QPluginLoader: don't instantiante multiple, identical instances

This can happen if the same project has two or more Q_IMPORT_PLUGIN
macros in their source. And that can happen when converting from qmake-
based builds to CMake, as qmake didn't generate a source file with the
macro but CMake does.

[ChangeLog][QtCore][QPluginLoader] staticInstances() will not call
duplicated registrations of the same instantiation function, which can
only happen as a result of duplicated Q_IMPORT_PLUGIN for the same
plugin name.

Fixes: QTBUG-102745
Pick-to: 6.2 6.5
Change-Id: Idd5e1bb52be047d7b4fffffd174fb9dd62d8583d
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 19 insertions, 7 deletions

diff --git a/tests/auto/corelib/plugin/qpluginloader/tst_qpluginloader.cpp b/tests/auto/corelib/plugin/qpluginloader/tst_qpluginloader.cpp
index adea6af515..e6d1785dca 100644
--- a/tests/auto/corelib/plugin/qpluginloader/tst_qpluginloader.cpp
+++ b/tests/auto/corelib/plugin/qpluginloader/tst_qpluginloader.cpp
@@ -206,6 +206,7 @@ private slots:
     void preloadedPlugin_data();
     void preloadedPlugin();
     void staticPlugins();
+    void reregisteredStaticPlugins();
 };
 
 Q_IMPORT_PLUGIN(StaticPlugin)
@@ -1080,19 +1081,18 @@ void tst_QPluginLoader::staticPlugins()
     const QObjectList instances = QPluginLoader::staticInstances();
     QVERIFY(instances.size());
 
-    bool found = false;
-    for (QObject *obj : instances) {
-        found = obj->metaObject()->className() == QLatin1String("StaticPlugin");
-        if (found)
-            break;
-    }
-    QVERIFY(found);
+    // ensure the our plugin only shows up once
+    int foundCount = std::count_if(instances.begin(), instances.end(), [](QObject *obj) {
+            return obj->metaObject()->className() == QLatin1String("StaticPlugin");
+    });
+    QCOMPARE(foundCount, 1);
 
     const auto plugins = QPluginLoader::staticPlugins();
     QCOMPARE(plugins.size(), instances.size());
 
     // find the metadata
     QJsonObject metaData;
+    bool found = false;
     for (const auto &p : plugins) {
         metaData = p.metaData();
         found = metaData.value("className").toString() == QLatin1String("StaticPlugin");
@@ -1108,6 +1108,18 @@ void tst_QPluginLoader::staticPlugins()
     QCOMPARE(metaData.value("URI").toString(), "qt.test.pluginloader.staticplugin");
 }
 
+void tst_QPluginLoader::reregisteredStaticPlugins()
+{
+    // the Q_IMPORT_PLUGIN macro will have already done this
+    qRegisterStaticPluginFunction(qt_static_plugin_StaticPlugin());
+    staticPlugins();
+    if (QTest::currentTestFailed())
+        return;
+
+    qRegisterStaticPluginFunction(qt_static_plugin_StaticPlugin());
+    staticPlugins();
+}
+
 
 QTEST_MAIN(tst_QPluginLoader)
 #include "tst_qpluginloader.moc"