How to get "set_languages" value within a package?

[poirierlouis]

Is it possible, inside xmake.lua of a package to get the languages value set by the user using set_languages? How?

My goal is to assert C++ version before installing a package. Or ideally, during on_check callback.

I'd appreciate your feedback :)
PS: didn't find happiness in documentation nor using AI prompt.

[krotname]

I don't think a package can reliably read the consuming target's set_languages() value directly.

set_languages() is target/option-level project configuration, while the package recipe is resolved in package context and may be reused by multiple targets with different language standards. In package scripts the documented interface is the package config API (package:config(...), package:configs()) plus explicit detection configs. The package detection helpers also take the standard explicitly, for example:

package:has_cxxfuncs("foo", {configs = {languages = "cxx17"}})
package:has_cxxsnippets("...", {configs = {languages = "c++20"}})

So for a package requirement I would make the C++ standard an explicit package config, then validate/use that config in on_check / on_install:

package("mypkg")
    add_configs("cxxstd", {
        description = "C++ standard used to build/check this package",
        default = "c++17",
        values = {"c++17", "c++20", "c++23"}
    })

    on_check(function (package)
        local cxxstd = package:config("cxxstd")
        assert(cxxstd == "c++20" or cxxstd == "c++23", "mypkg requires at least C++20")
        assert(package:has_cxxsnippets([[#include <version>
int main() { return 0; }]], {configs = {languages = cxxstd}}))
    end)

Then the consumer chooses it explicitly:

add_requires("mypkg", {configs = {cxxstd = "c++20"}})

If the check is really about a target rather than the package build, do it in target/project script context and inspect the target there; for a package recipe, pass the requirement as package config.

[poirierlouis]

Thanks, I can use add_configs without a default I guess.

It's actually to update a xrepo's package, where new version requires c++17 at least, while previous versions are c++11 and c++14 compatible only.
My goal was to assert, and therefore warn the end-user about the new requirement. Though in such case, and given your answer, it seems I shall not even add this check/assert at all.