# Dependency specifiers (PEP 508) in Rust

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A library for python
[dependency specifiers](https://packaging.python.org/en/latest/specifications/dependency-specifiers/),
better known as [PEP 508](https://peps.python.org/pep-0508/).

## Usage

**In Rust**

```rust
use std::str::FromStr;
use pep508_rs::Requirement;

let marker = r#"requests [security,tests] >= 2.8.1, == 2.8.* ; python_version > "3.8""#;
let dependency_specification = Requirement::from_str(marker).unwrap();
assert_eq!(dependency_specification.name, "requests");
assert_eq!(dependency_specification.extras, Some(vec!["security".to_string(), "tests".to_string()]));
```

**In Python**

```python
from pep508_rs import Requirement

requests = Requirement(
    'requests [security,tests] >= 2.8.1, == 2.8.* ; python_version > "3.8"'
)
assert requests.name == "requests"
assert requests.extras == ["security", "tests"]
assert [str(i) for i in requests.version_or_url] == [">= 2.8.1", "== 2.8.*"]
```

Python bindings are built with [maturin](https://github.com/PyO3/maturin), but you can also use the
normal `pip install .`

`Version` and `VersionSpecifier` from [pep440_rs](https://github.com/konstin/pep440-rs) are
reexported to avoid type mismatches.

## Markers

Markers allow you to install dependencies only in specific environments (python version, operating
system, architecture, etc.) or when a specific feature is activated. E.g. you can say
`importlib-metadata ; python_version < "3.8"` or `itsdangerous (>=1.1.0) ; extra == 'security'`.
Unfortunately, the marker grammar has some oversights (e.g.
<https://github.com/pypa/packaging.python.org/pull/1181>) and the design of comparisons (PEP 440
comparisons with lexicographic fallback) leads to confusing outcomes. This implementation tries to
carefully validate everything and emit warnings whenever bogus comparisons with unintended semantics
are made.

In python, warnings are by default sent to the normal python logging infrastructure:

```python
from pep508_rs import Requirement, MarkerEnvironment

env = MarkerEnvironment.current()
assert not Requirement("numpy; extra == 'science'").evaluate_markers(env, [])
assert Requirement("numpy; extra == 'science'").evaluate_markers(env, ["science"])
assert not Requirement(
    "numpy; extra == 'science' and extra == 'arrays'"
).evaluate_markers(env, ["science"])
assert Requirement(
    "numpy; extra == 'science' or extra == 'arrays'"
).evaluate_markers(env, ["science"])
```

```python
from pep508_rs import Requirement, MarkerEnvironment

env = MarkerEnvironment.current()
Requirement("numpy; python_version >= '3.9.'").evaluate_markers(env, [])
# This will log:
# "Expected PEP 440 version to compare with python_version, found '3.9.', "
# "evaluating to false: Version `3.9.` doesn't match PEP 440 rules"
```