🐉 NixEL

Parser for the Nix Expressions Language.

Features

• ✔️ Fast

  It parses all the files in Nixpkgs in under 25 seconds, single-threaded. [^benchmark-specs]

  It's written in Rust and a little bit of C++, Flex and GNU Bison.

• ✔️ Correct

  This library is a copy-paste of the original lexer and parser of Nix, with some types adapted for better ergonomy.

  No parser can get closer to the original implementation than this.

• ✔️ Reliable

  High coverage, battle-tested, and memory-safe[^memory-safe].

• ✔️ Useful

  It gives you comments, whitespace, starting and end positions, automatic string un-escaping, multiline string indentation handling, a typed API, and everything you need to parse the Nix language!

Usage

You can check out the documentation at docs.rs/nixel.

This is a full usage example:

```rust let input: String = String::from( r#" # Greet the user "Hello, World!" # Bye! "#, );

let parsed: nixel::Parsed = nixel::parse(input);

match &*parsed.expression { nixel::Expression::String(string) => { asserteq!( &string.span, &nixel::Span { start: nixel::Position { line: 3, column: 9 }.into(), end: nixel::Position { line: 3, column: 24 }.into(), } .into() ); asserteq!( &parsed.triviabefore(&string.span.start)[1], &nixel::Trivia::Comment(nixel::TriviaComment { content: "# Greet the user".into(), span: nixel::Span { start: nixel::Position { line: 2, column: 9 }.into(), end: nixel::Position { line: 2, column: 25 }.into(), } .into() }) ); asserteq!( &string.parts[0], &nixel::Part::Raw(nixel::PartRaw { content: "Hello, World!".into(), span: nixel::Span { start: nixel::Position { line: 3, column: 10 }.into(), end: nixel::Position { line: 3, column: 23 }.into(), } .into() }) ); asserteq!( &parsed.triviaafter(&string.span.end)[1], &nixel::Trivia::Comment(nixel::TriviaComment { content: "# Bye!".into(), span: nixel::Span { start: nixel::Position { line: 4, column: 9 }.into(), end: nixel::Position { line: 4, column: 15 }.into(), } .into() }) ); }, expression => unreachable!("Expected a String, got: {expression:#?}"), } ```

Or from the CLI using Rust's Debug trait:

```sh $ echo '1 + 2' | nix run github:kamadorueda/nixel -- --format=debug

BinaryOperation( BinaryOperation { left: Integer( Integer { value: "1", span: Span { start: Position { line: 1, column: 1, }, end: Position { line: 1, column: 2, }, }, }, ), operator: Addition, right: Integer( Integer { value: "2", span: Span { start: Position { line: 1, column: 5, }, end: Position { line: 1, column: 6, }, }, }, ), }, ) ```

Or from the CLI using JSON format:

```sh $ echo '1 + 2' | nix run github:kamadorueda/nixel -- --format=json

{ "BinaryOperation": { "left": { "Integer": { "value": "1", "span": { "start": { "line": 1, "column": 1 }, "end": { "line": 1, "column": 2 } } } }, "operator": "Addition", "right": { "Integer": { "value": "2", "span": { "start": { "line": 1, "column": 5 }, "end": { "line": 1, "column": 6 } } } } } } ```

You can check out more examples in the tests folder.

Alternatives

• rnix-parser.

License

Please read LICENSE.md.

Footnotes

- CPU: 4 physical, 4 logical, 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz
- MHz: from 400 to 4700 MHz
- BogoMips: 5606.40
- Cache L3: 12 MiB

The following command takes around 1 minute:

```bash
$ nix build --system x86_64-linux
$ time find /data/nixpkgs -type f -name '*.nix' \
  -exec ./result/bin/nixel --format=none {} \;

real  0m24.293s
user  0m15.066s
sys   0m8.955s
```

and by running an infinite loop of parsing cycles over Nixpkgs :).

```bash
$ nix build --system x86_64-linux
$ valgrind ./result/bin/nixel $file

  LEAK SUMMARY:
    definitely lost: 0 bytes in 0 blocks
    indirectly lost: 0 bytes in 0 blocks
      possibly lost: 0 bytes in 0 blocks
         suppressed: 0 bytes in 0 blocks
```