5 files changed, 42 insertions, 10 deletions
diff --git a/src/corelib/serialization/qjsonarray.h b/src/corelib/serialization/qjsonarray.h
index 0128a36470..a8c3760565 100644
--- a/src/corelib/serialization/qjsonarray.h
+++ b/src/corelib/serialization/qjsonarray.h
@@ -263,6 +263,7 @@ public:
 private:
     friend class QJsonValue;
     friend class QJsonValueConstRef;
+    friend class QJsonValueRef;
     friend class QJsonPrivate::Value;
     friend class QJsonDocument;
     friend class QCborArray;
diff --git a/src/corelib/serialization/qjsonobject.cpp b/src/corelib/serialization/qjsonobject.cpp
index 014224c4db..ee4ea8ce23 100644
--- a/src/corelib/serialization/qjsonobject.cpp
+++ b/src/corelib/serialization/qjsonobject.cpp
@@ -1428,6 +1428,7 @@ QString QJsonObject::keyAt(qsizetype i) const
     return o->stringAt(i * 2);
 }
 
+#if QT_VERSION < QT_VERSION_CHECK(7, 0, 0) && !defined(QT_BOOTSTRAPPED)
 /*!
     \internal
  */
@@ -1452,6 +1453,7 @@ void QJsonObject::setValueAt(qsizetype i, const QJsonValue &val)
         o->replaceAt(2 * i + 1, QCborValue::fromJsonValue(val));
     }
 }
+#endif // Qt 7
 
 /*!
     \internal
diff --git a/src/corelib/serialization/qjsonobject.h b/src/corelib/serialization/qjsonobject.h
index d9f6785631..74f6905b60 100644
--- a/src/corelib/serialization/qjsonobject.h
+++ b/src/corelib/serialization/qjsonobject.h
@@ -303,8 +303,10 @@ private:
     template <typename T> iterator insertImpl(T key, const QJsonValue &value);
 
     QString keyAt(qsizetype i) const;
+#if QT_VERSION < QT_VERSION_CHECK(7, 0, 0) && !defined(QT_BOOTSTRAPPED)
     QJsonValue valueAt(qsizetype i) const;
     void setValueAt(qsizetype i, const QJsonValue &val);
+#endif
     void removeAt(qsizetype i);
     template <typename T> iterator insertAt(qsizetype i, T key, const QJsonValue &val, bool exists);
 
diff --git a/src/corelib/serialization/qjsonvalue.cpp b/src/corelib/serialization/qjsonvalue.cpp
index 27cad8941e..9fecbbb626 100644
--- a/src/corelib/serialization/qjsonvalue.cpp
+++ b/src/corelib/serialization/qjsonvalue.cpp
@@ -919,25 +919,49 @@ bool QJsonValue::operator!=(const QJsonValue &other) const
     However, they are not explicitly documented here.
 */
 
-
-QJsonValueRef &QJsonValueRef::operator =(const QJsonValue &val)
+void QJsonValueRef::detach()
 {
+    QCborContainerPrivate *d = QJsonPrivate::Value::container(*this);
+    d = QCborContainerPrivate::detach(d, d->elements.size());
+
     if (is_object)
-        o->setValueAt(index, val);
+        o->o.reset(d);
     else
-        a->replace(index, val);
+        a->a.reset(d);
+}
 
-    return *this;
+static QJsonValueRef &assignToRef(QJsonValueRef &ref, const QCborValue &value, bool is_object)
+{
+    QCborContainerPrivate *d = QJsonPrivate::Value::container(ref);
+    qsizetype index = QJsonPrivate::Value::indexHelper(ref);
+    if (is_object && value.isUndefined()) {
+        d->removeAt(index);
+        d->removeAt(index - 1);
+    } else {
+        d->replaceAt(index, value);
+    }
+
+    return ref;
+}
+
+QJsonValueRef &QJsonValueRef::operator =(const QJsonValue &val)
+{
+    detach();
+    return assignToRef(*this, QCborValue::fromJsonValue(val), is_object);
 }
 
 QJsonValueRef &QJsonValueRef::operator =(const QJsonValueRef &ref)
 {
-    if (is_object)
-        o->setValueAt(index, ref);
-    else
-        a->replace(index, ref);
+    // ### optimize more?
+    const QCborContainerPrivate *d = QJsonPrivate::Value::container(ref);
+    qsizetype index = QJsonPrivate::Value::indexHelper(ref);
 
-    return *this;
+    if (d == QJsonPrivate::Value::container(*this) &&
+            index == QJsonPrivate::Value::indexHelper(*this))
+        return *this;     // self assignment
+
+    detach();
+    return assignToRef(*this, d->valueAt(index), is_object);
 }
 
 QVariant QJsonValueConstRef::toVariant() const
diff --git a/src/corelib/serialization/qjsonvalue.h b/src/corelib/serialization/qjsonvalue.h
index 4f9c3af578..f50bb08017 100644
--- a/src/corelib/serialization/qjsonvalue.h
+++ b/src/corelib/serialization/qjsonvalue.h
@@ -263,7 +263,10 @@ public:
 
 private:
     QJsonValue toValue() const;
+#else
+private:
 #endif // < Qt 7
+    void detach();
 };
 
 inline QJsonValue QCborValueConstRef::toJsonValue() const