Encapsulate QQmlContextData

This class is not a private detail of QQmlContext. And it is incredibly
hard to see who owns what in there. Let's add some civilization ...

We enforce refcounting for QQmlContextData across the code base, with
two exceptions:

1. QQmlContextPrivate may or may not own its QQmlContextData.
2. We may request a QQmlContextData owned by its parent QQmlContextData.

For these two cases we keep flags in QQmlContextData and when the
respective field (m_parent or m_publicContext) is reset, we release()
once.

Furthermore, QQmlContextData and QQmlGuardedContextData are moved to
their own files, in order to de-spaghettify qqmlcontext_p.h and
qqmlcontext.cpp.

When the QQmlEngine is deleted, any QQmlComponents drop their object
creators now, in order to release any context data held by those.
Before, the context data would be deleted, but the object creators would
retain the dangling pointer.

[ChangeLog][QML][Important Behavior Changes] QQmlContext::baseUrl() does
what the documentation says now: It prefers explicitly set baseUrls over
compilation unit URLs. Only if no baseUrl is set, the CU's URL is
returned. It used to prefer the CU's URL.

Change-Id: Ieeb5dcb07b45d891526191321386d5443b8f5738
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 131 insertions, 0 deletions

diff --git a/src/qml/qml/qqmlguardedcontextdata_p.h b/src/qml/qml/qqmlguardedcontextdata_p.h
new file mode 100644
index 0000000000..0b24c04305
--- /dev/null
+++ b/src/qml/qml/qqmlguardedcontextdata_p.h
@@ -0,0 +1,131 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQml module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QQMLGUARDEDCONTEXTDATA_P_H
+#define QQMLGUARDEDCONTEXTDATA_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtQml/private/qqmlglobal_p.h>
+#include <QtQml/private/qqmlcontextdata_p.h>
+
+QT_BEGIN_NAMESPACE
+
+class QQmlGuardedContextData
+{
+    Q_DISABLE_COPY(QQmlGuardedContextData);
+public:
+    QQmlGuardedContextData() = default;
+    ~QQmlGuardedContextData() { unlink(); }
+
+    QQmlGuardedContextData(QQmlGuardedContextData &&) = default;
+    QQmlGuardedContextData &operator=(QQmlGuardedContextData &&) = default;
+
+    QQmlGuardedContextData(QQmlRefPointer<QQmlContextData> data)
+    {
+        setContextData(std::move(data));
+    }
+
+    QQmlGuardedContextData &operator=(QQmlRefPointer<QQmlContextData> d)
+    {
+        setContextData(std::move(d));
+        return *this;
+    }
+
+    QQmlRefPointer<QQmlContextData> contextData() const { return m_contextData; }
+    void setContextData(QQmlRefPointer<QQmlContextData> contextData)
+    {
+        if (m_contextData.data() == contextData.data())
+            return;
+        unlink();
+
+        if (contextData) {
+            m_contextData = std::move(contextData);
+            m_next = m_contextData->m_contextGuards;
+            if (m_next)
+                m_next->m_prev = &m_next;
+
+            m_contextData->m_contextGuards = this;
+            m_prev = &m_contextData->m_contextGuards;
+        }
+    }
+
+    bool isNull() const { return !m_contextData; }
+
+    operator const QQmlRefPointer<QQmlContextData> &() const { return m_contextData; }
+    QQmlContextData &operator*() const { return m_contextData.operator*(); }
+    QQmlContextData *operator->() const { return m_contextData.operator->(); }
+
+    QQmlGuardedContextData *next() const { return m_next; }
+
+    void reset()
+    {
+        m_contextData = nullptr;
+        m_next = nullptr;
+        m_prev = nullptr;
+    }
+
+private:
+    void unlink()
+    {
+        if (m_prev) {
+            *m_prev = m_next;
+            if (m_next)
+                m_next->m_prev = m_prev;
+            reset();
+        }
+    }
+
+    QQmlRefPointer<QQmlContextData> m_contextData;
+    QQmlGuardedContextData  *m_next = nullptr;
+    QQmlGuardedContextData **m_prev = nullptr;
+};
+
+QT_END_NAMESPACE
+
+#endif // QQMLGUARDEDCONTEXTDATA_P_H