Synthetically reference type registration functions

Add unused volatile pointers to the type registration functions in each
import plugin. We need to do this in order to prevent the linker from
optimizing the registration away. There are two ways for this to happen:
When linking statically, the linker will examine the referenced symbols
on a per-object base and leave out all unreferenced objects. When
linking dynamically, the linker may do the same on a per-library base
and drop any unreferenced libraries from the dependencies. Forcing a
reference to the type registration function prevents both.

The volatile technique allows us to remove the previous qCDebug() hack.
Having an unused volatile auto variable should only result in a single
memory read as runtime overhead. The qCDebug() technique would generate
a read and a block of mostly dead code (as no one would ever use that
logging category).

Fixes: QTBUG-81622
Change-Id: I255667276dfd355b19baa17b1aad3db406bf1954
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

17 files changed, 101 insertions, 43 deletions

diff --git a/src/imports/folderlistmodel/plugin.cpp b/src/imports/folderlistmodel/plugin.cpp
index 28837655ef..7a38769b77 100644
--- a/src/imports/folderlistmodel/plugin.cpp
+++ b/src/imports/folderlistmodel/plugin.cpp
@@ -42,6 +42,8 @@
 
 #include "qquickfolderlistmodel.h"
 
+extern void qml_register_types_Qt_labs_folderlistmodel();
+
 QT_BEGIN_NAMESPACE
 
 //![class decl]
@@ -51,7 +53,12 @@ class QmlFolderListModelPlugin : public QQmlExtensionPlugin
     Q_PLUGIN_METADATA(IID QQmlExtensionInterface_iid)
 
 public:
-    QmlFolderListModelPlugin(QObject *parent = nullptr) : QQmlExtensionPlugin(parent) { }
+    QmlFolderListModelPlugin(QObject *parent = nullptr) : QQmlExtensionPlugin(parent)
+    {
+        volatile auto registration = &qml_register_types_Qt_labs_folderlistmodel;
+        Q_UNUSED(registration);
+    }
+
     void registerTypes(const char *uri) override
     {
         Q_ASSERT(QLatin1String(uri) == QLatin1String("Qt.labs.folderlistmodel"));
diff --git a/src/imports/labsanimation/plugin.cpp b/src/imports/labsanimation/plugin.cpp
index bd732a6aba..9c985f0dcf 100644
--- a/src/imports/labsanimation/plugin.cpp
+++ b/src/imports/labsanimation/plugin.cpp
@@ -42,6 +42,8 @@
 
 #include "qquickboundaryrule_p.h"
 
+extern void qml_register_types_Qt_labs_animation();
+
 QT_BEGIN_NAMESPACE
 
 /*!
@@ -66,7 +68,11 @@ class QtLabsAnimationPlugin : public QQmlEngineExtensionPlugin
     Q_OBJECT
     Q_PLUGIN_METADATA(IID QQmlEngineExtensionInterface_iid)
 public:
-    QtLabsAnimationPlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent) { }
+    QtLabsAnimationPlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent)
+    {
+        volatile auto registration = &qml_register_types_Qt_labs_animation;
+        Q_UNUSED(registration);
+    }
 };
 //![class decl]
 
diff --git a/src/imports/labsmodels/plugin.cpp b/src/imports/labsmodels/plugin.cpp
index feb4f3ba0a..ab5e0023a6 100644
--- a/src/imports/labsmodels/plugin.cpp
+++ b/src/imports/labsmodels/plugin.cpp
@@ -50,6 +50,8 @@
 #include "qqmldelegatecomponent_p.h"
 #endif
 
+extern void qml_register_types_Qt_labs_qmlmodels();
+
 QT_BEGIN_NAMESPACE
 
 /*!
@@ -74,7 +76,11 @@ class QtQmlLabsModelsPlugin : public QQmlEngineExtensionPlugin
     Q_OBJECT
     Q_PLUGIN_METADATA(IID QQmlEngineExtensionInterface_iid)
 public:
-    QtQmlLabsModelsPlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent) { }
+    QtQmlLabsModelsPlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent)
+    {
+        volatile auto registration = &qml_register_types_Qt_labs_qmlmodels;
+        Q_UNUSED(registration);
+    }
 };
 //![class decl]
 
diff --git a/src/imports/layouts/plugin.cpp b/src/imports/layouts/plugin.cpp
index c302b79164..af270c1732 100644
--- a/src/imports/layouts/plugin.cpp
+++ b/src/imports/layouts/plugin.cpp
@@ -42,6 +42,8 @@
 #include "qquicklinearlayout_p.h"
 #include "qquickstacklayout_p.h"
 
+extern void qml_register_types_QtQuick_Layouts();
+
 QT_BEGIN_NAMESPACE
 
 //![class decl]
@@ -52,6 +54,8 @@ class QtQuickLayoutsPlugin : public QQmlEngineExtensionPlugin
 public:
     QtQuickLayoutsPlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent)
     {
+        volatile auto registration = &qml_register_types_QtQuick_Layouts;
+        Q_UNUSED(registration);
     }
 };
 //![class decl]
diff --git a/src/imports/localstorage/plugin.cpp b/src/imports/localstorage/plugin.cpp
index ae9f37784d..e488b3d43c 100644
--- a/src/imports/localstorage/plugin.cpp
+++ b/src/imports/localstorage/plugin.cpp
@@ -42,6 +42,8 @@
 #include <QtQml/qqmlextensionplugin.h>
 #include <QtQml/qqml.h>
 
+extern void qml_register_types_QtQuick_LocalStorage();
+
 QT_BEGIN_NAMESPACE
 
 class QQmlLocalStoragePlugin : public QQmlEngineExtensionPlugin
@@ -52,6 +54,8 @@ class QQmlLocalStoragePlugin : public QQmlEngineExtensionPlugin
 public:
     QQmlLocalStoragePlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent)
     {
+        volatile auto registration = &qml_register_types_QtQuick_LocalStorage;
+        Q_UNUSED(registration);
     }
 };
 
diff --git a/src/imports/models/plugin.cpp b/src/imports/models/plugin.cpp
index 4aa9f27766..c15866cf05 100644
--- a/src/imports/models/plugin.cpp
+++ b/src/imports/models/plugin.cpp
@@ -37,17 +37,11 @@
 **
 ****************************************************************************/
 
-#include <QtQmlModels/private/qqmlobjectmodel_p.h>
-
+#include <QtQmlModels/private/qtqmlmodelsglobal_p.h>
 #include <QtQml/qqmlextensionplugin.h>
-#include <QtQml/qqml.h>
-
-#include <QtCore/qloggingcategory.h>
 
 QT_BEGIN_NAMESPACE
 
-Q_LOGGING_CATEGORY(qmlModelsPlugin, "qt.qmlModelsPlugin")
-
 /*!
     \qmlmodule QtQml.Models 2.\QtMinorVersion
     \title Qt QML Models QML Types
@@ -92,13 +86,8 @@ class QtQmlModelsPlugin : public QQmlEngineExtensionPlugin
 public:
     QtQmlModelsPlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent)
     {
-        if (qmlModelsPlugin().isDebugEnabled()) {
-            // Superficial debug message that causes the dependency between QtQmlWorkerScript
-            // and the workerscript plugin to be retained.
-            // As qCDebug() can be a noop, retrieve the className in a separate step.
-            const QString className = QQmlObjectModel::staticMetaObject.className();
-            qCDebug(qmlModelsPlugin) << "Loading QmlModels plugin:" << className;
-        }
+        volatile auto registration = &qml_register_types_QtQml_Models;
+        Q_UNUSED(registration);
     }
 };
 //![class decl]
diff --git a/src/imports/particles/plugin.cpp b/src/imports/particles/plugin.cpp
index 4f319db9f1..6629a660af 100644
--- a/src/imports/particles/plugin.cpp
+++ b/src/imports/particles/plugin.cpp
@@ -50,7 +50,12 @@ class QtQuick2ParticlesPlugin : public QQmlExtensionPlugin
     Q_OBJECT
     Q_PLUGIN_METADATA(IID QQmlExtensionInterface_iid)
 public:
-    QtQuick2ParticlesPlugin(QObject *parent = nullptr) : QQmlExtensionPlugin(parent) { }
+    QtQuick2ParticlesPlugin(QObject *parent = nullptr) : QQmlExtensionPlugin(parent)
+    {
+        volatile auto registration = &qml_register_types_QtQuick_Particles;
+        Q_UNUSED(registration);
+    }
+
     void registerTypes(const char *uri) override
     {
         Q_UNUSED(uri);
diff --git a/src/imports/qtqml/plugin.cpp b/src/imports/qtqml/plugin.cpp
index 6891755446..854ef6d2e6 100644
--- a/src/imports/qtqml/plugin.cpp
+++ b/src/imports/qtqml/plugin.cpp
@@ -37,10 +37,8 @@
 **
 ****************************************************************************/
 
+#include <QtQml/private/qtqmlglobal_p.h>
 #include <QtQml/qqmlextensionplugin.h>
-#include <QtQml/private/qqmlengine_p.h>
-#include <QtQml/private/qqmlcomponentattached_p.h>
-#include <QtQml/private/qqmlbind_p.h>
 
 #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
 #include <QtQmlModels/private/qqmlmodelsmodule_p.h>
@@ -71,7 +69,12 @@ class QtQmlPlugin : public QQmlExtensionPlugin
     Q_OBJECT
     Q_PLUGIN_METADATA(IID QQmlExtensionInterface_iid)
 public:
-    QtQmlPlugin(QObject *parent = nullptr) : QQmlExtensionPlugin(parent) { }
+    QtQmlPlugin(QObject *parent = nullptr) : QQmlExtensionPlugin(parent)
+    {
+        volatile auto registration = &qml_register_types_QtQml;
+        Q_UNUSED(registration);
+    }
+
     void registerTypes(const char *) override { QQmlModelsModule::registerQmlTypes(); }
 };
 #else
@@ -80,7 +83,11 @@ class QtQmlPlugin : public QQmlEngineExtensionPlugin
     Q_OBJECT
     Q_PLUGIN_METADATA(IID QQmlEngineExtensionInterface_iid)
 public:
-    QtQmlPlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent) {}
+    QtQmlPlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent)
+    {
+        volatile auto registration = &qml_register_types_QtQml;
+        Q_UNUSED(registration);
+    }
 };
 #endif
 //![class decl]
diff --git a/src/imports/qtquick2/plugin.cpp b/src/imports/qtquick2/plugin.cpp
index 0832e22e5d..20bc4a3cc0 100644
--- a/src/imports/qtquick2/plugin.cpp
+++ b/src/imports/qtquick2/plugin.cpp
@@ -57,7 +57,12 @@ class QtQuick2Plugin : public QQmlExtensionPlugin
     Q_OBJECT
     Q_PLUGIN_METADATA(IID QQmlExtensionInterface_iid)
 public:
-    QtQuick2Plugin(QObject *parent = nullptr) : QQmlExtensionPlugin(parent) { }
+    QtQuick2Plugin(QObject *parent = nullptr) : QQmlExtensionPlugin(parent)
+    {
+        volatile auto registration = &qml_register_types_QtQuick;
+        Q_UNUSED(registration);
+    }
+
     void registerTypes(const char *uri) override
     {
         Q_ASSERT(QLatin1String(uri) == QLatin1String("QtQuick"));
diff --git a/src/imports/settings/plugin.cpp b/src/imports/settings/plugin.cpp
index 24ff43ea6f..e8e640412b 100644
--- a/src/imports/settings/plugin.cpp
+++ b/src/imports/settings/plugin.cpp
@@ -42,6 +42,8 @@
 
 #include "qqmlsettings_p.h"
 
+extern void qml_register_types_Qt_labs_settings();
+
 QT_BEGIN_NAMESPACE
 
 class QmlSettingsPlugin : public QQmlEngineExtensionPlugin
@@ -50,7 +52,11 @@ class QmlSettingsPlugin : public QQmlEngineExtensionPlugin
     Q_PLUGIN_METADATA(IID QQmlEngineExtensionInterface_iid)
 
 public:
-    QmlSettingsPlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent) {}
+    QmlSettingsPlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent)
+    {
+        volatile auto registration = &qml_register_types_Qt_labs_settings;
+        Q_UNUSED(registration);
+    }
 };
 
 QT_END_NAMESPACE
diff --git a/src/imports/shapes/plugin.cpp b/src/imports/shapes/plugin.cpp
index 3855a93fc7..48eecbd8f1 100644
--- a/src/imports/shapes/plugin.cpp
+++ b/src/imports/shapes/plugin.cpp
@@ -52,6 +52,8 @@ public:
     QmlShapesPlugin(QObject *parent = nullptr)
         : QQmlExtensionPlugin(parent)
     {
+        volatile auto registration = &qml_register_types_QtQuick_Shapes;
+        Q_UNUSED(registration);
     }
 
     void registerTypes(const char *uri) override
diff --git a/src/imports/sharedimage/plugin.cpp b/src/imports/sharedimage/plugin.cpp
index 237fa64c61..d7c2ef8d17 100644
--- a/src/imports/sharedimage/plugin.cpp
+++ b/src/imports/sharedimage/plugin.cpp
@@ -99,6 +99,8 @@
     The shared image module does not provide any directly usable QML types.
 */
 
+extern void qml_register_types_Qt_labs_sharedimage();
+
 QT_BEGIN_NAMESPACE
 
 class QtQuickSharedImagePlugin : public QQmlEngineExtensionPlugin
@@ -106,7 +108,11 @@ class QtQuickSharedImagePlugin : public QQmlEngineExtensionPlugin
     Q_OBJECT
     Q_PLUGIN_METADATA(IID QQmlEngineExtensionInterface_iid)
 public:
-    QtQuickSharedImagePlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent) {}
+    QtQuickSharedImagePlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent)
+    {
+        volatile auto registration = &qml_register_types_Qt_labs_sharedimage;
+        Q_UNUSED(registration);
+    }
 
     void initializeEngine(QQmlEngine *engine, const char *uri) override
     {
diff --git a/src/imports/statemachine/plugin.cpp b/src/imports/statemachine/plugin.cpp
index 4c991994f3..c370504029 100644
--- a/src/imports/statemachine/plugin.cpp
+++ b/src/imports/statemachine/plugin.cpp
@@ -48,6 +48,8 @@
 #include <QQmlExtensionPlugin>
 #include <qqml.h>
 
+extern void qml_register_types_QtQml_StateMachine();
+
 QT_BEGIN_NAMESPACE
 
 class QtQmlStateMachinePlugin : public QQmlEngineExtensionPlugin
@@ -56,7 +58,11 @@ class QtQmlStateMachinePlugin : public QQmlEngineExtensionPlugin
     Q_PLUGIN_METADATA(IID QQmlEngineExtensionInterface_iid)
 
 public:
-    QtQmlStateMachinePlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent) { }
+    QtQmlStateMachinePlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent)
+    {
+        volatile auto registration = &qml_register_types_QtQml_StateMachine;
+        Q_UNUSED(registration);
+    }
 };
 
 QT_END_NAMESPACE
diff --git a/src/imports/testlib/main.cpp b/src/imports/testlib/main.cpp
index 1914c02dd0..83fc150e6c 100644
--- a/src/imports/testlib/main.cpp
+++ b/src/imports/testlib/main.cpp
@@ -50,6 +50,8 @@ QML_DECLARE_TYPE(QuickTestResult)
 QML_DECLARE_TYPE(QuickTestEvent)
 QML_DECLARE_TYPE(QuickTestUtil)
 
+extern void qml_register_types_QtTest();
+
 QT_BEGIN_NAMESPACE
 
 class QTestQmlModule : public QQmlEngineExtensionPlugin
@@ -58,7 +60,11 @@ class QTestQmlModule : public QQmlEngineExtensionPlugin
     Q_PLUGIN_METADATA(IID QQmlEngineExtensionInterface_iid)
 
 public:
-    QTestQmlModule(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent) { }
+    QTestQmlModule(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent)
+    {
+        volatile auto registration = &qml_register_types_QtTest;
+        Q_UNUSED(registration);
+    }
 };
 
 QT_END_NAMESPACE
diff --git a/src/imports/wavefrontmesh/plugin.cpp b/src/imports/wavefrontmesh/plugin.cpp
index 9bb7a45b2f..eea0db19db 100644
--- a/src/imports/wavefrontmesh/plugin.cpp
+++ b/src/imports/wavefrontmesh/plugin.cpp
@@ -42,6 +42,8 @@
 
 #include "qwavefrontmesh.h"
 
+extern void qml_register_types_Qt_labs_wavefrontmesh();
+
 QT_BEGIN_NAMESPACE
 
 class QmlWavefrontMeshPlugin : public QQmlEngineExtensionPlugin
@@ -52,6 +54,8 @@ public:
     QmlWavefrontMeshPlugin(QObject *parent = nullptr)
         : QQmlEngineExtensionPlugin(parent)
     {
+        volatile auto registration = &qml_register_types_Qt_labs_wavefrontmesh;
+        Q_UNUSED(registration);
     }
 };
 
diff --git a/src/imports/window/plugin.cpp b/src/imports/window/plugin.cpp
index ec4f2c5d2a..5152fa02ec 100644
--- a/src/imports/window/plugin.cpp
+++ b/src/imports/window/plugin.cpp
@@ -41,6 +41,8 @@
 
 #include "plugin.h"
 
+extern void qml_register_types_QtQuick_Window();
+
 QT_BEGIN_NAMESPACE
 
 /*!
@@ -64,7 +66,11 @@ class QtQuick2WindowPlugin : public QQmlEngineExtensionPlugin
     Q_OBJECT
     Q_PLUGIN_METADATA(IID QQmlEngineExtensionInterface_iid)
 public:
-    QtQuick2WindowPlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent) { }
+    QtQuick2WindowPlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent)
+    {
+        volatile auto registration = &qml_register_types_QtQuick_Window;
+        Q_UNUSED(registration);
+    }
 };
 //![class decl]
 
diff --git a/src/imports/workerscript/plugin.cpp b/src/imports/workerscript/plugin.cpp
index 0961979c53..1323b17ef4 100644
--- a/src/imports/workerscript/plugin.cpp
+++ b/src/imports/workerscript/plugin.cpp
@@ -37,17 +37,11 @@
 **
 ****************************************************************************/
 
-#include <QtQmlWorkerScript/private/qquickworkerscript_p.h>
-
+#include <QtQmlWorkerScript/private/qtqmlworkerscriptglobal_p.h>
 #include <QtQml/qqmlextensionplugin.h>
-#include <QtQml/qqml.h>
-
-#include <QtCore/qloggingcategory.h>
 
 QT_BEGIN_NAMESPACE
 
-Q_LOGGING_CATEGORY(workerScriptPlugin, "qt.workerScriptPlugin")
-
 /*!
     \qmlmodule QtQml.WorkerScript 2.\QtMinorVersion
     \title Qt QML WorkerScript QML Types
@@ -71,13 +65,8 @@ class QtQmlWorkerScriptPlugin : public QQmlEngineExtensionPlugin
 public:
     QtQmlWorkerScriptPlugin(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent)
     {
-        if (workerScriptPlugin().isDebugEnabled()) {
-            // Superficial debug message that causes the dependency between QtQmlWorkerScript
-            // and the workerscript plugin to be retained.
-            // As qCDebug() can be a noop, retrieve the className in a separate step.
-            const QString className = QQuickWorkerScript::staticMetaObject.className();
-            qCDebug(workerScriptPlugin) << "Loading WorkerScript plugin:" << className;
-        }
+        volatile auto registration = &qml_register_types_QtQml_WorkerScript;
+        Q_UNUSED(registration);
     }
 };