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Aspen Smith 59056cf705 feat(tvix/eval): Leak strings (with flag to disable) 
Default to always leaking strings, and copying strings by copying
pointers rather than cloning the underlying allocation. This (somewhat
bafflingly) doesn't seem to affect any benchmarks, but paves the way for
some tricks around string allocation that do.

Unfortunately, we can't do this (yet?) for contextful strings, for
reasons I don't currently understand but which I will address later,
when I address contextful strings more holistically.

I've left a flag in here to disable this, both to test the cloning logic
for strings for when/if we decide to bring this back, and to allow
people who care more about memory usage than perf to disable leaking.

Change-Id: Iec44bcbfe9b3d20389d2450b9a551792a79b9b26
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12045
Autosubmit: aspen <root@gws.fyi>
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
2024-08-05 10:49:27 +00:00
..
benches refactor(tvix/eval): Builderize Evaluation 2024-07-06 15:03:46 +00:00
builtin-macros refactor(tvix/eval): Generalize propagation of catchable values 2024-02-08 19:59:21 +00:00
proptest-regressions/value refactor(tvix/eval): flatten call stack of VM using generators 2023-03-13 20:30:59 +00:00
src feat(tvix/eval): Leak strings (with flag to disable) 2024-08-05 10:49:27 +00:00
tests refactor(tvix/eval): Builderize Evaluation 2024-07-06 15:03:46 +00:00
.skip-subtree feat(tvix/tests): check in Nix' language test suite 2022-08-24 21:25:41 +00:00
build.rs fix(tvix): make rstest pick up new test case files 2024-06-05 17:52:17 +00:00
Cargo.toml feat(tvix/eval): Leak strings (with flag to disable) 2024-08-05 10:49:27 +00:00
default.nix feat(tvix): add CI targets for checking crate features powerset 2024-06-03 16:35:51 +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.