🐉 NixEL
Parser for the Nix Expressions Language.
## Features
- ✔️ **Fast**
It parses all the files in [Nixpkgs](https://github.com/NixOS/nixpkgs)
in under 25 seconds, single-threaded.
[^benchmark-specs]
It's written in [Rust](https://www.rust-lang.org/)
and a little bit of [C++](https://isocpp.org/),
[Flex](https://github.com/westes/flex)
and [GNU Bison](https://www.gnu.org/software/bison/).
- ✔️ **Correct**
This library is a copy-paste of the original
[lexer](https://github.com/NixOS/nix/blob/dd1970c233a82328445b69e903574e14115ee933/src/libexpr/lexer.l)
and [parser](https://github.com/NixOS/nix/blob/dd1970c233a82328445b69e903574e14115ee933/src/libexpr/parser.y)
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](https://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) => {
assert_eq!(
&string.span,
&nixel::Span {
start: nixel::Position { line: 3, column: 9 }.into(),
end: nixel::Position { line: 3, column: 24 }.into(),
}
.into()
);
assert_eq!(
&parsed.trivia_before(&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()
})
);
assert_eq!(
&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()
})
);
assert_eq!(
&parsed.trivia_after(&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](https://github.com/kamadorueda/nixel/tree/main/tests/cases) folder.
## Alternatives
- [rnix-parser](https://github.com/nix-community/rnix-parser).
## License
Please read [LICENSE.md](./LICENSE.md).
## Footnotes
[^benchmark-specs]:
Running on a [machine](https://github.com/kamadorueda/machine) with:
- 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
```
[^memory-safe]:
Tested under real-life workloads using [Valgrind](https://valgrind.org/),
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
```