From d263147921800e7b6d357d1a48f28f21a8092b84 Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Sat, 27 Nov 2021 11:28:57 -0600
Subject: [PATCH] QJsonValueRef: optimize the assignment

Inline some content to avoid unnecessary round-trips through
qcborvalue.cpp, qjsonarray.cpp and qjsonobject.cpp.

Unlike the CBOR counterparts, JSON support has this extra functionality
that assigning Undefined causes the item to be removed from the object
(arrays don't have that behavior, they just become null).

And unlike QCborValueRef, we detach on assignment, not on the obtention
of the QJsonValueRef. This is more dangerous, so we may want to revise.

Change-Id: I89446ea06b5742efb194fffd16bb775e9566ca1a
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>
---
 src/corelib/serialization/qjsonarray.h    |  1 +
 src/corelib/serialization/qjsonobject.cpp |  2 +
 src/corelib/serialization/qjsonobject.h   |  2 +
 src/corelib/serialization/qjsonvalue.cpp  | 46 +++++++++++++++++------
 src/corelib/serialization/qjsonvalue.h    |  3 ++
 5 files changed, 43 insertions(+), 11 deletions(-)

diff --git a/src/corelib/serialization/qjsonarray.h b/src/corelib/serialization/qjsonarray.h
index 0128a36470c..a8c37605658 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 014224c4db1..ee4ea8ce238 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 d9f6785631a..74f6905b608 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 27cad8941ed..9fecbbb6266 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.
 */
 
+void QJsonValueRef::detach()
+{
+    QCborContainerPrivate *d = QJsonPrivate::Value::container(*this);
+    d = QCborContainerPrivate::detach(d, d->elements.size());
+
+    if (is_object)
+        o->o.reset(d);
+    else
+        a->a.reset(d);
+}
+
+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)
 {
-    if (is_object)
-        o->setValueAt(index, val);
-    else
-        a->replace(index, val);
-
-    return *this;
+    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 4f9c3af5788..f50bb08017d 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