I'm a mere user of Arch so I don't know what the official policy is, but from where I'm standing, it looks like---at least for the community repo---the policy i

I'm a mere user of Arch so I don't know what the official policy is, but from where I'm standing, it looks like---at least for the community repo---the policy is "do what works." You are indeed right that Go and Rust applications are packaged as-is without having all of their corresponding library dependencies packaged as well. But, for example, Haskell applications like pandoc do have all their libraries packaged. Compare the output of, say, `pacman -Si docker` and `pacman -Si pandoc`.