Revert "CMake: Warn if cmake_minimum_required has an unsupported low version"

This reverts commit 657525965b.

The change relied on reading the last value of the
CMAKE_MINIMUM_REQUIRED_VERSION variable before one of the Qt packages
is found to use it for the version check.

Even if a user project has a cmake_minimum_required() right at
the beginning of the project with a supported version specified,
the first project() call which loads a CMake toolchain file could
contain another cmake_minimum_required() call with a lower
(unsupported) version and that version would be used for the check,
failing the project configuration.

The Android NDK ships such a toolchain file, which requires version
'3.6'.

Thus, relying on the last value of CMAKE_MINIMUM_REQUIRED_VERSION is
not robust enough.

Pick-to: 6.2
Task-number: QTBUG-95018
Task-number: QTBUG-95832
Change-Id: Iff3cb0a46e6e878569dce9c5fe915a714a034904
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

.cmake.conf

@@ -1,24 +1,16 @@
 set(QT_REPO_MODULE_VERSION "6.3.0")
 set(QT_REPO_MODULE_PRERELEASE_VERSION_SEGMENT "alpha1")
 
-# Minimum required CMake version for building Qt.
+# Minimum requirement for building Qt
 set(QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_BUILDING_QT_SHARED "3.16")
 set(QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_BUILDING_QT_STATIC "3.21")
 
-# Minimum required CMake version for using Qt in a user project.
+# Minimum requirement for consuming Qt in a user project.
 # This might be different in the future, e.g. be lower than the requirement for
 # building Qt.
 set(QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_SHARED "3.16")
 set(QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_STATIC "3.21")
 
-# Minimum CMake version that needs to appear in the cmake_minimum_required() call of a Qt user
-# project, so that all policies defined up to the specified CMake version are using NEW behavior.
-# With a value of 3.16, all policies CMP0000-CMP0097 will use NEW behavior.
-#
-# For now, both shared and static Qt builds share the same minimum.
-set(QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_SHARED_IN_CMAKE_MIN_REQUIRED "3.16")
-set(QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_STATIC_IN_CMAKE_MIN_REQUIRED "3.16")
-
 # Policy settings for commands defined by qtbase. These will also be injected
 # into the top level policy scope of each Qt module when building Qt so that
 # modules have the same policy settings as qtbase by default. They can be

cmake/QtBaseGlobalTargets.cmake

@@ -153,13 +153,6 @@ qt_internal_export_modern_cmake_config_targets_file(TARGETS ${__export_targets}
 qt_internal_get_supported_min_cmake_version_for_using_qt(supported_min_version_for_using_qt)
 qt_internal_get_computed_min_cmake_version_for_using_qt(computed_min_version_for_using_qt)
 
-# Save the minimum required CMake version to use Qt that should appear in a project's
-# cmake_minimum_required() call.
-qt_internal_get_supported_min_cmake_version_for_using_qt_in_cmake_min_required(
-    supported_min_version_for_using_qt_in_cmake_min_required)
-qt_internal_get_computed_min_cmake_version_for_using_qt_in_cmake_min_required(
-    computed_min_version_for_using_qt_in_cmake_min_required)
-
 # Get the lower and upper policy range to embed into the Qt6 config file.
 qt_internal_get_min_new_policy_cmake_version(min_new_policy_version)
 qt_internal_get_max_new_policy_cmake_version(max_new_policy_version)

cmake/QtCMakeVersionHelpers.cmake

@@ -36,25 +36,6 @@ function(qt_internal_get_supported_min_cmake_version_for_using_qt out_var)
     set(${out_var} "${supported_version}" PARENT_SCOPE)
 endfunction()
 
-# Returns the minimum CMake version that needs to be specified in the cmake_minimum_required() call
-# of a Qt user project as originally advertised by Qt.
-function(qt_internal_get_supported_min_cmake_version_for_using_qt_in_cmake_min_required out_var)
-    if(NOT DEFINED BUILD_SHARED_LIBS)
-        message(FATAL_ERROR "BUILD_SHARED_LIBS is needed to decide the minimum CMake version. "
-            "It should have been set by this point.")
-    endif()
-
-    if(BUILD_SHARED_LIBS)
-        set(supported_version
-            "${QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_SHARED_IN_CMAKE_MIN_REQUIRED}")
-    else()
-        set(supported_version
-            "${QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_STATIC_IN_CMAKE_MIN_REQUIRED}")
-    endif()
-
-    set(${out_var} "${supported_version}" PARENT_SCOPE)
-endfunction()
-
 # Returns the computed minimum supported CMake version required to /build/ Qt.
 function(qt_internal_get_computed_min_cmake_version_for_building_qt out_var)
     # An explicit override for those that take it upon themselves to fix the build system
@@ -93,23 +74,6 @@ function(qt_internal_get_computed_min_cmake_version_for_using_qt out_var)
     set(${out_var} "${computed_min_version}" PARENT_SCOPE)
 endfunction()
 
-# Returns the computed minimum CMake version that needs to be specified in the
-# cmake_minimum_required() call of a Qt user project.
-function(qt_internal_get_computed_min_cmake_version_for_using_qt_in_cmake_min_required out_var)
-    # Allow overriding the version for user projects, without forcing
-    # each project developer to have to override it manually.
-    if(QT_FORCE_MIN_CMAKE_VERSION_FOR_USING_QT_IN_CMAKE_MIN_REQUIRED)
-        set(computed_min_version "${QT_FORCE_MIN_CMAKE_VERSION_FOR_USING_QT_IN_CMAKE_MIN_REQUIRED}")
-
-    # No override was given, thus initialize with the default minimum.
-    else()
-        qt_internal_get_supported_min_cmake_version_for_using_qt_in_cmake_min_required(
-            min_supported_version)
-        set(computed_min_version "${min_supported_version}")
-    endif()
-    set(${out_var} "${computed_min_version}" PARENT_SCOPE)
-endfunction()
-
 # Returns the oldest CMake version for which NEW policies should be enabled.
 # It can be older than the minimum supported or computed CMake version, as it
 # is only used for policy settings. The currently running CMake must not be

cmake/QtConfig.cmake.in

@@ -1,9 +1,5 @@
 @PACKAGE_INIT@
 
-# Used by __qt_internal_warn_if_project_min_cmake_version_is_not_met
-if(NOT _qt_project_last_cmake_minimum_required_version)
-    set(_qt_project_last_cmake_minimum_required_version "${CMAKE_MINIMUM_REQUIRED_VERSION}")
-endif()
 cmake_minimum_required(VERSION @min_new_policy_version@...@max_new_policy_version@)
 
 include("${CMAKE_CURRENT_LIST_DIR}/@INSTALL_CMAKE_NAMESPACE@ConfigExtras.cmake")

cmake/QtConfigExtras.cmake.in

@@ -1,7 +1,2 @@
 set(QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT "@supported_min_version_for_using_qt@")
 set(QT_COMPUTED_MIN_CMAKE_VERSION_FOR_USING_QT "@computed_min_version_for_using_qt@")
-
-set(QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_IN_CMAKE_MIN_REQUIRED
-    "@supported_min_version_for_using_qt_in_cmake_min_required@")
-set(QT_COMPUTED_MIN_CMAKE_VERSION_FOR_USING_QT_IN_CMAKE_MIN_REQUIRED
-    "@computed_min_version_for_using_qt_in_cmake_min_required@")

cmake/QtModuleConfig.cmake.in

@@ -1,9 +1,5 @@
 @PACKAGE_INIT@
 
-# Used by __qt_internal_warn_if_project_min_cmake_version_is_not_met
-if(NOT _qt_project_last_cmake_minimum_required_version)
-    set(_qt_project_last_cmake_minimum_required_version "${CMAKE_MINIMUM_REQUIRED_VERSION}")
-endif()
 cmake_minimum_required(VERSION @min_new_policy_version@...@max_new_policy_version@)
 
 include(CMakeFindDependencyMacro)

cmake/QtPublicCMakeVersionHelpers.cmake

@@ -4,12 +4,6 @@ function(__qt_internal_get_supported_min_cmake_version_for_using_qt out_var)
     set(${out_var} "${supported_version}" PARENT_SCOPE)
 endfunction()
 
-function(__qt_internal_get_supported_min_cmake_version_for_using_qt_in_cmake_min_required out_var)
-    # This is recorded in Qt6ConfigExtras.cmake
-    set(supported_version "${QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_IN_CMAKE_MIN_REQUIRED}")
-    set(${out_var} "${supported_version}" PARENT_SCOPE)
-endfunction()
-
 function(__qt_internal_get_computed_min_cmake_version_for_using_qt out_var)
     # Allow override when configuring user project.
     if(QT_FORCE_MIN_CMAKE_VERSION_FOR_USING_QT)
@@ -26,23 +20,6 @@ function(__qt_internal_get_computed_min_cmake_version_for_using_qt out_var)
     set(${out_var} "${computed_min_version}" PARENT_SCOPE)
 endfunction()
 
-function(__qt_internal_get_computed_min_cmake_version_for_using_qt_in_cmake_min_required out_var)
-    # Allow override when configuring user project.
-    if(QT_FORCE_MIN_CMAKE_VERSION_FOR_USING_QT_IN_CMAKE_MIN_REQUIRED)
-        set(computed_min_version "${QT_FORCE_MIN_CMAKE_VERSION_FOR_USING_QT_IN_CMAKE_MIN_REQUIRED}")
-
-    # Set in QtConfigExtras.cmake.
-    elseif(QT_COMPUTED_MIN_CMAKE_VERSION_FOR_USING_QT_IN_CMAKE_MIN_REQUIRED)
-        set(computed_min_version
-            "${QT_COMPUTED_MIN_CMAKE_VERSION_FOR_USING_QT_IN_CMAKE_MIN_REQUIRED}")
-    else()
-        message(FATAL_ERROR
-            "Qt Developer error: Can't compute the version that should appear in cmake_minimum_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)
@@ -57,22 +34,6 @@ function(__qt_internal_warn_if_min_cmake_version_not_met)
     endif()
 endfunction()
 
-function(__qt_internal_warn_if_project_min_cmake_version_is_not_met)
-    __qt_internal_get_supported_min_cmake_version_for_using_qt_in_cmake_min_required(
-        min_supported_version)
-    __qt_internal_get_computed_min_cmake_version_for_using_qt_in_cmake_min_required(
-        computed_min_version)
-
-    if(computed_min_version VERSION_LESS min_supported_version)
-        message(WARNING
-           "To use this Qt, the minimum CMake version that should appear in the project's "
-           "cmake_minimum_required() call should be: '${min_supported_version}'. "
-           "You have explicitly chosen to require a lower version: '${computed_min_version}'. "
-           "Using Qt with this 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.
@@ -105,23 +66,4 @@ function(__qt_internal_require_suitable_cmake_version_for_using_qt)
             "project. Using Qt with this CMake version is not officially supported. "
             "Use at your own risk.")
     endif()
-
-
-    # Check that the project has a supported version specified in the last cmake_minimum_required
-    # call before the Qt6 package was found.
-    __qt_internal_warn_if_project_min_cmake_version_is_not_met()
-    __qt_internal_get_computed_min_cmake_version_for_using_qt_in_cmake_min_required(
-        computed_min_version)
-
-    if(_qt_project_last_cmake_minimum_required_version VERSION_LESS computed_min_version)
-        message(FATAL_ERROR
-            "The last cmake_minimum_required() call before the Qt package was found had the "
-            "following version specified: '${_qt_project_last_cmake_minimum_required_version}' but "
-            "it needs to be ${computed_min_version} or higher to use Qt. "
-            "You can reduce the error into a warning by passing "
-            "-DQT_FORCE_MIN_CMAKE_VERSION_FOR_USING_QT_IN_CMAKE_MIN_REQUIRED=${_qt_project_last_cmake_minimum_required_version} "
-            "when configuring the project, but you do so at your own risk (it is not an officially "
-            "supported way of building Qt projects)."
-        )
-    endif()
 endfunction()