Tvix Evaluator ============== This project implements an interpreter for the Nix programming language. You can experiment with an online version of the evaluator: [tvixbolt][]. The interpreter aims to be compatible with `nixpkgs`, on the foundation of Nix 2.3. **Important note:** The evaluator is not yet feature-complete, and while the core mechanisms (compiler, runtime, ...) have stabilised somewhat, a lot of components are still changing rapidly. Please contact [TVL](https://tvl.fyi) with any questions you might have. ## Building tvix-eval Please check the `README.md` one level up for instructions on how to build this. The evaluator itself can also be built with standard Rust tooling (i.e. `cargo build`). If you would like to clone **only** the evaluator and build it directly with Rust tooling, you can do: ```bash git clone https://code.tvl.fyi/depot.git:/tvix/eval.git tvix-eval cd tvix-eval && cargo build ``` ## Tests Tvix currently has three language test suites for tvix-eval: * `nix_tests` and `tvix_tests` are based on the same mechanism borrowed from the C++ Nix implementation. They consist of Nix files as well as expected output (if applicable). The test cases are split into four categories: `eval-okay` (evaluates successfully with the expected output), `eval-fail` (fails to evaluate, no expected output), `parse-okay` (expression parses successfully, no expected output) and `parse-fail` (expression fails to parse, no expected output). Tvix currently ignores the last two types of test cases, since it doesn't implement its own parser. Both test suites have a `notyetpassing` directory. All test cases in here test behavior that is not yet supported by Tvix. They are considered to be expected failures, so you can't forget to move them into the test suite proper when fixing the incompatibility. Additionally, separate targets in the depot pipeline, under `//tvix/verify-lang-tests`, check both test suites (including `notyetpassing` directories) against C++ Nix 2.3 and the default C++ Nix version in nixpkgs. This way we can prevent accidentally introducing test cases for behavior that C++ Nix doesn't exhibit. * `nix_tests` has the test cases from C++ Nix's language test suite and is sporadically updated by manually syncing the directories. The `notyetpassing` directory shows how far it is until we pass it completely. * `tvix_tests` contains test cases written by the Tvix contributors. Some more or less duplicate test cases contained in `nix_tests`, but many cover relevant behavior that isn't by `nix_tests`. Consequently, it'd be nice to eventually merge the two test suites into a jointly maintained, common Nix language test suite. It also has a `notyetpassing` directory for missing behavior that is discovered while working on Tvix and isn't covered by the `nix_tests` suite. * `nix_oracle` can evaluate Nix expressions in Tvix and compare the result against C++ Nix (2.3) directly. Eventually it should gain the ability to property test generated Nix expressions. An additional feature is that it can evaluate expressions without `--strict`, so thunking behavior can be verified more easily. ## rnix-parser Tvix is written in memory of jD91mZM2, the author of [rnix-parser][] who sadly [passed away][rip]. Tvix makes heavy use of rnix-parser in its bytecode compiler. The parser is now maintained by Nix community members. [rnix-parser]: https://github.com/nix-community/rnix-parser [rip]: https://www.redox-os.org/news/open-source-mental-health/ [tvixbolt]: https://tvixbolt.tvl.su/