In reply to @bryan.bennett:matrix.org
If you use nix-direnv (or flakeenv) and the flake itself hasn't changed, the environment should be cached and a gcroot added for it so that gc doesn't clean it up :)

[mfed3@fed-gc:~/git/nixos-config]$ sudo nixos-rebuild switch --flake .
[sudo] password for mfed3: 
error:
       … while calling the 'seq' builtin

         at /nix/store/3pif36ks3f56py4wb1dkq6sh0nkf3ygj-source/lib/modules.nix:322:18:

          321|         options = checked options;
          322|         config = checked (removeAttrs config [ "_module" ]);
             |                  ^
          323|         _module = checked (config._module);

       … while evaluating a branch condition

         at /nix/store/3pif36ks3f56py4wb1dkq6sh0nkf3ygj-source/lib/modules.nix:261:9:

          260|       checkUnmatched =
          261|         if config._module.check && config._module.freeformType == null && merged.unmatchedDefns != [] then
             |         ^
          262|           let

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: getting status of '/nix/store/b0x9sbi7iqgkw5m01ccak1w7vl69fn8c-source/hosts/modules': No such file or directory

[mfed3@fed-gc:~/git/nixos-config]$ 

In reply to @charles:computer.surgery
Make sure you didn't typo your paths in your nix code