[question] How to handle the Standard version requirement in recipes?

Recipes should handle problems of incompatible standard version flags gracefully and raise ConanInvalidConfiguration appropriately.

[lasote]

We could follow 2 approaches, not necessarily incompatible:

• We would need probably a tool that report the applied compiler.cppstd setting taking into account that the input could be None and the applied one is the default from the applied compiler. That way we could raise if the minimum is not satisfied and the conan-index CI service will automatically skip the profiles with the compiler without a compiler that supports the minimum cppstd. But if the library only supports >=17 we might have an issue if we don’t explicitly apply a profile with the cppstd.

• We could always add something to the config.yml file to indicate the cppstd value (vaues? which ones?) to apply for that version.

[Minimonium]

Okay, I think now I get it how we should do.

The thing with cppstd is that we really need to consider the case when it’s not specified to be the case of using the default standard version of the current compiler. The reason for that is because while standard libraries don’t usually break ABI, projects are free to do it between different versions. For example to conditionally use std::string_view is the standard version is allowed. On the other hand, projects that are compatible with older standard versions should probably delete the setting in the package_id.

All it means that indeed if a project requires a >=17 than we need to handle it in CCI builds. How can we achieve it?

About the algorithm to handle the package configuration:

• We check the minimal standard version required with the check_min_cppstd. We need to handle if the tool doesn’t know about the current compiler, it could be a customer provided one.
• We check the minimal compiler version supported. The standard version support is a very fluid thing, can’t rely just on that.
• We need to warn if we lack information about any of these.

We can nicely wrap it into an additional tool.