025c67bf4d
Warning: This is probably the biggest refactor in tvix-eval history, so far. This replaces all instances of trampolines and recursion during evaluation of the VM loop with generators. A generator is an asynchronous function that can be suspended to yield a message (in our case, vm::generators::GeneratorRequest) and receive a response (vm::generators::GeneratorResponsee). The `genawaiter` crate provides an interpreter for generators that can drive their execution and lets us move control flow between the VM and suspended generators. To do this, massive changes have occured basically everywhere in the code. On a high-level: 1. The VM is now organised around a frame stack. A frame is either a call frame (execution of Tvix bytecode) or a generator frame (a running or suspended generator). The VM has an outer loop that pops a frame off the frame stack, and then enters an inner loop either driving the execution of the bytecode or the execution of a generator. Both types of frames have several branches that can result in the frame re-enqueuing itself, and enqueuing some other work (in the form of a different frame) on top of itself. The VM will eventually resume the frame when everything "above" it has been suspended. In this way, the VM's new frame stack takes over much of the work that was previously achieved by recursion. 2. All methods previously taking a VM have been refactored into async functions that instead emit/receive generator messages for communication with the VM. Notably, this includes *all* builtins. This has had some other effects: - Some test have been removed or commented out, either because they tested code that was mostly already dead (nix_eq) or because they now require generator scaffolding which we do not have in place for tests (yet). - Because generator functions are technically async (though no async IO is involved), we lose the ability to use much of the Rust standard library e.g. in builtins. This has led to many algorithms being unrolled into iterative versions instead of iterator combinations, and things like sorting had to be implemented from scratch. - Many call sites that previously saw a `Result<..., ErrorKind>` bubble up now only see the result value, as the error handling is encapsulated within the generator loop. This reduces number of places inside of builtin implementations where error context can be attached to calls that can fail. Currently what we gain in this tradeoff is significantly more detailed span information (which we still need to bubble up, this commit does not change the error display). We'll need to do some analysis later of how useful the errors turn out to be and potentially introduce some methods for attaching context to a generator frame again. This change is very difficult to do in stages, as it is very much an "all or nothing" change that affects huge parts of the codebase. I've tried to isolate changes that can be isolated into the parent CLs of this one, but this change is still quite difficult to wrap one's mind and I'm available to discuss it and explain things to any reviewer. Fixes: b/238, b/237, b/251 and potentially others. Change-Id: I39244163ff5bbecd169fe7b274df19262b515699 Reviewed-on: https://cl.tvl.fyi/c/depot/+/8104 Reviewed-by: raitobezarius <tvl@lahfa.xyz> Reviewed-by: Adam Joseph <adam@westernsemico.com> Tested-by: BuildkiteCI |
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| .. | ||
| .vscode | ||
| cli | ||
| docs | ||
| eval | ||
| nix-compat | ||
| nix_cli | ||
| proto | ||
| serde | ||
| store | ||
| verify-lang-tests | ||
| .gitignore | ||
| Cargo.lock | ||
| Cargo.nix | ||
| Cargo.toml | ||
| crate-hashes.json | ||
| default.nix | ||
| LICENSE | ||
| OWNERS | ||
| README.md | ||
Tvix
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 on our IRC channel, which you can join in several ways documented on tvl.fyi, or on 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.
Components
This folder contains the following components:
//tvix/eval- an implementation of the Nix programming language//tvix/nix-compat- library functions for compatibility with C++ Nix//tvix/cli- preliminary REPL & CLI implementation for Tvix//tvix/serde- Rust library for using the Nix language for app configuration//tvix/store- implementation of a file store for Tvix
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
tvixworkspace only (git clone https://code.tvl.fyi/depot.git:workspace=views/tvix.git),nix-shellprovides 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.
Compatibility
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 //tvix:crate2nixGenerate -- in //tvix itself and commit the changes
to the generated Cargo.nix file. This only applies to the full TVL checkout.
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.