Define RUBY_EXECUTABLE and Ruby_EXECUTABLE for packages which need it

[chhtz]

That line breaks cmake configuration for some packages on Ubuntu 22.04, since CMake changed that variable to Ruby_EXECUTABLE.

Related: rock-core/base-cmake#94

@doudou Do you know if there is a reason RUBY_EXECUTABLE was passed manually to some packages?

[pierrewillenbrockdfki]

The change in cmake is as follows:

old behavior:

find_package(THING) produces variables prefixed THING_, even if it is using FindThing scripts,
find_package(Thing) produces variables prefixed Thing_

new behavior:

find_package(THING) and find_package(Thing) produce variables prefixed Thing_, when the find script is called FindThing

and i think they discourage using find_package(THING) when the find scripts character casing differs.

I guess the fix is to look through everything and use find_package(Ruby), Ruby_ variables.

[pierrewillenbrockdfki]

As for this PR: i don't see the benefit in not defining RUBY_EXECUTABLE, though they might be unused.

I'll be on vacation for 2 weeks starting monday, 2025-09-08.

[chhtz]

According to this link, CMake's FindRuby actually will provide both Ruby_THING and RUBY_THING (the latter is discouraged to be used and deprecated since CMake 4.0)/ The problem is that some versions of FindRuby struggle if RUBY_EXECUTABLE is provided via -DRUBY_EXECUTABLE=ruby_path, giving a weird error like:

    -- Could NOT find Ruby (missing: Ruby_EXECUTABLE) (found suitable version "3.0.2", minimum required is "1.8.0")

(in Ubuntu 24.04, CMake 3.28.3, this seems not to be a problem anymore).

If there is a reason to pass Autoproj.config.ruby_executable, we need either check if cmake_version < 3.18 and provide RUBY_EXECUTABLE or Ruby_EXECUTABLE accordingly, or always pass both.
If there is no reason to manually pass Ruby_EXECUTABLE, I prefer to remove it.

[doudou]

According to this link, CMake's FindRuby actually will provide both Ruby_THING and RUBY_THING (the latter is discouraged to be used and deprecated since CMake 4.0)/ The problem is that some versions of FindRuby struggle if RUBY_EXECUTABLE is provided via -DRUBY_EXECUTABLE=ruby_path, giving a weird error like:

    -- Could NOT find Ruby (missing: Ruby_EXECUTABLE) (found suitable version "3.0.2", minimum required is "1.8.0")

(in Ubuntu 24.04, CMake 3.28.3, this seems not to be a problem anymore).

If there is a reason to pass Autoproj.config.ruby_executable, we need either check if cmake_version < 3.18 and provide RUBY_EXECUTABLE or Ruby_EXECUTABLE accordingly, or always pass both. If there is no reason to manually pass Ruby_EXECUTABLE, I prefer to remove it.

There is. We need to ensure everything ruby-related is using the same ruby implementation in the workspace.

[doudou]

These guarantee that all FindRuby find the same ruby executable. It is needed.

[chhtz]

These guarantee that all FindRuby find the same ruby executable. It is needed.

Ok, fair enough. (Even though, I guess always using the default should be the same everywhere as well, I guess you have use cases where you want to use the non-default ruby version).

I will work on another patch.

[chhtz]

This should work on Ubuntu 20.04, 22.04, and 24.04 now. The name (and location) of the helper method is open for discussion. Also, if there is an elegant way to determine the CMake version which is in use, one could define only the correct variable.

[chhtz]

I will update orocos-toolchain/autoproj#40 accordingly, once this gets merged

[doudou]

These guarantee that all FindRuby find the same ruby executable. It is needed.

Ok, fair enough. (Even though, I guess always using the default should be the same everywhere as well, I guess you have use cases where you want to use the non-default ruby version).

I will work on another patch.

On our side, we regularly end up not using the default...

[planthaber]

Wouldn't "set_cmake_ruby_executable" be a better name for the function. By just reading "use_ruby_executable pkg" in the package definition, i can't really figure out what it is supposed to do.

Also, if there is an elegant way to determine the CMake version which is in use, one could define only the correct variable.

https://stackoverflow.com/questions/43697154/detect-current-cmake-version-using-cmake:

if(CMAKE_VERSION VERSION_LESS "3.8.0") 
    message("Please consider to switch to CMake 3.8.0")
endif()

Other comparison operators are VERSION_EQUAL , VERSION_GREATER, VERSION_LESS_EQUAL and VERSION_GREATER_EQUAL

[chhtz]

Wouldn't "set_cmake_ruby_executable" be a better name for the function. By just reading "use_ruby_executable pkg" in the package definition, i can't really figure out what it is supposed to do.

I'm completely open regarding the name of the function ...

Also, if there is an elegant way to determine the CMake version which is in use, one could define only the correct variable.

https://stackoverflow.com/questions/43697154/detect-current-cmake-version-using-cmake:

if(CMAKE_VERSION VERSION_LESS "3.8.0") 
    message("Please consider to switch to CMake 3.8.0")
endif()

[...]

But this only works inside cmake, not from ruby, right? I could execute cmake --version or something and evaluate the result, but IMO that is over-complicating the issue (unless this is done by autoproj already and I can just take the result -- but a quick search did not give any results for me).

[planthaber]

True, it must be detected from ruby, not cmake.

It could be done using the OS version instead of the cmake version (when the default cmake is used).

[chhtz]

@planthaber I changed the macro name now. Do you want to merge?