Fix loading of Qt6*Plugin.cmake files of per-repo builds

When doing a per-repository build of Qt, as it is done for the installer
packages, the build of qtbase has no knowledge of plugins that might be
built and installed from other repositories. That means we must not
write a fixed list of known plugins when exporting Qt modules of qtbase.

In particular, qtsvg adds imageformat plugins that are supposed to be
picked up by qtbase's QtGui module when linking a project against a
statically linked Qt.
${install-prefix}/lib/cmake/Qt6Gui/Qt6GuiPlugins.cmake missed the
include statements for qtsvg's plugin config files and operated on a
fixed list of plugins, all from qtbase.

Apart from that, the Qt6::Gui target's property QT_PLUGINS did only
contain the qtbase plugins.

This patch fixes the situation in the following way:

1. All Qt6*PluginConfig.cmake files in
${install-prefix}/lib/cmake/Qt6Gui are detected and included.

2. From those file names, the target names of the plugins are
deduced. This is safe as the file name of those generated files is a
direct result of the plugin's target name.

3. The QT_PLUGINS property of the module is updated with the detected
plugin target names.

Fixes: QTBUG-89643
Change-Id: Ifc3c39aa9948277ead5ebb209ec5eff64746308b
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

2 files changed, 15 insertions, 10 deletions

diff --git a/cmake/QtPlugins.cmake.in b/cmake/QtPlugins.cmake.in
index d6d5c829b2..b5ecd6ba87 100644
--- a/cmake/QtPlugins.cmake.in
+++ b/cmake/QtPlugins.cmake.in
@@ -1,9 +1,20 @@
 include_guard(DIRECTORY)
-
 @QT_MODULE_PLUGIN_INCLUDES@
 
 if(NOT @BUILD_SHARED_LIBS@)
     set(_module_target "@INSTALL_CMAKE_NAMESPACE@::@QT_MODULE@")
+    get_target_property(_qt_plugins ${_module_target} QT_PLUGINS)
+
+    # Include all PluginConfig.cmake files and update the QT_PLUGINS property of the module.
+    file(GLOB _qt_plugin_config_files "${CMAKE_CURRENT_LIST_DIR}/@INSTALL_CMAKE_NAMESPACE@*PluginConfig.cmake")
+    foreach(_config_file ${_qt_plugin_config_files})
+        string(REGEX REPLACE "^.*/@INSTALL_CMAKE_NAMESPACE@(.*Plugin)Config.cmake$" "\\1" _qt_plugin "${_config_file}")
+        include("${_config_file}")
+        list(APPEND _qt_plugins ${_qt_plugin})
+    endforeach()
+    list(REMOVE_DUPLICATES _qt_plugins)
+    set_property(TARGET ${_module_target} PROPERTY QT_PLUGINS ${_qt_plugins})
+
     # Properties can't be set on aliased targets, so make sure to unalias the target. This is needed
     # when Qt examples are built as part of the Qt build itself.
     get_target_property(_aliased_target ${_module_target} ALIASED_TARGET)
@@ -35,7 +46,7 @@ if(NOT @BUILD_SHARED_LIBS@)
     endif()
 
     # The code in here uses the properties defined in qt_import_plugins (Qt6CoreMacros.cmake)
-    foreach(target @qt_plugins@)
+    foreach(target ${_qt_plugins})
         set(_plugin_target "@INSTALL_CMAKE_NAMESPACE@::${target}")
         set(_plugin_target_versionless "Qt::${target}")
         get_target_property(_classname "${_plugin_target}" QT_PLUGIN_CLASS_NAME)
diff --git a/cmake/QtPostProcessHelpers.cmake b/cmake/QtPostProcessHelpers.cmake
index 37213f13a5..9a36e2ada4 100644
--- a/cmake/QtPostProcessHelpers.cmake
+++ b/cmake/QtPostProcessHelpers.cmake
@@ -384,13 +384,6 @@ function(qt_internal_create_plugins_files)
         qt_path_join(config_install_dir ${QT_CONFIG_INSTALL_DIR} ${INSTALL_CMAKE_NAMESPACE}${QT_MODULE})
         set(QT_MODULE_PLUGIN_INCLUDES "")
 
-        get_target_property(qt_plugins "${QT_MODULE}" QT_PLUGINS)
-        if(qt_plugins)
-            foreach (pluginTarget ${qt_plugins})
-                set(QT_MODULE_PLUGIN_INCLUDES "${QT_MODULE_PLUGIN_INCLUDES}include(\"\${CMAKE_CURRENT_LIST_DIR}/${INSTALL_CMAKE_NAMESPACE}${pluginTarget}Config.cmake\")\n")
-            endforeach()
-        endif()
-
         if(QT_MODULE STREQUAL "Qml")
             set(QT_MODULE_PLUGIN_INCLUDES "${QT_MODULE_PLUGIN_INCLUDES}
 file(GLOB __qt_qml_plugins_config_file_list \"\${CMAKE_CURRENT_LIST_DIR}/QmlPlugins/${INSTALL_CMAKE_NAMESPACE}*Config.cmake\")
@@ -401,7 +394,8 @@ if (__qt_qml_plugins_config_file_list AND NOT QT_SKIP_AUTO_QML_PLUGIN_INCLUSION)
 endif()")
         endif()
 
-        if(QT_MODULE_PLUGIN_INCLUDES)
+        get_target_property(qt_plugins "${QT_MODULE}" QT_PLUGINS)
+        if(qt_plugins OR QT_MODULE_PLUGIN_INCLUDES)
             configure_file(
                 "${QT_CMAKE_DIR}/QtPlugins.cmake.in"
                 "${config_build_dir}/${INSTALL_CMAKE_NAMESPACE}${QT_MODULE}Plugins.cmake"