evix-0.1.0 is not a library.

evix

Experimental CLI utility using nix-bindings for the Nix C API, and a Rust replacement for nix-eval-jobs in Rust to leverage language features, and evaluate Nix expressions and stream derivation info as JSON lines in style.

Why evix?

Faster evaluation by using threads
Memory used for evaluation is reclaimed after nix-eval-jobs finish, so that the build can use it.
Evaluation of jobs can fail individually
It's really cool!

Usage

Exactly one input is required:

evix --flake .#hydraJobs
evix --expr 'import <nixpkgs> {}'
evix --file ./default.nix

# Evaluate the hydraJobs attribute of the patchelf flake
$ evix --flake 'github:NixOS/patchelf#hydraJobs'
copying path '/nix/store/jfdpyszsgvsnz68y36qi65irx7r6a52q-source' from 'https://cache.nixos.org'...
{"attr":"tarball","attrPath":["tarball"],"drvPath":"/nix/store/dbhsb9ji8ya2js87v1q5621lx87smw3l-patchelf-tarball-0.18.0.drv","name":"patchelf-tarball-0.18.0","outputs":{"out":null},"system":"x86_64-linux"}
{"attr":"coverage","attrPath":["coverage"],"drvPath":"/nix/store/h8fzgxxddi1470vad93j2y5s1lyxsii8-patchelf-coverage-0.18.0.drv","name":"patchelf-coverage-0.18.0","outputs":{"out":null},"system":"x86_64-linux"}
{"attr":"patchelf-win32","attrPath":["patchelf-win32"],"drvPath":"/nix/store/8kbg5mf09zyykcjvkmwna621ja8vm5pr-patchelf-i686-w64-mingw32-0.18.0.drv","name":"patchelf-i686-w64-mingw32-0.18.0","outputs":{"out":null},"system":"x86_64-linux"}
{"attr":"patchelf-win64","attrPath":["patchelf-win64"],"drvPath":"/nix/store/5zvjbw8y4k1fs3vhbb465ixhl032imgg-patchelf-x86_64-w64-mingw32-0.18.0.drv","name":"patchelf-x86_64-w64-mingw32-0.18.0","outputs":{"out":null},"system":"x86_64-linux"}
{"attr":"release","attrPath":["release"],"drvPath":"/nix/store/4l4cl6w4afn4g4bha5h6z0nm16vddnph-patchelf-0.18.0.drv","name":"patchelf-0.18.0","outputs":{"out":null},"system":"x86_64-linux"}

Options

Flag	Description
`--flake REF`	Evaluate a flake output
`--expr EXPR`	Evaluate an inline Nix expression
`--file PATH`	Evaluate a Nix file
`--arg NAME EXPR`	Pass a Nix expression argument
`--argstr NAME VALUE`	Pass a string argument
`--workers N`	Worker processes (default: 1)
`--max-memory-size MB`	Memory limit per worker; restarts when exceeded (default: 4096)
`--force-recurse`	Recurse into all attrsets, ignoring `recurseForDerivations`
`--gc-roots-dir DIR`	Register GC root symlinks for evaluated derivations

Output

Each line is a JSON object. Derivation attributes emit:

{
  "attr": "packages.x86_64-linux.hello",
  "attrPath": ["packages", "x86_64-linux", "hello"],
  "name": "hello-2.12.1",
  "system": "x86_64-linux",
  "drvPath": "/nix/store/...",
  "outputs": { "out": "/nix/store/..." }
}

Non-derivation attrsets emit child attribute names for further recursion:

{
  "attr": "packages.x86_64-linux",
  "attrPath": ["packages", "x86_64-linux"],
  "attrs": ["hello", "git", "vim"]
}

Errors are non-fatal unless "fatal": true:

{"attr": "...", "attrPath": [...], "error": "...", "fatal": false}

Architecture

The binary operates in two modes based on the _NEJ_WORKER environment variable:

Master (default): Spawns worker subprocesses, manages a work queue of attr paths, distributes work via stdin/stdout, and collects results.
Worker (_NEJ_WORKER=1): Evaluates Nix expressions, processes individual attr paths, and signals when memory limits are reached.

Workers are restarted automatically when they exceed the memory limit.

Building

Requires Rust 1.90.0+. Supported on x86_64-linux and aarch64-linux.

License

EUPL-1.2

evix 0.1.0