Mostly a holdout until https://github.com/nix-community/rnix-lsp gets autocompletion support for attributes and nixos modules.
This is a simple wrapper around
NIX_GET_COMPLETIONS=3 nix eval --read-only self#foo.bar that currently makes some assumptions about how nix/nixos is configured, see the README and source code for more.
It’s split into two sources:
nixpkgs, for pkgs, lib, and config.
nixos, for nixos modules.
The sources have some support for nested attributes by leveraging tree-sitter to get the surrounding context for the node at cursor, however this can be somewhat fragile.