QPlugin: suppress the "QTMETADATA !" magic in static plugins

The .qtmetadata section is already suppressed for static plugins, but we
carried this unnecessary magic string. For library file formats where we
don't have a scanner (Windows COFF PE), a library that linked multiple
static plugins could end up with multiple metadata found.

We can't suppress the header because the version of moc could be
different to the version of Qt, so we need to read the header version
too. Right now, the version isn't output by moc (all the logic is in
qplugin.h), but this could change again in the future. In any case, 4
extra bytes are not a big deal, so the header stays.

Change-Id: I3eb1bd30e0124f89a052fffd16a82088d8303081
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/plugin/qplugin.h

@@ -155,13 +155,26 @@ void Q_CORE_EXPORT qRegisterStaticPluginFunction(QStaticPlugin staticPlugin);
 // Since Qt 6.3
 template <auto (&PluginMetaData)> class QPluginMetaDataV2
 {
-    struct Payload {
+    struct RegularPayload {
         QPluginMetaData::MagicHeader header = {};
         quint8 payload[sizeof(PluginMetaData)] = {};
-        constexpr Payload() { QPluginMetaData::copy(payload, PluginMetaData); }
+        constexpr RegularPayload() { QPluginMetaData::copy(payload, PluginMetaData); }
     };
 
-#define QT_PLUGIN_METADATAV2_SECTION      QT_PLUGIN_METADATA_SECTION
+    struct StaticPayload {
+        QPluginMetaData::Header header = {};
+        quint8 payload[sizeof(PluginMetaData)] = {};
+        constexpr StaticPayload() { QPluginMetaData::copy(payload, PluginMetaData); }
+    };
+
+#if defined(QT_STATICPLUGIN)
+#  define QT_PLUGIN_METADATAV2_SECTION
+    using Payload = StaticPayload;
+#else
+#  define QT_PLUGIN_METADATAV2_SECTION      QT_PLUGIN_METADATA_SECTION
+    using Payload = RegularPayload;
+#endif
+
     Payload payload = {};
 
 public:

src/corelib/plugin/qpluginloader.cpp

@@ -477,12 +477,10 @@ QList<QStaticPlugin> QPluginLoader::staticPlugins()
 */
 QJsonObject QStaticPlugin::metaData() const
 {
-    Q_ASSERT(rawMetaDataSize >= qsizetype(sizeof(QPluginMetaData::MagicHeader)));
     auto ptr = static_cast<const char *>(rawMetaData);
-    ptr += sizeof(QPluginMetaData::MagicString);
 
     QString errMsg;
-    QJsonDocument doc = qJsonFromRawLibraryMetaData(ptr, rawMetaDataSize - sizeof(QPluginMetaData::MagicString), &errMsg);
+    QJsonDocument doc = qJsonFromRawLibraryMetaData(ptr, rawMetaDataSize, &errMsg);
     Q_ASSERT(doc.isObject());
     Q_ASSERT(errMsg.isEmpty());
     return doc.object();

tests/auto/tools/moc/tst_moc.cpp

@@ -1468,25 +1468,23 @@ void tst_Moc::environmentIncludePaths()
 // plugin_metadata.h contains a plugin which we register here. Since we're not building this
 // application as a plugin, we need top copy some of the initializer code found in qplugin.h:
 extern "C" QObject *qt_plugin_instance();
-#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
 extern "C" QPluginMetaData qt_plugin_query_metadata();
 class StaticPluginInstance{
 public:
     StaticPluginInstance() {
-        QStaticPlugin plugin(qt_plugin_instance, qt_plugin_query_metadata);
+        decltype(&qt_plugin_query_metadata) queryFn;
+        queryFn = []() {
+            // Static plugins don't carry the magic string (since Qt 6.3)
+            QPluginMetaData md = qt_plugin_query_metadata();
+            int delta = sizeof(QPluginMetaData::MagicString);
+            md.data = static_cast<const char *>(md.data) + delta;
+            md.size -= delta;
+            return md;
+        };
+        QStaticPlugin plugin(qt_plugin_instance, queryFn);
         qRegisterStaticPluginFunction(plugin);
     }
 };
-#else
-extern "C" const char *qt_plugin_query_metadata();
-class StaticPluginInstance{
-public:
-    StaticPluginInstance() {
-        QStaticPlugin plugin = { &qt_plugin_instance, &qt_plugin_query_metadata };
-        qRegisterStaticPluginFunction(plugin);
-    }
-};
-#endif
 static StaticPluginInstance staticInstance;
 
 void tst_Moc::specifyMetaTagsFromCmdline() {