1 files changed, 72 insertions, 0 deletions
diff --git a/cmake/QtPublicCMakeVersionHelpers.cmake b/cmake/QtPublicCMakeVersionHelpers.cmake
new file mode 100644
index 0000000000..de896d9d2f
--- /dev/null
+++ b/cmake/QtPublicCMakeVersionHelpers.cmake
@@ -0,0 +1,72 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+function(__qt_internal_get_supported_min_cmake_version_for_using_qt out_var)
+    # This is recorded in Qt6ConfigExtras.cmake
+    set(supported_version "${QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT}")
+    set(${out_var} "${supported_version}" PARENT_SCOPE)
+endfunction()
+
+function(__qt_internal_get_computed_min_cmake_version_for_using_qt out_var)
+    # Allow override when configuring user project.
+    if(QT_FORCE_MIN_CMAKE_VERSION_FOR_USING_QT)
+        set(computed_min_version "${QT_FORCE_MIN_CMAKE_VERSION_FOR_USING_QT}")
+
+    # Set in QtConfigExtras.cmake.
+    elseif(QT_COMPUTED_MIN_CMAKE_VERSION_FOR_USING_QT)
+        set(computed_min_version "${QT_COMPUTED_MIN_CMAKE_VERSION_FOR_USING_QT}")
+    else()
+        message(FATAL_ERROR
+            "Qt Developer error: Can't compute the minimum CMake version required to use this Qt.")
+    endif()
+
+    set(${out_var} "${computed_min_version}" PARENT_SCOPE)
+endfunction()
+
+function(__qt_internal_warn_if_min_cmake_version_not_met)
+    __qt_internal_get_supported_min_cmake_version_for_using_qt(min_supported_version)
+    __qt_internal_get_computed_min_cmake_version_for_using_qt(computed_min_version)
+
+    if(NOT min_supported_version STREQUAL computed_min_version
+            AND computed_min_version VERSION_LESS min_supported_version)
+        message(WARNING
+               "The minimum required CMake version to use Qt is: '${min_supported_version}'. "
+               "You have explicitly chosen to require a lower minimum CMake version: '${computed_min_version}'. "
+               "Using Qt with this CMake version is not officially supported. Use at your own risk."
+               )
+    endif()
+endfunction()
+
+function(__qt_internal_require_suitable_cmake_version_for_using_qt)
+    # Skip the public project check if we're building a Qt repo because it's too early to do
+    # it at find_package(Qt6) time.
+    # Instead, a separate check is done in qt_build_repo_begin.
+    # We detect a Qt repo by the presence of the QT_REPO_MODULE_VERSION variable set in .cmake.conf
+    # of each repo.
+    if(QT_REPO_MODULE_VERSION)
+        return()
+    endif()
+
+    # Only do the setup once per directory scope, because Qt6 is a dependency for many packages,
+    # and a recursive call will show the warning multiple times.
+    if(__qt_internal_set_up_cmake_minimum_required_version_already_done)
+        return()
+    endif()
+    set(__qt_internal_set_up_cmake_minimum_required_version_already_done TRUE PARENT_SCOPE)
+
+    # Check the overall minimum required CMake version when consuming any Qt CMake package.
+    __qt_internal_warn_if_min_cmake_version_not_met()
+    __qt_internal_get_computed_min_cmake_version_for_using_qt(computed_min_version)
+
+    if(CMAKE_VERSION VERSION_LESS computed_min_version)
+        set(major_minor "${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION}")
+        message(FATAL_ERROR
+            "CMake ${computed_min_version} or higher is required to use Qt. "
+            "You are running version ${CMAKE_VERSION} "
+            "Qt requires newer CMake features to work correctly. You can lower the minimum "
+            "required version by passing "
+            "-DQT_FORCE_MIN_CMAKE_VERSION_FOR_USING_QT=${major_minor} when configuring the "
+            "project. Using Qt with this CMake version is not officially supported. "
+            "Use at your own risk.")
+    endif()
+endfunction()