CMake: Require CMake 3.21 when building/using Qt on Apple platforms

Explicitly check that at least CMake 3.21 is used when building Qt or
when using Qt in a project.
This only affects macOS and iOS builds.

We check for 3.21 instead of 3.21.1 as described in the documentation
to avoid an error like:

 Policy VERSION range "3.21.1...3.21" specifies a larger minimum than
  maximum.

Until the technical limitation is addressed, if someone does end up
using 3.21.1, another existing check for "unsuitable" cmake versions
(as opposed to minimum required) will let them know they should use
something newer.

Amends 1cf3295cef321c9a587af2f2de7740c0cd3ca743.

Pick-to: 6.6
Fixes: QTBUG-114869
Change-Id: I2a479baaa63cfbe23af187cf0796e1c00042692b
Reviewed-by: Qt CI Bot <[email protected]>
Reviewed-by: Tor Arne Vestbø <[email protected]>
Reviewed-by: Alexey Edelev <[email protected]>

.cmake.conf

@@ -16,12 +16,14 @@ set(QT_COPYRIGHT "Copyright (C) ${QT_COPYRIGHT_YEAR} The Qt Company Ltd and othe
 # 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")
+set(QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_BUILDING_QT_APPLE "3.21")
 
 # 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")
+set(QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_APPLE "3.21")
 
 # 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

cmake/QtCMakeVersionHelpers.cmake

@@ -14,6 +14,8 @@ function(qt_internal_get_supported_min_cmake_version_for_building_qt out_var)
         set(supported_version "${QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_BUILDING_QT}")
 
     # We're building qtbase so the values come from .cmake.conf.
+    elseif(APPLE)
+        set(supported_version "${QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_BUILDING_QT_APPLE}")
     elseif(BUILD_SHARED_LIBS)
         set(supported_version "${QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_BUILDING_QT_SHARED}")
     else()
@@ -30,7 +32,9 @@ function(qt_internal_get_supported_min_cmake_version_for_using_qt out_var)
             "It should have been set by this point.")
     endif()
 
-    if(BUILD_SHARED_LIBS)
+    if(APPLE)
+        set(supported_version "${QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_APPLE}")
+    elseif(BUILD_SHARED_LIBS)
         set(supported_version "${QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_SHARED}")
     else()
         set(supported_version "${QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_STATIC}")