visit incompatible with cmake 4.0

[Febbe]

Describe the bug

Since the cmake configuration uses a lot of deprecated cmake_policies which are removed in cmake 4.0.0, the visit library does not compile anymore.

To Reproduce

Steps to reproduce the behavior. For example:

1. install cmake 4.0
2. run cmake configure

Expected behavior

Visit should configure.

Attachments

Caused by

if(COMMAND cmake_policy)
    cmake_policy(SET CMP0033 OLD)
    if(WIN32)
        # don't automatically link with qtmain
        cmake_policy(SET CMP0020 OLD)
        if(POLICY CMP0091) # introduced in cmake 3.15
            # Tell CMake to always use /MD, even for debug builds.
            # Done because prebuilt TP libraries are built with /MD and
            # if debug build of VisIt uses /MDd there are runtime issues.
            cmake_policy(SET CMP0091 NEW) # MSVC_RUNTIME_LIBRARY
            set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreadedDLL")
        endif()
    endif()
endif()

Desktop

• Windows 11
• compiler: clang version 18.1.4 Target: x86_64-pc-windows-msvc
• VisIt Version: main

[biagas]

Can you provide the exact errors you are seeing?
We won't necessarily be able to move to cmake 4.0 for the next release.
You can use version 3.24 instead, as that is the version I currently use for VisIt development on windows.

[Febbe]

The error message is:

[cmake] CMake Error at CMakeLists.txt:161 (cmake_policy):
[cmake]   Policy CMP0033 may not be set to OLD behavior because this version of CMake
[cmake]   no longer supports it.  The policy was introduced in CMake version 3.0.0,
[cmake]   and use of NEW behavior is now required.
[cmake] 
[cmake]   Please either update your CMakeLists.txt files to conform to the new
[cmake]   behavior or use an older version of CMake that still supports the old
[cmake]   behavior.  Run cmake --help-policy CMP0033 for more information.
[cmake] 
[cmake] 
[cmake] CMake Error at CMakeLists.txt:164 (cmake_policy):
[cmake]   Policy CMP0020 may not be set to OLD behavior because this version of CMake
[cmake]   no longer supports it.  The policy was introduced in CMake version 2.8.11,
[cmake]   and use of NEW behavior is now required.
[cmake] 
[cmake]   Please either update your CMakeLists.txt files to conform to the new
[cmake]   behavior or use an older version of CMake that still supports the old
[cmake]   behavior.  Run cmake --help-policy CMP0020 for more information.

We won't necessarily be able to move to CMake 4.0 for the next release.

That's not required at all. CMake 4.x will remove deprecated features, but it is partially backward compatible until CMake 3.5, with a warning that it will soon remove compatibility up to 3.10.
Fixing this is to modernize everything, which is deprecated and removed.
It's already yet deprecated with CMake 3.24

The following error is independent of this issue and happens in CMake 3.30:

[cmake] CMake Error at config-site/windows.cmake:14 (message):
[cmake]   Please set VISIT_WINDOWS_DIR to location of 'windowsbuild' files
[cmake] Call Stack (most recent call first):
[cmake]   CMakeLists.txt:269 (include)
[cmake]   CMakeLists.txt:308 (include_visit_config_site)

FYI, I use clang-cl with the MSVC-STL

[biagas]

CMP0033 will no longer be necessary when the CMake modernization effort withing VisIt is complete.
Looks like CMP0020 isn't needed anymore as well, since we use Qt 6.\

Regarding this error message: Please set VISIT_WINDOWS_DIR to location of 'windowsbuild' files, are you building from a clone of the repository or from a download of a Release source tarball?

[Febbe]

CMP0033 will no longer be necessary when the CMake modernization effort withing VisIt is complete. Looks like CMP0020 isn't needed anymore as well, since we use Qt 6.\

Nice to hear that. You might also want to reduce code bloat while doing that. It's very cumbersome, to include visit as subproject.
(add_subdirectory(<path_to_visit_src>))

Regarding this error message: Please set VISIT_WINDOWS_DIR to location of 'windowsbuild' files, are you building from a clone of the repository or from a download of a Release source tarball?

I cloned it for the error message, this problem is fixed in the fork I use in the other project. But that shouldn't happen either (a use of FetchContent might be the culprit here).

[cyrush]

Our build system will need to be cleaned up to remove deprecated logic. We are working on a large CMake modernization update, moving to CMake 4.0 will come after that update is done, post VisIt 3.5.0.