CMake: Add finalization to plugins created with qt_add_plugin

Add the MANUAL_FINALIZATION option to qt_add_plugin and run
qt_finalize_target like we do for qt_add_executable and qt_add_library.

Currently, the only user-visible effect is that resource files are put
into a FOLDER and not underneath a XXX_other_files target.

Change-Id: I430d87b5357f6d2ed7fe32198a73eb919f393dd8
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

src/corelib/Qt6CoreMacros.cmake

@@ -1984,6 +1984,7 @@ endmacro()
 
 function(qt6_add_plugin target)
     _qt_internal_get_add_plugin_keywords(opt_args single_args multi_args)
+    list(APPEND opt_args MANUAL_FINALIZATION)
 
     cmake_parse_arguments(PARSE_ARGV 1 arg "${opt_args}" "${single_args}" "${multi_args}")
 
@@ -2030,6 +2031,7 @@ function(qt6_add_plugin target)
     endif()
 
     _qt_internal_add_library(${target} ${type_to_create} ${arg_UNPARSED_ARGUMENTS})
+    set_property(TARGET ${target} PROPERTY _qt_expects_finalization TRUE)
 
     get_target_property(target_type "${target}" TYPE)
     if (target_type STREQUAL "STATIC_LIBRARY")
@@ -2107,6 +2109,23 @@ function(qt6_add_plugin target)
         endif()
         add_dependencies(qt_internal_plugins ${target})
     endif()
+
+    if(arg_MANUAL_FINALIZATION)
+        # Caller says they will call qt6_finalize_target() themselves later
+        return()
+    endif()
+
+    # Defer the finalization if we can. When the caller's project requires
+    # CMake 3.19 or later, this makes the calls to this function concise while
+    # still allowing target property modification before finalization.
+    if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.19)
+        # Need to wrap in an EVAL CODE or else ${target} won't be evaluated
+        # due to special behavior of cmake_language() argument handling
+        cmake_language(EVAL CODE "cmake_language(DEFER CALL qt6_finalize_target ${target})")
+    else()
+        set_target_properties("${target}" PROPERTIES _qt_is_immediately_finalized TRUE)
+        qt6_finalize_target("${target}")
+    endif()
 endfunction()
 
 if(NOT QT_NO_CREATE_VERSIONLESS_FUNCTIONS)

src/corelib/doc/src/cmake/qt_add_library.qdoc

@@ -51,6 +51,7 @@ library created. The \c{qt_add_library()} command does not consider
 Any \c{sources} provided will be passed through to the internal call to
 \c{add_library()}.
 
+\target qt_add_library finalization
 \section2 Finalization
 
 After a target is created, further processing or \e{finalization} steps may be

src/corelib/doc/src/cmake/qt_add_plugin.qdoc

@@ -21,6 +21,7 @@ qt_add_plugin(target
               [SHARED | STATIC]
               [CLASS_NAME class_name]
               [OUTPUT_TARGETS variable_name]
+              [MANUAL_FINALIZATION]
               sources...
 )
 \endcode
@@ -67,4 +68,17 @@ project should also install these internal targets. The names of these targets
 can be obtained by providing the \c OUTPUT_TARGETS option, followed by the name
 of a variable in which to return the target list.
 
+\section2 Finalization
+
+After a target is created, further processing or \e{finalization} steps may be
+needed. The finalization processing is implemented by the
+\l{qt6_finalize_target}{qt_finalize_target()} command.
+
+For details and the meaning of the \c{MANUAL_FINALIZATION} option, refer to the
+\l{qt_add_library finalization}{finalization documentation} for
+\c{qt_add_library}.
+
+\sa {qt6_finalize_target}{qt_finalize_target()},
+    {qt6_add_executable}{qt_add_executable()}
+
 */