Transitive inputs "not in registry"

[NobbZ]

Describe the bug

I want to use follows on the input of an input.

Though I get an error, that this is not in the registry.

Steps To Reproduce

1. Add an arbitrary nixpkgs input to a flake.nix.
2. Add the following to your flake.nix at appropriate location:

   inputs.rnix-lsp.url = "github:nix-community/rnix-lsp/master";
   inputs.rnix-lsp.inputs.nixpkgs.follows = "nixpkgs";
   inputs.rnix-lsp.inputs.naersk.inputs.nixpkgs.follows = "nixpkgs";

3. Update the flake.lock and observe error:

   error: cannot find flake 'flake:naersk' in the flake registries
   (use '--show-trace' to show detailed location information)
   

Expected behavior

The nixpkgs input of the naersk input of rnix-lsp is properly overwritten and follows "my" nixpkgs.

nix-env --version output

$ nix-env --version
nix-env (Nix) 2.6.0pre20211214_18e4851

Additional context

I tried this as a way to workaround #5609.

The same problem happens on 2.4 and 2.5:

$ nix shell github:nixos/nix/2.4 -c nix flake metadata
warning: Git tree '/home/…/Projects/system-config' is dirty
error: cannot find flake 'flake:naersk' in the flake registries
(use '--show-trace' to show detailed location information)
$ nix shell github:nixos/nix/2.5.0 -c nix flake metadata
warning: Git tree '/home/…/Projects/system-config' is dirty
error: cannot find flake 'flake:naersk' in the flake registries
(use '--show-trace' to show detailed location information)

[thufschmitt]

I can indeed reproduce this. More self-contained repro:

#!/usr/bin/env bash

set -euo pipefail
set -x

rm -rf A B C D
mkdir -p A B C D

cat <<EOF > A/flake.nix
{ outputs = _: {}; }
EOF
cat <<EOF > B/flake.nix
{
  inputs.A.url = "path:$PWD/A";
  outputs = _: {};
}
EOF
cat <<EOF > C/flake.nix
{
  inputs.B.url = "path:$PWD/B";
  outputs = _: {};
}
EOF
cat <<EOF > D/flake.nix
{
  inputs.C.url = "path:$PWD/C";
  inputs.A.url = "path:$PWD/A";
  inputs.C.inputs.B.inputs.A.follows = "A";
  outputs = _: {};
}
EOF

nix flake update ./D

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/how-should-i-setup-nested-flake-follows-to-use-top-level-nixpkgs/12670/4

[jali-clarke]

may have been fixed in #6036

[tejing1]

Nope. Running thuf's script still fails:

$ nix shell github:NixOS/nix\#nix
$ ./tempscript
+ rm -rf A B C D
+ mkdir -p A B C D
+ cat
+ cat
+ cat
+ cat
+ nix flake update ./D
error: cannot find flake 'flake:B' in the flake registries
(use '--show-trace' to show detailed location information)
$ nix --version
nix (Nix) 2.7.0pre20220211_4d67ecb

[tomberek]

The desired change to the resulting lockfile for the relevant "follows" line,

inputs.C.inputs.B.inputs.A.follows = "A";

should cause this:

diff --git a/flake.lock b/flake.lock.post
index 7d50628..c51a7d1 100644
--- a/flake.lock
+++ b/flake.lock.post
@@ -26,7 +26,7 @@
     },
     "B": {
       "inputs": {
-        "A": "A_2"
+        "A": ["A"]
       },
       "locked": {
         "lastModified": 1654174365,

I've tried a few combination such as bringing B to the top and they trying to override it:

{
  inputs.B.follows = "C/B";
  inputs.B.inputs.A.follows = "A";
  outputs = _: {};
}

but then the relevant line to follow A has no effect.

What does work is to bring everything to the top level:

{
  inputs.A.follows = "C/B/A";
  inputs.B.follows = "C/B";
  outputs = _: {};
}

This can work in some cases if all you need is top level access to those inputs, but it does not allow you to change them, which is where people run into this problem.