+++
title = "Announcing Lix 2.90 \"Vanilla Ice Cream\""
author = "Lix Team"
date = "2024-07-10"
+++

We at the Lix team are proud to announce our first release, version 2.90
"Vanilla Ice Cream". This release focuses on foundations and reliability, but
nevertheless contains several small but exciting user-facing features that are
exclusive to Lix.

Lix is a Nix implementation focused on reliability, predictability,
friendliness, developed by a community of people from
around the world. We have long term plans to incrementally evolve Nix to work
in more places, to make it more reliable and secure, and to update
the language and semantics to correct past mistakes and reduce
errors, all the while providing an amazing tooling experience.

Lix forks from CppNix version 2.18, which is the default version of Nix in
NixOS 23.11 and 24.05. It includes backports for most bug fixes in later versions of
CppNix, as well as various reliability improvements, and many improvements to user
experience. Our goal with Lix 2.90 is to create a better Nix 2.18: faster, more
user friendly, with fewer bugs, and fully compatible with previously-valid
Nix code including flakes.

Some highlights of this release include:

- `:doc` in `nix repl` now works on lambdas, in addition to built-in functions
  as before, thanks to [Lunaphied] and [jade]:

  ```
  dev/nixpkgs » nix repl -f .
  Lix 2.90.0-lixpre20240520-992c63f
  Type :? for help.
  Loading installable ''...
  Added 21430 variables.
  nix-repl> :doc lib.forEach
  Synopsis: func = xs: f: ...

        |    Apply the function to each element in the list.
        |    Same as `map`, but arguments flipped.
        |
        | Inputs
        |
        |    `xs`
        |
        |    : 1\. Function argument
        |
        |    `f`
        |
        |    : 2\. Function argument
        |
        | Type
        |
        |    ``
        |    forEach :: [a] -> (a -> b) -> [b]
        |    ``
        |
        | Examples
        |    :::{.example}

      # lib.lists.forEach usage example

        |    ``nix
        |    forEach [ 1 2 ] (x:
        |      toString x
        |    )
        |    => [ "1" "2" ]
        |    ``
        |
        |    :::

  /home/jade/dev/nixpkgs/lib/lists.nix:77

  ```
- `nix repl` supports creating shortcuts using the [`repl-overlays`][repl-overlays]
  setting, thanks to [wiggles]. For example, one can create a shortcut to
  `legacyPackages.${currentSystem}` with the following repl overlay, configured
  as a file in the `repl-overlays` setting in `~/.config/nix/nix.conf`:

  ```nix
  { currentSystem, ...}: final: prev: let
    optionalAttrs = predicate: attrs:
      if predicate
      then attrs
      else {};
  in
    optionalAttrs (prev ? legacyPackages && prev.legacyPackages ? ${currentSystem})
    {
      pkgs = prev.legacyPackages.${currentSystem};
    }
  ```

  Then:

  ```
  ~ » nix repl nixpkgs
  Lix 2.90.0-lixpre20240520-992c63f
  Type :? for help.
  Loading installable 'flake:nixpkgs#'...
  Added 5 variables.
  Loading 'repl-overlays'...
  Added 6 variables.
  nix-repl> pkgs.hello
  «derivation /nix/store/w0hjp1fnvyf1z30s29fj4im8c7bxqrql-hello-2.12.1.drv»
  ```
- Evaluation is 5-20% faster than 2.18, depending on which benchmark is in use,
  thanks to [eldritch horrors].
- Various user experience issues have been fixed. For example:
  - Error reporting has been fixed to be more accurate in several cases thanks
    to [wiggles], and errors give more details to diagnose them.

    For instance, type errors now give the actual value that caused the error.
  - `nix flake lock --update-input nixpkgs` is now the much more reasonable
    `nix flake update nixpkgs`.
  - `nix build -E` is now an alias for `nix build --expr`, mirroring `nix-build
    -E`.
  - Several very silly `--debugger` bugs that one runs into in normal usage
    have been fixed thanks to [wiggles], so the debugger actually works properly
    without a mental index of all the bugs in it.
  - The Lix evaluation cache no longer caches failures, so "cached failure" is an
    error of the past.
  - The REPL value printer now intelligently chooses whether to print on one
    line or multiple lines, rather than putting everything on one very long
    line.
  - Various failures that were silent in the past are no longer silent:
    - The Lix daemon warns when it rejects a setting from a client that requires
      being a trusted user, instead of silently ignoring it.
    - Remote builds failing to connect to a builder now print the error.
    - Crashing the daemon now indicates that is what probably happened.
    - Lix now generally crashes much harder in the case of bugs, such that bugs
      are easier to find and fix.
  - Various errors have been made more specific, like "path is invalid".
- Several hauntings have been exorcised from the codebase:
  - Flake input overrides like `foo.inputs.bar.inputs.nixpkgs` now work as
    documented rather than being ignored.
  - Store path names starting with `.` are now permitted, fixing some home-manager
    issues.
  - A crash when running patched kernels with non-default schedulers has been
    fixed.
  - Breakage inside the sandbox when running on systems with unprivileged user
    namespaces disabled has been fixed.
  - Various format string crashes have been fixed.
  - `nix doctor` now has correct output of client trustedness.

[wiggles]: https://github.com/9999years
[eldritch horrors]: https://git.lix.systems/pennae
[Lunaphied]: https://github.com/lunaphied
[jade]: https://jade.fyi

[repl-overlays]: https://docs.lix.systems/manual/lix/2.90/command-ref/conf-file.html#conf-repl-overlays

A lot of internal stability work and development process work has gone into
this release. For instance:
- Lix builds exclusively with the Meson build system. The historical CppNix
  Make-based build system has been removed altogether. This improves
  compile times as well as various aspects of the developer experience: the `clangd`
  language server just works with no configuration now, for instance.
- Lix has the beginnings of the infrastructure to do linting of its C++ code and work on
  modernization with automated tools.
- Lix enforces various aspects of [its
  styleguide][styleguide] with `pre-commit` hooks.
- A lot of onboarding and project planning information has been written down in
  the [Wiki]. In general we strive to be transparent with our plans and
  priorities, and to communicate them clearly.
- We have completed a release automation project, which should let us release more
  frequently given that our `main` is more or less releaseable on any given day.
- We have built out a lot of infrastructure which we own end-to-end, allowing
  us to quickly improve on pain points in the project ourselves.
  - We have [Single Sign-On](https://identity.lix.systems) permitting us to
    easily deploy more services that cleanly integrate together.
  - We use [Gerrit](https://gerrit.lix.systems) for reviews, which allows us to
    focus on providing prompt and high quality patch reviews by making it easy
    to review changes piece by piece, with CI testing of every commit.

    Gerrit is one of our secret superpowers in shipping correct code, since it,
    by its structure, enforces good commit history, reviewable code, and
    incremental changes.
  - We use [Forgejo](https://git.lix.systems) for code hosting and issue
    tracking, which we have customised to integrate natively with Gerrit and
    to work natively with Nix flakes for locking tarballs.
  - We have a [Wiki] with design documents, styleguide, and other project
    organisational information.

[Wiki]: https://wiki.lix.systems

[styleguide]: https://wiki.lix.systems/books/lix-contributors/chapter/style-guide

For a more comprehensive list of the changes in this release, see
[the release notes][release-notes].

[release-notes]: https://docs.lix.systems/manual/lix/2.90/release-notes/rl-2.90.html

The Lix team as well as several dozen beta testers have been running a
development release of Lix 2.90 in production every day for a couple of months,
and we do not expect any significant regressions compared to Nix 2.18. However,
if you find a bug or suspicious behaviour in Lix, feel free to mention it on
Matrix or [file a bug on Forgejo][bugs]. If you would like to participate in
beta testing of future Lix versions, we have a [guide on the wiki][beta-guide]
and a [Matrix channel][beta-channel] for running `main`.

[bugs]: https://git.lix.systems/lix-project/lix/issues
[beta-guide]: https://wiki.lix.systems/books/lix-contributors/page/lix-beta-guide
[beta-channel]: https://matrix.to/#/#open-beta:lix.systems

We would especially like to thank all the following groups for their hard work
and trust in contributing to this release:
- The several dozen Lix beta testers who have been running Lix `main` in
  production for over a month, and who have helped us fix the various
  longstanding CppNix bugs they have had stuck in their craw as well as put up
  with our work-in-progress infrastructure as we built it out.
- All the first time contributors who made their first contributions to a Nix
  implementation in Lix. We are eternally grateful to everyone who helped us out
  on the numerous important but tedious issues.
- All the people new to Nix who have trusted us by running experimental
  versions of Lix and given us feedback.
- The long time CppNix contributors who came to Lix and helped out with fixing
  many issues.
- The CppNix contributors and CppNix team, without whom we would not have this
  software, and who wrote many of the bug fixes we backported to Lix from CppNix
  versions > 2.18.
- Everyone else who has worked with us on starting to make this dream a
  reality.

We are very proud of what everyone has achieved with this release since we
begun in late February 2024, and we are just getting started. We are looking
forward to continue working together with everyone to build a better foundation
for the future evolution of Nix.