flake: don't refetch unmodified inputs by recursive follows

Closes #460

I managed to trigger the issue by having the following inputs (shortened):

    authentik-nix.url = "github:nix-community/authentik-nix";
    authentik-nix.inputs.poetry2nix.inputs.nixpkgs.follows = "nixpkgs";

When evaluating this using

    nix-eval-jobs --flake .#hydraJobs

I got the following error:

    error: cannot update unlocked flake input 'authentik-nix/poetry2nix' in pure mode

The issue we have here is that `authentik-nix/poetry2nix` was written
into the `overrideMap` which caused Nix to assume it's a new input and
tried to refetch it (#460) or errored out in pure mode
(nix-eval-jobs / Hydra).

The testcase unfortunately only involves checking for the output log
and makes sure that something *is* logged on the first fetch so that
the test doesn't rot when the logging changes since I didn't
manage to trigger the error above with the reproducer from #460. In
fact, I only managed to trigger the `cannot update unlocked flake input`
error in this context with `nix-eval-jobs`.

Change-Id: Ifd00091eec9a0067ed4bb3e5765a15d027328807

0 files changed, 0 insertions, 0 deletions