Establish a process for dealing with breaking changes

[fricklerhandwerk]

Problem

Currently there is no process for changing existing behavior (for whatever reason, but usually because it's undesired).

Checklist

• checked latest Nix manual (source)
• checked open documentation issues and pull requests for possible duplicates

Proposal

Write down a process that users can expect to be followed by maintainers.

Related:

• https://discourse.nixos.org/t/potential-rfc-idea-stability/27055
• [RFC 0137] Nix language versioning rfcs#137

[fricklerhandwerk]

@thufschmitt Why is this not documentation? Also I'd be really careful with creating new labels, as they tend to never go away. Deleting labels makes old issues much harder to discover. I think we already have too many.

[thufschmitt]

Why is this not documentation?

Dunno, why would it be? It's not a matter of documenting something, it's a matter of designing a process. Which would have to be documented of course, but that's just a part of it, same as a new feature in code.

[abathur]

Presumably starts as an RFC equivalent to https://github.com/NixOS/rfcs/blob/master/rfcs/0088-nixpkgs-breaking-change-policy.md (or perhaps updates that policy to clearly cover Nix as well?)

[thufschmitt]

Presumably starts as an RFC equivalent to https://github.com/NixOS/rfcs/blob/master/rfcs/0088-nixpkgs-breaking-change-policy.md (or perhaps updates that policy to clearly cover Nix as well?)

Indeed, that's certainly how things are likely to end-up. I'm not sure that we can add that to the nixpkgs policy (I'd have to re-read it, but Nix and Nixpkgs have some quite different constraints), but having this defined in an RFC seems to be the right way forward.

[roberth]

Presumably starts as an RFC equivalent to https://github.com/NixOS/rfcs/blob/master/rfcs/0088-nixpkgs-breaking-change-policy.md (or perhaps updates that policy to clearly cover Nix as well?)

Noting that Nixpkgs is very very free to make breaking changes because users can pin. Nix can't be pinned, and is expected to work with very old expressions. It's one of our unique selling points.