nix registry pin cannot handle a flake type change #16221

Describe the bug

I update my profile at my own pace by running nix registry pin nixpkgs && nix profile upgrade --all. At some point flake-regsitry.json was changed so that nixpkgs is now of type tarball. From that moment nix silently stopped updating the flake on nix registry pin, without any kind of warning.

I had to nix registry remove nixpkgs to fix the issue.

Steps To Reproduce

1. Pin a registry entry
2. Change the entry type (reproduced with type github → tarball)
3. Try to re-pin it. It will stay on the previously pinned value.

Expected behavior

The locked url is updated to the new type and value, or at the very least a warning is issued.

Metadata

nix-env (Nix) 2.34.7

Additional context

Checklist

• checked latest Nix manual (source)
• checked open bug issues and pull requests for possible duplicates
• reviewed the contributing guide

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