4f6f4e6588
Change-Id: If9dcd8e39f416c11460e66454df9f53096691699 Reviewed-on: https://cl.tvl.fyi/c/depot/+/2484 Tested-by: BuildkiteCI Reviewed-by: glittershark <grfn@gws.fyi>
179 lines
6.2 KiB
Markdown
179 lines
6.2 KiB
Markdown
Tvix, also known as TVL's fork of Nix
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-------------------------------------
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Nix is a new take on package management that is fairly unique. Because
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of its purity aspects, a lot of issues found in traditional package
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managers don't appear with Nix.
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To find out more about the tool, usage and installation instructions,
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please read the manual, which is available on the Nix website at
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<http://nixos.org/nix/manual>.
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This repository is [TVL's](https://tvl.fyi)'s fork of Nix, which we lovingly
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refer to as Tvix.
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## Fork background
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Nix is a fantastic project with over a decade of demonstrated
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real-world usage, but also with quite a few problems.
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First of all, the project consists of two main components: The Nix
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package collection ("[nixpkgs][]") and the package manager itself.
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The package collection is an enormous effort with hundreds of
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thousands of commits, encoding expert knowledge about lots of
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different software and ways of building and managing it. It is a very
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valuable piece of software.
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The package manager however is an old C++ project with severe code
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quality issues, little to no documentation, no consistent style and no
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unit test coverage.
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Its codebase is larger than it needs to be (often due to custom
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reimplementations of basic functionality) and is mostly ad-hoc
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structured, making it difficult to correctly implement large-scale
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improvements.
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In addition, the upstream Nix project is diverging from the opinions
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of some community members via the introduction of concepts such as Nix
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flakes.
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To counteract these things we have decided to fork Nix.
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## Fork goals
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The things listed here are explicitly in-scope for work on the fork.
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This list is not exhaustive, and it is very likely that many other
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smaller things will be discovered along the way.
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### nixpkgs compatibility
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This fork will maintain compatibility with nixpkgs as much as
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possible. If at any point we do need to diverge, we will do it in a
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way that is backwards compatible.
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### Code quality improvements
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Code quality encompasses several different issues.
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One goal is to slowly bring the codebase in line with the [Google C++
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style guide][google-style]. Apart from the trivial reformatting (which
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is already done), this means slowly chipping away at incorrectly
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structured type hierarchies, usage of exceptions, usage of raw
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pointers, global mutability and so on.
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Another goal is to reduce the amount of code in Nix by removing custom
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reimplementations of basic functionality (such as string splitting or
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reading files).
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For functionality that is not part of the C++17 standard library,
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[Abseil][] will be the primary external library used.
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### Explicit RPC mechanisms
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Nix currently uses homegrown mechanisms of interacting with other Nix
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binaries, for example for remote builds or interaction between the CLI
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and the Nix daemon.
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This will be replaced with [gRPC][].
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### New sandboxing mechanism
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Nix implements its own sandboxing mechanism. This was probably the
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correct decision at the time, but is not necessary anymore because
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Linux containers have become massively popular and lots of new tooling
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is now available.
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The goal is to replace the custom sandboxing implementation with
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pluggable [OCI runtimes][oci], which will make it possible to use
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arbitrary container runtimes such as [gVisor][] or [systemd-nspawn][]
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### Pluggable Nix store backends
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The current Nix store implementation will be removed from Nix' core
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and instead be refactored into a gRPC API that can be implemented by
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different backends.
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### Builds as graph reductions
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A Nix derivation that should be instantiated describes a build graph.
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This graph will become a first-class citizen, making it possible to
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distribute different parts of the computation to different nodes.
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Implementing this properly will also allow us to improve the
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implementation of import-from-derivation by explicitly moving through
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different graph reduction stages.
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## Fork non-goals
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To set expectations, there are some explicit non-goals, too.
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* Merging these changes back into upstream is not a goal, and maybe
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not even feasible. The core work has not even started yet and just
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basic cleanup has already created a diff of over 40 000 lines.
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This would likely also turn into a political effort, which we have
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no interest in.
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* Improved performance is not an (initial) goal. Nix performance is
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very unevenly distributed across the codebase (some things have seen
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a lot of ad-hoc optimisation, others are written like inefficient
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toy implementations) and we simply don't know what effect the
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cleanup will have.
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Once the codebase is in a better state we will be able to start
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optimising it again while retaining readability, but this is not a
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goal until a later point in time.
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* Compatibility with new upstream features is not a goal. Specifically
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we do not want Nix flakes, but other changes upstream makes will be
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considered for inclusion.
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* Support for non-Linux systems. Currently Nix support Mac OS and
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potentially other systems, but this support will be dropped.
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Once we have OCI-compatible sandboxes and a store protocol it will
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be possible to reintroduce these with less friction.
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## Building
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To build the project, set up an out-of-tree cmake directory and run cmake in
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nix-shell.
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```
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mkdir ~/build/tvix
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cd ~/build/tvix
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nix-shell $DEPOT_PATH -A third_party.nix.build-shell
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# Disable clang-tidy for quicker builds
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cmake $DEPOT_PATH/third_party/nix/ -DCLANG_TIDY_PATH=""
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make -j16 -l12
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# Run tests
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make test
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```
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## Contributing to the fork
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The TVL depot's default [contribution guidelines][contributing] apply.
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In addition, please make sure that submitted code builds and is
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formatted with `clang-format`, using the configuration found in this
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folder.
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## License
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Nix is released under the LGPL v2.1
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This product includes software developed by the OpenSSL Project for
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use in the [OpenSSL Toolkit](http://www.OpenSSL.org/).
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[nixpkgs]: https://github.com/NixOS/nixpkgs
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[google-style]: https://google.github.io/styleguide/cppguide.html
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[Abseil]: https://abseil.io/
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[gRPC]: https://grpc.io/
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[oci]: https://www.opencontainers.org/
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[gVisor]: https://gvisor.dev/
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[systemd-nspawn]: https://www.freedesktop.org/software/systemd/man/systemd-nspawn.html
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[contributing]: https://cs.tvl.fyi/depot/-/blob/docs/CONTRIBUTING.md
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