QVariant: reduce transitive includes

Forward declare more types in qvariant.h, and do the same for qdebug.h
(which will be removed from qvariant in a separate patch).

As we now only forward declare containers (e.g. QMap, QList, ...), code
which includes <QVariantMap>, <QVariantList>... breaks without further
adjustment: So far, those headers simply included qvariant.h. However,
by introducing new actual headers for those types and adjusting
sync.profile, we can avoid this issue.

To avoid breaking leaf modules and user code, we make the change opt-in:
Unless QT_LEAN_HEADERS is defined to a value of >= 1, we still
include the superfluous headers. We also set this macro in qtbase via
QT_EXTRA_INTERNAL_TARGET_DEFINES.

[ChangeLog][Potentially Source-Incompatible Changes] qvariant.h no
longer includes <QList>, <QMap>, <QHash>, <QVarLengthArray>, <QSet> and
<QObject>. Code that relied on transitive includes might need to
explicitly include those headers now. Notably, including <QVariant> (or
qvariant.h) is no longer sufficient when using QVariant(List|Map|Hash).
Using them now requires including respectively <QVariantList>,
<QVariantMap>, or <QVariantHash>. Alternatively, including <QVariant>
and the <QList>, <QMap> or <QHash> header also works.

[ChangeLog][Potentially Source-Incompatible Changes] qdebug.h no longer
includes <QSet>, <QHash>, <QVarLengthArray> and <QMap>. Code that relied
on transitive includes might need to explicitly include those headers
now.

Task-number: QTBUG-97601
Change-Id: I142e5de709ed0b305716369a3266389ab7fbbb71
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

.cmake.conf

@@ -22,3 +22,6 @@ set(QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_STATIC "3.21")
 #       in sync.
 set(QT_MIN_NEW_POLICY_CMAKE_VERSION "3.16")
 set(QT_MAX_NEW_POLICY_CMAKE_VERSION "3.21")
+
+# set (git) module specific defines
+set(QT_EXTRA_INTERNAL_TARGET_DEFINES "QT_LEAN_HEADERS=1")

src/corelib/CMakeLists.txt

@@ -145,6 +145,7 @@ qt_internal_add_module(Core
         kernel/qtimer.cpp kernel/qtimer.h
         kernel/qtranslator.cpp kernel/qtranslator.h kernel/qtranslator_p.h
         kernel/qvariant.cpp kernel/qvariant.h kernel/qvariant_p.h
+        kernel/qvariantmap.h kernel/qvarianthash.h kernel/qvariantlist.h
         plugin/qfactoryinterface.cpp plugin/qfactoryinterface.h
         plugin/qfactoryloader.cpp plugin/qfactoryloader_p.h
         plugin/qplugin.h plugin/qplugin_p.h

src/corelib/io/qdebug.h

@@ -41,14 +41,9 @@
 #ifndef QDEBUG_H
 #define QDEBUG_H
 
-#include <QtCore/qalgorithms.h>
-#include <QtCore/qhash.h>
-#include <QtCore/qlist.h>
-#include <QtCore/qmap.h>
+#include <QtCore/qcontainerfwd.h>
 #include <QtCore/qtextstream.h>
 #include <QtCore/qstring.h>
-#include <QtCore/qset.h>
-#include <QtCore/qvarlengtharray.h>
 #include <QtCore/qcontiguouscache.h>
 #include <QtCore/qsharedpointer.h>
 
@@ -58,6 +53,13 @@
 #include <map>
 #include <utility>
 
+#if !defined(QT_LEAN_HEADERS) || QT_LEAN_HEADERS < 1
+#  include <QtCore/qlist.h>
+#  include <QtCore/qmap.h>
+#  include <QtCore/qset.h>
+#  include <QtCore/qvarlengtharray.h>
+#endif
+
 QT_BEGIN_NAMESPACE
 
 class QT6_ONLY(Q_CORE_EXPORT) QDebug : public QIODeviceBase

src/corelib/kernel/qvariant.h

@@ -41,23 +41,22 @@
 #define QVARIANT_H
 
 #include <QtCore/qatomic.h>
-#include <QtCore/qbytearray.h>
-#include <QtCore/qlist.h>
+#include <QtCore/qcontainerfwd.h>
 #include <QtCore/qmetatype.h>
-#include <QtCore/qmap.h>
-#include <QtCore/qhash.h>
-#include <QtCore/qstring.h>
-#include <QtCore/qstringlist.h>
-#include <QtCore/qobject.h>
 #ifndef QT_NO_DEBUG_STREAM
 #include <QtCore/qdebug.h>
 #endif
-#ifndef QT_BOOTSTRAPPED
-#include <QtCore/qbytearraylist.h>
-#endif
 #include <memory>
 #include <type_traits>
 #include <variant>
+#if !defined(QT_LEAN_HEADERS) || QT_LEAN_HEADERS < 1
+#  include <QtCore/qlist.h>
+#  include <QtCore/qstringlist.h>
+#  include <QtCore/qbytearraylist.h>
+#  include <QtCore/qhash.h>
+#  include <QtCore/qmap.h>
+#  include <QtCore/qobject.h>
+#endif
 
 QT_BEGIN_NAMESPACE
 

src/corelib/kernel/qvarianthash.h

@@ -0,0 +1,56 @@
+/****************************************************************************
+**
+** Copyright (C) 2022 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore 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 QVARIANTHASH_H
+#define QVARIANTHASH_H
+
+#if 0
+#pragma qt_class(QVariantHash)
+#endif
+
+#include <QtCore/qglobal.h>
+
+#include <QtCore/QHash>
+#include <QtCore/QVariant>
+#include <QtCore/QString>
+
+QT_BEGIN_NAMESPACE
+QT_END_NAMESPACE
+
+#endif

src/corelib/kernel/qvariantlist.h

@@ -0,0 +1,55 @@
+/****************************************************************************
+**
+** Copyright (C) 2022 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore 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 QVARIANTLIST_H
+#define QVARIANTLIST_H
+
+#if 0
+#pragma qt_class(QVariantList)
+#endif
+
+#include <QtCore/qglobal.h>
+
+#include <QtCore/QList>
+#include <QtCore/QVariant>
+
+QT_BEGIN_NAMESPACE
+QT_END_NAMESPACE
+
+#endif

src/corelib/kernel/qvariantmap.h

@@ -0,0 +1,56 @@
+/****************************************************************************
+**
+** Copyright (C) 2022 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore 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 QVARIANTMAP_H
+#define QVARIANTMAP_H
+
+#if 0
+#pragma qt_class(QVariantMap)
+#endif
+
+#include <QtCore/qglobal.h>
+
+#include <QtCore/QMap>
+#include <QtCore/QVariant>
+#include <QtCore/QString>
+
+QT_BEGIN_NAMESPACE
+QT_END_NAMESPACE
+
+#endif

src/corelib/tools/qsharedpointer_impl.h

@@ -62,13 +62,17 @@ QT_END_NAMESPACE
 
 #include <new>
 #include <QtCore/qatomic.h>
-#include <QtCore/qobject.h>    // for qobject_cast
 #include <QtCore/qhashfunctions.h>
+#include <QtCore/qmetatype.h> // for IsPointerToTypeDerivedFromQObject
 
 #include <memory>
 
 QT_BEGIN_NAMESPACE
 
+class QObject;
+template <class T>
+T qobject_cast(const QObject *object);
+
 //
 // forward declarations
 //

sync.profile

@@ -51,7 +51,6 @@
     "qevent.h" => "QtEvents",
     "qnamespace.h" => "Qt",
     "qnumeric.h" => "QtNumeric",
-    "qvariant.h" => "QVariantHash,QVariantList,QVariantMap",
     "qvulkanfunctions.h" => "QVulkanFunctions,QVulkanDeviceFunctions",
     "qgl.h" => "QGL",
     "qtsqlglobal.h" => "QSql",