Fetch a flake from a flake reference, and return its output attributes and some metadata. For example:

(builtins.getFlake "nix/55bc52401966fbffa525c574c14f67b00bc4fb3a").packages.x86_64-linux.nix

Unless impure evaluation is allowed (--impure), the flake reference must be "locked", e.g. contain a Git revision or content hash. An example of an unlocked usage is:

(builtins.getFlake "github:edolstra/dwarffs").rev