Remove the description for versions before cmake 3.5

[halajohn]

Because cmake 4.0.0 has removed compatibility with versions of cmake before 3.5, using logic like the following will result in a cmake error:

cmake_minimum_required(VERSION 3.1)

  CMake Error at CMakeLists.txt:1 (cmake_minimum_required):
    Compatibility with CMake < 3.5 has been removed from CMake.

    Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
    to tell CMake that the project requires at least <min> but has been updated
    to work with policies introduced by <max> or earlier.

    Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway.


     Called from: [1]	/home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/clingo-sys-0.7.2/clingo/CMakeLists.txt

  thread 'main' panicked at /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/cmake-0.1.54/src/lib.rs:1119:5:

  command did not execute successfully, got: exit status: 1

Currently, for example, the GitHub workflow environments have gradually introduced cmake 4.0.0. This causes compilation errors for clingo and a series of wrappers built on it (such as clingo-sys, clingo-rs, etc.). For instance, in clingo-sys, clingo is compiled using the following method:

let dst = Config::new("clingo")
    .very_verbose(true)
    .define("CLINGO_BUILD_SHARED", "OFF")
    .define("CLINGO_BUILD_STATIC", "ON")
    .define("CLINGO_MANAGE_RPATH", "OFF")
    .define("CLINGO_BUILD_WITH_PYTHON", "OFF")
    .define("CLINGO_BUILD_WITH_LUA", "OFF")
    .define("CLINGO_INSTALL_LIB", "ON")
    .define("CLINGO_BUILD_APPS", "OFF")
    .define("CLASP_BUILD_APP", "OFF")
    .build();

Even setting environment variables (for example, using export CMAKE_ARGS="-DCMAKE_POLICY_VERSION_MINIMUM=3.5") does not affect this behavior.

Could you modify all instances of cmake_minimum_required(VERSION x.x) in clingo so that x.x is at least greater than 3.5? Thanks.

[alalazo]

As a workaround you can set https://cmake.org/cmake/help/latest/variable/CMAKE_POLICY_VERSION_MINIMUM.html:

CMAKE_POLICY_VERSION_MINIMUM=3.5

[halajohn]

Yes, I’ve tried this method—you can see it at the end of my post. The reason is that the way wrappers like clingo-sys/clingo-rs (which are built on top of clingo) internally construct clingo scripts doesn’t take this environment variable or command-line argument into account.

Of course, one option is for me to fork and modify every repo along the entire chain myself, but that’s a last resort. Unless there’s really no other way, I’d prefer not to go down that route.

[alalazo]

Yes, I’ve tried this method—you can see it at the end of my post.

I didn't try using CMAKE_ARGS, but from the docs I see:

Alternatively, users may set the CMAKE_POLICY_VERSION_MINIMUM environment variable to initialize the cache entry in new build trees automatically.

Did you try:

export CMAKE_POLICY_VERSION_MINIMUM=3.5

? With that I was able to build at least clingo in CI without modifying sources, and if I understand correctly it's the way to get this policy applied everywhere - even in subprojects etc. That said, I'm blank on Rust, so may be missing some obvious behavior.

[halajohn]

Yes, I also tried setting the environment variables directly, but it didn’t work. The difference between us is that you compiled Clingo directly, whereas I installed clingo-sys, which internally compiles Clingo by itself. This internal compilation process doesn’t consider environment variables—for example, as shown in the log below.

let dst = Config::new("clingo")
    .very_verbose(true)
    .define("CLINGO_BUILD_SHARED", "OFF")
    .define("CLINGO_BUILD_STATIC", "ON")
    .define("CLINGO_MANAGE_RPATH", "OFF")
    .define("CLINGO_BUILD_WITH_PYTHON", "OFF")
    .define("CLINGO_BUILD_WITH_LUA", "OFF")
    .define("CLINGO_INSTALL_LIB", "ON")
    .define("CLINGO_BUILD_APPS", "OFF")
    .define("CLASP_BUILD_APP", "OFF")
    .build();

If I want to influence the way clingo-sys internally compiles Clingo (i.e., the code segment below), I would need to modify the code of clingo-sys to make it accept environment variables that affect Clingo’s compilation. That way, the method you mentioned could actually be picked up during Clingo’s build process.

[BenKaufmann]

In my opinion, we have two separate issues:

• The compatibility issue with CMake < 3.5 in clingo (and clasp)
• The problem that clingo-sys and clingo-rs hard code the cmake options and/or don't provide a mechanism for passing extra args (e.g. something like yocto's EXTRA_OECMAKE).

[halajohn]

Exactly.

[rkaminsk]

@BenKaufmann, what do you think about dropping cmake < 3.5 compatibility and update our cmake config? I don't think this will be involved and I don't think it will be problematic for users.

[rkaminsk]

We are planning to require cmake 3.10 for the next release. Currently, we are still building clingo for Ubuntu 18.04, which ships this version. Hopefully, there are not many people who use more ancient systems (or at least can update their build tools).

[rkaminsk]

This should be addressed in the wip branch. The plan is to push a release some time next week.