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>
Qt6Config.cmake calls cmake_minimum_required to ensure a recent enough
CMake version is used in projects.
That call does not set policies in the calling subdirectory scope,
because find_package introduces a new policy scope.
If a project using Qt has a 'cmake_minimum_required(VERSION 3.1)'
call and is configured with a recent CMake, many policies will
still be set to OLD.
One such policy is CMP0071 (Run AUTOMOC on GENERATED files). The
policy value is queried at generation time rather than at target
definition time, which means we can't influence the policy value
(e.g. inside the implementation of qt_add_executable for example)
The inability to influence the policy value for targets created by our
own CMake functions is unfortunate and can lead to issues (in the case
of the above policy to compilation / linker issues).
Record the version of the last cmake_minimum_required call before
the Qt packages are found and error out if the version is lower than
the minimum supported one.
A project can reduce the error into a warning by specifying a
-DQT_FORCE_MIN_CMAKE_VERSION_FOR_USING_QT_IN_CMAKE_MIN_REQUIRED=3.xyz
option when configuring the project.
If the option is used and build issues arise, no official support is
given.
All the CMake example projects shipped with Qt specify a minimum
version of 3.16 already (which is the minimum for shared Qt builds),
so it shouldn't be an issue to require that in other user projects as
well.
Implementation wise, we follow the existing pattern to record
what the minimum and computed versions for static and shared Qt
builds are at qtbase configure time.
These are then checked before the Qt6 or QtFoo packages are
find_package'd.
Amends 6518bcc167
Pick-to: 6.2
Task-number: QTBUG-95018
Task-number: QTBUG-95832
Change-Id: I1a1d06d82f566c92192a699045127943604c8353
Reviewed-by: Craig Scott <craig.scott@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
This change introduces new behavior to error out when configuring user
projects if the CMake version used is too old for Qt to work with.
The main motivator is the requirement of new CMake features to ensure
object libraries are placed in the proper place on the link line in
static builds.
The minimum CMake version is computed based on whether Qt was
configured as shared or static libraries.
At the moment the required versions for building and using Qt are the
same.
The minimum versions are defined in qtbase/.cmake.conf in the
following variables
QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_BUILDING_QT_SHARED
QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_BUILDING_QT_STATIC
QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_SHARED
QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_STATIC
Qt Packagers can disable the version check when configuring Qt
by setting
QT_FORCE_MIN_CMAKE_VERSION_FOR_BUILDING_QT and
QT_FORCE_MIN_CMAKE_VERSION_FOR_USING_QT.
In this case it is the packagers responsibility to ensure such a Qt
works correctly with the specified CMake version.
User projects can also set QT_FORCE_MIN_CMAKE_VERSION_FOR_USING_QT
to disable the version check. Then it's the project's developer
responsibility to ensure such a Qt works correctly.
No official support is provided for these cases.
Implementation notes.
The versions required to build Qt are stored in
QtBuildInternalsExtra.cmake
whereas the versions required to use Qt are stored in a new
QtConfigExtras.cmake.
Also the policy range variables stored in
QtBuildInternalsExtra.cmake are now regular variables instead of cache
variables, to properly allow overrides per-repository.
Some renaming of functions and variables was done for a bit more
clarity and easier grep-ability.
Pick-to: 6.2
Task-number: QTBUG-95018
Change-Id: I4279f2e10b6d3977319237ba21e2f4ed676aa48b
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
