CMake: Create plugin initializers for static user plugins

Previously we only created object library static plugin initializers
for Qt plugins only, not user-project plugins.

The reason was that if a user tried to install the plugin target via
an export set, CMake would error out saying that the _init library is
not part of the same export set.

Introduce an OUTPUT_TARGETS option that would allow projects to get
the name of the generated _init target, so they can install it if
needed.
This was already done for qt6_add_qml_module, so we just introduce the
same option for qt6_add_plugin.

Now user static plugins will have an _init target created, which will
be propagated to consumers whenever the consumers link against the
plugin itself.

We also need an internal option to disable this propagation, because
it's handled a bit differently for Qt plugins which can be linked
either via finalizers or via usage requirements.

Amends 91c65dd80cdd2de666448c14202c0c63718152b6

As a result of the implementation change, cleanup example projects
to ensure that they build successfully (the important part is
specifying the CLASS_NAME).

Only plugandpaint works properly with both shared and static Qt
builds.

echoplugin works with a shared Qt build, but not a static one due to
some assumptions in the C++ code about shared plugins.

styleplugin doesn't seem to work properly neither with shared Qt
builds nor static Qt builds, at least on macOS. But it builds fine.
For some reason even if the plugin is found, the style is not applied.

Amends 4caac1feea025b0ad496141e8f16ab88c04c2caa

Pick-to: 6.2
Task-number: QTBUG-80863
Task-number: QTBUG-92933
Change-Id: I6f631cda9566229b7a63992b23d7d7fa50303eeb
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

11 files changed, 60 insertions, 136 deletions

diff --git a/examples/widgets/tools/echoplugin/CMakeLists.txt b/examples/widgets/tools/echoplugin/CMakeLists.txt
index 380cfcae8e..6e32a4de09 100644
--- a/examples/widgets/tools/echoplugin/CMakeLists.txt
+++ b/examples/widgets/tools/echoplugin/CMakeLists.txt
@@ -1,4 +1,15 @@
-# Generated from echoplugin.pro.
+cmake_minimum_required(VERSION 3.16)
+project(plugandpaint LANGUAGES CXX)
 
-qt_internal_add_example(echowindow)
-qt_internal_add_example(plugin)
+find_package(Qt6 COMPONENTS Core Gui Widgets)
+
+set(CMAKE_AUTOMOC ON)
+
+if(NOT DEFINED INSTALL_EXAMPLESDIR)
+    set(INSTALL_EXAMPLESDIR "examples")
+endif()
+
+set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/widgets/tools/echoplugin")
+
+add_subdirectory(plugin)
+add_subdirectory(echowindow)
diff --git a/examples/widgets/tools/echoplugin/echowindow/CMakeLists.txt b/examples/widgets/tools/echoplugin/echowindow/CMakeLists.txt
index 96e5e77bf4..83f0c88456 100644
--- a/examples/widgets/tools/echoplugin/echowindow/CMakeLists.txt
+++ b/examples/widgets/tools/echoplugin/echowindow/CMakeLists.txt
@@ -1,41 +1,25 @@
-# Generated from echowindow.pro.
-
-cmake_minimum_required(VERSION 3.16)
-project(echoplugin LANGUAGES CXX)
-
-set(CMAKE_INCLUDE_CURRENT_DIR ON)
-
-set(CMAKE_AUTOMOC ON)
-set(CMAKE_AUTORCC ON)
-set(CMAKE_AUTOUIC ON)
-
-if(NOT DEFINED INSTALL_EXAMPLESDIR)
-  set(INSTALL_EXAMPLESDIR "examples")
-endif()
-
-set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/widgets/tools/echoplugin")
-
-find_package(Qt6 COMPONENTS Core)
-find_package(Qt6 COMPONENTS Gui)
-find_package(Qt6 COMPONENTS Widgets)
-
-qt_add_executable(echopluginwindow # special case: renamed target
+qt_add_executable(echopluginwindow
     echointerface.h
     echowindow.cpp echowindow.h
     main.cpp
 )
-set_target_properties(echopluginwindow PROPERTIES # special case
+set_target_properties(echopluginwindow PROPERTIES
     WIN32_EXECUTABLE TRUE
     MACOSX_BUNDLE TRUE
 )
-target_link_libraries(echopluginwindow PUBLIC # special case
+target_link_libraries(echopluginwindow PRIVATE
     Qt::Core
     Qt::Gui
     Qt::Widgets
 )
 
-install(TARGETS echopluginwindow # special case: renamed target
+if(NOT QT6_IS_SHARED_LIBS_BUILD)
+    target_link_libraries(echopluginwindow PRIVATE
+        echoplugin
+    )
+endif()
+
+install(TARGETS echopluginwindow
     RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
     BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
-    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
 )
diff --git a/examples/widgets/tools/echoplugin/plugin/CMakeLists.txt b/examples/widgets/tools/echoplugin/plugin/CMakeLists.txt
index 7ce196c4e2..fb727aa1d7 100644
--- a/examples/widgets/tools/echoplugin/plugin/CMakeLists.txt
+++ b/examples/widgets/tools/echoplugin/plugin/CMakeLists.txt
@@ -1,31 +1,11 @@
-# Generated from plugin.pro.
-
-cmake_minimum_required(VERSION 3.16)
-project(echoplugin LANGUAGES CXX)
-
-set(CMAKE_INCLUDE_CURRENT_DIR ON)
-
-set(CMAKE_AUTOMOC ON)
-set(CMAKE_AUTORCC ON)
-set(CMAKE_AUTOUIC ON)
-
-if(NOT DEFINED INSTALL_EXAMPLESDIR)
-  set(INSTALL_EXAMPLESDIR "examples")
-endif()
-
-set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/widgets/tools/echoplugin/plugins")
-
-find_package(Qt6 COMPONENTS Core)
-find_package(Qt6 COMPONENTS Gui)
-find_package(Qt6 COMPONENTS Widgets)
-
-qt_add_plugin(echoplugin)
+qt_add_plugin(echoplugin
+    CLASS_NAME EchoPlugin
+)
 target_sources(echoplugin PRIVATE
     echoplugin.cpp echoplugin.h
 )
 set_target_properties(echoplugin PROPERTIES
-    WIN32_EXECUTABLE TRUE
-    MACOSX_BUNDLE TRUE
+    LIBRARY_OUTPUT_DIRECTORY "${PROJECT_BINARY_DIR}/echowindow"
 )
 target_include_directories(echoplugin PUBLIC
     ../echowindow
@@ -39,6 +19,5 @@ target_link_libraries(echoplugin PUBLIC
 
 install(TARGETS echoplugin
     RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
-    BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
     LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
 )
diff --git a/examples/widgets/tools/plugandpaint/CMakeLists.txt b/examples/widgets/tools/plugandpaint/CMakeLists.txt
index 1d4d412adf..e681812dad 100644
--- a/examples/widgets/tools/plugandpaint/CMakeLists.txt
+++ b/examples/widgets/tools/plugandpaint/CMakeLists.txt
@@ -1,5 +1,3 @@
-# Generated from plugandpaint.pro.
-# special case skip regeneration
 cmake_minimum_required(VERSION 3.16)
 project(plugandpaint LANGUAGES CXX)
 
diff --git a/examples/widgets/tools/plugandpaint/app/CMakeLists.txt b/examples/widgets/tools/plugandpaint/app/CMakeLists.txt
index 14cdaeb822..e3709ee0d3 100644
--- a/examples/widgets/tools/plugandpaint/app/CMakeLists.txt
+++ b/examples/widgets/tools/plugandpaint/app/CMakeLists.txt
@@ -1,6 +1,3 @@
-# Generated from app.pro.
-# special case skip regeneration
-
 qt_add_executable(plugandpaint
     interfaces.h
     main.cpp
@@ -12,13 +9,18 @@ set_target_properties(plugandpaint PROPERTIES
     WIN32_EXECUTABLE TRUE
     MACOSX_BUNDLE TRUE
 )
-target_link_libraries(plugandpaint PUBLIC
+target_link_libraries(plugandpaint PRIVATE
     Qt::Widgets
     pnp_basictools
 )
 
+if(NOT QT6_IS_SHARED_LIBS_BUILD)
+    target_link_libraries(plugandpaint PRIVATE
+        pnp_extrafilters
+    )
+endif()
+
 install(TARGETS plugandpaint
     RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
     BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
-    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
 )
diff --git a/examples/widgets/tools/plugandpaint/plugins/CMakeLists.txt b/examples/widgets/tools/plugandpaint/plugins/CMakeLists.txt
index 1e63da97ca..9a2d66d99e 100644
--- a/examples/widgets/tools/plugandpaint/plugins/CMakeLists.txt
+++ b/examples/widgets/tools/plugandpaint/plugins/CMakeLists.txt
@@ -1,4 +1,2 @@
-# Generated from plugins.pro.
-
 add_subdirectory(basictools)
 add_subdirectory(extrafilters)
diff --git a/examples/widgets/tools/plugandpaint/plugins/basictools/CMakeLists.txt b/examples/widgets/tools/plugandpaint/plugins/basictools/CMakeLists.txt
index c66f83ce62..0056205319 100644
--- a/examples/widgets/tools/plugandpaint/plugins/basictools/CMakeLists.txt
+++ b/examples/widgets/tools/plugandpaint/plugins/basictools/CMakeLists.txt
@@ -1,19 +1,15 @@
-# Generated from basictools.pro.
-# special case skip regeneration
-
-qt_add_plugin(pnp_basictools STATIC)
+qt_add_plugin(pnp_basictools
+    STATIC
+    CLASS_NAME BasicToolsPlugin
+)
 target_sources(pnp_basictools PRIVATE
     basictoolsplugin.cpp basictoolsplugin.h
 )
-set_target_properties(pnp_basictools PROPERTIES
-    WIN32_EXECUTABLE TRUE
-    MACOSX_BUNDLE TRUE
-)
 target_include_directories(pnp_basictools PUBLIC
     ../../app
 )
 
-target_link_libraries(pnp_basictools PUBLIC
+target_link_libraries(pnp_basictools PRIVATE
     Qt::Core
     Qt::Gui
     Qt::Widgets
diff --git a/examples/widgets/tools/plugandpaint/plugins/extrafilters/CMakeLists.txt b/examples/widgets/tools/plugandpaint/plugins/extrafilters/CMakeLists.txt
index 9227dd0537..2332f84399 100644
--- a/examples/widgets/tools/plugandpaint/plugins/extrafilters/CMakeLists.txt
+++ b/examples/widgets/tools/plugandpaint/plugins/extrafilters/CMakeLists.txt
@@ -1,19 +1,17 @@
-# Generated from extrafilters.pro.
-# special case skip regeneration
-
-qt_add_plugin(pnp_extrafilters)
+qt_add_plugin(pnp_extrafilters
+    CLASS_NAME ExtraFiltersPlugin
+)
 target_sources(pnp_extrafilters PRIVATE
     extrafiltersplugin.cpp extrafiltersplugin.h
 )
 set_target_properties(pnp_extrafilters PROPERTIES
-    MACOSX_BUNDLE TRUE
     LIBRARY_OUTPUT_DIRECTORY "${PROJECT_BINARY_DIR}/app"
 )
 target_include_directories(pnp_extrafilters PUBLIC
     ../../app
 )
 
-target_link_libraries(pnp_extrafilters PUBLIC
+target_link_libraries(pnp_extrafilters PRIVATE
     Qt::Core
     Qt::Gui
     Qt::Widgets
diff --git a/examples/widgets/tools/styleplugin/CMakeLists.txt b/examples/widgets/tools/styleplugin/CMakeLists.txt
index 6d3549dcad..33412f5306 100644
--- a/examples/widgets/tools/styleplugin/CMakeLists.txt
+++ b/examples/widgets/tools/styleplugin/CMakeLists.txt
@@ -1,19 +1,15 @@
-# Generated from styleplugin.pro.
-
-# special case begin
 cmake_minimum_required(VERSION 3.16)
 project(styleplugin LANGUAGES CXX)
 
-set(CMAKE_INCLUDE_CURRENT_DIR ON)
+find_package(Qt6 COMPONENTS Widgets)
 
 set(CMAKE_AUTOMOC ON)
-set(CMAKE_AUTORCC ON)
-set(CMAKE_AUTOUIC ON)
 
-set(INSTALL_EXAMPLEDIR "examples")
+if(NOT DEFINED INSTALL_EXAMPLESDIR)
+    set(INSTALL_EXAMPLESDIR "examples")
+endif()
 
-find_package(Qt6 COMPONENTS Widgets)
-# special case end
+set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/widgets/tools/styleplugin")
 
 add_subdirectory(stylewindow)
 add_subdirectory(plugin)
diff --git a/examples/widgets/tools/styleplugin/plugin/CMakeLists.txt b/examples/widgets/tools/styleplugin/plugin/CMakeLists.txt
index c33188d228..30a06231c1 100644
--- a/examples/widgets/tools/styleplugin/plugin/CMakeLists.txt
+++ b/examples/widgets/tools/styleplugin/plugin/CMakeLists.txt
@@ -1,34 +1,14 @@
-# Generated from plugin.pro.
-
-cmake_minimum_required(VERSION 3.16)
-project(simplestyleplugin LANGUAGES CXX)
-
-set(CMAKE_INCLUDE_CURRENT_DIR ON)
-
-set(CMAKE_AUTOMOC ON)
-set(CMAKE_AUTORCC ON)
-set(CMAKE_AUTOUIC ON)
-
-if(NOT DEFINED INSTALL_EXAMPLESDIR)
-  set(INSTALL_EXAMPLESDIR "examples")
-endif()
-
-set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/widgets/tools/styleplugin/styles")
-
-find_package(Qt6 COMPONENTS Core)
-find_package(Qt6 COMPONENTS Gui)
-find_package(Qt6 COMPONENTS Widgets)
-
-qt_add_plugin(simplestyleplugin)
+qt_add_plugin(simplestyleplugin
+    CLASS_NAME SimpleStylePlugin
+)
 target_sources(simplestyleplugin PRIVATE
     simplestyle.cpp simplestyle.h
     simplestyleplugin.cpp simplestyleplugin.h
 )
 set_target_properties(simplestyleplugin PROPERTIES
-    WIN32_EXECUTABLE TRUE
-    MACOSX_BUNDLE TRUE
+    LIBRARY_OUTPUT_DIRECTORY "${PROJECT_BINARY_DIR}/stylewindow/styles"
 )
-target_link_libraries(simplestyleplugin PUBLIC
+target_link_libraries(simplestyleplugin PRIVATE
     Qt::Core
     Qt::Gui
     Qt::Widgets
@@ -36,6 +16,5 @@ target_link_libraries(simplestyleplugin PUBLIC
 
 install(TARGETS simplestyleplugin
     RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
-    BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
     LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
 )
diff --git a/examples/widgets/tools/styleplugin/stylewindow/CMakeLists.txt b/examples/widgets/tools/styleplugin/stylewindow/CMakeLists.txt
index 264913f967..168c41fb60 100644
--- a/examples/widgets/tools/styleplugin/stylewindow/CMakeLists.txt
+++ b/examples/widgets/tools/styleplugin/stylewindow/CMakeLists.txt
@@ -1,24 +1,3 @@
-# Generated from stylewindow.pro.
-
-cmake_minimum_required(VERSION 3.16)
-project(styleplugin LANGUAGES CXX)
-
-set(CMAKE_INCLUDE_CURRENT_DIR ON)
-
-set(CMAKE_AUTOMOC ON)
-set(CMAKE_AUTORCC ON)
-set(CMAKE_AUTOUIC ON)
-
-if(NOT DEFINED INSTALL_EXAMPLESDIR)
-  set(INSTALL_EXAMPLESDIR "examples")
-endif()
-
-set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/widgets/tools/styleplugin")
-
-find_package(Qt6 COMPONENTS Core)
-find_package(Qt6 COMPONENTS Gui)
-find_package(Qt6 COMPONENTS Widgets)
-
 qt_add_executable(styleplugin
     main.cpp
     stylewindow.cpp stylewindow.h
@@ -27,14 +6,18 @@ set_target_properties(styleplugin PROPERTIES
     WIN32_EXECUTABLE TRUE
     MACOSX_BUNDLE TRUE
 )
-target_link_libraries(styleplugin PUBLIC
+target_link_libraries(styleplugin PRIVATE
     Qt::Core
     Qt::Gui
     Qt::Widgets
 )
+if(NOT QT6_IS_SHARED_LIBS_BUILD)
+    target_link_libraries(styleplugin PRIVATE
+        simplestyleplugin
+    )
+endif()
 
 install(TARGETS styleplugin
     RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
     BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
-    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
 )