CMake: Add support for auto-importing plugins in CMake

This commit adds transitive dependencies to the plugins, so that a
sane set of default plugins get auto-imported when linking against a
module. It also provides a new function, qt5_import_plugins(), which
allows you to override the set of plugins that get imported. The decision
of whether or not to import a specific plugin is based on several custom
target properties and a very clever generator expression.

Note that this change only imports plugins on static Qt builds. It
does nothing on shared Qt builds, as the shared libraries already have
their own plugin import mechanism.

[ChangeLog][CMake] Added ability to auto-import non-qml plugins on
CMake builds

Task-number: QTBUG-38913
Task-number: QTBUG-76562
Change-Id: I2d6c8908b521cf6ba1ebbbc33a87cb7ddd9935cf
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 34 insertions, 0 deletions

diff --git a/tests/auto/cmake/mockplugins/mockplugins1/fake.cpp b/tests/auto/cmake/mockplugins/mockplugins1/fake.cpp
new file mode 100644
index 0000000000..f95eba6055
--- /dev/null
+++ b/tests/auto/cmake/mockplugins/mockplugins1/fake.cpp
@@ -0,0 +1,34 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** 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 General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** 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-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtCore/QtGlobal>
+
+// Empty exported function needed to create .lib on Windows.
+Q_DECL_EXPORT void mockplugins1_foo() {
+
+}