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>

9 files changed, 193 insertions, 18 deletions

diff --git a/.cmake.conf b/.cmake.conf
index 57401cb9b9..ee63c78947 100644
--- a/.cmake.conf
+++ b/.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")
diff --git a/src/corelib/CMakeLists.txt b/src/corelib/CMakeLists.txt
index 1cf6a9c486..6f5e0ec6cf 100644
--- a/src/corelib/CMakeLists.txt
+++ b/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
diff --git a/src/corelib/io/qdebug.h b/src/corelib/io/qdebug.h
index fccf581ed9..32b3bf793d 100644
--- a/src/corelib/io/qdebug.h
+++ b/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
diff --git a/src/corelib/kernel/qvariant.h b/src/corelib/kernel/qvariant.h
index fc6b8e9563..ffc091ebf9 100644
--- a/src/corelib/kernel/qvariant.h
+++ b/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
 
diff --git a/src/corelib/kernel/qvarianthash.h b/src/corelib/kernel/qvarianthash.h
new file mode 100644
index 0000000000..3ace02eede
--- /dev/null
+++ b/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
diff --git a/src/corelib/kernel/qvariantlist.h b/src/corelib/kernel/qvariantlist.h
new file mode 100644
index 0000000000..9cecf2e484
--- /dev/null
+++ b/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
diff --git a/src/corelib/kernel/qvariantmap.h b/src/corelib/kernel/qvariantmap.h
new file mode 100644
index 0000000000..a2d0458902
--- /dev/null
+++ b/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
diff --git a/src/corelib/tools/qsharedpointer_impl.h b/src/corelib/tools/qsharedpointer_impl.h
index 1b982c0cf9..683dc496a4 100644
--- a/src/corelib/tools/qsharedpointer_impl.h
+++ b/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
 //
diff --git a/sync.profile b/sync.profile
index 83fab8ffe0..70f652ecf4 100644
--- a/sync.profile
+++ b/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",