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Profpatsch 5b2ba0efa1 refactor(tvix/eval): rewrite xml emitter to be simple-stupid 
In order to be compatible with the nix XML generator, it’s easier to
generate the XML directly, instead of going through a library which we
have to bend to do what we need.

Removes dependency on `xml-rs`, which came with a full XML parser that
we didn’t use. Only takes a tiny bit of code for the XML escaping,
somewhat simplified.

I add a little escaping value, to make sure we have the same behaviour
as nix proper.

Interestingly enough, we never need to escape XML attribute names,
because the `builtins.toXML` format encodes user-defined values as
attribute keys only. So we only escape attribute values.

Fixes: https://b.tvl.fyi/issues/399
Change-Id: If4d407d324864b3bb9aa3160e2ec6889f7727127
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11697
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
Autosubmit: Profpatsch <mail@profpatsch.de>
2024-05-22 10:32:55 +00:00
..
benches refactor(tvix/eval): move Evaluation::{default,new_pure}() again 2024-01-18 14:24:40 +00:00
builtin-macros refactor(tvix/eval): Generalize propagation of catchable values 2024-02-08 19:59:21 +00:00
docs docs(tvix/eval): add document about how binding construction works 2024-05-03 22:25:40 +00:00
proptest-regressions/value refactor(tvix/eval): flatten call stack of VM using generators 2023-03-13 20:30:59 +00:00
src refactor(tvix/eval): rewrite xml emitter to be simple-stupid 2024-05-22 10:32:55 +00:00
tests test(tvix): Fix tvix tests on macOS 2024-04-30 00:55:34 +00:00
.skip-subtree feat(tvix/tests): check in Nix' language test suite 2022-08-24 21:25:41 +00:00
build.rs feat(tvix/eval): implement builtins.currentSystem 2022-10-24 12:20:01 +00:00
Cargo.toml refactor(tvix/eval): rewrite xml emitter to be simple-stupid 2024-05-22 10:32:55 +00:00
default.nix refactor(tvix): build Rust projects using crate2nix 2022-12-15 17:26:45 +00:00
README.md chore: update links to tvixbolt 2024-02-24 10:17:56 +00:00

README.md

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 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:

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.

Tvix makes heavy use of rnix-parser in its bytecode compiler. The parser is now maintained by Nix community members.