Yocto: No package, trivial to add as a recipe to the meta-mender project.
In fact, I have already ported all the packages in vendor/ to buildroot found here
There are many pros and cons to removing the vendored directory, most of which boil down to the maintenance of keeping the packages up to date, the extra size of the vendor packages, and the complexity of compiling them instead of simply depending on them.
expected is in C++23. I don’t think it’s worth making this optional because support for it essentially ended in 2023, and C++23 “takes over” afterwards, which comes with recent g++ versions. We do need changes to actually use the C++23 version though, but this is mostly at the code level, and should be dependent on which C++ standard you use, not on system libraries. See optional also.
There actually is an liblmdb++-dev package in Ubuntu, but it doesn’t work. We already depend on the lmdb package in Yocto.
This is actually optional already, it just isn’t very obvious. If you compile with C++17 or later, then this dependency isn’t used. See this commit.
In general I agree that the dependencies should be optional, for exactly the reasons you mention. But all of them were added as vendored dependencies exactly because they are not easily available everywhere. So it’s not a priority for us to change it, since this approach is what we chose to be maximally compatible. That being said, I certainly don’t think we should stand in the way if others want to put in the work to make them optional.