Add the check for linker capabilities to resolve circular dependencies

'ld' only capable to resolve circular dependencies by wrapping the
suspected static libraries and objects using --start/end-group
arguments. We want to detect if linker is 'ld' at configure time to
decide how to link the resource objects if finalizers are not enabled.

The qt_config_compile_test function is extended with an extra argument
since it's required to pass custom cmake flags to the ld-related test.

Pick-to: 6.2
Change-Id: I484fcc99e2886952d8b0232f37e4e6a35d072931
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

cmake/QtBaseGlobalTargets.cmake

@@ -139,6 +139,7 @@ qt_internal_setup_public_platform_target()
 
 # defines PlatformCommonInternal PlatformModuleInternal PlatformPluginInternal PlatformToolInternal
 include(QtInternalTargets)
+qt_internal_run_common_config_tests()
 
 set(__export_targets Platform
                      GlobalConfig
@@ -237,6 +238,12 @@ qt_copy_or_install(FILES
     DESTINATION "${__GlobalConfig_install_dir}"
 )
 
+# Install public config.tests files.
+qt_copy_or_install(DIRECTORY
+    "cmake/config.tests"
+    DESTINATION "${__GlobalConfig_install_dir}"
+)
+
 # Install public CMake files.
 # The functions defined inside can be used in both public projects and while building Qt.
 # Usually we put such functions into Qt6CoreMacros.cmake, but that's getting bloated.

cmake/QtBuildInternals/QtBuildInternalsConfig.cmake

@@ -372,6 +372,11 @@ macro(qt_build_repo_begin)
     qt_build_internals_set_up_private_api()
     qt_enable_cmake_languages()
 
+    # QtBase has own call right after definition of internal platform-specific targets.
+    if(NOT PROJECT_NAME STREQUAL "QtBase")
+        qt_internal_run_common_config_tests()
+    endif()
+
     # Add global docs targets that will work both for per-repo builds, and super builds.
     if(NOT TARGET docs)
         add_custom_target(docs)
@@ -941,3 +946,36 @@ if ("STANDALONE_TEST" IN_LIST Qt6BuildInternals_FIND_COMPONENTS)
         list(GET _qt_core_version_list 2 PROJECT_VERSION_PATCH)
     endif()
 endif()
+
+function(qt_internal_static_link_order_test)
+    if(TARGET ${QT_CMAKE_EXPORT_NAMESPACE}::PlatformCommonInternal)
+        get_target_property(linker_options
+            ${QT_CMAKE_EXPORT_NAMESPACE}::PlatformCommonInternal INTERFACE_LINK_OPTIONS
+        )
+        string(JOIN " " linker_options ${linker_options})
+    endif()
+
+    qt_config_compile_test(static_link_order
+        LABEL "Check if linker can resolve circular dependencies"
+        PROJECT_PATH "${QT_CMAKE_DIR}/config.tests/static_link_order"
+        CMAKE_FLAGS "-DCMAKE_EXE_LINKER_FLAGS:STRING=${linker_options}"
+    )
+
+    if(TEST_static_link_order)
+        set_property(GLOBAL PROPERTY QT_LINK_ORDER_MATTERS FALSE)
+        set(summary_message "no")
+    else()
+        set_property(GLOBAL PROPERTY QT_LINK_ORDER_MATTERS TRUE)
+        set(summary_message "yes")
+    endif()
+    qt_configure_add_summary_entry(TYPE "message"
+        ARGS "Linker can resolve circular dependencies"
+        MESSAGE "${summary_message}"
+    )
+endfunction()
+
+function(qt_internal_run_common_config_tests)
+    qt_configure_add_summary_section(NAME "Common build options")
+    qt_internal_static_link_order_test()
+    qt_configure_end_summary_section()
+endfunction()

cmake/QtFeature.cmake

@@ -736,7 +736,7 @@ function(qt_config_compile_test name)
     endif()
 
     cmake_parse_arguments(arg "" "LABEL;PROJECT_PATH;C_STANDARD;CXX_STANDARD"
-        "COMPILE_OPTIONS;LIBRARIES;CODE;PACKAGES" ${ARGN})
+        "COMPILE_OPTIONS;LIBRARIES;CODE;PACKAGES;CMAKE_FLAGS" ${ARGN})
 
     if(arg_PROJECT_PATH)
         message(STATUS "Performing Test ${arg_LABEL}")
@@ -815,8 +815,12 @@ function(qt_config_compile_test name)
             endif()
         endif()
 
+        if(NOT arg_CMAKE_FLAGS)
+            set(arg_CMAKE_FLAGS "")
+        endif()
+
         try_compile(HAVE_${name} "${CMAKE_BINARY_DIR}/config.tests/${name}" "${arg_PROJECT_PATH}"
-                    "${name}" CMAKE_FLAGS ${flags})
+                    "${name}" CMAKE_FLAGS ${flags} ${arg_CMAKE_FLAGS})
 
         if(${HAVE_${name}})
             set(status_label "Success")

cmake/config.tests/static_link_order/CMakeLists.txt

@@ -0,0 +1,22 @@
+# The test represents the order-related issue that we have with the ld linker.
+#
+# CMake versions < 3.21.0 produce the following linker line:
+# <binary_name> main.cpp -o static_link_order_test libstaticLib.a objlib.cpp.o
+# Since 'static_link_order_test' doesn't have direct use of 'staticlib2.cpp.o' symbols
+# the translation unit is not linked. When we link objlib.cpp.o it cannot resolve symbols from
+# staticlib2.cpp.o.
+#
+# For now it's only applicable for ld-like linkers. 'lld' has no such issue.
+cmake_minimum_required(VERSION 3.14)
+
+project(static_link_order_test LANGUAGES CXX)
+
+add_library(objLib OBJECT objlib.cpp)
+add_library(staticLib STATIC staticlib1.cpp staticlib2.cpp)
+
+target_link_libraries(staticLib
+    INTERFACE objLib "$<TARGET_OBJECTS:objLib>"
+)
+
+add_executable(static_link_order_test main.cpp)
+target_link_libraries(static_link_order_test PRIVATE staticLib)

cmake/config.tests/static_link_order/main.cpp

@@ -0,0 +1,33 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the utils 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.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+void staticLibFunc1();
+
+int main() {
+    staticLibFunc1();
+}

cmake/config.tests/static_link_order/objlib.cpp

@@ -0,0 +1,33 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the utils 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.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+void staticLibFunc2();
+
+void objLibFunc() {
+    staticLibFunc2();
+}

cmake/config.tests/static_link_order/staticlib1.cpp

@@ -0,0 +1,33 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the utils 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.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+void objLibFunc();
+
+void staticLibFunc1() {
+    objLibFunc();
+}

cmake/config.tests/static_link_order/staticlib2.cpp

@@ -0,0 +1,30 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the utils 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.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+void staticLibFunc2() {
+}

src/corelib/Qt6CoreMacros.cmake

@@ -1479,10 +1479,24 @@ function(__qt_propagate_generated_resource target resource_name generated_source
             "$<NOT:$<STREQUAL:$<TARGET_PROPERTY:TYPE>,STATIC_LIBRARY>>"
         )
         set(resource_objects "$<TARGET_OBJECTS:$<TARGET_NAME:${resource_target}>>")
-        target_link_libraries(${target} INTERFACE
+
+        set(resource_linking_args ${target} INTERFACE
             "$<$<AND:${finalizer_mode_condition},${not_static_condition}>:${resource_objects}>"
         )
 
+        # TODO: The QT_LINK_ORDER_MATTERS flag is not defined for user projects.
+        # It makes sense to disable finalizers if linker may resolve circular dependencies
+        # between objects and static libraries.
+        # Follow-up changes should set _qt_resource_objects_finalizer_mode to FALSE by default
+        # and use target_link_libraries for user projects if the order doesn't affect the
+        # linker work.
+        get_property(link_order_matters GLOBAL PROPERTY QT_LINK_ORDER_MATTERS)
+        if(link_order_matters)
+            target_sources(${resource_linking_args})
+        else()
+            target_link_libraries(${resource_linking_args})
+        endif()
+
         if(NOT target STREQUAL "Core")
             # It's necessary to link the object library target, since we want to pass
             # the object library dependencies to the 'target'. Interface linking doesn't

tests/auto/cmake/test_static_resources/test_static_resources_propagation/CMakeLists.txt

@@ -58,8 +58,8 @@ add_test(NAME test_static_resources_propagation_non_qt
     COMMAND test_static_resources_propagation_non_qt
 )
 
-
-if(NOT GCC AND NOT MINGW AND NOT CLANG)
+get_property(link_order_matters GLOBAL PROPERTY QT_LINK_ORDER_MATTERS)
+if(NOT link_order_matters)
     ## Add the executable using add_executable, expecting resources to be linked regardless of order.
     add_executable(test_static_resources_propagation_non_ld main.cpp)
     set_target_properties(test_static_resources_propagation_non_ld PROPERTIES