                                         QLatin1String("/iconengines"),
+                                         Qt::CaseInsensitive);
+        if (iconFactoryLoader.keys().contains(QLatin1String("svg")))
+            m_supportsSvg = true;
 #endif //QT_NO_LIBRARY
+    }
 }
 
 QIconLoader *QIconLoader::instance()
@@ -339,6 +350,9 @@ bool QIconLoaderEngine::hasIcon() const
 // Lazily load the icon
 void QIconLoaderEngine::ensureLoaded()
 {
+
+    iconLoaderInstance()->ensureInitialized();
+
     if (!(iconLoaderInstance()->themeKey() == m_key)) {
 
         while (!m_entries.isEmpty())
diff --git a/src/gui/image/qiconloader_p.h b/src/gui/image/qiconloader_p.h
index 19f2dda..a6b5f5b 100644
--- a/src/gui/image/qiconloader_p.h
+++ b/src/gui/image/qiconloader_p.h
@@ -169,6 +169,7 @@ public:
     static QIconLoader *instance();
     void updateSystemTheme();
     void invalidateKey() { m_themeKey++; }
+    void ensureInitialized();
 
 private:
     QThemeIconEntries findIconHelper(const QString &themeName,
@@ -176,6 +177,7 @@ private:
                                      QStringList &visited) const;
     uint m_themeKey;
     bool m_supportsSvg;
+    bool m_initialized;
 
     mutable QString m_userTheme;
     mutable QString m_systemTheme;