Unset QT_PLUGIN_PATH. This avoids Qt version mismatches when QT_PLUGIN_PATH is set on the host. This is often the case on NixOS.

Author: JulianGro

src/deployment.h

@@ -76,7 +76,7 @@ inline bool createQtConf(appdir::AppDir &appDir) {
     return true;
 }
 
-inline bool createAppRunHook(appdir::AppDir &appDir) {
+inline bool createAppRunHook(appdir::AppDir &appDir, int qtMajorVersion) {
     auto hookPath = appDir.path() / "apprun-hooks" / "linuxdeploy-plugin-qt-hook.sh";
 
     try {
@@ -99,18 +99,25 @@ inline bool createAppRunHook(appdir::AppDir &appDir) {
         return false;
     }
 
-    // Old Qt versions only ship gtk2, new versions only gtk3. No Qt version had both.
-    const bool haveGtk3 = fs::exists(appDir.path() / "usr/plugins/platformthemes" / "libqgtk3.so");
-
     ofs << "# generated by linuxdeploy-plugin-qt" << std::endl
         << std::endl
-        << "# try to make Qt apps more \"native looking\" on Gtk-based desktops, if possible" << std::endl
-        << "# see https://github.com/AppImage/AppImageKit/issues/977#issue-462374883" << std::endl
-        << "case \"${XDG_CURRENT_DESKTOP}\" in" << std::endl
-        << "    *GNOME*|*gnome*|*XFCE*)" << std::endl
-        << "        export QT_QPA_PLATFORMTHEME=" << (haveGtk3 ? "gtk3" : "gtk2") << std::endl
-        << "        ;;" << std::endl
-        << "esac" << std::endl;
+        << "# Override QT_PLUGIN_PATH to fall back to defaults. NixOS sets QT_PLUGIN_PATH," << std::endl
+        << "# which causes AppImages with Qt to try and load system Qt plugins." << std::endl
+        << "# This usually fails due to the mismatched Qt versions." << std::endl
+        << "unset QT_PLUGIN_PATH" << std::endl;
+
+    if (qtMajorVersion >= 6) {
+        // Old Qt versions only ship gtk2, new versions only gtk3. No Qt version had both.
+        const bool haveGtk3 = fs::exists(appDir.path() / "usr/plugins/platformthemes" / "libqgtk3.so");
+        ofs << std::endl
+            << "# try to make Qt apps more \"native looking\" on Gtk-based desktops, if possible" << std::endl
+            << "# see https://github.com/AppImage/AppImageKit/issues/977#issue-462374883" << std::endl
+            << "case \"${XDG_CURRENT_DESKTOP}\" in" << std::endl
+            << "    *GNOME*|*gnome*|*XFCE*)" << std::endl
+            << "        export QT_QPA_PLATFORMTHEME=" << (haveGtk3 ? "gtk3" : "gtk2") << std::endl
+            << "        ;;" << std::endl
+            << "esac" << std::endl;
+    }
 
     return true;
 }

src/main.cpp

@@ -308,14 +308,10 @@ int main(const int argc, const char *const *const argv) {
         return 1;
     }
 
-    if (qtMajorVersion >= 6) {
-        ldLog() << std::endl << "-- Note: skipping AppRun hook creation on Qt " << qtMajorVersion << " --" << std::endl;
-    } else {
-        ldLog() << std::endl << "-- Creating AppRun hook --" << std::endl;
-        if (!createAppRunHook(appDir)) {
-            ldLog() << LD_ERROR << "Failed to create AppRun hook in AppDir" << std::endl;
-            return 1;
-        }
+    ldLog() << std::endl << "-- Creating AppRun hook --" << std::endl;
+    if (!createAppRunHook(appDir, qtMajorVersion)) {
+        ldLog() << LD_ERROR << "Failed to create AppRun hook in AppDir" << std::endl;
+        return 1;
     }
 
     ldLog() << std::endl << "Done!" << std::endl;