Adapt to plugin unloading changes

As of c2081016e in qtdeclarative, plugins are no longer unloaded on
macOS, and QQmlExtensionPlugin::unregisterTypes() should be used
instead.

This patch:
- Moves everything that was done in destructors to unregisterTypes().
- Ensures that the style selector is destroyed in
  QQuickStylePlugin::unregisterTypes() so that previous styles that
  were set do not stick around after qmlClearTypeRegistrations() is
  called. This ensures that runtime style-switching continues to work.
- Adds more logging output to make it easier to diagnose issues in the
  future.
- Adds more code comments to ease maintenance.

Change-Id: Ibbfeba4501d6ba0d5a257dcceace3498904a816e
Fixes: QTBUG-82811
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 9 insertions, 1 deletions

diff --git a/src/imports/controls/qtquickcontrols2plugin.cpp b/src/imports/controls/qtquickcontrols2plugin.cpp
index e0f18467..6730848f 100644
--- a/src/imports/controls/qtquickcontrols2plugin.cpp
+++ b/src/imports/controls/qtquickcontrols2plugin.cpp
@@ -79,6 +79,7 @@ public:
     ~QtQuickControls2Plugin();
 
     void registerTypes(const char *uri) override;
+    void unregisterTypes() override;
 
     QString name() const override;
     void initializeTheme(QQuickTheme *theme) override;
@@ -94,7 +95,8 @@ QtQuickControls2Plugin::QtQuickControls2Plugin(QObject *parent) : QQuickStylePlu
 
 QtQuickControls2Plugin::~QtQuickControls2Plugin()
 {
-    QQuickStylePrivate::reset();
+    // Intentionally empty: we use register/unregisterTypes() to do
+    // initialization and cleanup, as plugins are not unloaded on macOS.
 }
 
 static bool isDefaultStyle(const QString &style)
@@ -238,6 +240,12 @@ void QtQuickControls2Plugin::registerTypes(const char *uri)
     qmlRegisterRevision<QQuickText, 6>(import, 2, 3);
 }
 
+void QtQuickControls2Plugin::unregisterTypes()
+{
+    QQuickStylePlugin::unregisterTypes();
+    QQuickStylePrivate::reset();
+}
+
 QString QtQuickControls2Plugin::name() const
 {
     return QStringLiteral("Default");