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Tvix is a new implementation of the Nix language and package manager. See the announcement post for information about the background of this project.

Tvix is developed by TVL in our monorepo, the depot, at //tvix. Code reviews take place on Gerrit, bugs are filed in our issue tracker.

For more information about Tvix, feel free to reach out. We are interested in people who would like to help us review designs, brainstorm and describe requirements that we may not yet have considered.

Most of the discussion around development happens in our dedicated IRC channel, #tvix-dev on hackint, which is also reachable via XMPP at #tvix-dev@irc.hackint.org (sic!) and via Matrix at #tvix-dev:hackint.org.

There's also the IRC channel of the wider TVL community, less on-topic, or our mailing list.

Contributions to Tvix follow the TVL review flow and contribution guidelines.

WARNING: Tvix is not ready for use in production. None of our current APIs should be considered stable in any way.

WARNING: Any other instances of this project or repository are josh-mirrors. We do not accept code contributions or issues outside of the tooling and communication methods outlined above.


This folder contains the following components:

  • //tvix/castore - subtree storage/transfer in a content-addressed fashion
  • //tvix/cli - preliminary REPL & CLI implementation for Tvix
  • //tvix/eval - an implementation of the Nix programming language
  • //tvix/nar-bridge-go - a HTTP webserver providing a Nix HTTP Binary Cache interface in front of a tvix-store
  • //tvix/nix-compat - a Rust library for compatibility with C++ Nix, features like encodings and hashing schemes and formats
  • //tvix/serde - a Rust library for using the Nix language for app configuration
  • //tvix/store - a "filesystem" linking Nix store paths and metadata with the content-addressed layer

Some additional folders with auxiliary things exist and can be explored at your leisure.

Building the CLI

The CLI can also be built with standard Rust tooling (i.e. cargo build), as long as you are in a shell with the right dependencies.

  • If you cloned the full monorepo, it can be provided by mg shell //tvix:shell.
  • If you cloned the tvix workspace only (git clone https://code.tvl.fyi/depot.git:workspace=views/tvix.git), nix-shell provides it.

If you're in the TVL monorepo, you can also run mg build //tvix/cli (or mg build from inside that folder) for a more incremental build.

Please follow the depot-wide instructions on how to get mg and use the depot tooling.


Important note: We only use and test Nix builds of our software against Nix 2.3. There are a variety of bugs and subtle problems in newer Nix versions which we do not have the bandwidth to address, builds in newer Nix versions may or may not work.

Rust projects, crate2nix

Some parts of Tvix are written in Rust. To simplify the dependency management on the Nix side of these builds, we use crate2nix in a single Rust workspace in //tvix to maintain the Nix build configuration.

When making changes to Cargo dependency configuration in any of the Rust projects under //tvix, be sure to run mg run //tools:crate2nix-generate in //tvix itself and commit the changes to the generated Cargo.nix file. This only applies to the full TVL checkout.

When adding/removing a Cargo feature for a crate, you will want to add it to the features power set that gets tested in CI. For each crate there's a default.nix with a mkFeaturePowerset invocation, modify the list to include/remove the feature. Note that you don't want to add "collection" features, such as fs for tvix-[ca]store or default.

License structure

All code implemented for Tvix is licensed under the GPL-3.0, with the exception of the protocol buffer definitions used for communication between services which are available under a more permissive license (MIT).

The idea behind this structure is that any direct usage of our code (e.g. linking to it, embedding the evaluator, etc.) will fall under the terms of the GPL3, but users are free to implement their own components speaking these protocols under the terms of the MIT license.