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>

3 files changed, 220 insertions, 0 deletions

diff --git a/tests/auto/cmake/test_import_plugins/CMakeLists.txt b/tests/auto/cmake/test_import_plugins/CMakeLists.txt
new file mode 100644
index 0000000000..a793fe211d
--- /dev/null
+++ b/tests/auto/cmake/test_import_plugins/CMakeLists.txt
@@ -0,0 +1,111 @@
+
+cmake_minimum_required(VERSION 3.1)
+
+project(import_plugins_advanced)
+enable_testing()
+
+set(CMAKE_INCLUDE_CURRENT_DIR ON)
+
+if(EXISTS "${CMAKE_CURRENT_LIST_DIR}/FindPackageHints.cmake")
+    include("${CMAKE_CURRENT_LIST_DIR}/FindPackageHints.cmake")
+endif()
+
+# Need to find Qt5Core explicitly because the MockPlugins1 and MockPlugins2 config files
+# are in a different directory (the source dir) when doing a standalone tests build,
+# whereas Core is in the installed directory, and due to NO_DEFAULT_PATH being used
+# for the Core dependency call in Qt5MockPlugins, Core would not be found in the source
+# dir.
+find_package(Qt5 COMPONENTS Core REQUIRED HINTS ${Qt5Tests_PREFIX_PATH})
+get_target_property(qt_is_static Qt5::Core TYPE)
+
+# For a similar reason, we need to find the MockPlugins packages not via COMPONENTS argument,
+# but directly, because the location of Qt5Config.cmake is in the installed dir, while
+# the MockPlugins are in the source dir, and Qt5Config only looks for packages relative
+# to its own location.
+# The packages are still successfuly found, because the CMAKE_PREFIX_PATH populated by qmake
+# contains both the installed Qt dir, and the Qt source dir.
+find_package(Qt5MockPlugins1 REQUIRED HINTS ${Qt5Tests_PREFIX_PATH})
+find_package(Qt5MockPlugins2 REQUIRED HINTS ${Qt5Tests_PREFIX_PATH})
+
+function(create_test_executable TARGET_NAME)
+    set(CHECK_FILE ${CMAKE_BINARY_DIR}/${TARGET_NAME}_check.cpp)
+
+    set(EXPECTED_PLUGINS)
+    foreach(_p ${ARGN})
+        string(APPEND EXPECTED_PLUGINS "    \"${_p}\",\n")
+    endforeach()
+    configure_file("${CMAKE_SOURCE_DIR}/check.cpp.in" ${CHECK_FILE})
+
+    add_executable(${TARGET_NAME} main.cpp ${CHECK_FILE})
+    target_link_libraries(${TARGET_NAME} Qt5::MockPlugins1)
+    add_test(test_${TARGET_NAME} ${TARGET_NAME})
+endfunction()
+
+create_test_executable(default QMock1Plugin QMock2Plugin)
+# No call to qt5_import_plugins() for the default
+
+# TODO This test is known to fail because CMake currently doesn't have a way to
+# implement its own equivalent of the PLUGIN_EXTENDS mechanism at generate-
+# time (meaning a library only gets linked if a set of other libraries are
+# *also* linked.) CMake 3.14 or beyond may have such a mechanism, but until
+# then, this test is expected to fail, because QMock3Plugin is not being
+# linked even though MockPlugins2 is present.
+create_test_executable(default_link QMock1Plugin QMock2Plugin QMock3Plugin)
+target_link_libraries(default_link Qt5::MockPlugins2)
+set_property(TEST test_default_link PROPERTY DISABLED 1)
+# No call to qt5_import_plugins() for the default
+
+create_test_executable(manual QMock1Plugin QMock2Plugin QMock3Plugin QMock4Plugin)
+qt5_import_plugins(manual
+    INCLUDE Qt5::QMock3Plugin Qt5::QMock4Plugin
+)
+
+create_test_executable(manual_genex QMock1Plugin QMock2Plugin QMock3Plugin)
+qt5_import_plugins(manual_genex
+    INCLUDE $<1:Qt5::QMock3Plugin> $<0:Qt5::QMock4Plugin>
+)
+
+create_test_executable(blacklist QMock1Plugin)
+qt5_import_plugins(blacklist
+    EXCLUDE Qt5::QMock2Plugin Qt5::QMock3Plugin
+)
+
+create_test_executable(blacklist_genex QMock1Plugin)
+qt5_import_plugins(blacklist_genex
+    EXCLUDE $<1:Qt5::QMock2Plugin> $<1:Qt5::QMock3Plugin> $<0:Qt5::QMock1Plugin>
+)
+
+create_test_executable(override QMock3Plugin QMock4Plugin)
+qt5_import_plugins(override
+    INCLUDE_BY_TYPE mockplugin Qt5::QMock3Plugin Qt5::QMock4Plugin
+)
+
+create_test_executable(override_genex QMock3Plugin)
+qt5_import_plugins(override_genex
+    INCLUDE_BY_TYPE mockplugin $<1:Qt5::QMock3Plugin> $<0:Qt5::QMock4Plugin>
+)
+
+create_test_executable(override_mix QMock2Plugin QMock3Plugin)
+qt5_import_plugins(override_mix
+    INCLUDE Qt5::QMock2Plugin
+    INCLUDE_BY_TYPE mockplugin Qt5::QMock3Plugin
+)
+
+if(NOT WIN32)
+    # Compiling an empty static array fails on Windows.
+    create_test_executable(none)
+    qt5_import_plugins(none
+        EXCLUDE_BY_TYPE mockplugin
+    )
+endif()
+
+create_test_executable(none_mix QMock3Plugin QMock4Plugin)
+qt5_import_plugins(none_mix
+    INCLUDE Qt5::QMock3Plugin Qt5::QMock4Plugin
+    EXCLUDE_BY_TYPE mockplugin
+)
+
+create_test_executable(recursive QMock5Plugin QMock6Plugin)
+qt5_import_plugins(recursive
+    INCLUDE_BY_TYPE mockplugin Qt5::QMock5Plugin
+)
diff --git a/tests/auto/cmake/test_import_plugins/check.cpp.in b/tests/auto/cmake/test_import_plugins/check.cpp.in
new file mode 100644
index 0000000000..df6ea03d2d
--- /dev/null
+++ b/tests/auto/cmake/test_import_plugins/check.cpp.in
@@ -0,0 +1,8 @@
+#include <QString>
+#include <cstddef>
+
+QString expectedPlugins[] = {
+@EXPECTED_PLUGINS@
+};
+
+std::size_t numExpectedPlugins = sizeof(expectedPlugins) / sizeof(numExpectedPlugins);
diff --git a/tests/auto/cmake/test_import_plugins/main.cpp b/tests/auto/cmake/test_import_plugins/main.cpp
new file mode 100644
index 0000000000..9fcc81754b
--- /dev/null
+++ b/tests/auto/cmake/test_import_plugins/main.cpp
@@ -0,0 +1,101 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 Kitware, Inc.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QPluginLoader>
+#include <QSet>
+#include <QString>
+#include <QVector>
+
+#include <cstddef>
+#include <iostream>
+
+extern QString expectedPlugins[];
+extern std::size_t numExpectedPlugins;
+
+int main(int argc, char **argv)
+{
+#ifdef QT_STATIC
+    QSet<QString> expectedPluginSet;
+    for (std::size_t i = 0; i < numExpectedPlugins; i++) {
+        expectedPluginSet.insert(expectedPlugins[i]);
+    }
+
+    QVector<QStaticPlugin> plugins = QPluginLoader::staticPlugins();
+    QSet<QString> actualPluginSet;
+    for (QStaticPlugin plugin : plugins) {
+        actualPluginSet.insert(plugin.metaData()["className"].toString());
+    }
+
+    if (expectedPluginSet != actualPluginSet) {
+        std::cerr << "Loaded plugins do not match what was expected!" << std::endl
+                  << "Expected plugins:" << std::endl;
+
+        QList<QString> expectedPluginList = expectedPluginSet.toList();
+        expectedPluginList.sort();
+        for (QString plugin : expectedPluginList) {
+            std::cerr << (actualPluginSet.contains(plugin) ? "  " : "- ")
+                      << plugin.toStdString() << std::endl;
+        }
+
+        std::cerr << std::endl << "Actual plugins:" << std::endl;
+
+        QList<QString> actualPluginList = actualPluginSet.toList();
+        actualPluginList.sort();
+        for (QString plugin : actualPluginList) {
+            std::cerr << (expectedPluginSet.contains(plugin) ? "  " : "+ ")
+                      << plugin.toStdString() << std::endl;
+        }
+
+        return 1;
+    }
+
+#endif
+    return 0;
+}