value is a function while a set was expected while evaluating 'outputs'

Question

I'm getting the above error when attempting to check a flake; I'm trying to use flake-compat on a non-NixOS system for compatibility with home-manager.

This is the flake that's causing the trace below:

error: value is a function while a set was expected

       at /nix/store/l22dazwy8cgxdvndhq45br310nap92x3-source/etc/nixos/flake.nix:167:136:
    
          166|
          167|     outputs = inputs@{ self, nix, nixpkgs, flake-utils, flake-compat, ... }: with builtins; with nixpkgs.lib; with flake-utils.lib; let
             |
^
          168|

       … while evaluating 'outputs'

       at /nix/store/l22dazwy8cgxdvndhq45br310nap92x3-source/etc/nixos/flake.nix:167:15:

          166|
          167|     outputs = inputs@{ self, nix, nixpkgs, flake-utils, flake-compat, ... }: with builtins; with nixpkgs.lib; with flake-utils.lib; let
             |               ^
          168|

       … from call site

       at «string»:45:21:

           44|
           45|           outputs = flake.outputs (inputs // { self = result; });
             |                     ^
           46|

       … while evaluating anonymous lambda

       at «string»:10:13:

            9|     builtins.mapAttrs
           10|       (key: node:
             |             ^
           11|         let

       … from call site

       … while evaluating the attribute 'root'

       … while evaluating anonymous lambda

       at «string»:2:23:

            1|
            2| lockFileStr: rootSrc: rootSubdir:
             |                       ^
            3|

       … from call site

Unfortunately, I cannot provide a minimal reproducible example as I do not know from where in the flake this error is originating.

Answer 1

Turns out, my lib value was actually a function; unfortunately, since nix flakes is still unstable, it didn't quite show where this was happening.