3 files changed, 68 insertions, 2 deletions

diff --git a/src/corelib/kernel/qmetatype.cpp b/src/corelib/kernel/qmetatype.cpp
index 356a675517..5c1e4b4ddd 100644
--- a/src/corelib/kernel/qmetatype.cpp
+++ b/src/corelib/kernel/qmetatype.cpp
@@ -37,6 +37,8 @@
 **
 ****************************************************************************/
 
+#include <bitset>
+
 #include "qmetatype.h"
 #include "qmetatype_p.h"
 #include "qobjectdefs.h"
@@ -2416,6 +2418,50 @@ const QMetaObject *metaObjectForQWidget()
         return nullptr;
     return qMetaObjectWidgetsHelper;
 }
+
+void qt5CompatibilityHookPostRegister(int id, const QByteArray &normalizedTypeName)
+{
+    // In Qt6 QList got typedef'ed to QVector. To keep runtime behavior compatibility
+    // with Qt5 we install corresponding aliases. For example if one register
+    //   QVector<QVector<int>>
+    // we need to register the type plus all possible aliases:
+    //   QVector<QList<int>>
+    //   QList<QVector<int>>
+    //   QList<QList<int>>
+    // ### Qt6 TODO This is slow, as it allocates couple of strings we would need to
+    // if def this call with something like QT_NO_QLIST
+    const char *vectorName = "QVector<";
+    const char *listName = "QList<";
+
+    auto isSubstringOfAType = [](char c) { return c != ' ' && c != ',' && c != '<'; };
+    QVarLengthArray<int> indexes;
+
+    for (auto containerName: {vectorName, listName}) {
+        for (int i = normalizedTypeName.indexOf(containerName, 0); i != -1; i = normalizedTypeName.indexOf(containerName, i + 1)) {
+                if (!i || (i > 0 && !isSubstringOfAType(normalizedTypeName[i - 1])))
+                    indexes.append(i);
+            }
+    }
+    // To avoid problems with the constantly changing size we start replacements
+    // from the end of normalizedTypeName
+    std::sort(indexes.rbegin(), indexes.rend());
+
+    for (quint64 combination = 1; ; ++combination) {
+        std::bitset<64> bits(combination);
+        QByteArray name = normalizedTypeName;
+        for (auto j = 0; j < indexes.size(); ++j) {
+            if (bits.test(j)) {
+                auto i = indexes[j];
+                auto replaceFrom = normalizedTypeName[i + 1] == 'V' ? vectorName : listName;
+                auto replaceTo = normalizedTypeName[i + 1] == 'V' ? listName : vectorName;
+                name.replace(i, sizeof(replaceFrom), replaceTo);
+            }
+        }
+        QMetaType::registerNormalizedTypedef(name, id);
+        if (bits.count() >= size_t(indexes.size()))
+            break;
+    }
+}
 }
 
 namespace QtMetaTypePrivate {
diff --git a/src/corelib/kernel/qmetatype.h b/src/corelib/kernel/qmetatype.h
index 7b985be9fd..f6fe62e164 100644
--- a/src/corelib/kernel/qmetatype.h
+++ b/src/corelib/kernel/qmetatype.h
@@ -1645,6 +1645,23 @@ namespace QtPrivate
         static bool registerConverter(int) { return false; }
     };
 
+    template<class T>
+    struct Qt5CompatibilityHook
+    {
+        static inline void postRegister(int, const QByteArray &) {};
+    };
+
+    Q_CORE_EXPORT void qt5CompatibilityHookPostRegister(int id, const QByteArray &normalizedTypeName);
+
+    template<class T>
+    struct Qt5CompatibilityHook<QVector<T>>
+    {
+        static inline void postRegister(int id, const QByteArray &normalizedTypeName)
+        {
+            qt5CompatibilityHookPostRegister(id, normalizedTypeName);
+        }
+    };
+
     Q_CORE_EXPORT bool isBuiltinType(const QByteArray &type);
 } // namespace QtPrivate
 
@@ -1771,6 +1788,7 @@ int qRegisterNormalizedMetaType(const QT_PREPEND_NAMESPACE(QByteArray) &normaliz
         QtPrivate::AssociativeContainerConverterHelper<T>::registerConverter(id);
         QtPrivate::MetaTypePairHelper<T>::registerConverter(id);
         QtPrivate::MetaTypeSmartPointerHelper<T>::registerConverter(id);
+        QtPrivate::Qt5CompatibilityHook<T>::postRegister(id, normalizedTypeName);
     }
 
     return id;
diff --git a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp
index 2a4ee55fa8..d300c31001 100644
--- a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp
+++ b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp
@@ -572,12 +572,14 @@ void tst_QMetaType::typeName_data()
     QTest::newRow("124125534") << 124125534 << QString();
 
     // automatic registration
-    QTest::newRow("QList<int>") << ::qMetaTypeId<QList<int> >() << QString::fromLatin1("QList<int>");
     QTest::newRow("QHash<int,int>") << ::qMetaTypeId<QHash<int, int> >() << QString::fromLatin1("QHash<int,int>");
     QTest::newRow("QMap<int,int>") << ::qMetaTypeId<QMap<int, int> >() << QString::fromLatin1("QMap<int,int>");
-    QTest::newRow("QVector<QList<int>>") << ::qMetaTypeId<QVector<QList<int> > >() << QString::fromLatin1("QVector<QList<int> >");
     QTest::newRow("QVector<QMap<int,int>>") << ::qMetaTypeId<QVector<QMap<int, int> > >() << QString::fromLatin1("QVector<QMap<int,int> >");
 
+    // automatic registration with automatic QList to QVector aliasing
+    QTest::newRow("QList<int>") << ::qMetaTypeId<QList<int> >() << QString::fromLatin1("QVector<int>");
+    QTest::newRow("QVector<QList<int>>") << ::qMetaTypeId<QVector<QList<int> > >() << QString::fromLatin1("QVector<QVector<int> >");
+
     QTest::newRow("CustomQObject*") << ::qMetaTypeId<CustomQObject*>() << QString::fromLatin1("CustomQObject*");
     QTest::newRow("CustomGadget") << ::qMetaTypeId<CustomGadget>() << QString::fromLatin1("CustomGadget");
     QTest::newRow("CustomGadget*") << ::qMetaTypeId<CustomGadget*>() << QString::fromLatin1("CustomGadget*");