Dependency specifiers (PEP 508) in Rust

A library for python dependency specifiers, better known as PEP 508.

Usage

In 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

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, but you can also use the normal pip install .

Version and VersionSpecifier from 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:

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"])

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"